Knee

Over the past 3 decades, total knee arthroplasty (TKA) has been considered a safe and effective treatment for end-stage knee arthritis.¹ However, as the population, the incidence of obesity, and life expectancy continue to increase, the number of TKAs will rise as well.^2,3 It is expected that over the next 16 years, the number of TKAs performed annually will exceed 3 million in the United States alone.⁴ This projection represents an over 600% increase from 2005 figures.⁵ Given the demographic shift expected over the next 2 decades, patients are anticipated to undergo these procedures at younger ages compared with previous generations, such that those age 65 years or younger will account for more than 55% of primary TKAs.⁶ More important, given this exponential growth in primary TKAs, there will be a concordant rise in revision procedures. It is expected that, the annual number has roughly doubled from that recorded for 2005.⁴

Compared with primary TKAs, however, revision TKAs have had less promising results, with survivorship as low as 60% over shorter periods.^7,8 In addition, recent studies have found an even higher degree of dissatisfaction and functional limitations among revision TKA patients than among primary TKA patients, 15% to 30% of whom are unhappy with their procedures.^9-11 These shortcomings of revision TKAs are thought to result from several factors, including poor bone quality, insufficient bone stock, ligamentous instability, soft-tissue incompetence, infection, malalignment, problems with extensor mechanisms, and substantial pain of uncertain etiology.

Despite there being several complex factors that can lead to worse outcomes with revision TKAs, surgeons are expected to produce results equivalent to those of primary TKAs. It is therefore imperative to delineate the objective and subjective outcomes of revision techniques to identify areas in need of improvement. In this article, we provide a concise overview of revision TKA outcomes in order to stimulate manufacturers, surgeons, and hospitals to improve on implant designs, surgical techniques, and care guidelines for revision TKA. We review the evidence on 5 points: aseptic survivorship, functional outcomes, patient satisfaction, quality of life (QOL), and economic impact. In addition, we compare available outcome data for revision and primary TKAs.

1. Aseptic survivorship

Fehring and colleagues¹² in 2001 and Sharkey and colleagues¹³ in 2002 evaluated mechanisms of failure for revision TKA and reported many failures resulted from infection or were associated with the implant, and occurred within 2 years after the primary procedure. More recently, Dy and colleagues¹⁴ found the most common reason for revision was aseptic loosening, followed by infection. The present review focuses on aseptic femoral and tibial revision.

The failure rate for revision TKA is substantially higher than for primary TKA with the same type of prosthesis because of the complexity of the revision procedure, the increasing constraint of the implant design, and the higher degree of bone loss. (Appendix 1 lists risk factors for revision surgery. Appendix 2 is a complete list of survivorship outcomes of revision TKA.)

Sheng and colleagues¹⁵ in 2006 and Koskinen and colleagues¹⁶ in 2008 analyzed Finnish Arthroplasty Register data to determine failure rates for revision and primary TKA. Sheng and colleagues¹⁵ examined survivorship of 2637 revision TKAs (performed between 1990 and 2002) for all-cause endpoints after first revision procedure. Survivorship rates were 89% (5 years) and 79% (10 years), while Koskinen and colleagues¹⁶ noted all-cause survival rates of 80% at 15 years. More recently, in 2013, the New Zealand Orthopaedic Association¹⁷ analyzed New Zealand Joint Registry data for revision and re-revision rates (rates of revision per 100 component years) for 64,556 primary TKAs performed between 1999 and 2012. During the period studied, 1684 revisions were performed, reflecting a 2.6% revision rate, a 0.50% rate of revision per 100 component years, and a 13-year Kaplan-Meier survivorship of 94.5%. The most common reasons for revision were pain, deep infection, and tibial component loosening (Table 1).

Posterior stabilized implants

Laskin and Ohnsorge¹⁸ retrospectively reviewed the cases of 58 patients who underwent unilateral revision TKA (with a posterior stabilized implant), of which 42% were for coronal instability and 44% for a loose tibial component. At minimum 4-year follow-up, 52 of the 58 patients had anteroposterior instability of less than 5 mm. In addition, 5 years after surgery, aseptic survivorship was 96%. Meijer and colleagues¹⁹ conducted a retrospective comparative study of 69 revision TKAs (65 patients) in which 9 knees received a primary implant and 60 received a revision implant with stems and augmentation (60 = 37 posterior stabilized, 20 constrained, 3 rotating hinge). Survival rates for the primary implants were 100% (1 year), 73% (2 years), and 44% (5 years), and survival rates for the revision implants were significantly better: 95% (1 year), 92% (2 years), and 92% (5 years) (hazard ratio, 5.87; P = .008). The authors therefore indicated that it was unclear whether using a primary implant should still be an option in revision TKA and, if it is used, whether it should be limited to less complex situations in which bone loss and ligament damage are minimal (Table 2).

Constrained and semiconstrained implants

In a study of 234 knees (209 patients) with soft-tissue deficiency, Wilke and colleagues²⁰ evaluated the long-term survivorship of revision TKA with use of a semiconstrained modular fixed-bearing implant system. Overall Kaplan-Meier survival rates were 91% (5 years) and 81% (10 years) at a mean follow-up of 9 years. When aseptic revision was evaluated, however, the survival rates increased to 95% (5 years) and 90% (10 years). The authors noted that male sex was the only variable that significantly increased the risk for re-revision (hazard ratio, 2.07; P = .02), which they attributed to potentially higher activity levels. In 2006 and 2011, Lachiewicz and Soileau^21,22 evaluated the survival of first- and second-generation constrained condylar prostheses in primary TKA cases with severe valgus deformities, incompetent collateral ligaments, or severe flexion contractures. Of the 54 knees (44 patients) with first-generation prostheses, 42 (34 patients) had a mean follow-up of 9 years (range, 5-16 years). Ten-year survival with failure, defined as component revision for loosening, was 96%. The 27 TKAs using second-generation prostheses had a mean follow-up of about 5 years (range, 2-12 years). At final follow-up, there were no revisions for loosening or patellar problems, but 6 knees (22%) required lateral retinacular release of the patella (Table 3).

Rotating hinge implants

Neumann and colleagues²³ evaluated the clinical and radiographic outcomes of 24 rotating hinge prostheses used for aseptic loosening with substantial bone loss and collateral ligament instability. At a mean follow-up of 56 months (range, 3-5 years), there was no evidence of loosening of any implants, and nonprogressive radiolucent lines were found in only 2 tibial components. Kowalczewski and colleagues²⁴ evaluated the clinical and radiologic outcomes of 12 primary TKAs using a rotating hinge knee prosthesis at a minimum follow-up of 10 years. By most recent follow-up, no implants had been revised for loosening, and only 3 had nonprogressive radiolucent lines (Table 4).

Endoprostheses (modular segmental implants)

In a systematic review of 9 studies, Korim and colleagues²⁵ evaluated 241 endoprostheses used for limb salvage under nononcologic conditions. Mean follow-up was about 3 years (range, 1-5 years). The devices were used to treat various conditions, including periprosthetic fracture, bone loss with aseptic loosening, and ligament insufficiency. The overall reoperation rate was 17% (41/241 cases). Mechanical failures were less frequent (6%-19%) (Table 5).

2. Functional outcomes

The goal in both primary and revision TKA is to restore the function and mobility of the knee and to alleviate pain. Whereas primary TKAs are realistically predictable and reproducible in their outcomes, revision TKAs are vastly more complicated, which can result in worse postoperative outcomes and function. In addition, revision TKAs may require extensive surgical exposure, which causes more tissue and muscle damage, prolonging rehabilitation. (Appendix 3 is a complete list of studies of functional outcomes of revision TKA.)

This discrepancy in functional outcomes between primary and revision TKA begins as early as the postoperative inpatient rehabilitation period. Using the functional independence measurement (FIM), which estimates performance of activities of daily living, mobility, and cognition, Vincent and colleagues²⁶ evaluated the functional improvement produced by revision versus primary TKA during inpatient rehabilitation. They compared 424 consecutive primary TKAs with 138 revision TKAs. For both groups, FIM scores increased significantly (P = .015) between admission and discharge. On discharge, however, FIM scores were significantly (P = .01) higher for the primary group than the revision group (29 and 27 points, respectively). Furthermore, in the evaluation of mechanisms of failure, patients who had revision TKA for mechanical or pain-related problems did markedly better than those who had revision TKA for infection.

Compared with primary knee implants, revision implants require increasing constraint. We assume increasing constraint affects knee biomechanics, leading to worsening functional outcomes. In a study of 60 revision TKAs (57 patients) using posterior stabilized, condylar constrained, or rotating hinge prostheses, Vasso and colleagues²⁷ examined functional outcomes at a median follow-up of 9 years (range, 4-12 years). At most recent follow-up, mean International Knee Society (IKS) Knee and Function scores were 81 (range, 48-97) and 79 (range, 56-92), mean Hospital for Special Surgery (HSS) score was 84 (range, 62-98), and mean range of motion (ROM) was 121° (range, 98°-132°) (P < .001). Although there were no significant differences in IKS and HSS scores between prosthesis types, ROM was significantly (P < .01) wider in the posterior stabilized group than in the condylar constrained and rotating hinge groups (127° vs 112° and 108°), suggesting increasing constraint resulted in decreased ROM. Several studies have found increasing constraint might lead to reduced function.^28-30

However, Hwang and colleagues³¹ evaluated functional outcomes in 36 revision TKAs and noted that the cemented posterior stabilized (n = 8), condylar constrained (n = 25), and rotating hinge (n = 13) prostheses used did not differ in their mean Knee Society scores (78, 81, and 83, respectively).

There remains a marked disparity in patient limitations seen after revision versus primary TKA. Given the positive results being obtained with newer implants, studies might suggest recent generations of prostheses have allowed designs to be comparable. As design development continues, we may come closer to achieving outcomes comparable to those of primary TKA.

3. Patient satisfaction

Several recent reports have shown that 10% to 25% of patients who underwent primary TKA were dissatisfied with their surgery^30,32; other studies have found patient satisfaction often correlating to function and pain.^33-35 Given the worse outcomes for revision TKA (outlined in the preceding section), the substantial pain accompanying a second, more complex procedure, and the extensive rehabilitation expected, we suspect patients who undergo revision TKA are even less satisfied with their surgery than their primary counterparts are. (See Appendix 4 for a complete list of studies of patient satisfaction after revision TKA.)

Barrack and colleagues³² evaluated a consecutive series of 238 patients followed up for at least 1 year after revision TKA. Patients were asked to rate their degree of satisfaction with both their primary procedure and the revision and to indicate their expectations regarding their revision prosthesis. Mean satisfaction score was 7.4 (maximum = 10), with 13% of patients dissatisfied, 18% somewhat satisfied, and 69% satisfied. Seventy-four percent of patients expected their revision prosthesis to last longer than the primary prosthesis.

Greidanus and colleagues³⁶ evaluated patient satisfaction in 60 revision TKA cases and 199 primary TKA cases at 2-year follow-up. The primary TKA group had significantly (P < .01) higher satisfaction scores in a comparison with the revision TKA group: Global (86 vs 73), Pain Relief (88 vs 70), Function (83 vs 67), and Recreation (77 vs 62). These findings support the satisfaction rates reported by Dahm and colleagues^33,34: 91% for primary TKA patients and 77% for revision TKA patients.

4. Quality of life

Procedure complexity leads to reduced survivorship, function, and mobility, longer rehabilitation, and decreased QOL for revision TKA patients relative to primary TKA patients.³⁷ (See Appendix 5 for a complete list of studies of QOL outcomes of revision TKA.)

Greidanus and colleagues³⁶ evaluated joint-specific QOL (using the 12-item Oxford Knee Score; OKS) and generic QOL (using the 12-Item Short Form Health Survey; SF-12) in 60 revision TKA cases and 199 primary TKA cases at a mean follow-up of 2 years. (The OKS survey is used to evaluate patient perspectives on TKA outcomes,³⁸ and the multipurpose SF-12 questionnaire is used to assess mental and physical function and general health-related QOL.³⁹) Compared with the revision TKA group, the primary TKA group had significantly higher OKS after surgery (78 vs 68; P = .01) as well as significantly higher SF-12 scores: Global (84 vs 72; P = .01), Mental (54 vs 50; P = .03), and Physical (43 vs 37; P = .01). Similarly, Ghomrawi and colleagues⁴⁰ evaluated patterns of improvement in 308 patients (318 knees) who had revision TKA. At 24-month follow-up, mean SF-36 Physical and Mental scores were 35 and 52, respectively.

Deehan and colleagues⁴¹ used the Nottingham Health Profile (NHP) to compare 94 patients’ health-related QOL scores before revision TKA with their scores 3 months, 1 year, and 5 years after revision. NHP Pain subscale scores were significantly lower 3 and 12 months after surgery than before surgery, but this difference was no longer seen at the 5-year follow-up. There was no significant improvement in scores on the other 5 NHP subscales (Sleep, Energy, Emotion, Mobility, Social Isolation) at any time points.

As shown in the literature, patients’ QOL outcomes improve after revision TKA, but these gains are not at the level of patients who undergo primary TKA.^36,41 Given that revision surgery is more extensive, and that perhaps revision patients have poorer muscle function, they usually do not return to the level they attained after their index procedure.

5. Economic impact

Consistent with the outcomes already described, the economic impact of revision TKAs is excess expenditures and costs to patients and health care institutions.⁴² The sources of this impact are higher implant costs, extra operative trays and times, longer hospital stays, more rehabilitation, and increased medication use.⁴³ Revision TKA costs range from $49,000 to more than $100,000—a tremendous increase over primary TKA costs ($25,000-$30,000).^43-45 Furthermore, the annual economic burden associated with revision TKA, now $2.7 billion, is expected to exceed $13 billion by 2030.⁴⁶ In the United States, about $23.2 billion will be spent on 926,527 primary TKAs in 2015; significantly, the costs associated with revising just 10% of these cases account for almost 50% of the total cost of the primary procedures.⁴⁶

In a retrospective cost-identification multicenter cohort study, Bozic and colleagues⁴⁷ found that both-component and single-component revisions, compared with primary procedures, were associated with significantly increased operative time (~265 and 221 minutes vs 200 minutes), use of allograft bone (23% and 14% vs 1%), length of stay (5.4 and 5.7 days vs 5.0 days), and percentage of patients discharged to extended-care facilities (26% and 26% vs 25%) (P < .0001). Hospital costs for both- and single-component revisions were 138% and 114% higher than costs for primary procedures (P < .0001). More recently, Kallala and colleagues⁴⁴ analyzed UK National Health Service data and compared the costs of revision for infection with revision for other causes (pain, instability, aseptic loosening, fracture). Mean length of stay associated with revision for infection (21.5 days) was more than double that associated with revision for aseptic loosening (9.5 days; P < .0001), and mean cost of revision for septic causes (£30,011) was more than 3 times that of revision for other causes (£9655; P < .0001). The authors concluded that the higher costs of revision knee surgery have a considerable economic impact, especially in infection cases.

With more extensive procedures, long-stem or more constrained prostheses are often needed to obtain adequate fixation and stability. The resulting increased, substantial economic burden is felt by patients and the health care system. Given that health care reimbursements are declining, hospitals that perform revision TKAs can sustain marked financial losses. Some centers are asking whether it is cost-effective to continue to perform these types of procedures. We must find new ways to provide revision procedures using less costly implants and tools so that centers will continue to make these procedures available to patients.

Conclusion

Given the exponential growth in primary TKAs, there will be a concordant increase in revision TKAs in the decades to come. This review provides a concise overview of revision TKA outcomes. Given the low level of evidence regarding revision TKAs, we need further higher quality studies of their prostheses and outcomes. Specifically, we need systematic reviews and meta-analyses to provide higher quality evidence regarding outcomes of using individual prosthetic designs.

Over the past 3 decades, total knee arthroplasty (TKA) has been considered a safe and effective treatment for end-stage knee arthritis.¹ However, as the population, the incidence of obesity, and life expectancy continue to increase, the number of TKAs will rise as well.^2,3 It is expected that over the next 16 years, the number of TKAs performed annually will exceed 3 million in the United States alone.⁴ This projection represents an over 600% increase from 2005 figures.⁵ Given the demographic shift expected over the next 2 decades, patients are anticipated to undergo these procedures at younger ages compared with previous generations, such that those age 65 years or younger will account for more than 55% of primary TKAs.⁶ More important, given this exponential growth in primary TKAs, there will be a concordant rise in revision procedures. It is expected that, the annual number has roughly doubled from that recorded for 2005.⁴

Compared with primary TKAs, however, revision TKAs have had less promising results, with survivorship as low as 60% over shorter periods.^7,8 In addition, recent studies have found an even higher degree of dissatisfaction and functional limitations among revision TKA patients than among primary TKA patients, 15% to 30% of whom are unhappy with their procedures.^9-11 These shortcomings of revision TKAs are thought to result from several factors, including poor bone quality, insufficient bone stock, ligamentous instability, soft-tissue incompetence, infection, malalignment, problems with extensor mechanisms, and substantial pain of uncertain etiology.

Despite there being several complex factors that can lead to worse outcomes with revision TKAs, surgeons are expected to produce results equivalent to those of primary TKAs. It is therefore imperative to delineate the objective and subjective outcomes of revision techniques to identify areas in need of improvement. In this article, we provide a concise overview of revision TKA outcomes in order to stimulate manufacturers, surgeons, and hospitals to improve on implant designs, surgical techniques, and care guidelines for revision TKA. We review the evidence on 5 points: aseptic survivorship, functional outcomes, patient satisfaction, quality of life (QOL), and economic impact. In addition, we compare available outcome data for revision and primary TKAs.

1. Aseptic survivorship

Fehring and colleagues¹² in 2001 and Sharkey and colleagues¹³ in 2002 evaluated mechanisms of failure for revision TKA and reported many failures resulted from infection or were associated with the implant, and occurred within 2 years after the primary procedure. More recently, Dy and colleagues¹⁴ found the most common reason for revision was aseptic loosening, followed by infection. The present review focuses on aseptic femoral and tibial revision.

The failure rate for revision TKA is substantially higher than for primary TKA with the same type of prosthesis because of the complexity of the revision procedure, the increasing constraint of the implant design, and the higher degree of bone loss. (Appendix 1 lists risk factors for revision surgery. Appendix 2 is a complete list of survivorship outcomes of revision TKA.)

Sheng and colleagues¹⁵ in 2006 and Koskinen and colleagues¹⁶ in 2008 analyzed Finnish Arthroplasty Register data to determine failure rates for revision and primary TKA. Sheng and colleagues¹⁵ examined survivorship of 2637 revision TKAs (performed between 1990 and 2002) for all-cause endpoints after first revision procedure. Survivorship rates were 89% (5 years) and 79% (10 years), while Koskinen and colleagues¹⁶ noted all-cause survival rates of 80% at 15 years. More recently, in 2013, the New Zealand Orthopaedic Association¹⁷ analyzed New Zealand Joint Registry data for revision and re-revision rates (rates of revision per 100 component years) for 64,556 primary TKAs performed between 1999 and 2012. During the period studied, 1684 revisions were performed, reflecting a 2.6% revision rate, a 0.50% rate of revision per 100 component years, and a 13-year Kaplan-Meier survivorship of 94.5%. The most common reasons for revision were pain, deep infection, and tibial component loosening (Table 1).

Posterior stabilized implants

Laskin and Ohnsorge¹⁸ retrospectively reviewed the cases of 58 patients who underwent unilateral revision TKA (with a posterior stabilized implant), of which 42% were for coronal instability and 44% for a loose tibial component. At minimum 4-year follow-up, 52 of the 58 patients had anteroposterior instability of less than 5 mm. In addition, 5 years after surgery, aseptic survivorship was 96%. Meijer and colleagues¹⁹ conducted a retrospective comparative study of 69 revision TKAs (65 patients) in which 9 knees received a primary implant and 60 received a revision implant with stems and augmentation (60 = 37 posterior stabilized, 20 constrained, 3 rotating hinge). Survival rates for the primary implants were 100% (1 year), 73% (2 years), and 44% (5 years), and survival rates for the revision implants were significantly better: 95% (1 year), 92% (2 years), and 92% (5 years) (hazard ratio, 5.87; P = .008). The authors therefore indicated that it was unclear whether using a primary implant should still be an option in revision TKA and, if it is used, whether it should be limited to less complex situations in which bone loss and ligament damage are minimal (Table 2).

Constrained and semiconstrained implants

In a study of 234 knees (209 patients) with soft-tissue deficiency, Wilke and colleagues²⁰ evaluated the long-term survivorship of revision TKA with use of a semiconstrained modular fixed-bearing implant system. Overall Kaplan-Meier survival rates were 91% (5 years) and 81% (10 years) at a mean follow-up of 9 years. When aseptic revision was evaluated, however, the survival rates increased to 95% (5 years) and 90% (10 years). The authors noted that male sex was the only variable that significantly increased the risk for re-revision (hazard ratio, 2.07; P = .02), which they attributed to potentially higher activity levels. In 2006 and 2011, Lachiewicz and Soileau^21,22 evaluated the survival of first- and second-generation constrained condylar prostheses in primary TKA cases with severe valgus deformities, incompetent collateral ligaments, or severe flexion contractures. Of the 54 knees (44 patients) with first-generation prostheses, 42 (34 patients) had a mean follow-up of 9 years (range, 5-16 years). Ten-year survival with failure, defined as component revision for loosening, was 96%. The 27 TKAs using second-generation prostheses had a mean follow-up of about 5 years (range, 2-12 years). At final follow-up, there were no revisions for loosening or patellar problems, but 6 knees (22%) required lateral retinacular release of the patella (Table 3).

Rotating hinge implants

Neumann and colleagues²³ evaluated the clinical and radiographic outcomes of 24 rotating hinge prostheses used for aseptic loosening with substantial bone loss and collateral ligament instability. At a mean follow-up of 56 months (range, 3-5 years), there was no evidence of loosening of any implants, and nonprogressive radiolucent lines were found in only 2 tibial components. Kowalczewski and colleagues²⁴ evaluated the clinical and radiologic outcomes of 12 primary TKAs using a rotating hinge knee prosthesis at a minimum follow-up of 10 years. By most recent follow-up, no implants had been revised for loosening, and only 3 had nonprogressive radiolucent lines (Table 4).

Endoprostheses (modular segmental implants)

In a systematic review of 9 studies, Korim and colleagues²⁵ evaluated 241 endoprostheses used for limb salvage under nononcologic conditions. Mean follow-up was about 3 years (range, 1-5 years). The devices were used to treat various conditions, including periprosthetic fracture, bone loss with aseptic loosening, and ligament insufficiency. The overall reoperation rate was 17% (41/241 cases). Mechanical failures were less frequent (6%-19%) (Table 5).

2. Functional outcomes

The goal in both primary and revision TKA is to restore the function and mobility of the knee and to alleviate pain. Whereas primary TKAs are realistically predictable and reproducible in their outcomes, revision TKAs are vastly more complicated, which can result in worse postoperative outcomes and function. In addition, revision TKAs may require extensive surgical exposure, which causes more tissue and muscle damage, prolonging rehabilitation. (Appendix 3 is a complete list of studies of functional outcomes of revision TKA.)

This discrepancy in functional outcomes between primary and revision TKA begins as early as the postoperative inpatient rehabilitation period. Using the functional independence measurement (FIM), which estimates performance of activities of daily living, mobility, and cognition, Vincent and colleagues²⁶ evaluated the functional improvement produced by revision versus primary TKA during inpatient rehabilitation. They compared 424 consecutive primary TKAs with 138 revision TKAs. For both groups, FIM scores increased significantly (P = .015) between admission and discharge. On discharge, however, FIM scores were significantly (P = .01) higher for the primary group than the revision group (29 and 27 points, respectively). Furthermore, in the evaluation of mechanisms of failure, patients who had revision TKA for mechanical or pain-related problems did markedly better than those who had revision TKA for infection.

Compared with primary knee implants, revision implants require increasing constraint. We assume increasing constraint affects knee biomechanics, leading to worsening functional outcomes. In a study of 60 revision TKAs (57 patients) using posterior stabilized, condylar constrained, or rotating hinge prostheses, Vasso and colleagues²⁷ examined functional outcomes at a median follow-up of 9 years (range, 4-12 years). At most recent follow-up, mean International Knee Society (IKS) Knee and Function scores were 81 (range, 48-97) and 79 (range, 56-92), mean Hospital for Special Surgery (HSS) score was 84 (range, 62-98), and mean range of motion (ROM) was 121° (range, 98°-132°) (P < .001). Although there were no significant differences in IKS and HSS scores between prosthesis types, ROM was significantly (P < .01) wider in the posterior stabilized group than in the condylar constrained and rotating hinge groups (127° vs 112° and 108°), suggesting increasing constraint resulted in decreased ROM. Several studies have found increasing constraint might lead to reduced function.^28-30

However, Hwang and colleagues³¹ evaluated functional outcomes in 36 revision TKAs and noted that the cemented posterior stabilized (n = 8), condylar constrained (n = 25), and rotating hinge (n = 13) prostheses used did not differ in their mean Knee Society scores (78, 81, and 83, respectively).

