Arthroplasty/Joint Replacement

Unicompartmental knee arthroplasty (UKA) is considered a less invasive approach for the treatment of unicompartmental knee arthritis when compared with total knee arthroplasty (TKA), with optimal preservation of kinematics.¹ Despite excellent functional outcomes, conversion to TKA may be necessary if the UKA fails, or in patients with progressive knee arthritis. Some studies have found UKA conversion to TKA to be comparable with primary TKA,^2,3 whereas others have found that conversion often requires bone graft, augments, and stemmed components and has increased complications and inferior results compared to primary TKA.^4-7 While some studies report that <10% of UKA conversions to TKA require augments,² others have found that as many as 76% require augments.^4-8

Schwarzkopf and colleagues⁹ recently demonstrated that UKA conversion to TKA is comparable with primary TKA when a conservative tibial resection is performed during the index procedure. However, they reported increased complexity when greater tibial resection was performed and thicker polyethylene inserts were used at the time of the index UKA. The odds ratio of needing an augment or stem during the conversion to TKA was 26.8 (95% confidence interval, 3.71-194) when an aggressive tibial resection was performed during the UKA.⁹ Tibial resection thickness may thus be predictive of anticipated complexity of UKA revision to TKA and may aid in preoperative planning.

Robotic assistance has been shown to enhance the accuracy of bone preparation, implant component alignment, and soft tissue balance in UKA.^10-15 It has yet to be determined whether this improved accuracy translates to improved clinical performance or longevity of the UKA implant. However, the enhanced accuracy of robotic technology may result in more conservative tibial resection when compared to conventional UKA and may be advantageous if conversion to TKA becomes necessary.

The purpose of this study was to compare the distribution of polyethylene insert sizes implanted during conventional and robotic-assisted UKA. We hypothesized that robotic assistance would demonstrate more conservative tibial resection compared to conventional methods of bone preparation.

Methods

We retrospectively compared the distribution of polyethylene insert sizes implanted during consecutive conventional and robotic-assisted UKA procedures. Several manufacturers were queried to provide a listing of the polyethylene insert sizes utilized, ranging from 8 mm to 14 mm. The analysis included 8421 robotic-assisted UKA cases and 27,989 conventional UKA cases. Data were provided by Zimmer Biomet and Smith & Nephew regarding conventional cases, as well as Blue Belt Technologies (now part of Smith & Nephew) and MAKO Surgical (now part of Stryker) regarding robotic-assisted cases. (Dr. Lonner has an ongoing relationship as a consultant with Blue Belt Technologies, whose data was utilized in this study.) Using tibial insert thickness as a surrogate measure of the extent of tibial resection, an insert size of ≥10 mm was defined as aggressive while <10 mm was considered conservative. This cutoff was established based on its corresponding resection level with primary TKA and the anticipated need for augments. Statistical analysis was performed using a Mann-Whitney-Wilcoxon test. Significance was set at P < .05.

Results

Tibial resection thickness was found to be most commonly conservative in nature, with sizes 8-mm and 9-mm polyethylene inserts utilized in the majority of both robotic-assisted and conventional UKA cases. However, statistically more 8-mm and 9-mm polyethylene inserts were used in the robotic group (93.6%) than in the conventional group (84.5%) (P < .0001; Figure). Aggressive tibial resection, requiring tibial inserts ≥10 mm, was performed in 6.4% of robotic-assisted cases and 15.5% of conventional cases.

Only .29% of robotic-assisted cases required tibial inserts ≥10 mm, whereas 5.7% of patients undergoing conventional UKA had tibial inserts ≥10 mm. In this analysis, the maximum tibial component thickness was 11 mm in robotic-assisted UKA and 14 mm in conventional UKA. The distribution of conventional UKA tibial resection thicknesses is significantly greater in comparison to robotic-assisted UKA, which more reproducibly achieved accurate and precise conservative resection. No significant differences were noted in the percentages of polyethylene sizes between Blue Belt Technologies or MAKO cases.

Discussion

Robotic assistance enhances the accuracy of bone preparation, implant component alignment, and soft tissue balance in UKA.^10-15 It has yet to be determined whether this improved accuracy translates to improved clinical performance or longevity of the UKA implant. However, we demonstrate that the enhanced accuracy of robotic technology results in more conservative tibial resection when compared to conventional techniques with a potential benefit suggested in the literature upon conversion to TKA.

The findings of this study have important implications for patients undergoing conversion of UKA to TKA, potentially optimizing the ease of revision and clinical outcomes. The outcomes of UKA conversion to TKA are often considered inferior to those of primary TKA, compromised by bone loss, need for augmentation, and challenges of restoring the joint line and rotation.^9,16-22 Barrett and Scott¹⁸ reported only 66% of patients had good or excellent results at an average of 4.6 years of follow-up after UKA conversion to TKA. Over 50% required stemmed implants and bone graft or bone cement augmentation to address osseous insufficiency. The authors suggested that the primary determinant of the complexity of the conversion to TKA was the surgical technique used in the index procedure. They concluded that UKA conversion to TKA can be as successful as a primary TKA and primary TKA implants can be used without bone augmentation or stems during the revision procedure if minimal tibial bone is resected at the time of the index UKA.¹⁸ Schwarzkopf and colleagues⁹ supported this conclusion when they found that aggressive tibial resection during UKA resulted in the need for bone graft, stem, wedge, or augment in 70% of cases when converted to TKA. Similarly, Khan and colleagues²³ found that 26% of patients required bone grafting and 26% required some form of augmentation, and Springer and colleagues³ reported that 68% required a graft, augment, or stem.^3,22 Using data from the New Zealand Joint Registry, Pearse and colleagues⁵ reported that revision TKA components were necessary in 28% of patients and concluded that converting a UKA to TKA gives a less reliable result than primary TKA, and with functional results that are not significantly better than a revision from a TKA.

Conservative tibial resection during UKA minimizes the complexity and concerns of bone loss upon conversion to TKA. Schwarzkopf and colleagues⁹ found 96.6% of patients with conservative tibial resection received a primary TKA implant, without augments or stems. Furthermore, patients with a primary TKA implant showed improved tibial survivorship, with revision as an end point, compared with patients who received a TKA implant that required stems and augments or bone graft for support.⁹ Also emphasizing the importance of minimal tibial resection, O’Donnell and colleagues⁸ compared a cohort of patients undergoing conversion of a minimal resection resurfacing onlay-type UKA to TKA with a cohort of patients undergoing primary TKA. They found that 40% of patients required bone grafting for contained defects, 3.6% required metal augments, and 1.8% required stems.⁸ There was no significant difference between the groups in terms of range of motion, functional outcome, or radiologic outcomes. The authors concluded that revision of minimal resection resurfacing implants to TKA is associated with similar results to primary TKA and is superior to revision of UKA with greater bone loss. Prior studies have shown that one of the advantages of robotic-assisted UKA is the accuracy and precision of bone resection. The present study supports this premise by showing that tibial resection is significantly more conservative using robotic-assisted techniques when using tibial component thickness as a surrogate for extent of bone resection. While our study did not address implant durability or the impact of conservative resection on conversion to TKA, studies referenced above suggest that the conservative nature of bone preparation would have a relevant impact on the revision of the implant to TKA.

Our study is a retrospective case series that reports tibial component thickness as a surrogate for volume of tibial resection during UKA. While the implication is that more conservative tibial resection may optimize durability and ease of conversion to TKA, future study will be needed to compare robotic-assisted and conventional cases of UKA upon conversion to TKA in order to ascertain whether the more conventional resections of robotic-assisted UKA in fact lead to revision that is comparable with primary TKA in terms of bone loss at the time of revision, components utilized, the need for bone graft, augments, or stems, and clinical outcomes. Given the method of data collection in this study, we could not control for clinical deformity, selection bias, surgeon experience, or medial vs lateral knee compartments. These potential confounders represent weaknesses of this study.

In conclusion, conversion of UKA to TKA may be associated with significant osseous insufficiency, which may compromise patient outcomes in comparison to primary TKA. Studies have shown that UKA conversion to TKA is comparable to primary TKA when minimal tibial resection is performed during the UKA, and the need for augmentation, grafting or stems is increased with more aggressive tibial resection. This study has shown that when robotic assistance is utilized, tibial resection is more precise, less variable, and more conservative compared to conventional techniques.

Am J Orthop. 2016;45(7):E465-E468. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Unicompartmental knee arthroplasty (UKA) is considered a less invasive approach for the treatment of unicompartmental knee arthritis when compared with total knee arthroplasty (TKA), with optimal preservation of kinematics.¹ Despite excellent functional outcomes, conversion to TKA may be necessary if the UKA fails, or in patients with progressive knee arthritis. Some studies have found UKA conversion to TKA to be comparable with primary TKA,^2,3 whereas others have found that conversion often requires bone graft, augments, and stemmed components and has increased complications and inferior results compared to primary TKA.^4-7 While some studies report that <10% of UKA conversions to TKA require augments,² others have found that as many as 76% require augments.^4-8

Schwarzkopf and colleagues⁹ recently demonstrated that UKA conversion to TKA is comparable with primary TKA when a conservative tibial resection is performed during the index procedure. However, they reported increased complexity when greater tibial resection was performed and thicker polyethylene inserts were used at the time of the index UKA. The odds ratio of needing an augment or stem during the conversion to TKA was 26.8 (95% confidence interval, 3.71-194) when an aggressive tibial resection was performed during the UKA.⁹ Tibial resection thickness may thus be predictive of anticipated complexity of UKA revision to TKA and may aid in preoperative planning.

Robotic assistance has been shown to enhance the accuracy of bone preparation, implant component alignment, and soft tissue balance in UKA.^10-15 It has yet to be determined whether this improved accuracy translates to improved clinical performance or longevity of the UKA implant. However, the enhanced accuracy of robotic technology may result in more conservative tibial resection when compared to conventional UKA and may be advantageous if conversion to TKA becomes necessary.

The purpose of this study was to compare the distribution of polyethylene insert sizes implanted during conventional and robotic-assisted UKA. We hypothesized that robotic assistance would demonstrate more conservative tibial resection compared to conventional methods of bone preparation.

Methods

We retrospectively compared the distribution of polyethylene insert sizes implanted during consecutive conventional and robotic-assisted UKA procedures. Several manufacturers were queried to provide a listing of the polyethylene insert sizes utilized, ranging from 8 mm to 14 mm. The analysis included 8421 robotic-assisted UKA cases and 27,989 conventional UKA cases. Data were provided by Zimmer Biomet and Smith & Nephew regarding conventional cases, as well as Blue Belt Technologies (now part of Smith & Nephew) and MAKO Surgical (now part of Stryker) regarding robotic-assisted cases. (Dr. Lonner has an ongoing relationship as a consultant with Blue Belt Technologies, whose data was utilized in this study.) Using tibial insert thickness as a surrogate measure of the extent of tibial resection, an insert size of ≥10 mm was defined as aggressive while <10 mm was considered conservative. This cutoff was established based on its corresponding resection level with primary TKA and the anticipated need for augments. Statistical analysis was performed using a Mann-Whitney-Wilcoxon test. Significance was set at P < .05.

Results

Tibial resection thickness was found to be most commonly conservative in nature, with sizes 8-mm and 9-mm polyethylene inserts utilized in the majority of both robotic-assisted and conventional UKA cases. However, statistically more 8-mm and 9-mm polyethylene inserts were used in the robotic group (93.6%) than in the conventional group (84.5%) (P < .0001; Figure). Aggressive tibial resection, requiring tibial inserts ≥10 mm, was performed in 6.4% of robotic-assisted cases and 15.5% of conventional cases.

Only .29% of robotic-assisted cases required tibial inserts ≥10 mm, whereas 5.7% of patients undergoing conventional UKA had tibial inserts ≥10 mm. In this analysis, the maximum tibial component thickness was 11 mm in robotic-assisted UKA and 14 mm in conventional UKA. The distribution of conventional UKA tibial resection thicknesses is significantly greater in comparison to robotic-assisted UKA, which more reproducibly achieved accurate and precise conservative resection. No significant differences were noted in the percentages of polyethylene sizes between Blue Belt Technologies or MAKO cases.

Discussion

Robotic assistance enhances the accuracy of bone preparation, implant component alignment, and soft tissue balance in UKA.^10-15 It has yet to be determined whether this improved accuracy translates to improved clinical performance or longevity of the UKA implant. However, we demonstrate that the enhanced accuracy of robotic technology results in more conservative tibial resection when compared to conventional techniques with a potential benefit suggested in the literature upon conversion to TKA.

The findings of this study have important implications for patients undergoing conversion of UKA to TKA, potentially optimizing the ease of revision and clinical outcomes. The outcomes of UKA conversion to TKA are often considered inferior to those of primary TKA, compromised by bone loss, need for augmentation, and challenges of restoring the joint line and rotation.^9,16-22 Barrett and Scott¹⁸ reported only 66% of patients had good or excellent results at an average of 4.6 years of follow-up after UKA conversion to TKA. Over 50% required stemmed implants and bone graft or bone cement augmentation to address osseous insufficiency. The authors suggested that the primary determinant of the complexity of the conversion to TKA was the surgical technique used in the index procedure. They concluded that UKA conversion to TKA can be as successful as a primary TKA and primary TKA implants can be used without bone augmentation or stems during the revision procedure if minimal tibial bone is resected at the time of the index UKA.¹⁸ Schwarzkopf and colleagues⁹ supported this conclusion when they found that aggressive tibial resection during UKA resulted in the need for bone graft, stem, wedge, or augment in 70% of cases when converted to TKA. Similarly, Khan and colleagues²³ found that 26% of patients required bone grafting and 26% required some form of augmentation, and Springer and colleagues³ reported that 68% required a graft, augment, or stem.^3,22 Using data from the New Zealand Joint Registry, Pearse and colleagues⁵ reported that revision TKA components were necessary in 28% of patients and concluded that converting a UKA to TKA gives a less reliable result than primary TKA, and with functional results that are not significantly better than a revision from a TKA.

Conservative tibial resection during UKA minimizes the complexity and concerns of bone loss upon conversion to TKA. Schwarzkopf and colleagues⁹ found 96.6% of patients with conservative tibial resection received a primary TKA implant, without augments or stems. Furthermore, patients with a primary TKA implant showed improved tibial survivorship, with revision as an end point, compared with patients who received a TKA implant that required stems and augments or bone graft for support.⁹ Also emphasizing the importance of minimal tibial resection, O’Donnell and colleagues⁸ compared a cohort of patients undergoing conversion of a minimal resection resurfacing onlay-type UKA to TKA with a cohort of patients undergoing primary TKA. They found that 40% of patients required bone grafting for contained defects, 3.6% required metal augments, and 1.8% required stems.⁸ There was no significant difference between the groups in terms of range of motion, functional outcome, or radiologic outcomes. The authors concluded that revision of minimal resection resurfacing implants to TKA is associated with similar results to primary TKA and is superior to revision of UKA with greater bone loss. Prior studies have shown that one of the advantages of robotic-assisted UKA is the accuracy and precision of bone resection. The present study supports this premise by showing that tibial resection is significantly more conservative using robotic-assisted techniques when using tibial component thickness as a surrogate for extent of bone resection. While our study did not address implant durability or the impact of conservative resection on conversion to TKA, studies referenced above suggest that the conservative nature of bone preparation would have a relevant impact on the revision of the implant to TKA.

Our study is a retrospective case series that reports tibial component thickness as a surrogate for volume of tibial resection during UKA. While the implication is that more conservative tibial resection may optimize durability and ease of conversion to TKA, future study will be needed to compare robotic-assisted and conventional cases of UKA upon conversion to TKA in order to ascertain whether the more conventional resections of robotic-assisted UKA in fact lead to revision that is comparable with primary TKA in terms of bone loss at the time of revision, components utilized, the need for bone graft, augments, or stems, and clinical outcomes. Given the method of data collection in this study, we could not control for clinical deformity, selection bias, surgeon experience, or medial vs lateral knee compartments. These potential confounders represent weaknesses of this study.

In conclusion, conversion of UKA to TKA may be associated with significant osseous insufficiency, which may compromise patient outcomes in comparison to primary TKA. Studies have shown that UKA conversion to TKA is comparable to primary TKA when minimal tibial resection is performed during the UKA, and the need for augmentation, grafting or stems is increased with more aggressive tibial resection. This study has shown that when robotic assistance is utilized, tibial resection is more precise, less variable, and more conservative compared to conventional techniques.

Am J Orthop. 2016;45(7):E465-E468. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Unicompartmental knee arthroplasty (UKA) is considered a less invasive approach for the treatment of unicompartmental knee arthritis when compared with total knee arthroplasty (TKA), with optimal preservation of kinematics.¹ Despite excellent functional outcomes, conversion to TKA may be necessary if the UKA fails, or in patients with progressive knee arthritis. Some studies have found UKA conversion to TKA to be comparable with primary TKA,^2,3 whereas others have found that conversion often requires bone graft, augments, and stemmed components and has increased complications and inferior results compared to primary TKA.^4-7 While some studies report that <10% of UKA conversions to TKA require augments,² others have found that as many as 76% require augments.^4-8

Schwarzkopf and colleagues⁹ recently demonstrated that UKA conversion to TKA is comparable with primary TKA when a conservative tibial resection is performed during the index procedure. However, they reported increased complexity when greater tibial resection was performed and thicker polyethylene inserts were used at the time of the index UKA. The odds ratio of needing an augment or stem during the conversion to TKA was 26.8 (95% confidence interval, 3.71-194) when an aggressive tibial resection was performed during the UKA.⁹ Tibial resection thickness may thus be predictive of anticipated complexity of UKA revision to TKA and may aid in preoperative planning.

Robotic assistance has been shown to enhance the accuracy of bone preparation, implant component alignment, and soft tissue balance in UKA.^10-15 It has yet to be determined whether this improved accuracy translates to improved clinical performance or longevity of the UKA implant. However, the enhanced accuracy of robotic technology may result in more conservative tibial resection when compared to conventional UKA and may be advantageous if conversion to TKA becomes necessary.

The purpose of this study was to compare the distribution of polyethylene insert sizes implanted during conventional and robotic-assisted UKA. We hypothesized that robotic assistance would demonstrate more conservative tibial resection compared to conventional methods of bone preparation.

Methods

We retrospectively compared the distribution of polyethylene insert sizes implanted during consecutive conventional and robotic-assisted UKA procedures. Several manufacturers were queried to provide a listing of the polyethylene insert sizes utilized, ranging from 8 mm to 14 mm. The analysis included 8421 robotic-assisted UKA cases and 27,989 conventional UKA cases. Data were provided by Zimmer Biomet and Smith & Nephew regarding conventional cases, as well as Blue Belt Technologies (now part of Smith & Nephew) and MAKO Surgical (now part of Stryker) regarding robotic-assisted cases. (Dr. Lonner has an ongoing relationship as a consultant with Blue Belt Technologies, whose data was utilized in this study.) Using tibial insert thickness as a surrogate measure of the extent of tibial resection, an insert size of ≥10 mm was defined as aggressive while <10 mm was considered conservative. This cutoff was established based on its corresponding resection level with primary TKA and the anticipated need for augments. Statistical analysis was performed using a Mann-Whitney-Wilcoxon test. Significance was set at P < .05.

Results

Tibial resection thickness was found to be most commonly conservative in nature, with sizes 8-mm and 9-mm polyethylene inserts utilized in the majority of both robotic-assisted and conventional UKA cases. However, statistically more 8-mm and 9-mm polyethylene inserts were used in the robotic group (93.6%) than in the conventional group (84.5%) (P < .0001; Figure). Aggressive tibial resection, requiring tibial inserts ≥10 mm, was performed in 6.4% of robotic-assisted cases and 15.5% of conventional cases.

Only .29% of robotic-assisted cases required tibial inserts ≥10 mm, whereas 5.7% of patients undergoing conventional UKA had tibial inserts ≥10 mm. In this analysis, the maximum tibial component thickness was 11 mm in robotic-assisted UKA and 14 mm in conventional UKA. The distribution of conventional UKA tibial resection thicknesses is significantly greater in comparison to robotic-assisted UKA, which more reproducibly achieved accurate and precise conservative resection. No significant differences were noted in the percentages of polyethylene sizes between Blue Belt Technologies or MAKO cases.

Discussion

Robotic assistance enhances the accuracy of bone preparation, implant component alignment, and soft tissue balance in UKA.^10-15 It has yet to be determined whether this improved accuracy translates to improved clinical performance or longevity of the UKA implant. However, we demonstrate that the enhanced accuracy of robotic technology results in more conservative tibial resection when compared to conventional techniques with a potential benefit suggested in the literature upon conversion to TKA.

The findings of this study have important implications for patients undergoing conversion of UKA to TKA, potentially optimizing the ease of revision and clinical outcomes. The outcomes of UKA conversion to TKA are often considered inferior to those of primary TKA, compromised by bone loss, need for augmentation, and challenges of restoring the joint line and rotation.^9,16-22 Barrett and Scott¹⁸ reported only 66% of patients had good or excellent results at an average of 4.6 years of follow-up after UKA conversion to TKA. Over 50% required stemmed implants and bone graft or bone cement augmentation to address osseous insufficiency. The authors suggested that the primary determinant of the complexity of the conversion to TKA was the surgical technique used in the index procedure. They concluded that UKA conversion to TKA can be as successful as a primary TKA and primary TKA implants can be used without bone augmentation or stems during the revision procedure if minimal tibial bone is resected at the time of the index UKA.¹⁸ Schwarzkopf and colleagues⁹ supported this conclusion when they found that aggressive tibial resection during UKA resulted in the need for bone graft, stem, wedge, or augment in 70% of cases when converted to TKA. Similarly, Khan and colleagues²³ found that 26% of patients required bone grafting and 26% required some form of augmentation, and Springer and colleagues³ reported that 68% required a graft, augment, or stem.^3,22 Using data from the New Zealand Joint Registry, Pearse and colleagues⁵ reported that revision TKA components were necessary in 28% of patients and concluded that converting a UKA to TKA gives a less reliable result than primary TKA, and with functional results that are not significantly better than a revision from a TKA.

Conservative tibial resection during UKA minimizes the complexity and concerns of bone loss upon conversion to TKA. Schwarzkopf and colleagues⁹ found 96.6% of patients with conservative tibial resection received a primary TKA implant, without augments or stems. Furthermore, patients with a primary TKA implant showed improved tibial survivorship, with revision as an end point, compared with patients who received a TKA implant that required stems and augments or bone graft for support.⁹ Also emphasizing the importance of minimal tibial resection, O’Donnell and colleagues⁸ compared a cohort of patients undergoing conversion of a minimal resection resurfacing onlay-type UKA to TKA with a cohort of patients undergoing primary TKA. They found that 40% of patients required bone grafting for contained defects, 3.6% required metal augments, and 1.8% required stems.⁸ There was no significant difference between the groups in terms of range of motion, functional outcome, or radiologic outcomes. The authors concluded that revision of minimal resection resurfacing implants to TKA is associated with similar results to primary TKA and is superior to revision of UKA with greater bone loss. Prior studies have shown that one of the advantages of robotic-assisted UKA is the accuracy and precision of bone resection. The present study supports this premise by showing that tibial resection is significantly more conservative using robotic-assisted techniques when using tibial component thickness as a surrogate for extent of bone resection. While our study did not address implant durability or the impact of conservative resection on conversion to TKA, studies referenced above suggest that the conservative nature of bone preparation would have a relevant impact on the revision of the implant to TKA.

Our study is a retrospective case series that reports tibial component thickness as a surrogate for volume of tibial resection during UKA. While the implication is that more conservative tibial resection may optimize durability and ease of conversion to TKA, future study will be needed to compare robotic-assisted and conventional cases of UKA upon conversion to TKA in order to ascertain whether the more conventional resections of robotic-assisted UKA in fact lead to revision that is comparable with primary TKA in terms of bone loss at the time of revision, components utilized, the need for bone graft, augments, or stems, and clinical outcomes. Given the method of data collection in this study, we could not control for clinical deformity, selection bias, surgeon experience, or medial vs lateral knee compartments. These potential confounders represent weaknesses of this study.

In conclusion, conversion of UKA to TKA may be associated with significant osseous insufficiency, which may compromise patient outcomes in comparison to primary TKA. Studies have shown that UKA conversion to TKA is comparable to primary TKA when minimal tibial resection is performed during the UKA, and the need for augmentation, grafting or stems is increased with more aggressive tibial resection. This study has shown that when robotic assistance is utilized, tibial resection is more precise, less variable, and more conservative compared to conventional techniques.

Am J Orthop. 2016;45(7):E465-E468. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Leg-length discrepancy (LLD) is common in the general population¹ and particularly in patients with degenerative joint diseases of the hip and knee.² Common complications of LLD include femoral, sciatic, and peroneal nerve palsy; lower back pain; gait abnormalities³; and general dissatisfaction. LLD is a concern for orthopedic surgeons who perform total knee arthroplasty (TKA) because limb lengthening is common after this procedure.^4,5 Surgeons are aware of the limb lengthening that occurs during TKA,^4,5 and studies have confirmed that LLD usually decreases after TKA.^4,5

Despite surgeons’ best efforts, some patients still perceive LLD after surgery, though the incidence of perceived LLD in patients who have had TKA has not been well documented. Aside from actual, objectively measured LLD, there may be other factors that lead patients to perceive LLD. Study results have suggested that preoperative varus–valgus alignment of the knee joint may correlate with how much an operative leg is lengthened after TKA^4,5; however, the outcome investigated was objective LLD measurements, not perceived LLD. Understanding the factors that may influence patients’ ability to perceive LLD would allow surgeons to preoperatively identify patients who are at higher risk for postoperative perceived LLD. This information, along with expected time to resolution of postoperative perceived LLD, would allow surgeons to educate their patients accordingly.

We conducted a study to determine the incidence of perceived LLD before and after primary TKA in patients with unilateral osteoarthritis and to determine the correlation between mechanical axis of the knee and perceived LLD before and after surgery. Given that surgery may correct mechanical axis misalignment, we investigated the correlation between this correction and its ability to change patients’ preoperative and postoperative perceived LLD. We hypothesized that a large correction of mechanical axis would lead patients to perceive LLD after surgery. The relationship of body mass index (BMI) and age to patients’ perceived LLD was also assessed. The incidence and time frame of resolution of postoperative perceived LLD were determined.

Methods

Approval for this study was received from the Institutional Review Board at our institution, Rush University Medical Center in Chicago, Illinois. Seventy-three patients undergoing primary TKA performed by 3 surgeons at 2 institutions between February 2010 and January 2013 were prospectively enrolled. Inclusion criteria were age 18 years to 90 years and primary TKA for unilateral osteoarthritis; exclusion criteria were allergy or intolerance to the study materials, operative treatment of affected joint or its underlying etiology within prior month, previous surgeries (other than arthroscopy) on affected joint, previous surgeries (on unaffected lower extremity) that may influence preoperative and postoperative leg lengths, and any substance abuse or dependence within the past 6 months. Patients provided written informed consent for total knee arthroplasty.

All surgeries were performed by Dr. Levine, Dr. Della Valle, and Dr. Sporer using the medial parapatellar or midvastus approach with tourniquet. Similar standard postoperative rehabilitation protocols with early mobilization were used in all cases.

During clinical evaluation, patient demographic data were collected and LLD surveys administered. Patients were asked, before surgery and 3 to 6 weeks, 3 months, 6 months, and 1 year after surgery, if they perceived LLD. A patient who no longer perceived LLD after surgery was no longer followed for this study.

At the preoperative clinic visit and at the 3-month or 6-week postoperative visit, standing mechanical axis radiographs were viewed by 2 of the authors (not the primary surgeons) using PACS (picture archiving and communication system software). The mechanical axis of the operative leg was measured with ImageJ software by taking the angle from the center of the femur to the middle of the ankle joint, with the vertex assigned to the middle of the knee joint.

We used a 2-tailed unpaired t test to determine the relationship of preoperative mechanical axis to perceived LLD (or lack thereof) before surgery. The data were analyzed for separate varus and valgus deformities. Then we determined the relationship of postoperative mechanical axis to perceived LLD (or lack thereof) after surgery. The McNemar test was used to determine the effect of surgery on patients’ LLD perceptions.

To determine the relationship between preoperative-to-postoperative change in mechanical axis and change in LLD perceptions, we divided patients into 4 groups. Group 1 had both preoperative and postoperative perceived LLD, group 2 had no preoperative or postoperative perceived LLD, group 3 had preoperative perceived LLD but no postoperative perceived LLD, and group 4 had postoperative perceived LLD but no preoperative perceived LLD. The absolute value of the difference between preoperative and postoperative mechanical axis was then determined, relative to 180°, to account for changes in varus to valgus deformity before and after surgery and vice versa. Analysis of variance (ANOVA) was used to detect differences between groups. This analysis was then stratified based on BMI and age.

 

Results

Of the 73 enrolled patients, 2 were excluded from results analysis because of inadequate data—one did not complete the postoperative LLD survey, and the other did not have postoperative standing mechanical axis radiographs—leaving 71 patients (27 men, 44 women) with adequate data. Mean (SD) age of all patients was 65 (8.4) years (range, 47-89 years). Mean (SD) BMI was 35.1 (9.9; range, 20.2-74.8).

Of the 71 patients with adequate data, 18 had preoperative perceived LLD and 53 did not; in addition, 7 had postoperative perceived LLD and 64 did not. All 7 patients with postoperative perceived LLD noted resolution of LLD, at a mean of 8.5 weeks (range, 3 weeks-3 months). There was a significant difference between the 18 patients with preoperative perceived LLD and the 7 with postoperative perceived LLD (P = .035, analyzed with the McNemar test).

Table 1 lists the mean preoperative mechanical axis measurements for patients with and without preoperative perceived LLD.

There was no significant difference between the 2 groups (P = .27). There was also no significant difference in preoperative mechanical axis when cases were separated and analyzed as varus and valgus deformities (varus P = .53, valgus P = .20).

Table 2 lists the mean postoperative mechanical axis measurements for patients with and without postoperative perceived LLD.

There was no significant difference between the 2 groups (P = .42). There was also no significant difference in postoperative mechanical axis for separate varus (P = .29) and valgus (P = .52) deformities.

Table 3 lists the mean absolute values of mechanical axis correction (preoperative to postoperative) for the 4 patient groups described in the Methods section.

ANOVA revealed no significant statistical difference in these values among the groups (P = .9229). There were also no significant statistical differences when the groups were stratified by age (40-59.9 years, P = .5973; 60-69.9 years, P = .6263; 70 years or older, P = .3779) or when ANOVA was used to compare the groups’ mean ages (P = .3183). In addition, the 4 groups were not significantly statistically different in BMI: obese (BMI >30; P = .3891) and nonobese (BMI <29.9; P = .9862).

Discussion

In this study, 18 patients (25%) had preoperative perceived LLD, proving that perceived LLD is common in patients who undergo TKA for unilateral osteoarthritis. Surgeons should give their patients a preoperative survey on perceived LLD, as survey responses may inform and influence surgical decisions and strategies.

Of the 18 patients with preoperative perceived LLD, only 1 had postoperative perceived LLD. That perceived LLD decreased after surgery makes sense given the widely accepted notion that actual LLD is common before primary TKA but in most cases is corrected during surgery.^4,5 As LLD correction during surgery is so successful, surgeons should tell their patients with preoperative perceived LLD that in most cases it will be fixed after TKA.

Although the incidence of perceived LLD decreased after TKA (as mentioned earlier), the decrease seemed to be restricted mostly to patients with preoperative perceived LLD, and the underlying LLD was most probably corrected by the surgery. However, surgery introduced perceived LLD in 6 cases, supporting the notion that it is crucial to understand which patients are at higher risk for postoperative perceived LLD and what if any time frame can be expected for resolution in these cases. In our study, all cases of perceived LLD had resolved by a mean follow-up of 8.5 weeks (range, 3 weeks-3 months). This phenomenon of resolution may be attributed to some of the physical, objective LLD corrections that naturally occur throughout the postoperative course,⁴ though psychological factors may also be involved. Our study results suggest patients should be counseled that, though about 10% of patients perceive LLD after primary TKA, the vast majority of perceived LLD cases resolve within 3 months.

One study goal was to determine the relationship between the mechanical axis of the knee and perceived LLD both before and after surgery. There were no significant relationships. This was also true when cases of varus and valgus deformity were analyzed separately.

Another study goal was to determine if a surgical change in the mechanical alignment of the knee would influence preoperative-to-postoperative LLD perceptions. In our analysis, patients were divided into 4 groups based on their preoperative and postoperative LLD perceptions (see Methods section). ANOVA revealed no significant differences in absolute values of mechanical axis correction among the 4 groups. Likewise, there were no correlations between BMI and age and mechanical axis correction among the groups, suggesting LLD perception is unrelated to any of these variables. Ideally, if a relationship between a threshold knee alignment value and perceived LLD existed, surgeons would be able to counsel patients at higher risk for perceived LLD about how their knee alignment may contribute to their perception. Unfortunately, our study results did not show any significant statistical relationships in this regard.

The problem of LLD in patients undergoing TKA is not new, and much research is needed to determine the correlation between perceived versus actual discrepancies, and why they occur. Our study results confirmed that TKA corrects most cases of preoperative perceived LLD but introduces perceived LLD in other cases. Whether preoperative or postoperative LLD is merely perceived or is in fact an actual discrepancy remains to be seen.

One limitation of this study was its lack of leg-length measurements. Although we studied knee alignment specifically, it would have been useful to compare perceived LLD with measured leg lengths, either clinically or radiographically, especially since leg lengths obviously play a role in any perceived LLD. We used mechanical alignment as a surrogate for actual LLD because we hypothesized that alignment may contribute to patients’ perceived discrepancies.

Another limitation was the relatively small sample. Only 24 cases of perceived LLD were analyzed. Given our low rates of perceived LLD (25% before surgery, 10% after surgery), it is difficult to study a large enough TKA group to establish a statistically significant number of cases. Nevertheless, investigators may use larger groups to establish more meaningful relationships.

A third limitation was that alignment was measured on the operative side but not the contralateral side. As we were focusing on perceived discrepancy, contralateral knee alignment may play an important role. Our study involved patients with unilateral osteoarthritis, so it would be reasonable to assume the nonoperative knee was almost neutral in alignment in most cases. However, given that varus/valgus misalignment is a known risk factor for osteoarthritis,⁶ many of our patients with unilateral disease may very well have had preexisting misalignment of both knees. The undetermined alignment of the nonoperative side may be a confounding variable in the relationship between operative knee alignment and perceived LLD.

Fourth, not all patients were surveyed 3 weeks after surgery. Some were first surveyed at 6 weeks, and it is possible there were cases of transient postoperative LLD that resolved before that point. Therefore, our reported incidence of postoperative LLD could have missed some cases. In addition, our mean 8.5-week period for LLD resolution may not have accounted for these resolved cases of transient perceived LLD.

Am J Orthop. 2016;45(7):E429-E433. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Leg-length discrepancy (LLD) is common in the general population¹ and particularly in patients with degenerative joint diseases of the hip and knee.² Common complications of LLD include femoral, sciatic, and peroneal nerve palsy; lower back pain; gait abnormalities³; and general dissatisfaction. LLD is a concern for orthopedic surgeons who perform total knee arthroplasty (TKA) because limb lengthening is common after this procedure.^4,5 Surgeons are aware of the limb lengthening that occurs during TKA,^4,5 and studies have confirmed that LLD usually decreases after TKA.^4,5

Despite surgeons’ best efforts, some patients still perceive LLD after surgery, though the incidence of perceived LLD in patients who have had TKA has not been well documented. Aside from actual, objectively measured LLD, there may be other factors that lead patients to perceive LLD. Study results have suggested that preoperative varus–valgus alignment of the knee joint may correlate with how much an operative leg is lengthened after TKA^4,5; however, the outcome investigated was objective LLD measurements, not perceived LLD. Understanding the factors that may influence patients’ ability to perceive LLD would allow surgeons to preoperatively identify patients who are at higher risk for postoperative perceived LLD. This information, along with expected time to resolution of postoperative perceived LLD, would allow surgeons to educate their patients accordingly.

We conducted a study to determine the incidence of perceived LLD before and after primary TKA in patients with unilateral osteoarthritis and to determine the correlation between mechanical axis of the knee and perceived LLD before and after surgery. Given that surgery may correct mechanical axis misalignment, we investigated the correlation between this correction and its ability to change patients’ preoperative and postoperative perceived LLD. We hypothesized that a large correction of mechanical axis would lead patients to perceive LLD after surgery. The relationship of body mass index (BMI) and age to patients’ perceived LLD was also assessed. The incidence and time frame of resolution of postoperative perceived LLD were determined.

Methods

Approval for this study was received from the Institutional Review Board at our institution, Rush University Medical Center in Chicago, Illinois. Seventy-three patients undergoing primary TKA performed by 3 surgeons at 2 institutions between February 2010 and January 2013 were prospectively enrolled. Inclusion criteria were age 18 years to 90 years and primary TKA for unilateral osteoarthritis; exclusion criteria were allergy or intolerance to the study materials, operative treatment of affected joint or its underlying etiology within prior month, previous surgeries (other than arthroscopy) on affected joint, previous surgeries (on unaffected lower extremity) that may influence preoperative and postoperative leg lengths, and any substance abuse or dependence within the past 6 months. Patients provided written informed consent for total knee arthroplasty.

All surgeries were performed by Dr. Levine, Dr. Della Valle, and Dr. Sporer using the medial parapatellar or midvastus approach with tourniquet. Similar standard postoperative rehabilitation protocols with early mobilization were used in all cases.

During clinical evaluation, patient demographic data were collected and LLD surveys administered. Patients were asked, before surgery and 3 to 6 weeks, 3 months, 6 months, and 1 year after surgery, if they perceived LLD. A patient who no longer perceived LLD after surgery was no longer followed for this study.

At the preoperative clinic visit and at the 3-month or 6-week postoperative visit, standing mechanical axis radiographs were viewed by 2 of the authors (not the primary surgeons) using PACS (picture archiving and communication system software). The mechanical axis of the operative leg was measured with ImageJ software by taking the angle from the center of the femur to the middle of the ankle joint, with the vertex assigned to the middle of the knee joint.

We used a 2-tailed unpaired t test to determine the relationship of preoperative mechanical axis to perceived LLD (or lack thereof) before surgery. The data were analyzed for separate varus and valgus deformities. Then we determined the relationship of postoperative mechanical axis to perceived LLD (or lack thereof) after surgery. The McNemar test was used to determine the effect of surgery on patients’ LLD perceptions.

To determine the relationship between preoperative-to-postoperative change in mechanical axis and change in LLD perceptions, we divided patients into 4 groups. Group 1 had both preoperative and postoperative perceived LLD, group 2 had no preoperative or postoperative perceived LLD, group 3 had preoperative perceived LLD but no postoperative perceived LLD, and group 4 had postoperative perceived LLD but no preoperative perceived LLD. The absolute value of the difference between preoperative and postoperative mechanical axis was then determined, relative to 180°, to account for changes in varus to valgus deformity before and after surgery and vice versa. Analysis of variance (ANOVA) was used to detect differences between groups. This analysis was then stratified based on BMI and age.

 

Results

Of the 73 enrolled patients, 2 were excluded from results analysis because of inadequate data—one did not complete the postoperative LLD survey, and the other did not have postoperative standing mechanical axis radiographs—leaving 71 patients (27 men, 44 women) with adequate data. Mean (SD) age of all patients was 65 (8.4) years (range, 47-89 years). Mean (SD) BMI was 35.1 (9.9; range, 20.2-74.8).

Of the 71 patients with adequate data, 18 had preoperative perceived LLD and 53 did not; in addition, 7 had postoperative perceived LLD and 64 did not. All 7 patients with postoperative perceived LLD noted resolution of LLD, at a mean of 8.5 weeks (range, 3 weeks-3 months). There was a significant difference between the 18 patients with preoperative perceived LLD and the 7 with postoperative perceived LLD (P = .035, analyzed with the McNemar test).

Table 1 lists the mean preoperative mechanical axis measurements for patients with and without preoperative perceived LLD.

There was no significant difference between the 2 groups (P = .27). There was also no significant difference in preoperative mechanical axis when cases were separated and analyzed as varus and valgus deformities (varus P = .53, valgus P = .20).

Table 2 lists the mean postoperative mechanical axis measurements for patients with and without postoperative perceived LLD.

There was no significant difference between the 2 groups (P = .42). There was also no significant difference in postoperative mechanical axis for separate varus (P = .29) and valgus (P = .52) deformities.

Table 3 lists the mean absolute values of mechanical axis correction (preoperative to postoperative) for the 4 patient groups described in the Methods section.

ANOVA revealed no significant statistical difference in these values among the groups (P = .9229). There were also no significant statistical differences when the groups were stratified by age (40-59.9 years, P = .5973; 60-69.9 years, P = .6263; 70 years or older, P = .3779) or when ANOVA was used to compare the groups’ mean ages (P = .3183). In addition, the 4 groups were not significantly statistically different in BMI: obese (BMI >30; P = .3891) and nonobese (BMI <29.9; P = .9862).

Discussion

In this study, 18 patients (25%) had preoperative perceived LLD, proving that perceived LLD is common in patients who undergo TKA for unilateral osteoarthritis. Surgeons should give their patients a preoperative survey on perceived LLD, as survey responses may inform and influence surgical decisions and strategies.

Of the 18 patients with preoperative perceived LLD, only 1 had postoperative perceived LLD. That perceived LLD decreased after surgery makes sense given the widely accepted notion that actual LLD is common before primary TKA but in most cases is corrected during surgery.^4,5 As LLD correction during surgery is so successful, surgeons should tell their patients with preoperative perceived LLD that in most cases it will be fixed after TKA.

Although the incidence of perceived LLD decreased after TKA (as mentioned earlier), the decrease seemed to be restricted mostly to patients with preoperative perceived LLD, and the underlying LLD was most probably corrected by the surgery. However, surgery introduced perceived LLD in 6 cases, supporting the notion that it is crucial to understand which patients are at higher risk for postoperative perceived LLD and what if any time frame can be expected for resolution in these cases. In our study, all cases of perceived LLD had resolved by a mean follow-up of 8.5 weeks (range, 3 weeks-3 months). This phenomenon of resolution may be attributed to some of the physical, objective LLD corrections that naturally occur throughout the postoperative course,⁴ though psychological factors may also be involved. Our study results suggest patients should be counseled that, though about 10% of patients perceive LLD after primary TKA, the vast majority of perceived LLD cases resolve within 3 months.