There remains a marked disparity in patient limitations seen after revision versus primary TKA. Given the positive results being obtained with newer implants, studies might suggest recent generations of prostheses have allowed designs to be comparable. As design development continues, we may come closer to achieving outcomes comparable to those of primary TKA.

3. Patient satisfaction

Several recent reports have shown that 10% to 25% of patients who underwent primary TKA were dissatisfied with their surgery^30,32; other studies have found patient satisfaction often correlating to function and pain.^33-35 Given the worse outcomes for revision TKA (outlined in the preceding section), the substantial pain accompanying a second, more complex procedure, and the extensive rehabilitation expected, we suspect patients who undergo revision TKA are even less satisfied with their surgery than their primary counterparts are. (See Appendix 4 for a complete list of studies of patient satisfaction after revision TKA.)

Barrack and colleagues³² evaluated a consecutive series of 238 patients followed up for at least 1 year after revision TKA. Patients were asked to rate their degree of satisfaction with both their primary procedure and the revision and to indicate their expectations regarding their revision prosthesis. Mean satisfaction score was 7.4 (maximum = 10), with 13% of patients dissatisfied, 18% somewhat satisfied, and 69% satisfied. Seventy-four percent of patients expected their revision prosthesis to last longer than the primary prosthesis.

Greidanus and colleagues³⁶ evaluated patient satisfaction in 60 revision TKA cases and 199 primary TKA cases at 2-year follow-up. The primary TKA group had significantly (P < .01) higher satisfaction scores in a comparison with the revision TKA group: Global (86 vs 73), Pain Relief (88 vs 70), Function (83 vs 67), and Recreation (77 vs 62). These findings support the satisfaction rates reported by Dahm and colleagues^33,34: 91% for primary TKA patients and 77% for revision TKA patients.

4. Quality of life

Procedure complexity leads to reduced survivorship, function, and mobility, longer rehabilitation, and decreased QOL for revision TKA patients relative to primary TKA patients.³⁷ (See Appendix 5 for a complete list of studies of QOL outcomes of revision TKA.)

Greidanus and colleagues³⁶ evaluated joint-specific QOL (using the 12-item Oxford Knee Score; OKS) and generic QOL (using the 12-Item Short Form Health Survey; SF-12) in 60 revision TKA cases and 199 primary TKA cases at a mean follow-up of 2 years. (The OKS survey is used to evaluate patient perspectives on TKA outcomes,³⁸ and the multipurpose SF-12 questionnaire is used to assess mental and physical function and general health-related QOL.³⁹) Compared with the revision TKA group, the primary TKA group had significantly higher OKS after surgery (78 vs 68; P = .01) as well as significantly higher SF-12 scores: Global (84 vs 72; P = .01), Mental (54 vs 50; P = .03), and Physical (43 vs 37; P = .01). Similarly, Ghomrawi and colleagues⁴⁰ evaluated patterns of improvement in 308 patients (318 knees) who had revision TKA. At 24-month follow-up, mean SF-36 Physical and Mental scores were 35 and 52, respectively.

Deehan and colleagues⁴¹ used the Nottingham Health Profile (NHP) to compare 94 patients’ health-related QOL scores before revision TKA with their scores 3 months, 1 year, and 5 years after revision. NHP Pain subscale scores were significantly lower 3 and 12 months after surgery than before surgery, but this difference was no longer seen at the 5-year follow-up. There was no significant improvement in scores on the other 5 NHP subscales (Sleep, Energy, Emotion, Mobility, Social Isolation) at any time points.

As shown in the literature, patients’ QOL outcomes improve after revision TKA, but these gains are not at the level of patients who undergo primary TKA.^36,41 Given that revision surgery is more extensive, and that perhaps revision patients have poorer muscle function, they usually do not return to the level they attained after their index procedure.

5. Economic impact

Consistent with the outcomes already described, the economic impact of revision TKAs is excess expenditures and costs to patients and health care institutions.⁴² The sources of this impact are higher implant costs, extra operative trays and times, longer hospital stays, more rehabilitation, and increased medication use.⁴³ Revision TKA costs range from $49,000 to more than $100,000—a tremendous increase over primary TKA costs ($25,000-$30,000).^43-45 Furthermore, the annual economic burden associated with revision TKA, now $2.7 billion, is expected to exceed $13 billion by 2030.⁴⁶ In the United States, about $23.2 billion will be spent on 926,527 primary TKAs in 2015; significantly, the costs associated with revising just 10% of these cases account for almost 50% of the total cost of the primary procedures.⁴⁶

In a retrospective cost-identification multicenter cohort study, Bozic and colleagues⁴⁷ found that both-component and single-component revisions, compared with primary procedures, were associated with significantly increased operative time (~265 and 221 minutes vs 200 minutes), use of allograft bone (23% and 14% vs 1%), length of stay (5.4 and 5.7 days vs 5.0 days), and percentage of patients discharged to extended-care facilities (26% and 26% vs 25%) (P < .0001). Hospital costs for both- and single-component revisions were 138% and 114% higher than costs for primary procedures (P < .0001). More recently, Kallala and colleagues⁴⁴ analyzed UK National Health Service data and compared the costs of revision for infection with revision for other causes (pain, instability, aseptic loosening, fracture). Mean length of stay associated with revision for infection (21.5 days) was more than double that associated with revision for aseptic loosening (9.5 days; P < .0001), and mean cost of revision for septic causes (£30,011) was more than 3 times that of revision for other causes (£9655; P < .0001). The authors concluded that the higher costs of revision knee surgery have a considerable economic impact, especially in infection cases.

With more extensive procedures, long-stem or more constrained prostheses are often needed to obtain adequate fixation and stability. The resulting increased, substantial economic burden is felt by patients and the health care system. Given that health care reimbursements are declining, hospitals that perform revision TKAs can sustain marked financial losses. Some centers are asking whether it is cost-effective to continue to perform these types of procedures. We must find new ways to provide revision procedures using less costly implants and tools so that centers will continue to make these procedures available to patients.

Conclusion

Given the exponential growth in primary TKAs, there will be a concordant increase in revision TKAs in the decades to come. This review provides a concise overview of revision TKA outcomes. Given the low level of evidence regarding revision TKAs, we need further higher quality studies of their prostheses and outcomes. Specifically, we need systematic reviews and meta-analyses to provide higher quality evidence regarding outcomes of using individual prosthetic designs.

Over the past 3 decades, total knee arthroplasty (TKA) has been considered a safe and effective treatment for end-stage knee arthritis.¹ However, as the population, the incidence of obesity, and life expectancy continue to increase, the number of TKAs will rise as well.^2,3 It is expected that over the next 16 years, the number of TKAs performed annually will exceed 3 million in the United States alone.⁴ This projection represents an over 600% increase from 2005 figures.⁵ Given the demographic shift expected over the next 2 decades, patients are anticipated to undergo these procedures at younger ages compared with previous generations, such that those age 65 years or younger will account for more than 55% of primary TKAs.⁶ More important, given this exponential growth in primary TKAs, there will be a concordant rise in revision procedures. It is expected that, the annual number has roughly doubled from that recorded for 2005.⁴

Compared with primary TKAs, however, revision TKAs have had less promising results, with survivorship as low as 60% over shorter periods.^7,8 In addition, recent studies have found an even higher degree of dissatisfaction and functional limitations among revision TKA patients than among primary TKA patients, 15% to 30% of whom are unhappy with their procedures.^9-11 These shortcomings of revision TKAs are thought to result from several factors, including poor bone quality, insufficient bone stock, ligamentous instability, soft-tissue incompetence, infection, malalignment, problems with extensor mechanisms, and substantial pain of uncertain etiology.

Despite there being several complex factors that can lead to worse outcomes with revision TKAs, surgeons are expected to produce results equivalent to those of primary TKAs. It is therefore imperative to delineate the objective and subjective outcomes of revision techniques to identify areas in need of improvement. In this article, we provide a concise overview of revision TKA outcomes in order to stimulate manufacturers, surgeons, and hospitals to improve on implant designs, surgical techniques, and care guidelines for revision TKA. We review the evidence on 5 points: aseptic survivorship, functional outcomes, patient satisfaction, quality of life (QOL), and economic impact. In addition, we compare available outcome data for revision and primary TKAs.

1. Aseptic survivorship

Fehring and colleagues¹² in 2001 and Sharkey and colleagues¹³ in 2002 evaluated mechanisms of failure for revision TKA and reported many failures resulted from infection or were associated with the implant, and occurred within 2 years after the primary procedure. More recently, Dy and colleagues¹⁴ found the most common reason for revision was aseptic loosening, followed by infection. The present review focuses on aseptic femoral and tibial revision.

The failure rate for revision TKA is substantially higher than for primary TKA with the same type of prosthesis because of the complexity of the revision procedure, the increasing constraint of the implant design, and the higher degree of bone loss. (Appendix 1 lists risk factors for revision surgery. Appendix 2 is a complete list of survivorship outcomes of revision TKA.)

Sheng and colleagues¹⁵ in 2006 and Koskinen and colleagues¹⁶ in 2008 analyzed Finnish Arthroplasty Register data to determine failure rates for revision and primary TKA. Sheng and colleagues¹⁵ examined survivorship of 2637 revision TKAs (performed between 1990 and 2002) for all-cause endpoints after first revision procedure. Survivorship rates were 89% (5 years) and 79% (10 years), while Koskinen and colleagues¹⁶ noted all-cause survival rates of 80% at 15 years. More recently, in 2013, the New Zealand Orthopaedic Association¹⁷ analyzed New Zealand Joint Registry data for revision and re-revision rates (rates of revision per 100 component years) for 64,556 primary TKAs performed between 1999 and 2012. During the period studied, 1684 revisions were performed, reflecting a 2.6% revision rate, a 0.50% rate of revision per 100 component years, and a 13-year Kaplan-Meier survivorship of 94.5%. The most common reasons for revision were pain, deep infection, and tibial component loosening (Table 1).

Posterior stabilized implants

Laskin and Ohnsorge¹⁸ retrospectively reviewed the cases of 58 patients who underwent unilateral revision TKA (with a posterior stabilized implant), of which 42% were for coronal instability and 44% for a loose tibial component. At minimum 4-year follow-up, 52 of the 58 patients had anteroposterior instability of less than 5 mm. In addition, 5 years after surgery, aseptic survivorship was 96%. Meijer and colleagues¹⁹ conducted a retrospective comparative study of 69 revision TKAs (65 patients) in which 9 knees received a primary implant and 60 received a revision implant with stems and augmentation (60 = 37 posterior stabilized, 20 constrained, 3 rotating hinge). Survival rates for the primary implants were 100% (1 year), 73% (2 years), and 44% (5 years), and survival rates for the revision implants were significantly better: 95% (1 year), 92% (2 years), and 92% (5 years) (hazard ratio, 5.87; P = .008). The authors therefore indicated that it was unclear whether using a primary implant should still be an option in revision TKA and, if it is used, whether it should be limited to less complex situations in which bone loss and ligament damage are minimal (Table 2).

Constrained and semiconstrained implants

In a study of 234 knees (209 patients) with soft-tissue deficiency, Wilke and colleagues²⁰ evaluated the long-term survivorship of revision TKA with use of a semiconstrained modular fixed-bearing implant system. Overall Kaplan-Meier survival rates were 91% (5 years) and 81% (10 years) at a mean follow-up of 9 years. When aseptic revision was evaluated, however, the survival rates increased to 95% (5 years) and 90% (10 years). The authors noted that male sex was the only variable that significantly increased the risk for re-revision (hazard ratio, 2.07; P = .02), which they attributed to potentially higher activity levels. In 2006 and 2011, Lachiewicz and Soileau^21,22 evaluated the survival of first- and second-generation constrained condylar prostheses in primary TKA cases with severe valgus deformities, incompetent collateral ligaments, or severe flexion contractures. Of the 54 knees (44 patients) with first-generation prostheses, 42 (34 patients) had a mean follow-up of 9 years (range, 5-16 years). Ten-year survival with failure, defined as component revision for loosening, was 96%. The 27 TKAs using second-generation prostheses had a mean follow-up of about 5 years (range, 2-12 years). At final follow-up, there were no revisions for loosening or patellar problems, but 6 knees (22%) required lateral retinacular release of the patella (Table 3).

Rotating hinge implants

Neumann and colleagues²³ evaluated the clinical and radiographic outcomes of 24 rotating hinge prostheses used for aseptic loosening with substantial bone loss and collateral ligament instability. At a mean follow-up of 56 months (range, 3-5 years), there was no evidence of loosening of any implants, and nonprogressive radiolucent lines were found in only 2 tibial components. Kowalczewski and colleagues²⁴ evaluated the clinical and radiologic outcomes of 12 primary TKAs using a rotating hinge knee prosthesis at a minimum follow-up of 10 years. By most recent follow-up, no implants had been revised for loosening, and only 3 had nonprogressive radiolucent lines (Table 4).

Endoprostheses (modular segmental implants)

In a systematic review of 9 studies, Korim and colleagues²⁵ evaluated 241 endoprostheses used for limb salvage under nononcologic conditions. Mean follow-up was about 3 years (range, 1-5 years). The devices were used to treat various conditions, including periprosthetic fracture, bone loss with aseptic loosening, and ligament insufficiency. The overall reoperation rate was 17% (41/241 cases). Mechanical failures were less frequent (6%-19%) (Table 5).

2. Functional outcomes

The goal in both primary and revision TKA is to restore the function and mobility of the knee and to alleviate pain. Whereas primary TKAs are realistically predictable and reproducible in their outcomes, revision TKAs are vastly more complicated, which can result in worse postoperative outcomes and function. In addition, revision TKAs may require extensive surgical exposure, which causes more tissue and muscle damage, prolonging rehabilitation. (Appendix 3 is a complete list of studies of functional outcomes of revision TKA.)

This discrepancy in functional outcomes between primary and revision TKA begins as early as the postoperative inpatient rehabilitation period. Using the functional independence measurement (FIM), which estimates performance of activities of daily living, mobility, and cognition, Vincent and colleagues²⁶ evaluated the functional improvement produced by revision versus primary TKA during inpatient rehabilitation. They compared 424 consecutive primary TKAs with 138 revision TKAs. For both groups, FIM scores increased significantly (P = .015) between admission and discharge. On discharge, however, FIM scores were significantly (P = .01) higher for the primary group than the revision group (29 and 27 points, respectively). Furthermore, in the evaluation of mechanisms of failure, patients who had revision TKA for mechanical or pain-related problems did markedly better than those who had revision TKA for infection.

Compared with primary knee implants, revision implants require increasing constraint. We assume increasing constraint affects knee biomechanics, leading to worsening functional outcomes. In a study of 60 revision TKAs (57 patients) using posterior stabilized, condylar constrained, or rotating hinge prostheses, Vasso and colleagues²⁷ examined functional outcomes at a median follow-up of 9 years (range, 4-12 years). At most recent follow-up, mean International Knee Society (IKS) Knee and Function scores were 81 (range, 48-97) and 79 (range, 56-92), mean Hospital for Special Surgery (HSS) score was 84 (range, 62-98), and mean range of motion (ROM) was 121° (range, 98°-132°) (P < .001). Although there were no significant differences in IKS and HSS scores between prosthesis types, ROM was significantly (P < .01) wider in the posterior stabilized group than in the condylar constrained and rotating hinge groups (127° vs 112° and 108°), suggesting increasing constraint resulted in decreased ROM. Several studies have found increasing constraint might lead to reduced function.^28-30

However, Hwang and colleagues³¹ evaluated functional outcomes in 36 revision TKAs and noted that the cemented posterior stabilized (n = 8), condylar constrained (n = 25), and rotating hinge (n = 13) prostheses used did not differ in their mean Knee Society scores (78, 81, and 83, respectively).

There remains a marked disparity in patient limitations seen after revision versus primary TKA. Given the positive results being obtained with newer implants, studies might suggest recent generations of prostheses have allowed designs to be comparable. As design development continues, we may come closer to achieving outcomes comparable to those of primary TKA.

3. Patient satisfaction

Several recent reports have shown that 10% to 25% of patients who underwent primary TKA were dissatisfied with their surgery^30,32; other studies have found patient satisfaction often correlating to function and pain.^33-35 Given the worse outcomes for revision TKA (outlined in the preceding section), the substantial pain accompanying a second, more complex procedure, and the extensive rehabilitation expected, we suspect patients who undergo revision TKA are even less satisfied with their surgery than their primary counterparts are. (See Appendix 4 for a complete list of studies of patient satisfaction after revision TKA.)

Barrack and colleagues³² evaluated a consecutive series of 238 patients followed up for at least 1 year after revision TKA. Patients were asked to rate their degree of satisfaction with both their primary procedure and the revision and to indicate their expectations regarding their revision prosthesis. Mean satisfaction score was 7.4 (maximum = 10), with 13% of patients dissatisfied, 18% somewhat satisfied, and 69% satisfied. Seventy-four percent of patients expected their revision prosthesis to last longer than the primary prosthesis.

Greidanus and colleagues³⁶ evaluated patient satisfaction in 60 revision TKA cases and 199 primary TKA cases at 2-year follow-up. The primary TKA group had significantly (P < .01) higher satisfaction scores in a comparison with the revision TKA group: Global (86 vs 73), Pain Relief (88 vs 70), Function (83 vs 67), and Recreation (77 vs 62). These findings support the satisfaction rates reported by Dahm and colleagues^33,34: 91% for primary TKA patients and 77% for revision TKA patients.

4. Quality of life

Procedure complexity leads to reduced survivorship, function, and mobility, longer rehabilitation, and decreased QOL for revision TKA patients relative to primary TKA patients.³⁷ (See Appendix 5 for a complete list of studies of QOL outcomes of revision TKA.)

Greidanus and colleagues³⁶ evaluated joint-specific QOL (using the 12-item Oxford Knee Score; OKS) and generic QOL (using the 12-Item Short Form Health Survey; SF-12) in 60 revision TKA cases and 199 primary TKA cases at a mean follow-up of 2 years. (The OKS survey is used to evaluate patient perspectives on TKA outcomes,³⁸ and the multipurpose SF-12 questionnaire is used to assess mental and physical function and general health-related QOL.³⁹) Compared with the revision TKA group, the primary TKA group had significantly higher OKS after surgery (78 vs 68; P = .01) as well as significantly higher SF-12 scores: Global (84 vs 72; P = .01), Mental (54 vs 50; P = .03), and Physical (43 vs 37; P = .01). Similarly, Ghomrawi and colleagues⁴⁰ evaluated patterns of improvement in 308 patients (318 knees) who had revision TKA. At 24-month follow-up, mean SF-36 Physical and Mental scores were 35 and 52, respectively.

Deehan and colleagues⁴¹ used the Nottingham Health Profile (NHP) to compare 94 patients’ health-related QOL scores before revision TKA with their scores 3 months, 1 year, and 5 years after revision. NHP Pain subscale scores were significantly lower 3 and 12 months after surgery than before surgery, but this difference was no longer seen at the 5-year follow-up. There was no significant improvement in scores on the other 5 NHP subscales (Sleep, Energy, Emotion, Mobility, Social Isolation) at any time points.

As shown in the literature, patients’ QOL outcomes improve after revision TKA, but these gains are not at the level of patients who undergo primary TKA.^36,41 Given that revision surgery is more extensive, and that perhaps revision patients have poorer muscle function, they usually do not return to the level they attained after their index procedure.

5. Economic impact

Consistent with the outcomes already described, the economic impact of revision TKAs is excess expenditures and costs to patients and health care institutions.⁴² The sources of this impact are higher implant costs, extra operative trays and times, longer hospital stays, more rehabilitation, and increased medication use.⁴³ Revision TKA costs range from $49,000 to more than $100,000—a tremendous increase over primary TKA costs ($25,000-$30,000).^43-45 Furthermore, the annual economic burden associated with revision TKA, now $2.7 billion, is expected to exceed $13 billion by 2030.⁴⁶ In the United States, about $23.2 billion will be spent on 926,527 primary TKAs in 2015; significantly, the costs associated with revising just 10% of these cases account for almost 50% of the total cost of the primary procedures.⁴⁶

In a retrospective cost-identification multicenter cohort study, Bozic and colleagues⁴⁷ found that both-component and single-component revisions, compared with primary procedures, were associated with significantly increased operative time (~265 and 221 minutes vs 200 minutes), use of allograft bone (23% and 14% vs 1%), length of stay (5.4 and 5.7 days vs 5.0 days), and percentage of patients discharged to extended-care facilities (26% and 26% vs 25%) (P < .0001). Hospital costs for both- and single-component revisions were 138% and 114% higher than costs for primary procedures (P < .0001). More recently, Kallala and colleagues⁴⁴ analyzed UK National Health Service data and compared the costs of revision for infection with revision for other causes (pain, instability, aseptic loosening, fracture). Mean length of stay associated with revision for infection (21.5 days) was more than double that associated with revision for aseptic loosening (9.5 days; P < .0001), and mean cost of revision for septic causes (£30,011) was more than 3 times that of revision for other causes (£9655; P < .0001). The authors concluded that the higher costs of revision knee surgery have a considerable economic impact, especially in infection cases.

With more extensive procedures, long-stem or more constrained prostheses are often needed to obtain adequate fixation and stability. The resulting increased, substantial economic burden is felt by patients and the health care system. Given that health care reimbursements are declining, hospitals that perform revision TKAs can sustain marked financial losses. Some centers are asking whether it is cost-effective to continue to perform these types of procedures. We must find new ways to provide revision procedures using less costly implants and tools so that centers will continue to make these procedures available to patients.

Conclusion

Given the exponential growth in primary TKAs, there will be a concordant increase in revision TKAs in the decades to come. This review provides a concise overview of revision TKA outcomes. Given the low level of evidence regarding revision TKAs, we need further higher quality studies of their prostheses and outcomes. Specifically, we need systematic reviews and meta-analyses to provide higher quality evidence regarding outcomes of using individual prosthetic designs.

Before 1990, a considerable number of revisions were performed, largely for implant-associated failures, in the first few years after index primary knee arthroplasties.^1,2 Since then, surgeons, manufacturers, and hospitals have collaborated to improve implant designs, techniques, and care guidelines.^3,4 Despite the substantial improvements in designs, which led to implant longevity of more than 15 years in many cases, these devices still have limited life spans. Large studies have estimated that the risk for revision required after primary knee arthroplasty ranges from as low as 5% at 15 years to up to 9% at 10 years.^4,5

The surgical goals of revision total knee arthroplasty (TKA) are to obtain stable fixation of the prosthesis to host bone, to obtain a stable range of motion compatible with the patient’s activities of daily living, and to achieve these goals while using the smallest amount of prosthetic augments and constraint so that the soft tissues may share in load transfer.⁶ As prosthetic constraint increases, the soft tissues participate less in load sharing, and increasing stresses are put on the implant–bone interface, which further increases the risk for early implant loosening.⁷ Hence, as characteristics of a revision implant become more constrained, there is often a higher rate of aseptic loosening expected.⁸

Controversy remains regarding the ideal implant type for revision TKA. To ensure the success of revision surgery and to reduce the risks for postoperative dissatisfaction, complications, and re-revision, orthopedists must understand the types of revision implant designs available, particularly as each has its own indications and potential complications.

In this article, we review the classification systems used for revision TKA as well as the types of prosthetic designs that can be used: posterior stabilized, nonlinked constrained, rotating hinge, and modular segmental.

1. Classification of bone loss and soft-tissue integrity

To further understand revision TKA, we must consider the complexity level of these cases, particularly by evaluating degree of bone loss and soft-tissue deficiency. The most accepted way to assess bone loss both before and during surgery is to use the AORI (Anderson Orthopaedic Research Institute) classification system.⁹ Bone loss can be classified into 3 types: I, in which metaphyseal bone is intact and small bone defects do not compromise component stability; II, in which metaphyseal bone is damaged and cancellous bone loss requires cement fill, augments, or bone graft; and III, in which metaphyseal bone is deficient, and lost bone comprises a major portion of condyle or plateau and occasionally requires bone grafts or custom implants (Table 1). These patterns of bone loss are occasionally associated with detachment of the collateral ligament or patellar tendon.

In addition to understanding bone loss in revision TKA, surgeons must be aware of soft-tissue deficiencies (eg, collateral ligaments, extensor mechanism), which also influence type and amount of prosthesis constraint. Specifically, constraint choice depends on amount of bone loss and on the condition of stabilizing tissues, such as the collateral ligaments. Under conditions of minimal bone loss and intact peripheral ligaments, a less constrained device, such as a primary posterior stabilized system, can be considered. When ligaments are present but insufficient, a semiconstrained device is recommended. In the presence of medial collateral ligament attenuation or complete medial or lateral collateral ligament dysfunction, a fully constrained prosthesis is required.⁸ Therefore, amount of bone loss or soft-tissue deficiency often dictates which prosthesis to use.

For radiographic classification, the Knee Society roentgenographic evaluation and scoring system¹⁰ has been implemented to allow for uniform reporting of radiographic results and to ensure adequate preoperative planning and postoperative assessment of component alignment. This system incorporates the evaluation of alignment in the coronal, sagittal, and patellofemoral planes and assesses radiolucency using zones dividing the implant–bone interface into segments to allow for easier classification of areas of lucency. More recently, a modified version of the Knee Society system was constructed.¹¹ This modification simplifies zone classifications and accommodates more complex revision knee designs and stem extensions.

2. Posterior stabilized designs

Cruciate-retaining prostheses are seldom applicable in the revision TKA setting because of frequent damage to the posterior cruciate ligament, except in the case of simple polyethylene exchanges or, potentially, revisions of failed unicompartmental TKAs. Thus, posterior stabilized designs are the first-line choice for revision TKA (Figure 1). These prostheses are indicated only when the posterior cruciate ligament is incompetent and in the setting of adequate flexion and extension and medial and lateral collateral ligament balancing.

However, studies have shown that posterior stabilized TKAs have a limited role in revision TKAs, as the amount of ligamentous and bony damage is often underestimated in these patients, and use of a primary implant in a revision setting often requires additional augments, all of which may have contributed to the high failure rate. Thus, this design should be used only when the patient has adequate bone stock (AORI type I) and collateral ligament tension. This situation further emphasizes the importance of performing intraoperative testing for ligamentous balance and bone deficit evaluation in order to determine the most appropriate implant (Table 2).

3. Nonlinked constrained designs

Nonlinked constrained (condylar constrained) designs are the devices most commonly used for revision TKAs (>50% of revision knees). These prostheses provide increased articular constraint, which is required in patients with persistent instability, despite appropriate soft-tissue balancing. Increased articular constraint allows for more knee stability by providing progressive varus-valgus, coronal, and rotational stability with the aid of taller and wider tibial posts.¹² Specifically, these implants incorporate a tibial post that fits closely between the femoral condyles, allowing for less motion compared with a standard posterior stabilized design.¹²

In addition, these designs may be used with augments, stems, and allografts when bone loss is more substantial. In particular, stem extensions allow for load distribution to the diaphyseal regions of the tibia and femur and thereby aid in reducing the increased stress at the bone–implant interface, which is a common concern with these implants. However, these extensions cost more, require intramedullary invasion, and are associated with higher rates of leg and thigh pain.¹²

These prostheses are often implicated in cases involving a high degree of bone loss (eg, AORI type II or III). They are ideally used in cases in which complete revision of both tibial and femoral components is needed and are indicated in cases of incompetent posterior cruciate ligament, partial functional loss of medial or lateral collateral ligaments, or flexion-extension mismatch.¹³ Furthermore, use of a constrained prosthesis is recommended in the setting of varus or valgus instability, or repeated dislocations of a posterior stabilized design (Table 2).

Ten-year survivorship ranges from 85% to 96%, but this is substantially lower than the 95% to 96% for condylar constrained prostheses used in primary TKAs.^14-17 Moreover, the large discrepancy between survivorship of primary TKA and revision TKA with a constrained prosthesis further affirms that the complexity of revision surgery, rather than the prosthesis used, may have more deleterious effects on outcomes. However, surgeons must be aware that increased constraint leads to increased stress on the prosthetic interfaces with associated aseptic loosening and early failure, and this continues to be a legitimate concern.

4. Rotating hinge designs

Many patients who undergo revision TKA can be managed with a posterior stabilizing or nonlinked constrained design. However, in patients who present with severe ligamentous instability and bone loss (AORI type II or III), a rotating hinge prostheses, or highly constrained device, is often recommended (Figure 2).¹⁸ By using a rotating mobile-bearing platform, this prosthesis permits axial rotation through a metal-reinforced polyethylene-post articulation in the tibial tray. In addition, it involves use of modular diaphyseal-engaging stems and diaphyseal sleeves, which allow for the bypass of bony defects and areas of bone loss (Table 2).

However, the rigid biomechanics of hinged prostheses is associated with increased risk for aseptic loosening (aseptic 10-year survival, 60%-80%), imparted by the transfer of stresses across the bone. The higher risk for early loosening, osteolysis, and excessive wear—caused by the highly restricted biomechanics of early generations of fixed hinged designs—has led to the development of new devices with mobile mechanics. Prosthetic designs have been improved with an added rotational axis to reduce torsional stress, a patellar resurfacing option, and better stem fixation and patellofemoral kinematics. Overall, these are aimed to improve rates of instability and aseptic loosening, with promising results demonstrated in the literature.

5. Modular segmental arthroplasty designs

Segmental arthroplasty prostheses, which typically are end-of-the-line revision TKA options, are applicable only in cases of extensive bone loss (more than can be treated with allografts or augments; AORI type 3), complete ligamentous disruption/absence, loss of periprosthetic soft tissue, and multiple previous revision procedures (Figure 3). Despite the limited indications for these prostheses, they yield quick return to function without graft nonunion or resorption, and they augment ingrowth/ongrowth. Furthermore, the next surgical option could be fusion or amputation. When failures were specifically evaluated for aseptic loosening across 4 studies, the survival rate ranged from 83% to 99.5%, with the most frequent complication being infection (up to 33% in one series).^6,19-21

The major roles for segmental arthroplasty prostheses in primary TKAs are in the setting of oncologic conditions that require bony excision, or unreconstuctable fractures about the knee. Used after ancillary metastatic disease, these prostheses demonstrate positive results, according to several reports.^22,23 In the setting of revision TKA, however, these prostheses should be used only when other surgical options are unfeasible, given the high risk for infection and the re-revision rates. Currently, revision TKAs with tumor prostheses have a high failure rate (up to 50%) because of the extensive surgery and the lack of bony and soft-tissue support (Table 2).

Conclusion

Orthopedists performing revision TKAs must consider bone stock and remaining ligament stability. In particular, they should choose implants for least constraint and adequate knee stability, as these are essential in minimizing the stresses on the implant–bone interface. Ultimately, functional outcomes, survivorship, and postoperative satisfaction determine the success of these designs. However, predictors of outcomes of revision surgery are often multifactorial, and surgeons must also consider procedure complexity and patient-specific characteristics.

Before 1990, a considerable number of revisions were performed, largely for implant-associated failures, in the first few years after index primary knee arthroplasties.^1,2 Since then, surgeons, manufacturers, and hospitals have collaborated to improve implant designs, techniques, and care guidelines.^3,4 Despite the substantial improvements in designs, which led to implant longevity of more than 15 years in many cases, these devices still have limited life spans. Large studies have estimated that the risk for revision required after primary knee arthroplasty ranges from as low as 5% at 15 years to up to 9% at 10 years.^4,5

The surgical goals of revision total knee arthroplasty (TKA) are to obtain stable fixation of the prosthesis to host bone, to obtain a stable range of motion compatible with the patient’s activities of daily living, and to achieve these goals while using the smallest amount of prosthetic augments and constraint so that the soft tissues may share in load transfer.⁶ As prosthetic constraint increases, the soft tissues participate less in load sharing, and increasing stresses are put on the implant–bone interface, which further increases the risk for early implant loosening.⁷ Hence, as characteristics of a revision implant become more constrained, there is often a higher rate of aseptic loosening expected.⁸

Controversy remains regarding the ideal implant type for revision TKA. To ensure the success of revision surgery and to reduce the risks for postoperative dissatisfaction, complications, and re-revision, orthopedists must understand the types of revision implant designs available, particularly as each has its own indications and potential complications.

In this article, we review the classification systems used for revision TKA as well as the types of prosthetic designs that can be used: posterior stabilized, nonlinked constrained, rotating hinge, and modular segmental.

1. Classification of bone loss and soft-tissue integrity

To further understand revision TKA, we must consider the complexity level of these cases, particularly by evaluating degree of bone loss and soft-tissue deficiency. The most accepted way to assess bone loss both before and during surgery is to use the AORI (Anderson Orthopaedic Research Institute) classification system.⁹ Bone loss can be classified into 3 types: I, in which metaphyseal bone is intact and small bone defects do not compromise component stability; II, in which metaphyseal bone is damaged and cancellous bone loss requires cement fill, augments, or bone graft; and III, in which metaphyseal bone is deficient, and lost bone comprises a major portion of condyle or plateau and occasionally requires bone grafts or custom implants (Table 1). These patterns of bone loss are occasionally associated with detachment of the collateral ligament or patellar tendon.

In addition to understanding bone loss in revision TKA, surgeons must be aware of soft-tissue deficiencies (eg, collateral ligaments, extensor mechanism), which also influence type and amount of prosthesis constraint. Specifically, constraint choice depends on amount of bone loss and on the condition of stabilizing tissues, such as the collateral ligaments. Under conditions of minimal bone loss and intact peripheral ligaments, a less constrained device, such as a primary posterior stabilized system, can be considered. When ligaments are present but insufficient, a semiconstrained device is recommended. In the presence of medial collateral ligament attenuation or complete medial or lateral collateral ligament dysfunction, a fully constrained prosthesis is required.⁸ Therefore, amount of bone loss or soft-tissue deficiency often dictates which prosthesis to use.

For radiographic classification, the Knee Society roentgenographic evaluation and scoring system¹⁰ has been implemented to allow for uniform reporting of radiographic results and to ensure adequate preoperative planning and postoperative assessment of component alignment. This system incorporates the evaluation of alignment in the coronal, sagittal, and patellofemoral planes and assesses radiolucency using zones dividing the implant–bone interface into segments to allow for easier classification of areas of lucency. More recently, a modified version of the Knee Society system was constructed.¹¹ This modification simplifies zone classifications and accommodates more complex revision knee designs and stem extensions.

2. Posterior stabilized designs

Cruciate-retaining prostheses are seldom applicable in the revision TKA setting because of frequent damage to the posterior cruciate ligament, except in the case of simple polyethylene exchanges or, potentially, revisions of failed unicompartmental TKAs. Thus, posterior stabilized designs are the first-line choice for revision TKA (Figure 1). These prostheses are indicated only when the posterior cruciate ligament is incompetent and in the setting of adequate flexion and extension and medial and lateral collateral ligament balancing.

However, studies have shown that posterior stabilized TKAs have a limited role in revision TKAs, as the amount of ligamentous and bony damage is often underestimated in these patients, and use of a primary implant in a revision setting often requires additional augments, all of which may have contributed to the high failure rate. Thus, this design should be used only when the patient has adequate bone stock (AORI type I) and collateral ligament tension. This situation further emphasizes the importance of performing intraoperative testing for ligamentous balance and bone deficit evaluation in order to determine the most appropriate implant (Table 2).

3. Nonlinked constrained designs

Nonlinked constrained (condylar constrained) designs are the devices most commonly used for revision TKAs (>50% of revision knees). These prostheses provide increased articular constraint, which is required in patients with persistent instability, despite appropriate soft-tissue balancing. Increased articular constraint allows for more knee stability by providing progressive varus-valgus, coronal, and rotational stability with the aid of taller and wider tibial posts.¹² Specifically, these implants incorporate a tibial post that fits closely between the femoral condyles, allowing for less motion compared with a standard posterior stabilized design.¹²

In addition, these designs may be used with augments, stems, and allografts when bone loss is more substantial. In particular, stem extensions allow for load distribution to the diaphyseal regions of the tibia and femur and thereby aid in reducing the increased stress at the bone–implant interface, which is a common concern with these implants. However, these extensions cost more, require intramedullary invasion, and are associated with higher rates of leg and thigh pain.¹²

These prostheses are often implicated in cases involving a high degree of bone loss (eg, AORI type II or III). They are ideally used in cases in which complete revision of both tibial and femoral components is needed and are indicated in cases of incompetent posterior cruciate ligament, partial functional loss of medial or lateral collateral ligaments, or flexion-extension mismatch.¹³ Furthermore, use of a constrained prosthesis is recommended in the setting of varus or valgus instability, or repeated dislocations of a posterior stabilized design (Table 2).

Ten-year survivorship ranges from 85% to 96%, but this is substantially lower than the 95% to 96% for condylar constrained prostheses used in primary TKAs.^14-17 Moreover, the large discrepancy between survivorship of primary TKA and revision TKA with a constrained prosthesis further affirms that the complexity of revision surgery, rather than the prosthesis used, may have more deleterious effects on outcomes. However, surgeons must be aware that increased constraint leads to increased stress on the prosthetic interfaces with associated aseptic loosening and early failure, and this continues to be a legitimate concern.

4. Rotating hinge designs

Many patients who undergo revision TKA can be managed with a posterior stabilizing or nonlinked constrained design. However, in patients who present with severe ligamentous instability and bone loss (AORI type II or III), a rotating hinge prostheses, or highly constrained device, is often recommended (Figure 2).¹⁸ By using a rotating mobile-bearing platform, this prosthesis permits axial rotation through a metal-reinforced polyethylene-post articulation in the tibial tray. In addition, it involves use of modular diaphyseal-engaging stems and diaphyseal sleeves, which allow for the bypass of bony defects and areas of bone loss (Table 2).

However, the rigid biomechanics of hinged prostheses is associated with increased risk for aseptic loosening (aseptic 10-year survival, 60%-80%), imparted by the transfer of stresses across the bone. The higher risk for early loosening, osteolysis, and excessive wear—caused by the highly restricted biomechanics of early generations of fixed hinged designs—has led to the development of new devices with mobile mechanics. Prosthetic designs have been improved with an added rotational axis to reduce torsional stress, a patellar resurfacing option, and better stem fixation and patellofemoral kinematics. Overall, these are aimed to improve rates of instability and aseptic loosening, with promising results demonstrated in the literature.

5. Modular segmental arthroplasty designs

Segmental arthroplasty prostheses, which typically are end-of-the-line revision TKA options, are applicable only in cases of extensive bone loss (more than can be treated with allografts or augments; AORI type 3), complete ligamentous disruption/absence, loss of periprosthetic soft tissue, and multiple previous revision procedures (Figure 3). Despite the limited indications for these prostheses, they yield quick return to function without graft nonunion or resorption, and they augment ingrowth/ongrowth. Furthermore, the next surgical option could be fusion or amputation. When failures were specifically evaluated for aseptic loosening across 4 studies, the survival rate ranged from 83% to 99.5%, with the most frequent complication being infection (up to 33% in one series).^6,19-21

The major roles for segmental arthroplasty prostheses in primary TKAs are in the setting of oncologic conditions that require bony excision, or unreconstuctable fractures about the knee. Used after ancillary metastatic disease, these prostheses demonstrate positive results, according to several reports.^22,23 In the setting of revision TKA, however, these prostheses should be used only when other surgical options are unfeasible, given the high risk for infection and the re-revision rates. Currently, revision TKAs with tumor prostheses have a high failure rate (up to 50%) because of the extensive surgery and the lack of bony and soft-tissue support (Table 2).

Conclusion

Orthopedists performing revision TKAs must consider bone stock and remaining ligament stability. In particular, they should choose implants for least constraint and adequate knee stability, as these are essential in minimizing the stresses on the implant–bone interface. Ultimately, functional outcomes, survivorship, and postoperative satisfaction determine the success of these designs. However, predictors of outcomes of revision surgery are often multifactorial, and surgeons must also consider procedure complexity and patient-specific characteristics.

Before 1990, a considerable number of revisions were performed, largely for implant-associated failures, in the first few years after index primary knee arthroplasties.^1,2 Since then, surgeons, manufacturers, and hospitals have collaborated to improve implant designs, techniques, and care guidelines.^3,4 Despite the substantial improvements in designs, which led to implant longevity of more than 15 years in many cases, these devices still have limited life spans. Large studies have estimated that the risk for revision required after primary knee arthroplasty ranges from as low as 5% at 15 years to up to 9% at 10 years.^4,5

The surgical goals of revision total knee arthroplasty (TKA) are to obtain stable fixation of the prosthesis to host bone, to obtain a stable range of motion compatible with the patient’s activities of daily living, and to achieve these goals while using the smallest amount of prosthetic augments and constraint so that the soft tissues may share in load transfer.⁶ As prosthetic constraint increases, the soft tissues participate less in load sharing, and increasing stresses are put on the implant–bone interface, which further increases the risk for early implant loosening.⁷ Hence, as characteristics of a revision implant become more constrained, there is often a higher rate of aseptic loosening expected.⁸

Controversy remains regarding the ideal implant type for revision TKA. To ensure the success of revision surgery and to reduce the risks for postoperative dissatisfaction, complications, and re-revision, orthopedists must understand the types of revision implant designs available, particularly as each has its own indications and potential complications.

In this article, we review the classification systems used for revision TKA as well as the types of prosthetic designs that can be used: posterior stabilized, nonlinked constrained, rotating hinge, and modular segmental.

1. Classification of bone loss and soft-tissue integrity

To further understand revision TKA, we must consider the complexity level of these cases, particularly by evaluating degree of bone loss and soft-tissue deficiency. The most accepted way to assess bone loss both before and during surgery is to use the AORI (Anderson Orthopaedic Research Institute) classification system.⁹ Bone loss can be classified into 3 types: I, in which metaphyseal bone is intact and small bone defects do not compromise component stability; II, in which metaphyseal bone is damaged and cancellous bone loss requires cement fill, augments, or bone graft; and III, in which metaphyseal bone is deficient, and lost bone comprises a major portion of condyle or plateau and occasionally requires bone grafts or custom implants (Table 1). These patterns of bone loss are occasionally associated with detachment of the collateral ligament or patellar tendon.

In addition to understanding bone loss in revision TKA, surgeons must be aware of soft-tissue deficiencies (eg, collateral ligaments, extensor mechanism), which also influence type and amount of prosthesis constraint. Specifically, constraint choice depends on amount of bone loss and on the condition of stabilizing tissues, such as the collateral ligaments. Under conditions of minimal bone loss and intact peripheral ligaments, a less constrained device, such as a primary posterior stabilized system, can be considered. When ligaments are present but insufficient, a semiconstrained device is recommended. In the presence of medial collateral ligament attenuation or complete medial or lateral collateral ligament dysfunction, a fully constrained prosthesis is required.⁸ Therefore, amount of bone loss or soft-tissue deficiency often dictates which prosthesis to use.

For radiographic classification, the Knee Society roentgenographic evaluation and scoring system¹⁰ has been implemented to allow for uniform reporting of radiographic results and to ensure adequate preoperative planning and postoperative assessment of component alignment. This system incorporates the evaluation of alignment in the coronal, sagittal, and patellofemoral planes and assesses radiolucency using zones dividing the implant–bone interface into segments to allow for easier classification of areas of lucency. More recently, a modified version of the Knee Society system was constructed.¹¹ This modification simplifies zone classifications and accommodates more complex revision knee designs and stem extensions.

2. Posterior stabilized designs

Cruciate-retaining prostheses are seldom applicable in the revision TKA setting because of frequent damage to the posterior cruciate ligament, except in the case of simple polyethylene exchanges or, potentially, revisions of failed unicompartmental TKAs. Thus, posterior stabilized designs are the first-line choice for revision TKA (Figure 1). These prostheses are indicated only when the posterior cruciate ligament is incompetent and in the setting of adequate flexion and extension and medial and lateral collateral ligament balancing.

However, studies have shown that posterior stabilized TKAs have a limited role in revision TKAs, as the amount of ligamentous and bony damage is often underestimated in these patients, and use of a primary implant in a revision setting often requires additional augments, all of which may have contributed to the high failure rate. Thus, this design should be used only when the patient has adequate bone stock (AORI type I) and collateral ligament tension. This situation further emphasizes the importance of performing intraoperative testing for ligamentous balance and bone deficit evaluation in order to determine the most appropriate implant (Table 2).

3. Nonlinked constrained designs

Nonlinked constrained (condylar constrained) designs are the devices most commonly used for revision TKAs (>50% of revision knees). These prostheses provide increased articular constraint, which is required in patients with persistent instability, despite appropriate soft-tissue balancing. Increased articular constraint allows for more knee stability by providing progressive varus-valgus, coronal, and rotational stability with the aid of taller and wider tibial posts.¹² Specifically, these implants incorporate a tibial post that fits closely between the femoral condyles, allowing for less motion compared with a standard posterior stabilized design.¹²

In addition, these designs may be used with augments, stems, and allografts when bone loss is more substantial. In particular, stem extensions allow for load distribution to the diaphyseal regions of the tibia and femur and thereby aid in reducing the increased stress at the bone–implant interface, which is a common concern with these implants. However, these extensions cost more, require intramedullary invasion, and are associated with higher rates of leg and thigh pain.¹²

These prostheses are often implicated in cases involving a high degree of bone loss (eg, AORI type II or III). They are ideally used in cases in which complete revision of both tibial and femoral components is needed and are indicated in cases of incompetent posterior cruciate ligament, partial functional loss of medial or lateral collateral ligaments, or flexion-extension mismatch.¹³ Furthermore, use of a constrained prosthesis is recommended in the setting of varus or valgus instability, or repeated dislocations of a posterior stabilized design (Table 2).

Ten-year survivorship ranges from 85% to 96%, but this is substantially lower than the 95% to 96% for condylar constrained prostheses used in primary TKAs.^14-17 Moreover, the large discrepancy between survivorship of primary TKA and revision TKA with a constrained prosthesis further affirms that the complexity of revision surgery, rather than the prosthesis used, may have more deleterious effects on outcomes. However, surgeons must be aware that increased constraint leads to increased stress on the prosthetic interfaces with associated aseptic loosening and early failure, and this continues to be a legitimate concern.

4. Rotating hinge designs

Many patients who undergo revision TKA can be managed with a posterior stabilizing or nonlinked constrained design. However, in patients who present with severe ligamentous instability and bone loss (AORI type II or III), a rotating hinge prostheses, or highly constrained device, is often recommended (Figure 2).¹⁸ By using a rotating mobile-bearing platform, this prosthesis permits axial rotation through a metal-reinforced polyethylene-post articulation in the tibial tray. In addition, it involves use of modular diaphyseal-engaging stems and diaphyseal sleeves, which allow for the bypass of bony defects and areas of bone loss (Table 2).

However, the rigid biomechanics of hinged prostheses is associated with increased risk for aseptic loosening (aseptic 10-year survival, 60%-80%), imparted by the transfer of stresses across the bone. The higher risk for early loosening, osteolysis, and excessive wear—caused by the highly restricted biomechanics of early generations of fixed hinged designs—has led to the development of new devices with mobile mechanics. Prosthetic designs have been improved with an added rotational axis to reduce torsional stress, a patellar resurfacing option, and better stem fixation and patellofemoral kinematics. Overall, these are aimed to improve rates of instability and aseptic loosening, with promising results demonstrated in the literature.

5. Modular segmental arthroplasty designs

Segmental arthroplasty prostheses, which typically are end-of-the-line revision TKA options, are applicable only in cases of extensive bone loss (more than can be treated with allografts or augments; AORI type 3), complete ligamentous disruption/absence, loss of periprosthetic soft tissue, and multiple previous revision procedures (Figure 3). Despite the limited indications for these prostheses, they yield quick return to function without graft nonunion or resorption, and they augment ingrowth/ongrowth. Furthermore, the next surgical option could be fusion or amputation. When failures were specifically evaluated for aseptic loosening across 4 studies, the survival rate ranged from 83% to 99.5%, with the most frequent complication being infection (up to 33% in one series).^6,19-21

The major roles for segmental arthroplasty prostheses in primary TKAs are in the setting of oncologic conditions that require bony excision, or unreconstuctable fractures about the knee. Used after ancillary metastatic disease, these prostheses demonstrate positive results, according to several reports.^22,23 In the setting of revision TKA, however, these prostheses should be used only when other surgical options are unfeasible, given the high risk for infection and the re-revision rates. Currently, revision TKAs with tumor prostheses have a high failure rate (up to 50%) because of the extensive surgery and the lack of bony and soft-tissue support (Table 2).

Conclusion

Orthopedists performing revision TKAs must consider bone stock and remaining ligament stability. In particular, they should choose implants for least constraint and adequate knee stability, as these are essential in minimizing the stresses on the implant–bone interface. Ultimately, functional outcomes, survivorship, and postoperative satisfaction determine the success of these designs. However, predictors of outcomes of revision surgery are often multifactorial, and surgeons must also consider procedure complexity and patient-specific characteristics.

The metal-backed patella was originally designed to address the shortcomings of cemented, all-polyethylene patellae: deformation, aseptic loosening, stress fractures of polyethylene, and possible thermal damage from bone cement.^1-3 Several long-term studies have found very good outcomes with use of all-polyethylene patellae.^4-6 However, complications of using an all-polyethylene patella reportedly accounted for up to half of all knee revisions, and during revision surgery patellar bone stock was often found to have been compromised.⁷

The intention behind the design of press-fit metal-backed patellae was to address the shortcomings of all-polyethylene patellae by eliminating the need for bone cement and providing stiffness that would help resist polyethylene deformation while decreasing implant–bone interface stresses.⁸ However, early design iterations of metal-backed patellae demonstrated short-term failures—most commonly, local polyethylene wear damaging the locking mechanism and subsequent dissociation or fracture from the metal baseplate; polyethylene delamination from the metal baseplate; and failure of interface fixation.^9,10 On the other hand, good fixation with bony ingrowth was observed in both titanium and cobalt-chromium porous-coated patellae.^1,3,9,11-13 Overall, however, negative outcomes reported for metal-backed patellae led many surgeons to abandon these components and return to using cemented all-polyethylene patellae.