One study goal was to determine the relationship between the mechanical axis of the knee and perceived LLD both before and after surgery. There were no significant relationships. This was also true when cases of varus and valgus deformity were analyzed separately.

Another study goal was to determine if a surgical change in the mechanical alignment of the knee would influence preoperative-to-postoperative LLD perceptions. In our analysis, patients were divided into 4 groups based on their preoperative and postoperative LLD perceptions (see Methods section). ANOVA revealed no significant differences in absolute values of mechanical axis correction among the 4 groups. Likewise, there were no correlations between BMI and age and mechanical axis correction among the groups, suggesting LLD perception is unrelated to any of these variables. Ideally, if a relationship between a threshold knee alignment value and perceived LLD existed, surgeons would be able to counsel patients at higher risk for perceived LLD about how their knee alignment may contribute to their perception. Unfortunately, our study results did not show any significant statistical relationships in this regard.

The problem of LLD in patients undergoing TKA is not new, and much research is needed to determine the correlation between perceived versus actual discrepancies, and why they occur. Our study results confirmed that TKA corrects most cases of preoperative perceived LLD but introduces perceived LLD in other cases. Whether preoperative or postoperative LLD is merely perceived or is in fact an actual discrepancy remains to be seen.

One limitation of this study was its lack of leg-length measurements. Although we studied knee alignment specifically, it would have been useful to compare perceived LLD with measured leg lengths, either clinically or radiographically, especially since leg lengths obviously play a role in any perceived LLD. We used mechanical alignment as a surrogate for actual LLD because we hypothesized that alignment may contribute to patients’ perceived discrepancies.

Another limitation was the relatively small sample. Only 24 cases of perceived LLD were analyzed. Given our low rates of perceived LLD (25% before surgery, 10% after surgery), it is difficult to study a large enough TKA group to establish a statistically significant number of cases. Nevertheless, investigators may use larger groups to establish more meaningful relationships.

A third limitation was that alignment was measured on the operative side but not the contralateral side. As we were focusing on perceived discrepancy, contralateral knee alignment may play an important role. Our study involved patients with unilateral osteoarthritis, so it would be reasonable to assume the nonoperative knee was almost neutral in alignment in most cases. However, given that varus/valgus misalignment is a known risk factor for osteoarthritis,⁶ many of our patients with unilateral disease may very well have had preexisting misalignment of both knees. The undetermined alignment of the nonoperative side may be a confounding variable in the relationship between operative knee alignment and perceived LLD.

Fourth, not all patients were surveyed 3 weeks after surgery. Some were first surveyed at 6 weeks, and it is possible there were cases of transient postoperative LLD that resolved before that point. Therefore, our reported incidence of postoperative LLD could have missed some cases. In addition, our mean 8.5-week period for LLD resolution may not have accounted for these resolved cases of transient perceived LLD.

Am J Orthop. 2016;45(7):E429-E433. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Leg-length discrepancy (LLD) is common in the general population¹ and particularly in patients with degenerative joint diseases of the hip and knee.² Common complications of LLD include femoral, sciatic, and peroneal nerve palsy; lower back pain; gait abnormalities³; and general dissatisfaction. LLD is a concern for orthopedic surgeons who perform total knee arthroplasty (TKA) because limb lengthening is common after this procedure.^4,5 Surgeons are aware of the limb lengthening that occurs during TKA,^4,5 and studies have confirmed that LLD usually decreases after TKA.^4,5

Despite surgeons’ best efforts, some patients still perceive LLD after surgery, though the incidence of perceived LLD in patients who have had TKA has not been well documented. Aside from actual, objectively measured LLD, there may be other factors that lead patients to perceive LLD. Study results have suggested that preoperative varus–valgus alignment of the knee joint may correlate with how much an operative leg is lengthened after TKA^4,5; however, the outcome investigated was objective LLD measurements, not perceived LLD. Understanding the factors that may influence patients’ ability to perceive LLD would allow surgeons to preoperatively identify patients who are at higher risk for postoperative perceived LLD. This information, along with expected time to resolution of postoperative perceived LLD, would allow surgeons to educate their patients accordingly.

We conducted a study to determine the incidence of perceived LLD before and after primary TKA in patients with unilateral osteoarthritis and to determine the correlation between mechanical axis of the knee and perceived LLD before and after surgery. Given that surgery may correct mechanical axis misalignment, we investigated the correlation between this correction and its ability to change patients’ preoperative and postoperative perceived LLD. We hypothesized that a large correction of mechanical axis would lead patients to perceive LLD after surgery. The relationship of body mass index (BMI) and age to patients’ perceived LLD was also assessed. The incidence and time frame of resolution of postoperative perceived LLD were determined.

Methods

Approval for this study was received from the Institutional Review Board at our institution, Rush University Medical Center in Chicago, Illinois. Seventy-three patients undergoing primary TKA performed by 3 surgeons at 2 institutions between February 2010 and January 2013 were prospectively enrolled. Inclusion criteria were age 18 years to 90 years and primary TKA for unilateral osteoarthritis; exclusion criteria were allergy or intolerance to the study materials, operative treatment of affected joint or its underlying etiology within prior month, previous surgeries (other than arthroscopy) on affected joint, previous surgeries (on unaffected lower extremity) that may influence preoperative and postoperative leg lengths, and any substance abuse or dependence within the past 6 months. Patients provided written informed consent for total knee arthroplasty.

All surgeries were performed by Dr. Levine, Dr. Della Valle, and Dr. Sporer using the medial parapatellar or midvastus approach with tourniquet. Similar standard postoperative rehabilitation protocols with early mobilization were used in all cases.

During clinical evaluation, patient demographic data were collected and LLD surveys administered. Patients were asked, before surgery and 3 to 6 weeks, 3 months, 6 months, and 1 year after surgery, if they perceived LLD. A patient who no longer perceived LLD after surgery was no longer followed for this study.

At the preoperative clinic visit and at the 3-month or 6-week postoperative visit, standing mechanical axis radiographs were viewed by 2 of the authors (not the primary surgeons) using PACS (picture archiving and communication system software). The mechanical axis of the operative leg was measured with ImageJ software by taking the angle from the center of the femur to the middle of the ankle joint, with the vertex assigned to the middle of the knee joint.

We used a 2-tailed unpaired t test to determine the relationship of preoperative mechanical axis to perceived LLD (or lack thereof) before surgery. The data were analyzed for separate varus and valgus deformities. Then we determined the relationship of postoperative mechanical axis to perceived LLD (or lack thereof) after surgery. The McNemar test was used to determine the effect of surgery on patients’ LLD perceptions.

To determine the relationship between preoperative-to-postoperative change in mechanical axis and change in LLD perceptions, we divided patients into 4 groups. Group 1 had both preoperative and postoperative perceived LLD, group 2 had no preoperative or postoperative perceived LLD, group 3 had preoperative perceived LLD but no postoperative perceived LLD, and group 4 had postoperative perceived LLD but no preoperative perceived LLD. The absolute value of the difference between preoperative and postoperative mechanical axis was then determined, relative to 180°, to account for changes in varus to valgus deformity before and after surgery and vice versa. Analysis of variance (ANOVA) was used to detect differences between groups. This analysis was then stratified based on BMI and age.

 

Results

Of the 73 enrolled patients, 2 were excluded from results analysis because of inadequate data—one did not complete the postoperative LLD survey, and the other did not have postoperative standing mechanical axis radiographs—leaving 71 patients (27 men, 44 women) with adequate data. Mean (SD) age of all patients was 65 (8.4) years (range, 47-89 years). Mean (SD) BMI was 35.1 (9.9; range, 20.2-74.8).

Of the 71 patients with adequate data, 18 had preoperative perceived LLD and 53 did not; in addition, 7 had postoperative perceived LLD and 64 did not. All 7 patients with postoperative perceived LLD noted resolution of LLD, at a mean of 8.5 weeks (range, 3 weeks-3 months). There was a significant difference between the 18 patients with preoperative perceived LLD and the 7 with postoperative perceived LLD (P = .035, analyzed with the McNemar test).

Table 1 lists the mean preoperative mechanical axis measurements for patients with and without preoperative perceived LLD.

There was no significant difference between the 2 groups (P = .27). There was also no significant difference in preoperative mechanical axis when cases were separated and analyzed as varus and valgus deformities (varus P = .53, valgus P = .20).

Table 2 lists the mean postoperative mechanical axis measurements for patients with and without postoperative perceived LLD.

There was no significant difference between the 2 groups (P = .42). There was also no significant difference in postoperative mechanical axis for separate varus (P = .29) and valgus (P = .52) deformities.

Table 3 lists the mean absolute values of mechanical axis correction (preoperative to postoperative) for the 4 patient groups described in the Methods section.

ANOVA revealed no significant statistical difference in these values among the groups (P = .9229). There were also no significant statistical differences when the groups were stratified by age (40-59.9 years, P = .5973; 60-69.9 years, P = .6263; 70 years or older, P = .3779) or when ANOVA was used to compare the groups’ mean ages (P = .3183). In addition, the 4 groups were not significantly statistically different in BMI: obese (BMI >30; P = .3891) and nonobese (BMI <29.9; P = .9862).

Discussion

In this study, 18 patients (25%) had preoperative perceived LLD, proving that perceived LLD is common in patients who undergo TKA for unilateral osteoarthritis. Surgeons should give their patients a preoperative survey on perceived LLD, as survey responses may inform and influence surgical decisions and strategies.

Of the 18 patients with preoperative perceived LLD, only 1 had postoperative perceived LLD. That perceived LLD decreased after surgery makes sense given the widely accepted notion that actual LLD is common before primary TKA but in most cases is corrected during surgery.^4,5 As LLD correction during surgery is so successful, surgeons should tell their patients with preoperative perceived LLD that in most cases it will be fixed after TKA.

Although the incidence of perceived LLD decreased after TKA (as mentioned earlier), the decrease seemed to be restricted mostly to patients with preoperative perceived LLD, and the underlying LLD was most probably corrected by the surgery. However, surgery introduced perceived LLD in 6 cases, supporting the notion that it is crucial to understand which patients are at higher risk for postoperative perceived LLD and what if any time frame can be expected for resolution in these cases. In our study, all cases of perceived LLD had resolved by a mean follow-up of 8.5 weeks (range, 3 weeks-3 months). This phenomenon of resolution may be attributed to some of the physical, objective LLD corrections that naturally occur throughout the postoperative course,⁴ though psychological factors may also be involved. Our study results suggest patients should be counseled that, though about 10% of patients perceive LLD after primary TKA, the vast majority of perceived LLD cases resolve within 3 months.

One study goal was to determine the relationship between the mechanical axis of the knee and perceived LLD both before and after surgery. There were no significant relationships. This was also true when cases of varus and valgus deformity were analyzed separately.

Another study goal was to determine if a surgical change in the mechanical alignment of the knee would influence preoperative-to-postoperative LLD perceptions. In our analysis, patients were divided into 4 groups based on their preoperative and postoperative LLD perceptions (see Methods section). ANOVA revealed no significant differences in absolute values of mechanical axis correction among the 4 groups. Likewise, there were no correlations between BMI and age and mechanical axis correction among the groups, suggesting LLD perception is unrelated to any of these variables. Ideally, if a relationship between a threshold knee alignment value and perceived LLD existed, surgeons would be able to counsel patients at higher risk for perceived LLD about how their knee alignment may contribute to their perception. Unfortunately, our study results did not show any significant statistical relationships in this regard.

The problem of LLD in patients undergoing TKA is not new, and much research is needed to determine the correlation between perceived versus actual discrepancies, and why they occur. Our study results confirmed that TKA corrects most cases of preoperative perceived LLD but introduces perceived LLD in other cases. Whether preoperative or postoperative LLD is merely perceived or is in fact an actual discrepancy remains to be seen.

One limitation of this study was its lack of leg-length measurements. Although we studied knee alignment specifically, it would have been useful to compare perceived LLD with measured leg lengths, either clinically or radiographically, especially since leg lengths obviously play a role in any perceived LLD. We used mechanical alignment as a surrogate for actual LLD because we hypothesized that alignment may contribute to patients’ perceived discrepancies.

Another limitation was the relatively small sample. Only 24 cases of perceived LLD were analyzed. Given our low rates of perceived LLD (25% before surgery, 10% after surgery), it is difficult to study a large enough TKA group to establish a statistically significant number of cases. Nevertheless, investigators may use larger groups to establish more meaningful relationships.

A third limitation was that alignment was measured on the operative side but not the contralateral side. As we were focusing on perceived discrepancy, contralateral knee alignment may play an important role. Our study involved patients with unilateral osteoarthritis, so it would be reasonable to assume the nonoperative knee was almost neutral in alignment in most cases. However, given that varus/valgus misalignment is a known risk factor for osteoarthritis,⁶ many of our patients with unilateral disease may very well have had preexisting misalignment of both knees. The undetermined alignment of the nonoperative side may be a confounding variable in the relationship between operative knee alignment and perceived LLD.

Fourth, not all patients were surveyed 3 weeks after surgery. Some were first surveyed at 6 weeks, and it is possible there were cases of transient postoperative LLD that resolved before that point. Therefore, our reported incidence of postoperative LLD could have missed some cases. In addition, our mean 8.5-week period for LLD resolution may not have accounted for these resolved cases of transient perceived LLD.

Am J Orthop. 2016;45(7):E429-E433. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Risk factors for dislocation after reverse total shoulder arthroplasty (RTSA) are not clearly defined. Prosthetic dislocation can result in poor patient satisfaction, worse functional outcomes, and return to the operating room.^1-3 As a result, identification of modifiable risk factors for complications represents an important research initiative for shoulder surgeons.

There is a paucity of literature devoted to the study of dislocation after RTSA. Chalmers and colleagues⁴ found a 2.9% (11/385) incidence of early dislocation within 3 months after index surgery—an improvement over the 15.8% reported for early instability over the period 2004–2006.⁵ As prosthesis design has improved and surgeons have become more comfortable with the RTSA prosthesis, surgical indications have expanded,^6,7 and dislocation rates appear to have decreased. Although the most common indication for RTSA continues to be cuff tear arthropathy (CTA),⁶ there has been increased use in rheumatoid arthritis^8-10; proximal humerus fractures, especially in cases of poor bone quality and unreliable fixation of tuberosities^11-13; and failed previous shoulder reconstruction.^14,15 As RTSA is performed more often, limiting the complications will become more important for both patient care and economics.

We conducted a study to analyze dislocation rates at our institution and to identify both modifiable and nonmodifiable risk factors for dislocation after RTSA. By identifying risk factors for dislocation, we will be able to implement additional perioperative clinical measures to reduce the incidence of dislocation.

Materials and Methods

This retrospective study of dislocation after RTSA was conducted at the Rothman Institute of Orthopedics and Methodist Hospital (Thomas Jefferson University Hospitals, Philadelphia, PA). After obtaining Institutional Review Board approval for the study, we searched our institution’s electronic database of shoulder arthroplasties to identify all RTSAs performed at our 2 large-volume urban institutions between September 27, 2010 and December 31, 2013. For the record search, International Classification of Diseases, Ninth Revision (ICD-9) codes were used (Table 1).

These unique procedure codes are used by the hospital system for billing, but are not always specific to assigned procedures. Therefore, the individual operative reports identified were reviewed to identify the patients who actually underwent RTSA. From this database, all patients who underwent RTSA were selected. Using the subpopulation of patients who underwent RTSA, we searched individual medical records to identify patients who had a dislocation after RTSA. This information was cross-referenced with ICD-9 codes for shoulder dislocation (831.0, 831.01, 831.02, 831.03) to ensure that all patients were identified.

The medical records of each patient were used to identify independent variables that could be associated with dislocation rate. Demographic variables included sex, age, and race. Preoperative clinical data included body mass index (BMI), etiology of shoulder disease leading to RTSA, individual comorbidities, and Charlson Comorbidity Index (CCI)¹⁶ modified to be used with ICD-9 codes.¹⁷ In addition, prior shoulder surgery history and arthroplasty type (primary or revision) were determined. Postoperative considerations were time to dislocation, mechanism of dislocation, and intervention(s) needed for dislocation. Although the institutional database did not include operative variables such as prosthesis type and surgical approach, all 6 surgeons in this study were using a standard deltopectoral approach in beach-chair position with a Grammont style prosthesis for RTSA cases.

Descriptive statistics for RTSA patients and the dislocation subpopulation were compiled. Bivariate analysis was used to evaluate which of the previously described variables influenced dislocation rates. Last, multivariate logistic regression analysis was performed to evaluate which factors were independent predictors of dislocation. We included demographic variables (age, sex, ethnicity), clinical variables (BMI, individual comorbidities, CCI), and surgical variables (primary vs revision, diagnosis at time of surgery). All statistical analyses were performed with Excel 2013 (Microsoft) and SPSS Statistics Version 20.0 (SPSS Inc.).

Results

From the database, we identified 487 patients who underwent 510 RTSAs during the study period. These surgeries were performed by 6 shoulder and elbow fellowship–trained surgeons. Of the 510 RTSAs, 393 (77.1%) were primary cases, and 117 (22.9%) were revision cases.

Of the 510 shoulders that underwent RTSA, 15 (2.9%; 14 patients) dislocated. Of these 15 cases, 5 were primary (1.3% of all primary cases) and 10 were revision (8.5% of all revision cases). Mean time from index surgery to diagnosis of dislocation was 58.2 days (range, 0-319 days). One dislocation occurred immediately after surgery, 2 after falls, 4 from patient-identified low-energy mechanisms of injury, and 8 without known inciting events. Nine dislocations (60%) did not have a subscapularis repair (7 were irreparable, 2 underwent subscapularis peel without repair), and the other 6 were repaired primarily (Table 2).

In addition, 11 dislocations (73.3%) previously underwent open or arthroscopic shoulder surgery. All patients who had a dislocation after RTSA returned to the operating room at least once; no dislocation was successfully treated with closed reduction in the clinic. The 15 dislocations underwent 17 surgeries: 7 isolated polyethylene exchanges, 2 isolated closed reductions, 1 hematoma aspiration with closed reduction, 1 open reduction, 2 humeral component revisions with polyethylene exchange, 1 humeral augmentation with polyethylene exchange, 2 glenosphere exchanges with polyethylene exchange, and 1 polyethylene exchange with concurrent subscapularis repair.

Male patients accounted for 32.2% of the study population but 60.0% of the dislocations (P = .019) (Table 3).

In addition, mean BMI was 33.2 for patients with dislocation and 29.5 for patients without dislocation (P = .039) (Table 3). Revision arthroplasty was found to be a risk factor for dislocation in univariate analysis: 66.7% of the dislocations occurred after revision RTSA, and only 21.6% of nondislocated shoulders were revision cases (P < .001) (Table 4).

Patients who underwent RTSA for CTA had a very low incidence of dislocation (0.35%, 1/285), accounting for 6.7% of the dislocated group and 57.6% of the nondislocated group (P < .001) (Table 4). The 1 patient with a dislocation after primary RTSA for CTA had an indolent infection at time of surgery after dislocation.

Multivariate logistic regression analysis revealed revision arthroplasty (OR = 7.515; P = .042) and increased BMI (OR = 1.09; P = .047) to be independent risk factors for dislocation after RTSA. Analysis also found a diagnosis of primary CTA to be independently associated with lower risk of dislocation after RTSA (OR = 0.025; P = .008). Last, the previously described risk factor of male sex was found not to be a significant independent risk factor, though it did trend positively (OR = 3.011; P = .071).

 

Discussion

With more RTSAs being performed, evaluation of their common complications becomes increasingly important.¹⁸ We found a 3.0% rate of dislocation after RTSA, which is consistent with the most recently reported incidence⁴ and falls within the previously described range of 0% to 8.6%.^19-26 Of the clinical risk factors identified in this study, those previously described were prior surgery, subscapularis insufficiency, higher BMI, and male sex.⁴ However, our finding of lower risk of dislocation after RTSA for primary rotator cuff pathology was not previously described. Although Chalmers and colleagues⁴ did not report this lower risk, 3 (27.3%) of their 11 patients with dislocation had primary CTA, compared with 1 (6.7%) of 15 patients in the present study.⁴ Our literature review did not identify any studies that independently reported the dislocation rate in patients who underwent RTSA for rotator cuff failure.

The risk factors of subscapularis irreparability and revision surgery suggest the importance of the soft-tissue envelope and bony anatomy in dislocation prevention. Previous analyses have suggested implant malpositioning,^27,28 poor subscapularis quality,²⁹ and inadequate muscle tensioning^5,30-32 as risk factors for RTSA. Patients with an irreparable subscapularis tendon have often had multiple surgeries with compromise to the muscle/soft-tissue envelope or bony anatomy of the shoulder. A biomechanical study by Gutiérrez and colleagues³¹ found the compressive forces of the soft tissue at the glenohumeral joint to be the most important contributor to stability in the RTSA prosthesis. In clinical studies, the role of the subscapularis in preventing instability after RTSA remains unclear. Edwards and colleagues²⁹ prospectively compared dislocation rates in patients with reparable and irreparable subscapularis tendons during RTSA and found a higher rate of dislocation in the irreparable subscapularis group. Of note, patients in the irreparable subscapularis group also had more complex diagnoses, including proximal humeral nonunion, fixed glenohumeral dislocation, and failed prior arthroplasty. Clark and colleagues³³ retrospectively analyzed subscapularis repair in 2 RTSA groups and found no appreciable effect on complication rate, dislocation events, range-of-motion gains, or pain relief.

Our finding that higher BMI is an independent risk factor was previously described.⁴ The association is unclear but could be related to implant positioning, difficulty in intraoperative assessment of muscle tensioning, or body habitus that may generate a lever arm for impingement and dislocation when the arm is in adduction. Last, our finding that male sex is a risk factor for dislocation approached significance, and this relationship was previously reported.⁴ This could be attributable to a higher rate of activity or of indolent infection in male patients.^34,35Besides studying risk factors for dislocation after RTSA, we investigated treatment. None of our patients were treated successfully and definitively with closed reduction in the clinic. This finding diverges from findings in studies by Teusink and colleagues² and Chalmers and colleagues,⁴who respectively reported 62% and 44% rates of success with closed reduction. Our cohort of 14 patients with 15 dislocations required a total of 17 trips to the operating room after dislocation. This significantly higher rate of return to the operating room suggests that dislocation after RTSA may be a more costly and morbid problem than has been previously described.

This study had several weaknesses. Despite its large consecutive series of patients, the study was retrospective, and several variables that would be documented and controlled in a prospective study could not be measured here. Specifically, neither preoperative physical examination nor patient-specific assessments of pain or function were consistently obtained. Similarly, postoperative patient-specific instruments of outcomes evaluation were not obtained consistently, so results of patients with dislocation could not be compared with those of a control group. In addition, preoperative and postoperative radiographs were not consistently present in our electronic medical records, so the influence of preoperative bony anatomy, intraoperative limb lengthening, and any implant malpositioning could not be determined. Furthermore, operative details, such as reparability of the subscapularis, were not fully available for the control group and could not be included in statistical analysis. In addition, that the known dislocation risk factor of male sex⁴ was identified here but was not significant in multivariate regression analysis suggests that this study may not have been adequately powered to identify a significant difference in dislocation rate between the sexes. Last, though our results suggested associations between the aforementioned variables and dislocation after RTSA, a truly causative relationship could not be confirmed with this study design or analysis. Therefore, our study findings are hypothesis-generating and may indicate a benefit to greater deltoid tensioning, use of retentive liners, or more conservative rehabilitation protocols for high-risk patients.

Conclusion

Dislocation after RTSA is an uncommon complication that often requires a return to the operating room. This study identified a modifiable risk factor (higher BMI) and 3 nonmodifiable risk factors (male sex, subscapularis insufficiency, revision surgery) for dislocation after RTSA. In contrast, patients who undergo RTSA for primary rotator cuff pathology are unlikely to dislocate after surgery. This low risk of dislocation after RTSA for primary cuff pathology was not previously described. Patients in the higher risk category may benefit from preoperative lifestyle modification, intraoperative techniques for increasing stability, and more conservative therapy after surgery. In addition, unlike previous investigations, this study did not find closed reduction in the clinic alone to be successful in definitively treating this patient population.

Am J Orthop. 2016;45(7):E444-E450. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Risk factors for dislocation after reverse total shoulder arthroplasty (RTSA) are not clearly defined. Prosthetic dislocation can result in poor patient satisfaction, worse functional outcomes, and return to the operating room.^1-3 As a result, identification of modifiable risk factors for complications represents an important research initiative for shoulder surgeons.

There is a paucity of literature devoted to the study of dislocation after RTSA. Chalmers and colleagues⁴ found a 2.9% (11/385) incidence of early dislocation within 3 months after index surgery—an improvement over the 15.8% reported for early instability over the period 2004–2006.⁵ As prosthesis design has improved and surgeons have become more comfortable with the RTSA prosthesis, surgical indications have expanded,^6,7 and dislocation rates appear to have decreased. Although the most common indication for RTSA continues to be cuff tear arthropathy (CTA),⁶ there has been increased use in rheumatoid arthritis^8-10; proximal humerus fractures, especially in cases of poor bone quality and unreliable fixation of tuberosities^11-13; and failed previous shoulder reconstruction.^14,15 As RTSA is performed more often, limiting the complications will become more important for both patient care and economics.

We conducted a study to analyze dislocation rates at our institution and to identify both modifiable and nonmodifiable risk factors for dislocation after RTSA. By identifying risk factors for dislocation, we will be able to implement additional perioperative clinical measures to reduce the incidence of dislocation.

Materials and Methods

This retrospective study of dislocation after RTSA was conducted at the Rothman Institute of Orthopedics and Methodist Hospital (Thomas Jefferson University Hospitals, Philadelphia, PA). After obtaining Institutional Review Board approval for the study, we searched our institution’s electronic database of shoulder arthroplasties to identify all RTSAs performed at our 2 large-volume urban institutions between September 27, 2010 and December 31, 2013. For the record search, International Classification of Diseases, Ninth Revision (ICD-9) codes were used (Table 1).

These unique procedure codes are used by the hospital system for billing, but are not always specific to assigned procedures. Therefore, the individual operative reports identified were reviewed to identify the patients who actually underwent RTSA. From this database, all patients who underwent RTSA were selected. Using the subpopulation of patients who underwent RTSA, we searched individual medical records to identify patients who had a dislocation after RTSA. This information was cross-referenced with ICD-9 codes for shoulder dislocation (831.0, 831.01, 831.02, 831.03) to ensure that all patients were identified.

The medical records of each patient were used to identify independent variables that could be associated with dislocation rate. Demographic variables included sex, age, and race. Preoperative clinical data included body mass index (BMI), etiology of shoulder disease leading to RTSA, individual comorbidities, and Charlson Comorbidity Index (CCI)¹⁶ modified to be used with ICD-9 codes.¹⁷ In addition, prior shoulder surgery history and arthroplasty type (primary or revision) were determined. Postoperative considerations were time to dislocation, mechanism of dislocation, and intervention(s) needed for dislocation. Although the institutional database did not include operative variables such as prosthesis type and surgical approach, all 6 surgeons in this study were using a standard deltopectoral approach in beach-chair position with a Grammont style prosthesis for RTSA cases.

Descriptive statistics for RTSA patients and the dislocation subpopulation were compiled. Bivariate analysis was used to evaluate which of the previously described variables influenced dislocation rates. Last, multivariate logistic regression analysis was performed to evaluate which factors were independent predictors of dislocation. We included demographic variables (age, sex, ethnicity), clinical variables (BMI, individual comorbidities, CCI), and surgical variables (primary vs revision, diagnosis at time of surgery). All statistical analyses were performed with Excel 2013 (Microsoft) and SPSS Statistics Version 20.0 (SPSS Inc.).

Results

From the database, we identified 487 patients who underwent 510 RTSAs during the study period. These surgeries were performed by 6 shoulder and elbow fellowship–trained surgeons. Of the 510 RTSAs, 393 (77.1%) were primary cases, and 117 (22.9%) were revision cases.

Of the 510 shoulders that underwent RTSA, 15 (2.9%; 14 patients) dislocated. Of these 15 cases, 5 were primary (1.3% of all primary cases) and 10 were revision (8.5% of all revision cases). Mean time from index surgery to diagnosis of dislocation was 58.2 days (range, 0-319 days). One dislocation occurred immediately after surgery, 2 after falls, 4 from patient-identified low-energy mechanisms of injury, and 8 without known inciting events. Nine dislocations (60%) did not have a subscapularis repair (7 were irreparable, 2 underwent subscapularis peel without repair), and the other 6 were repaired primarily (Table 2).

In addition, 11 dislocations (73.3%) previously underwent open or arthroscopic shoulder surgery. All patients who had a dislocation after RTSA returned to the operating room at least once; no dislocation was successfully treated with closed reduction in the clinic. The 15 dislocations underwent 17 surgeries: 7 isolated polyethylene exchanges, 2 isolated closed reductions, 1 hematoma aspiration with closed reduction, 1 open reduction, 2 humeral component revisions with polyethylene exchange, 1 humeral augmentation with polyethylene exchange, 2 glenosphere exchanges with polyethylene exchange, and 1 polyethylene exchange with concurrent subscapularis repair.

Male patients accounted for 32.2% of the study population but 60.0% of the dislocations (P = .019) (Table 3).

In addition, mean BMI was 33.2 for patients with dislocation and 29.5 for patients without dislocation (P = .039) (Table 3). Revision arthroplasty was found to be a risk factor for dislocation in univariate analysis: 66.7% of the dislocations occurred after revision RTSA, and only 21.6% of nondislocated shoulders were revision cases (P < .001) (Table 4).

Patients who underwent RTSA for CTA had a very low incidence of dislocation (0.35%, 1/285), accounting for 6.7% of the dislocated group and 57.6% of the nondislocated group (P < .001) (Table 4). The 1 patient with a dislocation after primary RTSA for CTA had an indolent infection at time of surgery after dislocation.

Multivariate logistic regression analysis revealed revision arthroplasty (OR = 7.515; P = .042) and increased BMI (OR = 1.09; P = .047) to be independent risk factors for dislocation after RTSA. Analysis also found a diagnosis of primary CTA to be independently associated with lower risk of dislocation after RTSA (OR = 0.025; P = .008). Last, the previously described risk factor of male sex was found not to be a significant independent risk factor, though it did trend positively (OR = 3.011; P = .071).

 

Discussion

With more RTSAs being performed, evaluation of their common complications becomes increasingly important.¹⁸ We found a 3.0% rate of dislocation after RTSA, which is consistent with the most recently reported incidence⁴ and falls within the previously described range of 0% to 8.6%.^19-26 Of the clinical risk factors identified in this study, those previously described were prior surgery, subscapularis insufficiency, higher BMI, and male sex.⁴ However, our finding of lower risk of dislocation after RTSA for primary rotator cuff pathology was not previously described. Although Chalmers and colleagues⁴ did not report this lower risk, 3 (27.3%) of their 11 patients with dislocation had primary CTA, compared with 1 (6.7%) of 15 patients in the present study.⁴ Our literature review did not identify any studies that independently reported the dislocation rate in patients who underwent RTSA for rotator cuff failure.

The risk factors of subscapularis irreparability and revision surgery suggest the importance of the soft-tissue envelope and bony anatomy in dislocation prevention. Previous analyses have suggested implant malpositioning,^27,28 poor subscapularis quality,²⁹ and inadequate muscle tensioning^5,30-32 as risk factors for RTSA. Patients with an irreparable subscapularis tendon have often had multiple surgeries with compromise to the muscle/soft-tissue envelope or bony anatomy of the shoulder. A biomechanical study by Gutiérrez and colleagues³¹ found the compressive forces of the soft tissue at the glenohumeral joint to be the most important contributor to stability in the RTSA prosthesis. In clinical studies, the role of the subscapularis in preventing instability after RTSA remains unclear. Edwards and colleagues²⁹ prospectively compared dislocation rates in patients with reparable and irreparable subscapularis tendons during RTSA and found a higher rate of dislocation in the irreparable subscapularis group. Of note, patients in the irreparable subscapularis group also had more complex diagnoses, including proximal humeral nonunion, fixed glenohumeral dislocation, and failed prior arthroplasty. Clark and colleagues³³ retrospectively analyzed subscapularis repair in 2 RTSA groups and found no appreciable effect on complication rate, dislocation events, range-of-motion gains, or pain relief.

Our finding that higher BMI is an independent risk factor was previously described.⁴ The association is unclear but could be related to implant positioning, difficulty in intraoperative assessment of muscle tensioning, or body habitus that may generate a lever arm for impingement and dislocation when the arm is in adduction. Last, our finding that male sex is a risk factor for dislocation approached significance, and this relationship was previously reported.⁴ This could be attributable to a higher rate of activity or of indolent infection in male patients.^34,35Besides studying risk factors for dislocation after RTSA, we investigated treatment. None of our patients were treated successfully and definitively with closed reduction in the clinic. This finding diverges from findings in studies by Teusink and colleagues² and Chalmers and colleagues,⁴who respectively reported 62% and 44% rates of success with closed reduction. Our cohort of 14 patients with 15 dislocations required a total of 17 trips to the operating room after dislocation. This significantly higher rate of return to the operating room suggests that dislocation after RTSA may be a more costly and morbid problem than has been previously described.

This study had several weaknesses. Despite its large consecutive series of patients, the study was retrospective, and several variables that would be documented and controlled in a prospective study could not be measured here. Specifically, neither preoperative physical examination nor patient-specific assessments of pain or function were consistently obtained. Similarly, postoperative patient-specific instruments of outcomes evaluation were not obtained consistently, so results of patients with dislocation could not be compared with those of a control group. In addition, preoperative and postoperative radiographs were not consistently present in our electronic medical records, so the influence of preoperative bony anatomy, intraoperative limb lengthening, and any implant malpositioning could not be determined. Furthermore, operative details, such as reparability of the subscapularis, were not fully available for the control group and could not be included in statistical analysis. In addition, that the known dislocation risk factor of male sex⁴ was identified here but was not significant in multivariate regression analysis suggests that this study may not have been adequately powered to identify a significant difference in dislocation rate between the sexes. Last, though our results suggested associations between the aforementioned variables and dislocation after RTSA, a truly causative relationship could not be confirmed with this study design or analysis. Therefore, our study findings are hypothesis-generating and may indicate a benefit to greater deltoid tensioning, use of retentive liners, or more conservative rehabilitation protocols for high-risk patients.

Conclusion

Dislocation after RTSA is an uncommon complication that often requires a return to the operating room. This study identified a modifiable risk factor (higher BMI) and 3 nonmodifiable risk factors (male sex, subscapularis insufficiency, revision surgery) for dislocation after RTSA. In contrast, patients who undergo RTSA for primary rotator cuff pathology are unlikely to dislocate after surgery. This low risk of dislocation after RTSA for primary cuff pathology was not previously described. Patients in the higher risk category may benefit from preoperative lifestyle modification, intraoperative techniques for increasing stability, and more conservative therapy after surgery. In addition, unlike previous investigations, this study did not find closed reduction in the clinic alone to be successful in definitively treating this patient population.

Am J Orthop. 2016;45(7):E444-E450. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Risk factors for dislocation after reverse total shoulder arthroplasty (RTSA) are not clearly defined. Prosthetic dislocation can result in poor patient satisfaction, worse functional outcomes, and return to the operating room.^1-3 As a result, identification of modifiable risk factors for complications represents an important research initiative for shoulder surgeons.

There is a paucity of literature devoted to the study of dislocation after RTSA. Chalmers and colleagues⁴ found a 2.9% (11/385) incidence of early dislocation within 3 months after index surgery—an improvement over the 15.8% reported for early instability over the period 2004–2006.⁵ As prosthesis design has improved and surgeons have become more comfortable with the RTSA prosthesis, surgical indications have expanded,^6,7 and dislocation rates appear to have decreased. Although the most common indication for RTSA continues to be cuff tear arthropathy (CTA),⁶ there has been increased use in rheumatoid arthritis^8-10; proximal humerus fractures, especially in cases of poor bone quality and unreliable fixation of tuberosities^11-13; and failed previous shoulder reconstruction.^14,15 As RTSA is performed more often, limiting the complications will become more important for both patient care and economics.

We conducted a study to analyze dislocation rates at our institution and to identify both modifiable and nonmodifiable risk factors for dislocation after RTSA. By identifying risk factors for dislocation, we will be able to implement additional perioperative clinical measures to reduce the incidence of dislocation.

Materials and Methods

This retrospective study of dislocation after RTSA was conducted at the Rothman Institute of Orthopedics and Methodist Hospital (Thomas Jefferson University Hospitals, Philadelphia, PA). After obtaining Institutional Review Board approval for the study, we searched our institution’s electronic database of shoulder arthroplasties to identify all RTSAs performed at our 2 large-volume urban institutions between September 27, 2010 and December 31, 2013. For the record search, International Classification of Diseases, Ninth Revision (ICD-9) codes were used (Table 1).

These unique procedure codes are used by the hospital system for billing, but are not always specific to assigned procedures. Therefore, the individual operative reports identified were reviewed to identify the patients who actually underwent RTSA. From this database, all patients who underwent RTSA were selected. Using the subpopulation of patients who underwent RTSA, we searched individual medical records to identify patients who had a dislocation after RTSA. This information was cross-referenced with ICD-9 codes for shoulder dislocation (831.0, 831.01, 831.02, 831.03) to ensure that all patients were identified.

The medical records of each patient were used to identify independent variables that could be associated with dislocation rate. Demographic variables included sex, age, and race. Preoperative clinical data included body mass index (BMI), etiology of shoulder disease leading to RTSA, individual comorbidities, and Charlson Comorbidity Index (CCI)¹⁶ modified to be used with ICD-9 codes.¹⁷ In addition, prior shoulder surgery history and arthroplasty type (primary or revision) were determined. Postoperative considerations were time to dislocation, mechanism of dislocation, and intervention(s) needed for dislocation. Although the institutional database did not include operative variables such as prosthesis type and surgical approach, all 6 surgeons in this study were using a standard deltopectoral approach in beach-chair position with a Grammont style prosthesis for RTSA cases.

Descriptive statistics for RTSA patients and the dislocation subpopulation were compiled. Bivariate analysis was used to evaluate which of the previously described variables influenced dislocation rates. Last, multivariate logistic regression analysis was performed to evaluate which factors were independent predictors of dislocation. We included demographic variables (age, sex, ethnicity), clinical variables (BMI, individual comorbidities, CCI), and surgical variables (primary vs revision, diagnosis at time of surgery). All statistical analyses were performed with Excel 2013 (Microsoft) and SPSS Statistics Version 20.0 (SPSS Inc.).

Results

From the database, we identified 487 patients who underwent 510 RTSAs during the study period. These surgeries were performed by 6 shoulder and elbow fellowship–trained surgeons. Of the 510 RTSAs, 393 (77.1%) were primary cases, and 117 (22.9%) were revision cases.

Of the 510 shoulders that underwent RTSA, 15 (2.9%; 14 patients) dislocated. Of these 15 cases, 5 were primary (1.3% of all primary cases) and 10 were revision (8.5% of all revision cases). Mean time from index surgery to diagnosis of dislocation was 58.2 days (range, 0-319 days). One dislocation occurred immediately after surgery, 2 after falls, 4 from patient-identified low-energy mechanisms of injury, and 8 without known inciting events. Nine dislocations (60%) did not have a subscapularis repair (7 were irreparable, 2 underwent subscapularis peel without repair), and the other 6 were repaired primarily (Table 2).

In addition, 11 dislocations (73.3%) previously underwent open or arthroscopic shoulder surgery. All patients who had a dislocation after RTSA returned to the operating room at least once; no dislocation was successfully treated with closed reduction in the clinic. The 15 dislocations underwent 17 surgeries: 7 isolated polyethylene exchanges, 2 isolated closed reductions, 1 hematoma aspiration with closed reduction, 1 open reduction, 2 humeral component revisions with polyethylene exchange, 1 humeral augmentation with polyethylene exchange, 2 glenosphere exchanges with polyethylene exchange, and 1 polyethylene exchange with concurrent subscapularis repair.

Male patients accounted for 32.2% of the study population but 60.0% of the dislocations (P = .019) (Table 3).

In addition, mean BMI was 33.2 for patients with dislocation and 29.5 for patients without dislocation (P = .039) (Table 3). Revision arthroplasty was found to be a risk factor for dislocation in univariate analysis: 66.7% of the dislocations occurred after revision RTSA, and only 21.6% of nondislocated shoulders were revision cases (P < .001) (Table 4).

Patients who underwent RTSA for CTA had a very low incidence of dislocation (0.35%, 1/285), accounting for 6.7% of the dislocated group and 57.6% of the nondislocated group (P < .001) (Table 4). The 1 patient with a dislocation after primary RTSA for CTA had an indolent infection at time of surgery after dislocation.

Multivariate logistic regression analysis revealed revision arthroplasty (OR = 7.515; P = .042) and increased BMI (OR = 1.09; P = .047) to be independent risk factors for dislocation after RTSA. Analysis also found a diagnosis of primary CTA to be independently associated with lower risk of dislocation after RTSA (OR = 0.025; P = .008). Last, the previously described risk factor of male sex was found not to be a significant independent risk factor, though it did trend positively (OR = 3.011; P = .071).

 

Discussion

With more RTSAs being performed, evaluation of their common complications becomes increasingly important.¹⁸ We found a 3.0% rate of dislocation after RTSA, which is consistent with the most recently reported incidence⁴ and falls within the previously described range of 0% to 8.6%.^19-26 Of the clinical risk factors identified in this study, those previously described were prior surgery, subscapularis insufficiency, higher BMI, and male sex.⁴ However, our finding of lower risk of dislocation after RTSA for primary rotator cuff pathology was not previously described. Although Chalmers and colleagues⁴ did not report this lower risk, 3 (27.3%) of their 11 patients with dislocation had primary CTA, compared with 1 (6.7%) of 15 patients in the present study.⁴ Our literature review did not identify any studies that independently reported the dislocation rate in patients who underwent RTSA for rotator cuff failure.