Negative outcomes of earlier metal-backed patellae designs have overshadowed reports of positive outcomes achieved with careful attention paid to component design, patellar tracking, and surgical technique.^2,3,14 Subsequent design improvements (eg, a third stabilizing peg, thicker polyethylene, improved conformity) produced excellent outcomes.^8,12,15 The advantages of using a metal-backed patella (eg, uniform load sharing, decreased polyethylene deformation, potential for biological fixation) may be unjustly outweighed by the fear of patellar component failure.³

Our 30-plus years of experience with metal-backed patellar components reflect the evolving effect of component design on outcome. Much as reported elsewhere, we found earlier component failures were caused by poor locking mechanisms, thin polyethylene, poor tracking, and minimal femur contact. Over the past decade, however, our outcomes with Duracon metal-backed patellae (Stryker) have been encouraging. We think these positive outcomes, seen over minimum 5-year follow-up, are largely attributable to the thicker polyethylene and improved articular conformity of this component relative to earlier designs. We have also found it helpful to adhere to certain criteria when implanting metal-backed patellae, and we think adhering to these criteria, along with improved component design, indicates use of press-fit metal-backed patellae. In this article, we report our failure incidence with use of this device at minimum 5-year follow-up.

Materials and Methods

In this single-center study, we performed clinical and independent radiographic reviews of 88 primary press-fit metal-backed patellae with minimum 5-year follow-up. All components were the same design (Duracon metal-backed patella) from the same manufacturer (Stryker).

This study, which began in September 2003, was reviewed and approved by the Western Institutional Review Board (WIRB). Either the investigator (Dr. Hedley) or the clinical study coordinator gave study candidates a full explanation of the study and answered any questions. Patients who still wanted to participate in the study signed WIRB consent forms after their index surgery but before minimum 5-year follow-up.

Device Description

This Duracon patella has a porous-coated cobalt-chromium metal back intended for press-fit fixation, 3 cobalt-chromium porous-coated pegs, and a preassembled polyethylene anterior surface (Figure 1). Four sizes are available to fit the peripheral shape of the resected patella.

This patella has 3 styles: symmetric, asymmetric, and conversion. In this study, we used only the asymmetric and conversion styles. The design of each style incorporates medial/lateral facets intended to conform to the convex intercondylar radii of the femoral component, thereby allowing the patella to ride deeply in the recessed patellofemoral groove. The asymmetric patella is a resurfacing component with a generous polyethylene thickness (4.6 mm at its thinnest) and a larger lateral facet for more bone coverage. The asymmetric patella naturally medializes component placement. The articulating surface of the conversion patella is identical to that of the asymmetric patella. However, the conversion patella allows for exchange of the polyethylene portion of the implant without revising a stable, well-fixed metal baseplate.

Patient Selection

Candidates were recruited from a group of metal-backed patella patients within Dr. Hedley’s medical practice. All candidates had undergone primary total knee arthroplasty and received a Duracon press-fit metal-backed patella. All recruited patients had undergone primary knee arthroplasty at least 5 years before clinical and radiographic evaluation. Patients were included in the study if they had a diagnosis of noninflammatory degenerative joint disease (eg, osteoarthritis, traumatic arthritis, avascular necrosis). Patients with body mass index higher than 40 were excluded from the study.

Surgical Technique

The patella is everted completely or as much as feasible. Debridement is done circumferentially around the patella. Adherent fat and pseudomeniscus are stripped back until the surgeon sees the entry point of the quadriceps tendon fibers above and the patella tendon fibers below. The cut is then made at this level to remove as much bone as needed to restore the normal height of the patella with the implant in place. The cut is usually made by hand—without guides but with the patella stabilized with a towel clip above and below to prevent any movement during the action.

The desired cut must be absolutely planar, and this should be checked by placing the edge of the blade across the interface. Repeated passes with the saw blade are needed if the cut is not 100% planar. Once the cut is made, the patella is sized with the patella sizers and drill guide. After the appropriate size is selected, the patella is drilled with a bit that is slightly undersized from the size of the pegs (1/32 inch smaller than the bit supplied by the manufacturer).

Once the patella is prepared, the rest of the knee arthroplasty is performed. The patella is press-fit as the last component to be inserted.

Radiologic Review

Radiographic analysis was performed by an independent reviewer according to the current Knee Society total knee arthroplasty roentgenographic evaluation and scoring system (Figure 2).¹⁶ The reviewer was an orthopedist specializing in hip and knee surgery. Radiographs the reviewer deemed questionable were shown to another independent hip and knee surgeon for validation. In all cases, the second reviewer confirmed the first reviewer’s initial recorded observations.

KSS (Knee Society Scale), WOMAC (Western Ontario and McMaster Universities Arthritis Index), and SF-36 (36-Item Short Form Health Survey) were also used to evaluate effectiveness in this protocol.

Survivorship Calculations

Kaplan-Meier survivorship was determined for all metal-backed patellae. For survival analysis, only knees with radiographic data were included (74 knees). Mean follow-up was 75.8 months (range, 60-105 months).

Seventy-four patients (88 knees) met the study criteria (Table). At minimum 5-year follow-up, complete data were acquired for 59 patients (72 knees). Of the total group, 14 knees did not have radiographic data. Those knees were categorized as lost to follow-up and were excluded from the survivorship analysis. The status of patients enrolled in the study at minimum 5-year follow-up is shown in the Table.

Mann-Whitney U test (nonparametric t test) was used to compare WOMAC and SF-36 scores between the “complete” and the “WOMAC and SF-36 only” data groups.

Statistical Analysis

Kaplan-Meier survivorship probabilities (asymmetric method) were calculated using SAS Version 9.2 (SAS Institute); 95% pointwise confidence limits were used.

The Mann-Whitney U test is a nonparametric analogue to the independent-samples t test. It was used here to compare WOMAC and SF-36 scores of patients with “complete” data with scores of patients with “WOMAC and SF-36 only” data. In either group, for patients who had primary bilateral knee arthroplasty, mean WOMAC and SF-36 scores were used.

Comparisons were made between the unilateral and bilateral knee arthroplasty groups. There were no differences in age, height, or weight (Mann-Whitney U test) or in sex, primary diagnosis, or number of patients lost to follow-up (Fisher exact test). Fisher exact test (vs χ² test) was used for the contingency table analysis because of small cell sizes (eg, ≤10 females in ‘‘both knees” group), suggesting the unilateral and bilateral patients did not differ in demographics.

For all patient-reported questionnaires, bilateral patients were given the opportunity to note any differences between their knee arthroplasties, but none of these patients made any special notations. We interpreted this to mean that all survey responses from bilateral patients were applicable to both knee arthroplasties.

Results

Seventy-four patients (88 knees) were enrolled in the study: 31 women (41.2%) and 43 men (58.1%). At time of surgery, mean age was 59.7 years (range, 40-86 years), and mean body mass index was 30.6 (range, 19.1-39.6). Eighty-three knees were diagnosed with osteoarthritis, and 5 knees were diagnosed with posttraumatic arthritis. Mean time to follow-up was 74.8 months (range, 60-105 months). Fourteen knees (14 patients) were considered lost to follow-up. However, 8 patients (8 knees) were contacted by telephone about the status of their knee(s), and all 8 completed and returned the minimum 5-year follow-up WOMAC and SF-36 forms; they did not return for their minimum 5-year clinical or radiographic evaluations.

Asymmetric patellae were used in 24 knees, conversion patellae in 64 knees (88 knees total). Forty-nine months after surgery, 1 patella was revised for loosening at its interface with the bone. The 51-year-old active female patient’s asymmetric patella was revised to a conversion patella. The decision to implant another metal-backed device was based on its high density; proper intrusion of acrylic cement would have been questionable. Some early wear was observed on the tibial insert, which was replaced. Sixty-eight months after the revision, the patient was asymptomatic, with a KSS Pain score of 96 and a KSS Function score of 100 (Figure 3). Another revision, for tibial insert exchange only, was performed 48 months after surgery. During this revision, the patella was evaluated and found to be well fixed and functioning normally.

Survivorship of the Duracon metal-backed patella at minimum 5-year follow-up was estimated to be 93.95%, with bounds of 73.61% and 98.74%.

Radiographic analysis revealed no radiolucencies larger than 1 mm (Figure 4). Seventeen 1-mm radiolucencies were recorded: 6 (35.3%) in zone 1, 2 (11.8%) in zone 2, and 9 (52.9%) in zone 4. Twelve (70.6%) of the 17 radiolucencies were in the left knee. Nine radiolucencies were in women and 8 in men. Most (55.6%) of the women’s radiolucencies were in zone 1, and most (75.0%) of the men’s were in zone 4. There were no loose beads other than in the case that was later revised.

KSS, WOMAC, and SF-36 scores and radiographic reviews were used to evaluate effectiveness in accordance with the protocol. At minimum 5-year follow-up, mean KSS Pain score was 94.10 (range, 55-100), and mean KSS Function score was 92.67 (range, 60-100). Mean WOMAC score was 2.21 (range, 0-19.70), mean SF-36 Physical score was 83.65 (range, 30.70-100), and mean SF-36 Mental score was 89.41 (range, 1.4-100).

The preceding calculations do not include WOMAC and SF-36 data for the 8 patients (8 knees) who were counted as lost to follow-up but who submitted minimum 5-year follow-up data. We compared these 8 patients with the 60 patients (74 knees) who had complete WOMAC and SF-36 data at the end of the study in order to determine whether there were any statistically significant differences between the 2 groups’ mean scores. No statistically significant differences were detected in any WOMAC or SF-36 category (α = 0.05).

Discussion

Metal-backed patellar components were originally designed to address the shortcomings (eg, fracture, deformation, aseptic loosening) of cemented all-polyethylene patellae.^1-3 It was thought that the stiffness of the metal could help resist polyethylene deformation and that the press-fit interface with bone might eliminate issues related to bone cement.⁸ However, short-term failures were reported with early metal-backed designs.^9,10 At the same time, good fixation with bone ingrowth was observed in both titanium and cobalt-chromium porous-coated patellae.^1,3,9-12,17 Further, reports of poor outcomes with some metal-backed patella designs overshadowed reports of positive outcomes.^2,3 In all reports (of both poor and positive outcomes), component design, patellar tracking, and surgical technique were cited as contributing to implant success.^2,3,14,17,18 Subsequent design improvements (eg, use of a third stabilizing peg, thicker polyethylene, improved conformity) produced excellent outcomes.^8,12,15

Our early results are similar to those reported in the literature, and we observed markedly better outcomes that we think resulted from component design improvements. Over the past decade, this has been particularly true with our use of the Duracon metal-backed patella, which has thicker polyethylene, better articular conformity, and a third stabilizing peg, all of which were previously noted as contributing to a successful metal-backed patellar component.^{2,12,14,15,19} In our study, all 72 knees radiographically evaluated and independently reviewed at minimum 5-year follow-up had well-fixed press-fit metal-backed patellae. Seventeen patellae had 1-mm radiolucencies; the other 59 had no radiolucencies in any zone around the patella–bone interface.

One of the most important aspects of removing a metal-backed patellar component from a patella is that the remaining bone stock is often far superior to the stock available after revision of a cemented patella. Careful removal should leave an excellent bony bed for reimplantation.

We think that surgeons should adhere to certain indications and contraindications when implanting metal-backed patellae and that doing so can contribute to successful outcomes. Type of bone stock available should be considered, as successful biological fixation relies on a good blood supply. A dense (or thin) patella in which intrusion of acrylic cement is improbable or impossible may favor use of a metal-backed patella. Cement is not an adhesive but a grout, so successful cementation requires intrusion of cement into the interstices of the cancellous bone. As adequate intrusion of cement into dense bone is not possible, cementation may not be the best option. Some patellae have failed because of peg “shear-off,”⁹ likely caused not by failure of peg strength but by failure of cement fixation at the nonpeg interface.^20,21 Polyethylene pegs fail when used as the sole method of fixation (they were never designed for that). In addition, we think younger patients are often indicated for a metal-backed patella because, over the long term, loosening of a cemented patella (and the accompanying stress shielding and osteolysis) may cause severe patellar bone destruction. Last, we have found that abnormally high or small patellae are not good candidates for cement fixation because they tend to work themselves loose riding on and off the superior flange. These types of patellae appear to have a much sturdier and longer lasting interface than cement, once biological fixation has occurred.

In summary, we think the indications for a metal-backed implant are a patella that is dense or sclerotic; a patella that is thin, abnormally high, or small; and a younger patient. In addition, a metal-backed implant is not indicated for soft, osteoporotic bone.

This study had a few limitations. Fourteen knees (14 patients), or 15.9% of all knees in the study, were categorized as lost to follow-up. Comparing the WOMAC and SF-36 scores of 8 patients (8 knees) who completed minimum 5-year follow-up but were not clinically evaluated with the scores of patients who had complete data, we found no statistically significant differences in any category. However, 5-year follow-up clinical data were available for those 8 patients. Nevertheless, 74 knees were available for radiologic evaluation, and during telephone interviews all 8 patients indicated they had their original implant(s) and were asymptomatic.

Our experience with the Duracon metal-backed patella has been encouraging. In the study reported here, there were no failures caused by dissociation of plastic. We think that, because the porous coating is under almost constant compression, biological fixation is likely in most instances, as observed in our minimum 5-year radiologic results. Given our minimum 5-year follow-up results with uncemented metal-backed patellae, we think their use may be a viable alternative to use of all-polyethylene patellae.

The metal-backed patella was originally designed to address the shortcomings of cemented, all-polyethylene patellae: deformation, aseptic loosening, stress fractures of polyethylene, and possible thermal damage from bone cement.^1-3 Several long-term studies have found very good outcomes with use of all-polyethylene patellae.^4-6 However, complications of using an all-polyethylene patella reportedly accounted for up to half of all knee revisions, and during revision surgery patellar bone stock was often found to have been compromised.⁷

The intention behind the design of press-fit metal-backed patellae was to address the shortcomings of all-polyethylene patellae by eliminating the need for bone cement and providing stiffness that would help resist polyethylene deformation while decreasing implant–bone interface stresses.⁸ However, early design iterations of metal-backed patellae demonstrated short-term failures—most commonly, local polyethylene wear damaging the locking mechanism and subsequent dissociation or fracture from the metal baseplate; polyethylene delamination from the metal baseplate; and failure of interface fixation.^9,10 On the other hand, good fixation with bony ingrowth was observed in both titanium and cobalt-chromium porous-coated patellae.^1,3,9,11-13 Overall, however, negative outcomes reported for metal-backed patellae led many surgeons to abandon these components and return to using cemented all-polyethylene patellae.

Negative outcomes of earlier metal-backed patellae designs have overshadowed reports of positive outcomes achieved with careful attention paid to component design, patellar tracking, and surgical technique.^2,3,14 Subsequent design improvements (eg, a third stabilizing peg, thicker polyethylene, improved conformity) produced excellent outcomes.^8,12,15 The advantages of using a metal-backed patella (eg, uniform load sharing, decreased polyethylene deformation, potential for biological fixation) may be unjustly outweighed by the fear of patellar component failure.³

Our 30-plus years of experience with metal-backed patellar components reflect the evolving effect of component design on outcome. Much as reported elsewhere, we found earlier component failures were caused by poor locking mechanisms, thin polyethylene, poor tracking, and minimal femur contact. Over the past decade, however, our outcomes with Duracon metal-backed patellae (Stryker) have been encouraging. We think these positive outcomes, seen over minimum 5-year follow-up, are largely attributable to the thicker polyethylene and improved articular conformity of this component relative to earlier designs. We have also found it helpful to adhere to certain criteria when implanting metal-backed patellae, and we think adhering to these criteria, along with improved component design, indicates use of press-fit metal-backed patellae. In this article, we report our failure incidence with use of this device at minimum 5-year follow-up.

Materials and Methods

In this single-center study, we performed clinical and independent radiographic reviews of 88 primary press-fit metal-backed patellae with minimum 5-year follow-up. All components were the same design (Duracon metal-backed patella) from the same manufacturer (Stryker).

This study, which began in September 2003, was reviewed and approved by the Western Institutional Review Board (WIRB). Either the investigator (Dr. Hedley) or the clinical study coordinator gave study candidates a full explanation of the study and answered any questions. Patients who still wanted to participate in the study signed WIRB consent forms after their index surgery but before minimum 5-year follow-up.

Device Description

This Duracon patella has a porous-coated cobalt-chromium metal back intended for press-fit fixation, 3 cobalt-chromium porous-coated pegs, and a preassembled polyethylene anterior surface (Figure 1). Four sizes are available to fit the peripheral shape of the resected patella.

This patella has 3 styles: symmetric, asymmetric, and conversion. In this study, we used only the asymmetric and conversion styles. The design of each style incorporates medial/lateral facets intended to conform to the convex intercondylar radii of the femoral component, thereby allowing the patella to ride deeply in the recessed patellofemoral groove. The asymmetric patella is a resurfacing component with a generous polyethylene thickness (4.6 mm at its thinnest) and a larger lateral facet for more bone coverage. The asymmetric patella naturally medializes component placement. The articulating surface of the conversion patella is identical to that of the asymmetric patella. However, the conversion patella allows for exchange of the polyethylene portion of the implant without revising a stable, well-fixed metal baseplate.

Patient Selection

Candidates were recruited from a group of metal-backed patella patients within Dr. Hedley’s medical practice. All candidates had undergone primary total knee arthroplasty and received a Duracon press-fit metal-backed patella. All recruited patients had undergone primary knee arthroplasty at least 5 years before clinical and radiographic evaluation. Patients were included in the study if they had a diagnosis of noninflammatory degenerative joint disease (eg, osteoarthritis, traumatic arthritis, avascular necrosis). Patients with body mass index higher than 40 were excluded from the study.

Surgical Technique

The patella is everted completely or as much as feasible. Debridement is done circumferentially around the patella. Adherent fat and pseudomeniscus are stripped back until the surgeon sees the entry point of the quadriceps tendon fibers above and the patella tendon fibers below. The cut is then made at this level to remove as much bone as needed to restore the normal height of the patella with the implant in place. The cut is usually made by hand—without guides but with the patella stabilized with a towel clip above and below to prevent any movement during the action.

The desired cut must be absolutely planar, and this should be checked by placing the edge of the blade across the interface. Repeated passes with the saw blade are needed if the cut is not 100% planar. Once the cut is made, the patella is sized with the patella sizers and drill guide. After the appropriate size is selected, the patella is drilled with a bit that is slightly undersized from the size of the pegs (1/32 inch smaller than the bit supplied by the manufacturer).

Once the patella is prepared, the rest of the knee arthroplasty is performed. The patella is press-fit as the last component to be inserted.

Radiologic Review

Radiographic analysis was performed by an independent reviewer according to the current Knee Society total knee arthroplasty roentgenographic evaluation and scoring system (Figure 2).¹⁶ The reviewer was an orthopedist specializing in hip and knee surgery. Radiographs the reviewer deemed questionable were shown to another independent hip and knee surgeon for validation. In all cases, the second reviewer confirmed the first reviewer’s initial recorded observations.

KSS (Knee Society Scale), WOMAC (Western Ontario and McMaster Universities Arthritis Index), and SF-36 (36-Item Short Form Health Survey) were also used to evaluate effectiveness in this protocol.

Survivorship Calculations

Kaplan-Meier survivorship was determined for all metal-backed patellae. For survival analysis, only knees with radiographic data were included (74 knees). Mean follow-up was 75.8 months (range, 60-105 months).

Seventy-four patients (88 knees) met the study criteria (Table). At minimum 5-year follow-up, complete data were acquired for 59 patients (72 knees). Of the total group, 14 knees did not have radiographic data. Those knees were categorized as lost to follow-up and were excluded from the survivorship analysis. The status of patients enrolled in the study at minimum 5-year follow-up is shown in the Table.

Mann-Whitney U test (nonparametric t test) was used to compare WOMAC and SF-36 scores between the “complete” and the “WOMAC and SF-36 only” data groups.

Statistical Analysis

Kaplan-Meier survivorship probabilities (asymmetric method) were calculated using SAS Version 9.2 (SAS Institute); 95% pointwise confidence limits were used.

The Mann-Whitney U test is a nonparametric analogue to the independent-samples t test. It was used here to compare WOMAC and SF-36 scores of patients with “complete” data with scores of patients with “WOMAC and SF-36 only” data. In either group, for patients who had primary bilateral knee arthroplasty, mean WOMAC and SF-36 scores were used.

Comparisons were made between the unilateral and bilateral knee arthroplasty groups. There were no differences in age, height, or weight (Mann-Whitney U test) or in sex, primary diagnosis, or number of patients lost to follow-up (Fisher exact test). Fisher exact test (vs χ² test) was used for the contingency table analysis because of small cell sizes (eg, ≤10 females in ‘‘both knees” group), suggesting the unilateral and bilateral patients did not differ in demographics.

For all patient-reported questionnaires, bilateral patients were given the opportunity to note any differences between their knee arthroplasties, but none of these patients made any special notations. We interpreted this to mean that all survey responses from bilateral patients were applicable to both knee arthroplasties.

Results

Seventy-four patients (88 knees) were enrolled in the study: 31 women (41.2%) and 43 men (58.1%). At time of surgery, mean age was 59.7 years (range, 40-86 years), and mean body mass index was 30.6 (range, 19.1-39.6). Eighty-three knees were diagnosed with osteoarthritis, and 5 knees were diagnosed with posttraumatic arthritis. Mean time to follow-up was 74.8 months (range, 60-105 months). Fourteen knees (14 patients) were considered lost to follow-up. However, 8 patients (8 knees) were contacted by telephone about the status of their knee(s), and all 8 completed and returned the minimum 5-year follow-up WOMAC and SF-36 forms; they did not return for their minimum 5-year clinical or radiographic evaluations.

Asymmetric patellae were used in 24 knees, conversion patellae in 64 knees (88 knees total). Forty-nine months after surgery, 1 patella was revised for loosening at its interface with the bone. The 51-year-old active female patient’s asymmetric patella was revised to a conversion patella. The decision to implant another metal-backed device was based on its high density; proper intrusion of acrylic cement would have been questionable. Some early wear was observed on the tibial insert, which was replaced. Sixty-eight months after the revision, the patient was asymptomatic, with a KSS Pain score of 96 and a KSS Function score of 100 (Figure 3). Another revision, for tibial insert exchange only, was performed 48 months after surgery. During this revision, the patella was evaluated and found to be well fixed and functioning normally.

Survivorship of the Duracon metal-backed patella at minimum 5-year follow-up was estimated to be 93.95%, with bounds of 73.61% and 98.74%.

Radiographic analysis revealed no radiolucencies larger than 1 mm (Figure 4). Seventeen 1-mm radiolucencies were recorded: 6 (35.3%) in zone 1, 2 (11.8%) in zone 2, and 9 (52.9%) in zone 4. Twelve (70.6%) of the 17 radiolucencies were in the left knee. Nine radiolucencies were in women and 8 in men. Most (55.6%) of the women’s radiolucencies were in zone 1, and most (75.0%) of the men’s were in zone 4. There were no loose beads other than in the case that was later revised.

KSS, WOMAC, and SF-36 scores and radiographic reviews were used to evaluate effectiveness in accordance with the protocol. At minimum 5-year follow-up, mean KSS Pain score was 94.10 (range, 55-100), and mean KSS Function score was 92.67 (range, 60-100). Mean WOMAC score was 2.21 (range, 0-19.70), mean SF-36 Physical score was 83.65 (range, 30.70-100), and mean SF-36 Mental score was 89.41 (range, 1.4-100).

The preceding calculations do not include WOMAC and SF-36 data for the 8 patients (8 knees) who were counted as lost to follow-up but who submitted minimum 5-year follow-up data. We compared these 8 patients with the 60 patients (74 knees) who had complete WOMAC and SF-36 data at the end of the study in order to determine whether there were any statistically significant differences between the 2 groups’ mean scores. No statistically significant differences were detected in any WOMAC or SF-36 category (α = 0.05).

Discussion

Metal-backed patellar components were originally designed to address the shortcomings (eg, fracture, deformation, aseptic loosening) of cemented all-polyethylene patellae.^1-3 It was thought that the stiffness of the metal could help resist polyethylene deformation and that the press-fit interface with bone might eliminate issues related to bone cement.⁸ However, short-term failures were reported with early metal-backed designs.^9,10 At the same time, good fixation with bone ingrowth was observed in both titanium and cobalt-chromium porous-coated patellae.^1,3,9-12,17 Further, reports of poor outcomes with some metal-backed patella designs overshadowed reports of positive outcomes.^2,3 In all reports (of both poor and positive outcomes), component design, patellar tracking, and surgical technique were cited as contributing to implant success.^2,3,14,17,18 Subsequent design improvements (eg, use of a third stabilizing peg, thicker polyethylene, improved conformity) produced excellent outcomes.^8,12,15

Our early results are similar to those reported in the literature, and we observed markedly better outcomes that we think resulted from component design improvements. Over the past decade, this has been particularly true with our use of the Duracon metal-backed patella, which has thicker polyethylene, better articular conformity, and a third stabilizing peg, all of which were previously noted as contributing to a successful metal-backed patellar component.^{2,12,14,15,19} In our study, all 72 knees radiographically evaluated and independently reviewed at minimum 5-year follow-up had well-fixed press-fit metal-backed patellae. Seventeen patellae had 1-mm radiolucencies; the other 59 had no radiolucencies in any zone around the patella–bone interface.

One of the most important aspects of removing a metal-backed patellar component from a patella is that the remaining bone stock is often far superior to the stock available after revision of a cemented patella. Careful removal should leave an excellent bony bed for reimplantation.

We think that surgeons should adhere to certain indications and contraindications when implanting metal-backed patellae and that doing so can contribute to successful outcomes. Type of bone stock available should be considered, as successful biological fixation relies on a good blood supply. A dense (or thin) patella in which intrusion of acrylic cement is improbable or impossible may favor use of a metal-backed patella. Cement is not an adhesive but a grout, so successful cementation requires intrusion of cement into the interstices of the cancellous bone. As adequate intrusion of cement into dense bone is not possible, cementation may not be the best option. Some patellae have failed because of peg “shear-off,”⁹ likely caused not by failure of peg strength but by failure of cement fixation at the nonpeg interface.^20,21 Polyethylene pegs fail when used as the sole method of fixation (they were never designed for that). In addition, we think younger patients are often indicated for a metal-backed patella because, over the long term, loosening of a cemented patella (and the accompanying stress shielding and osteolysis) may cause severe patellar bone destruction. Last, we have found that abnormally high or small patellae are not good candidates for cement fixation because they tend to work themselves loose riding on and off the superior flange. These types of patellae appear to have a much sturdier and longer lasting interface than cement, once biological fixation has occurred.

In summary, we think the indications for a metal-backed implant are a patella that is dense or sclerotic; a patella that is thin, abnormally high, or small; and a younger patient. In addition, a metal-backed implant is not indicated for soft, osteoporotic bone.

This study had a few limitations. Fourteen knees (14 patients), or 15.9% of all knees in the study, were categorized as lost to follow-up. Comparing the WOMAC and SF-36 scores of 8 patients (8 knees) who completed minimum 5-year follow-up but were not clinically evaluated with the scores of patients who had complete data, we found no statistically significant differences in any category. However, 5-year follow-up clinical data were available for those 8 patients. Nevertheless, 74 knees were available for radiologic evaluation, and during telephone interviews all 8 patients indicated they had their original implant(s) and were asymptomatic.

Our experience with the Duracon metal-backed patella has been encouraging. In the study reported here, there were no failures caused by dissociation of plastic. We think that, because the porous coating is under almost constant compression, biological fixation is likely in most instances, as observed in our minimum 5-year radiologic results. Given our minimum 5-year follow-up results with uncemented metal-backed patellae, we think their use may be a viable alternative to use of all-polyethylene patellae.

The metal-backed patella was originally designed to address the shortcomings of cemented, all-polyethylene patellae: deformation, aseptic loosening, stress fractures of polyethylene, and possible thermal damage from bone cement.^1-3 Several long-term studies have found very good outcomes with use of all-polyethylene patellae.^4-6 However, complications of using an all-polyethylene patella reportedly accounted for up to half of all knee revisions, and during revision surgery patellar bone stock was often found to have been compromised.⁷

The intention behind the design of press-fit metal-backed patellae was to address the shortcomings of all-polyethylene patellae by eliminating the need for bone cement and providing stiffness that would help resist polyethylene deformation while decreasing implant–bone interface stresses.⁸ However, early design iterations of metal-backed patellae demonstrated short-term failures—most commonly, local polyethylene wear damaging the locking mechanism and subsequent dissociation or fracture from the metal baseplate; polyethylene delamination from the metal baseplate; and failure of interface fixation.^9,10 On the other hand, good fixation with bony ingrowth was observed in both titanium and cobalt-chromium porous-coated patellae.^1,3,9,11-13 Overall, however, negative outcomes reported for metal-backed patellae led many surgeons to abandon these components and return to using cemented all-polyethylene patellae.

Negative outcomes of earlier metal-backed patellae designs have overshadowed reports of positive outcomes achieved with careful attention paid to component design, patellar tracking, and surgical technique.^2,3,14 Subsequent design improvements (eg, a third stabilizing peg, thicker polyethylene, improved conformity) produced excellent outcomes.^8,12,15 The advantages of using a metal-backed patella (eg, uniform load sharing, decreased polyethylene deformation, potential for biological fixation) may be unjustly outweighed by the fear of patellar component failure.³

Our 30-plus years of experience with metal-backed patellar components reflect the evolving effect of component design on outcome. Much as reported elsewhere, we found earlier component failures were caused by poor locking mechanisms, thin polyethylene, poor tracking, and minimal femur contact. Over the past decade, however, our outcomes with Duracon metal-backed patellae (Stryker) have been encouraging. We think these positive outcomes, seen over minimum 5-year follow-up, are largely attributable to the thicker polyethylene and improved articular conformity of this component relative to earlier designs. We have also found it helpful to adhere to certain criteria when implanting metal-backed patellae, and we think adhering to these criteria, along with improved component design, indicates use of press-fit metal-backed patellae. In this article, we report our failure incidence with use of this device at minimum 5-year follow-up.

Materials and Methods

In this single-center study, we performed clinical and independent radiographic reviews of 88 primary press-fit metal-backed patellae with minimum 5-year follow-up. All components were the same design (Duracon metal-backed patella) from the same manufacturer (Stryker).

This study, which began in September 2003, was reviewed and approved by the Western Institutional Review Board (WIRB). Either the investigator (Dr. Hedley) or the clinical study coordinator gave study candidates a full explanation of the study and answered any questions. Patients who still wanted to participate in the study signed WIRB consent forms after their index surgery but before minimum 5-year follow-up.

Device Description

This Duracon patella has a porous-coated cobalt-chromium metal back intended for press-fit fixation, 3 cobalt-chromium porous-coated pegs, and a preassembled polyethylene anterior surface (Figure 1). Four sizes are available to fit the peripheral shape of the resected patella.

This patella has 3 styles: symmetric, asymmetric, and conversion. In this study, we used only the asymmetric and conversion styles. The design of each style incorporates medial/lateral facets intended to conform to the convex intercondylar radii of the femoral component, thereby allowing the patella to ride deeply in the recessed patellofemoral groove. The asymmetric patella is a resurfacing component with a generous polyethylene thickness (4.6 mm at its thinnest) and a larger lateral facet for more bone coverage. The asymmetric patella naturally medializes component placement. The articulating surface of the conversion patella is identical to that of the asymmetric patella. However, the conversion patella allows for exchange of the polyethylene portion of the implant without revising a stable, well-fixed metal baseplate.

Patient Selection

Candidates were recruited from a group of metal-backed patella patients within Dr. Hedley’s medical practice. All candidates had undergone primary total knee arthroplasty and received a Duracon press-fit metal-backed patella. All recruited patients had undergone primary knee arthroplasty at least 5 years before clinical and radiographic evaluation. Patients were included in the study if they had a diagnosis of noninflammatory degenerative joint disease (eg, osteoarthritis, traumatic arthritis, avascular necrosis). Patients with body mass index higher than 40 were excluded from the study.

Surgical Technique

The patella is everted completely or as much as feasible. Debridement is done circumferentially around the patella. Adherent fat and pseudomeniscus are stripped back until the surgeon sees the entry point of the quadriceps tendon fibers above and the patella tendon fibers below. The cut is then made at this level to remove as much bone as needed to restore the normal height of the patella with the implant in place. The cut is usually made by hand—without guides but with the patella stabilized with a towel clip above and below to prevent any movement during the action.

The desired cut must be absolutely planar, and this should be checked by placing the edge of the blade across the interface. Repeated passes with the saw blade are needed if the cut is not 100% planar. Once the cut is made, the patella is sized with the patella sizers and drill guide. After the appropriate size is selected, the patella is drilled with a bit that is slightly undersized from the size of the pegs (1/32 inch smaller than the bit supplied by the manufacturer).

Once the patella is prepared, the rest of the knee arthroplasty is performed. The patella is press-fit as the last component to be inserted.

Radiologic Review

Radiographic analysis was performed by an independent reviewer according to the current Knee Society total knee arthroplasty roentgenographic evaluation and scoring system (Figure 2).¹⁶ The reviewer was an orthopedist specializing in hip and knee surgery. Radiographs the reviewer deemed questionable were shown to another independent hip and knee surgeon for validation. In all cases, the second reviewer confirmed the first reviewer’s initial recorded observations.

KSS (Knee Society Scale), WOMAC (Western Ontario and McMaster Universities Arthritis Index), and SF-36 (36-Item Short Form Health Survey) were also used to evaluate effectiveness in this protocol.

Survivorship Calculations

Kaplan-Meier survivorship was determined for all metal-backed patellae. For survival analysis, only knees with radiographic data were included (74 knees). Mean follow-up was 75.8 months (range, 60-105 months).

Seventy-four patients (88 knees) met the study criteria (Table). At minimum 5-year follow-up, complete data were acquired for 59 patients (72 knees). Of the total group, 14 knees did not have radiographic data. Those knees were categorized as lost to follow-up and were excluded from the survivorship analysis. The status of patients enrolled in the study at minimum 5-year follow-up is shown in the Table.

Mann-Whitney U test (nonparametric t test) was used to compare WOMAC and SF-36 scores between the “complete” and the “WOMAC and SF-36 only” data groups.

Statistical Analysis

Kaplan-Meier survivorship probabilities (asymmetric method) were calculated using SAS Version 9.2 (SAS Institute); 95% pointwise confidence limits were used.

The Mann-Whitney U test is a nonparametric analogue to the independent-samples t test. It was used here to compare WOMAC and SF-36 scores of patients with “complete” data with scores of patients with “WOMAC and SF-36 only” data. In either group, for patients who had primary bilateral knee arthroplasty, mean WOMAC and SF-36 scores were used.

Comparisons were made between the unilateral and bilateral knee arthroplasty groups. There were no differences in age, height, or weight (Mann-Whitney U test) or in sex, primary diagnosis, or number of patients lost to follow-up (Fisher exact test). Fisher exact test (vs χ² test) was used for the contingency table analysis because of small cell sizes (eg, ≤10 females in ‘‘both knees” group), suggesting the unilateral and bilateral patients did not differ in demographics.

For all patient-reported questionnaires, bilateral patients were given the opportunity to note any differences between their knee arthroplasties, but none of these patients made any special notations. We interpreted this to mean that all survey responses from bilateral patients were applicable to both knee arthroplasties.

Results

Seventy-four patients (88 knees) were enrolled in the study: 31 women (41.2%) and 43 men (58.1%). At time of surgery, mean age was 59.7 years (range, 40-86 years), and mean body mass index was 30.6 (range, 19.1-39.6). Eighty-three knees were diagnosed with osteoarthritis, and 5 knees were diagnosed with posttraumatic arthritis. Mean time to follow-up was 74.8 months (range, 60-105 months). Fourteen knees (14 patients) were considered lost to follow-up. However, 8 patients (8 knees) were contacted by telephone about the status of their knee(s), and all 8 completed and returned the minimum 5-year follow-up WOMAC and SF-36 forms; they did not return for their minimum 5-year clinical or radiographic evaluations.

Asymmetric patellae were used in 24 knees, conversion patellae in 64 knees (88 knees total). Forty-nine months after surgery, 1 patella was revised for loosening at its interface with the bone. The 51-year-old active female patient’s asymmetric patella was revised to a conversion patella. The decision to implant another metal-backed device was based on its high density; proper intrusion of acrylic cement would have been questionable. Some early wear was observed on the tibial insert, which was replaced. Sixty-eight months after the revision, the patient was asymptomatic, with a KSS Pain score of 96 and a KSS Function score of 100 (Figure 3). Another revision, for tibial insert exchange only, was performed 48 months after surgery. During this revision, the patella was evaluated and found to be well fixed and functioning normally.

Survivorship of the Duracon metal-backed patella at minimum 5-year follow-up was estimated to be 93.95%, with bounds of 73.61% and 98.74%.

Radiographic analysis revealed no radiolucencies larger than 1 mm (Figure 4). Seventeen 1-mm radiolucencies were recorded: 6 (35.3%) in zone 1, 2 (11.8%) in zone 2, and 9 (52.9%) in zone 4. Twelve (70.6%) of the 17 radiolucencies were in the left knee. Nine radiolucencies were in women and 8 in men. Most (55.6%) of the women’s radiolucencies were in zone 1, and most (75.0%) of the men’s were in zone 4. There were no loose beads other than in the case that was later revised.

KSS, WOMAC, and SF-36 scores and radiographic reviews were used to evaluate effectiveness in accordance with the protocol. At minimum 5-year follow-up, mean KSS Pain score was 94.10 (range, 55-100), and mean KSS Function score was 92.67 (range, 60-100). Mean WOMAC score was 2.21 (range, 0-19.70), mean SF-36 Physical score was 83.65 (range, 30.70-100), and mean SF-36 Mental score was 89.41 (range, 1.4-100).

The preceding calculations do not include WOMAC and SF-36 data for the 8 patients (8 knees) who were counted as lost to follow-up but who submitted minimum 5-year follow-up data. We compared these 8 patients with the 60 patients (74 knees) who had complete WOMAC and SF-36 data at the end of the study in order to determine whether there were any statistically significant differences between the 2 groups’ mean scores. No statistically significant differences were detected in any WOMAC or SF-36 category (α = 0.05).

Discussion

Metal-backed patellar components were originally designed to address the shortcomings (eg, fracture, deformation, aseptic loosening) of cemented all-polyethylene patellae.^1-3 It was thought that the stiffness of the metal could help resist polyethylene deformation and that the press-fit interface with bone might eliminate issues related to bone cement.⁸ However, short-term failures were reported with early metal-backed designs.^9,10 At the same time, good fixation with bone ingrowth was observed in both titanium and cobalt-chromium porous-coated patellae.^1,3,9-12,17 Further, reports of poor outcomes with some metal-backed patella designs overshadowed reports of positive outcomes.^2,3 In all reports (of both poor and positive outcomes), component design, patellar tracking, and surgical technique were cited as contributing to implant success.^2,3,14,17,18 Subsequent design improvements (eg, use of a third stabilizing peg, thicker polyethylene, improved conformity) produced excellent outcomes.^8,12,15

Our early results are similar to those reported in the literature, and we observed markedly better outcomes that we think resulted from component design improvements. Over the past decade, this has been particularly true with our use of the Duracon metal-backed patella, which has thicker polyethylene, better articular conformity, and a third stabilizing peg, all of which were previously noted as contributing to a successful metal-backed patellar component.^{2,12,14,15,19} In our study, all 72 knees radiographically evaluated and independently reviewed at minimum 5-year follow-up had well-fixed press-fit metal-backed patellae. Seventeen patellae had 1-mm radiolucencies; the other 59 had no radiolucencies in any zone around the patella–bone interface.

One of the most important aspects of removing a metal-backed patellar component from a patella is that the remaining bone stock is often far superior to the stock available after revision of a cemented patella. Careful removal should leave an excellent bony bed for reimplantation.

We think that surgeons should adhere to certain indications and contraindications when implanting metal-backed patellae and that doing so can contribute to successful outcomes. Type of bone stock available should be considered, as successful biological fixation relies on a good blood supply. A dense (or thin) patella in which intrusion of acrylic cement is improbable or impossible may favor use of a metal-backed patella. Cement is not an adhesive but a grout, so successful cementation requires intrusion of cement into the interstices of the cancellous bone. As adequate intrusion of cement into dense bone is not possible, cementation may not be the best option. Some patellae have failed because of peg “shear-off,”⁹ likely caused not by failure of peg strength but by failure of cement fixation at the nonpeg interface.^20,21 Polyethylene pegs fail when used as the sole method of fixation (they were never designed for that). In addition, we think younger patients are often indicated for a metal-backed patella because, over the long term, loosening of a cemented patella (and the accompanying stress shielding and osteolysis) may cause severe patellar bone destruction. Last, we have found that abnormally high or small patellae are not good candidates for cement fixation because they tend to work themselves loose riding on and off the superior flange. These types of patellae appear to have a much sturdier and longer lasting interface than cement, once biological fixation has occurred.

In summary, we think the indications for a metal-backed implant are a patella that is dense or sclerotic; a patella that is thin, abnormally high, or small; and a younger patient. In addition, a metal-backed implant is not indicated for soft, osteoporotic bone.

This study had a few limitations. Fourteen knees (14 patients), or 15.9% of all knees in the study, were categorized as lost to follow-up. Comparing the WOMAC and SF-36 scores of 8 patients (8 knees) who completed minimum 5-year follow-up but were not clinically evaluated with the scores of patients who had complete data, we found no statistically significant differences in any category. However, 5-year follow-up clinical data were available for those 8 patients. Nevertheless, 74 knees were available for radiologic evaluation, and during telephone interviews all 8 patients indicated they had their original implant(s) and were asymptomatic.

Our experience with the Duracon metal-backed patella has been encouraging. In the study reported here, there were no failures caused by dissociation of plastic. We think that, because the porous coating is under almost constant compression, biological fixation is likely in most instances, as observed in our minimum 5-year radiologic results. Given our minimum 5-year follow-up results with uncemented metal-backed patellae, we think their use may be a viable alternative to use of all-polyethylene patellae.

Degenerative arthritis is a widespread chronic condition with an incidence of almost 43 million and annual health care costs of $60 billion in the United States alone.1 Although many cases can be managed symptomatically with medical therapy and intra-articular injections,2 many patients experience disease progression resulting in decreased ambulatory ability and work productivity. For these patients, elective hip and knee arthroplasties can drastically improve quality of life and functionality.3,4 Over the past decade, there has been a marked increase in the number of primary and revision total hip and knee arthroplasties performed in the United States. By 2030, the demand for primary total hip arthroplasties will grow an estimated 174%, to 572,000 procedures. Likewise, the demand for primary total knee arthroplasties is projected to grow by 673%, to 3.48 million procedures.5 However, though better surgical techniques and technology have led to improved functional outcomes, there is still substantial risk for complications in the perioperative period, especially in the geriatric population, in which substantial comorbidities are common.6-9

Acute kidney injury (AKI) is a common public health problem in hospitalized patients and in patients undergoing procedures. More than one-third of all AKI cases occur in surgical settings.^10,11 Over the past decade, both community-acquired and in-hospital AKIs rapidly increased in incidence in all major clinical settings.^12-14 Patients with AKI have high rates of adverse outcomes during hospitalization and discharge.^11,15 Sequelae of AKIs include worsening chronic kidney disease (CKD) and progression to end-stage renal disease, necessitating either long-term dialysis or transplantation.¹² This in turn leads to exacerbated disability, diminished quality of life, and disproportionate burden on health care resources.

Much of our knowledge about postoperative AKI has been derived from cardiovascular, thoracic, and abdominal surgery settings. However, there is a paucity of data on epidemiology and trends for either AKI or associated outcomes in patients undergoing major orthopedic surgery. The few studies to date either were single-center or had inadequate sample sizes for appropriately powered analysis of the risk factors and outcomes related to AKI.¹⁶

In the study reported here, we analyzed a large cohort of patients from a nationwide multicenter database to determine the incidence of and risk factors for AKI. We also examined the mortality and adverse discharges associated with AKI after major joint surgery. Lastly, we assessed temporal trends in both incidence and outcomes of AKI, including the death risk attributable to AKI.

Methods

Database

We extracted our study cohort from the Nationwide Inpatient Sample (NIS) and the National Inpatient Sample of Healthcare Cost and Utilization Project (HCUP) compiled by the Agency for Healthcare Research and Quality.¹⁷ NIS, the largest inpatient care database in the United States, stores data from almost 8 million stays in about 1000 hospitals across the country each year. Its participating hospital pool consists of about 20% of US community hospitals, resulting in a sampling frame comprising about 90% of all hospital discharges in the United States. This allows for calculation of precise, weighted nationwide estimates. Data elements within NIS are drawn from hospital discharge abstracts that indicate all procedures performed. NIS also stores information on patient characteristics, length of stay (LOS), discharge disposition, postoperative morbidity, and observed in-hospital mortality. However, it stores no information on long-term follow-up or complications after discharge.

Data Analysis

For the period 2002–2012, we queried the NIS database for hip and knee arthroplasties with primary diagnosis codes for osteoarthritis and secondary codes for AKI. We excluded patients under age 18 years and patients with diagnosis codes for hip and knee fracture/necrosis, inflammatory/infectious arthritis, or bone neoplasms (Table 1). We then extracted baseline characteristics of the study population. Patient-level characteristics included age, sex, race, quartile classification of median household income according to postal (ZIP) code, and primary payer (Medicare/Medicaid, private insurance, self-pay, no charge). Hospital-level characteristics included hospital location (urban, rural), hospital bed size (small, medium, large), region (Northeast, Midwest/North Central, South, West), and teaching status. We defined illness severity and likelihood of death using Deyo’s modification of the Charlson Comorbidity Index (CCI), which draws on principal and secondary ICD-9-CM (International Classification of Diseases, Ninth Revision-Clinical Modification) diagnosis codes, procedure codes, and patient demographics to estimate a patient’s mortality risk. This method reliably predicts mortality and readmission in the orthopedic population.^18,19 We assessed the effect of AKI on 4 outcomes, including in-hospital mortality, discharge disposition, LOS, and cost of stay. Discharge disposition was grouped by either (a) home or short-term facility or (b) adverse discharge. Home or short-term facility covered routine, short-term hospital, against medical advice, home intravenous provider, another rehabilitation facility, another institution for outpatient services, institution for outpatient services, discharged alive, and destination unknown; adverse discharge covered skilled nursing facility, intermediate care, hospice home, hospice medical facility, long-term care hospital, and certified nursing facility. This dichotomization of discharge disposition is often used in studies of NIS data.²⁰

Statistical Analyses

We compared the baseline characteristics of hospitalized patients with and without AKI. To test for significance, we used the χ² test for categorical variables, the Student t test for normally distributed continuous variables, the Wilcoxon rank sum test for non-normally distributed continuous variables, and the Cochran-Armitage test for trends in AKI incidence. We used survey logistic regression models to calculate adjusted odds ratios (ORs) with 95% confidence intervals (95% CIs) in order to estimate the predictors of AKI and the impact of AKI on hospital outcomes. We constructed final models after adjusting for confounders, testing for potential interactions, and ensuring no multicolinearity between covariates. Last, we computed the risk proportion of death attributable to AKI, indicating the proportion of deaths that could potentially be avoided if AKI and its complications were abrogated.²¹

We performed all statistical analyses with SAS Version 9.3 (SAS Institute) using designated weight values to produce weighted national estimates. The threshold for statistical significance was set at P < .01 (with ORs and 95% CIs that excluded 1).

Results

AKI Incidence, Risk Factors, and Trends

We identified 7,235,251 patients who underwent elective hip or knee arthroplasty for osteoarthritis between 2002 and 2012—an estimate consistent with data from the Centers for Disease Control and Prevention.²² Of that total, 94,367 (1.3%) had AKI. The proportion of discharges diagnosed with AKI increased rapidly over the decade, from 0.5% in 2002 to 1.8% to 1.9% in the period 2010–2012. This upward trend was highly significant (P_trend < .001) (Figure 1). Patients with AKI (vs patients without AKI) were more likely to be older (mean age, 70 vs 66 years; P < .001), male (50.8% vs 38.4%; P < .001), and black (10.07% vs 5.15%; P<. 001). They were also found to have a significantly higher comorbidity score (mean CCI, 2.8 vs 1.5; P < .001) and higher proportions of comorbidities, including hypertension, CKD, atrial fibrillation, diabetes mellitus (DM), congestive heart failure, chronic liver disease, and hepatitis C virus infection. In addition, AKI was associated with perioperative myocardial infarction (MI), sepsis, cardiac catheterization, and blood transfusion. Regarding socioeconomic characteristics, patients with AKI were more likely to have Medicare/Medicaid insurance (72.26% vs 58.06%; P < .001) and to belong to the extremes of income categories (Table 2).

Using multivariable logistic regression, we found that increased age (1.11 increase in adjusted OR for every year older; 95% CI, 1.09-1.14; P < .001), male sex (adjusted OR, 1.65; 95% CI, 1.60-1.71; P < .001), and black race (adjusted OR, 1.57; 95% CI, 1.45-1.69; P < .001) were significantly associated with postoperative AKI. Regarding comorbidities, baseline CKD (adjusted OR, 8.64; 95% CI, 8.14-9.18; P < .001) and congestive heart failure (adjusted OR, 2.74; 95% CI, 2.57-2.92; P< .0001) were most significantly associated with AKI. Perioperative events, including sepsis (adjusted OR, 35.64; 95% CI, 30.28-41.96; P < .0001), MI (adjusted OR, 6.14; 95% CI, 5.17-7.28; P < .0001), and blood transfusion (adjusted OR, 2.28; 95% CI, 2.15-2.42; P < .0001), were also strongly associated with postoperative AKI. Last, compared with urban hospitals and small hospital bed size, rural hospitals (adjusted OR, 0.70; 95% CI, 0.60-0.81; P< .001) and large bed size (adjusted OR, 0.82; 95% CI, 0.70-0.93; P = .003) were associated with lower probability of developing AKI (Table 3).