The risk factors of subscapularis irreparability and revision surgery suggest the importance of the soft-tissue envelope and bony anatomy in dislocation prevention. Previous analyses have suggested implant malpositioning,^27,28 poor subscapularis quality,²⁹ and inadequate muscle tensioning^5,30-32 as risk factors for RTSA. Patients with an irreparable subscapularis tendon have often had multiple surgeries with compromise to the muscle/soft-tissue envelope or bony anatomy of the shoulder. A biomechanical study by Gutiérrez and colleagues³¹ found the compressive forces of the soft tissue at the glenohumeral joint to be the most important contributor to stability in the RTSA prosthesis. In clinical studies, the role of the subscapularis in preventing instability after RTSA remains unclear. Edwards and colleagues²⁹ prospectively compared dislocation rates in patients with reparable and irreparable subscapularis tendons during RTSA and found a higher rate of dislocation in the irreparable subscapularis group. Of note, patients in the irreparable subscapularis group also had more complex diagnoses, including proximal humeral nonunion, fixed glenohumeral dislocation, and failed prior arthroplasty. Clark and colleagues³³ retrospectively analyzed subscapularis repair in 2 RTSA groups and found no appreciable effect on complication rate, dislocation events, range-of-motion gains, or pain relief.

Our finding that higher BMI is an independent risk factor was previously described.⁴ The association is unclear but could be related to implant positioning, difficulty in intraoperative assessment of muscle tensioning, or body habitus that may generate a lever arm for impingement and dislocation when the arm is in adduction. Last, our finding that male sex is a risk factor for dislocation approached significance, and this relationship was previously reported.⁴ This could be attributable to a higher rate of activity or of indolent infection in male patients.^34,35Besides studying risk factors for dislocation after RTSA, we investigated treatment. None of our patients were treated successfully and definitively with closed reduction in the clinic. This finding diverges from findings in studies by Teusink and colleagues² and Chalmers and colleagues,⁴who respectively reported 62% and 44% rates of success with closed reduction. Our cohort of 14 patients with 15 dislocations required a total of 17 trips to the operating room after dislocation. This significantly higher rate of return to the operating room suggests that dislocation after RTSA may be a more costly and morbid problem than has been previously described.

This study had several weaknesses. Despite its large consecutive series of patients, the study was retrospective, and several variables that would be documented and controlled in a prospective study could not be measured here. Specifically, neither preoperative physical examination nor patient-specific assessments of pain or function were consistently obtained. Similarly, postoperative patient-specific instruments of outcomes evaluation were not obtained consistently, so results of patients with dislocation could not be compared with those of a control group. In addition, preoperative and postoperative radiographs were not consistently present in our electronic medical records, so the influence of preoperative bony anatomy, intraoperative limb lengthening, and any implant malpositioning could not be determined. Furthermore, operative details, such as reparability of the subscapularis, were not fully available for the control group and could not be included in statistical analysis. In addition, that the known dislocation risk factor of male sex⁴ was identified here but was not significant in multivariate regression analysis suggests that this study may not have been adequately powered to identify a significant difference in dislocation rate between the sexes. Last, though our results suggested associations between the aforementioned variables and dislocation after RTSA, a truly causative relationship could not be confirmed with this study design or analysis. Therefore, our study findings are hypothesis-generating and may indicate a benefit to greater deltoid tensioning, use of retentive liners, or more conservative rehabilitation protocols for high-risk patients.

Conclusion

Dislocation after RTSA is an uncommon complication that often requires a return to the operating room. This study identified a modifiable risk factor (higher BMI) and 3 nonmodifiable risk factors (male sex, subscapularis insufficiency, revision surgery) for dislocation after RTSA. In contrast, patients who undergo RTSA for primary rotator cuff pathology are unlikely to dislocate after surgery. This low risk of dislocation after RTSA for primary cuff pathology was not previously described. Patients in the higher risk category may benefit from preoperative lifestyle modification, intraoperative techniques for increasing stability, and more conservative therapy after surgery. In addition, unlike previous investigations, this study did not find closed reduction in the clinic alone to be successful in definitively treating this patient population.

Am J Orthop. 2016;45(7):E444-E450. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Musculoskeletal allografts are becoming increasingly accepted as a viable alternative to autografts in a variety of orthopedic procedures. A 2006 American Orthopaedic Society for Sports Medicine (AOSSM) survey indicated that 86% of the participating 365 orthopedic surgeons use allografts in their practice.¹ Although the overwhelming majority of orthopedic surgeons use allografts, they share common concerns, including safety, tissue integrity, and biologic incorporation. It is essential for the orthopedic surgeon to understand the current standards of tissue banking, risks and benefits related to the use of allografts, and common indications for safe use in clinical practice. This article reviews the current status of musculoskeletal allografts, including tissue procurement and processing, infections, complications, and specific uses tailored to ligament reconstruction.

Donor Bank, Processing, Sterilization, and Regulation

In the United States, the American Association of Tissue Banks (AATB) is responsible for establishing the standards for more than 100 accredited tissue banks. These tissue banks recover tissue from approximately 30,000 donors annually and account for an estimated 90% of the available musculoskeletal allografts used in the United States. While not all tissue banks are accredited by the AATB, all are required to register with the Food and Drug Administration (FDA), which allows for unannounced inspections of any facility. Facilities are required to abide by the FDA-implemented Current Good Tissue Practices (CGTP), which encompasses regulations on all donor tissue collected after May 2005 to help prevent the transmission of communicable diseases. The FDA released an updated draft in January 2009 that emphasizes safe practices and regulations spanning from environmental control to specific equipment.²

The safety of a transplanted allograft tissue begins within the tissue bank. Donor screening and testing is the first step in reducing the risk of transmission. Screening consists of collecting medical and social history from the family and any healthcare resources to assess the eligibility of the donor. If prior blood donations or autopsy information is available, that information is scrutinized. Donor tissue undergoes nucleic acid testing (NAT), which is required by both the AATB and FDA. All donor tissue must be screened for both types of human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), treponema pallidum, and human transmissible spongiform encephalopathies.³ NAT of donor tissue effectively reduces the risk of viral transmission. Additionally, routine preprocessing swabs for bacterial and fungal cultures are performed, although the sensitivity of these cultures ranges from 78% to 92%.⁴

After donor screening and testing, allograft tissues are usually obtained under aseptic conditions, though this is not FDA-required.⁵ Once procured, the tissue undergoes sterilization. Currently, there is no standard method ubiquitous to all tissue banks, nor does the FDA require a specific method. Rather, the FDA and AATB require tissue banks to validate their sterilization process and provide supporting data. The goal of sterilization is to inactivate viruses and eradicate bacteria while maintaining the biological and mechanical properties of the tissue. The AATB requires a Sterility Assurance Level (SAL) of 10^-6, meaning there is no more than one in a million chance that a nonviral viable microbe exists on or within the tissue. Sterilization techniques may include both radiation and a variety of chemical reagents. Gamma irradiation is a commonly used method of sterilizing soft tissue allografts, although some studies indicate that it is detrimental to tissue biology.⁶ Newer methods of sterilization are being tested, one of which includes carbon dioxide in combination with antioxidants and irradiation. Bui and colleagues⁷ directly compared the biomechanical and histological properties of allograft tissue after either the standard 25 kGy gamma irradiation or supercritical carbon dioxide techniques. Although there is no histological difference, the samples treated with supercritical carbon dioxide had less biomechanical damage.⁷ Finally, the terminally sterilized allograft tissue is frozen to temperatures between -40°C and -80°C.⁵

Infections

One major concern of allografts is the risk of disease transmission. While numerous studies have investigated the incidence of bacterial infection following transplantation of allograft tissue, there are challenges associated with differentiating common postoperative infections from ones directly associated with the transmission of bacteria within the graft. There is a wide array of reported incidences of infection in the literature, from the Tomford and colleagues⁸ 1981 study that reported a 6.9% rateto the 2001 study by Munting and colleagues,⁹ who reported 0% in their series. Multiple confounding variables exist, such as possible contamination during handling of an otherwise noncontaminated or properly sterilized allograft with inappropriate inclusion of all postoperative infections. In contrast, recognizing viral transmission has been somewhat easier, although reporting of these incidences has been variable in the past. In either case, there is no accredited reporting system for infections related to allografts.

 

Bacterial Transmission

Clostridium species. Clostridium species are commonly found among intestinal flora. There is a general consensus that between 24 to 48 hours after death intestinal flora transmigrates into the surrounding tissue and blood. Therefore, a commonly accepted recommendation is that cadaveric tissue needs to be excised prior to 24 hours postmortem.¹⁰

In 2001, a 23-year-old man underwent reconstructive knee surgery with a femoral condyle allograft. A few days after surgery, he became septic and ultimately died from the infection. Clostridium sordellii was cultured from the tissue. Several days later, a 17-year-old boy underwent reconstructive knee surgery with a fresh femoral condyle and frozen meniscus from the same donor. Twenty-four hours after surgery, he developed a fever and was readmitted a week later for presumed infection and treated effectively with penicillin and ampicillin/sulbactam. Tissue from the same cadaveric donor had been transplanted into 7 other patients without reports of infection. In a 2002 Centers for Disease Control and Prevention (CDC) update report,¹¹ there were 26 total bacterial cases from allografts and 13 cases were attributed to Clostridium. Malinin and colleagues¹⁰ reviewed 795 consecutive cadaveric donors and found that 64 (8.1%) had positive cultures for Clostridia. Of all the positive cultures for Clostridia, 81.3% had positive blood cultures, 57.8% had positive bone marrow aspirate cultures, and 46.9% had positive tissue cultures. They concluded that multiple cultures are required for cadaveric tissue donors in order to reach a higher sensitivity for Clostridial contamination, and these should be done routinely to guide the sterilization process.

Strep species. In 2003, a 17-year-old boy underwent anterior cruciate ligament (ACL) reconstruction with a patellar tendon allograft.¹² About 1 week later, he was admitted for signs of infection and received intravenous antibiotics. He required surgical debridement, and intraoperative cultures grew Group A Streptococcus (GAS) that was also identified in the postmortem donor cultures. The tissues underwent processing in an antimicrobial solution and postprocessing cultures were negative for bacteria, but they were not sterilized. Tissues from this donor had been implanted in 5 other patients without report of infection. Following this event, recommendations have been made for prompt rejection of tissue with cultures positive for GAS, unless a sterilizing procedure is used.

Other bacteria. According to the 2002 CDC update, 11 of the 26 cases of bacterial infection reported to the agency were a combination of gram-negative bacilli, polymicrobial flora, or culture negative.¹¹

Viral Transmission

The most effective way to prevent transmission of a viral disease from allografts is thorough donor screening. Since the AATB implemented NAT in 2005 for HIV and HCV, there have been no reported cases of transmission.³ Even prior to this, regular blood screening along with social questionnaires completed by donors or donor families eliminated high-risk donors and significantly decreased the rate of transmission.

Human Immunodeficiency Virus. The first reported case of HIV transmission via implantation of allograft was in 1988. Further investigation revealed that there were 8 transmissions between 1984 and 1986, when routine screening of donors had not yet been implemented. The last reported case of HIV transmission occurred in 1996 with an untested donor.¹³Hepatitis C Virus. There are several reported cases of HCV transmission that occurred where the donors initially tested negative for HCV. In one case, 40 allografts from the same donor were transplanted over a period of nearly 2 years. This resulted in at least 8 patients being infected with HCV.¹⁴ Another case of HCV transmission was reported in 2005 after a patient developed acute HCV 6 weeks after transplantation of a patellar tendon allograft. Further investigation revealed that there had been 3 additional cases over a year from the same donor. Researchers determined that if the initial case had been reported, at least 3 transmissions could have been prevented.¹⁵Human T-cell Lymphotropic Virus (HTLV).The first reported transmission of HTLV was in 1991. This was reported in an asymptomatic patient who received a femoral head allograft from a donor who had been previously infected via a blood transfusion.¹⁶Zika virus. With recent outbreaks of the Zika virus, the FDA recently released recommendations regarding the screening and deferral of donors, mainly for blood transfusion. Orthopedists should take into consideration the potential for transmission through allografts. The FDA states that all potential donors should be screened for Zika virus using questionnaires and whole blood tests. Symptomatic donors are deferred at least 4 weeks following resolution of symptoms. While this is a recent recommendation from the FDA, orthopedists must be cognizant of the potential harms from this unfamiliar and evolving situation.¹⁷

Graft Specifics

Anterior Cruciate Ligament

ACL reconstruction is one of the most commonly performed surgeries by orthopedic surgeons, with an estimated 200,000 reconstructions per year.¹⁸Despite the popularity of this surgery, controversies remain regarding the optimal graft for reconstruction.^19,20 One would provide adequate strength, be readily available, not elicit an immunologic response from the host, rapidly incorporate, elicit low morbidity, and vascularize early. Current options include both autografts and allografts. Common autograft options include patellar bone-tendon-bone (PBTB), hamstrings tendon, quadriceps tendon, and iliotibial band. PBTB autograft remains a common choice among orthopedic surgeons, as it allows early incorporation of the graft into bone and eliminates immune rejection. However, donor site morbidity, including anterior knee pain, weakness of knee extension, joint stiffness, increased postoperative pain, and iatrogenic patella fractures, have been reported in the literature.²¹ Commonly used allograft options include donor bone-patellar tendon-bone, quadriceps tendon, Achilles tendon, anterior and posterior tibialis tendons, hamstring tendons, and iliotibial band. Allografts provide the advantage of avoiding donor site morbidity, being readily available, allowing for shorter operative times, and providing lower postoperative pain compared to autografts, although they carry the risk of disease transmission, rejection, and slower incorporation into bone.^22-27

 

Autograft donor site morbidities. One of the general disadvantages of autografts is the donor site morbidity associated with harvesting the grafts. In specific, PBTB grafts allow for bony blocks on both ends of the graft to incorporate into the host bone. However, this technique comes with the risk of disrupting the extensor mechanism.^28,29 Milankov and colleagues³⁰ published a retrospective review of over 2000 ACLs using autologous PBTB graft. They noted a 0.45% incidence of patella fracture and 0.18% patellar tendon rupture.³⁰ Others have reported that intraoperative repair of the patellar tendon after tendon harvesting can increase infrapatellar fibrosis, thus increasing the risk for stiffness.^31-33

Hamstring autografts include the semitendinosus and the gracilis tendons. The harvesting process is technically demanding and can be complicated by inadvertent amputation of the tendons, making the graft unsuitable for reconstructive purposes.³⁴ Additionally, several reports have identified persistent numbness and hyperesthesia following hamstring harvesting due to iatrogenic injury to the prepatellar branches of the saphenous nerve.^35,36A comprehensive review by Slone and colleagues³⁷ reported comparable functional outcomes with quadriceps tendon autograft compared to PBTB; however, this comes with the risk of postoperative hematoma formation and the potential for thigh compartment syndrome.

Biology and Biomechanics of Allografts

One of the major disadvantages of allografts is the reduced ability to incorporate into the host tissue. Several in vitro and animal studies have suggested that allografts incorporate in the host slower than autografts.^24,26,38 Early studies by Jackson and colleagues²⁴ on goat models demonstrated that allografts and autografts have similar structural and biological properties initially, but allografts display significantly slower incorporation into the host tissue at 6 months. Histologically, allografts demonstrated lower revascularization, a smaller cross-sectional area, and a prolonged inflammatory response at 6 months postoperatively.^24,39,40 Muramatsu and colleagues⁴¹ further showed through the use of magnetic resonance imaging a slower rate of revascularization of allografts over 2 years post-reconstruction.

Given the delayed biologic incorporation of allografts, studies have identified a lower strength-to-failure rate in the early postoperative period compared to autografts. An animal model study by Nikolaou and colleagues³⁸ showed that the strength of allografts was lower for up to 2 years following surgery. Additional biomechanical studies demonstrated that allografts were nearly 75% structurally weaker compared to autografts at 1 year following surgery.⁴²

Acknowledging these limitations, one should use caution when choosing to use an allograft or starting aggressive early rehabilitation after an allograft reconstruction, especially in athletes and young patients.

Clinical Outcomes

Although in vitro studies demonstrate inferior strength and delayed incorporation of allografts in the early postoperative period, there is still controversy surrounding the clinical and functional outcomes. Numerous studies have identified allografts as a viable option for ACL reconstruction, with similar reported patient satisfaction scores compared to autografts.^43,44

The MOON Consortium recently published a prospective study of nearly 2500 subjects looking to identify risk factors for failure of ACL reconstruction. The study found that allografts had an odds ratio for failure 5.2 times that of PBTB autografts, correlating this factor to an increased re-tear rate of 6.9% in the allograft group compared to 3.2% in the PBTB group (P < .01).⁴⁵ The elevated risk is more prevalent in younger patients, especially athletic teenagers. This issue has been reiterated in multiple studies.^45-50A meta-analysis by Hu and colleagues²³ identified 9 studies, either randomized control trials or prospective cohort studies, that looked at clinical outcomes between the different graft choices. They showed there was no significant difference between graft options in terms of instrumental laxity (P = .59), Lachman test (P = .41), pivot shift test (P = .88), and multiple functional outcome scores, including the International Knee Documentation Committee (IKDC), Lysholm, and Tegner scores.^23,51-59Processing and sterilization techniques are thought to play a role in allograft failure. Guo and other researchers have demonstrated a significantly higher rate of failure for patients who received gamma-irradiated allografts compared to fresh frozen allografts.^23,58-64 With improved sterilization techniques and a strict selection process of donors, gamma radiation has fallen out of favor to protect the biological characteristics of the tissue graft.^5,65,66Several factors need to be considered when selecting between allograft or autograft tissue for ligamentous reconstruction. The selection must be balanced between the surgeon’s experience, patient and surgeon preferences, age of the patient, level of physical activity, primary or revision surgical setting, multiligamentous failure, geographical availability of donor grafts, and economical factors.

Medial Patellofemoral Ligament Reconstruction

Another relatively recent application for allografts has been described for the reconstruction of the medial patellofemoral ligament (MPFL) in recurrent lateral patellar dislocations.^67-74

Typically, MPFL reconstructions make use of autografts, including quadriceps tendon, patellar tendon, and hamstring ligaments. However, allografts have the potential to limit postoperative donor site morbidity and to allow a faster rehabilitation.^75,76 Allografts include semitendinosus, gracilis, anterior tibialis, posterior tibialis, and quadriceps tendons.

Calvo Rodríguez and colleagues⁷⁶ performed a retrospective review in 2015 comparing allografts to autografts for MPFL reconstruction with respect to postoperative knee function and re-dislocation rates. Among the collective 28 patients, there was no difference in overall functional scores or dislocation rates between the grafts. Although this was a retrospective review and had a small number of subjects, the findings identify allografts as a reliable graft option for MPFL reconstruction.⁷⁶While there has been a surge of interest in techniques for MPFL reconstruction, there is limited research available regarding the superiority of allografts compared to autografts. For this specific application, it seems that clinical outcomes correlate more to adequate stabilization of the patellofemoral joint than to the type of graft used.^77,78 Future research should be dedicated to prospective randomized control trials to delineate any disadvantages to using allografts for MPFL reconstruction.

 

Discussion

Musculoskeletal allografts are gaining popularity for ligamentous reconstruction as their safety and efficacy continue to improve. With the great majority of tissue banks being accredited by the AATB and specific regulations such as NAT screening becoming common practice, infection rates and transmission of diseases have become incredibly rare. However, a thorough consideration needs to be taken into account when choosing between autograft and allograft on a case-by-case basis (Table).

Although the incidence of donor site complications is low with autografts, there are inherent risks, such as harvest site hyperesthesia, persistent numbness, cosmetic dissatisfaction, pain, weakness, functional implications, and unsuitability of the harvested graft. While it may appear that allografts may obviate donor site morbidity, one must consider the reduced potential for the donor tissue to incorporate into the host. Several studies have suggested that incorporation into the host tissue is inferior and slower for allografts. With this knowledge, factors such as clinical outcomes, future expectations, rehabilitation protocol, and individual patient characteristics all need to be considered when selecting the source of the tissue to be transplanted. Given that there is a growing need for availability of allografts, a well-rounded understanding of the biologic and physiologic aspects of the transplanted tissues is imperative. Future research will need to focus on improving the rate and quality of the biological incorporation of the transplanted graft into the host while eliminating the risk of disease transmission and infection.

Am J Orthop. 2016;45(7):446-453. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Musculoskeletal allografts are becoming increasingly accepted as a viable alternative to autografts in a variety of orthopedic procedures. A 2006 American Orthopaedic Society for Sports Medicine (AOSSM) survey indicated that 86% of the participating 365 orthopedic surgeons use allografts in their practice.¹ Although the overwhelming majority of orthopedic surgeons use allografts, they share common concerns, including safety, tissue integrity, and biologic incorporation. It is essential for the orthopedic surgeon to understand the current standards of tissue banking, risks and benefits related to the use of allografts, and common indications for safe use in clinical practice. This article reviews the current status of musculoskeletal allografts, including tissue procurement and processing, infections, complications, and specific uses tailored to ligament reconstruction.

Donor Bank, Processing, Sterilization, and Regulation

In the United States, the American Association of Tissue Banks (AATB) is responsible for establishing the standards for more than 100 accredited tissue banks. These tissue banks recover tissue from approximately 30,000 donors annually and account for an estimated 90% of the available musculoskeletal allografts used in the United States. While not all tissue banks are accredited by the AATB, all are required to register with the Food and Drug Administration (FDA), which allows for unannounced inspections of any facility. Facilities are required to abide by the FDA-implemented Current Good Tissue Practices (CGTP), which encompasses regulations on all donor tissue collected after May 2005 to help prevent the transmission of communicable diseases. The FDA released an updated draft in January 2009 that emphasizes safe practices and regulations spanning from environmental control to specific equipment.²

The safety of a transplanted allograft tissue begins within the tissue bank. Donor screening and testing is the first step in reducing the risk of transmission. Screening consists of collecting medical and social history from the family and any healthcare resources to assess the eligibility of the donor. If prior blood donations or autopsy information is available, that information is scrutinized. Donor tissue undergoes nucleic acid testing (NAT), which is required by both the AATB and FDA. All donor tissue must be screened for both types of human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), treponema pallidum, and human transmissible spongiform encephalopathies.³ NAT of donor tissue effectively reduces the risk of viral transmission. Additionally, routine preprocessing swabs for bacterial and fungal cultures are performed, although the sensitivity of these cultures ranges from 78% to 92%.⁴

After donor screening and testing, allograft tissues are usually obtained under aseptic conditions, though this is not FDA-required.⁵ Once procured, the tissue undergoes sterilization. Currently, there is no standard method ubiquitous to all tissue banks, nor does the FDA require a specific method. Rather, the FDA and AATB require tissue banks to validate their sterilization process and provide supporting data. The goal of sterilization is to inactivate viruses and eradicate bacteria while maintaining the biological and mechanical properties of the tissue. The AATB requires a Sterility Assurance Level (SAL) of 10^-6, meaning there is no more than one in a million chance that a nonviral viable microbe exists on or within the tissue. Sterilization techniques may include both radiation and a variety of chemical reagents. Gamma irradiation is a commonly used method of sterilizing soft tissue allografts, although some studies indicate that it is detrimental to tissue biology.⁶ Newer methods of sterilization are being tested, one of which includes carbon dioxide in combination with antioxidants and irradiation. Bui and colleagues⁷ directly compared the biomechanical and histological properties of allograft tissue after either the standard 25 kGy gamma irradiation or supercritical carbon dioxide techniques. Although there is no histological difference, the samples treated with supercritical carbon dioxide had less biomechanical damage.⁷ Finally, the terminally sterilized allograft tissue is frozen to temperatures between -40°C and -80°C.⁵

Infections

One major concern of allografts is the risk of disease transmission. While numerous studies have investigated the incidence of bacterial infection following transplantation of allograft tissue, there are challenges associated with differentiating common postoperative infections from ones directly associated with the transmission of bacteria within the graft. There is a wide array of reported incidences of infection in the literature, from the Tomford and colleagues⁸ 1981 study that reported a 6.9% rateto the 2001 study by Munting and colleagues,⁹ who reported 0% in their series. Multiple confounding variables exist, such as possible contamination during handling of an otherwise noncontaminated or properly sterilized allograft with inappropriate inclusion of all postoperative infections. In contrast, recognizing viral transmission has been somewhat easier, although reporting of these incidences has been variable in the past. In either case, there is no accredited reporting system for infections related to allografts.

 

Bacterial Transmission

Clostridium species. Clostridium species are commonly found among intestinal flora. There is a general consensus that between 24 to 48 hours after death intestinal flora transmigrates into the surrounding tissue and blood. Therefore, a commonly accepted recommendation is that cadaveric tissue needs to be excised prior to 24 hours postmortem.¹⁰

In 2001, a 23-year-old man underwent reconstructive knee surgery with a femoral condyle allograft. A few days after surgery, he became septic and ultimately died from the infection. Clostridium sordellii was cultured from the tissue. Several days later, a 17-year-old boy underwent reconstructive knee surgery with a fresh femoral condyle and frozen meniscus from the same donor. Twenty-four hours after surgery, he developed a fever and was readmitted a week later for presumed infection and treated effectively with penicillin and ampicillin/sulbactam. Tissue from the same cadaveric donor had been transplanted into 7 other patients without reports of infection. In a 2002 Centers for Disease Control and Prevention (CDC) update report,¹¹ there were 26 total bacterial cases from allografts and 13 cases were attributed to Clostridium. Malinin and colleagues¹⁰ reviewed 795 consecutive cadaveric donors and found that 64 (8.1%) had positive cultures for Clostridia. Of all the positive cultures for Clostridia, 81.3% had positive blood cultures, 57.8% had positive bone marrow aspirate cultures, and 46.9% had positive tissue cultures. They concluded that multiple cultures are required for cadaveric tissue donors in order to reach a higher sensitivity for Clostridial contamination, and these should be done routinely to guide the sterilization process.

Strep species. In 2003, a 17-year-old boy underwent anterior cruciate ligament (ACL) reconstruction with a patellar tendon allograft.¹² About 1 week later, he was admitted for signs of infection and received intravenous antibiotics. He required surgical debridement, and intraoperative cultures grew Group A Streptococcus (GAS) that was also identified in the postmortem donor cultures. The tissues underwent processing in an antimicrobial solution and postprocessing cultures were negative for bacteria, but they were not sterilized. Tissues from this donor had been implanted in 5 other patients without report of infection. Following this event, recommendations have been made for prompt rejection of tissue with cultures positive for GAS, unless a sterilizing procedure is used.

Other bacteria. According to the 2002 CDC update, 11 of the 26 cases of bacterial infection reported to the agency were a combination of gram-negative bacilli, polymicrobial flora, or culture negative.¹¹

Viral Transmission

The most effective way to prevent transmission of a viral disease from allografts is thorough donor screening. Since the AATB implemented NAT in 2005 for HIV and HCV, there have been no reported cases of transmission.³ Even prior to this, regular blood screening along with social questionnaires completed by donors or donor families eliminated high-risk donors and significantly decreased the rate of transmission.

Human Immunodeficiency Virus. The first reported case of HIV transmission via implantation of allograft was in 1988. Further investigation revealed that there were 8 transmissions between 1984 and 1986, when routine screening of donors had not yet been implemented. The last reported case of HIV transmission occurred in 1996 with an untested donor.¹³Hepatitis C Virus. There are several reported cases of HCV transmission that occurred where the donors initially tested negative for HCV. In one case, 40 allografts from the same donor were transplanted over a period of nearly 2 years. This resulted in at least 8 patients being infected with HCV.¹⁴ Another case of HCV transmission was reported in 2005 after a patient developed acute HCV 6 weeks after transplantation of a patellar tendon allograft. Further investigation revealed that there had been 3 additional cases over a year from the same donor. Researchers determined that if the initial case had been reported, at least 3 transmissions could have been prevented.¹⁵Human T-cell Lymphotropic Virus (HTLV).The first reported transmission of HTLV was in 1991. This was reported in an asymptomatic patient who received a femoral head allograft from a donor who had been previously infected via a blood transfusion.¹⁶Zika virus. With recent outbreaks of the Zika virus, the FDA recently released recommendations regarding the screening and deferral of donors, mainly for blood transfusion. Orthopedists should take into consideration the potential for transmission through allografts. The FDA states that all potential donors should be screened for Zika virus using questionnaires and whole blood tests. Symptomatic donors are deferred at least 4 weeks following resolution of symptoms. While this is a recent recommendation from the FDA, orthopedists must be cognizant of the potential harms from this unfamiliar and evolving situation.¹⁷

Graft Specifics

Anterior Cruciate Ligament

ACL reconstruction is one of the most commonly performed surgeries by orthopedic surgeons, with an estimated 200,000 reconstructions per year.¹⁸Despite the popularity of this surgery, controversies remain regarding the optimal graft for reconstruction.^19,20 One would provide adequate strength, be readily available, not elicit an immunologic response from the host, rapidly incorporate, elicit low morbidity, and vascularize early. Current options include both autografts and allografts. Common autograft options include patellar bone-tendon-bone (PBTB), hamstrings tendon, quadriceps tendon, and iliotibial band. PBTB autograft remains a common choice among orthopedic surgeons, as it allows early incorporation of the graft into bone and eliminates immune rejection. However, donor site morbidity, including anterior knee pain, weakness of knee extension, joint stiffness, increased postoperative pain, and iatrogenic patella fractures, have been reported in the literature.²¹ Commonly used allograft options include donor bone-patellar tendon-bone, quadriceps tendon, Achilles tendon, anterior and posterior tibialis tendons, hamstring tendons, and iliotibial band. Allografts provide the advantage of avoiding donor site morbidity, being readily available, allowing for shorter operative times, and providing lower postoperative pain compared to autografts, although they carry the risk of disease transmission, rejection, and slower incorporation into bone.^22-27

 

Autograft donor site morbidities. One of the general disadvantages of autografts is the donor site morbidity associated with harvesting the grafts. In specific, PBTB grafts allow for bony blocks on both ends of the graft to incorporate into the host bone. However, this technique comes with the risk of disrupting the extensor mechanism.^28,29 Milankov and colleagues³⁰ published a retrospective review of over 2000 ACLs using autologous PBTB graft. They noted a 0.45% incidence of patella fracture and 0.18% patellar tendon rupture.³⁰ Others have reported that intraoperative repair of the patellar tendon after tendon harvesting can increase infrapatellar fibrosis, thus increasing the risk for stiffness.^31-33

Hamstring autografts include the semitendinosus and the gracilis tendons. The harvesting process is technically demanding and can be complicated by inadvertent amputation of the tendons, making the graft unsuitable for reconstructive purposes.³⁴ Additionally, several reports have identified persistent numbness and hyperesthesia following hamstring harvesting due to iatrogenic injury to the prepatellar branches of the saphenous nerve.^35,36A comprehensive review by Slone and colleagues³⁷ reported comparable functional outcomes with quadriceps tendon autograft compared to PBTB; however, this comes with the risk of postoperative hematoma formation and the potential for thigh compartment syndrome.

Biology and Biomechanics of Allografts

One of the major disadvantages of allografts is the reduced ability to incorporate into the host tissue. Several in vitro and animal studies have suggested that allografts incorporate in the host slower than autografts.^24,26,38 Early studies by Jackson and colleagues²⁴ on goat models demonstrated that allografts and autografts have similar structural and biological properties initially, but allografts display significantly slower incorporation into the host tissue at 6 months. Histologically, allografts demonstrated lower revascularization, a smaller cross-sectional area, and a prolonged inflammatory response at 6 months postoperatively.^24,39,40 Muramatsu and colleagues⁴¹ further showed through the use of magnetic resonance imaging a slower rate of revascularization of allografts over 2 years post-reconstruction.

Given the delayed biologic incorporation of allografts, studies have identified a lower strength-to-failure rate in the early postoperative period compared to autografts. An animal model study by Nikolaou and colleagues³⁸ showed that the strength of allografts was lower for up to 2 years following surgery. Additional biomechanical studies demonstrated that allografts were nearly 75% structurally weaker compared to autografts at 1 year following surgery.⁴²

Acknowledging these limitations, one should use caution when choosing to use an allograft or starting aggressive early rehabilitation after an allograft reconstruction, especially in athletes and young patients.

Clinical Outcomes

Although in vitro studies demonstrate inferior strength and delayed incorporation of allografts in the early postoperative period, there is still controversy surrounding the clinical and functional outcomes. Numerous studies have identified allografts as a viable option for ACL reconstruction, with similar reported patient satisfaction scores compared to autografts.^43,44

The MOON Consortium recently published a prospective study of nearly 2500 subjects looking to identify risk factors for failure of ACL reconstruction. The study found that allografts had an odds ratio for failure 5.2 times that of PBTB autografts, correlating this factor to an increased re-tear rate of 6.9% in the allograft group compared to 3.2% in the PBTB group (P < .01).⁴⁵ The elevated risk is more prevalent in younger patients, especially athletic teenagers. This issue has been reiterated in multiple studies.^45-50A meta-analysis by Hu and colleagues²³ identified 9 studies, either randomized control trials or prospective cohort studies, that looked at clinical outcomes between the different graft choices. They showed there was no significant difference between graft options in terms of instrumental laxity (P = .59), Lachman test (P = .41), pivot shift test (P = .88), and multiple functional outcome scores, including the International Knee Documentation Committee (IKDC), Lysholm, and Tegner scores.^23,51-59Processing and sterilization techniques are thought to play a role in allograft failure. Guo and other researchers have demonstrated a significantly higher rate of failure for patients who received gamma-irradiated allografts compared to fresh frozen allografts.^23,58-64 With improved sterilization techniques and a strict selection process of donors, gamma radiation has fallen out of favor to protect the biological characteristics of the tissue graft.^5,65,66Several factors need to be considered when selecting between allograft or autograft tissue for ligamentous reconstruction. The selection must be balanced between the surgeon’s experience, patient and surgeon preferences, age of the patient, level of physical activity, primary or revision surgical setting, multiligamentous failure, geographical availability of donor grafts, and economical factors.

Medial Patellofemoral Ligament Reconstruction

Another relatively recent application for allografts has been described for the reconstruction of the medial patellofemoral ligament (MPFL) in recurrent lateral patellar dislocations.^67-74

Typically, MPFL reconstructions make use of autografts, including quadriceps tendon, patellar tendon, and hamstring ligaments. However, allografts have the potential to limit postoperative donor site morbidity and to allow a faster rehabilitation.^75,76 Allografts include semitendinosus, gracilis, anterior tibialis, posterior tibialis, and quadriceps tendons.

Calvo Rodríguez and colleagues⁷⁶ performed a retrospective review in 2015 comparing allografts to autografts for MPFL reconstruction with respect to postoperative knee function and re-dislocation rates. Among the collective 28 patients, there was no difference in overall functional scores or dislocation rates between the grafts. Although this was a retrospective review and had a small number of subjects, the findings identify allografts as a reliable graft option for MPFL reconstruction.⁷⁶While there has been a surge of interest in techniques for MPFL reconstruction, there is limited research available regarding the superiority of allografts compared to autografts. For this specific application, it seems that clinical outcomes correlate more to adequate stabilization of the patellofemoral joint than to the type of graft used.^77,78 Future research should be dedicated to prospective randomized control trials to delineate any disadvantages to using allografts for MPFL reconstruction.

 

Discussion

Musculoskeletal allografts are gaining popularity for ligamentous reconstruction as their safety and efficacy continue to improve. With the great majority of tissue banks being accredited by the AATB and specific regulations such as NAT screening becoming common practice, infection rates and transmission of diseases have become incredibly rare. However, a thorough consideration needs to be taken into account when choosing between autograft and allograft on a case-by-case basis (Table).

Although the incidence of donor site complications is low with autografts, there are inherent risks, such as harvest site hyperesthesia, persistent numbness, cosmetic dissatisfaction, pain, weakness, functional implications, and unsuitability of the harvested graft. While it may appear that allografts may obviate donor site morbidity, one must consider the reduced potential for the donor tissue to incorporate into the host. Several studies have suggested that incorporation into the host tissue is inferior and slower for allografts. With this knowledge, factors such as clinical outcomes, future expectations, rehabilitation protocol, and individual patient characteristics all need to be considered when selecting the source of the tissue to be transplanted. Given that there is a growing need for availability of allografts, a well-rounded understanding of the biologic and physiologic aspects of the transplanted tissues is imperative. Future research will need to focus on improving the rate and quality of the biological incorporation of the transplanted graft into the host while eliminating the risk of disease transmission and infection.

Am J Orthop. 2016;45(7):446-453. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Musculoskeletal allografts are becoming increasingly accepted as a viable alternative to autografts in a variety of orthopedic procedures. A 2006 American Orthopaedic Society for Sports Medicine (AOSSM) survey indicated that 86% of the participating 365 orthopedic surgeons use allografts in their practice.¹ Although the overwhelming majority of orthopedic surgeons use allografts, they share common concerns, including safety, tissue integrity, and biologic incorporation. It is essential for the orthopedic surgeon to understand the current standards of tissue banking, risks and benefits related to the use of allografts, and common indications for safe use in clinical practice. This article reviews the current status of musculoskeletal allografts, including tissue procurement and processing, infections, complications, and specific uses tailored to ligament reconstruction.

Donor Bank, Processing, Sterilization, and Regulation

In the United States, the American Association of Tissue Banks (AATB) is responsible for establishing the standards for more than 100 accredited tissue banks. These tissue banks recover tissue from approximately 30,000 donors annually and account for an estimated 90% of the available musculoskeletal allografts used in the United States. While not all tissue banks are accredited by the AATB, all are required to register with the Food and Drug Administration (FDA), which allows for unannounced inspections of any facility. Facilities are required to abide by the FDA-implemented Current Good Tissue Practices (CGTP), which encompasses regulations on all donor tissue collected after May 2005 to help prevent the transmission of communicable diseases. The FDA released an updated draft in January 2009 that emphasizes safe practices and regulations spanning from environmental control to specific equipment.²

The safety of a transplanted allograft tissue begins within the tissue bank. Donor screening and testing is the first step in reducing the risk of transmission. Screening consists of collecting medical and social history from the family and any healthcare resources to assess the eligibility of the donor. If prior blood donations or autopsy information is available, that information is scrutinized. Donor tissue undergoes nucleic acid testing (NAT), which is required by both the AATB and FDA. All donor tissue must be screened for both types of human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), treponema pallidum, and human transmissible spongiform encephalopathies.³ NAT of donor tissue effectively reduces the risk of viral transmission. Additionally, routine preprocessing swabs for bacterial and fungal cultures are performed, although the sensitivity of these cultures ranges from 78% to 92%.⁴

After donor screening and testing, allograft tissues are usually obtained under aseptic conditions, though this is not FDA-required.⁵ Once procured, the tissue undergoes sterilization. Currently, there is no standard method ubiquitous to all tissue banks, nor does the FDA require a specific method. Rather, the FDA and AATB require tissue banks to validate their sterilization process and provide supporting data. The goal of sterilization is to inactivate viruses and eradicate bacteria while maintaining the biological and mechanical properties of the tissue. The AATB requires a Sterility Assurance Level (SAL) of 10^-6, meaning there is no more than one in a million chance that a nonviral viable microbe exists on or within the tissue. Sterilization techniques may include both radiation and a variety of chemical reagents. Gamma irradiation is a commonly used method of sterilizing soft tissue allografts, although some studies indicate that it is detrimental to tissue biology.⁶ Newer methods of sterilization are being tested, one of which includes carbon dioxide in combination with antioxidants and irradiation. Bui and colleagues⁷ directly compared the biomechanical and histological properties of allograft tissue after either the standard 25 kGy gamma irradiation or supercritical carbon dioxide techniques. Although there is no histological difference, the samples treated with supercritical carbon dioxide had less biomechanical damage.⁷ Finally, the terminally sterilized allograft tissue is frozen to temperatures between -40°C and -80°C.⁵

Infections

One major concern of allografts is the risk of disease transmission. While numerous studies have investigated the incidence of bacterial infection following transplantation of allograft tissue, there are challenges associated with differentiating common postoperative infections from ones directly associated with the transmission of bacteria within the graft. There is a wide array of reported incidences of infection in the literature, from the Tomford and colleagues⁸ 1981 study that reported a 6.9% rateto the 2001 study by Munting and colleagues,⁹ who reported 0% in their series. Multiple confounding variables exist, such as possible contamination during handling of an otherwise noncontaminated or properly sterilized allograft with inappropriate inclusion of all postoperative infections. In contrast, recognizing viral transmission has been somewhat easier, although reporting of these incidences has been variable in the past. In either case, there is no accredited reporting system for infections related to allografts.

 

Bacterial Transmission

Clostridium species. Clostridium species are commonly found among intestinal flora. There is a general consensus that between 24 to 48 hours after death intestinal flora transmigrates into the surrounding tissue and blood. Therefore, a commonly accepted recommendation is that cadaveric tissue needs to be excised prior to 24 hours postmortem.¹⁰

In 2001, a 23-year-old man underwent reconstructive knee surgery with a femoral condyle allograft. A few days after surgery, he became septic and ultimately died from the infection. Clostridium sordellii was cultured from the tissue. Several days later, a 17-year-old boy underwent reconstructive knee surgery with a fresh femoral condyle and frozen meniscus from the same donor. Twenty-four hours after surgery, he developed a fever and was readmitted a week later for presumed infection and treated effectively with penicillin and ampicillin/sulbactam. Tissue from the same cadaveric donor had been transplanted into 7 other patients without reports of infection. In a 2002 Centers for Disease Control and Prevention (CDC) update report,¹¹ there were 26 total bacterial cases from allografts and 13 cases were attributed to Clostridium. Malinin and colleagues¹⁰ reviewed 795 consecutive cadaveric donors and found that 64 (8.1%) had positive cultures for Clostridia. Of all the positive cultures for Clostridia, 81.3% had positive blood cultures, 57.8% had positive bone marrow aspirate cultures, and 46.9% had positive tissue cultures. They concluded that multiple cultures are required for cadaveric tissue donors in order to reach a higher sensitivity for Clostridial contamination, and these should be done routinely to guide the sterilization process.

Strep species. In 2003, a 17-year-old boy underwent anterior cruciate ligament (ACL) reconstruction with a patellar tendon allograft.¹² About 1 week later, he was admitted for signs of infection and received intravenous antibiotics. He required surgical debridement, and intraoperative cultures grew Group A Streptococcus (GAS) that was also identified in the postmortem donor cultures. The tissues underwent processing in an antimicrobial solution and postprocessing cultures were negative for bacteria, but they were not sterilized. Tissues from this donor had been implanted in 5 other patients without report of infection. Following this event, recommendations have been made for prompt rejection of tissue with cultures positive for GAS, unless a sterilizing procedure is used.

Other bacteria. According to the 2002 CDC update, 11 of the 26 cases of bacterial infection reported to the agency were a combination of gram-negative bacilli, polymicrobial flora, or culture negative.¹¹

Viral Transmission

The most effective way to prevent transmission of a viral disease from allografts is thorough donor screening. Since the AATB implemented NAT in 2005 for HIV and HCV, there have been no reported cases of transmission.³ Even prior to this, regular blood screening along with social questionnaires completed by donors or donor families eliminated high-risk donors and significantly decreased the rate of transmission.