Figure 2 elucidates the frequency of AKI based on a combination of key preoperative comorbid conditions and postoperative complications—demonstrating that the proportion of AKI cases associated with other postoperative complications is significantly higher in the CKD and concomitant DM/CKD patient populations. Patients hospitalized with CKD exhibited higher rates of AKI in cases involving blood transfusion (20.9% vs 1.8%; P < .001), acute MI (48.9% vs 13.8%; P < .001), and sepsis (74.7% vs 36.3%;P< .001) relative to patients without CKD. Similarly, patients with concomitant DM/CKD exhibited higher rates of AKI in cases involving blood transfusion (23% vs 1.9%; P< .001), acute MI (51.1% vs 12.1%; P< .001), and sepsis (75% vs 38.2%; P < .001) relative to patients without either condition. However, patients hospitalized with DM alone exhibited only marginally higher rates of AKI in cases involving blood transfusion (4.7% vs 2%; P < .01) and acute MI (19.2% vs 16.7%; P< .01) and a lower rate in cases involving sepsis (38.2% vs 41.7%; P < .01) relative to patients without DM. These data suggest that CKD is the most significant clinically relevant risk factor for AKI and that CKD may synergize with DM to raise the risk for AKI.

Outcomes

We then analyzed the impact of AKI on hospital outcomes, including in-hospital mortality, discharge disposition, LOS, and cost of care. Mortality was significantly higher in patients with AKI than in patients without it (2.08% vs 0.06%; P < .001). Even after adjusting for confounders (eg, demographics, comorbidity burden, perioperative sepsis, hospital-level characteristics), AKI was still associated with strikingly higher odds of in-hospital death (adjusted OR, 11.32; 95% CI, 9.34-13.74; P < .001). However, analysis of temporal trends indicated that the odds for adjusted mortality associated with AKI decreased from 18.09 to 9.45 (P_trend = .01) over the period 2002–2012 (Figure 3). This decrease in odds of death was countered by an increase in incidence of AKI, resulting in a stable attributable risk proportion (97.9% in 2002 to 97.3% in 2012; P_trend = .90) (Table 4). Regarding discharge disposition, patients with AKI were much less likely to be discharged home (41.35% vs 62.59%; P < .001) and more likely to be discharged to long-term care (56.37% vs 37.03%; P< .001). After adjustment for confounders, AKI was associated with significantly increased odds of adverse discharge (adjusted OR, 2.24; 95% CI, 2.12-2.36; P< .001). Analysis of temporal trends revealed no appreciable decrease in the adjusted odds of adverse discharge between 2002 (adjusted OR, 1.87; 95% CI, 1.37-2.55; P < .001) and 2012 (adjusted OR, 1.93; 95% CI, 1.76-2.11; P < .001) (Figure 4, Table 5). Last, both mean LOS (5 days vs 3 days; P < .001) and mean cost of hospitalization (US $22,269 vs $15,757; P < .001) were significantly higher in patients with AKI.

Discussion

In this study, we found that the incidence of AKI among hospitalized patients increased 4-fold between 2002 and 2012. Moreover, we identified numerous patient-specific, hospital-specific, perioperative risk factors for AKI. Most important, we found that AKI was associated with a strikingly higher risk of in-hospital death, and surviving patients were more likely to experience adverse discharge. Although the adjusted mortality rate associated with AKI decreased over that decade, the attributable risk proportion remained stable.

Few studies have addressed this significant public health concern. In one recent study in Australia, Kimmel and colleagues¹⁶ identified risk factors for AKI but lacked data on AKI outcomes. In a study of complications and mortality occurring after orthopedic surgery, Belmont and colleagues²² categorized complications as either local or systemic but did not examine renal complications. Only 2 other major studies have been conducted on renal outcomes associated with major joint surgery, and both were limited to patients with acute hip fractures. The first included acute fracture surgery patients and omitted elective joint surgery patients, and it evaluated admission renal function but not postoperative AKI.²² The second study had a sample size of only 170 patients.²³ Thus, the literature leaves us with a crucial knowledge gap in renal outcomes and their postoperative impact in elective arthroplasties.

The present study filled this information gap by examining the incidence, risk factors, outcomes, and temporal trends of AKI after elective hip and knee arthroplasties. The increasing incidence of AKI in this surgical setting is similar to that of AKI in other surgical settings (cardiac and noncardiac).²¹ Although our analysis was limited by lack of perioperative management data, patients undergoing elective joint arthroplasty can experience kidney dysfunction for several reasons, including volume depletion, postoperative sepsis, and influence of medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), especially in older patients with more comorbidities and a higher burden of CKD. Each of these factors can cause renal dysfunction in patients having orthopedic procedures.²⁴ Moreover, NSAID use among elective joint arthroplasty patients is likely higher because of an emphasis on multimodal analgesia, as recent randomized controlled trials have demonstrated the efficacy of NSAID use in controlling pain without increasing bleeding.^25-27 Our results also demonstrated that the absolute incidence of AKI after orthopedic surgery is relatively low. One possible explanation for this phenomenon is that the definitions used were based on ICD-9-CM codes that underestimate the true incidence of AKI.

Consistent with other studies, we found that certain key preoperative comorbid conditions and postoperative events were associated with higher AKI risk. We stratified the rate of AKI associated with each postoperative event (sepsis, acute MI, cardiac catheterization, need for transfusion) by DM/CKD comorbidity. CKD was associated with significantly higher AKI risk across all postoperative complications. This information may provide clinicians with bedside information that can be used to determine which patients may be at higher or lower risk for AKI.

Our analysis of patient outcomes revealed that, though AKI was relatively uncommon, it increased the risk for death during hospitalization more than 10-fold between 2002 and 2012. Although the adjusted OR of in-hospital mortality decreased over the decade studied, the concurrent increase in AKI incidence caused the attributable risk of death associated with AKI to essentially remain the same. This observation is consistent with recent reports from cardiac surgery settings.²¹ These data together suggest that ameliorating occurrences of AKI would decrease mortality and increase quality of care for patients undergoing elective joint surgeries.

We also examined the effect of AKI on resource use by studying LOS, costs, and risk for adverse discharge. Much as in other surgical settings, AKI increased both LOS and overall hospitalization costs. More important, AKI was associated with increased adverse discharge (discharge to long-term care or nursing homes). Although exact reasons are unclear, we can speculate that postoperative renal dysfunction precludes early rehabilitation, impeding desired functional outcome and disposition.^28,29 Given the projected increases in primary and revision hip and knee arthroplasties,⁵ these data predict that the impact of AKI on health outcomes will increase alarmingly in coming years.

There are limitations to our study. First, it was based on administrative data and lacked patient-level and laboratory data. As reported, the sensitivity of AKI codes remains moderate,³⁰ so the true burden may be higher than indicated here. As the definition of AKI was based on administrative coding, we also could not estimate severity, though previous studies have found that administrative codes typically capture a more severe form of disease.³¹ Another limitation is that, because the data were deidentified, we could not delineate the risk for recurrent AKI in repeated surgical procedures, though this cohort unlikely was large enough to qualitatively affect our results. The third limitation is that, though we used CCI to adjust for the comorbidity burden, we were unable to account for other unmeasured confounders associated with increased AKI incidence, such as specific medication use. In addition, given the lack of patient-level data, we could not analyze the specific factors responsible for AKI in the perioperative period. Nevertheless, the strengths of a nationally representative sample, such as large sample size and generalizability, outweigh these limitations.

Conclusion

AKI is potentially an important quality indicator of elective joint surgery, and reducing its incidence is therefore essential for quality improvement. Given that hip and knee arthroplasties are projected to increase exponentially, as is the burden of comorbid conditions in this population, postoperative AKI will continue to have an incremental impact on health and health care resources. Thus, a carefully planned approach of interdisciplinary perioperative care is warranted to reduce both the risk and the consequences of this devastating condition.

Degenerative arthritis is a widespread chronic condition with an incidence of almost 43 million and annual health care costs of $60 billion in the United States alone.1 Although many cases can be managed symptomatically with medical therapy and intra-articular injections,2 many patients experience disease progression resulting in decreased ambulatory ability and work productivity. For these patients, elective hip and knee arthroplasties can drastically improve quality of life and functionality.3,4 Over the past decade, there has been a marked increase in the number of primary and revision total hip and knee arthroplasties performed in the United States. By 2030, the demand for primary total hip arthroplasties will grow an estimated 174%, to 572,000 procedures. Likewise, the demand for primary total knee arthroplasties is projected to grow by 673%, to 3.48 million procedures.5 However, though better surgical techniques and technology have led to improved functional outcomes, there is still substantial risk for complications in the perioperative period, especially in the geriatric population, in which substantial comorbidities are common.6-9

Acute kidney injury (AKI) is a common public health problem in hospitalized patients and in patients undergoing procedures. More than one-third of all AKI cases occur in surgical settings.^10,11 Over the past decade, both community-acquired and in-hospital AKIs rapidly increased in incidence in all major clinical settings.^12-14 Patients with AKI have high rates of adverse outcomes during hospitalization and discharge.^11,15 Sequelae of AKIs include worsening chronic kidney disease (CKD) and progression to end-stage renal disease, necessitating either long-term dialysis or transplantation.¹² This in turn leads to exacerbated disability, diminished quality of life, and disproportionate burden on health care resources.

Much of our knowledge about postoperative AKI has been derived from cardiovascular, thoracic, and abdominal surgery settings. However, there is a paucity of data on epidemiology and trends for either AKI or associated outcomes in patients undergoing major orthopedic surgery. The few studies to date either were single-center or had inadequate sample sizes for appropriately powered analysis of the risk factors and outcomes related to AKI.¹⁶

In the study reported here, we analyzed a large cohort of patients from a nationwide multicenter database to determine the incidence of and risk factors for AKI. We also examined the mortality and adverse discharges associated with AKI after major joint surgery. Lastly, we assessed temporal trends in both incidence and outcomes of AKI, including the death risk attributable to AKI.

Methods

Database

We extracted our study cohort from the Nationwide Inpatient Sample (NIS) and the National Inpatient Sample of Healthcare Cost and Utilization Project (HCUP) compiled by the Agency for Healthcare Research and Quality.¹⁷ NIS, the largest inpatient care database in the United States, stores data from almost 8 million stays in about 1000 hospitals across the country each year. Its participating hospital pool consists of about 20% of US community hospitals, resulting in a sampling frame comprising about 90% of all hospital discharges in the United States. This allows for calculation of precise, weighted nationwide estimates. Data elements within NIS are drawn from hospital discharge abstracts that indicate all procedures performed. NIS also stores information on patient characteristics, length of stay (LOS), discharge disposition, postoperative morbidity, and observed in-hospital mortality. However, it stores no information on long-term follow-up or complications after discharge.

Data Analysis

For the period 2002–2012, we queried the NIS database for hip and knee arthroplasties with primary diagnosis codes for osteoarthritis and secondary codes for AKI. We excluded patients under age 18 years and patients with diagnosis codes for hip and knee fracture/necrosis, inflammatory/infectious arthritis, or bone neoplasms (Table 1). We then extracted baseline characteristics of the study population. Patient-level characteristics included age, sex, race, quartile classification of median household income according to postal (ZIP) code, and primary payer (Medicare/Medicaid, private insurance, self-pay, no charge). Hospital-level characteristics included hospital location (urban, rural), hospital bed size (small, medium, large), region (Northeast, Midwest/North Central, South, West), and teaching status. We defined illness severity and likelihood of death using Deyo’s modification of the Charlson Comorbidity Index (CCI), which draws on principal and secondary ICD-9-CM (International Classification of Diseases, Ninth Revision-Clinical Modification) diagnosis codes, procedure codes, and patient demographics to estimate a patient’s mortality risk. This method reliably predicts mortality and readmission in the orthopedic population.^18,19 We assessed the effect of AKI on 4 outcomes, including in-hospital mortality, discharge disposition, LOS, and cost of stay. Discharge disposition was grouped by either (a) home or short-term facility or (b) adverse discharge. Home or short-term facility covered routine, short-term hospital, against medical advice, home intravenous provider, another rehabilitation facility, another institution for outpatient services, institution for outpatient services, discharged alive, and destination unknown; adverse discharge covered skilled nursing facility, intermediate care, hospice home, hospice medical facility, long-term care hospital, and certified nursing facility. This dichotomization of discharge disposition is often used in studies of NIS data.²⁰

Statistical Analyses

We compared the baseline characteristics of hospitalized patients with and without AKI. To test for significance, we used the χ² test for categorical variables, the Student t test for normally distributed continuous variables, the Wilcoxon rank sum test for non-normally distributed continuous variables, and the Cochran-Armitage test for trends in AKI incidence. We used survey logistic regression models to calculate adjusted odds ratios (ORs) with 95% confidence intervals (95% CIs) in order to estimate the predictors of AKI and the impact of AKI on hospital outcomes. We constructed final models after adjusting for confounders, testing for potential interactions, and ensuring no multicolinearity between covariates. Last, we computed the risk proportion of death attributable to AKI, indicating the proportion of deaths that could potentially be avoided if AKI and its complications were abrogated.²¹

We performed all statistical analyses with SAS Version 9.3 (SAS Institute) using designated weight values to produce weighted national estimates. The threshold for statistical significance was set at P < .01 (with ORs and 95% CIs that excluded 1).

Results

AKI Incidence, Risk Factors, and Trends

We identified 7,235,251 patients who underwent elective hip or knee arthroplasty for osteoarthritis between 2002 and 2012—an estimate consistent with data from the Centers for Disease Control and Prevention.²² Of that total, 94,367 (1.3%) had AKI. The proportion of discharges diagnosed with AKI increased rapidly over the decade, from 0.5% in 2002 to 1.8% to 1.9% in the period 2010–2012. This upward trend was highly significant (P_trend < .001) (Figure 1). Patients with AKI (vs patients without AKI) were more likely to be older (mean age, 70 vs 66 years; P < .001), male (50.8% vs 38.4%; P < .001), and black (10.07% vs 5.15%; P<. 001). They were also found to have a significantly higher comorbidity score (mean CCI, 2.8 vs 1.5; P < .001) and higher proportions of comorbidities, including hypertension, CKD, atrial fibrillation, diabetes mellitus (DM), congestive heart failure, chronic liver disease, and hepatitis C virus infection. In addition, AKI was associated with perioperative myocardial infarction (MI), sepsis, cardiac catheterization, and blood transfusion. Regarding socioeconomic characteristics, patients with AKI were more likely to have Medicare/Medicaid insurance (72.26% vs 58.06%; P < .001) and to belong to the extremes of income categories (Table 2).

Using multivariable logistic regression, we found that increased age (1.11 increase in adjusted OR for every year older; 95% CI, 1.09-1.14; P < .001), male sex (adjusted OR, 1.65; 95% CI, 1.60-1.71; P < .001), and black race (adjusted OR, 1.57; 95% CI, 1.45-1.69; P < .001) were significantly associated with postoperative AKI. Regarding comorbidities, baseline CKD (adjusted OR, 8.64; 95% CI, 8.14-9.18; P < .001) and congestive heart failure (adjusted OR, 2.74; 95% CI, 2.57-2.92; P< .0001) were most significantly associated with AKI. Perioperative events, including sepsis (adjusted OR, 35.64; 95% CI, 30.28-41.96; P < .0001), MI (adjusted OR, 6.14; 95% CI, 5.17-7.28; P < .0001), and blood transfusion (adjusted OR, 2.28; 95% CI, 2.15-2.42; P < .0001), were also strongly associated with postoperative AKI. Last, compared with urban hospitals and small hospital bed size, rural hospitals (adjusted OR, 0.70; 95% CI, 0.60-0.81; P< .001) and large bed size (adjusted OR, 0.82; 95% CI, 0.70-0.93; P = .003) were associated with lower probability of developing AKI (Table 3).

Figure 2 elucidates the frequency of AKI based on a combination of key preoperative comorbid conditions and postoperative complications—demonstrating that the proportion of AKI cases associated with other postoperative complications is significantly higher in the CKD and concomitant DM/CKD patient populations. Patients hospitalized with CKD exhibited higher rates of AKI in cases involving blood transfusion (20.9% vs 1.8%; P < .001), acute MI (48.9% vs 13.8%; P < .001), and sepsis (74.7% vs 36.3%;P< .001) relative to patients without CKD. Similarly, patients with concomitant DM/CKD exhibited higher rates of AKI in cases involving blood transfusion (23% vs 1.9%; P< .001), acute MI (51.1% vs 12.1%; P< .001), and sepsis (75% vs 38.2%; P < .001) relative to patients without either condition. However, patients hospitalized with DM alone exhibited only marginally higher rates of AKI in cases involving blood transfusion (4.7% vs 2%; P < .01) and acute MI (19.2% vs 16.7%; P< .01) and a lower rate in cases involving sepsis (38.2% vs 41.7%; P < .01) relative to patients without DM. These data suggest that CKD is the most significant clinically relevant risk factor for AKI and that CKD may synergize with DM to raise the risk for AKI.

Outcomes

We then analyzed the impact of AKI on hospital outcomes, including in-hospital mortality, discharge disposition, LOS, and cost of care. Mortality was significantly higher in patients with AKI than in patients without it (2.08% vs 0.06%; P < .001). Even after adjusting for confounders (eg, demographics, comorbidity burden, perioperative sepsis, hospital-level characteristics), AKI was still associated with strikingly higher odds of in-hospital death (adjusted OR, 11.32; 95% CI, 9.34-13.74; P < .001). However, analysis of temporal trends indicated that the odds for adjusted mortality associated with AKI decreased from 18.09 to 9.45 (P_trend = .01) over the period 2002–2012 (Figure 3). This decrease in odds of death was countered by an increase in incidence of AKI, resulting in a stable attributable risk proportion (97.9% in 2002 to 97.3% in 2012; P_trend = .90) (Table 4). Regarding discharge disposition, patients with AKI were much less likely to be discharged home (41.35% vs 62.59%; P < .001) and more likely to be discharged to long-term care (56.37% vs 37.03%; P< .001). After adjustment for confounders, AKI was associated with significantly increased odds of adverse discharge (adjusted OR, 2.24; 95% CI, 2.12-2.36; P< .001). Analysis of temporal trends revealed no appreciable decrease in the adjusted odds of adverse discharge between 2002 (adjusted OR, 1.87; 95% CI, 1.37-2.55; P < .001) and 2012 (adjusted OR, 1.93; 95% CI, 1.76-2.11; P < .001) (Figure 4, Table 5). Last, both mean LOS (5 days vs 3 days; P < .001) and mean cost of hospitalization (US $22,269 vs $15,757; P < .001) were significantly higher in patients with AKI.

Discussion

In this study, we found that the incidence of AKI among hospitalized patients increased 4-fold between 2002 and 2012. Moreover, we identified numerous patient-specific, hospital-specific, perioperative risk factors for AKI. Most important, we found that AKI was associated with a strikingly higher risk of in-hospital death, and surviving patients were more likely to experience adverse discharge. Although the adjusted mortality rate associated with AKI decreased over that decade, the attributable risk proportion remained stable.

Few studies have addressed this significant public health concern. In one recent study in Australia, Kimmel and colleagues¹⁶ identified risk factors for AKI but lacked data on AKI outcomes. In a study of complications and mortality occurring after orthopedic surgery, Belmont and colleagues²² categorized complications as either local or systemic but did not examine renal complications. Only 2 other major studies have been conducted on renal outcomes associated with major joint surgery, and both were limited to patients with acute hip fractures. The first included acute fracture surgery patients and omitted elective joint surgery patients, and it evaluated admission renal function but not postoperative AKI.²² The second study had a sample size of only 170 patients.²³ Thus, the literature leaves us with a crucial knowledge gap in renal outcomes and their postoperative impact in elective arthroplasties.

The present study filled this information gap by examining the incidence, risk factors, outcomes, and temporal trends of AKI after elective hip and knee arthroplasties. The increasing incidence of AKI in this surgical setting is similar to that of AKI in other surgical settings (cardiac and noncardiac).²¹ Although our analysis was limited by lack of perioperative management data, patients undergoing elective joint arthroplasty can experience kidney dysfunction for several reasons, including volume depletion, postoperative sepsis, and influence of medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), especially in older patients with more comorbidities and a higher burden of CKD. Each of these factors can cause renal dysfunction in patients having orthopedic procedures.²⁴ Moreover, NSAID use among elective joint arthroplasty patients is likely higher because of an emphasis on multimodal analgesia, as recent randomized controlled trials have demonstrated the efficacy of NSAID use in controlling pain without increasing bleeding.^25-27 Our results also demonstrated that the absolute incidence of AKI after orthopedic surgery is relatively low. One possible explanation for this phenomenon is that the definitions used were based on ICD-9-CM codes that underestimate the true incidence of AKI.

Consistent with other studies, we found that certain key preoperative comorbid conditions and postoperative events were associated with higher AKI risk. We stratified the rate of AKI associated with each postoperative event (sepsis, acute MI, cardiac catheterization, need for transfusion) by DM/CKD comorbidity. CKD was associated with significantly higher AKI risk across all postoperative complications. This information may provide clinicians with bedside information that can be used to determine which patients may be at higher or lower risk for AKI.

Our analysis of patient outcomes revealed that, though AKI was relatively uncommon, it increased the risk for death during hospitalization more than 10-fold between 2002 and 2012. Although the adjusted OR of in-hospital mortality decreased over the decade studied, the concurrent increase in AKI incidence caused the attributable risk of death associated with AKI to essentially remain the same. This observation is consistent with recent reports from cardiac surgery settings.²¹ These data together suggest that ameliorating occurrences of AKI would decrease mortality and increase quality of care for patients undergoing elective joint surgeries.

We also examined the effect of AKI on resource use by studying LOS, costs, and risk for adverse discharge. Much as in other surgical settings, AKI increased both LOS and overall hospitalization costs. More important, AKI was associated with increased adverse discharge (discharge to long-term care or nursing homes). Although exact reasons are unclear, we can speculate that postoperative renal dysfunction precludes early rehabilitation, impeding desired functional outcome and disposition.^28,29 Given the projected increases in primary and revision hip and knee arthroplasties,⁵ these data predict that the impact of AKI on health outcomes will increase alarmingly in coming years.

There are limitations to our study. First, it was based on administrative data and lacked patient-level and laboratory data. As reported, the sensitivity of AKI codes remains moderate,³⁰ so the true burden may be higher than indicated here. As the definition of AKI was based on administrative coding, we also could not estimate severity, though previous studies have found that administrative codes typically capture a more severe form of disease.³¹ Another limitation is that, because the data were deidentified, we could not delineate the risk for recurrent AKI in repeated surgical procedures, though this cohort unlikely was large enough to qualitatively affect our results. The third limitation is that, though we used CCI to adjust for the comorbidity burden, we were unable to account for other unmeasured confounders associated with increased AKI incidence, such as specific medication use. In addition, given the lack of patient-level data, we could not analyze the specific factors responsible for AKI in the perioperative period. Nevertheless, the strengths of a nationally representative sample, such as large sample size and generalizability, outweigh these limitations.

Conclusion

AKI is potentially an important quality indicator of elective joint surgery, and reducing its incidence is therefore essential for quality improvement. Given that hip and knee arthroplasties are projected to increase exponentially, as is the burden of comorbid conditions in this population, postoperative AKI will continue to have an incremental impact on health and health care resources. Thus, a carefully planned approach of interdisciplinary perioperative care is warranted to reduce both the risk and the consequences of this devastating condition.

Degenerative arthritis is a widespread chronic condition with an incidence of almost 43 million and annual health care costs of $60 billion in the United States alone.1 Although many cases can be managed symptomatically with medical therapy and intra-articular injections,2 many patients experience disease progression resulting in decreased ambulatory ability and work productivity. For these patients, elective hip and knee arthroplasties can drastically improve quality of life and functionality.3,4 Over the past decade, there has been a marked increase in the number of primary and revision total hip and knee arthroplasties performed in the United States. By 2030, the demand for primary total hip arthroplasties will grow an estimated 174%, to 572,000 procedures. Likewise, the demand for primary total knee arthroplasties is projected to grow by 673%, to 3.48 million procedures.5 However, though better surgical techniques and technology have led to improved functional outcomes, there is still substantial risk for complications in the perioperative period, especially in the geriatric population, in which substantial comorbidities are common.6-9

Acute kidney injury (AKI) is a common public health problem in hospitalized patients and in patients undergoing procedures. More than one-third of all AKI cases occur in surgical settings.^10,11 Over the past decade, both community-acquired and in-hospital AKIs rapidly increased in incidence in all major clinical settings.^12-14 Patients with AKI have high rates of adverse outcomes during hospitalization and discharge.^11,15 Sequelae of AKIs include worsening chronic kidney disease (CKD) and progression to end-stage renal disease, necessitating either long-term dialysis or transplantation.¹² This in turn leads to exacerbated disability, diminished quality of life, and disproportionate burden on health care resources.

Much of our knowledge about postoperative AKI has been derived from cardiovascular, thoracic, and abdominal surgery settings. However, there is a paucity of data on epidemiology and trends for either AKI or associated outcomes in patients undergoing major orthopedic surgery. The few studies to date either were single-center or had inadequate sample sizes for appropriately powered analysis of the risk factors and outcomes related to AKI.¹⁶

In the study reported here, we analyzed a large cohort of patients from a nationwide multicenter database to determine the incidence of and risk factors for AKI. We also examined the mortality and adverse discharges associated with AKI after major joint surgery. Lastly, we assessed temporal trends in both incidence and outcomes of AKI, including the death risk attributable to AKI.

Methods

Database

We extracted our study cohort from the Nationwide Inpatient Sample (NIS) and the National Inpatient Sample of Healthcare Cost and Utilization Project (HCUP) compiled by the Agency for Healthcare Research and Quality.¹⁷ NIS, the largest inpatient care database in the United States, stores data from almost 8 million stays in about 1000 hospitals across the country each year. Its participating hospital pool consists of about 20% of US community hospitals, resulting in a sampling frame comprising about 90% of all hospital discharges in the United States. This allows for calculation of precise, weighted nationwide estimates. Data elements within NIS are drawn from hospital discharge abstracts that indicate all procedures performed. NIS also stores information on patient characteristics, length of stay (LOS), discharge disposition, postoperative morbidity, and observed in-hospital mortality. However, it stores no information on long-term follow-up or complications after discharge.

Data Analysis

For the period 2002–2012, we queried the NIS database for hip and knee arthroplasties with primary diagnosis codes for osteoarthritis and secondary codes for AKI. We excluded patients under age 18 years and patients with diagnosis codes for hip and knee fracture/necrosis, inflammatory/infectious arthritis, or bone neoplasms (Table 1). We then extracted baseline characteristics of the study population. Patient-level characteristics included age, sex, race, quartile classification of median household income according to postal (ZIP) code, and primary payer (Medicare/Medicaid, private insurance, self-pay, no charge). Hospital-level characteristics included hospital location (urban, rural), hospital bed size (small, medium, large), region (Northeast, Midwest/North Central, South, West), and teaching status. We defined illness severity and likelihood of death using Deyo’s modification of the Charlson Comorbidity Index (CCI), which draws on principal and secondary ICD-9-CM (International Classification of Diseases, Ninth Revision-Clinical Modification) diagnosis codes, procedure codes, and patient demographics to estimate a patient’s mortality risk. This method reliably predicts mortality and readmission in the orthopedic population.^18,19 We assessed the effect of AKI on 4 outcomes, including in-hospital mortality, discharge disposition, LOS, and cost of stay. Discharge disposition was grouped by either (a) home or short-term facility or (b) adverse discharge. Home or short-term facility covered routine, short-term hospital, against medical advice, home intravenous provider, another rehabilitation facility, another institution for outpatient services, institution for outpatient services, discharged alive, and destination unknown; adverse discharge covered skilled nursing facility, intermediate care, hospice home, hospice medical facility, long-term care hospital, and certified nursing facility. This dichotomization of discharge disposition is often used in studies of NIS data.²⁰

Statistical Analyses

We compared the baseline characteristics of hospitalized patients with and without AKI. To test for significance, we used the χ² test for categorical variables, the Student t test for normally distributed continuous variables, the Wilcoxon rank sum test for non-normally distributed continuous variables, and the Cochran-Armitage test for trends in AKI incidence. We used survey logistic regression models to calculate adjusted odds ratios (ORs) with 95% confidence intervals (95% CIs) in order to estimate the predictors of AKI and the impact of AKI on hospital outcomes. We constructed final models after adjusting for confounders, testing for potential interactions, and ensuring no multicolinearity between covariates. Last, we computed the risk proportion of death attributable to AKI, indicating the proportion of deaths that could potentially be avoided if AKI and its complications were abrogated.²¹

We performed all statistical analyses with SAS Version 9.3 (SAS Institute) using designated weight values to produce weighted national estimates. The threshold for statistical significance was set at P < .01 (with ORs and 95% CIs that excluded 1).

Results

AKI Incidence, Risk Factors, and Trends

We identified 7,235,251 patients who underwent elective hip or knee arthroplasty for osteoarthritis between 2002 and 2012—an estimate consistent with data from the Centers for Disease Control and Prevention.²² Of that total, 94,367 (1.3%) had AKI. The proportion of discharges diagnosed with AKI increased rapidly over the decade, from 0.5% in 2002 to 1.8% to 1.9% in the period 2010–2012. This upward trend was highly significant (P_trend < .001) (Figure 1). Patients with AKI (vs patients without AKI) were more likely to be older (mean age, 70 vs 66 years; P < .001), male (50.8% vs 38.4%; P < .001), and black (10.07% vs 5.15%; P<. 001). They were also found to have a significantly higher comorbidity score (mean CCI, 2.8 vs 1.5; P < .001) and higher proportions of comorbidities, including hypertension, CKD, atrial fibrillation, diabetes mellitus (DM), congestive heart failure, chronic liver disease, and hepatitis C virus infection. In addition, AKI was associated with perioperative myocardial infarction (MI), sepsis, cardiac catheterization, and blood transfusion. Regarding socioeconomic characteristics, patients with AKI were more likely to have Medicare/Medicaid insurance (72.26% vs 58.06%; P < .001) and to belong to the extremes of income categories (Table 2).

Using multivariable logistic regression, we found that increased age (1.11 increase in adjusted OR for every year older; 95% CI, 1.09-1.14; P < .001), male sex (adjusted OR, 1.65; 95% CI, 1.60-1.71; P < .001), and black race (adjusted OR, 1.57; 95% CI, 1.45-1.69; P < .001) were significantly associated with postoperative AKI. Regarding comorbidities, baseline CKD (adjusted OR, 8.64; 95% CI, 8.14-9.18; P < .001) and congestive heart failure (adjusted OR, 2.74; 95% CI, 2.57-2.92; P< .0001) were most significantly associated with AKI. Perioperative events, including sepsis (adjusted OR, 35.64; 95% CI, 30.28-41.96; P < .0001), MI (adjusted OR, 6.14; 95% CI, 5.17-7.28; P < .0001), and blood transfusion (adjusted OR, 2.28; 95% CI, 2.15-2.42; P < .0001), were also strongly associated with postoperative AKI. Last, compared with urban hospitals and small hospital bed size, rural hospitals (adjusted OR, 0.70; 95% CI, 0.60-0.81; P< .001) and large bed size (adjusted OR, 0.82; 95% CI, 0.70-0.93; P = .003) were associated with lower probability of developing AKI (Table 3).

Figure 2 elucidates the frequency of AKI based on a combination of key preoperative comorbid conditions and postoperative complications—demonstrating that the proportion of AKI cases associated with other postoperative complications is significantly higher in the CKD and concomitant DM/CKD patient populations. Patients hospitalized with CKD exhibited higher rates of AKI in cases involving blood transfusion (20.9% vs 1.8%; P < .001), acute MI (48.9% vs 13.8%; P < .001), and sepsis (74.7% vs 36.3%;P< .001) relative to patients without CKD. Similarly, patients with concomitant DM/CKD exhibited higher rates of AKI in cases involving blood transfusion (23% vs 1.9%; P< .001), acute MI (51.1% vs 12.1%; P< .001), and sepsis (75% vs 38.2%; P < .001) relative to patients without either condition. However, patients hospitalized with DM alone exhibited only marginally higher rates of AKI in cases involving blood transfusion (4.7% vs 2%; P < .01) and acute MI (19.2% vs 16.7%; P< .01) and a lower rate in cases involving sepsis (38.2% vs 41.7%; P < .01) relative to patients without DM. These data suggest that CKD is the most significant clinically relevant risk factor for AKI and that CKD may synergize with DM to raise the risk for AKI.

Outcomes

We then analyzed the impact of AKI on hospital outcomes, including in-hospital mortality, discharge disposition, LOS, and cost of care. Mortality was significantly higher in patients with AKI than in patients without it (2.08% vs 0.06%; P < .001). Even after adjusting for confounders (eg, demographics, comorbidity burden, perioperative sepsis, hospital-level characteristics), AKI was still associated with strikingly higher odds of in-hospital death (adjusted OR, 11.32; 95% CI, 9.34-13.74; P < .001). However, analysis of temporal trends indicated that the odds for adjusted mortality associated with AKI decreased from 18.09 to 9.45 (P_trend = .01) over the period 2002–2012 (Figure 3). This decrease in odds of death was countered by an increase in incidence of AKI, resulting in a stable attributable risk proportion (97.9% in 2002 to 97.3% in 2012; P_trend = .90) (Table 4). Regarding discharge disposition, patients with AKI were much less likely to be discharged home (41.35% vs 62.59%; P < .001) and more likely to be discharged to long-term care (56.37% vs 37.03%; P< .001). After adjustment for confounders, AKI was associated with significantly increased odds of adverse discharge (adjusted OR, 2.24; 95% CI, 2.12-2.36; P< .001). Analysis of temporal trends revealed no appreciable decrease in the adjusted odds of adverse discharge between 2002 (adjusted OR, 1.87; 95% CI, 1.37-2.55; P < .001) and 2012 (adjusted OR, 1.93; 95% CI, 1.76-2.11; P < .001) (Figure 4, Table 5). Last, both mean LOS (5 days vs 3 days; P < .001) and mean cost of hospitalization (US $22,269 vs $15,757; P < .001) were significantly higher in patients with AKI.

Discussion

In this study, we found that the incidence of AKI among hospitalized patients increased 4-fold between 2002 and 2012. Moreover, we identified numerous patient-specific, hospital-specific, perioperative risk factors for AKI. Most important, we found that AKI was associated with a strikingly higher risk of in-hospital death, and surviving patients were more likely to experience adverse discharge. Although the adjusted mortality rate associated with AKI decreased over that decade, the attributable risk proportion remained stable.

Few studies have addressed this significant public health concern. In one recent study in Australia, Kimmel and colleagues¹⁶ identified risk factors for AKI but lacked data on AKI outcomes. In a study of complications and mortality occurring after orthopedic surgery, Belmont and colleagues²² categorized complications as either local or systemic but did not examine renal complications. Only 2 other major studies have been conducted on renal outcomes associated with major joint surgery, and both were limited to patients with acute hip fractures. The first included acute fracture surgery patients and omitted elective joint surgery patients, and it evaluated admission renal function but not postoperative AKI.²² The second study had a sample size of only 170 patients.²³ Thus, the literature leaves us with a crucial knowledge gap in renal outcomes and their postoperative impact in elective arthroplasties.

The present study filled this information gap by examining the incidence, risk factors, outcomes, and temporal trends of AKI after elective hip and knee arthroplasties. The increasing incidence of AKI in this surgical setting is similar to that of AKI in other surgical settings (cardiac and noncardiac).²¹ Although our analysis was limited by lack of perioperative management data, patients undergoing elective joint arthroplasty can experience kidney dysfunction for several reasons, including volume depletion, postoperative sepsis, and influence of medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs), especially in older patients with more comorbidities and a higher burden of CKD. Each of these factors can cause renal dysfunction in patients having orthopedic procedures.²⁴ Moreover, NSAID use among elective joint arthroplasty patients is likely higher because of an emphasis on multimodal analgesia, as recent randomized controlled trials have demonstrated the efficacy of NSAID use in controlling pain without increasing bleeding.^25-27 Our results also demonstrated that the absolute incidence of AKI after orthopedic surgery is relatively low. One possible explanation for this phenomenon is that the definitions used were based on ICD-9-CM codes that underestimate the true incidence of AKI.

Consistent with other studies, we found that certain key preoperative comorbid conditions and postoperative events were associated with higher AKI risk. We stratified the rate of AKI associated with each postoperative event (sepsis, acute MI, cardiac catheterization, need for transfusion) by DM/CKD comorbidity. CKD was associated with significantly higher AKI risk across all postoperative complications. This information may provide clinicians with bedside information that can be used to determine which patients may be at higher or lower risk for AKI.

Our analysis of patient outcomes revealed that, though AKI was relatively uncommon, it increased the risk for death during hospitalization more than 10-fold between 2002 and 2012. Although the adjusted OR of in-hospital mortality decreased over the decade studied, the concurrent increase in AKI incidence caused the attributable risk of death associated with AKI to essentially remain the same. This observation is consistent with recent reports from cardiac surgery settings.²¹ These data together suggest that ameliorating occurrences of AKI would decrease mortality and increase quality of care for patients undergoing elective joint surgeries.

We also examined the effect of AKI on resource use by studying LOS, costs, and risk for adverse discharge. Much as in other surgical settings, AKI increased both LOS and overall hospitalization costs. More important, AKI was associated with increased adverse discharge (discharge to long-term care or nursing homes). Although exact reasons are unclear, we can speculate that postoperative renal dysfunction precludes early rehabilitation, impeding desired functional outcome and disposition.^28,29 Given the projected increases in primary and revision hip and knee arthroplasties,⁵ these data predict that the impact of AKI on health outcomes will increase alarmingly in coming years.

There are limitations to our study. First, it was based on administrative data and lacked patient-level and laboratory data. As reported, the sensitivity of AKI codes remains moderate,³⁰ so the true burden may be higher than indicated here. As the definition of AKI was based on administrative coding, we also could not estimate severity, though previous studies have found that administrative codes typically capture a more severe form of disease.³¹ Another limitation is that, because the data were deidentified, we could not delineate the risk for recurrent AKI in repeated surgical procedures, though this cohort unlikely was large enough to qualitatively affect our results. The third limitation is that, though we used CCI to adjust for the comorbidity burden, we were unable to account for other unmeasured confounders associated with increased AKI incidence, such as specific medication use. In addition, given the lack of patient-level data, we could not analyze the specific factors responsible for AKI in the perioperative period. Nevertheless, the strengths of a nationally representative sample, such as large sample size and generalizability, outweigh these limitations.

Conclusion

AKI is potentially an important quality indicator of elective joint surgery, and reducing its incidence is therefore essential for quality improvement. Given that hip and knee arthroplasties are projected to increase exponentially, as is the burden of comorbid conditions in this population, postoperative AKI will continue to have an incremental impact on health and health care resources. Thus, a carefully planned approach of interdisciplinary perioperative care is warranted to reduce both the risk and the consequences of this devastating condition.

Medial-compartment partial knee arthroplasty (unicompartmental replacement) is an accepted surgical intervention for anteromedial osteoarthritis of the knee.1 The radiographic investigations required in the workup of these patients should include weight-bearing standing anteroposterior (AP), lateral, and sunrise (Merchant) views, as well as a valgus stress AP radiograph to assess the functionality of the lateral compartment. The method of properly obtaining the valgus stress film has been well described by the Oxford Group.2 Its recommended radiographic technique requires that a surgeon or a radiologic technologist perform the valgus stress maneuver, manually, while another technologist shoots the film. The 2 consequences of this technique are that it requires 2 individuals to obtain the film, and it subjects the individual who is applying the stress to some level of radiation exposure, which is undesirable. Because of this and the time inconvenience, many surgeons omit the valgus stress radiograph, which can lead to the adverse outcome of missing a lateral compartment that is functionally incompetent, resulting in the potential for early lateral compartment progression of osteoarthritis and the need for revision surgery, usually to a total knee arthroplasty.

In an attempt to mitigate these barriers to obtaining the necessary valgus stress radiograph, Dr. Mauerhan’s team developed a technique that could be done with the assistance of the patient and would require only 1 technologist to perform. Additionally, this project was a quality improvement initiative, because it lowered radiation exposure to all personnel involved in obtaining the correct films.

Materials and Methods

We initiated the project using weight-bearing strategies to impart the valgus stress view of the knee. After trying several different wedges and blocks, and varying patient instructions, we realized a different approach to this problem would be required to find an acceptable solution. We redirected our efforts to effectively performing the stress view with the patient in a supine position on the radiograph table. Ultimately, we decided that a much stiffer wedge and a denser object to squeeze would facilitate obtaining a proper film. Considering all available options, a youth size 4 soccer ball (diameter, 11 in) was introduced along with a slightly larger positioning wedge. The soccer ball was wrapped with 4-in Coban wrap (3M) to create a nonslip surface. This change in patient positioning, along with a standardized 7º to 10º cephalic radiographic tube angulation, helped to correct issues with tibial plateau visualization. Once these changes were enacted, we obtained fairly consistent positive results, and we instituted this patient-directed valgus stress view of the knee, along with a manual valgus stress view for comparison.

The protocol for obtaining the patient-directed valgus stress view of the knee is as follows: The patient lays supine with a dense 45º spine-positioning wedge (Burlington Medical Supplies) placed under both knees and the patient’s heels on the examining table. The radiographic tube is angled cephalad 7º to 10º centered on the inferior pole of the patella, using a 40-in source to image-receptor distance, collimated to part; the image receptor is placed under the affected knee, below the positioning wedge. The affected knee is rotated to the “true” AP position (the patella will be centered between the femoral condyles on the AP exposure), and the ball is placed between the patient’s legs just above the ankle joint. The technologist demonstrates to the patient how to squeeze the ball while maintaining contact of heels with the table. The technologist can exit the room and obtain the exposure, which is taken while the patient is squeezing the ball, as shown in Figures 1A and 1B. Examples of the standing AP, manual stress, and patient-directed valgus radiographs are shown in Figures 2A-2C. The entire technique is demonstrated in the Video.

Vidyard Video

 

 

Results

During the 9 months of this quality improvement project, 78 examinations were performed. Five studies did not show complete correction of the varus deformity. Of these, 3 showed complete correction on a manual valgus stress radiograph, and 2 did not, contraindicating the use of partial knee replacement. Three patients displayed collapse of the lateral compartment, indicating a nonfunctional lateral compartment, and, therefore, were also a contraindication to partial knee arthroplasty. The remaining 70 patients had identical radiographic results with both the manual and patient-directed valgus stress tests. There was no instance of examination failure or need to repeat as a result of difficulty of the examination for the patient. Repeat films because of positioning errors were very rare, usually early in the learning curve, and no more prevalent than when using the manual stress method. The technique was reproducible and easy to teach and adopt.

 

 

Discussion

In total, 73 patients (93.5%) with the patient-directed stress film showed the desired result, either correction of the medial compartment narrowing in conjunction with an intact lateral compartment or narrowing of the lateral compartment. Of the 5 patients (6.5%) whose patient-directed stress films did not show correction of the varus deformity, 3 patients displayed correction with a manually applied stress radiograph and 2 did not. Based on this observation, our recommendation would be for those patients who do not show adequate correction on the patient-directed stress radiograph to have a manual examination to establish the presence or absence of the desired correction.

Performing a valgus stress radiograph is an integral part of the investigation to determine if the patient is an appropriate candidate for partial knee arthroplasty.3 The historical, manually performed valgus stress radiograph requires 2 individuals, 1 to apply the stress with the patient on the table and 1 to shoot the exposure. For the individual or individuals applying this stress, there is an increased radiation exposure that would be undesirable over a long career. The authors developed a new technique using a commercially available spinal positioning wedge and 11-in youth soccer ball wrapped with Coban wrap, as described, which is economical and easy to obtain and use in the clinical setting. We believe this cost-effective method will offer surgeons who perform partial knee arthroplasty a novel method to obtain the important information gleaned from the valgus stress radiograph and to improve surgical outcomes through the preoperative assessment of the lateral compartment. Additionally, as a quality and safety improvement initiative, we believe this technique will reduce radiographic exposure for those performing these studies, and, because the examination can be carried out by a single technologist, it will significantly improve efficiency in the radiology suite.

Conclusion

We have developed a new method of obtaining the important valgus stress radiograph as part of the workup of patients with medial-compartment osteoarthritis of the knee. The technique can be performed with easily obtainable, commercially available products and is reliable 93.5% of the time. It also adds to the efficiency of the radiology suite and reduces radiographic exposure for technologists.

Medial-compartment partial knee arthroplasty (unicompartmental replacement) is an accepted surgical intervention for anteromedial osteoarthritis of the knee.1 The radiographic investigations required in the workup of these patients should include weight-bearing standing anteroposterior (AP), lateral, and sunrise (Merchant) views, as well as a valgus stress AP radiograph to assess the functionality of the lateral compartment. The method of properly obtaining the valgus stress film has been well described by the Oxford Group.2 Its recommended radiographic technique requires that a surgeon or a radiologic technologist perform the valgus stress maneuver, manually, while another technologist shoots the film. The 2 consequences of this technique are that it requires 2 individuals to obtain the film, and it subjects the individual who is applying the stress to some level of radiation exposure, which is undesirable. Because of this and the time inconvenience, many surgeons omit the valgus stress radiograph, which can lead to the adverse outcome of missing a lateral compartment that is functionally incompetent, resulting in the potential for early lateral compartment progression of osteoarthritis and the need for revision surgery, usually to a total knee arthroplasty.

In an attempt to mitigate these barriers to obtaining the necessary valgus stress radiograph, Dr. Mauerhan’s team developed a technique that could be done with the assistance of the patient and would require only 1 technologist to perform. Additionally, this project was a quality improvement initiative, because it lowered radiation exposure to all personnel involved in obtaining the correct films.

Materials and Methods

We initiated the project using weight-bearing strategies to impart the valgus stress view of the knee. After trying several different wedges and blocks, and varying patient instructions, we realized a different approach to this problem would be required to find an acceptable solution. We redirected our efforts to effectively performing the stress view with the patient in a supine position on the radiograph table. Ultimately, we decided that a much stiffer wedge and a denser object to squeeze would facilitate obtaining a proper film. Considering all available options, a youth size 4 soccer ball (diameter, 11 in) was introduced along with a slightly larger positioning wedge. The soccer ball was wrapped with 4-in Coban wrap (3M) to create a nonslip surface. This change in patient positioning, along with a standardized 7º to 10º cephalic radiographic tube angulation, helped to correct issues with tibial plateau visualization. Once these changes were enacted, we obtained fairly consistent positive results, and we instituted this patient-directed valgus stress view of the knee, along with a manual valgus stress view for comparison.

The protocol for obtaining the patient-directed valgus stress view of the knee is as follows: The patient lays supine with a dense 45º spine-positioning wedge (Burlington Medical Supplies) placed under both knees and the patient’s heels on the examining table. The radiographic tube is angled cephalad 7º to 10º centered on the inferior pole of the patella, using a 40-in source to image-receptor distance, collimated to part; the image receptor is placed under the affected knee, below the positioning wedge. The affected knee is rotated to the “true” AP position (the patella will be centered between the femoral condyles on the AP exposure), and the ball is placed between the patient’s legs just above the ankle joint. The technologist demonstrates to the patient how to squeeze the ball while maintaining contact of heels with the table. The technologist can exit the room and obtain the exposure, which is taken while the patient is squeezing the ball, as shown in Figures 1A and 1B. Examples of the standing AP, manual stress, and patient-directed valgus radiographs are shown in Figures 2A-2C. The entire technique is demonstrated in the Video.

Vidyard Video

 

 

Results

During the 9 months of this quality improvement project, 78 examinations were performed. Five studies did not show complete correction of the varus deformity. Of these, 3 showed complete correction on a manual valgus stress radiograph, and 2 did not, contraindicating the use of partial knee replacement. Three patients displayed collapse of the lateral compartment, indicating a nonfunctional lateral compartment, and, therefore, were also a contraindication to partial knee arthroplasty. The remaining 70 patients had identical radiographic results with both the manual and patient-directed valgus stress tests. There was no instance of examination failure or need to repeat as a result of difficulty of the examination for the patient. Repeat films because of positioning errors were very rare, usually early in the learning curve, and no more prevalent than when using the manual stress method. The technique was reproducible and easy to teach and adopt.

 

 

Discussion

In total, 73 patients (93.5%) with the patient-directed stress film showed the desired result, either correction of the medial compartment narrowing in conjunction with an intact lateral compartment or narrowing of the lateral compartment. Of the 5 patients (6.5%) whose patient-directed stress films did not show correction of the varus deformity, 3 patients displayed correction with a manually applied stress radiograph and 2 did not. Based on this observation, our recommendation would be for those patients who do not show adequate correction on the patient-directed stress radiograph to have a manual examination to establish the presence or absence of the desired correction.

Performing a valgus stress radiograph is an integral part of the investigation to determine if the patient is an appropriate candidate for partial knee arthroplasty.3 The historical, manually performed valgus stress radiograph requires 2 individuals, 1 to apply the stress with the patient on the table and 1 to shoot the exposure. For the individual or individuals applying this stress, there is an increased radiation exposure that would be undesirable over a long career. The authors developed a new technique using a commercially available spinal positioning wedge and 11-in youth soccer ball wrapped with Coban wrap, as described, which is economical and easy to obtain and use in the clinical setting. We believe this cost-effective method will offer surgeons who perform partial knee arthroplasty a novel method to obtain the important information gleaned from the valgus stress radiograph and to improve surgical outcomes through the preoperative assessment of the lateral compartment. Additionally, as a quality and safety improvement initiative, we believe this technique will reduce radiographic exposure for those performing these studies, and, because the examination can be carried out by a single technologist, it will significantly improve efficiency in the radiology suite.

Conclusion

We have developed a new method of obtaining the important valgus stress radiograph as part of the workup of patients with medial-compartment osteoarthritis of the knee. The technique can be performed with easily obtainable, commercially available products and is reliable 93.5% of the time. It also adds to the efficiency of the radiology suite and reduces radiographic exposure for technologists.