Human Immunodeficiency Virus. The first reported case of HIV transmission via implantation of allograft was in 1988. Further investigation revealed that there were 8 transmissions between 1984 and 1986, when routine screening of donors had not yet been implemented. The last reported case of HIV transmission occurred in 1996 with an untested donor.¹³Hepatitis C Virus. There are several reported cases of HCV transmission that occurred where the donors initially tested negative for HCV. In one case, 40 allografts from the same donor were transplanted over a period of nearly 2 years. This resulted in at least 8 patients being infected with HCV.¹⁴ Another case of HCV transmission was reported in 2005 after a patient developed acute HCV 6 weeks after transplantation of a patellar tendon allograft. Further investigation revealed that there had been 3 additional cases over a year from the same donor. Researchers determined that if the initial case had been reported, at least 3 transmissions could have been prevented.¹⁵Human T-cell Lymphotropic Virus (HTLV).The first reported transmission of HTLV was in 1991. This was reported in an asymptomatic patient who received a femoral head allograft from a donor who had been previously infected via a blood transfusion.¹⁶Zika virus. With recent outbreaks of the Zika virus, the FDA recently released recommendations regarding the screening and deferral of donors, mainly for blood transfusion. Orthopedists should take into consideration the potential for transmission through allografts. The FDA states that all potential donors should be screened for Zika virus using questionnaires and whole blood tests. Symptomatic donors are deferred at least 4 weeks following resolution of symptoms. While this is a recent recommendation from the FDA, orthopedists must be cognizant of the potential harms from this unfamiliar and evolving situation.¹⁷

Graft Specifics

Anterior Cruciate Ligament

ACL reconstruction is one of the most commonly performed surgeries by orthopedic surgeons, with an estimated 200,000 reconstructions per year.¹⁸Despite the popularity of this surgery, controversies remain regarding the optimal graft for reconstruction.^19,20 One would provide adequate strength, be readily available, not elicit an immunologic response from the host, rapidly incorporate, elicit low morbidity, and vascularize early. Current options include both autografts and allografts. Common autograft options include patellar bone-tendon-bone (PBTB), hamstrings tendon, quadriceps tendon, and iliotibial band. PBTB autograft remains a common choice among orthopedic surgeons, as it allows early incorporation of the graft into bone and eliminates immune rejection. However, donor site morbidity, including anterior knee pain, weakness of knee extension, joint stiffness, increased postoperative pain, and iatrogenic patella fractures, have been reported in the literature.²¹ Commonly used allograft options include donor bone-patellar tendon-bone, quadriceps tendon, Achilles tendon, anterior and posterior tibialis tendons, hamstring tendons, and iliotibial band. Allografts provide the advantage of avoiding donor site morbidity, being readily available, allowing for shorter operative times, and providing lower postoperative pain compared to autografts, although they carry the risk of disease transmission, rejection, and slower incorporation into bone.^22-27

 

Autograft donor site morbidities. One of the general disadvantages of autografts is the donor site morbidity associated with harvesting the grafts. In specific, PBTB grafts allow for bony blocks on both ends of the graft to incorporate into the host bone. However, this technique comes with the risk of disrupting the extensor mechanism.^28,29 Milankov and colleagues³⁰ published a retrospective review of over 2000 ACLs using autologous PBTB graft. They noted a 0.45% incidence of patella fracture and 0.18% patellar tendon rupture.³⁰ Others have reported that intraoperative repair of the patellar tendon after tendon harvesting can increase infrapatellar fibrosis, thus increasing the risk for stiffness.^31-33

Hamstring autografts include the semitendinosus and the gracilis tendons. The harvesting process is technically demanding and can be complicated by inadvertent amputation of the tendons, making the graft unsuitable for reconstructive purposes.³⁴ Additionally, several reports have identified persistent numbness and hyperesthesia following hamstring harvesting due to iatrogenic injury to the prepatellar branches of the saphenous nerve.^35,36A comprehensive review by Slone and colleagues³⁷ reported comparable functional outcomes with quadriceps tendon autograft compared to PBTB; however, this comes with the risk of postoperative hematoma formation and the potential for thigh compartment syndrome.

Biology and Biomechanics of Allografts

One of the major disadvantages of allografts is the reduced ability to incorporate into the host tissue. Several in vitro and animal studies have suggested that allografts incorporate in the host slower than autografts.^24,26,38 Early studies by Jackson and colleagues²⁴ on goat models demonstrated that allografts and autografts have similar structural and biological properties initially, but allografts display significantly slower incorporation into the host tissue at 6 months. Histologically, allografts demonstrated lower revascularization, a smaller cross-sectional area, and a prolonged inflammatory response at 6 months postoperatively.^24,39,40 Muramatsu and colleagues⁴¹ further showed through the use of magnetic resonance imaging a slower rate of revascularization of allografts over 2 years post-reconstruction.

Given the delayed biologic incorporation of allografts, studies have identified a lower strength-to-failure rate in the early postoperative period compared to autografts. An animal model study by Nikolaou and colleagues³⁸ showed that the strength of allografts was lower for up to 2 years following surgery. Additional biomechanical studies demonstrated that allografts were nearly 75% structurally weaker compared to autografts at 1 year following surgery.⁴²

Acknowledging these limitations, one should use caution when choosing to use an allograft or starting aggressive early rehabilitation after an allograft reconstruction, especially in athletes and young patients.

Clinical Outcomes

Although in vitro studies demonstrate inferior strength and delayed incorporation of allografts in the early postoperative period, there is still controversy surrounding the clinical and functional outcomes. Numerous studies have identified allografts as a viable option for ACL reconstruction, with similar reported patient satisfaction scores compared to autografts.^43,44

The MOON Consortium recently published a prospective study of nearly 2500 subjects looking to identify risk factors for failure of ACL reconstruction. The study found that allografts had an odds ratio for failure 5.2 times that of PBTB autografts, correlating this factor to an increased re-tear rate of 6.9% in the allograft group compared to 3.2% in the PBTB group (P < .01).⁴⁵ The elevated risk is more prevalent in younger patients, especially athletic teenagers. This issue has been reiterated in multiple studies.^45-50A meta-analysis by Hu and colleagues²³ identified 9 studies, either randomized control trials or prospective cohort studies, that looked at clinical outcomes between the different graft choices. They showed there was no significant difference between graft options in terms of instrumental laxity (P = .59), Lachman test (P = .41), pivot shift test (P = .88), and multiple functional outcome scores, including the International Knee Documentation Committee (IKDC), Lysholm, and Tegner scores.^23,51-59Processing and sterilization techniques are thought to play a role in allograft failure. Guo and other researchers have demonstrated a significantly higher rate of failure for patients who received gamma-irradiated allografts compared to fresh frozen allografts.^23,58-64 With improved sterilization techniques and a strict selection process of donors, gamma radiation has fallen out of favor to protect the biological characteristics of the tissue graft.^5,65,66Several factors need to be considered when selecting between allograft or autograft tissue for ligamentous reconstruction. The selection must be balanced between the surgeon’s experience, patient and surgeon preferences, age of the patient, level of physical activity, primary or revision surgical setting, multiligamentous failure, geographical availability of donor grafts, and economical factors.

Medial Patellofemoral Ligament Reconstruction

Another relatively recent application for allografts has been described for the reconstruction of the medial patellofemoral ligament (MPFL) in recurrent lateral patellar dislocations.^67-74

Typically, MPFL reconstructions make use of autografts, including quadriceps tendon, patellar tendon, and hamstring ligaments. However, allografts have the potential to limit postoperative donor site morbidity and to allow a faster rehabilitation.^75,76 Allografts include semitendinosus, gracilis, anterior tibialis, posterior tibialis, and quadriceps tendons.

Calvo Rodríguez and colleagues⁷⁶ performed a retrospective review in 2015 comparing allografts to autografts for MPFL reconstruction with respect to postoperative knee function and re-dislocation rates. Among the collective 28 patients, there was no difference in overall functional scores or dislocation rates between the grafts. Although this was a retrospective review and had a small number of subjects, the findings identify allografts as a reliable graft option for MPFL reconstruction.⁷⁶While there has been a surge of interest in techniques for MPFL reconstruction, there is limited research available regarding the superiority of allografts compared to autografts. For this specific application, it seems that clinical outcomes correlate more to adequate stabilization of the patellofemoral joint than to the type of graft used.^77,78 Future research should be dedicated to prospective randomized control trials to delineate any disadvantages to using allografts for MPFL reconstruction.

 

Discussion

Musculoskeletal allografts are gaining popularity for ligamentous reconstruction as their safety and efficacy continue to improve. With the great majority of tissue banks being accredited by the AATB and specific regulations such as NAT screening becoming common practice, infection rates and transmission of diseases have become incredibly rare. However, a thorough consideration needs to be taken into account when choosing between autograft and allograft on a case-by-case basis (Table).

Although the incidence of donor site complications is low with autografts, there are inherent risks, such as harvest site hyperesthesia, persistent numbness, cosmetic dissatisfaction, pain, weakness, functional implications, and unsuitability of the harvested graft. While it may appear that allografts may obviate donor site morbidity, one must consider the reduced potential for the donor tissue to incorporate into the host. Several studies have suggested that incorporation into the host tissue is inferior and slower for allografts. With this knowledge, factors such as clinical outcomes, future expectations, rehabilitation protocol, and individual patient characteristics all need to be considered when selecting the source of the tissue to be transplanted. Given that there is a growing need for availability of allografts, a well-rounded understanding of the biologic and physiologic aspects of the transplanted tissues is imperative. Future research will need to focus on improving the rate and quality of the biological incorporation of the transplanted graft into the host while eliminating the risk of disease transmission and infection.

Am J Orthop. 2016;45(7):446-453. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

In 1975, Skolnick and colleagues¹ introduced unicompartmental knee arthroplasty (UKA) for patients with isolated unicompartmental osteoarthritis (OA). They reported a study of 14 UKA procedures, of which 12 were at the medial and 2 at the lateral side. Forty years since this procedure was introduced, UKA is used in 8% to 12% of all knee arthroplasties.^2-6 A minority of these procedures are performed at the lateral side (5%-10%).^6-8

The considerable anatomical and kinematical differences between compartments^9-14 make it impossible to directly compare outcomes of medial and lateral UKA. For example, a greater degree of femoral roll and more posterior translation at the lateral side in flexion^9,10,13 can contribute to different pattern and volume differences of cartilage wear.¹⁵ Because of these differences, and because of implant design factors and lower surgical volume, lateral UKA is considered a technically more challenging surgery compared to medial UKA.^12,16,17

Since isolated lateral compartment OA is relatively scarce, current literature on lateral UKA is limited, and most studies combine medial and lateral outcomes to report UKA outcomes and failure modes.^3,4,18-20 However, as the UKA has grown in popularity over the last decade,^2,21-25 the number of reports about the lateral UKA also has increased. Recent studies reported excellent short-term survivorship results of the lateral UKA (96%-99%)^26,27 and smaller lateral UKA studies reported the 10-year survivorship with varying outcomes from good (84%)^14,28-30 to excellent (94%-100%).^8,31,32 Indeed, a recent systematic review showed survivorship of lateral UKA at 5, 10, and 15 years of 93%, 91%, and 89%, respectively.³³Because of the differences between the medial and lateral compartment, it is important to know the failure modes of lateral UKA in order to improve clinical outcomes and revision rates. We performed a systematic review of cohort studies and registry-based studies that reported lateral UKA failure to assess the causes of lateral UKA failure. In addition, we compared the failure modes in cohort studies with those found in registry-based studies.

Patients and Methods

Search Strategy and Criteria

Databases of PubMed, Embase, and Cochrane (Cochrane Central Register of Clinical Trials) were searched with the terms “knee, arthroplasty, replacement,” “unicompartmental,” “unicondylar,” “partial,” “UKA,” “UKR,” “UCA,” “UCR,” “PKA,” “PKR,” “PCA,” “prosthesis failure,” “reoperation,” “survivorship,” and “treatment failure.” After removal of duplicates, 2 authors (JPvdL and HAZ) scanned the articles for their title and abstract to assess eligibility for the study.

The full text of these eligible articles was further viewed and useful studies were selected using the inclusion and exclusion criteria. The references of these articles were scanned for additional studies and national registries (Figure).

Inclusion criteria were: (I) English language articles describing studies in humans published in the last 25 years, (II) retrospective and prospective studies, (III) featured lateral UKA, (IV) OA was indication for surgery, and (V) included failure modes data. The exclusion criteria were studies that featured: (I) only a specific group of failure (eg, bearing dislocations only), (II) previous surgery in ipsilateral knee (high tibial osteotomy, medial UKA), (III) acute concurrent knee diagnoses (acute anterior cruciate ligament rupture, acute meniscal tear), (IV) combined reporting of medial and lateral UKA, or (V) multiple studies with the same patient database.

Data Collection

All studies that reported modes of failure were used in this study and these failure modes were noted in a datasheet in Microsoft Excel 2011 (Microsoft).

The data of failures of lateral UKA are presented in Table 1 and are divided in cohort studies and registry-based studies. The final failure mode rates were presented in percentages (Table 2).

Statistical Analysis

For this systematic review, statistical analysis was performed with IBM SPSS Statistics 22 (SPSS Inc.). We performed chi square tests and Fisher’s exact tests to assess a difference between cohort studies and registry-based studies with the null hypothesis of no difference between both groups. A difference was considered significant when P < .05.

Results

Through the search of the databases, 1294 studies were identified and 26 handpicked studies were added. Initially, based on the title and abstract, 184 of these studies were found eligible.

After reviewing the full text of these articles, 25 studies (23 cohort studies and 2 registry-based studies) met the inclusion criteria and were included for the analysis of lateral UKA failure (Figure).

A total of 366 lateral UKA failures were included. The most common failure modes were progression of OA (29%), aseptic loosening (23%), and bearing dislocation (10%). Infection (6%), instability (6%), unexplained pain (6%), and fractures (4%) were less common causes of failure of lateral UKA (Table 2).

One hundred fifty-five of these failures were reported in the cohort studies. The most common modes of failure were OA progression (36%), bearing dislocation (17%) and aseptic loosening (16%). Less common were infection (10%), fractures (5%), pain (5%), and other causes (6%). In registry-based studies, with 211 lateral UKA failures, the most common modes of failure were aseptic loosening (28%), OA progression (24%), other causes (12%), instability (10%), pain (7%), bearing dislocation (5%), and polyethylene wear (4%) (Table 2).

When pooling cohort and registry-based studies, progression of OA was significantly more common than aseptic loosening (29% vs 23%, respectively; P < .01). It was also significantly more common in the cohort studies (36% vs 16%, respectively; P < .01) but no significant difference was found between progression of OA and aseptic loosening in registry-based studies (24% and 28%, respectively; P = .16) (Table 2).

When comparing cohort with registry-based studies, progression of OA was higher in cohort studies (36% vs. 24%; P < .01). Other failures modes that were more common in cohort studies compared with registry-based studies were bearing dislocation (17% vs 5%, respectively; P < .01) and infections (10% vs 3%, P < .01). Failure modes that were more common in registry-based studies than cohort studies were aseptic loosening (28% vs 16%, respectively; P < .01), other causes (12% vs 6%, respectively, P = .02), and instability (10% vs 1%, respectively, P < .01) (Table 2).

 

Discussion

In this systematic review, the most common failure modes in lateral UKA review were OA progression (29%), aseptic loosening (23%), and bearing dislocation (10%). Progression of OA and bearing dislocation were the most common modes of failure in cohort studies (36% and 17%, respectively), while aseptic loosening and OA progression were the most common failure modes in registry-based studies (28% and 24%, respectively).

As mentioned above, there are differences in anatomy and kinematics between the medial and lateral compartment. When the lateral UKA failure modes are compared with studies reporting medial UKA failure modes, differences in failure modes are seen.³⁴ Siddiqui and Ahmad³⁵ performed a systematic review of outcomes after UKA revision and presented a table with the failure modes of included studies. Unfortunately they did not report the ratio of medial and lateral UKA. However, when assuming an average percentage of 90% to 95% of medial UKA,^6,7,36 the main failure mode in their review in 17 out of 21 studies was aseptic loosening. Indeed, a recent systematic review on medial UKA failure modes showed that aseptic loosening is the most common cause of failure following this procedure.³⁴ Similarly, a search through registry-based studies^6,7 and large cohort studies^37-40 that only reported medial UKA failures showed that the majority of these studies^7,37-39 also reported aseptic loosening as the main cause of failure in medial UKA. When comparing the results of our systematic review of lateral UKA failures with the results of these studies of medial UKA failures, it seems that OA progression seems to play a more dominant role in failures of lateral UKA, while aseptic loosening seems to be more common in medial UKA.

Differences in anatomy and kinematics of the medial and lateral compartment can explain this. Malalignment of the joint is an important factor in the etiology of OA^41,42 and biomechanical studies showed that this malalignment can cause decreased viability and further degenerative changes of cartilage of the knee.⁴³ Hernigou and Deschamps⁴⁴ showed that the alignment of the knee after medial UKA is an important factor in postoperative joint changes. They found that overcorrection of varus deformity during medial UKA surgery, measured by the hip-knee-ankle (HKA) angle, was associated with increased OA at the lateral condyle and less tibial wear of the medial UKA. Undercorrection of the varus caused an increase in tibial wear of polyethylene. Chatellard and colleagues⁴⁵ found the same results in the correction of varus, measured by HKA. In addition, they found that when the prosthetic (medial) joint space was smaller than healthy (lateral) joint space, this was correlated with lower prosthesis survival. A smaller joint space at the healthy side was correlated with OA progression at the lateral compartment and tibial component wear.

These studies explain the mechanism of progression of OA and aseptic loosening. Harrington⁴⁶ assessed the load in patients with valgus and varus deformity. Patients with a valgus deformity have high mechanical load on the lateral condyle during the static phase, but during the dynamic phase, a major part of this load shifts to the medial condyle. In the patients with varus deformity, the mechanical load was noted on the medial condyle during both the static and dynamic phase. Ohdera and colleagues⁴⁷ advised, based on this biomechanical study and their own experiences, to correct the knee during lateral UKA to a slight valgus angle (5°-7°) to prevent OA progression at the medial side. van der List and colleagues⁴⁸ similarly showed that undercorrection of 3° to 7° was correlated with better functional outcomes when compared to more neutral alignment. Moreover, Khamaisy and colleagues⁴⁹ recently showed that overcorrection during UKA surgery is more common in lateral than medial UKA.

These studies are important to understanding why OA progression is more common as a failure mode in lateral UKA. The shift of mechanical load from the lateral to medial epicondyle during the dynamic phase also could explain why aseptic loosening is less common in lateral UKA. As Hernigou and Deschamps⁴⁴ and Chatellard and colleagues⁴⁵ stated, undercorrection of varus deformity in medial UKA is associated with higher mechanical load on the medial prosthesis side and smaller joint space width. These factors are correlated with mechanical failure of medial UKA. We think this process can be applied to lateral UKA, with the addition that the mechanical load is higher on the healthy medial compartment during the dynamic phase. This causes more forces on the healthy (medial) side in lateral UKA, and in medial UKA more forces on the prosthesis (medial) side, which results in more OA progression in lateral UKA and more aseptic loosening in medial UKA. This finding is consistent with the results of our review of more OA progression and less aseptic loosening in lateral UKA. This study also suggests that medial and lateral UKA should not be reported together in studies that present survivorship, failure modes, or clinical outcomes.

A large discrepancy was seen in bearing dislocation between cohort studies (17%) and registry-based studies (5%). When we take a closer look to the bearing dislocation failures in the cohort studies, most of the failures were reported in only 2 cohort studies.^50,51 In a study by Pandit and colleagues,⁵⁰ 3 different prosthesis designs were used in 3 different time periods. In the first series of lateral UKA (1983-1991), 6 out of 51 (12%) bearings dislocated. In the second series (1998-2004), a modified technique was used and 3 out of 65 (5%) bearings dislocated. In the third series (2004-2008), a modified technique and a domed tibial component was used and only 1 out of 68 bearings dislocated (1%). In a study published in 1996, Gunther and colleagues⁵¹ also used surgical techniques and implants that were modified over the course of the study period. Because of these modified techniques, different implant designs, and year of publication, bearing dislocation most likely plays a smaller role than the 17% reported in the cohort studies. This discrepancy is a good example of the important role for the registries and registry-based studies in reporting failure modes and survivorship, especially in lateral UKA due to the low surgical frequency. Pabinger and colleagues⁵² recently performed a systematic review of cohort studies and registry-based studies in which they stated that the reliability in non-registry-based studies should be questioned and they considered registry-based studies superior in reporting UKA outcomes and revision rates. Furthermore, given the differences in anatomic and kinematic differences between the medial and lateral compartment and different failure modes between medial and lateral UKA, it would be better if future studies presented the medial and lateral failures separately. As stated above, most large cohort studies and especially annual registries currently do not report modes of failure of medial and lateral UKA separately.^3,4,18-20

There are limitations in this study. First, this systematic review is not a full meta-analysis but a pooled analysis of collected study series and retrospective studies. Therefore, we cannot exclude sampling bias, confounders, and selection bias from the literature. We included all studies reporting failure modes of lateral UKA and excluded all case reports. We made a conscious choice about including all lateral UKA failures because this is the first systematic review of lateral UKA failure modes. Another limitation is that the follow-up period of the studies differed (Table 1) and we did not correct for the follow-up period. As stated in the example of bearing dislocations, some of these studies reported old or different techniques, while other, more recently published studies used more modified techniques^11,29,53-56 Unfortunately, most studies did not report the time of arthroplasty survival and therefore we could not correct for the follow-up period.

In conclusion, progression of OA is the most common failure mode in lateral UKA, followed by aseptic loosening. Anatomic and kinematic factors such as alignment, mechanical forces during dynamic phase, and correction of valgus seem to play important roles in failure modes of lateral UKA. In the future, failure modes of medial and lateral UKA should be reported separately.

Am J Orthop. 2016;45(7):432-438, 462. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

In 1975, Skolnick and colleagues¹ introduced unicompartmental knee arthroplasty (UKA) for patients with isolated unicompartmental osteoarthritis (OA). They reported a study of 14 UKA procedures, of which 12 were at the medial and 2 at the lateral side. Forty years since this procedure was introduced, UKA is used in 8% to 12% of all knee arthroplasties.^2-6 A minority of these procedures are performed at the lateral side (5%-10%).^6-8

The considerable anatomical and kinematical differences between compartments^9-14 make it impossible to directly compare outcomes of medial and lateral UKA. For example, a greater degree of femoral roll and more posterior translation at the lateral side in flexion^9,10,13 can contribute to different pattern and volume differences of cartilage wear.¹⁵ Because of these differences, and because of implant design factors and lower surgical volume, lateral UKA is considered a technically more challenging surgery compared to medial UKA.^12,16,17

Since isolated lateral compartment OA is relatively scarce, current literature on lateral UKA is limited, and most studies combine medial and lateral outcomes to report UKA outcomes and failure modes.^3,4,18-20 However, as the UKA has grown in popularity over the last decade,^2,21-25 the number of reports about the lateral UKA also has increased. Recent studies reported excellent short-term survivorship results of the lateral UKA (96%-99%)^26,27 and smaller lateral UKA studies reported the 10-year survivorship with varying outcomes from good (84%)^14,28-30 to excellent (94%-100%).^8,31,32 Indeed, a recent systematic review showed survivorship of lateral UKA at 5, 10, and 15 years of 93%, 91%, and 89%, respectively.³³Because of the differences between the medial and lateral compartment, it is important to know the failure modes of lateral UKA in order to improve clinical outcomes and revision rates. We performed a systematic review of cohort studies and registry-based studies that reported lateral UKA failure to assess the causes of lateral UKA failure. In addition, we compared the failure modes in cohort studies with those found in registry-based studies.

Patients and Methods

Search Strategy and Criteria

Databases of PubMed, Embase, and Cochrane (Cochrane Central Register of Clinical Trials) were searched with the terms “knee, arthroplasty, replacement,” “unicompartmental,” “unicondylar,” “partial,” “UKA,” “UKR,” “UCA,” “UCR,” “PKA,” “PKR,” “PCA,” “prosthesis failure,” “reoperation,” “survivorship,” and “treatment failure.” After removal of duplicates, 2 authors (JPvdL and HAZ) scanned the articles for their title and abstract to assess eligibility for the study.

The full text of these eligible articles was further viewed and useful studies were selected using the inclusion and exclusion criteria. The references of these articles were scanned for additional studies and national registries (Figure).

Inclusion criteria were: (I) English language articles describing studies in humans published in the last 25 years, (II) retrospective and prospective studies, (III) featured lateral UKA, (IV) OA was indication for surgery, and (V) included failure modes data. The exclusion criteria were studies that featured: (I) only a specific group of failure (eg, bearing dislocations only), (II) previous surgery in ipsilateral knee (high tibial osteotomy, medial UKA), (III) acute concurrent knee diagnoses (acute anterior cruciate ligament rupture, acute meniscal tear), (IV) combined reporting of medial and lateral UKA, or (V) multiple studies with the same patient database.

Data Collection

All studies that reported modes of failure were used in this study and these failure modes were noted in a datasheet in Microsoft Excel 2011 (Microsoft).

The data of failures of lateral UKA are presented in Table 1 and are divided in cohort studies and registry-based studies. The final failure mode rates were presented in percentages (Table 2).

Statistical Analysis

For this systematic review, statistical analysis was performed with IBM SPSS Statistics 22 (SPSS Inc.). We performed chi square tests and Fisher’s exact tests to assess a difference between cohort studies and registry-based studies with the null hypothesis of no difference between both groups. A difference was considered significant when P < .05.

Results

Through the search of the databases, 1294 studies were identified and 26 handpicked studies were added. Initially, based on the title and abstract, 184 of these studies were found eligible.

After reviewing the full text of these articles, 25 studies (23 cohort studies and 2 registry-based studies) met the inclusion criteria and were included for the analysis of lateral UKA failure (Figure).

A total of 366 lateral UKA failures were included. The most common failure modes were progression of OA (29%), aseptic loosening (23%), and bearing dislocation (10%). Infection (6%), instability (6%), unexplained pain (6%), and fractures (4%) were less common causes of failure of lateral UKA (Table 2).

One hundred fifty-five of these failures were reported in the cohort studies. The most common modes of failure were OA progression (36%), bearing dislocation (17%) and aseptic loosening (16%). Less common were infection (10%), fractures (5%), pain (5%), and other causes (6%). In registry-based studies, with 211 lateral UKA failures, the most common modes of failure were aseptic loosening (28%), OA progression (24%), other causes (12%), instability (10%), pain (7%), bearing dislocation (5%), and polyethylene wear (4%) (Table 2).

When pooling cohort and registry-based studies, progression of OA was significantly more common than aseptic loosening (29% vs 23%, respectively; P < .01). It was also significantly more common in the cohort studies (36% vs 16%, respectively; P < .01) but no significant difference was found between progression of OA and aseptic loosening in registry-based studies (24% and 28%, respectively; P = .16) (Table 2).

When comparing cohort with registry-based studies, progression of OA was higher in cohort studies (36% vs. 24%; P < .01). Other failures modes that were more common in cohort studies compared with registry-based studies were bearing dislocation (17% vs 5%, respectively; P < .01) and infections (10% vs 3%, P < .01). Failure modes that were more common in registry-based studies than cohort studies were aseptic loosening (28% vs 16%, respectively; P < .01), other causes (12% vs 6%, respectively, P = .02), and instability (10% vs 1%, respectively, P < .01) (Table 2).

 

Discussion

In this systematic review, the most common failure modes in lateral UKA review were OA progression (29%), aseptic loosening (23%), and bearing dislocation (10%). Progression of OA and bearing dislocation were the most common modes of failure in cohort studies (36% and 17%, respectively), while aseptic loosening and OA progression were the most common failure modes in registry-based studies (28% and 24%, respectively).

As mentioned above, there are differences in anatomy and kinematics between the medial and lateral compartment. When the lateral UKA failure modes are compared with studies reporting medial UKA failure modes, differences in failure modes are seen.³⁴ Siddiqui and Ahmad³⁵ performed a systematic review of outcomes after UKA revision and presented a table with the failure modes of included studies. Unfortunately they did not report the ratio of medial and lateral UKA. However, when assuming an average percentage of 90% to 95% of medial UKA,^6,7,36 the main failure mode in their review in 17 out of 21 studies was aseptic loosening. Indeed, a recent systematic review on medial UKA failure modes showed that aseptic loosening is the most common cause of failure following this procedure.³⁴ Similarly, a search through registry-based studies^6,7 and large cohort studies^37-40 that only reported medial UKA failures showed that the majority of these studies^7,37-39 also reported aseptic loosening as the main cause of failure in medial UKA. When comparing the results of our systematic review of lateral UKA failures with the results of these studies of medial UKA failures, it seems that OA progression seems to play a more dominant role in failures of lateral UKA, while aseptic loosening seems to be more common in medial UKA.

Differences in anatomy and kinematics of the medial and lateral compartment can explain this. Malalignment of the joint is an important factor in the etiology of OA^41,42 and biomechanical studies showed that this malalignment can cause decreased viability and further degenerative changes of cartilage of the knee.⁴³ Hernigou and Deschamps⁴⁴ showed that the alignment of the knee after medial UKA is an important factor in postoperative joint changes. They found that overcorrection of varus deformity during medial UKA surgery, measured by the hip-knee-ankle (HKA) angle, was associated with increased OA at the lateral condyle and less tibial wear of the medial UKA. Undercorrection of the varus caused an increase in tibial wear of polyethylene. Chatellard and colleagues⁴⁵ found the same results in the correction of varus, measured by HKA. In addition, they found that when the prosthetic (medial) joint space was smaller than healthy (lateral) joint space, this was correlated with lower prosthesis survival. A smaller joint space at the healthy side was correlated with OA progression at the lateral compartment and tibial component wear.

These studies explain the mechanism of progression of OA and aseptic loosening. Harrington⁴⁶ assessed the load in patients with valgus and varus deformity. Patients with a valgus deformity have high mechanical load on the lateral condyle during the static phase, but during the dynamic phase, a major part of this load shifts to the medial condyle. In the patients with varus deformity, the mechanical load was noted on the medial condyle during both the static and dynamic phase. Ohdera and colleagues⁴⁷ advised, based on this biomechanical study and their own experiences, to correct the knee during lateral UKA to a slight valgus angle (5°-7°) to prevent OA progression at the medial side. van der List and colleagues⁴⁸ similarly showed that undercorrection of 3° to 7° was correlated with better functional outcomes when compared to more neutral alignment. Moreover, Khamaisy and colleagues⁴⁹ recently showed that overcorrection during UKA surgery is more common in lateral than medial UKA.

These studies are important to understanding why OA progression is more common as a failure mode in lateral UKA. The shift of mechanical load from the lateral to medial epicondyle during the dynamic phase also could explain why aseptic loosening is less common in lateral UKA. As Hernigou and Deschamps⁴⁴ and Chatellard and colleagues⁴⁵ stated, undercorrection of varus deformity in medial UKA is associated with higher mechanical load on the medial prosthesis side and smaller joint space width. These factors are correlated with mechanical failure of medial UKA. We think this process can be applied to lateral UKA, with the addition that the mechanical load is higher on the healthy medial compartment during the dynamic phase. This causes more forces on the healthy (medial) side in lateral UKA, and in medial UKA more forces on the prosthesis (medial) side, which results in more OA progression in lateral UKA and more aseptic loosening in medial UKA. This finding is consistent with the results of our review of more OA progression and less aseptic loosening in lateral UKA. This study also suggests that medial and lateral UKA should not be reported together in studies that present survivorship, failure modes, or clinical outcomes.

A large discrepancy was seen in bearing dislocation between cohort studies (17%) and registry-based studies (5%). When we take a closer look to the bearing dislocation failures in the cohort studies, most of the failures were reported in only 2 cohort studies.^50,51 In a study by Pandit and colleagues,⁵⁰ 3 different prosthesis designs were used in 3 different time periods. In the first series of lateral UKA (1983-1991), 6 out of 51 (12%) bearings dislocated. In the second series (1998-2004), a modified technique was used and 3 out of 65 (5%) bearings dislocated. In the third series (2004-2008), a modified technique and a domed tibial component was used and only 1 out of 68 bearings dislocated (1%). In a study published in 1996, Gunther and colleagues⁵¹ also used surgical techniques and implants that were modified over the course of the study period. Because of these modified techniques, different implant designs, and year of publication, bearing dislocation most likely plays a smaller role than the 17% reported in the cohort studies. This discrepancy is a good example of the important role for the registries and registry-based studies in reporting failure modes and survivorship, especially in lateral UKA due to the low surgical frequency. Pabinger and colleagues⁵² recently performed a systematic review of cohort studies and registry-based studies in which they stated that the reliability in non-registry-based studies should be questioned and they considered registry-based studies superior in reporting UKA outcomes and revision rates. Furthermore, given the differences in anatomic and kinematic differences between the medial and lateral compartment and different failure modes between medial and lateral UKA, it would be better if future studies presented the medial and lateral failures separately. As stated above, most large cohort studies and especially annual registries currently do not report modes of failure of medial and lateral UKA separately.^3,4,18-20

There are limitations in this study. First, this systematic review is not a full meta-analysis but a pooled analysis of collected study series and retrospective studies. Therefore, we cannot exclude sampling bias, confounders, and selection bias from the literature. We included all studies reporting failure modes of lateral UKA and excluded all case reports. We made a conscious choice about including all lateral UKA failures because this is the first systematic review of lateral UKA failure modes. Another limitation is that the follow-up period of the studies differed (Table 1) and we did not correct for the follow-up period. As stated in the example of bearing dislocations, some of these studies reported old or different techniques, while other, more recently published studies used more modified techniques^11,29,53-56 Unfortunately, most studies did not report the time of arthroplasty survival and therefore we could not correct for the follow-up period.

In conclusion, progression of OA is the most common failure mode in lateral UKA, followed by aseptic loosening. Anatomic and kinematic factors such as alignment, mechanical forces during dynamic phase, and correction of valgus seem to play important roles in failure modes of lateral UKA. In the future, failure modes of medial and lateral UKA should be reported separately.

Am J Orthop. 2016;45(7):432-438, 462. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

In 1975, Skolnick and colleagues¹ introduced unicompartmental knee arthroplasty (UKA) for patients with isolated unicompartmental osteoarthritis (OA). They reported a study of 14 UKA procedures, of which 12 were at the medial and 2 at the lateral side. Forty years since this procedure was introduced, UKA is used in 8% to 12% of all knee arthroplasties.^2-6 A minority of these procedures are performed at the lateral side (5%-10%).^6-8

The considerable anatomical and kinematical differences between compartments^9-14 make it impossible to directly compare outcomes of medial and lateral UKA. For example, a greater degree of femoral roll and more posterior translation at the lateral side in flexion^9,10,13 can contribute to different pattern and volume differences of cartilage wear.¹⁵ Because of these differences, and because of implant design factors and lower surgical volume, lateral UKA is considered a technically more challenging surgery compared to medial UKA.^12,16,17

Since isolated lateral compartment OA is relatively scarce, current literature on lateral UKA is limited, and most studies combine medial and lateral outcomes to report UKA outcomes and failure modes.^3,4,18-20 However, as the UKA has grown in popularity over the last decade,^2,21-25 the number of reports about the lateral UKA also has increased. Recent studies reported excellent short-term survivorship results of the lateral UKA (96%-99%)^26,27 and smaller lateral UKA studies reported the 10-year survivorship with varying outcomes from good (84%)^14,28-30 to excellent (94%-100%).^8,31,32 Indeed, a recent systematic review showed survivorship of lateral UKA at 5, 10, and 15 years of 93%, 91%, and 89%, respectively.³³Because of the differences between the medial and lateral compartment, it is important to know the failure modes of lateral UKA in order to improve clinical outcomes and revision rates. We performed a systematic review of cohort studies and registry-based studies that reported lateral UKA failure to assess the causes of lateral UKA failure. In addition, we compared the failure modes in cohort studies with those found in registry-based studies.

Patients and Methods

Search Strategy and Criteria

Databases of PubMed, Embase, and Cochrane (Cochrane Central Register of Clinical Trials) were searched with the terms “knee, arthroplasty, replacement,” “unicompartmental,” “unicondylar,” “partial,” “UKA,” “UKR,” “UCA,” “UCR,” “PKA,” “PKR,” “PCA,” “prosthesis failure,” “reoperation,” “survivorship,” and “treatment failure.” After removal of duplicates, 2 authors (JPvdL and HAZ) scanned the articles for their title and abstract to assess eligibility for the study.

The full text of these eligible articles was further viewed and useful studies were selected using the inclusion and exclusion criteria. The references of these articles were scanned for additional studies and national registries (Figure).

Inclusion criteria were: (I) English language articles describing studies in humans published in the last 25 years, (II) retrospective and prospective studies, (III) featured lateral UKA, (IV) OA was indication for surgery, and (V) included failure modes data. The exclusion criteria were studies that featured: (I) only a specific group of failure (eg, bearing dislocations only), (II) previous surgery in ipsilateral knee (high tibial osteotomy, medial UKA), (III) acute concurrent knee diagnoses (acute anterior cruciate ligament rupture, acute meniscal tear), (IV) combined reporting of medial and lateral UKA, or (V) multiple studies with the same patient database.

Data Collection

All studies that reported modes of failure were used in this study and these failure modes were noted in a datasheet in Microsoft Excel 2011 (Microsoft).

The data of failures of lateral UKA are presented in Table 1 and are divided in cohort studies and registry-based studies. The final failure mode rates were presented in percentages (Table 2).

Statistical Analysis

For this systematic review, statistical analysis was performed with IBM SPSS Statistics 22 (SPSS Inc.). We performed chi square tests and Fisher’s exact tests to assess a difference between cohort studies and registry-based studies with the null hypothesis of no difference between both groups. A difference was considered significant when P < .05.

Results

Through the search of the databases, 1294 studies were identified and 26 handpicked studies were added. Initially, based on the title and abstract, 184 of these studies were found eligible.

After reviewing the full text of these articles, 25 studies (23 cohort studies and 2 registry-based studies) met the inclusion criteria and were included for the analysis of lateral UKA failure (Figure).

A total of 366 lateral UKA failures were included. The most common failure modes were progression of OA (29%), aseptic loosening (23%), and bearing dislocation (10%). Infection (6%), instability (6%), unexplained pain (6%), and fractures (4%) were less common causes of failure of lateral UKA (Table 2).

One hundred fifty-five of these failures were reported in the cohort studies. The most common modes of failure were OA progression (36%), bearing dislocation (17%) and aseptic loosening (16%). Less common were infection (10%), fractures (5%), pain (5%), and other causes (6%). In registry-based studies, with 211 lateral UKA failures, the most common modes of failure were aseptic loosening (28%), OA progression (24%), other causes (12%), instability (10%), pain (7%), bearing dislocation (5%), and polyethylene wear (4%) (Table 2).

When pooling cohort and registry-based studies, progression of OA was significantly more common than aseptic loosening (29% vs 23%, respectively; P < .01). It was also significantly more common in the cohort studies (36% vs 16%, respectively; P < .01) but no significant difference was found between progression of OA and aseptic loosening in registry-based studies (24% and 28%, respectively; P = .16) (Table 2).

When comparing cohort with registry-based studies, progression of OA was higher in cohort studies (36% vs. 24%; P < .01). Other failures modes that were more common in cohort studies compared with registry-based studies were bearing dislocation (17% vs 5%, respectively; P < .01) and infections (10% vs 3%, P < .01). Failure modes that were more common in registry-based studies than cohort studies were aseptic loosening (28% vs 16%, respectively; P < .01), other causes (12% vs 6%, respectively, P = .02), and instability (10% vs 1%, respectively, P < .01) (Table 2).

 

Discussion

In this systematic review, the most common failure modes in lateral UKA review were OA progression (29%), aseptic loosening (23%), and bearing dislocation (10%). Progression of OA and bearing dislocation were the most common modes of failure in cohort studies (36% and 17%, respectively), while aseptic loosening and OA progression were the most common failure modes in registry-based studies (28% and 24%, respectively).

As mentioned above, there are differences in anatomy and kinematics between the medial and lateral compartment. When the lateral UKA failure modes are compared with studies reporting medial UKA failure modes, differences in failure modes are seen.³⁴ Siddiqui and Ahmad³⁵ performed a systematic review of outcomes after UKA revision and presented a table with the failure modes of included studies. Unfortunately they did not report the ratio of medial and lateral UKA. However, when assuming an average percentage of 90% to 95% of medial UKA,^6,7,36 the main failure mode in their review in 17 out of 21 studies was aseptic loosening. Indeed, a recent systematic review on medial UKA failure modes showed that aseptic loosening is the most common cause of failure following this procedure.³⁴ Similarly, a search through registry-based studies^6,7 and large cohort studies^37-40 that only reported medial UKA failures showed that the majority of these studies^7,37-39 also reported aseptic loosening as the main cause of failure in medial UKA. When comparing the results of our systematic review of lateral UKA failures with the results of these studies of medial UKA failures, it seems that OA progression seems to play a more dominant role in failures of lateral UKA, while aseptic loosening seems to be more common in medial UKA.

Differences in anatomy and kinematics of the medial and lateral compartment can explain this. Malalignment of the joint is an important factor in the etiology of OA^41,42 and biomechanical studies showed that this malalignment can cause decreased viability and further degenerative changes of cartilage of the knee.⁴³ Hernigou and Deschamps⁴⁴ showed that the alignment of the knee after medial UKA is an important factor in postoperative joint changes. They found that overcorrection of varus deformity during medial UKA surgery, measured by the hip-knee-ankle (HKA) angle, was associated with increased OA at the lateral condyle and less tibial wear of the medial UKA. Undercorrection of the varus caused an increase in tibial wear of polyethylene. Chatellard and colleagues⁴⁵ found the same results in the correction of varus, measured by HKA. In addition, they found that when the prosthetic (medial) joint space was smaller than healthy (lateral) joint space, this was correlated with lower prosthesis survival. A smaller joint space at the healthy side was correlated with OA progression at the lateral compartment and tibial component wear.

These studies explain the mechanism of progression of OA and aseptic loosening. Harrington⁴⁶ assessed the load in patients with valgus and varus deformity. Patients with a valgus deformity have high mechanical load on the lateral condyle during the static phase, but during the dynamic phase, a major part of this load shifts to the medial condyle. In the patients with varus deformity, the mechanical load was noted on the medial condyle during both the static and dynamic phase. Ohdera and colleagues⁴⁷ advised, based on this biomechanical study and their own experiences, to correct the knee during lateral UKA to a slight valgus angle (5°-7°) to prevent OA progression at the medial side. van der List and colleagues⁴⁸ similarly showed that undercorrection of 3° to 7° was correlated with better functional outcomes when compared to more neutral alignment. Moreover, Khamaisy and colleagues⁴⁹ recently showed that overcorrection during UKA surgery is more common in lateral than medial UKA.

These studies are important to understanding why OA progression is more common as a failure mode in lateral UKA. The shift of mechanical load from the lateral to medial epicondyle during the dynamic phase also could explain why aseptic loosening is less common in lateral UKA. As Hernigou and Deschamps⁴⁴ and Chatellard and colleagues⁴⁵ stated, undercorrection of varus deformity in medial UKA is associated with higher mechanical load on the medial prosthesis side and smaller joint space width. These factors are correlated with mechanical failure of medial UKA. We think this process can be applied to lateral UKA, with the addition that the mechanical load is higher on the healthy medial compartment during the dynamic phase. This causes more forces on the healthy (medial) side in lateral UKA, and in medial UKA more forces on the prosthesis (medial) side, which results in more OA progression in lateral UKA and more aseptic loosening in medial UKA. This finding is consistent with the results of our review of more OA progression and less aseptic loosening in lateral UKA. This study also suggests that medial and lateral UKA should not be reported together in studies that present survivorship, failure modes, or clinical outcomes.

A large discrepancy was seen in bearing dislocation between cohort studies (17%) and registry-based studies (5%). When we take a closer look to the bearing dislocation failures in the cohort studies, most of the failures were reported in only 2 cohort studies.^50,51 In a study by Pandit and colleagues,⁵⁰ 3 different prosthesis designs were used in 3 different time periods. In the first series of lateral UKA (1983-1991), 6 out of 51 (12%) bearings dislocated. In the second series (1998-2004), a modified technique was used and 3 out of 65 (5%) bearings dislocated. In the third series (2004-2008), a modified technique and a domed tibial component was used and only 1 out of 68 bearings dislocated (1%). In a study published in 1996, Gunther and colleagues⁵¹ also used surgical techniques and implants that were modified over the course of the study period. Because of these modified techniques, different implant designs, and year of publication, bearing dislocation most likely plays a smaller role than the 17% reported in the cohort studies. This discrepancy is a good example of the important role for the registries and registry-based studies in reporting failure modes and survivorship, especially in lateral UKA due to the low surgical frequency. Pabinger and colleagues⁵² recently performed a systematic review of cohort studies and registry-based studies in which they stated that the reliability in non-registry-based studies should be questioned and they considered registry-based studies superior in reporting UKA outcomes and revision rates. Furthermore, given the differences in anatomic and kinematic differences between the medial and lateral compartment and different failure modes between medial and lateral UKA, it would be better if future studies presented the medial and lateral failures separately. As stated above, most large cohort studies and especially annual registries currently do not report modes of failure of medial and lateral UKA separately.^3,4,18-20

There are limitations in this study. First, this systematic review is not a full meta-analysis but a pooled analysis of collected study series and retrospective studies. Therefore, we cannot exclude sampling bias, confounders, and selection bias from the literature. We included all studies reporting failure modes of lateral UKA and excluded all case reports. We made a conscious choice about including all lateral UKA failures because this is the first systematic review of lateral UKA failure modes. Another limitation is that the follow-up period of the studies differed (Table 1) and we did not correct for the follow-up period. As stated in the example of bearing dislocations, some of these studies reported old or different techniques, while other, more recently published studies used more modified techniques^11,29,53-56 Unfortunately, most studies did not report the time of arthroplasty survival and therefore we could not correct for the follow-up period.

In conclusion, progression of OA is the most common failure mode in lateral UKA, followed by aseptic loosening. Anatomic and kinematic factors such as alignment, mechanical forces during dynamic phase, and correction of valgus seem to play important roles in failure modes of lateral UKA. In the future, failure modes of medial and lateral UKA should be reported separately.

Am J Orthop. 2016;45(7):432-438, 462. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

The annual number of total shoulder arthroplasties (TSAs) is rising with the growing elderly population and development of new technologies such as reverse shoulder arthroplasty.¹ In 2008, 47,000 shoulder arthroplasties were performed in the US compared with 19,000 in 1998.¹ As of 2011, there were 53,000 shoulder arthroplasties performed annually.² Pain control after shoulder procedures, particularly TSA, is challenging. ³

Several modalities exist to manage pain after shoulder arthroplasty. The interscalene brachial plexus nerve block is considered the “gold standard” for shoulder analgesia. A new approach is the periarticular injection method, in which the surgeon administers a local anesthetic intraoperatively. Liposomal bupivacaine (Exparel, Pacira Pharmaceuticals, Inc.) is a nonopioid anesthetic that has been shown to improve pain control, shorten hospital stays, and decrease costs for total knee and hip arthroplasty compared with nerve blocks.^4-6 Patients who were treated with liposomal bupivacaine consumed less opioid medication than a placebo group.⁷

Our purpose was to compare intraoperative local liposomal bupivacaine injection with preoperative single-shot interscalene nerve block (ISNB) in terms of pain control, opioid use, and length of hospital stay (LOS) after shoulder arthroplasty. We hypothesized that patients in the liposomal bupivacaine group would have lower pain scores, less opioid use, and shorter LOS compared with patients in the ISNB group.

Methods

A retrospective cohort analysis was conducted with 58 patients who underwent shoulder arthroplasty by 1 surgeon at our academically affiliated community hospital from January 2012 through January 2015. ISNBs were the standard at the beginning of the study period and were used until Exparel became available on the hospital formulary in 2013. We began using Exparel for all shoulder arthroplasties in November 2013. No other changes were made in the perioperative management of our arthroplasty patients during this period. Patients who underwent TSA, reverse TSA, or hemiarthroplasty of the shoulder were included. Patients who underwent revision TSA were excluded. Twenty-one patients received ISNBs and 37 received liposomal bupivacaine injections. This study was approved by our Institutional Review Board.

Baseline data for each patient were age, sex, body mass index, and the American Society of Anesthesiologists (ASA) Physical Status Classification. The primary outcome measure was the numeric rating scale (NRS) pain score at 4 post-operative time intervals. The NRS pain score has a range of 0 to 10, with 10 representing severe pain. Data were gathered from nursing and physical therapy notes in patient charts. The postoperative time intervals were 0 to 1 hour, 8 to 14 hours, 18 to 24 hours, and 27 to 36 hours. Available NRS scores for these time intervals were averaged. Patients were included if they had pain scores for at least 3 of the postoperative time intervals documented in their charts. Secondary outcome measures were LOS and opioid consumption during hospital admission. Intravenous acetaminophen use was also measured in both groups. All data on opioids were converted to oral morphine equivalents using the method described by Schneider and colleagues.⁸

A board-certified, fellowship-trained anesthesiologist, experienced in regional anesthesia, administered the single-shot ISNB before surgery. The block was administered under ultrasound guidance using a 44-mm, 22-gauge needle with the patient in the supine position. No indwelling catheter was used. The medication consisted of 30 mL of 5% ropivacaine (5 mg/mL). The surgeon injected liposomal bupivacaine (266 mg diluted into 40 mL of injectable saline) near the end of the procedure throughout the pericapsular area and multiple layers of the wound, per manufacturer guidelines.⁹ A 60-mL syringe with a 20-gauge needle was used. All operations were performed by 1 board-certified, fellowship-trained surgeon using a standard deltopectoral approach with the same surgical equipment. The same postoperative pain protocol was used for all patients, including intravenous acetaminophen and patient-controlled analgesia. Additional oral pain medication was provided as needed for all patients. Physical therapy protocols were identical between groups.

Statistical Analysis

Mean patient ages in the 2 treatment groups were compared using the Student t test. Sex distribution and the ASA scores were compared using a χ² test and a Fisher exact test, respectively. Arthroplasty types were compared using a Fisher exact test. The medians and interquartile ranges of the NRS scores at each time point measured were tabulated by treatment group, and at each time point the difference between groups was tested using nonparametric rank sum tests.

We tested the longitudinal trajectory of NRS scores over time, accounting for repeated measurements in the same patients using linear mixed model analysis. Treatment group, time period as a categorical variable, and the interaction between treatment and time period were included as fixed effects, and patient identification number was included as the random effect. An initial omnibus test was performed for all treatment and treatment-by-time interaction effects. Subsequently, the treatment-by-time interaction was tested for each of the time periods. The association of day of discharge (as a categorical variable) with treatment was tested using the Fisher exact test. All analyses were conducted using Stata, version 13, software (StataCorp LP). P values <.05 were considered significant.

 

Sample Size Analysis

We calculated the minimum detectable effect size with 80% power at an alpha level of 0.05 for the nonparametric rank sum test in terms of the proportion of every possible pair of patients treated with the 2 treatments, where the patient treated with liposomal bupivacaine has a lower pain score than the patient treated with ISNB. For pain score at 18 to 24 hours, the sample sizes of 33 patients treated with liposomal bupivacaine and 20 treated with ISNB, the minimum detectable effect size is 73%.

Results

Fifty-eight patient charts (21 in the ISNB group and 37 in the liposomal bupivacaine group) were reviewed for the study. Patient sex distribution, mean age, mean body mass index, and mean baseline ASA scores were not statistically different (Table 1).

In the ISNB group, 5 patients had hemiarthroplasty, 12 had TSA, and 4 had reverse TSA. In the liposomal bupivacaine group, 1 patient had hemiarthroplasty, 23 had TSA, and 13 had reverse TSA. Frequency of procedure types was significantly different between groups (P = .039), with the liposomal bupivacaine group undergoing fewer hemiarthroplasties.

The primary outcome measure, NRS pain score, showed no significant differences between groups at 0 to 1 hour after surgery (P = .99) or 8 to 14 hours after surgery (P = .208).

At 18 to 24 hours after surgery, the liposomal bupivacaine group had a lower mean NRS score than the ISNB group (P = .001). This was statistically significant when taking repeated measures of variance into account (Figure 1). Mean NRS score was also lower for the liposomal bupivacaine group at 27 to 36 hours after surgery (P = .029).

This was a significant difference when repeated measures of variance was considered (Table 2).

There was no difference in the amount of intravenous acetaminophen given during the hospital stay between groups. There was no significant difference in opioid consumption on postoperative day 1 in the hospital (P = .59) (Figure 2). However, there were significant differences between groups on postoperative days 2 and 3.

On postoperative day 2, the ISNB group required significantly more opioids (mean, 112 mg morphine equivalents) than the liposomal bupivacaine group (mean, 37 mg morphine equivalents) (P = .001). The ISNB group also required significantly more opioids (mean, 25 mg morphine equivalents) on postoperative day 3 than the liposomal bupivacaine group (mean, 5 mg) (P = .002).

Sixteen of 37 patients in the liposomal bupivacaine group and 2 of 21 in the ISNB group were discharged on the day after surgery (P = .010) (Table 3).

The mean LOS was 46 ± 20 hours for the liposomal bupivacaine group and 57 ± 14 hours for the ISNB group (P = .012).

There were no major cardiac or respiratory events in either group. No long-term paresthesias or neuropathies were noted. There were no readmissions for either group.

Discussion

Postoperative pain control after shoulder arthroplasty can be challenging, and several modalities have been tried in various combinations to minimize pain and decrease adverse effects of opioid medications. The most common method for pain relief after shoulder arthroplasty is the ISNB. Several studies of ISNBs have shown improved pain control after shoulder arthroplasty with associated decreased opioid consumption and related side effects.¹⁰ Patient rehabilitation and satisfaction have improved with the increasing use of peripheral nerve blocks.¹¹

Despite the well-established benefits of ISNBs, several limitations exist. Although the superior portion of the shoulder is well covered by an ISNB, the inferior portion of the brachial plexus can remain uncovered or only partially covered.¹² Complications of ISNBs include hemidiaphragmatic paresis, rebound pain 24 hours after surgery,¹³ chronic neurologic complications,¹⁴ and substantial respiratory and cardiovascular events.¹⁵ Nerve blocks also require additional time and resources in the perioperative period, including an anesthesiologist with specialized training, assistants, and ultrasonography or nerve stimulation equipment contraindicated in patients taking blood thinners.¹⁶

Periarticular injections of local anesthetics have also shown promise in reducing pain after arthroplasty.⁴ Benefits include an enhanced safety profile because local injection avoids the concurrent blockade of the phrenic nerve and recurrent laryngeal nerve and has not been associated with the risk of peripheral neuropathies. Further, local injection is a simple technique that can be performed during surgery without additional personnel or expertise. A limitation of this approach is the relatively short duration of effectiveness of the local anesthetic and uncertainty regarding the best agent and the ideal volume of injection.⁶ Liposomal bupivacaine is a new agent (approved by the US Food and Drug Administration in 2011¹⁷) with a sustained release over 72 to 96 hours.¹⁸ The most common adverse effects of liposomal bupivacaine are nausea, vomiting, constipation, pyrexia, dizziness, and headache.¹⁹ Chondrotoxicity and granulomatous inflammation are more serious, yet rare, complications of liposomal bupivacaine.²⁰

We found that liposomal bupivacaine injections were associated with lower pain scores compared with ISNB at 18 to 24 hours after surgery. This correlated with less opioid consumption in the liposomal bupivacaine group than in the ISNB group on the second postoperative day. These differences in pain values are consistent with the known pharmacokinetics of liposomal bupivacaine.¹⁸ Peak plasma levels normally occur approximately 24 hours after injection, leaving the early postoperative period relatively uncovered by anesthetic agent. This finding of relatively poor pain control early after surgery has also been noted in patients undergoing knee arthroplasty.⁵ On the basis of the findings of this study, we have added standard bupivacaine injections to our separate liposomal bupivacaine injection to cover early postoperative pain. Opioid consumption was significantly lower in the liposomal bupivacaine group than in the ISNB group on postoperative days 2 and 3. We did not measure adverse events related to opioid consumption, so we cannot comment on whether the decreased opioid consumption was associated with the rate of adverse events. However, other studies^21,22 have established this relationship.

We found the liposomal bupivacaine group to have earlier discharges to home. Sixteen of 37 patients in the liposomal bupivacaine group compared with 2 of 21 patients in the ISNB group were discharged on the day after surgery. A mean reduction in LOS of 18 hours for the liposomal bupivacaine group was statistically significant (P = .012). This reduction in LOS has important implications for hospitals and value analysis committees considering whether to keep a new, more expensive local anesthetic on formulary. Savings from reduced LOS and improvements in patient satisfaction may justify the expense (approximately $300 per 266-mg vial) of Exparel.

From a societal cost perspective, liposomal bupivacaine is more economical compared with ISNB, which adds approximately $1500 to the cost of anesthesia per patient.²³ Eliminating the costs associated with ISNB administration in shoulder arthroplasties could result in substantial savings to our healthcare system. More research examining time savings and exact costs of each procedure is needed to determine the true cost effectiveness of each approach.

Limitations of our study include the retrospective design, relatively small numbers of patients in each group, missing data for some patients at various time points, variation in the types of procedures in each group, and lack of long-term outcome measures. It is important to note that we did not confirm the success of the nerve block after administration. However, this study reflects the effectiveness of each of the modalities in actual clinical conditions (as opposed to a controlled experimental setting). The actual effectiveness of a nerve block varies, even when performed by an experienced anesthesiologist with ultrasound guidance. Furthermore, immediate postoperative pain scores in the nerve block group are consistent with those of prior research reporting pain values ranging from 4 to 5 and a mean duration of effect ranging from 9 to 14 hours.^23,24 Additionally, the patients, surgeon, and nursing team were not blinded to the treatment group. Although we did note a significant difference in the types of procedures between groups, this finding is related to the greater number of hemiarthroplasties performed in the ISNB group (N = 5) compared with the liposomal group (N = 1). Because of this variation and the decreased invasiveness of hemiarthroplasties, the bias is against the liposomal group. Finally, our primary outcome variable was pain, which is a subjective, self-reported measure. However, our opioid consumption data and LOS data corroborate the improved pain scores in the liposomal bupivacaine group.

Limiting the study to a single surgeon may limit external validity. Another limitation is the lack of data on adverse events related to opioid medication use. There was no additional experimental group to determine whether less expensive local anesthetics injected locally would perform similarly to liposomal bupivacaine. In total knee arthroplasty, periarticular injections of liposomal bupivacaine were not as effective as less expensive periarticular injections.²⁵ It is unclear which agents (and in what doses or combinations) should be used for periarticular injections. Finally, we acknowledge that our retrospective study design cannot account for all potential factors affecting discharge time.

This is the first comparative study of liposomal bupivacaine and ISNB in TSA. The study design allowed us to control for variables such as surgical technique, postoperative protocols (including use and type of sling), and use of other pain modalities such as patient-controlled analgesia and intravenous acetaminophen that are likely to affect postoperative pain and LOS. This study provides preliminary data that confirm relative equipoise between liposomal bupivacaine and ISNB, which is needed for the ethical conduct of a randomized controlled trial. Such a trial would allow for a more robust comparison, and this retrospective study provides appropriate pilot data on which to base this design and the clinical information needed to counsel patients during enrollment.

Our results suggest that liposomal bupivacaine may provide superior or similar pain relief compared with ISNB after shoulder arthroplasty. Additionally, the use of liposomal bupivacaine was associated with decreased opioid consumption and earlier discharge to home compared with ISNB. These findings have important implications for pain control after TSA because pain represents a major concern for patients and providers after surgery. In addition to clinical improvements, use of liposomal bupivacaine may save time and eliminate costs associated with administering nerve blocks. Local injection may also be used in patients who are contraindicated for ISNB such as those with obesity, pulmonary disease, or peripheral neuropathy. Although we cannot definitively suggest that liposomal bupivacaine is superior to the current gold standard ISNB for pain control after shoulder arthroplasty, our results suggest a relative clinical equipoise between these modalities. Larger analytical studies, including randomized trials, should be performed to explore the potential benefits of liposomal bupivacaine injections for pain control after shoulder arthroplasty.

Am J Orthop. 2016;45(7):424-430. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

The annual number of total shoulder arthroplasties (TSAs) is rising with the growing elderly population and development of new technologies such as reverse shoulder arthroplasty.¹ In 2008, 47,000 shoulder arthroplasties were performed in the US compared with 19,000 in 1998.¹ As of 2011, there were 53,000 shoulder arthroplasties performed annually.² Pain control after shoulder procedures, particularly TSA, is challenging. ³

Several modalities exist to manage pain after shoulder arthroplasty. The interscalene brachial plexus nerve block is considered the “gold standard” for shoulder analgesia. A new approach is the periarticular injection method, in which the surgeon administers a local anesthetic intraoperatively. Liposomal bupivacaine (Exparel, Pacira Pharmaceuticals, Inc.) is a nonopioid anesthetic that has been shown to improve pain control, shorten hospital stays, and decrease costs for total knee and hip arthroplasty compared with nerve blocks.^4-6 Patients who were treated with liposomal bupivacaine consumed less opioid medication than a placebo group.⁷

Our purpose was to compare intraoperative local liposomal bupivacaine injection with preoperative single-shot interscalene nerve block (ISNB) in terms of pain control, opioid use, and length of hospital stay (LOS) after shoulder arthroplasty. We hypothesized that patients in the liposomal bupivacaine group would have lower pain scores, less opioid use, and shorter LOS compared with patients in the ISNB group.

Methods

A retrospective cohort analysis was conducted with 58 patients who underwent shoulder arthroplasty by 1 surgeon at our academically affiliated community hospital from January 2012 through January 2015. ISNBs were the standard at the beginning of the study period and were used until Exparel became available on the hospital formulary in 2013. We began using Exparel for all shoulder arthroplasties in November 2013. No other changes were made in the perioperative management of our arthroplasty patients during this period. Patients who underwent TSA, reverse TSA, or hemiarthroplasty of the shoulder were included. Patients who underwent revision TSA were excluded. Twenty-one patients received ISNBs and 37 received liposomal bupivacaine injections. This study was approved by our Institutional Review Board.

Baseline data for each patient were age, sex, body mass index, and the American Society of Anesthesiologists (ASA) Physical Status Classification. The primary outcome measure was the numeric rating scale (NRS) pain score at 4 post-operative time intervals. The NRS pain score has a range of 0 to 10, with 10 representing severe pain. Data were gathered from nursing and physical therapy notes in patient charts. The postoperative time intervals were 0 to 1 hour, 8 to 14 hours, 18 to 24 hours, and 27 to 36 hours. Available NRS scores for these time intervals were averaged. Patients were included if they had pain scores for at least 3 of the postoperative time intervals documented in their charts. Secondary outcome measures were LOS and opioid consumption during hospital admission. Intravenous acetaminophen use was also measured in both groups. All data on opioids were converted to oral morphine equivalents using the method described by Schneider and colleagues.⁸

A board-certified, fellowship-trained anesthesiologist, experienced in regional anesthesia, administered the single-shot ISNB before surgery. The block was administered under ultrasound guidance using a 44-mm, 22-gauge needle with the patient in the supine position. No indwelling catheter was used. The medication consisted of 30 mL of 5% ropivacaine (5 mg/mL). The surgeon injected liposomal bupivacaine (266 mg diluted into 40 mL of injectable saline) near the end of the procedure throughout the pericapsular area and multiple layers of the wound, per manufacturer guidelines.⁹ A 60-mL syringe with a 20-gauge needle was used. All operations were performed by 1 board-certified, fellowship-trained surgeon using a standard deltopectoral approach with the same surgical equipment. The same postoperative pain protocol was used for all patients, including intravenous acetaminophen and patient-controlled analgesia. Additional oral pain medication was provided as needed for all patients. Physical therapy protocols were identical between groups.

Statistical Analysis

Mean patient ages in the 2 treatment groups were compared using the Student t test. Sex distribution and the ASA scores were compared using a χ² test and a Fisher exact test, respectively. Arthroplasty types were compared using a Fisher exact test. The medians and interquartile ranges of the NRS scores at each time point measured were tabulated by treatment group, and at each time point the difference between groups was tested using nonparametric rank sum tests.

We tested the longitudinal trajectory of NRS scores over time, accounting for repeated measurements in the same patients using linear mixed model analysis. Treatment group, time period as a categorical variable, and the interaction between treatment and time period were included as fixed effects, and patient identification number was included as the random effect. An initial omnibus test was performed for all treatment and treatment-by-time interaction effects. Subsequently, the treatment-by-time interaction was tested for each of the time periods. The association of day of discharge (as a categorical variable) with treatment was tested using the Fisher exact test. All analyses were conducted using Stata, version 13, software (StataCorp LP). P values <.05 were considered significant.

 

Sample Size Analysis

We calculated the minimum detectable effect size with 80% power at an alpha level of 0.05 for the nonparametric rank sum test in terms of the proportion of every possible pair of patients treated with the 2 treatments, where the patient treated with liposomal bupivacaine has a lower pain score than the patient treated with ISNB. For pain score at 18 to 24 hours, the sample sizes of 33 patients treated with liposomal bupivacaine and 20 treated with ISNB, the minimum detectable effect size is 73%.

Results

Fifty-eight patient charts (21 in the ISNB group and 37 in the liposomal bupivacaine group) were reviewed for the study. Patient sex distribution, mean age, mean body mass index, and mean baseline ASA scores were not statistically different (Table 1).

In the ISNB group, 5 patients had hemiarthroplasty, 12 had TSA, and 4 had reverse TSA. In the liposomal bupivacaine group, 1 patient had hemiarthroplasty, 23 had TSA, and 13 had reverse TSA. Frequency of procedure types was significantly different between groups (P = .039), with the liposomal bupivacaine group undergoing fewer hemiarthroplasties.

The primary outcome measure, NRS pain score, showed no significant differences between groups at 0 to 1 hour after surgery (P = .99) or 8 to 14 hours after surgery (P = .208).

At 18 to 24 hours after surgery, the liposomal bupivacaine group had a lower mean NRS score than the ISNB group (P = .001). This was statistically significant when taking repeated measures of variance into account (Figure 1). Mean NRS score was also lower for the liposomal bupivacaine group at 27 to 36 hours after surgery (P = .029).

This was a significant difference when repeated measures of variance was considered (Table 2).

There was no difference in the amount of intravenous acetaminophen given during the hospital stay between groups. There was no significant difference in opioid consumption on postoperative day 1 in the hospital (P = .59) (Figure 2). However, there were significant differences between groups on postoperative days 2 and 3.

On postoperative day 2, the ISNB group required significantly more opioids (mean, 112 mg morphine equivalents) than the liposomal bupivacaine group (mean, 37 mg morphine equivalents) (P = .001). The ISNB group also required significantly more opioids (mean, 25 mg morphine equivalents) on postoperative day 3 than the liposomal bupivacaine group (mean, 5 mg) (P = .002).

Sixteen of 37 patients in the liposomal bupivacaine group and 2 of 21 in the ISNB group were discharged on the day after surgery (P = .010) (Table 3).

The mean LOS was 46 ± 20 hours for the liposomal bupivacaine group and 57 ± 14 hours for the ISNB group (P = .012).

There were no major cardiac or respiratory events in either group. No long-term paresthesias or neuropathies were noted. There were no readmissions for either group.

Discussion

Postoperative pain control after shoulder arthroplasty can be challenging, and several modalities have been tried in various combinations to minimize pain and decrease adverse effects of opioid medications. The most common method for pain relief after shoulder arthroplasty is the ISNB. Several studies of ISNBs have shown improved pain control after shoulder arthroplasty with associated decreased opioid consumption and related side effects.¹⁰ Patient rehabilitation and satisfaction have improved with the increasing use of peripheral nerve blocks.¹¹

Despite the well-established benefits of ISNBs, several limitations exist. Although the superior portion of the shoulder is well covered by an ISNB, the inferior portion of the brachial plexus can remain uncovered or only partially covered.¹² Complications of ISNBs include hemidiaphragmatic paresis, rebound pain 24 hours after surgery,¹³ chronic neurologic complications,¹⁴ and substantial respiratory and cardiovascular events.¹⁵ Nerve blocks also require additional time and resources in the perioperative period, including an anesthesiologist with specialized training, assistants, and ultrasonography or nerve stimulation equipment contraindicated in patients taking blood thinners.¹⁶

Periarticular injections of local anesthetics have also shown promise in reducing pain after arthroplasty.⁴ Benefits include an enhanced safety profile because local injection avoids the concurrent blockade of the phrenic nerve and recurrent laryngeal nerve and has not been associated with the risk of peripheral neuropathies. Further, local injection is a simple technique that can be performed during surgery without additional personnel or expertise. A limitation of this approach is the relatively short duration of effectiveness of the local anesthetic and uncertainty regarding the best agent and the ideal volume of injection.⁶ Liposomal bupivacaine is a new agent (approved by the US Food and Drug Administration in 2011¹⁷) with a sustained release over 72 to 96 hours.¹⁸ The most common adverse effects of liposomal bupivacaine are nausea, vomiting, constipation, pyrexia, dizziness, and headache.¹⁹ Chondrotoxicity and granulomatous inflammation are more serious, yet rare, complications of liposomal bupivacaine.²⁰

We found that liposomal bupivacaine injections were associated with lower pain scores compared with ISNB at 18 to 24 hours after surgery. This correlated with less opioid consumption in the liposomal bupivacaine group than in the ISNB group on the second postoperative day. These differences in pain values are consistent with the known pharmacokinetics of liposomal bupivacaine.¹⁸ Peak plasma levels normally occur approximately 24 hours after injection, leaving the early postoperative period relatively uncovered by anesthetic agent. This finding of relatively poor pain control early after surgery has also been noted in patients undergoing knee arthroplasty.⁵ On the basis of the findings of this study, we have added standard bupivacaine injections to our separate liposomal bupivacaine injection to cover early postoperative pain. Opioid consumption was significantly lower in the liposomal bupivacaine group than in the ISNB group on postoperative days 2 and 3. We did not measure adverse events related to opioid consumption, so we cannot comment on whether the decreased opioid consumption was associated with the rate of adverse events. However, other studies^21,22 have established this relationship.

We found the liposomal bupivacaine group to have earlier discharges to home. Sixteen of 37 patients in the liposomal bupivacaine group compared with 2 of 21 patients in the ISNB group were discharged on the day after surgery. A mean reduction in LOS of 18 hours for the liposomal bupivacaine group was statistically significant (P = .012). This reduction in LOS has important implications for hospitals and value analysis committees considering whether to keep a new, more expensive local anesthetic on formulary. Savings from reduced LOS and improvements in patient satisfaction may justify the expense (approximately $300 per 266-mg vial) of Exparel.

From a societal cost perspective, liposomal bupivacaine is more economical compared with ISNB, which adds approximately $1500 to the cost of anesthesia per patient.²³ Eliminating the costs associated with ISNB administration in shoulder arthroplasties could result in substantial savings to our healthcare system. More research examining time savings and exact costs of each procedure is needed to determine the true cost effectiveness of each approach.

Limitations of our study include the retrospective design, relatively small numbers of patients in each group, missing data for some patients at various time points, variation in the types of procedures in each group, and lack of long-term outcome measures. It is important to note that we did not confirm the success of the nerve block after administration. However, this study reflects the effectiveness of each of the modalities in actual clinical conditions (as opposed to a controlled experimental setting). The actual effectiveness of a nerve block varies, even when performed by an experienced anesthesiologist with ultrasound guidance. Furthermore, immediate postoperative pain scores in the nerve block group are consistent with those of prior research reporting pain values ranging from 4 to 5 and a mean duration of effect ranging from 9 to 14 hours.^23,24 Additionally, the patients, surgeon, and nursing team were not blinded to the treatment group. Although we did note a significant difference in the types of procedures between groups, this finding is related to the greater number of hemiarthroplasties performed in the ISNB group (N = 5) compared with the liposomal group (N = 1). Because of this variation and the decreased invasiveness of hemiarthroplasties, the bias is against the liposomal group. Finally, our primary outcome variable was pain, which is a subjective, self-reported measure. However, our opioid consumption data and LOS data corroborate the improved pain scores in the liposomal bupivacaine group.

Limiting the study to a single surgeon may limit external validity. Another limitation is the lack of data on adverse events related to opioid medication use. There was no additional experimental group to determine whether less expensive local anesthetics injected locally would perform similarly to liposomal bupivacaine. In total knee arthroplasty, periarticular injections of liposomal bupivacaine were not as effective as less expensive periarticular injections.²⁵ It is unclear which agents (and in what doses or combinations) should be used for periarticular injections. Finally, we acknowledge that our retrospective study design cannot account for all potential factors affecting discharge time.

This is the first comparative study of liposomal bupivacaine and ISNB in TSA. The study design allowed us to control for variables such as surgical technique, postoperative protocols (including use and type of sling), and use of other pain modalities such as patient-controlled analgesia and intravenous acetaminophen that are likely to affect postoperative pain and LOS. This study provides preliminary data that confirm relative equipoise between liposomal bupivacaine and ISNB, which is needed for the ethical conduct of a randomized controlled trial. Such a trial would allow for a more robust comparison, and this retrospective study provides appropriate pilot data on which to base this design and the clinical information needed to counsel patients during enrollment.

Our results suggest that liposomal bupivacaine may provide superior or similar pain relief compared with ISNB after shoulder arthroplasty. Additionally, the use of liposomal bupivacaine was associated with decreased opioid consumption and earlier discharge to home compared with ISNB. These findings have important implications for pain control after TSA because pain represents a major concern for patients and providers after surgery. In addition to clinical improvements, use of liposomal bupivacaine may save time and eliminate costs associated with administering nerve blocks. Local injection may also be used in patients who are contraindicated for ISNB such as those with obesity, pulmonary disease, or peripheral neuropathy. Although we cannot definitively suggest that liposomal bupivacaine is superior to the current gold standard ISNB for pain control after shoulder arthroplasty, our results suggest a relative clinical equipoise between these modalities. Larger analytical studies, including randomized trials, should be performed to explore the potential benefits of liposomal bupivacaine injections for pain control after shoulder arthroplasty.

Am J Orthop. 2016;45(7):424-430. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

The annual number of total shoulder arthroplasties (TSAs) is rising with the growing elderly population and development of new technologies such as reverse shoulder arthroplasty.¹ In 2008, 47,000 shoulder arthroplasties were performed in the US compared with 19,000 in 1998.¹ As of 2011, there were 53,000 shoulder arthroplasties performed annually.² Pain control after shoulder procedures, particularly TSA, is challenging. ³

Several modalities exist to manage pain after shoulder arthroplasty. The interscalene brachial plexus nerve block is considered the “gold standard” for shoulder analgesia. A new approach is the periarticular injection method, in which the surgeon administers a local anesthetic intraoperatively. Liposomal bupivacaine (Exparel, Pacira Pharmaceuticals, Inc.) is a nonopioid anesthetic that has been shown to improve pain control, shorten hospital stays, and decrease costs for total knee and hip arthroplasty compared with nerve blocks.^4-6 Patients who were treated with liposomal bupivacaine consumed less opioid medication than a placebo group.⁷

Our purpose was to compare intraoperative local liposomal bupivacaine injection with preoperative single-shot interscalene nerve block (ISNB) in terms of pain control, opioid use, and length of hospital stay (LOS) after shoulder arthroplasty. We hypothesized that patients in the liposomal bupivacaine group would have lower pain scores, less opioid use, and shorter LOS compared with patients in the ISNB group.

Methods

A retrospective cohort analysis was conducted with 58 patients who underwent shoulder arthroplasty by 1 surgeon at our academically affiliated community hospital from January 2012 through January 2015. ISNBs were the standard at the beginning of the study period and were used until Exparel became available on the hospital formulary in 2013. We began using Exparel for all shoulder arthroplasties in November 2013. No other changes were made in the perioperative management of our arthroplasty patients during this period. Patients who underwent TSA, reverse TSA, or hemiarthroplasty of the shoulder were included. Patients who underwent revision TSA were excluded. Twenty-one patients received ISNBs and 37 received liposomal bupivacaine injections. This study was approved by our Institutional Review Board.

Baseline data for each patient were age, sex, body mass index, and the American Society of Anesthesiologists (ASA) Physical Status Classification. The primary outcome measure was the numeric rating scale (NRS) pain score at 4 post-operative time intervals. The NRS pain score has a range of 0 to 10, with 10 representing severe pain. Data were gathered from nursing and physical therapy notes in patient charts. The postoperative time intervals were 0 to 1 hour, 8 to 14 hours, 18 to 24 hours, and 27 to 36 hours. Available NRS scores for these time intervals were averaged. Patients were included if they had pain scores for at least 3 of the postoperative time intervals documented in their charts. Secondary outcome measures were LOS and opioid consumption during hospital admission. Intravenous acetaminophen use was also measured in both groups. All data on opioids were converted to oral morphine equivalents using the method described by Schneider and colleagues.⁸

A board-certified, fellowship-trained anesthesiologist, experienced in regional anesthesia, administered the single-shot ISNB before surgery. The block was administered under ultrasound guidance using a 44-mm, 22-gauge needle with the patient in the supine position. No indwelling catheter was used. The medication consisted of 30 mL of 5% ropivacaine (5 mg/mL). The surgeon injected liposomal bupivacaine (266 mg diluted into 40 mL of injectable saline) near the end of the procedure throughout the pericapsular area and multiple layers of the wound, per manufacturer guidelines.⁹ A 60-mL syringe with a 20-gauge needle was used. All operations were performed by 1 board-certified, fellowship-trained surgeon using a standard deltopectoral approach with the same surgical equipment. The same postoperative pain protocol was used for all patients, including intravenous acetaminophen and patient-controlled analgesia. Additional oral pain medication was provided as needed for all patients. Physical therapy protocols were identical between groups.

Statistical Analysis

Mean patient ages in the 2 treatment groups were compared using the Student t test. Sex distribution and the ASA scores were compared using a χ² test and a Fisher exact test, respectively. Arthroplasty types were compared using a Fisher exact test. The medians and interquartile ranges of the NRS scores at each time point measured were tabulated by treatment group, and at each time point the difference between groups was tested using nonparametric rank sum tests.

We tested the longitudinal trajectory of NRS scores over time, accounting for repeated measurements in the same patients using linear mixed model analysis. Treatment group, time period as a categorical variable, and the interaction between treatment and time period were included as fixed effects, and patient identification number was included as the random effect. An initial omnibus test was performed for all treatment and treatment-by-time interaction effects. Subsequently, the treatment-by-time interaction was tested for each of the time periods. The association of day of discharge (as a categorical variable) with treatment was tested using the Fisher exact test. All analyses were conducted using Stata, version 13, software (StataCorp LP). P values <.05 were considered significant.

 

Sample Size Analysis

We calculated the minimum detectable effect size with 80% power at an alpha level of 0.05 for the nonparametric rank sum test in terms of the proportion of every possible pair of patients treated with the 2 treatments, where the patient treated with liposomal bupivacaine has a lower pain score than the patient treated with ISNB. For pain score at 18 to 24 hours, the sample sizes of 33 patients treated with liposomal bupivacaine and 20 treated with ISNB, the minimum detectable effect size is 73%.

Results

Fifty-eight patient charts (21 in the ISNB group and 37 in the liposomal bupivacaine group) were reviewed for the study. Patient sex distribution, mean age, mean body mass index, and mean baseline ASA scores were not statistically different (Table 1).

In the ISNB group, 5 patients had hemiarthroplasty, 12 had TSA, and 4 had reverse TSA. In the liposomal bupivacaine group, 1 patient had hemiarthroplasty, 23 had TSA, and 13 had reverse TSA. Frequency of procedure types was significantly different between groups (P = .039), with the liposomal bupivacaine group undergoing fewer hemiarthroplasties.

The primary outcome measure, NRS pain score, showed no significant differences between groups at 0 to 1 hour after surgery (P = .99) or 8 to 14 hours after surgery (P = .208).

At 18 to 24 hours after surgery, the liposomal bupivacaine group had a lower mean NRS score than the ISNB group (P = .001). This was statistically significant when taking repeated measures of variance into account (Figure 1). Mean NRS score was also lower for the liposomal bupivacaine group at 27 to 36 hours after surgery (P = .029).

This was a significant difference when repeated measures of variance was considered (Table 2).

There was no difference in the amount of intravenous acetaminophen given during the hospital stay between groups. There was no significant difference in opioid consumption on postoperative day 1 in the hospital (P = .59) (Figure 2). However, there were significant differences between groups on postoperative days 2 and 3.

On postoperative day 2, the ISNB group required significantly more opioids (mean, 112 mg morphine equivalents) than the liposomal bupivacaine group (mean, 37 mg morphine equivalents) (P = .001). The ISNB group also required significantly more opioids (mean, 25 mg morphine equivalents) on postoperative day 3 than the liposomal bupivacaine group (mean, 5 mg) (P = .002).

Sixteen of 37 patients in the liposomal bupivacaine group and 2 of 21 in the ISNB group were discharged on the day after surgery (P = .010) (Table 3).

The mean LOS was 46 ± 20 hours for the liposomal bupivacaine group and 57 ± 14 hours for the ISNB group (P = .012).

There were no major cardiac or respiratory events in either group. No long-term paresthesias or neuropathies were noted. There were no readmissions for either group.

Discussion

Postoperative pain control after shoulder arthroplasty can be challenging, and several modalities have been tried in various combinations to minimize pain and decrease adverse effects of opioid medications. The most common method for pain relief after shoulder arthroplasty is the ISNB. Several studies of ISNBs have shown improved pain control after shoulder arthroplasty with associated decreased opioid consumption and related side effects.¹⁰ Patient rehabilitation and satisfaction have improved with the increasing use of peripheral nerve blocks.¹¹

Despite the well-established benefits of ISNBs, several limitations exist. Although the superior portion of the shoulder is well covered by an ISNB, the inferior portion of the brachial plexus can remain uncovered or only partially covered.¹² Complications of ISNBs include hemidiaphragmatic paresis, rebound pain 24 hours after surgery,¹³ chronic neurologic complications,¹⁴ and substantial respiratory and cardiovascular events.¹⁵ Nerve blocks also require additional time and resources in the perioperative period, including an anesthesiologist with specialized training, assistants, and ultrasonography or nerve stimulation equipment contraindicated in patients taking blood thinners.¹⁶

Periarticular injections of local anesthetics have also shown promise in reducing pain after arthroplasty.⁴ Benefits include an enhanced safety profile because local injection avoids the concurrent blockade of the phrenic nerve and recurrent laryngeal nerve and has not been associated with the risk of peripheral neuropathies. Further, local injection is a simple technique that can be performed during surgery without additional personnel or expertise. A limitation of this approach is the relatively short duration of effectiveness of the local anesthetic and uncertainty regarding the best agent and the ideal volume of injection.⁶ Liposomal bupivacaine is a new agent (approved by the US Food and Drug Administration in 2011¹⁷) with a sustained release over 72 to 96 hours.¹⁸ The most common adverse effects of liposomal bupivacaine are nausea, vomiting, constipation, pyrexia, dizziness, and headache.¹⁹ Chondrotoxicity and granulomatous inflammation are more serious, yet rare, complications of liposomal bupivacaine.²⁰

We found that liposomal bupivacaine injections were associated with lower pain scores compared with ISNB at 18 to 24 hours after surgery. This correlated with less opioid consumption in the liposomal bupivacaine group than in the ISNB group on the second postoperative day. These differences in pain values are consistent with the known pharmacokinetics of liposomal bupivacaine.¹⁸ Peak plasma levels normally occur approximately 24 hours after injection, leaving the early postoperative period relatively uncovered by anesthetic agent. This finding of relatively poor pain control early after surgery has also been noted in patients undergoing knee arthroplasty.⁵ On the basis of the findings of this study, we have added standard bupivacaine injections to our separate liposomal bupivacaine injection to cover early postoperative pain. Opioid consumption was significantly lower in the liposomal bupivacaine group than in the ISNB group on postoperative days 2 and 3. We did not measure adverse events related to opioid consumption, so we cannot comment on whether the decreased opioid consumption was associated with the rate of adverse events. However, other studies^21,22 have established this relationship.

We found the liposomal bupivacaine group to have earlier discharges to home. Sixteen of 37 patients in the liposomal bupivacaine group compared with 2 of 21 patients in the ISNB group were discharged on the day after surgery. A mean reduction in LOS of 18 hours for the liposomal bupivacaine group was statistically significant (P = .012). This reduction in LOS has important implications for hospitals and value analysis committees considering whether to keep a new, more expensive local anesthetic on formulary. Savings from reduced LOS and improvements in patient satisfaction may justify the expense (approximately $300 per 266-mg vial) of Exparel.

From a societal cost perspective, liposomal bupivacaine is more economical compared with ISNB, which adds approximately $1500 to the cost of anesthesia per patient.²³ Eliminating the costs associated with ISNB administration in shoulder arthroplasties could result in substantial savings to our healthcare system. More research examining time savings and exact costs of each procedure is needed to determine the true cost effectiveness of each approach.

Limitations of our study include the retrospective design, relatively small numbers of patients in each group, missing data for some patients at various time points, variation in the types of procedures in each group, and lack of long-term outcome measures. It is important to note that we did not confirm the success of the nerve block after administration. However, this study reflects the effectiveness of each of the modalities in actual clinical conditions (as opposed to a controlled experimental setting). The actual effectiveness of a nerve block varies, even when performed by an experienced anesthesiologist with ultrasound guidance. Furthermore, immediate postoperative pain scores in the nerve block group are consistent with those of prior research reporting pain values ranging from 4 to 5 and a mean duration of effect ranging from 9 to 14 hours.^23,24 Additionally, the patients, surgeon, and nursing team were not blinded to the treatment group. Although we did note a significant difference in the types of procedures between groups, this finding is related to the greater number of hemiarthroplasties performed in the ISNB group (N = 5) compared with the liposomal group (N = 1). Because of this variation and the decreased invasiveness of hemiarthroplasties, the bias is against the liposomal group. Finally, our primary outcome variable was pain, which is a subjective, self-reported measure. However, our opioid consumption data and LOS data corroborate the improved pain scores in the liposomal bupivacaine group.

Limiting the study to a single surgeon may limit external validity. Another limitation is the lack of data on adverse events related to opioid medication use. There was no additional experimental group to determine whether less expensive local anesthetics injected locally would perform similarly to liposomal bupivacaine. In total knee arthroplasty, periarticular injections of liposomal bupivacaine were not as effective as less expensive periarticular injections.²⁵ It is unclear which agents (and in what doses or combinations) should be used for periarticular injections. Finally, we acknowledge that our retrospective study design cannot account for all potential factors affecting discharge time.

This is the first comparative study of liposomal bupivacaine and ISNB in TSA. The study design allowed us to control for variables such as surgical technique, postoperative protocols (including use and type of sling), and use of other pain modalities such as patient-controlled analgesia and intravenous acetaminophen that are likely to affect postoperative pain and LOS. This study provides preliminary data that confirm relative equipoise between liposomal bupivacaine and ISNB, which is needed for the ethical conduct of a randomized controlled trial. Such a trial would allow for a more robust comparison, and this retrospective study provides appropriate pilot data on which to base this design and the clinical information needed to counsel patients during enrollment.

Our results suggest that liposomal bupivacaine may provide superior or similar pain relief compared with ISNB after shoulder arthroplasty. Additionally, the use of liposomal bupivacaine was associated with decreased opioid consumption and earlier discharge to home compared with ISNB. These findings have important implications for pain control after TSA because pain represents a major concern for patients and providers after surgery. In addition to clinical improvements, use of liposomal bupivacaine may save time and eliminate costs associated with administering nerve blocks. Local injection may also be used in patients who are contraindicated for ISNB such as those with obesity, pulmonary disease, or peripheral neuropathy. Although we cannot definitively suggest that liposomal bupivacaine is superior to the current gold standard ISNB for pain control after shoulder arthroplasty, our results suggest a relative clinical equipoise between these modalities. Larger analytical studies, including randomized trials, should be performed to explore the potential benefits of liposomal bupivacaine injections for pain control after shoulder arthroplasty.

Am J Orthop. 2016;45(7):424-430. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Hospital readmissions are undesirable and expensive.¹ The Centers for Medicare & Medicaid Services (CMS) use hospital readmission rates as one measure of healthcare quality and hospital performance.² In addition, the Patient Protection and Affordable Care Act of 2010 established a provision that decreases payments to hospitals with above-average readmission rates.³ Total knee arthroplasties (TKAs) and total hip arthroplasties (THAs) are among the most common surgical procedures leading to readmission and cost almost $20 billion dollars annually in the Medicare population alone.¹ Identifying factors that lead to readmissions after certain popular procedures may be a way to improve healthcare quality and outcomes while decreasing costs.

One such operation is shoulder arthroplasty (SA), which has surged in popularity over the past decade and is projected to increase faster than TKAs and THAs.^4-6 SA is used to treat a variety of shoulder conditions, including osteoarthritis, inflammatory arthritis, severe proximal humeral fracture, avascular necrosis, and rotator cuff tear arthropathy.^7-12 Much as with knee and hip arthroplasty, good outcomes have been reported with SA: decreased pain, improved range of motion, and high patient satisfaction.^10,13 However, there have been few studies of rates of readmission after SA and the associated risk factors.^3,14,15 The reported rates of early readmission after SA have ranged from 5.6% to 7.3%.^3,14,15 These rates are comparable to rates of readmission after TKA (4.0%-6.6%) and THA (3.5%-8.4%).^15-17Recently, CMS introduced legislation to void payments for hospital-acquired conditions (HACs), preventable medical conditions that patients develop during or as a result of their hospital care and that were not present on admission.¹⁸ Although many factors contribute to readmission, a recent study regarding all-cause readmission during the first 30 days after discharge found that almost 50% of 30-day readmissions after knee and hip replacements were potentially preventable.¹⁹ HACs resulting in readmission after SAs make up 9.3% to 34.5% of all readmissions, after anatomical total shoulder arthroplasties (ATSAs) and reverse total shoulder arthroplasties (RTSAs).^3,14 The most common HACs include retained foreign body after surgery, air embolism, falls and trauma, catheter-associated urinary tract infection (CAUTI), surgical-site infection, deep vein thrombosis (DVT), and pulmonary embolism (PE).¹⁸ Raines and colleagues¹⁶ found that HACs accounted for 41.7% of all complications in knee or hip arthroplasty and that HACs were the greatest predictors of early readmission after both procedures.

We conducted a study to evaluate rates of readmission within 30 days after ATSA and RTSA and to describe the independent risk factors for readmission. We hypothesized that the rate of readmission after SA would be similar to the rate after knee and hip arthroplasty and that readmission risk factors would be similar. Elucidating these rates and associated risk factors may ultimately help to minimize the burden of disability on patients and the burden of financial costs on healthcare institutions.

Materials and Methods

Institutional Review Board approval was not required for this study, and all data used were de-identified to Health Insurance Portability and Accountability Act (HIPAA) standards. We used the American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) database for this study. The NSQIP was developed in the 1990s to improve surgical quality in the Veterans Health Administration and was later adapted by the ACS.²⁰ NSQIP follows patients for 30 days after operations and provides clinical data and outcome measures that are closely regulated and internally audited.²¹ The program has continued to expand and now includes more than 400 institutions. The NSQIP database has been validated as a reliable source of surgical outcomes data, including outcomes data for orthopedic procedures, and has been used in other studies of readmissions.^17,22

In the present study, the ACS-NSQIP files for the period 2011-2013 were queried for all total shoulder arthroplasties (TSAs) (Current Procedural Terminology [CPT] code 23472, which includes ATSA and RTSA). Descriptive analysis was performed to determine the overall readmission rate as well as the percentages of readmissions for medical and surgical complications. Reasons for readmission were collected from 2012 and 2013 (information from 2011 was absent).

The various patient parameters compiled within the database were examined in a review of ATSAs and RTSAs. Demographics, comorbidities, operative characteristics, and predischarge complications were amassed from these data. Demographics included age, sex, race, body mass index, smoking status, preoperative functional health status, and American Society of Anesthesiologists (ASA) score. Comorbidities included diabetes mellitus, hypertension, chronic corticosteroid use, coagulation disorder, peripheral vascular disease, chronic obstructive pulmonary disease (COPD), cardiac comorbidity (including congestive heart failure, history of myocardial infarction, previous coronary intervention or cardiac surgery, and angina), renal comorbidity (including acute renal failure and preoperative dialysis), neurologic comorbidity (including impaired sensorium, hemiplegia, history of transient ischemic attack, and history of cerebrovascular accident with or without residual deficit), and preoperative blood transfusion. Operative characteristics included resident involvement, operative time more than 1 SD from the mean (>164.4 minutes), intraoperative blood transfusion, and revision surgery. Predischarge complications included pneumonia, CAUTI, DVT, PE, postoperative bleeding that required transfusion, cerebrovascular accident, myocardial infarction, and sepsis. Surgical-site infection, CAUTI, DVT, and PE were selected for analysis because these HACs are common in our cohort.

After the data on these characteristics were collected, univariate analysis was performed to determine association with any readmission. Factors with P < .20 were then entered into multivariate analysis to determine independent risk factors for readmission. This P value was selected to make the model inclusive of any potentially important predictor. Univariate analysis was performed using the Fisher exact test. Multivariate analysis was performed using backward conditional binary logistic regression. Statistical significance was set at P < .05. All analysis was performed with SPSS Version 22.0 (SPSS).

 

Results

This study included a combined total of 3501 ATSAs and RTSAs performed between 2011 and 2013. The overall readmission rate was 2.7%. The associated diagnosis for readmission was available for 54% of the readmitted patients. Of the known readmission diagnoses, 33% were secondary to HACs.

Three independent risk factors for readmission were identified: revision surgery (odds ratio [OR], 2.59), 3 or more comorbidities (OR, 2.02), and extended length of stay (LOS, >4.3 days) during index admission (OR, 2.48). These factors, plus P values and ORs, are listed in Table 1.

Of the 51 readmissions, 34 (67%) were for medical complications, and 17 (33%) were for surgical complications. Pneumonia was the most common medical complication (11.8%), followed by UTI (7.8%), DVT (5.9%), PE (5.9%), and renal insufficiency (3.9%). Surgical-site infection was the most common surgical complication (13.7%), followed by prosthetic joint dislocation (9.8%) and hematoma (3.9%).

Of the HACs, 41.2% were surgical-site infections, 23.5% were CAUTIs, 17.6% were DVTs, and 17.6% were PEs (Table 2).

Other risk factors significantly (P < .05) associated with readmission were age over 75 years, dependent functional status, ASA score of 4 or higher, cardiac comorbidity, 2 or more comorbidities, postoperative CAUTI, extended LOS, and revision surgery (Table 3).

The most common comorbidities were hypertension (67.8%), diabetes (16.6%), and COPD (6.3%). Readmitted patients were more likely to be female (56.3%) than male (43.6%). The majority of patients were white (86.1%), and 48.1% were obese (body mass index, >30). In addition, 16.9% of readmissions had resident involvement in the operation, and 13.2% of readmissions had an operative time >164.4 minutes. Of readmitted patients, 3.8% required a postoperative blood transfusion (Table 4).

Discussion

Hospital readmissions are important because they represent quality of care and play a role in patient outcomes. Arthroplasty research has focused mainly on readmissions after primary knee and hip replacements.^23-25

Given the increasing popularity of SAs, we initiated the present study to quantify short-term rates of readmission after ATSAs and RTSAs and to determine independent risk factors for readmission based on data from a national database. The results identified a 30-day readmission rate of 2.7%. Risk factors for readmission included revision surgery, 3 or more comorbidities, and extended LOS during the index admission.

Historical rates of early readmission after SA¹⁴ are comparable to those found in our study. Previously identified risk factors have included increasing age, Medicaid insurance status, low-volume surgical centers, and SA type.³ Mahoney and colleagues¹⁴ reported a 90-day readmission rate of 5.9%, but, when they removed hemiarthroplasty replacement from the analysis and shortened the readmission timeline to 30 days, the readmission rate was identical to the 2.7% rate in the present study. In their series from a single high-volume institution, the highest 90-day readmission rate was found for hemiarthroplasty (8.8%), followed by RTSA (6.6%) and ATSA (4.5%). In a study by Schairer and colleagues,³ the readmission rate was also influenced by replacement type, but their results differed from those of Mahoney and colleagues.¹⁴ Schairer and colleagues³ analyzed data from 7 state inpatient databases and found that the highest readmission rate was associated with RTSA (11.2%), followed by hemiarthroplasty (8.2%) and ATSA (6.0%). In both series, RTSA readmission rates were higher than ATSA readmission rates—consistent with the complication profiles of these procedures, with RTSA often provided as a surgery of last resort, after failure of other procedures, including ATSA.²⁶ The lower 30-day readmission rate in the present study may be attributable to the fact that some surgical and medical complications may not have developed within this short time. Nonetheless, the majority of readmissions typically present within the first 30 days after SA.^14,15 Other factors, including hospital volume, surgeon volume, race, and hospital type, may also influence readmission rates but could not be compared between studies.^27,28

The present study found that revision surgery, 3 or more comorbidities, and extended LOS (>4.3 days) more than doubled the risk of readmission. Published SA revision rates range from 5% to 42%, with most revisions performed for instability, dislocation, infection, and component loosening.^6,29 Complication rates are higher for revision SA than for primary SA, which may explain why revisions predispose patients to readmission.³⁰ Compared with primary SAs, revision SAs are also more likely to be RTSAs, and these salvage procedures have been found to have high complication rates.³¹ In the present study, the most common comorbidities were hypertension, diabetes, and COPD; the literature supports these as some of the most common comorbid medical conditions in patients who undergo ATSA or RTSA.^5,26,32 Furthermore, all 3 of these comorbidities have been shown to be independent predictors of increased postoperative complications in patients who undergo SA, which ultimately would increase the risk of readmission.^3,26,33,34 Last, extended LOS has also been shown to increase the risk of unplanned readmissions after orthopedic procedures.³⁵ Risk factors associated with increased LOS after ATSA or RTSA include female sex, advanced age, multiple comorbidities, and postoperative complications.³²Several other factors must be noted with respect to individual risk for readmission. In the present study, age over 75 years, dependent functional status, ASA score of 4 or higher, and cardiac comorbidity were found to have a significant association with readmission. Increased age is a risk factor for increased postoperative complications, more medical comorbidities, and increased LOS.^34,36 Older people are at higher risk of developing osteoarthritis and rotator cuff tear arthropathy and are more likely to undergo SA.^5,6 Older people also are more likely to be dependent, which itself is a risk factor for readmission.¹⁹ An ASA score of 3 or 4 has been found to be associated with increased LOS and complications after SA, and cardiac comorbidities predispose patients to a variety of complications.^34,36,37In studies that have combined surgical and medical factors, rates of complications early after ATSA and RTSA have ranged from 3.6% to 17.8%.^26,38,39 After SAs, medical complications (80%) are more common than surgical complications (20%).³⁹ In the present cohort, many more readmissions were for medical complications (67%) than for surgical complications (33%). In addition, Schairer and colleagues³ found medical complications associated with more than 80% of readmissions after SA.³ Infection was the most common medical reason (pneumonia) and surgical reason (surgical-site infection) for readmission—consistent with findings of other studies.^3,35,40 Infection has accounted for 9.4% to 41.4% of readmissions after ATSA and RTSA.^3,14In joint arthroplasty, infection occurs more often in patients with coexisting medical comorbidities, leading to higher mortality and increased LOS.⁴¹ Prosthetic joint dislocation was common as well—similar to findings in other studies.^3,10In the present study, 33% of known readmission diagnoses were secondary to HACs. Surgical-site infection was the most common, followed by CAUTI, DVT, and PE. In another study, of knee and hip arthroplasties, HACs accounted for more than 40% of all complications and were the strongest predictor of early readmission.¹⁶ In SA studies, HACs were responsible for 9.3% to 34.5% of readmissions after ATSA and RTSA.^3,14 Our finding (33%) is more in line with Mahoney and colleagues¹⁴ (34.5%) than Schairer and colleagues³ (9.3%). One explanation for the large discrepancy with Schairer and colleagues³ is that UTI was not among the medical reasons for readmission in their study, but it was in ours. Another difference is that we used a database that included data from multiple institutions. Last, Schairer and colleagues³ excluded revision SAs from their analysis (complication rates are higher for revision SAs than for primary SAs³⁰). They also excluded cases of SA used for fracture (shown to increase the risk for PE⁴²). The US Department of Health and Human Services estimated that patients experienced 1.3 million fewer HACs during the period 2010-2013, corresponding to a 17% decline over the 3 years.⁴³ This translates to an estimated 50,000 fewer mortalities, and $12 billion saved in healthcare costs, over the same period.⁴³ Preventing HACs helps reduce readmission rates while improving patient outcomes and decreasing healthcare costs.

This study had several limitations. We could not differentiate between ATSA and RTSA readmission rates because, for the study period, these procedures are collectively organized under a common CPT code in the NSQIP database. Readmission and complication rates are higher for RTSAs than for ATSAs.^3,14 In addition, our data were limited to hospitals that were participating in NSQIP, which could lead to selection bias. We studied rates of only those readmissions and complications that occurred within 30 days, but many complications develop after 30 days, and these increase the readmission rate. Last, reasons for readmission were not recorded for 2011, so this information was available only for the final 2 years of the study. Despite these limitations, NSQIP still allows for a powerful study, as it includes multiple institutions and a very large cohort.

 

Conclusion

With medical costs increasing, focus has shifted to quality care and good outcomes with the goal of reducing readmissions and complications after various procedures. SA has recently become more popular because of its multiple indications, and this trend will continue. In the present study, the rate of readmission within 30 days after ATSA or RTSA was 2.7%. Revision surgery, 3 or more comorbidities, and extended LOS were independent risk factors that more than doubled the risk of readmission. Understanding the risk factors for short-term readmission will allow for better patient care and decreased costs, and will benefit the healthcare system as a whole.

Am J Orthop. 2016;45(6):E386-E392. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Hospital readmissions are undesirable and expensive.¹ The Centers for Medicare & Medicaid Services (CMS) use hospital readmission rates as one measure of healthcare quality and hospital performance.² In addition, the Patient Protection and Affordable Care Act of 2010 established a provision that decreases payments to hospitals with above-average readmission rates.³ Total knee arthroplasties (TKAs) and total hip arthroplasties (THAs) are among the most common surgical procedures leading to readmission and cost almost $20 billion dollars annually in the Medicare population alone.¹ Identifying factors that lead to readmissions after certain popular procedures may be a way to improve healthcare quality and outcomes while decreasing costs.

One such operation is shoulder arthroplasty (SA), which has surged in popularity over the past decade and is projected to increase faster than TKAs and THAs.^4-6 SA is used to treat a variety of shoulder conditions, including osteoarthritis, inflammatory arthritis, severe proximal humeral fracture, avascular necrosis, and rotator cuff tear arthropathy.^7-12 Much as with knee and hip arthroplasty, good outcomes have been reported with SA: decreased pain, improved range of motion, and high patient satisfaction.^10,13 However, there have been few studies of rates of readmission after SA and the associated risk factors.^3,14,15 The reported rates of early readmission after SA have ranged from 5.6% to 7.3%.^3,14,15 These rates are comparable to rates of readmission after TKA (4.0%-6.6%) and THA (3.5%-8.4%).^15-17Recently, CMS introduced legislation to void payments for hospital-acquired conditions (HACs), preventable medical conditions that patients develop during or as a result of their hospital care and that were not present on admission.¹⁸ Although many factors contribute to readmission, a recent study regarding all-cause readmission during the first 30 days after discharge found that almost 50% of 30-day readmissions after knee and hip replacements were potentially preventable.¹⁹ HACs resulting in readmission after SAs make up 9.3% to 34.5% of all readmissions, after anatomical total shoulder arthroplasties (ATSAs) and reverse total shoulder arthroplasties (RTSAs).^3,14 The most common HACs include retained foreign body after surgery, air embolism, falls and trauma, catheter-associated urinary tract infection (CAUTI), surgical-site infection, deep vein thrombosis (DVT), and pulmonary embolism (PE).¹⁸ Raines and colleagues¹⁶ found that HACs accounted for 41.7% of all complications in knee or hip arthroplasty and that HACs were the greatest predictors of early readmission after both procedures.

We conducted a study to evaluate rates of readmission within 30 days after ATSA and RTSA and to describe the independent risk factors for readmission. We hypothesized that the rate of readmission after SA would be similar to the rate after knee and hip arthroplasty and that readmission risk factors would be similar. Elucidating these rates and associated risk factors may ultimately help to minimize the burden of disability on patients and the burden of financial costs on healthcare institutions.

Materials and Methods

Institutional Review Board approval was not required for this study, and all data used were de-identified to Health Insurance Portability and Accountability Act (HIPAA) standards. We used the American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) database for this study. The NSQIP was developed in the 1990s to improve surgical quality in the Veterans Health Administration and was later adapted by the ACS.²⁰ NSQIP follows patients for 30 days after operations and provides clinical data and outcome measures that are closely regulated and internally audited.²¹ The program has continued to expand and now includes more than 400 institutions. The NSQIP database has been validated as a reliable source of surgical outcomes data, including outcomes data for orthopedic procedures, and has been used in other studies of readmissions.^17,22

In the present study, the ACS-NSQIP files for the period 2011-2013 were queried for all total shoulder arthroplasties (TSAs) (Current Procedural Terminology [CPT] code 23472, which includes ATSA and RTSA). Descriptive analysis was performed to determine the overall readmission rate as well as the percentages of readmissions for medical and surgical complications. Reasons for readmission were collected from 2012 and 2013 (information from 2011 was absent).

The various patient parameters compiled within the database were examined in a review of ATSAs and RTSAs. Demographics, comorbidities, operative characteristics, and predischarge complications were amassed from these data. Demographics included age, sex, race, body mass index, smoking status, preoperative functional health status, and American Society of Anesthesiologists (ASA) score. Comorbidities included diabetes mellitus, hypertension, chronic corticosteroid use, coagulation disorder, peripheral vascular disease, chronic obstructive pulmonary disease (COPD), cardiac comorbidity (including congestive heart failure, history of myocardial infarction, previous coronary intervention or cardiac surgery, and angina), renal comorbidity (including acute renal failure and preoperative dialysis), neurologic comorbidity (including impaired sensorium, hemiplegia, history of transient ischemic attack, and history of cerebrovascular accident with or without residual deficit), and preoperative blood transfusion. Operative characteristics included resident involvement, operative time more than 1 SD from the mean (>164.4 minutes), intraoperative blood transfusion, and revision surgery. Predischarge complications included pneumonia, CAUTI, DVT, PE, postoperative bleeding that required transfusion, cerebrovascular accident, myocardial infarction, and sepsis. Surgical-site infection, CAUTI, DVT, and PE were selected for analysis because these HACs are common in our cohort.

After the data on these characteristics were collected, univariate analysis was performed to determine association with any readmission. Factors with P < .20 were then entered into multivariate analysis to determine independent risk factors for readmission. This P value was selected to make the model inclusive of any potentially important predictor. Univariate analysis was performed using the Fisher exact test. Multivariate analysis was performed using backward conditional binary logistic regression. Statistical significance was set at P < .05. All analysis was performed with SPSS Version 22.0 (SPSS).

 

Results

This study included a combined total of 3501 ATSAs and RTSAs performed between 2011 and 2013. The overall readmission rate was 2.7%. The associated diagnosis for readmission was available for 54% of the readmitted patients. Of the known readmission diagnoses, 33% were secondary to HACs.

Three independent risk factors for readmission were identified: revision surgery (odds ratio [OR], 2.59), 3 or more comorbidities (OR, 2.02), and extended length of stay (LOS, >4.3 days) during index admission (OR, 2.48). These factors, plus P values and ORs, are listed in Table 1.

Of the 51 readmissions, 34 (67%) were for medical complications, and 17 (33%) were for surgical complications. Pneumonia was the most common medical complication (11.8%), followed by UTI (7.8%), DVT (5.9%), PE (5.9%), and renal insufficiency (3.9%). Surgical-site infection was the most common surgical complication (13.7%), followed by prosthetic joint dislocation (9.8%) and hematoma (3.9%).

Of the HACs, 41.2% were surgical-site infections, 23.5% were CAUTIs, 17.6% were DVTs, and 17.6% were PEs (Table 2).

Other risk factors significantly (P < .05) associated with readmission were age over 75 years, dependent functional status, ASA score of 4 or higher, cardiac comorbidity, 2 or more comorbidities, postoperative CAUTI, extended LOS, and revision surgery (Table 3).

The most common comorbidities were hypertension (67.8%), diabetes (16.6%), and COPD (6.3%). Readmitted patients were more likely to be female (56.3%) than male (43.6%). The majority of patients were white (86.1%), and 48.1% were obese (body mass index, >30). In addition, 16.9% of readmissions had resident involvement in the operation, and 13.2% of readmissions had an operative time >164.4 minutes. Of readmitted patients, 3.8% required a postoperative blood transfusion (Table 4).

Discussion

Hospital readmissions are important because they represent quality of care and play a role in patient outcomes. Arthroplasty research has focused mainly on readmissions after primary knee and hip replacements.^23-25

Given the increasing popularity of SAs, we initiated the present study to quantify short-term rates of readmission after ATSAs and RTSAs and to determine independent risk factors for readmission based on data from a national database. The results identified a 30-day readmission rate of 2.7%. Risk factors for readmission included revision surgery, 3 or more comorbidities, and extended LOS during the index admission.

Historical rates of early readmission after SA¹⁴ are comparable to those found in our study. Previously identified risk factors have included increasing age, Medicaid insurance status, low-volume surgical centers, and SA type.³ Mahoney and colleagues¹⁴ reported a 90-day readmission rate of 5.9%, but, when they removed hemiarthroplasty replacement from the analysis and shortened the readmission timeline to 30 days, the readmission rate was identical to the 2.7% rate in the present study. In their series from a single high-volume institution, the highest 90-day readmission rate was found for hemiarthroplasty (8.8%), followed by RTSA (6.6%) and ATSA (4.5%). In a study by Schairer and colleagues,³ the readmission rate was also influenced by replacement type, but their results differed from those of Mahoney and colleagues.¹⁴ Schairer and colleagues³ analyzed data from 7 state inpatient databases and found that the highest readmission rate was associated with RTSA (11.2%), followed by hemiarthroplasty (8.2%) and ATSA (6.0%). In both series, RTSA readmission rates were higher than ATSA readmission rates—consistent with the complication profiles of these procedures, with RTSA often provided as a surgery of last resort, after failure of other procedures, including ATSA.²⁶ The lower 30-day readmission rate in the present study may be attributable to the fact that some surgical and medical complications may not have developed within this short time. Nonetheless, the majority of readmissions typically present within the first 30 days after SA.^14,15 Other factors, including hospital volume, surgeon volume, race, and hospital type, may also influence readmission rates but could not be compared between studies.^27,28

The present study found that revision surgery, 3 or more comorbidities, and extended LOS (>4.3 days) more than doubled the risk of readmission. Published SA revision rates range from 5% to 42%, with most revisions performed for instability, dislocation, infection, and component loosening.^6,29 Complication rates are higher for revision SA than for primary SA, which may explain why revisions predispose patients to readmission.³⁰ Compared with primary SAs, revision SAs are also more likely to be RTSAs, and these salvage procedures have been found to have high complication rates.³¹ In the present study, the most common comorbidities were hypertension, diabetes, and COPD; the literature supports these as some of the most common comorbid medical conditions in patients who undergo ATSA or RTSA.^5,26,32 Furthermore, all 3 of these comorbidities have been shown to be independent predictors of increased postoperative complications in patients who undergo SA, which ultimately would increase the risk of readmission.^3,26,33,34 Last, extended LOS has also been shown to increase the risk of unplanned readmissions after orthopedic procedures.³⁵ Risk factors associated with increased LOS after ATSA or RTSA include female sex, advanced age, multiple comorbidities, and postoperative complications.³²Several other factors must be noted with respect to individual risk for readmission. In the present study, age over 75 years, dependent functional status, ASA score of 4 or higher, and cardiac comorbidity were found to have a significant association with readmission. Increased age is a risk factor for increased postoperative complications, more medical comorbidities, and increased LOS.^34,36 Older people are at higher risk of developing osteoarthritis and rotator cuff tear arthropathy and are more likely to undergo SA.^5,6 Older people also are more likely to be dependent, which itself is a risk factor for readmission.¹⁹ An ASA score of 3 or 4 has been found to be associated with increased LOS and complications after SA, and cardiac comorbidities predispose patients to a variety of complications.^34,36,37In studies that have combined surgical and medical factors, rates of complications early after ATSA and RTSA have ranged from 3.6% to 17.8%.^26,38,39 After SAs, medical complications (80%) are more common than surgical complications (20%).³⁹ In the present cohort, many more readmissions were for medical complications (67%) than for surgical complications (33%). In addition, Schairer and colleagues³ found medical complications associated with more than 80% of readmissions after SA.³ Infection was the most common medical reason (pneumonia) and surgical reason (surgical-site infection) for readmission—consistent with findings of other studies.^3,35,40 Infection has accounted for 9.4% to 41.4% of readmissions after ATSA and RTSA.^3,14In joint arthroplasty, infection occurs more often in patients with coexisting medical comorbidities, leading to higher mortality and increased LOS.⁴¹ Prosthetic joint dislocation was common as well—similar to findings in other studies.^3,10In the present study, 33% of known readmission diagnoses were secondary to HACs. Surgical-site infection was the most common, followed by CAUTI, DVT, and PE. In another study, of knee and hip arthroplasties, HACs accounted for more than 40% of all complications and were the strongest predictor of early readmission.¹⁶ In SA studies, HACs were responsible for 9.3% to 34.5% of readmissions after ATSA and RTSA.^3,14 Our finding (33%) is more in line with Mahoney and colleagues¹⁴ (34.5%) than Schairer and colleagues³ (9.3%). One explanation for the large discrepancy with Schairer and colleagues³ is that UTI was not among the medical reasons for readmission in their study, but it was in ours. Another difference is that we used a database that included data from multiple institutions. Last, Schairer and colleagues³ excluded revision SAs from their analysis (complication rates are higher for revision SAs than for primary SAs³⁰). They also excluded cases of SA used for fracture (shown to increase the risk for PE⁴²). The US Department of Health and Human Services estimated that patients experienced 1.3 million fewer HACs during the period 2010-2013, corresponding to a 17% decline over the 3 years.⁴³ This translates to an estimated 50,000 fewer mortalities, and $12 billion saved in healthcare costs, over the same period.⁴³ Preventing HACs helps reduce readmission rates while improving patient outcomes and decreasing healthcare costs.

This study had several limitations. We could not differentiate between ATSA and RTSA readmission rates because, for the study period, these procedures are collectively organized under a common CPT code in the NSQIP database. Readmission and complication rates are higher for RTSAs than for ATSAs.^3,14 In addition, our data were limited to hospitals that were participating in NSQIP, which could lead to selection bias. We studied rates of only those readmissions and complications that occurred within 30 days, but many complications develop after 30 days, and these increase the readmission rate. Last, reasons for readmission were not recorded for 2011, so this information was available only for the final 2 years of the study. Despite these limitations, NSQIP still allows for a powerful study, as it includes multiple institutions and a very large cohort.

 

Conclusion

With medical costs increasing, focus has shifted to quality care and good outcomes with the goal of reducing readmissions and complications after various procedures. SA has recently become more popular because of its multiple indications, and this trend will continue. In the present study, the rate of readmission within 30 days after ATSA or RTSA was 2.7%. Revision surgery, 3 or more comorbidities, and extended LOS were independent risk factors that more than doubled the risk of readmission. Understanding the risk factors for short-term readmission will allow for better patient care and decreased costs, and will benefit the healthcare system as a whole.

Am J Orthop. 2016;45(6):E386-E392. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Hospital readmissions are undesirable and expensive.¹ The Centers for Medicare & Medicaid Services (CMS) use hospital readmission rates as one measure of healthcare quality and hospital performance.² In addition, the Patient Protection and Affordable Care Act of 2010 established a provision that decreases payments to hospitals with above-average readmission rates.³ Total knee arthroplasties (TKAs) and total hip arthroplasties (THAs) are among the most common surgical procedures leading to readmission and cost almost $20 billion dollars annually in the Medicare population alone.¹ Identifying factors that lead to readmissions after certain popular procedures may be a way to improve healthcare quality and outcomes while decreasing costs.

One such operation is shoulder arthroplasty (SA), which has surged in popularity over the past decade and is projected to increase faster than TKAs and THAs.^4-6 SA is used to treat a variety of shoulder conditions, including osteoarthritis, inflammatory arthritis, severe proximal humeral fracture, avascular necrosis, and rotator cuff tear arthropathy.^7-12 Much as with knee and hip arthroplasty, good outcomes have been reported with SA: decreased pain, improved range of motion, and high patient satisfaction.^10,13 However, there have been few studies of rates of readmission after SA and the associated risk factors.^3,14,15 The reported rates of early readmission after SA have ranged from 5.6% to 7.3%.^3,14,15 These rates are comparable to rates of readmission after TKA (4.0%-6.6%) and THA (3.5%-8.4%).^15-17Recently, CMS introduced legislation to void payments for hospital-acquired conditions (HACs), preventable medical conditions that patients develop during or as a result of their hospital care and that were not present on admission.¹⁸ Although many factors contribute to readmission, a recent study regarding all-cause readmission during the first 30 days after discharge found that almost 50% of 30-day readmissions after knee and hip replacements were potentially preventable.¹⁹ HACs resulting in readmission after SAs make up 9.3% to 34.5% of all readmissions, after anatomical total shoulder arthroplasties (ATSAs) and reverse total shoulder arthroplasties (RTSAs).^3,14 The most common HACs include retained foreign body after surgery, air embolism, falls and trauma, catheter-associated urinary tract infection (CAUTI), surgical-site infection, deep vein thrombosis (DVT), and pulmonary embolism (PE).¹⁸ Raines and colleagues¹⁶ found that HACs accounted for 41.7% of all complications in knee or hip arthroplasty and that HACs were the greatest predictors of early readmission after both procedures.

We conducted a study to evaluate rates of readmission within 30 days after ATSA and RTSA and to describe the independent risk factors for readmission. We hypothesized that the rate of readmission after SA would be similar to the rate after knee and hip arthroplasty and that readmission risk factors would be similar. Elucidating these rates and associated risk factors may ultimately help to minimize the burden of disability on patients and the burden of financial costs on healthcare institutions.

Materials and Methods

Institutional Review Board approval was not required for this study, and all data used were de-identified to Health Insurance Portability and Accountability Act (HIPAA) standards. We used the American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) database for this study. The NSQIP was developed in the 1990s to improve surgical quality in the Veterans Health Administration and was later adapted by the ACS.²⁰ NSQIP follows patients for 30 days after operations and provides clinical data and outcome measures that are closely regulated and internally audited.²¹ The program has continued to expand and now includes more than 400 institutions. The NSQIP database has been validated as a reliable source of surgical outcomes data, including outcomes data for orthopedic procedures, and has been used in other studies of readmissions.^17,22

In the present study, the ACS-NSQIP files for the period 2011-2013 were queried for all total shoulder arthroplasties (TSAs) (Current Procedural Terminology [CPT] code 23472, which includes ATSA and RTSA). Descriptive analysis was performed to determine the overall readmission rate as well as the percentages of readmissions for medical and surgical complications. Reasons for readmission were collected from 2012 and 2013 (information from 2011 was absent).

The various patient parameters compiled within the database were examined in a review of ATSAs and RTSAs. Demographics, comorbidities, operative characteristics, and predischarge complications were amassed from these data. Demographics included age, sex, race, body mass index, smoking status, preoperative functional health status, and American Society of Anesthesiologists (ASA) score. Comorbidities included diabetes mellitus, hypertension, chronic corticosteroid use, coagulation disorder, peripheral vascular disease, chronic obstructive pulmonary disease (COPD), cardiac comorbidity (including congestive heart failure, history of myocardial infarction, previous coronary intervention or cardiac surgery, and angina), renal comorbidity (including acute renal failure and preoperative dialysis), neurologic comorbidity (including impaired sensorium, hemiplegia, history of transient ischemic attack, and history of cerebrovascular accident with or without residual deficit), and preoperative blood transfusion. Operative characteristics included resident involvement, operative time more than 1 SD from the mean (>164.4 minutes), intraoperative blood transfusion, and revision surgery. Predischarge complications included pneumonia, CAUTI, DVT, PE, postoperative bleeding that required transfusion, cerebrovascular accident, myocardial infarction, and sepsis. Surgical-site infection, CAUTI, DVT, and PE were selected for analysis because these HACs are common in our cohort.

After the data on these characteristics were collected, univariate analysis was performed to determine association with any readmission. Factors with P < .20 were then entered into multivariate analysis to determine independent risk factors for readmission. This P value was selected to make the model inclusive of any potentially important predictor. Univariate analysis was performed using the Fisher exact test. Multivariate analysis was performed using backward conditional binary logistic regression. Statistical significance was set at P < .05. All analysis was performed with SPSS Version 22.0 (SPSS).

 

Results

This study included a combined total of 3501 ATSAs and RTSAs performed between 2011 and 2013. The overall readmission rate was 2.7%. The associated diagnosis for readmission was available for 54% of the readmitted patients. Of the known readmission diagnoses, 33% were secondary to HACs.

Three independent risk factors for readmission were identified: revision surgery (odds ratio [OR], 2.59), 3 or more comorbidities (OR, 2.02), and extended length of stay (LOS, >4.3 days) during index admission (OR, 2.48). These factors, plus P values and ORs, are listed in Table 1.

Of the 51 readmissions, 34 (67%) were for medical complications, and 17 (33%) were for surgical complications. Pneumonia was the most common medical complication (11.8%), followed by UTI (7.8%), DVT (5.9%), PE (5.9%), and renal insufficiency (3.9%). Surgical-site infection was the most common surgical complication (13.7%), followed by prosthetic joint dislocation (9.8%) and hematoma (3.9%).

Of the HACs, 41.2% were surgical-site infections, 23.5% were CAUTIs, 17.6% were DVTs, and 17.6% were PEs (Table 2).

Other risk factors significantly (P < .05) associated with readmission were age over 75 years, dependent functional status, ASA score of 4 or higher, cardiac comorbidity, 2 or more comorbidities, postoperative CAUTI, extended LOS, and revision surgery (Table 3).

The most common comorbidities were hypertension (67.8%), diabetes (16.6%), and COPD (6.3%). Readmitted patients were more likely to be female (56.3%) than male (43.6%). The majority of patients were white (86.1%), and 48.1% were obese (body mass index, >30). In addition, 16.9% of readmissions had resident involvement in the operation, and 13.2% of readmissions had an operative time >164.4 minutes. Of readmitted patients, 3.8% required a postoperative blood transfusion (Table 4).

Discussion

Hospital readmissions are important because they represent quality of care and play a role in patient outcomes. Arthroplasty research has focused mainly on readmissions after primary knee and hip replacements.^23-25

Given the increasing popularity of SAs, we initiated the present study to quantify short-term rates of readmission after ATSAs and RTSAs and to determine independent risk factors for readmission based on data from a national database. The results identified a 30-day readmission rate of 2.7%. Risk factors for readmission included revision surgery, 3 or more comorbidities, and extended LOS during the index admission.

Historical rates of early readmission after SA¹⁴ are comparable to those found in our study. Previously identified risk factors have included increasing age, Medicaid insurance status, low-volume surgical centers, and SA type.³ Mahoney and colleagues¹⁴ reported a 90-day readmission rate of 5.9%, but, when they removed hemiarthroplasty replacement from the analysis and shortened the readmission timeline to 30 days, the readmission rate was identical to the 2.7% rate in the present study. In their series from a single high-volume institution, the highest 90-day readmission rate was found for hemiarthroplasty (8.8%), followed by RTSA (6.6%) and ATSA (4.5%). In a study by Schairer and colleagues,³ the readmission rate was also influenced by replacement type, but their results differed from those of Mahoney and colleagues.¹⁴ Schairer and colleagues³ analyzed data from 7 state inpatient databases and found that the highest readmission rate was associated with RTSA (11.2%), followed by hemiarthroplasty (8.2%) and ATSA (6.0%). In both series, RTSA readmission rates were higher than ATSA readmission rates—consistent with the complication profiles of these procedures, with RTSA often provided as a surgery of last resort, after failure of other procedures, including ATSA.²⁶ The lower 30-day readmission rate in the present study may be attributable to the fact that some surgical and medical complications may not have developed within this short time. Nonetheless, the majority of readmissions typically present within the first 30 days after SA.^14,15 Other factors, including hospital volume, surgeon volume, race, and hospital type, may also influence readmission rates but could not be compared between studies.^27,28

The present study found that revision surgery, 3 or more comorbidities, and extended LOS (>4.3 days) more than doubled the risk of readmission. Published SA revision rates range from 5% to 42%, with most revisions performed for instability, dislocation, infection, and component loosening.^6,29 Complication rates are higher for revision SA than for primary SA, which may explain why revisions predispose patients to readmission.³⁰ Compared with primary SAs, revision SAs are also more likely to be RTSAs, and these salvage procedures have been found to have high complication rates.³¹ In the present study, the most common comorbidities were hypertension, diabetes, and COPD; the literature supports these as some of the most common comorbid medical conditions in patients who undergo ATSA or RTSA.^5,26,32 Furthermore, all 3 of these comorbidities have been shown to be independent predictors of increased postoperative complications in patients who undergo SA, which ultimately would increase the risk of readmission.^3,26,33,34 Last, extended LOS has also been shown to increase the risk of unplanned readmissions after orthopedic procedures.³⁵ Risk factors associated with increased LOS after ATSA or RTSA include female sex, advanced age, multiple comorbidities, and postoperative complications.³²Several other factors must be noted with respect to individual risk for readmission. In the present study, age over 75 years, dependent functional status, ASA score of 4 or higher, and cardiac comorbidity were found to have a significant association with readmission. Increased age is a risk factor for increased postoperative complications, more medical comorbidities, and increased LOS.^34,36 Older people are at higher risk of developing osteoarthritis and rotator cuff tear arthropathy and are more likely to undergo SA.^5,6 Older people also are more likely to be dependent, which itself is a risk factor for readmission.¹⁹ An ASA score of 3 or 4 has been found to be associated with increased LOS and complications after SA, and cardiac comorbidities predispose patients to a variety of complications.^34,36,37In studies that have combined surgical and medical factors, rates of complications early after ATSA and RTSA have ranged from 3.6% to 17.8%.^26,38,39 After SAs, medical complications (80%) are more common than surgical complications (20%).³⁹ In the present cohort, many more readmissions were for medical complications (67%) than for surgical complications (33%). In addition, Schairer and colleagues³ found medical complications associated with more than 80% of readmissions after SA.³ Infection was the most common medical reason (pneumonia) and surgical reason (surgical-site infection) for readmission—consistent with findings of other studies.^3,35,40 Infection has accounted for 9.4% to 41.4% of readmissions after ATSA and RTSA.^3,14In joint arthroplasty, infection occurs more often in patients with coexisting medical comorbidities, leading to higher mortality and increased LOS.⁴¹ Prosthetic joint dislocation was common as well—similar to findings in other studies.^3,10In the present study, 33% of known readmission diagnoses were secondary to HACs. Surgical-site infection was the most common, followed by CAUTI, DVT, and PE. In another study, of knee and hip arthroplasties, HACs accounted for more than 40% of all complications and were the strongest predictor of early readmission.¹⁶ In SA studies, HACs were responsible for 9.3% to 34.5% of readmissions after ATSA and RTSA.^3,14 Our finding (33%) is more in line with Mahoney and colleagues¹⁴ (34.5%) than Schairer and colleagues³ (9.3%). One explanation for the large discrepancy with Schairer and colleagues³ is that UTI was not among the medical reasons for readmission in their study, but it was in ours. Another difference is that we used a database that included data from multiple institutions. Last, Schairer and colleagues³ excluded revision SAs from their analysis (complication rates are higher for revision SAs than for primary SAs³⁰). They also excluded cases of SA used for fracture (shown to increase the risk for PE⁴²). The US Department of Health and Human Services estimated that patients experienced 1.3 million fewer HACs during the period 2010-2013, corresponding to a 17% decline over the 3 years.⁴³ This translates to an estimated 50,000 fewer mortalities, and $12 billion saved in healthcare costs, over the same period.⁴³ Preventing HACs helps reduce readmission rates while improving patient outcomes and decreasing healthcare costs.

This study had several limitations. We could not differentiate between ATSA and RTSA readmission rates because, for the study period, these procedures are collectively organized under a common CPT code in the NSQIP database. Readmission and complication rates are higher for RTSAs than for ATSAs.^3,14 In addition, our data were limited to hospitals that were participating in NSQIP, which could lead to selection bias. We studied rates of only those readmissions and complications that occurred within 30 days, but many complications develop after 30 days, and these increase the readmission rate. Last, reasons for readmission were not recorded for 2011, so this information was available only for the final 2 years of the study. Despite these limitations, NSQIP still allows for a powerful study, as it includes multiple institutions and a very large cohort.

 

Conclusion

With medical costs increasing, focus has shifted to quality care and good outcomes with the goal of reducing readmissions and complications after various procedures. SA has recently become more popular because of its multiple indications, and this trend will continue. In the present study, the rate of readmission within 30 days after ATSA or RTSA was 2.7%. Revision surgery, 3 or more comorbidities, and extended LOS were independent risk factors that more than doubled the risk of readmission. Understanding the risk factors for short-term readmission will allow for better patient care and decreased costs, and will benefit the healthcare system as a whole.

Am J Orthop. 2016;45(6):E386-E392. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Venous thromboembolism (VTE) after shoulder arthroplasty (SA) is relatively uncommon. Reported rates of VTE development are highly variable, ranging from 0.2% to 13% (pulmonary embolism [PE], 0.2%-10.8%; deep venous thrombosis [DVT], 0.1%-13%).^1-4 Sources of this variability include different methods of capturing cases (small clinical series vs large database studies, which capture mainly hospital readmissions), differences in defining or detecting VTE, and different patient populations (fracture vs osteoarthritis).^1-3 Most studies have also tried to identify factors associated with increased risk for VTE. Risk factors associated with development of VTE after SA include history of VTE, advanced age, prolonged operating room time, higher body mass index (BMI), trauma, history of cancer, female sex, and raised Charlson Comorbidity Index (CCI).^1-7 Limitations of clinical series include the smaller number of reporting institutions—a potential source of bias given regional variability.^1,3,4,7 Limitations of large state or national databases include capturing only events coded during inpatient admission and capturing readmissions for complications at the same institution. This underreporting may lead to very conservative estimates of VTE incidence.^2,5,6,8

In this study, we retrospectively identified all the SAs performed at a single institution over a 13-year period and evaluated the cases for development of VTE (DVT, PE). We hypothesized that the VTE rate would be lower than the very high rates reported by Hoxie and colleagues¹ and Willis and colleagues⁴ but higher than those reported for large state or national databases.^2,3 We also evaluated clotting risk factors, including many never analyzed before.

Materials and Methods

After obtaining Institutional Review Board approval for this study, we searched our database for all SAs performed at our institution between January 1999 and May 2012 and identified cases in which symptomatic VTE developed within the first 90 days after surgery. Charts were reviewed for information on medical history, surgical procedure, and in-hospital and out-of-hospital care within the 90-day postoperative period. We recorded data on symptomatic VTE (DVT, PE) as documented by lower or upper extremity duplex ultrasonography (US) or chest computed tomography (CT) angiography. There had been no routine screening of patients; duplex US or CT angiography was performed only if a patient was clinically symptomatic (leg swelling, leg pain, shortness of breath, tachycardia, chest pain) for a potential DVT or PE. For a patient who had repeat SAs on the same shoulder or bilateral SAs at different times, only the first procedure was included in the analysis. Arthroplasties performed for fracture were excluded.

Study data were collected and managed with REDCap (Research Electronic Data Capture) tools hosted at the University of Utah School of Medicine.⁹ Continuous and discrete data collected on medical history and postoperative course included BMI, age at surgery, preoperative hemoglobin (Hb) and hematocrit (Hct) levels, days in hospital, days until out of bed and days until ambulation (both documented in nursing and physical therapy notes), postoperative Hb and Hct levels, and CCI. Categorical data included sex, diagnosis (primary osteoarthritis, rotator cuff arthropathy, rheumatoid arthritis, failed hemiarthroplasty [HA], failed total SA [TSA], others), attending surgeon, procedure (TSA, HA, reverse TSA, revision SA), anesthesia (general endotracheal anesthesia [GETA] alone, interscalene nerve block alone, GETA plus block), prophylactic use of aspirin after surgery, presence of various medical comorbidities (diabetes, hypertension, cardiac disease, clotting disorders, cancer), hormone replacement therapy, family history of a clotting disorder, and VTE consequences (cardiac events, death).

Statistical Analysis

Descriptive statistics were calculated to summarize aspects of the surgical procedures, the study cohort’s demographics and medical histories, and the incidence of VTE. Logistic regression analysis was performed to explore the association between development of VTE (DVT, PE) and potential risk factors. Unadjusted odds ratios (ORs) were estimated for the risk factors of age, BMI, revision SA, CCI, prophylactic use of aspirin after surgery, preoperative history of VTE, preoperative and postoperative Hb and Hct levels, diabetes, anesthesia (GETA with and without interscalene nerve block), family history of a clotting disorder, days until out of bed, hormone replacement therapy, race, discharge home or to rehabilitation, distance traveled for surgery, hypertension, cardiac disease, cement use, and history of cancer. In addition, ORs were adjusted for age, BMI, and revision SA. For all statistical tests, significance was set at P < .05. All analyses were performed with SAS Version 9.3 (SAS Institute).

Results

We identified 533 SAs: 245 anatomical TSAs, 112 reverse TSAs, 92 HAs, and 84 revision SAs. Three different surgeons performed the procedures, and no patients were lost to follow-up within the first 90 days after surgery. Although SAs were performed for various diagnoses, more than 50% (274) of the SAs were for primary osteoarthritis; 97 were performed for rotator cuff arthropathy, 16 for rheumatoid arthritis, 43 for failed HA, 23 for failed TSA, and 79 for other diagnoses.

 

Of the 533 patients, 288 were female and 245 were male. Mean age at surgery was 65.2 years (range, 16-93 years). Mean (SD) BMI was 29.2 (6.4) kg/m². Mean (SD) preoperative Hb level was 13.7 (1.8) g/dL, and mean preoperative Hct level was 40.1% (4.8%). Mean (SD) length of hospital stay was 2.6 (1.5) days. Mean (SD) time before patients were out of bed was 1.1 (0.7) days. On postoperative day 1, mean Hb level was 11.1 (1.7) g/dL, and mean (SD) Hct level was 33.2% (4.8%). Mean (SD) CCI was 1.1 (0.9).

Anesthesia for the 533 patients consisted of GETA (209 patients, 39.0%), interscalene nerve block (2, 0.4%), or GETA with nerve block (314, 59.0%). After surgery, 125 patients (24.3%) received aspirin as prophylaxis. Diabetes was reported by 83 patients, hypertension by 286, cardiac disease by 74, a history of a clotting disorder by 2, a family history of a clotting disorder by 8, ongoing cancer by 4, a history of cancer by 67, and hormone replacement therapy by 104.

For the entire cohort of 533 patients, the symptomatic VTE rate was 2.6% (14 patients), the DVT rate was 0.9% (5), and the PE rate was 2.3% (12). Although VTE did not cause any deaths, there were 3 cardiac events.

Risk factors significantly associated with increased risk for VTE were raised CCI (OR, 1.858; 95% confidence interval [CI], 1.295–2.665), preoperative thrombotic event (OR, 5.532; 95% CI, 1.651–18.535), lower preoperative Hb level (OR, 0.705; 95% CI, 0.486–1.022), lower preoperative Hct level (OR, 0.877; 95% CI, 0.763–1.007), lower postoperative Hb level (OR, 0.720; 95% CI, 0.506–1.026), diabetes (OR, 5.646; 95% CI, 1.926–16.554), use of GETA without interscalene nerve block (OR, 0.111; 95% CI, 0.014–0.857), higher BMI (OR, 1.148; 95% CI, 1.062–1.241), and revision SA (OR, 5.777; 95% CI, 1.664–20.057).

All factors had significant adjusted ORs, whereas only BMI, revision SA, CCI, diabetes, and use of GETA without nerve block had significant unadjusted ORs (Tables 1, 2).

Discussion

VTE after SA is rare. We report an overall VTE incidence of 2.6%, with DVT at 0.9% and PE at 2.3%. These rates are similar to those reported in clinical series and significantly higher than those reported for large institutional or national databases.^2-7 Our results also support a previously reported trend: The ratio of PE to DVT for SA is significantly higher than historically reported ratios for lower extremity arthroplasty.^2,6-8 We have identified many VTE risk factors: raised CCI, preoperative thrombotic event, lower preoperative Hb and Hct levels, lower postoperative Hb level, diabetes, use of GETA without interscalene nerve block, higher BMI, and revision SA. Results of other studies support 3 findings (higher BMI, raised CCI, preoperative thrombotic event); new findings include correlation with Hb and Hct levels, diabetes, type of anesthesia, and revision SA.^6,7 Identification of these other factors may be useful in making treatment decisions in patients symptomatic after SA and in lowering the threshold for performing diagnostic tests in these patients at risk for VTE.

Reported rates of VTE after SA are highly variable, ranging from 0.2% to 13%.¹⁰ Our rationale for investigating VTE rates at a single institution was to estimate the rates that can be expected in a university-based practice and to determine whether these rates are high enough to warrant routine thromboprophylaxis. The rate variability seems to result in part from variability in the data sources. Most studies that have reported very low VTE rates typically used large state or national databases, which likely were subject to underreporting.

Lyman and colleagues⁶ found 0.5% DVT and 0.2% PE rates in a New York state hospital database, but only in-hospital immediate postoperative symptomatic complications were included; slightly delayed complications may have been missed. Farng and colleagues⁵ reported a 0.6% VTE rate, but only inpatient (immediate postoperative or readmission) events were included; all outpatient events were missed. Jameson and colleagues,² using a national database that included only cases involving inpatient treatment, reported 0% DVT and 0.2% PE rates, again missing outpatient events, and relying on appropriate coding to capture events. Using electronic health records from a large healthcare system, Navarro and colleagues⁸ queried for VTE cases and reported 0.5% DVT and 0.5% PE rates. The inclusiveness of their data source for the outcome of interest was potentially improved relative to national or statewide databases—and the resulting data reported in their study should reflect that improvement. However, the authors relied on ICD–9 (International Classification of Diseases, Ninth Revision) coding to screen for VTE events and excluded patients with prior VTE, preoperative prophylaxis (enoxaparin or warfarin), or follow-up of <90 days. As patients with prior VTE are those most at risk (present study OR, 6-7), excluding them significantly reduces the overall incidence of clotting reported.

Only 4 studies specifically used information drawn directly from physicians’ clinic notes, vs data retrieved (using code-based queries) from databases.^1,3,4,7 These studies may provide a better representation of the rate of VTE after SA, as they were not reliant on codes, included both inpatient and outpatient events, and were inclusive of outpatient follow-up of at least 3 months.

Three of the 4 studies used the Mayo Clinic Total Joint Registry.^1,3,4 Hoxie and colleagues¹ reported an 11% rate of PE after HA performed for fracture (we excluded SA for fracture). As several other investigators have reported an association between trauma and increased risk for VTE, postoperative anticoagulation should be considered in this patient population (though it was not the focus of the present study).^6-8 Sperling and Cofield³ and Singh and colleagues⁷ reported on the risk for PE among SA patients at the Mayo Clinic. Sperling and Cofield³ included only those events that occurred within the first 7 days after surgery; Singh and colleagues⁷ included events out to 90 days after surgery. Sperling and Cofield³ reported a 0.17% PE rate; Singh and colleagues⁷ reported 0.6% PE and 0.1% DVT rates. Sperling and Cofield³ reported on 2885 SAs; Singh and colleagues⁷ reported on 4019 SAs from the same database. As it is unclear whether these 2 studies had complete information on all patients, underreporting may be an issue. Information was obtained through “clinic visits, medical records and/or standardized mailed and telephone-administered questionnaires.”⁷The fourth study, a prospective study of 100 patients by Willis and colleagues,⁴ had the best data on development of symptomatic PE after SA. The authors reported a 2% PE rate and a high (13%) DVT rate. Because US was not performed before the surgical procedures, the number of patients with new and existing DVT cases could not be determined. However, all PEs were new, and the 2% rate found there is similar to the 2.3% in our study. Therefore, we think these rates capture the data most accurately and avoid the underreporting that marks large databases.⁴Studies have identified various factors that increase the risk for VTE after SA. Singh and colleagues⁷ identified the risk factors of age over 70 years, female sex, higher BMI (25-29.9 kg/m²), CCI above 1, traumatic etiology, prior history of VTE, and HA. However, their use of univariate regression analysis may have confounded the effects—one factor may have become a surrogate for another (ie, trauma and HA, as most fractures treated with SA during the study period were treated with HA). Lyman and colleagues⁶ also found advanced age and trauma were associated with higher VTE risk, and reported prior history of cancer as a risk factor as well. Navarro and colleagues⁸ identified trauma as a risk factor, as in the other 2 studies.^6,7 Our data support prior history of VTE, higher BMI, and raised CCI as increasing the risk for VTE.

Other factors identified in the present study are use of GETA without interscalene nerve block, lower preoperative and postoperative Hb levels, diabetes, and revision SA. Because of the limited number of events, only ORs with and without limited control of confounders were performed. Just as in the study by Singh and colleagues,⁷ uncontrolled confounding could have occurred. A nerve block may be protective, as less postoperative pain may allow patients quicker mobilization and therapy. Diabetes may be a surrogate for other medical comorbidities, as reflected by the higher overall risk with raised CCI. Lower preoperative and postoperative Hb levels were associated with clotting and may be representative of patients with poorer overall health and more complicated surgical procedures (eg, revision SA). In an earlier study, we found increased risk for transfusions in revision SA relative to primary SA.¹¹ Lower preoperative Hb level correlated with development of VTE after lower extremity arthroplasty.¹² Postoperative use of aspirin was not found to significantly reduce the incidence of clotting, though this finding may have resulted from lack of power. Therefore, from the present data, there is nothing to conclude about the efficacy of aspirin in preventing thrombosis.

Our findings can be placed in the context of the Virchow triad. Specifically, 3 categories of factors are thought to contribute to thrombosis: hypercoagulability, hemodynamic stasis, and endothelial injury. In grouping factors, we identified prior thrombotic event and obesity as increasing hypercoagulability; revision SA, more comorbidities, lower Hb and Hct levels, diabetes, and GETA as increasing hemodynamic stasis; and revision SA (longer operating room times) as leading to stasis. More comorbidities can be associated with delayed postoperative ambulation, and diabetes and lower Hb and Hct levels can be surrogates for more comorbidities. Surgery performed with the patient under GETA without interscalene nerve block can lead to higher levels of pain and less early mobility.

The present findings have made us more aware of patients at risk for VTE, and we have lowered our threshold for evaluating them for potential clots. Before this study, we used warfarin or enoxaparin for anticoagulation in patients with a history of VTE or active cancer. We are continuing this protocol, but not with other patients. Patients with many comorbidities, lower preoperative Hb level, revision SA, high BMI, or diabetes are carefully monitored for clots early in the postoperative course. Our new threshold for these high-risk patients is to order diagnostic testing, including duplex US or CT angiography. Now, even mild oxygen requirements or mild tachycardia within postoperative week 1 typically prompt a study in these patients. We hope this increased awareness will limit the potential negative consequences associated with development of VTE. Given the present data, we do not think the simple presence of increased comorbidities, lower preoperative Hb, revision SA, high BMI or diabetes should rule out performing SA; rather, it should increase surgeons’ postoperative vigilance in evaluating for potential clots.

Limitations of our study include its retrospective nature and reliance on clinic chart review. Patients were not directly questioned about venous thrombus at follow-up, so all events may not have been captured. Although retrospective review has its drawbacks, it allows for accurate identification of events, even uncoded events. Therefore, more events are likely to be captured with this technique than with large database analyses using only coding information. We tried to identify as many cases as possible by reviewing all outpatient records (orthopedic, nonorthopedic), inpatient records, radiologic studies, and scanned outside records. Another limitation is that having a small number of VTE events limited our ability to perform a multivariate analysis, and uncontrolled confounding likely resulted. Only a very large multi-institutional study can capture enough events to allow a multivariate analysis. A third limitation is that the small number of events may have underpowered the study. Having more patients would have allowed other potential factors to be identified as being significantly associated with VTE. Last, as the study captured only symptomatic VTE events, it may have underreported VTE events. Given our complete review of the medical records, however, most clinically significant events likely were captured.

 

Conclusion

VTE after SA is rare. In our single-institution study, the symptomatic DVT rate was 0.9%, and the symptomatic PE rate was 2.3%. Risk factors associated with clotting included prior VTE, higher BMI, lower preoperative and postoperative Hb levels, raised CCI, diabetes, use of GETA without interscalene nerve block, and revision SA. Risk factors can be used to identify patients who may benefit from a more scrutinized postoperative evaluation and from increased surgeon awareness of the potential for VTE development. Rates of VTE can be used to counsel SA patients regarding overall surgical risks.

Am J Orthop. 2016;45(6):E379-E385. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Venous thromboembolism (VTE) after shoulder arthroplasty (SA) is relatively uncommon. Reported rates of VTE development are highly variable, ranging from 0.2% to 13% (pulmonary embolism [PE], 0.2%-10.8%; deep venous thrombosis [DVT], 0.1%-13%).^1-4 Sources of this variability include different methods of capturing cases (small clinical series vs large database studies, which capture mainly hospital readmissions), differences in defining or detecting VTE, and different patient populations (fracture vs osteoarthritis).^1-3 Most studies have also tried to identify factors associated with increased risk for VTE. Risk factors associated with development of VTE after SA include history of VTE, advanced age, prolonged operating room time, higher body mass index (BMI), trauma, history of cancer, female sex, and raised Charlson Comorbidity Index (CCI).^1-7 Limitations of clinical series include the smaller number of reporting institutions—a potential source of bias given regional variability.^1,3,4,7 Limitations of large state or national databases include capturing only events coded during inpatient admission and capturing readmissions for complications at the same institution. This underreporting may lead to very conservative estimates of VTE incidence.^2,5,6,8

In this study, we retrospectively identified all the SAs performed at a single institution over a 13-year period and evaluated the cases for development of VTE (DVT, PE). We hypothesized that the VTE rate would be lower than the very high rates reported by Hoxie and colleagues¹ and Willis and colleagues⁴ but higher than those reported for large state or national databases.^2,3 We also evaluated clotting risk factors, including many never analyzed before.

Materials and Methods

After obtaining Institutional Review Board approval for this study, we searched our database for all SAs performed at our institution between January 1999 and May 2012 and identified cases in which symptomatic VTE developed within the first 90 days after surgery. Charts were reviewed for information on medical history, surgical procedure, and in-hospital and out-of-hospital care within the 90-day postoperative period. We recorded data on symptomatic VTE (DVT, PE) as documented by lower or upper extremity duplex ultrasonography (US) or chest computed tomography (CT) angiography. There had been no routine screening of patients; duplex US or CT angiography was performed only if a patient was clinically symptomatic (leg swelling, leg pain, shortness of breath, tachycardia, chest pain) for a potential DVT or PE. For a patient who had repeat SAs on the same shoulder or bilateral SAs at different times, only the first procedure was included in the analysis. Arthroplasties performed for fracture were excluded.

Study data were collected and managed with REDCap (Research Electronic Data Capture) tools hosted at the University of Utah School of Medicine.⁹ Continuous and discrete data collected on medical history and postoperative course included BMI, age at surgery, preoperative hemoglobin (Hb) and hematocrit (Hct) levels, days in hospital, days until out of bed and days until ambulation (both documented in nursing and physical therapy notes), postoperative Hb and Hct levels, and CCI. Categorical data included sex, diagnosis (primary osteoarthritis, rotator cuff arthropathy, rheumatoid arthritis, failed hemiarthroplasty [HA], failed total SA [TSA], others), attending surgeon, procedure (TSA, HA, reverse TSA, revision SA), anesthesia (general endotracheal anesthesia [GETA] alone, interscalene nerve block alone, GETA plus block), prophylactic use of aspirin after surgery, presence of various medical comorbidities (diabetes, hypertension, cardiac disease, clotting disorders, cancer), hormone replacement therapy, family history of a clotting disorder, and VTE consequences (cardiac events, death).

Statistical Analysis

Descriptive statistics were calculated to summarize aspects of the surgical procedures, the study cohort’s demographics and medical histories, and the incidence of VTE. Logistic regression analysis was performed to explore the association between development of VTE (DVT, PE) and potential risk factors. Unadjusted odds ratios (ORs) were estimated for the risk factors of age, BMI, revision SA, CCI, prophylactic use of aspirin after surgery, preoperative history of VTE, preoperative and postoperative Hb and Hct levels, diabetes, anesthesia (GETA with and without interscalene nerve block), family history of a clotting disorder, days until out of bed, hormone replacement therapy, race, discharge home or to rehabilitation, distance traveled for surgery, hypertension, cardiac disease, cement use, and history of cancer. In addition, ORs were adjusted for age, BMI, and revision SA. For all statistical tests, significance was set at P < .05. All analyses were performed with SAS Version 9.3 (SAS Institute).

Results

We identified 533 SAs: 245 anatomical TSAs, 112 reverse TSAs, 92 HAs, and 84 revision SAs. Three different surgeons performed the procedures, and no patients were lost to follow-up within the first 90 days after surgery. Although SAs were performed for various diagnoses, more than 50% (274) of the SAs were for primary osteoarthritis; 97 were performed for rotator cuff arthropathy, 16 for rheumatoid arthritis, 43 for failed HA, 23 for failed TSA, and 79 for other diagnoses.

 

Of the 533 patients, 288 were female and 245 were male. Mean age at surgery was 65.2 years (range, 16-93 years). Mean (SD) BMI was 29.2 (6.4) kg/m². Mean (SD) preoperative Hb level was 13.7 (1.8) g/dL, and mean preoperative Hct level was 40.1% (4.8%). Mean (SD) length of hospital stay was 2.6 (1.5) days. Mean (SD) time before patients were out of bed was 1.1 (0.7) days. On postoperative day 1, mean Hb level was 11.1 (1.7) g/dL, and mean (SD) Hct level was 33.2% (4.8%). Mean (SD) CCI was 1.1 (0.9).

Anesthesia for the 533 patients consisted of GETA (209 patients, 39.0%), interscalene nerve block (2, 0.4%), or GETA with nerve block (314, 59.0%). After surgery, 125 patients (24.3%) received aspirin as prophylaxis. Diabetes was reported by 83 patients, hypertension by 286, cardiac disease by 74, a history of a clotting disorder by 2, a family history of a clotting disorder by 8, ongoing cancer by 4, a history of cancer by 67, and hormone replacement therapy by 104.

For the entire cohort of 533 patients, the symptomatic VTE rate was 2.6% (14 patients), the DVT rate was 0.9% (5), and the PE rate was 2.3% (12). Although VTE did not cause any deaths, there were 3 cardiac events.

Risk factors significantly associated with increased risk for VTE were raised CCI (OR, 1.858; 95% confidence interval [CI], 1.295–2.665), preoperative thrombotic event (OR, 5.532; 95% CI, 1.651–18.535), lower preoperative Hb level (OR, 0.705; 95% CI, 0.486–1.022), lower preoperative Hct level (OR, 0.877; 95% CI, 0.763–1.007), lower postoperative Hb level (OR, 0.720; 95% CI, 0.506–1.026), diabetes (OR, 5.646; 95% CI, 1.926–16.554), use of GETA without interscalene nerve block (OR, 0.111; 95% CI, 0.014–0.857), higher BMI (OR, 1.148; 95% CI, 1.062–1.241), and revision SA (OR, 5.777; 95% CI, 1.664–20.057).

All factors had significant adjusted ORs, whereas only BMI, revision SA, CCI, diabetes, and use of GETA without nerve block had significant unadjusted ORs (Tables 1, 2).

Discussion

VTE after SA is rare. We report an overall VTE incidence of 2.6%, with DVT at 0.9% and PE at 2.3%. These rates are similar to those reported in clinical series and significantly higher than those reported for large institutional or national databases.^2-7 Our results also support a previously reported trend: The ratio of PE to DVT for SA is significantly higher than historically reported ratios for lower extremity arthroplasty.^2,6-8 We have identified many VTE risk factors: raised CCI, preoperative thrombotic event, lower preoperative Hb and Hct levels, lower postoperative Hb level, diabetes, use of GETA without interscalene nerve block, higher BMI, and revision SA. Results of other studies support 3 findings (higher BMI, raised CCI, preoperative thrombotic event); new findings include correlation with Hb and Hct levels, diabetes, type of anesthesia, and revision SA.^6,7 Identification of these other factors may be useful in making treatment decisions in patients symptomatic after SA and in lowering the threshold for performing diagnostic tests in these patients at risk for VTE.

Reported rates of VTE after SA are highly variable, ranging from 0.2% to 13%.¹⁰ Our rationale for investigating VTE rates at a single institution was to estimate the rates that can be expected in a university-based practice and to determine whether these rates are high enough to warrant routine thromboprophylaxis. The rate variability seems to result in part from variability in the data sources. Most studies that have reported very low VTE rates typically used large state or national databases, which likely were subject to underreporting.

Lyman and colleagues⁶ found 0.5% DVT and 0.2% PE rates in a New York state hospital database, but only in-hospital immediate postoperative symptomatic complications were included; slightly delayed complications may have been missed. Farng and colleagues⁵ reported a 0.6% VTE rate, but only inpatient (immediate postoperative or readmission) events were included; all outpatient events were missed. Jameson and colleagues,² using a national database that included only cases involving inpatient treatment, reported 0% DVT and 0.2% PE rates, again missing outpatient events, and relying on appropriate coding to capture events. Using electronic health records from a large healthcare system, Navarro and colleagues⁸ queried for VTE cases and reported 0.5% DVT and 0.5% PE rates. The inclusiveness of their data source for the outcome of interest was potentially improved relative to national or statewide databases—and the resulting data reported in their study should reflect that improvement. However, the authors relied on ICD–9 (International Classification of Diseases, Ninth Revision) coding to screen for VTE events and excluded patients with prior VTE, preoperative prophylaxis (enoxaparin or warfarin), or follow-up of <90 days. As patients with prior VTE are those most at risk (present study OR, 6-7), excluding them significantly reduces the overall incidence of clotting reported.

Only 4 studies specifically used information drawn directly from physicians’ clinic notes, vs data retrieved (using code-based queries) from databases.^1,3,4,7 These studies may provide a better representation of the rate of VTE after SA, as they were not reliant on codes, included both inpatient and outpatient events, and were inclusive of outpatient follow-up of at least 3 months.

Three of the 4 studies used the Mayo Clinic Total Joint Registry.^1,3,4 Hoxie and colleagues¹ reported an 11% rate of PE after HA performed for fracture (we excluded SA for fracture). As several other investigators have reported an association between trauma and increased risk for VTE, postoperative anticoagulation should be considered in this patient population (though it was not the focus of the present study).^6-8 Sperling and Cofield³ and Singh and colleagues⁷ reported on the risk for PE among SA patients at the Mayo Clinic. Sperling and Cofield³ included only those events that occurred within the first 7 days after surgery; Singh and colleagues⁷ included events out to 90 days after surgery. Sperling and Cofield³ reported a 0.17% PE rate; Singh and colleagues⁷ reported 0.6% PE and 0.1% DVT rates. Sperling and Cofield³ reported on 2885 SAs; Singh and colleagues⁷ reported on 4019 SAs from the same database. As it is unclear whether these 2 studies had complete information on all patients, underreporting may be an issue. Information was obtained through “clinic visits, medical records and/or standardized mailed and telephone-administered questionnaires.”⁷The fourth study, a prospective study of 100 patients by Willis and colleagues,⁴ had the best data on development of symptomatic PE after SA. The authors reported a 2% PE rate and a high (13%) DVT rate. Because US was not performed before the surgical procedures, the number of patients with new and existing DVT cases could not be determined. However, all PEs were new, and the 2% rate found there is similar to the 2.3% in our study. Therefore, we think these rates capture the data most accurately and avoid the underreporting that marks large databases.⁴Studies have identified various factors that increase the risk for VTE after SA. Singh and colleagues⁷ identified the risk factors of age over 70 years, female sex, higher BMI (25-29.9 kg/m²), CCI above 1, traumatic etiology, prior history of VTE, and HA. However, their use of univariate regression analysis may have confounded the effects—one factor may have become a surrogate for another (ie, trauma and HA, as most fractures treated with SA during the study period were treated with HA). Lyman and colleagues⁶ also found advanced age and trauma were associated with higher VTE risk, and reported prior history of cancer as a risk factor as well. Navarro and colleagues⁸ identified trauma as a risk factor, as in the other 2 studies.^6,7 Our data support prior history of VTE, higher BMI, and raised CCI as increasing the risk for VTE.

Other factors identified in the present study are use of GETA without interscalene nerve block, lower preoperative and postoperative Hb levels, diabetes, and revision SA. Because of the limited number of events, only ORs with and without limited control of confounders were performed. Just as in the study by Singh and colleagues,⁷ uncontrolled confounding could have occurred. A nerve block may be protective, as less postoperative pain may allow patients quicker mobilization and therapy. Diabetes may be a surrogate for other medical comorbidities, as reflected by the higher overall risk with raised CCI. Lower preoperative and postoperative Hb levels were associated with clotting and may be representative of patients with poorer overall health and more complicated surgical procedures (eg, revision SA). In an earlier study, we found increased risk for transfusions in revision SA relative to primary SA.¹¹ Lower preoperative Hb level correlated with development of VTE after lower extremity arthroplasty.¹² Postoperative use of aspirin was not found to significantly reduce the incidence of clotting, though this finding may have resulted from lack of power. Therefore, from the present data, there is nothing to conclude about the efficacy of aspirin in preventing thrombosis.

Our findings can be placed in the context of the Virchow triad. Specifically, 3 categories of factors are thought to contribute to thrombosis: hypercoagulability, hemodynamic stasis, and endothelial injury. In grouping factors, we identified prior thrombotic event and obesity as increasing hypercoagulability; revision SA, more comorbidities, lower Hb and Hct levels, diabetes, and GETA as increasing hemodynamic stasis; and revision SA (longer operating room times) as leading to stasis. More comorbidities can be associated with delayed postoperative ambulation, and diabetes and lower Hb and Hct levels can be surrogates for more comorbidities. Surgery performed with the patient under GETA without interscalene nerve block can lead to higher levels of pain and less early mobility.

The present findings have made us more aware of patients at risk for VTE, and we have lowered our threshold for evaluating them for potential clots. Before this study, we used warfarin or enoxaparin for anticoagulation in patients with a history of VTE or active cancer. We are continuing this protocol, but not with other patients. Patients with many comorbidities, lower preoperative Hb level, revision SA, high BMI, or diabetes are carefully monitored for clots early in the postoperative course. Our new threshold for these high-risk patients is to order diagnostic testing, including duplex US or CT angiography. Now, even mild oxygen requirements or mild tachycardia within postoperative week 1 typically prompt a study in these patients. We hope this increased awareness will limit the potential negative consequences associated with development of VTE. Given the present data, we do not think the simple presence of increased comorbidities, lower preoperative Hb, revision SA, high BMI or diabetes should rule out performing SA; rather, it should increase surgeons’ postoperative vigilance in evaluating for potential clots.

Limitations of our study include its retrospective nature and reliance on clinic chart review. Patients were not directly questioned about venous thrombus at follow-up, so all events may not have been captured. Although retrospective review has its drawbacks, it allows for accurate identification of events, even uncoded events. Therefore, more events are likely to be captured with this technique than with large database analyses using only coding information. We tried to identify as many cases as possible by reviewing all outpatient records (orthopedic, nonorthopedic), inpatient records, radiologic studies, and scanned outside records. Another limitation is that having a small number of VTE events limited our ability to perform a multivariate analysis, and uncontrolled confounding likely resulted. Only a very large multi-institutional study can capture enough events to allow a multivariate analysis. A third limitation is that the small number of events may have underpowered the study. Having more patients would have allowed other potential factors to be identified as being significantly associated with VTE. Last, as the study captured only symptomatic VTE events, it may have underreported VTE events. Given our complete review of the medical records, however, most clinically significant events likely were captured.

 

Conclusion

VTE after SA is rare. In our single-institution study, the symptomatic DVT rate was 0.9%, and the symptomatic PE rate was 2.3%. Risk factors associated with clotting included prior VTE, higher BMI, lower preoperative and postoperative Hb levels, raised CCI, diabetes, use of GETA without interscalene nerve block, and revision SA. Risk factors can be used to identify patients who may benefit from a more scrutinized postoperative evaluation and from increased surgeon awareness of the potential for VTE development. Rates of VTE can be used to counsel SA patients regarding overall surgical risks.

Am J Orthop. 2016;45(6):E379-E385. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

Venous thromboembolism (VTE) after shoulder arthroplasty (SA) is relatively uncommon. Reported rates of VTE development are highly variable, ranging from 0.2% to 13% (pulmonary embolism [PE], 0.2%-10.8%; deep venous thrombosis [DVT], 0.1%-13%).^1-4 Sources of this variability include different methods of capturing cases (small clinical series vs large database studies, which capture mainly hospital readmissions), differences in defining or detecting VTE, and different patient populations (fracture vs osteoarthritis).^1-3 Most studies have also tried to identify factors associated with increased risk for VTE. Risk factors associated with development of VTE after SA include history of VTE, advanced age, prolonged operating room time, higher body mass index (BMI), trauma, history of cancer, female sex, and raised Charlson Comorbidity Index (CCI).^1-7 Limitations of clinical series include the smaller number of reporting institutions—a potential source of bias given regional variability.^1,3,4,7 Limitations of large state or national databases include capturing only events coded during inpatient admission and capturing readmissions for complications at the same institution. This underreporting may lead to very conservative estimates of VTE incidence.^2,5,6,8

In this study, we retrospectively identified all the SAs performed at a single institution over a 13-year period and evaluated the cases for development of VTE (DVT, PE). We hypothesized that the VTE rate would be lower than the very high rates reported by Hoxie and colleagues¹ and Willis and colleagues⁴ but higher than those reported for large state or national databases.^2,3 We also evaluated clotting risk factors, including many never analyzed before.

Materials and Methods

After obtaining Institutional Review Board approval for this study, we searched our database for all SAs performed at our institution between January 1999 and May 2012 and identified cases in which symptomatic VTE developed within the first 90 days after surgery. Charts were reviewed for information on medical history, surgical procedure, and in-hospital and out-of-hospital care within the 90-day postoperative period. We recorded data on symptomatic VTE (DVT, PE) as documented by lower or upper extremity duplex ultrasonography (US) or chest computed tomography (CT) angiography. There had been no routine screening of patients; duplex US or CT angiography was performed only if a patient was clinically symptomatic (leg swelling, leg pain, shortness of breath, tachycardia, chest pain) for a potential DVT or PE. For a patient who had repeat SAs on the same shoulder or bilateral SAs at different times, only the first procedure was included in the analysis. Arthroplasties performed for fracture were excluded.

Study data were collected and managed with REDCap (Research Electronic Data Capture) tools hosted at the University of Utah School of Medicine.⁹ Continuous and discrete data collected on medical history and postoperative course included BMI, age at surgery, preoperative hemoglobin (Hb) and hematocrit (Hct) levels, days in hospital, days until out of bed and days until ambulation (both documented in nursing and physical therapy notes), postoperative Hb and Hct levels, and CCI. Categorical data included sex, diagnosis (primary osteoarthritis, rotator cuff arthropathy, rheumatoid arthritis, failed hemiarthroplasty [HA], failed total SA [TSA], others), attending surgeon, procedure (TSA, HA, reverse TSA, revision SA), anesthesia (general endotracheal anesthesia [GETA] alone, interscalene nerve block alone, GETA plus block), prophylactic use of aspirin after surgery, presence of various medical comorbidities (diabetes, hypertension, cardiac disease, clotting disorders, cancer), hormone replacement therapy, family history of a clotting disorder, and VTE consequences (cardiac events, death).

Statistical Analysis

Descriptive statistics were calculated to summarize aspects of the surgical procedures, the study cohort’s demographics and medical histories, and the incidence of VTE. Logistic regression analysis was performed to explore the association between development of VTE (DVT, PE) and potential risk factors. Unadjusted odds ratios (ORs) were estimated for the risk factors of age, BMI, revision SA, CCI, prophylactic use of aspirin after surgery, preoperative history of VTE, preoperative and postoperative Hb and Hct levels, diabetes, anesthesia (GETA with and without interscalene nerve block), family history of a clotting disorder, days until out of bed, hormone replacement therapy, race, discharge home or to rehabilitation, distance traveled for surgery, hypertension, cardiac disease, cement use, and history of cancer. In addition, ORs were adjusted for age, BMI, and revision SA. For all statistical tests, significance was set at P < .05. All analyses were performed with SAS Version 9.3 (SAS Institute).

Results

We identified 533 SAs: 245 anatomical TSAs, 112 reverse TSAs, 92 HAs, and 84 revision SAs. Three different surgeons performed the procedures, and no patients were lost to follow-up within the first 90 days after surgery. Although SAs were performed for various diagnoses, more than 50% (274) of the SAs were for primary osteoarthritis; 97 were performed for rotator cuff arthropathy, 16 for rheumatoid arthritis, 43 for failed HA, 23 for failed TSA, and 79 for other diagnoses.

 

Of the 533 patients, 288 were female and 245 were male. Mean age at surgery was 65.2 years (range, 16-93 years). Mean (SD) BMI was 29.2 (6.4) kg/m². Mean (SD) preoperative Hb level was 13.7 (1.8) g/dL, and mean preoperative Hct level was 40.1% (4.8%). Mean (SD) length of hospital stay was 2.6 (1.5) days. Mean (SD) time before patients were out of bed was 1.1 (0.7) days. On postoperative day 1, mean Hb level was 11.1 (1.7) g/dL, and mean (SD) Hct level was 33.2% (4.8%). Mean (SD) CCI was 1.1 (0.9).

Anesthesia for the 533 patients consisted of GETA (209 patients, 39.0%), interscalene nerve block (2, 0.4%), or GETA with nerve block (314, 59.0%). After surgery, 125 patients (24.3%) received aspirin as prophylaxis. Diabetes was reported by 83 patients, hypertension by 286, cardiac disease by 74, a history of a clotting disorder by 2, a family history of a clotting disorder by 8, ongoing cancer by 4, a history of cancer by 67, and hormone replacement therapy by 104.

For the entire cohort of 533 patients, the symptomatic VTE rate was 2.6% (14 patients), the DVT rate was 0.9% (5), and the PE rate was 2.3% (12). Although VTE did not cause any deaths, there were 3 cardiac events.

Risk factors significantly associated with increased risk for VTE were raised CCI (OR, 1.858; 95% confidence interval [CI], 1.295–2.665), preoperative thrombotic event (OR, 5.532; 95% CI, 1.651–18.535), lower preoperative Hb level (OR, 0.705; 95% CI, 0.486–1.022), lower preoperative Hct level (OR, 0.877; 95% CI, 0.763–1.007), lower postoperative Hb level (OR, 0.720; 95% CI, 0.506–1.026), diabetes (OR, 5.646; 95% CI, 1.926–16.554), use of GETA without interscalene nerve block (OR, 0.111; 95% CI, 0.014–0.857), higher BMI (OR, 1.148; 95% CI, 1.062–1.241), and revision SA (OR, 5.777; 95% CI, 1.664–20.057).

All factors had significant adjusted ORs, whereas only BMI, revision SA, CCI, diabetes, and use of GETA without nerve block had significant unadjusted ORs (Tables 1, 2).

Discussion

VTE after SA is rare. We report an overall VTE incidence of 2.6%, with DVT at 0.9% and PE at 2.3%. These rates are similar to those reported in clinical series and significantly higher than those reported for large institutional or national databases.^2-7 Our results also support a previously reported trend: The ratio of PE to DVT for SA is significantly higher than historically reported ratios for lower extremity arthroplasty.^2,6-8 We have identified many VTE risk factors: raised CCI, preoperative thrombotic event, lower preoperative Hb and Hct levels, lower postoperative Hb level, diabetes, use of GETA without interscalene nerve block, higher BMI, and revision SA. Results of other studies support 3 findings (higher BMI, raised CCI, preoperative thrombotic event); new findings include correlation with Hb and Hct levels, diabetes, type of anesthesia, and revision SA.^6,7 Identification of these other factors may be useful in making treatment decisions in patients symptomatic after SA and in lowering the threshold for performing diagnostic tests in these patients at risk for VTE.

Reported rates of VTE after SA are highly variable, ranging from 0.2% to 13%.¹⁰ Our rationale for investigating VTE rates at a single institution was to estimate the rates that can be expected in a university-based practice and to determine whether these rates are high enough to warrant routine thromboprophylaxis. The rate variability seems to result in part from variability in the data sources. Most studies that have reported very low VTE rates typically used large state or national databases, which likely were subject to underreporting.

Lyman and colleagues⁶ found 0.5% DVT and 0.2% PE rates in a New York state hospital database, but only in-hospital immediate postoperative symptomatic complications were included; slightly delayed complications may have been missed. Farng and colleagues⁵ reported a 0.6% VTE rate, but only inpatient (immediate postoperative or readmission) events were included; all outpatient events were missed. Jameson and colleagues,² using a national database that included only cases involving inpatient treatment, reported 0% DVT and 0.2% PE rates, again missing outpatient events, and relying on appropriate coding to capture events. Using electronic health records from a large healthcare system, Navarro and colleagues⁸ queried for VTE cases and reported 0.5% DVT and 0.5% PE rates. The inclusiveness of their data source for the outcome of interest was potentially improved relative to national or statewide databases—and the resulting data reported in their study should reflect that improvement. However, the authors relied on ICD–9 (International Classification of Diseases, Ninth Revision) coding to screen for VTE events and excluded patients with prior VTE, preoperative prophylaxis (enoxaparin or warfarin), or follow-up of <90 days. As patients with prior VTE are those most at risk (present study OR, 6-7), excluding them significantly reduces the overall incidence of clotting reported.

Only 4 studies specifically used information drawn directly from physicians’ clinic notes, vs data retrieved (using code-based queries) from databases.^1,3,4,7 These studies may provide a better representation of the rate of VTE after SA, as they were not reliant on codes, included both inpatient and outpatient events, and were inclusive of outpatient follow-up of at least 3 months.

Three of the 4 studies used the Mayo Clinic Total Joint Registry.^1,3,4 Hoxie and colleagues¹ reported an 11% rate of PE after HA performed for fracture (we excluded SA for fracture). As several other investigators have reported an association between trauma and increased risk for VTE, postoperative anticoagulation should be considered in this patient population (though it was not the focus of the present study).^6-8 Sperling and Cofield³ and Singh and colleagues⁷ reported on the risk for PE among SA patients at the Mayo Clinic. Sperling and Cofield³ included only those events that occurred within the first 7 days after surgery; Singh and colleagues⁷ included events out to 90 days after surgery. Sperling and Cofield³ reported a 0.17% PE rate; Singh and colleagues⁷ reported 0.6% PE and 0.1% DVT rates. Sperling and Cofield³ reported on 2885 SAs; Singh and colleagues⁷ reported on 4019 SAs from the same database. As it is unclear whether these 2 studies had complete information on all patients, underreporting may be an issue. Information was obtained through “clinic visits, medical records and/or standardized mailed and telephone-administered questionnaires.”⁷The fourth study, a prospective study of 100 patients by Willis and colleagues,⁴ had the best data on development of symptomatic PE after SA. The authors reported a 2% PE rate and a high (13%) DVT rate. Because US was not performed before the surgical procedures, the number of patients with new and existing DVT cases could not be determined. However, all PEs were new, and the 2% rate found there is similar to the 2.3% in our study. Therefore, we think these rates capture the data most accurately and avoid the underreporting that marks large databases.⁴Studies have identified various factors that increase the risk for VTE after SA. Singh and colleagues⁷ identified the risk factors of age over 70 years, female sex, higher BMI (25-29.9 kg/m²), CCI above 1, traumatic etiology, prior history of VTE, and HA. However, their use of univariate regression analysis may have confounded the effects—one factor may have become a surrogate for another (ie, trauma and HA, as most fractures treated with SA during the study period were treated with HA). Lyman and colleagues⁶ also found advanced age and trauma were associated with higher VTE risk, and reported prior history of cancer as a risk factor as well. Navarro and colleagues⁸ identified trauma as a risk factor, as in the other 2 studies.^6,7 Our data support prior history of VTE, higher BMI, and raised CCI as increasing the risk for VTE.

Other factors identified in the present study are use of GETA without interscalene nerve block, lower preoperative and postoperative Hb levels, diabetes, and revision SA. Because of the limited number of events, only ORs with and without limited control of confounders were performed. Just as in the study by Singh and colleagues,⁷ uncontrolled confounding could have occurred. A nerve block may be protective, as less postoperative pain may allow patients quicker mobilization and therapy. Diabetes may be a surrogate for other medical comorbidities, as reflected by the higher overall risk with raised CCI. Lower preoperative and postoperative Hb levels were associated with clotting and may be representative of patients with poorer overall health and more complicated surgical procedures (eg, revision SA). In an earlier study, we found increased risk for transfusions in revision SA relative to primary SA.¹¹ Lower preoperative Hb level correlated with development of VTE after lower extremity arthroplasty.¹² Postoperative use of aspirin was not found to significantly reduce the incidence of clotting, though this finding may have resulted from lack of power. Therefore, from the present data, there is nothing to conclude about the efficacy of aspirin in preventing thrombosis.

Our findings can be placed in the context of the Virchow triad. Specifically, 3 categories of factors are thought to contribute to thrombosis: hypercoagulability, hemodynamic stasis, and endothelial injury. In grouping factors, we identified prior thrombotic event and obesity as increasing hypercoagulability; revision SA, more comorbidities, lower Hb and Hct levels, diabetes, and GETA as increasing hemodynamic stasis; and revision SA (longer operating room times) as leading to stasis. More comorbidities can be associated with delayed postoperative ambulation, and diabetes and lower Hb and Hct levels can be surrogates for more comorbidities. Surgery performed with the patient under GETA without interscalene nerve block can lead to higher levels of pain and less early mobility.

The present findings have made us more aware of patients at risk for VTE, and we have lowered our threshold for evaluating them for potential clots. Before this study, we used warfarin or enoxaparin for anticoagulation in patients with a history of VTE or active cancer. We are continuing this protocol, but not with other patients. Patients with many comorbidities, lower preoperative Hb level, revision SA, high BMI, or diabetes are carefully monitored for clots early in the postoperative course. Our new threshold for these high-risk patients is to order diagnostic testing, including duplex US or CT angiography. Now, even mild oxygen requirements or mild tachycardia within postoperative week 1 typically prompt a study in these patients. We hope this increased awareness will limit the potential negative consequences associated with development of VTE. Given the present data, we do not think the simple presence of increased comorbidities, lower preoperative Hb, revision SA, high BMI or diabetes should rule out performing SA; rather, it should increase surgeons’ postoperative vigilance in evaluating for potential clots.

Limitations of our study include its retrospective nature and reliance on clinic chart review. Patients were not directly questioned about venous thrombus at follow-up, so all events may not have been captured. Although retrospective review has its drawbacks, it allows for accurate identification of events, even uncoded events. Therefore, more events are likely to be captured with this technique than with large database analyses using only coding information. We tried to identify as many cases as possible by reviewing all outpatient records (orthopedic, nonorthopedic), inpatient records, radiologic studies, and scanned outside records. Another limitation is that having a small number of VTE events limited our ability to perform a multivariate analysis, and uncontrolled confounding likely resulted. Only a very large multi-institutional study can capture enough events to allow a multivariate analysis. A third limitation is that the small number of events may have underpowered the study. Having more patients would have allowed other potential factors to be identified as being significantly associated with VTE. Last, as the study captured only symptomatic VTE events, it may have underreported VTE events. Given our complete review of the medical records, however, most clinically significant events likely were captured.

 

Conclusion

VTE after SA is rare. In our single-institution study, the symptomatic DVT rate was 0.9%, and the symptomatic PE rate was 2.3%. Risk factors associated with clotting included prior VTE, higher BMI, lower preoperative and postoperative Hb levels, raised CCI, diabetes, use of GETA without interscalene nerve block, and revision SA. Risk factors can be used to identify patients who may benefit from a more scrutinized postoperative evaluation and from increased surgeon awareness of the potential for VTE development. Rates of VTE can be used to counsel SA patients regarding overall surgical risks.

Am J Orthop. 2016;45(6):E379-E385. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

End-stage osteoarthritis of the hip is a debilitating disease that is reliably treated with total hip arthroplasty (THA).¹ Up to 35% of patients who undergo THA eventually require contralateral THA.^2,3 In patients who present with advanced bilateral disease and undergo unilateral THA, the risk of ultimately requiring a contralateral procedure is as high as 97%.^3-6 In patients with bilateral hip disease, function is not fully optimized until both hips have been replaced, particularly in the setting of fixed flexion contractures.^7-9 Naturally, there has been some interest in simultaneous bilateral THAs for select patients.

The potential benefits of bilateral THAs over staged procedures include faster overall rehabilitation, exposure to a single anesthetic, reduced hospital length of stay (LOS), and cost savings.^10-12 However, opinion on recommending bilateral THAs is mixed. Although bilateral procedures historically have been fraught with perioperative complications,^13,14 advances in surgical and anesthetic techniques have led to improved outcomes.¹⁵ Whether surgical approach is a factor in these outcomes is unclear.

The popularity of the direct anterior (DA) approach for THA has increased in recent years.¹⁶ Although the relative advantages of various approaches remain in debate, one potential benefit of the DA approach is supine positioning, which allows simultaneous bilateral THAs to be performed without the need for repositioning before proceeding with the contralateral side. However, simultaneous bilateral THAs performed through the DA approach and those performed through other surgical approaches are lacking in comparative outcomes data.¹⁷In this study, we evaluated operative times, transfusion requirements, hospital discharge data, and 90-day complication rates in patients who had simultaneous bilateral THAs through either the DA approach or the posterior approach.

Methods

Study Design

This single-center study was conducted at the Mayo Clinic in Rochester, Minnesota. After obtaining approval from our Institutional Review Board, we performed a retrospective cohort analysis. We used our institution’s total joint registry to identify all patients who underwent simultaneous bilateral THAs through either the DA approach or the posterior approach. The first bilateral THAs to use the DA approach at our institution were performed in 2012. To ensure that the DA and posterior groups’ perioperative management would be similar, we included only cases performed between 2012 and 2014.

There were 19 patients in the DA group and 21 in the posterior group. The groups were similar in mean age (54 vs 54 years; P = .90), sex (73% vs 57% males; P = .33), body mass index (BMI; 25 vs 28 kg/m²; P = .38), preoperative hemoglobin level (14.3 vs 14.0 g/dL; P = .37), preoperative diagnosis (71.1% vs 78.6% degenerative joint disease; P = .75), and American Society of Anesthesiologists (ASA) score (1.9 vs 2.0; P = .63) (Table 1).

All patients had clinical follow-up of at least 90 days.

Patient Care

All cases were performed by 1 of 3 dedicated arthroplasty surgeons (Dr. Taunton, Dr. Sierra, Dr. Trousdale). Dr. Taunton exclusively uses the DA approach, and Dr. Sierra and Dr. Trousdale exclusively use the posterior approach. Patients in both groups received preoperative medical clearance and attended the same preoperative education class.

Patients in the DA group were positioned supine on an orthopedic table that allows hyperextension and adduction of the operative leg. Both hips were prepared and draped simultaneously. The most symptomatic hip was operated on first, with a sterile drape covering the contralateral hip. Between hips, fluoroscopy was moved to the other side of the operative suite, but no changes in positioning or preparation were necessary. A deep drain was placed on each side, and then was removed the morning of postoperative day 1. The same set of instruments was used on both sides.

Patients in the posterior group were positioned lateral on a regular operative table with hip rests. The most symptomatic hip was operated on first. After wound closure and dressing application, the patient was flipped to allow access to the contralateral hip and was prepared and draped again. The same instruments were used on each side. Drains were not used.

All patients received the same comprehensive multimodal pain management, which combined general and epidural anesthesia (remaining in place until postoperative day 2) and included an oral pain regimen of scheduled acetaminophen and as-needed tramadol and oxycodone. In all cases, intraoperative blood salvage and intravenous tranexamic acid (1 g at time of incision on first hip, 1 g at wound closure on second hip) were used. Preoperative autologous blood donation was not used. For deep vein thrombosis prophylaxis, patients were treated with bilateral sequential compression devices while hospitalized, but chemoprophylaxis was different between groups. Patients in the DA group received prophylactic low-molecular-weight heparin for 10 days, followed by twice-daily aspirin (325 mg) for 4 weeks. Patients in the posterior group received warfarin (goal international normalized ratio, 1.7-2.2) for 3 weeks, followed by twice-daily aspirin (325 mg) for 3 weeks. The decision to transfuse allogenic red blood cells was made by the treating surgeon, based on standardized hospital protocols, wherein patients are transfused for hemoglobin levels under 7.0 g/dL, or for hemoglobin levels less than 8.0 g/dL in the presence of persistent symptoms. All patients received care on an orthopedic specialty floor and were assisted by the same physical therapists. Discharge disposition was coordinated with the same group of social workers.

Two to 3 months after surgery, patients returned for routine examination and radiographs. All patients were followed up for at least 90 days.

 

Statistical Analysis

All outcomes were analyzed with appropriate summary statistics. Chi-square tests or logistic regression analyses (for categorical outcomes) were used to compare baseline covariates with perioperative outcomes, and 2-sample tests or Wilcoxon rank-sum tests were used to compare outcomes measured on a continuous scale. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated as appropriate. Operative time was calculated by adding time from incision to wound closure for both hips (room turnover time between hips was not included). Anesthesia time was defined as total time patients were in the operating room. All statistical tests were 2-sided, and the threshold for statistical significance was set at α = 0.05.

Results

Compared with patients who underwent simultaneous bilateral THAs through the posterior approach, patients who underwent simultaneous bilateral THAs through the DA approach had longer mean operative times (153 vs 106 min; P < .001) and anesthesia times (257 vs 221 min; P = .007). The 2 groups’ hospital stays were similar in length (3.1 vs 3.5 days; P = .31), but patients in the DA group were more likely to be discharged home (100.0% vs 71.4%; P = .02) (Table 2).

Discharge location was not associated with sex (OR, 1.08; 95% CI, 0.22-5.17; P = .99), age 60 years or older (OR, 0.65; 95% CI, 0.07-6.41; P = .99), hospital LOS of 4 days or more (OR, 1.05; 95% CI, 0.17-6.60; P = .99), BMI of 30 kg/m² or higher (OR, 1.04; 95% CI, 0.17-6.60; P = .99), or ASA score of 3 (OR, 0.65; 95% CI, 0.07-6.41; P = .99) (Table 3).

Patients in the DA group were more likely to have sufficient intraoperative blood salvage for autologous transfusion (89.5% vs 57.1%; OR, 6.4; 95% CI, 1.16-34.94; P = .03) (Table 3) and received more mean units of salvaged autologous blood (1.4 vs 0.5; P = .003) (Table 2). Allogenic blood was not given to any patients in the DA group, but 3 patients in the posterior group (14.3%) required allogenic blood transfusion (P = .23) (Table 2). Salvaged autologous and allogenic blood transfusion was not associated with sex, age 60 years or older, or hospital LOS of 4 days or more (Table 3). The groups’ mean hemoglobin levels, measured the morning of postoperative day 1, were similar: 10.6 g/dL (range, 8.5-12.4 g/dL) for the DA group and 10.3 g/dL (range 8.6-12.3 g/dL) for the posterior group (Table 2).

In-hospital complications were uncommon in both groups (5% vs 14%; P = .61) (Table 2). One patient in the posterior group sustained a unilateral dislocation the day of surgery, and closed reduction was required; other complications (1 ileus, 2 tachyarrhythmias) did not require intervention. Ninety-day complications were also rare; 1 patient in the posterior group developed a hematoma with wound drainage, and this was successfully managed conservatively. There were no reoperations or readmissions in either group (Table 2).

Discussion

Although bilateral procedures account for less than 1% of THAs in the United States,¹¹ debate about their role in patients with severe bilateral hip disease continues. The potential benefits of a single episode of care must be weighed against the slightly increased risk for systemic complications.^7,10-15 Recent innovations in perioperative management have been shown to minimize complications,¹⁵ but it is unclear whether surgical approach affects perioperative outcomes. Our goals in this study were to evaluate operative times, transfusion requirements, hospital discharge data, and 90-day complication rates in patients who underwent simultaneous bilateral THAs through either the DA approach or the posterior approach.

Patients in our DA group had longer operative and anesthesia times. Other studies have found longer operative times for the DA approach relative to the posterior approach in unilateral THAs.¹⁸ One potential benefit of the DA approach in the setting of simultaneous bilateral THAs is the ability to prepare and drape both sides before surgery and thereby keep the interruption between hips to a minimum. In the present study, however, time saved during turnover between hips was overshadowed by the time added for each THA.

Although it was uncommon for complications to occur within 90 days after surgery in this study, many patients are needed to fully investigate these rare occurrences. Because of inherent selection bias, these risks are difficult to directly compare in patients who undergo unilateral procedures. Although small studies have failed to clarify the issue,^7,19,20 a recent review of the almost 20,000 bilateral THA cases in the US Nationwide Inpatient Sample database found that bilateral (vs unilateral) THAs were associated with increased risk of local and systemic complications.¹¹ Therefore, bilateral THAs should be reserved for select cases, with attention given to excluding patients with preexisting cardiopulmonary disease and providing appropriate preoperative counseling.

Most studies have reported a higher transfusion rate in bilateral THAs relative to staged procedures.^7,21-23 Allogenic blood transfusion leads to immune suppression, coagulopathy, and other systemic effects in general, and has been specifically associated with infection in patients who undergo total joint arthroplasty.^24-29 Parvizi and colleagues¹⁷ reported reduced blood loss and fewer blood transfusions in patients who had simultaneous bilateral THAs through the DA approach, compared with the direct lateral approach. Patients in our DA group received more salvaged autologous blood, which we suppose was a function of longer operative times. However, postoperative hemoglobin levels and allogenic blood transfusion rates were statistically similar between the 2 groups. It is important to consider the increased risk of required allogenic blood transfusion associated with simultaneous bilateral THAs, but it is not fully clear if this risk is lower in THAs performed through the DA approach relative to other approaches. In our experience, the required transfusion risk is limited in DA and posterior approaches with use of contemporary perioperative blood management strategies.

Although hospital LOS is longer with simultaneous bilateral THAs than with unilateral THAs, historically it is shorter than the combined LOS of staged bilateral THAs.²⁰ Patients in our study had a relatively short LOS after bilateral THAs, and there was no difference in LOS between groups. However, patients were more likely to be discharged home after bilateral THAs through the DA approach vs the posterior approach. Although discharge location was not affected by age, sex, ASA score, or LOS, unrecognized social factors unrelated to surgical approach likely influenced this finding.

This study should be interpreted in light of important limitations. Foremost, although data were prospectively collected, we examined them retrospectively. Thus, it is possible there may be unaccounted for differences between our DA and posterior THA groups. For example, the DA and posterior approaches were used by different surgeons with differing experience, technique, and preferences, all of which could have affected outcomes. Furthermore, our sample was relatively small (simultaneous bilateral THAs are performed relatively infrequently). Last, although anesthesia, pain management, blood conservation, and physical therapy were similar for the 2 groups, there was no standardized protocol for determining eligibility for simultaneous bilateral THAs.

In conclusion, we found that simultaneous bilateral THAs can be safely performed through either the DA approach or the posterior approach. Although the transition between hips is shorter with the DA approach, this time savings is overshadowed by the increased duration of each procedure. Transfusion rates are low in both groups, and in-hospital and 90-day complications are quite rare. Furthermore, patients can routinely be discharged home without elevating readmission rates. We will continue to perform simultaneous bilateral THAs through the DA approach or the posterior approach, according to surgeon preference.

Am J Orthop. 2016;45(6):E373-E378. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

End-stage osteoarthritis of the hip is a debilitating disease that is reliably treated with total hip arthroplasty (THA).¹ Up to 35% of patients who undergo THA eventually require contralateral THA.^2,3 In patients who present with advanced bilateral disease and undergo unilateral THA, the risk of ultimately requiring a contralateral procedure is as high as 97%.^3-6 In patients with bilateral hip disease, function is not fully optimized until both hips have been replaced, particularly in the setting of fixed flexion contractures.^7-9 Naturally, there has been some interest in simultaneous bilateral THAs for select patients.

The potential benefits of bilateral THAs over staged procedures include faster overall rehabilitation, exposure to a single anesthetic, reduced hospital length of stay (LOS), and cost savings.^10-12 However, opinion on recommending bilateral THAs is mixed. Although bilateral procedures historically have been fraught with perioperative complications,^13,14 advances in surgical and anesthetic techniques have led to improved outcomes.¹⁵ Whether surgical approach is a factor in these outcomes is unclear.

The popularity of the direct anterior (DA) approach for THA has increased in recent years.¹⁶ Although the relative advantages of various approaches remain in debate, one potential benefit of the DA approach is supine positioning, which allows simultaneous bilateral THAs to be performed without the need for repositioning before proceeding with the contralateral side. However, simultaneous bilateral THAs performed through the DA approach and those performed through other surgical approaches are lacking in comparative outcomes data.¹⁷In this study, we evaluated operative times, transfusion requirements, hospital discharge data, and 90-day complication rates in patients who had simultaneous bilateral THAs through either the DA approach or the posterior approach.

Methods

Study Design

This single-center study was conducted at the Mayo Clinic in Rochester, Minnesota. After obtaining approval from our Institutional Review Board, we performed a retrospective cohort analysis. We used our institution’s total joint registry to identify all patients who underwent simultaneous bilateral THAs through either the DA approach or the posterior approach. The first bilateral THAs to use the DA approach at our institution were performed in 2012. To ensure that the DA and posterior groups’ perioperative management would be similar, we included only cases performed between 2012 and 2014.

There were 19 patients in the DA group and 21 in the posterior group. The groups were similar in mean age (54 vs 54 years; P = .90), sex (73% vs 57% males; P = .33), body mass index (BMI; 25 vs 28 kg/m²; P = .38), preoperative hemoglobin level (14.3 vs 14.0 g/dL; P = .37), preoperative diagnosis (71.1% vs 78.6% degenerative joint disease; P = .75), and American Society of Anesthesiologists (ASA) score (1.9 vs 2.0; P = .63) (Table 1).

All patients had clinical follow-up of at least 90 days.

Patient Care

All cases were performed by 1 of 3 dedicated arthroplasty surgeons (Dr. Taunton, Dr. Sierra, Dr. Trousdale). Dr. Taunton exclusively uses the DA approach, and Dr. Sierra and Dr. Trousdale exclusively use the posterior approach. Patients in both groups received preoperative medical clearance and attended the same preoperative education class.

Patients in the DA group were positioned supine on an orthopedic table that allows hyperextension and adduction of the operative leg. Both hips were prepared and draped simultaneously. The most symptomatic hip was operated on first, with a sterile drape covering the contralateral hip. Between hips, fluoroscopy was moved to the other side of the operative suite, but no changes in positioning or preparation were necessary. A deep drain was placed on each side, and then was removed the morning of postoperative day 1. The same set of instruments was used on both sides.

Patients in the posterior group were positioned lateral on a regular operative table with hip rests. The most symptomatic hip was operated on first. After wound closure and dressing application, the patient was flipped to allow access to the contralateral hip and was prepared and draped again. The same instruments were used on each side. Drains were not used.

All patients received the same comprehensive multimodal pain management, which combined general and epidural anesthesia (remaining in place until postoperative day 2) and included an oral pain regimen of scheduled acetaminophen and as-needed tramadol and oxycodone. In all cases, intraoperative blood salvage and intravenous tranexamic acid (1 g at time of incision on first hip, 1 g at wound closure on second hip) were used. Preoperative autologous blood donation was not used. For deep vein thrombosis prophylaxis, patients were treated with bilateral sequential compression devices while hospitalized, but chemoprophylaxis was different between groups. Patients in the DA group received prophylactic low-molecular-weight heparin for 10 days, followed by twice-daily aspirin (325 mg) for 4 weeks. Patients in the posterior group received warfarin (goal international normalized ratio, 1.7-2.2) for 3 weeks, followed by twice-daily aspirin (325 mg) for 3 weeks. The decision to transfuse allogenic red blood cells was made by the treating surgeon, based on standardized hospital protocols, wherein patients are transfused for hemoglobin levels under 7.0 g/dL, or for hemoglobin levels less than 8.0 g/dL in the presence of persistent symptoms. All patients received care on an orthopedic specialty floor and were assisted by the same physical therapists. Discharge disposition was coordinated with the same group of social workers.

Two to 3 months after surgery, patients returned for routine examination and radiographs. All patients were followed up for at least 90 days.

 

Statistical Analysis

All outcomes were analyzed with appropriate summary statistics. Chi-square tests or logistic regression analyses (for categorical outcomes) were used to compare baseline covariates with perioperative outcomes, and 2-sample tests or Wilcoxon rank-sum tests were used to compare outcomes measured on a continuous scale. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated as appropriate. Operative time was calculated by adding time from incision to wound closure for both hips (room turnover time between hips was not included). Anesthesia time was defined as total time patients were in the operating room. All statistical tests were 2-sided, and the threshold for statistical significance was set at α = 0.05.

Results

Compared with patients who underwent simultaneous bilateral THAs through the posterior approach, patients who underwent simultaneous bilateral THAs through the DA approach had longer mean operative times (153 vs 106 min; P < .001) and anesthesia times (257 vs 221 min; P = .007). The 2 groups’ hospital stays were similar in length (3.1 vs 3.5 days; P = .31), but patients in the DA group were more likely to be discharged home (100.0% vs 71.4%; P = .02) (Table 2).

Discharge location was not associated with sex (OR, 1.08; 95% CI, 0.22-5.17; P = .99), age 60 years or older (OR, 0.65; 95% CI, 0.07-6.41; P = .99), hospital LOS of 4 days or more (OR, 1.05; 95% CI, 0.17-6.60; P = .99), BMI of 30 kg/m² or higher (OR, 1.04; 95% CI, 0.17-6.60; P = .99), or ASA score of 3 (OR, 0.65; 95% CI, 0.07-6.41; P = .99) (Table 3).

Patients in the DA group were more likely to have sufficient intraoperative blood salvage for autologous transfusion (89.5% vs 57.1%; OR, 6.4; 95% CI, 1.16-34.94; P = .03) (Table 3) and received more mean units of salvaged autologous blood (1.4 vs 0.5; P = .003) (Table 2). Allogenic blood was not given to any patients in the DA group, but 3 patients in the posterior group (14.3%) required allogenic blood transfusion (P = .23) (Table 2). Salvaged autologous and allogenic blood transfusion was not associated with sex, age 60 years or older, or hospital LOS of 4 days or more (Table 3). The groups’ mean hemoglobin levels, measured the morning of postoperative day 1, were similar: 10.6 g/dL (range, 8.5-12.4 g/dL) for the DA group and 10.3 g/dL (range 8.6-12.3 g/dL) for the posterior group (Table 2).

In-hospital complications were uncommon in both groups (5% vs 14%; P = .61) (Table 2). One patient in the posterior group sustained a unilateral dislocation the day of surgery, and closed reduction was required; other complications (1 ileus, 2 tachyarrhythmias) did not require intervention. Ninety-day complications were also rare; 1 patient in the posterior group developed a hematoma with wound drainage, and this was successfully managed conservatively. There were no reoperations or readmissions in either group (Table 2).

Discussion

Although bilateral procedures account for less than 1% of THAs in the United States,¹¹ debate about their role in patients with severe bilateral hip disease continues. The potential benefits of a single episode of care must be weighed against the slightly increased risk for systemic complications.^7,10-15 Recent innovations in perioperative management have been shown to minimize complications,¹⁵ but it is unclear whether surgical approach affects perioperative outcomes. Our goals in this study were to evaluate operative times, transfusion requirements, hospital discharge data, and 90-day complication rates in patients who underwent simultaneous bilateral THAs through either the DA approach or the posterior approach.

Patients in our DA group had longer operative and anesthesia times. Other studies have found longer operative times for the DA approach relative to the posterior approach in unilateral THAs.¹⁸ One potential benefit of the DA approach in the setting of simultaneous bilateral THAs is the ability to prepare and drape both sides before surgery and thereby keep the interruption between hips to a minimum. In the present study, however, time saved during turnover between hips was overshadowed by the time added for each THA.

Although it was uncommon for complications to occur within 90 days after surgery in this study, many patients are needed to fully investigate these rare occurrences. Because of inherent selection bias, these risks are difficult to directly compare in patients who undergo unilateral procedures. Although small studies have failed to clarify the issue,^7,19,20 a recent review of the almost 20,000 bilateral THA cases in the US Nationwide Inpatient Sample database found that bilateral (vs unilateral) THAs were associated with increased risk of local and systemic complications.¹¹ Therefore, bilateral THAs should be reserved for select cases, with attention given to excluding patients with preexisting cardiopulmonary disease and providing appropriate preoperative counseling.

Most studies have reported a higher transfusion rate in bilateral THAs relative to staged procedures.^7,21-23 Allogenic blood transfusion leads to immune suppression, coagulopathy, and other systemic effects in general, and has been specifically associated with infection in patients who undergo total joint arthroplasty.^24-29 Parvizi and colleagues¹⁷ reported reduced blood loss and fewer blood transfusions in patients who had simultaneous bilateral THAs through the DA approach, compared with the direct lateral approach. Patients in our DA group received more salvaged autologous blood, which we suppose was a function of longer operative times. However, postoperative hemoglobin levels and allogenic blood transfusion rates were statistically similar between the 2 groups. It is important to consider the increased risk of required allogenic blood transfusion associated with simultaneous bilateral THAs, but it is not fully clear if this risk is lower in THAs performed through the DA approach relative to other approaches. In our experience, the required transfusion risk is limited in DA and posterior approaches with use of contemporary perioperative blood management strategies.

Although hospital LOS is longer with simultaneous bilateral THAs than with unilateral THAs, historically it is shorter than the combined LOS of staged bilateral THAs.²⁰ Patients in our study had a relatively short LOS after bilateral THAs, and there was no difference in LOS between groups. However, patients were more likely to be discharged home after bilateral THAs through the DA approach vs the posterior approach. Although discharge location was not affected by age, sex, ASA score, or LOS, unrecognized social factors unrelated to surgical approach likely influenced this finding.

This study should be interpreted in light of important limitations. Foremost, although data were prospectively collected, we examined them retrospectively. Thus, it is possible there may be unaccounted for differences between our DA and posterior THA groups. For example, the DA and posterior approaches were used by different surgeons with differing experience, technique, and preferences, all of which could have affected outcomes. Furthermore, our sample was relatively small (simultaneous bilateral THAs are performed relatively infrequently). Last, although anesthesia, pain management, blood conservation, and physical therapy were similar for the 2 groups, there was no standardized protocol for determining eligibility for simultaneous bilateral THAs.

In conclusion, we found that simultaneous bilateral THAs can be safely performed through either the DA approach or the posterior approach. Although the transition between hips is shorter with the DA approach, this time savings is overshadowed by the increased duration of each procedure. Transfusion rates are low in both groups, and in-hospital and 90-day complications are quite rare. Furthermore, patients can routinely be discharged home without elevating readmission rates. We will continue to perform simultaneous bilateral THAs through the DA approach or the posterior approach, according to surgeon preference.

Am J Orthop. 2016;45(6):E373-E378. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.

End-stage osteoarthritis of the hip is a debilitating disease that is reliably treated with total hip arthroplasty (THA).¹ Up to 35% of patients who undergo THA eventually require contralateral THA.^2,3 In patients who present with advanced bilateral disease and undergo unilateral THA, the risk of ultimately requiring a contralateral procedure is as high as 97%.^3-6 In patients with bilateral hip disease, function is not fully optimized until both hips have been replaced, particularly in the setting of fixed flexion contractures.^7-9 Naturally, there has been some interest in simultaneous bilateral THAs for select patients.

The potential benefits of bilateral THAs over staged procedures include faster overall rehabilitation, exposure to a single anesthetic, reduced hospital length of stay (LOS), and cost savings.^10-12 However, opinion on recommending bilateral THAs is mixed. Although bilateral procedures historically have been fraught with perioperative complications,^13,14 advances in surgical and anesthetic techniques have led to improved outcomes.¹⁵ Whether surgical approach is a factor in these outcomes is unclear.

The popularity of the direct anterior (DA) approach for THA has increased in recent years.¹⁶ Although the relative advantages of various approaches remain in debate, one potential benefit of the DA approach is supine positioning, which allows simultaneous bilateral THAs to be performed without the need for repositioning before proceeding with the contralateral side. However, simultaneous bilateral THAs performed through the DA approach and those performed through other surgical approaches are lacking in comparative outcomes data.¹⁷In this study, we evaluated operative times, transfusion requirements, hospital discharge data, and 90-day complication rates in patients who had simultaneous bilateral THAs through either the DA approach or the posterior approach.

Methods

Study Design

This single-center study was conducted at the Mayo Clinic in Rochester, Minnesota. After obtaining approval from our Institutional Review Board, we performed a retrospective cohort analysis. We used our institution’s total joint registry to identify all patients who underwent simultaneous bilateral THAs through either the DA approach or the posterior approach. The first bilateral THAs to use the DA approach at our institution were performed in 2012. To ensure that the DA and posterior groups’ perioperative management would be similar, we included only cases performed between 2012 and 2014.

There were 19 patients in the DA group and 21 in the posterior group. The groups were similar in mean age (54 vs 54 years; P = .90), sex (73% vs 57% males; P = .33), body mass index (BMI; 25 vs 28 kg/m²; P = .38), preoperative hemoglobin level (14.3 vs 14.0 g/dL; P = .37), preoperative diagnosis (71.1% vs 78.6% degenerative joint disease; P = .75), and American Society of Anesthesiologists (ASA) score (1.9 vs 2.0; P = .63) (Table 1).

All patients had clinical follow-up of at least 90 days.

Patient Care

All cases were performed by 1 of 3 dedicated arthroplasty surgeons (Dr. Taunton, Dr. Sierra, Dr. Trousdale). Dr. Taunton exclusively uses the DA approach, and Dr. Sierra and Dr. Trousdale exclusively use the posterior approach. Patients in both groups received preoperative medical clearance and attended the same preoperative education class.

Patients in the DA group were positioned supine on an orthopedic table that allows hyperextension and adduction of the operative leg. Both hips were prepared and draped simultaneously. The most symptomatic hip was operated on first, with a sterile drape covering the contralateral hip. Between hips, fluoroscopy was moved to the other side of the operative suite, but no changes in positioning or preparation were necessary. A deep drain was placed on each side, and then was removed the morning of postoperative day 1. The same set of instruments was used on both sides.

Patients in the posterior group were positioned lateral on a regular operative table with hip rests. The most symptomatic hip was operated on first. After wound closure and dressing application, the patient was flipped to allow access to the contralateral hip and was prepared and draped again. The same instruments were used on each side. Drains were not used.

All patients received the same comprehensive multimodal pain management, which combined general and epidural anesthesia (remaining in place until postoperative day 2) and included an oral pain regimen of scheduled acetaminophen and as-needed tramadol and oxycodone. In all cases, intraoperative blood salvage and intravenous tranexamic acid (1 g at time of incision on first hip, 1 g at wound closure on second hip) were used. Preoperative autologous blood donation was not used. For deep vein thrombosis prophylaxis, patients were treated with bilateral sequential compression devices while hospitalized, but chemoprophylaxis was different between groups. Patients in the DA group received prophylactic low-molecular-weight heparin for 10 days, followed by twice-daily aspirin (325 mg) for 4 weeks. Patients in the posterior group received warfarin (goal international normalized ratio, 1.7-2.2) for 3 weeks, followed by twice-daily aspirin (325 mg) for 3 weeks. The decision to transfuse allogenic red blood cells was made by the treating surgeon, based on standardized hospital protocols, wherein patients are transfused for hemoglobin levels under 7.0 g/dL, or for hemoglobin levels less than 8.0 g/dL in the presence of persistent symptoms. All patients received care on an orthopedic specialty floor and were assisted by the same physical therapists. Discharge disposition was coordinated with the same group of social workers.

Two to 3 months after surgery, patients returned for routine examination and radiographs. All patients were followed up for at least 90 days.

 

Statistical Analysis

All outcomes were analyzed with appropriate summary statistics. Chi-square tests or logistic regression analyses (for categorical outcomes) were used to compare baseline covariates with perioperative outcomes, and 2-sample tests or Wilcoxon rank-sum tests were used to compare outcomes measured on a continuous scale. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated as appropriate. Operative time was calculated by adding time from incision to wound closure for both hips (room turnover time between hips was not included). Anesthesia time was defined as total time patients were in the operating room. All statistical tests were 2-sided, and the threshold for statistical significance was set at α = 0.05.

Results

Compared with patients who underwent simultaneous bilateral THAs through the posterior approach, patients who underwent simultaneous bilateral THAs through the DA approach had longer mean operative times (153 vs 106 min; P < .001) and anesthesia times (257 vs 221 min; P = .007). The 2 groups’ hospital stays were similar in length (3.1 vs 3.5 days; P = .31), but patients in the DA group were more likely to be discharged home (100.0% vs 71.4%; P = .02) (Table 2).

Discharge location was not associated with sex (OR, 1.08; 95% CI, 0.22-5.17; P = .99), age 60 years or older (OR, 0.65; 95% CI, 0.07-6.41; P = .99), hospital LOS of 4 days or more (OR, 1.05; 95% CI, 0.17-6.60; P = .99), BMI of 30 kg/m² or higher (OR, 1.04; 95% CI, 0.17-6.60; P = .99), or ASA score of 3 (OR, 0.65; 95% CI, 0.07-6.41; P = .99) (Table 3).

Patients in the DA group were more likely to have sufficient intraoperative blood salvage for autologous transfusion (89.5% vs 57.1%; OR, 6.4; 95% CI, 1.16-34.94; P = .03) (Table 3) and received more mean units of salvaged autologous blood (1.4 vs 0.5; P = .003) (Table 2). Allogenic blood was not given to any patients in the DA group, but 3 patients in the posterior group (14.3%) required allogenic blood transfusion (P = .23) (Table 2). Salvaged autologous and allogenic blood transfusion was not associated with sex, age 60 years or older, or hospital LOS of 4 days or more (Table 3). The groups’ mean hemoglobin levels, measured the morning of postoperative day 1, were similar: 10.6 g/dL (range, 8.5-12.4 g/dL) for the DA group and 10.3 g/dL (range 8.6-12.3 g/dL) for the posterior group (Table 2).

In-hospital complications were uncommon in both groups (5% vs 14%; P = .61) (Table 2). One patient in the posterior group sustained a unilateral dislocation the day of surgery, and closed reduction was required; other complications (1 ileus, 2 tachyarrhythmias) did not require intervention. Ninety-day complications were also rare; 1 patient in the posterior group developed a hematoma with wound drainage, and this was successfully managed conservatively. There were no reoperations or readmissions in either group (Table 2).

Discussion

Although bilateral procedures account for less than 1% of THAs in the United States,¹¹ debate about their role in patients with severe bilateral hip disease continues. The potential benefits of a single episode of care must be weighed against the slightly increased risk for systemic complications.^7,10-15 Recent innovations in perioperative management have been shown to minimize complications,¹⁵ but it is unclear whether surgical approach affects perioperative outcomes. Our goals in this study were to evaluate operative times, transfusion requirements, hospital discharge data, and 90-day complication rates in patients who underwent simultaneous bilateral THAs through either the DA approach or the posterior approach.

Patients in our DA group had longer operative and anesthesia times. Other studies have found longer operative times for the DA approach relative to the posterior approach in unilateral THAs.¹⁸ One potential benefit of the DA approach in the setting of simultaneous bilateral THAs is the ability to prepare and drape both sides before surgery and thereby keep the interruption between hips to a minimum. In the present study, however, time saved during turnover between hips was overshadowed by the time added for each THA.

Although it was uncommon for complications to occur within 90 days after surgery in this study, many patients are needed to fully investigate these rare occurrences. Because of inherent selection bias, these risks are difficult to directly compare in patients who undergo unilateral procedures. Although small studies have failed to clarify the issue,^7,19,20 a recent review of the almost 20,000 bilateral THA cases in the US Nationwide Inpatient Sample database found that bilateral (vs unilateral) THAs were associated with increased risk of local and systemic complications.¹¹ Therefore, bilateral THAs should be reserved for select cases, with attention given to excluding patients with preexisting cardiopulmonary disease and providing appropriate preoperative counseling.

Most studies have reported a higher transfusion rate in bilateral THAs relative to staged procedures.^7,21-23 Allogenic blood transfusion leads to immune suppression, coagulopathy, and other systemic effects in general, and has been specifically associated with infection in patients who undergo total joint arthroplasty.^24-29 Parvizi and colleagues¹⁷ reported reduced blood loss and fewer blood transfusions in patients who had simultaneous bilateral THAs through the DA approach, compared with the direct lateral approach. Patients in our DA group received more salvaged autologous blood, which we suppose was a function of longer operative times. However, postoperative hemoglobin levels and allogenic blood transfusion rates were statistically similar between the 2 groups. It is important to consider the increased risk of required allogenic blood transfusion associated with simultaneous bilateral THAs, but it is not fully clear if this risk is lower in THAs performed through the DA approach relative to other approaches. In our experience, the required transfusion risk is limited in DA and posterior approaches with use of contemporary perioperative blood management strategies.

Although hospital LOS is longer with simultaneous bilateral THAs than with unilateral THAs, historically it is shorter than the combined LOS of staged bilateral THAs.²⁰ Patients in our study had a relatively short LOS after bilateral THAs, and there was no difference in LOS between groups. However, patients were more likely to be discharged home after bilateral THAs through the DA approach vs the posterior approach. Although discharge location was not affected by age, sex, ASA score, or LOS, unrecognized social factors unrelated to surgical approach likely influenced this finding.

This study should be interpreted in light of important limitations. Foremost, although data were prospectively collected, we examined them retrospectively. Thus, it is possible there may be unaccounted for differences between our DA and posterior THA groups. For example, the DA and posterior approaches were used by different surgeons with differing experience, technique, and preferences, all of which could have affected outcomes. Furthermore, our sample was relatively small (simultaneous bilateral THAs are performed relatively infrequently). Last, although anesthesia, pain management, blood conservation, and physical therapy were similar for the 2 groups, there was no standardized protocol for determining eligibility for simultaneous bilateral THAs.

In conclusion, we found that simultaneous bilateral THAs can be safely performed through either the DA approach or the posterior approach. Although the transition between hips is shorter with the DA approach, this time savings is overshadowed by the increased duration of each procedure. Transfusion rates are low in both groups, and in-hospital and 90-day complications are quite rare. Furthermore, patients can routinely be discharged home without elevating readmission rates. We will continue to perform simultaneous bilateral THAs through the DA approach or the posterior approach, according to surgeon preference.

Am J Orthop. 2016;45(6):E373-E378. Copyright Frontline Medical Communications Inc. 2016. All rights reserved.