Medial-compartment partial knee arthroplasty (unicompartmental replacement) is an accepted surgical intervention for anteromedial osteoarthritis of the knee.1 The radiographic investigations required in the workup of these patients should include weight-bearing standing anteroposterior (AP), lateral, and sunrise (Merchant) views, as well as a valgus stress AP radiograph to assess the functionality of the lateral compartment. The method of properly obtaining the valgus stress film has been well described by the Oxford Group.2 Its recommended radiographic technique requires that a surgeon or a radiologic technologist perform the valgus stress maneuver, manually, while another technologist shoots the film. The 2 consequences of this technique are that it requires 2 individuals to obtain the film, and it subjects the individual who is applying the stress to some level of radiation exposure, which is undesirable. Because of this and the time inconvenience, many surgeons omit the valgus stress radiograph, which can lead to the adverse outcome of missing a lateral compartment that is functionally incompetent, resulting in the potential for early lateral compartment progression of osteoarthritis and the need for revision surgery, usually to a total knee arthroplasty.

In an attempt to mitigate these barriers to obtaining the necessary valgus stress radiograph, Dr. Mauerhan’s team developed a technique that could be done with the assistance of the patient and would require only 1 technologist to perform. Additionally, this project was a quality improvement initiative, because it lowered radiation exposure to all personnel involved in obtaining the correct films.

Materials and Methods

We initiated the project using weight-bearing strategies to impart the valgus stress view of the knee. After trying several different wedges and blocks, and varying patient instructions, we realized a different approach to this problem would be required to find an acceptable solution. We redirected our efforts to effectively performing the stress view with the patient in a supine position on the radiograph table. Ultimately, we decided that a much stiffer wedge and a denser object to squeeze would facilitate obtaining a proper film. Considering all available options, a youth size 4 soccer ball (diameter, 11 in) was introduced along with a slightly larger positioning wedge. The soccer ball was wrapped with 4-in Coban wrap (3M) to create a nonslip surface. This change in patient positioning, along with a standardized 7º to 10º cephalic radiographic tube angulation, helped to correct issues with tibial plateau visualization. Once these changes were enacted, we obtained fairly consistent positive results, and we instituted this patient-directed valgus stress view of the knee, along with a manual valgus stress view for comparison.

The protocol for obtaining the patient-directed valgus stress view of the knee is as follows: The patient lays supine with a dense 45º spine-positioning wedge (Burlington Medical Supplies) placed under both knees and the patient’s heels on the examining table. The radiographic tube is angled cephalad 7º to 10º centered on the inferior pole of the patella, using a 40-in source to image-receptor distance, collimated to part; the image receptor is placed under the affected knee, below the positioning wedge. The affected knee is rotated to the “true” AP position (the patella will be centered between the femoral condyles on the AP exposure), and the ball is placed between the patient’s legs just above the ankle joint. The technologist demonstrates to the patient how to squeeze the ball while maintaining contact of heels with the table. The technologist can exit the room and obtain the exposure, which is taken while the patient is squeezing the ball, as shown in Figures 1A and 1B. Examples of the standing AP, manual stress, and patient-directed valgus radiographs are shown in Figures 2A-2C. The entire technique is demonstrated in the Video.

Vidyard Video

 

 

Results

During the 9 months of this quality improvement project, 78 examinations were performed. Five studies did not show complete correction of the varus deformity. Of these, 3 showed complete correction on a manual valgus stress radiograph, and 2 did not, contraindicating the use of partial knee replacement. Three patients displayed collapse of the lateral compartment, indicating a nonfunctional lateral compartment, and, therefore, were also a contraindication to partial knee arthroplasty. The remaining 70 patients had identical radiographic results with both the manual and patient-directed valgus stress tests. There was no instance of examination failure or need to repeat as a result of difficulty of the examination for the patient. Repeat films because of positioning errors were very rare, usually early in the learning curve, and no more prevalent than when using the manual stress method. The technique was reproducible and easy to teach and adopt.

 

 

Discussion

In total, 73 patients (93.5%) with the patient-directed stress film showed the desired result, either correction of the medial compartment narrowing in conjunction with an intact lateral compartment or narrowing of the lateral compartment. Of the 5 patients (6.5%) whose patient-directed stress films did not show correction of the varus deformity, 3 patients displayed correction with a manually applied stress radiograph and 2 did not. Based on this observation, our recommendation would be for those patients who do not show adequate correction on the patient-directed stress radiograph to have a manual examination to establish the presence or absence of the desired correction.

Performing a valgus stress radiograph is an integral part of the investigation to determine if the patient is an appropriate candidate for partial knee arthroplasty.3 The historical, manually performed valgus stress radiograph requires 2 individuals, 1 to apply the stress with the patient on the table and 1 to shoot the exposure. For the individual or individuals applying this stress, there is an increased radiation exposure that would be undesirable over a long career. The authors developed a new technique using a commercially available spinal positioning wedge and 11-in youth soccer ball wrapped with Coban wrap, as described, which is economical and easy to obtain and use in the clinical setting. We believe this cost-effective method will offer surgeons who perform partial knee arthroplasty a novel method to obtain the important information gleaned from the valgus stress radiograph and to improve surgical outcomes through the preoperative assessment of the lateral compartment. Additionally, as a quality and safety improvement initiative, we believe this technique will reduce radiographic exposure for those performing these studies, and, because the examination can be carried out by a single technologist, it will significantly improve efficiency in the radiology suite.

Conclusion

We have developed a new method of obtaining the important valgus stress radiograph as part of the workup of patients with medial-compartment osteoarthritis of the knee. The technique can be performed with easily obtainable, commercially available products and is reliable 93.5% of the time. It also adds to the efficiency of the radiology suite and reduces radiographic exposure for technologists.

Patients more often recovered faster from a total knee arthroplasty (TKA) when they received a periarticular injection of analgesic medication than when they received a femoral nerve block for the same surgery on the opposite knee in a study.

The study included 16 recipients of bilateral primary TKA, who received a femoral nerve block at their first TKA operation and a periarticular injection of an extended-release bupivacaine liposome mixture at the second operation. An average of 2.3 years passed between the two procedures, and the same surgeon performed all surgeries, which occurred between March 2009 and August 2013. Two patients were excluded from the study because of subacute rehabilitation admission delay and a third patient was left out of the study because of respiratory failure, resulting in admission to the ICU.

Following the TKA with a periarticular injection of analgesic medication, the average number of inpatient physical therapy sessions a patient completed was 2.3 (standard deviation: 1.0); the average number of inpatient physical therapy sessions a patient completed after having the TKA with femoral nerve block was 3.5 (SD: 1.3). The average number of hospital days following the TKA with periarticular injection was also a smaller number. The mean number of hospital days following the periarticular injection was 1.5 (SD: 0.6 days). compared with 1.9 days (SD: 0.6 days; P is less than .032) following the femoral nerve block.

“Our data demonstrate that periarticular injection of analgesia allowed patients to complete their inpatient physical therapy sessions and to be discharged sooner, compared with femoral nerve block. This finding suggests that patients who receive periarticular injection of analgesia are able to ambulate independently faster because it does not affect postoperative motor function,” according to Dr. Brandon J. Horn and his colleagues.

Read the full study in the Journal of the American Osteopathic Association (doi: 10.7556/jaoa.2015.146).

klennon@frontlinemedcom.com

Patients more often recovered faster from a total knee arthroplasty (TKA) when they received a periarticular injection of analgesic medication than when they received a femoral nerve block for the same surgery on the opposite knee in a study.

The study included 16 recipients of bilateral primary TKA, who received a femoral nerve block at their first TKA operation and a periarticular injection of an extended-release bupivacaine liposome mixture at the second operation. An average of 2.3 years passed between the two procedures, and the same surgeon performed all surgeries, which occurred between March 2009 and August 2013. Two patients were excluded from the study because of subacute rehabilitation admission delay and a third patient was left out of the study because of respiratory failure, resulting in admission to the ICU.

Following the TKA with a periarticular injection of analgesic medication, the average number of inpatient physical therapy sessions a patient completed was 2.3 (standard deviation: 1.0); the average number of inpatient physical therapy sessions a patient completed after having the TKA with femoral nerve block was 3.5 (SD: 1.3). The average number of hospital days following the TKA with periarticular injection was also a smaller number. The mean number of hospital days following the periarticular injection was 1.5 (SD: 0.6 days). compared with 1.9 days (SD: 0.6 days; P is less than .032) following the femoral nerve block.

“Our data demonstrate that periarticular injection of analgesia allowed patients to complete their inpatient physical therapy sessions and to be discharged sooner, compared with femoral nerve block. This finding suggests that patients who receive periarticular injection of analgesia are able to ambulate independently faster because it does not affect postoperative motor function,” according to Dr. Brandon J. Horn and his colleagues.

Read the full study in the Journal of the American Osteopathic Association (doi: 10.7556/jaoa.2015.146).

klennon@frontlinemedcom.com

Patients more often recovered faster from a total knee arthroplasty (TKA) when they received a periarticular injection of analgesic medication than when they received a femoral nerve block for the same surgery on the opposite knee in a study.

The study included 16 recipients of bilateral primary TKA, who received a femoral nerve block at their first TKA operation and a periarticular injection of an extended-release bupivacaine liposome mixture at the second operation. An average of 2.3 years passed between the two procedures, and the same surgeon performed all surgeries, which occurred between March 2009 and August 2013. Two patients were excluded from the study because of subacute rehabilitation admission delay and a third patient was left out of the study because of respiratory failure, resulting in admission to the ICU.

Following the TKA with a periarticular injection of analgesic medication, the average number of inpatient physical therapy sessions a patient completed was 2.3 (standard deviation: 1.0); the average number of inpatient physical therapy sessions a patient completed after having the TKA with femoral nerve block was 3.5 (SD: 1.3). The average number of hospital days following the TKA with periarticular injection was also a smaller number. The mean number of hospital days following the periarticular injection was 1.5 (SD: 0.6 days). compared with 1.9 days (SD: 0.6 days; P is less than .032) following the femoral nerve block.

“Our data demonstrate that periarticular injection of analgesia allowed patients to complete their inpatient physical therapy sessions and to be discharged sooner, compared with femoral nerve block. This finding suggests that patients who receive periarticular injection of analgesia are able to ambulate independently faster because it does not affect postoperative motor function,” according to Dr. Brandon J. Horn and his colleagues.

Read the full study in the Journal of the American Osteopathic Association (doi: 10.7556/jaoa.2015.146).

klennon@frontlinemedcom.com

Vancomycin is a glycopeptide antibiotic that exhibits bactericidal activity against gram-positive cocci. It is commonly recommended for surgical prophylaxis in cases of suspected bacterial resistance or penicillin allergy.¹ Two main types of hypersensitivity reactions associated with vancomycin can have similar presentations. Red man syndrome is an anaphylactoid reaction caused by direct release of histamine from mast cells via a nonimmunologic mechanism, and is the more common of the 2 reactions. The second type is an anaphylactic reaction, which is an immunoglobulin E (IgE)–mediated systemic event and requires exposure to become sensitized.^2,3

We present a patient who had received vancomycin on at least 12 occasions without incident. On this occasion, however, she developed a true anaphylactic reaction causing acute hemodynamic collapse that she survived after extensive resuscitation. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 55-year-old woman had a history of metastatic giant cell tumor of the right proximal tibia. She was originally treated 27 years ago for proximal tibial resection and reconstruction with a custom proximal tibial prosthesis. Four months later, she underwent resection of multiple pulmonary metastases via bilateral thoracotomies in a single surgical setting. After this, the patient had no evidence of recurrent metastatic disease. In subsequent years, the patient underwent multiple revision surgeries for problems such as hardware failure, patellar maltracking, and infection. The patient underwent 19 operations, including several nonorthopedic procedures. Because the patient had a rash after receiving penicillin as a child, she was thought to be allergic to penicillin. Consequently, she received vancomycin as antibiotic prophylaxis for the majority of these procedures. She also received extended courses of vancomycin of at least 6 weeks on 2 separate occasions. During her most recent revision procedure, 6 weeks prior to the procedure under discussion, the patient took vancomycin without incident. She was then found to have a prosthetic infection with Staphylococcus epidermidis, the same organism isolated in her previous infections, and she was advised to undergo a staged revision.

After a preoperative medical evaluation by her primary care physician, the patient was taken to the operating room for prosthesis removal and antibiotic spacer placement. She was anemic with a hemoglobin level of 8.8 g/dL; her erythrocyte sedimentation rate (ESR) was 102 mm/h (normal, <22 mm/h) and her C-reactive protein (CRP) was 38 mg/L (normal, <3 mg/L), but, otherwise, her laboratory values were normal, including a white blood cell count (WBC) of 8100/µL. Her electrocardiogram showed a normal sinus rhythm with nonspecific ST- and T-wave changes. Antibiotics were held until after cultures were taken. General endotracheal tube anesthesia was induced with 2 mg midazolam, 100 µg fentanyl, 180 mg propofol, and 140 mg succinylcholine, followed by 10 mg vecuronium, and maintained with desflurane. A tourniquet was not used per the surgeon’s routine. Dissection was carried down to the prosthesis and showed a small amount of purulent fluid. Transfusion of 1 unit of packed red blood cells (pRBC) was started during the approach owing to relatively low preoperative hemoglobin and significant blood loss. Approximately 500 mL of blood was lost during the approach secondary to the extensive dissection and the local inflammatory response from infection and recent surgery. After cultures were taken, and approximately 10 minutes after blood transfusion began, infusion of 1 g vancomycin in 250 mL normal saline was started via an infusion pump to run over 1 hour.

After infusion of 5 mL vancomycin, the patient’s blood pressure dropped from 117/63 mm Hg to 63/30 mm Hg; her pulse concurrently dropped from 90 to 50 beats/min. Vancomycin infusion was immediately stopped, anesthesia gasses were turned off, and patient received a bolus of normal saline with a second unit of pRBC. Patient received boluses of 0.5 mg to 1.0 mg epinephrine and 100 µg phenylephrine without sustained increase in blood pressure, which had dropped to 54/24 mm Hg, although the patient became tachycardic to ~120 beats/min after epinephrine. A sudden drop in end-tidal CO₂ from 40s mm Hg to 20s mm Hg was also noted, indicating continuous but significantly decreased perfusion of the lungs.

We elected to abort the procedure, and a vacuum-assisted closure (VAC) dressing was applied to the open wound. After 15 minutes, the patient’s pulses, which had been faint, became impalpable, and cardiopulmonary resuscitation was initiated for about 7 minutes. The patient received 40 units vasopressin with repeated boluses of 0.5 mg epinephrine; a norepinephrine continuous infusion was started with the return of pulses. The patient also received 50 mg diphenhydramine, 125 mg methylprednisolone, and 20 mg famotidine for suspected anaphylaxis. A central venous line and arterial line were placed, and blood was drawn for laboratory analysis. The patient was noted to have clear breath sounds with no obvious rash, and her urine remained clear. Blood gas showed a profound metabolic acidosis, with pH of 7.09, base deficit of 5.9, and lactate of 8.9. The patient was treated with bicarbonate infusion. The patient was noted to ooze significantly during central venous line and arterial line placement, despite apparently normal coagulation during the surgical approach. Coagulation values were consistent with disseminated intravascular coagulation (DIC): prothrombin time, 57 s (international normalized ratio, 6.7); partial thromboplastin time, >200 s; thrombin time, 110 s; D-dimer, >10,000 ng/mL (normal, 0-200 ng/mL); and fibrinogen, <60 mg/dL (normal, 222-475 mg/dL). The patient’s thromboelastogram showed a flat line indicating an absence of clotting. Interestingly, the platelet count remained near the preoperative level at 338×10³/µL. The patient’s blood pressure remained labile and was responsive primarily to epinephrine boluses, of which she received a total of 5 mg. After 1 hour of resuscitation, during which time the patient received a total of 5 L crystalloid and 3 units pRBC, the patient was transferred to the intensive care unit (ICU), intubated, and started on a titrated epinephrine infusion.

Upon arrival in the ICU, the patient quickly stabilized hemodynamically. She was weaned from all inotropic support within 2 hours of arrival. The patient lost 800 mL of blood through wound VAC over the first 12 hours postoperatively and required a total of 11 units of pRBC, 6 units fresh frozen plasma, and 3 units of pooled cryoprecipitate, all of which were compatible. Laboratory values, including arterial pH, lactic acid, and coagulation studies, normalized on the evening of surgery, and, by the next morning, the patient was alert and was extubated without difficulty. Steroids were tapered without hemodynamic compromise while the patient was in the ICU. Cardiology examination revealed no abnormalities. Because of the temporal association of blood transfusion with cardiovascular collapse, pRBC units were retested for antibodies and cultured. Both of these investigations were negative. Wound cultures again were positive for Staphylococcus epidermidis, and blood cultures were negative. The patient was started on daptomycin based on susceptibility profiles. Serum histamine levels taken during initial resuscitation in the operating room were normal. The serum tryptase level obtained at the same time was markedly elevated at >700 ng/mL (normal, <11.5 ng/mL), although this information was not available until several days later.

The patient underwent 2 additional surgeries during the same admission, including the prosthesis removal and tobramycin cement spacer placement, without incident. She was discharged home, again without incident. The patient was later evaluated by an outside allergist and underwent skin puncture and intradermal allergy testing. The results were consistent with a strong IgE-mediated hypersensitivity. Interestingly, she was found not to have a penicillin allergy.

Discussion

Vancomycin hypersensitivity reactions include the anaphylactoid reaction red man syndrome and a true IgE-mediated anaphylactic reaction. Red man syndrome is much more common, with reported rates in infected patients from 3.7% to 47%,^4,5 when vancomycin is given at the suggested  rate of 1 g over 1 hour. The reaction occurs because of histamine release from mast cells and basophils, and does not require previous sensitization.³ The rate of infusion is directly related to the development of symptoms, with 100% of patients developing symptoms in 1 study with rapid infusion (1 g over 10 min).⁶ Red man syndrome can typically be prevented by slowing the rate of infusion or by giving an H₁ blocker.³ Anaphylaxis is more rare but can occur.⁷ Anaphylaxis is mediated by vancomycin-specific IgE, which requires previous exposure, as was the case with our patient. Interestingly, the patient had received vancomycin many times without any signs of a hypersensitivity reaction. Antihistamines are not effective in treating anaphylaxis, and epinephrine is the first-line agent.³ This was clearly demonstrated in this case, as there was a significant hemodynamic response to epinephrine and a negligible response to other vasopressors, specifically norepinephrine and vasopressin.

Most hypersensitivity reactions during the course of a surgical procedure occur with induction of anesthesia, with neuromuscular blocking agents and antibiotics being the most common causes.⁸ In our case, antibiotics were held until after deep cultures were taken. Given the time from induction to the anaphylactic reaction, it is unlikely the reaction resulted from the induction agents or the neuromuscular blocking agent. The possibility of a transfusion reaction was also investigated, since a unit of pRBC was still being transfused when symptoms began. An acute hemolytic transfusion reaction has the classic triad of fever, flank pain, and hemoglobinuria, and can also present as DIC.⁹ Under anesthesia, DIC can often be the presenting sign. In this case, a hemolytic transfusion reaction appeared very unlikely. All of the blood components the patient received were rechecked and found to be compatible, posttransfusion analysis showed no evidence of hemolysis in any sample, and the direct antiglobulin test was negative in all components.

To our knowledge, there are no reported cases of vancomycin-induced anaphylaxis with concomitant DIC. Symptoms of anaphylaxis after exposure to a possible antigen include rapid onset of hypotension or rapid onset of signs in at least 2 organ systems, including cutaneous, gastrointestinal, respiratory, and cardiovascular.¹⁰ Anaphylaxis with DIC is rare after exposure to any substance but has been reported.¹¹ In fact, induction of systemic anaphylaxis in mice is known to cause DIC, with platelet-activating factor suggested as an important common mediator. A similar mechanism is suspected in humans.¹²

Confirmation of, and, certainly, prediction of, a vancomycin hypersensitivity reaction is difficult. Histamine levels can be used as a measure of mast-cell degranulation, but serum levels peak within 5 minutes and quickly return to baseline, limiting its diagnostic usefulness.³ Tryptase is an enzyme found in the secretory granules of mast cells. It has become an accepted marker of acute anaphylaxis, and, in vancomycin hypersensitivity reactions, can also distinguish between anaphylactic and anaphylactoid reactions.¹³ Tryptase levels peak 1 to 2 hours after the reaction, making this easier to measure than histamine, but results may not be available for several days, making it useful only in retrospect, as in our case. Skin testing is probably the best way to confirm a hypersensitivity reaction, although even this has been questioned with vancomycin because some find a high false-positive rate³, while others think the false-negative rate is likely too high.⁷ In this case, we were able to confirm our initial clinical suspicion with both an elevated tryptase level and a positive skin test.

Conclusion

We present a rare case of vancomycin anaphylaxis with DIC after repeated and prolonged previous exposure, which was treated acutely with hemodynamic resuscitation, replacement of blood components, steroids, and, most importantly, repeated boluses of epinephrine. Although several papers have described successful vancomycin desensitization⁷, this was fortunately not necessary in this case because the causative organism was sensitive to other acceptable antibiotics. The patient has been treated with systemic daptomycin and a tobramycin cement spacer without further incident.

Vancomycin is a glycopeptide antibiotic that exhibits bactericidal activity against gram-positive cocci. It is commonly recommended for surgical prophylaxis in cases of suspected bacterial resistance or penicillin allergy.¹ Two main types of hypersensitivity reactions associated with vancomycin can have similar presentations. Red man syndrome is an anaphylactoid reaction caused by direct release of histamine from mast cells via a nonimmunologic mechanism, and is the more common of the 2 reactions. The second type is an anaphylactic reaction, which is an immunoglobulin E (IgE)–mediated systemic event and requires exposure to become sensitized.^2,3

We present a patient who had received vancomycin on at least 12 occasions without incident. On this occasion, however, she developed a true anaphylactic reaction causing acute hemodynamic collapse that she survived after extensive resuscitation. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 55-year-old woman had a history of metastatic giant cell tumor of the right proximal tibia. She was originally treated 27 years ago for proximal tibial resection and reconstruction with a custom proximal tibial prosthesis. Four months later, she underwent resection of multiple pulmonary metastases via bilateral thoracotomies in a single surgical setting. After this, the patient had no evidence of recurrent metastatic disease. In subsequent years, the patient underwent multiple revision surgeries for problems such as hardware failure, patellar maltracking, and infection. The patient underwent 19 operations, including several nonorthopedic procedures. Because the patient had a rash after receiving penicillin as a child, she was thought to be allergic to penicillin. Consequently, she received vancomycin as antibiotic prophylaxis for the majority of these procedures. She also received extended courses of vancomycin of at least 6 weeks on 2 separate occasions. During her most recent revision procedure, 6 weeks prior to the procedure under discussion, the patient took vancomycin without incident. She was then found to have a prosthetic infection with Staphylococcus epidermidis, the same organism isolated in her previous infections, and she was advised to undergo a staged revision.

After a preoperative medical evaluation by her primary care physician, the patient was taken to the operating room for prosthesis removal and antibiotic spacer placement. She was anemic with a hemoglobin level of 8.8 g/dL; her erythrocyte sedimentation rate (ESR) was 102 mm/h (normal, <22 mm/h) and her C-reactive protein (CRP) was 38 mg/L (normal, <3 mg/L), but, otherwise, her laboratory values were normal, including a white blood cell count (WBC) of 8100/µL. Her electrocardiogram showed a normal sinus rhythm with nonspecific ST- and T-wave changes. Antibiotics were held until after cultures were taken. General endotracheal tube anesthesia was induced with 2 mg midazolam, 100 µg fentanyl, 180 mg propofol, and 140 mg succinylcholine, followed by 10 mg vecuronium, and maintained with desflurane. A tourniquet was not used per the surgeon’s routine. Dissection was carried down to the prosthesis and showed a small amount of purulent fluid. Transfusion of 1 unit of packed red blood cells (pRBC) was started during the approach owing to relatively low preoperative hemoglobin and significant blood loss. Approximately 500 mL of blood was lost during the approach secondary to the extensive dissection and the local inflammatory response from infection and recent surgery. After cultures were taken, and approximately 10 minutes after blood transfusion began, infusion of 1 g vancomycin in 250 mL normal saline was started via an infusion pump to run over 1 hour.

After infusion of 5 mL vancomycin, the patient’s blood pressure dropped from 117/63 mm Hg to 63/30 mm Hg; her pulse concurrently dropped from 90 to 50 beats/min. Vancomycin infusion was immediately stopped, anesthesia gasses were turned off, and patient received a bolus of normal saline with a second unit of pRBC. Patient received boluses of 0.5 mg to 1.0 mg epinephrine and 100 µg phenylephrine without sustained increase in blood pressure, which had dropped to 54/24 mm Hg, although the patient became tachycardic to ~120 beats/min after epinephrine. A sudden drop in end-tidal CO₂ from 40s mm Hg to 20s mm Hg was also noted, indicating continuous but significantly decreased perfusion of the lungs.

We elected to abort the procedure, and a vacuum-assisted closure (VAC) dressing was applied to the open wound. After 15 minutes, the patient’s pulses, which had been faint, became impalpable, and cardiopulmonary resuscitation was initiated for about 7 minutes. The patient received 40 units vasopressin with repeated boluses of 0.5 mg epinephrine; a norepinephrine continuous infusion was started with the return of pulses. The patient also received 50 mg diphenhydramine, 125 mg methylprednisolone, and 20 mg famotidine for suspected anaphylaxis. A central venous line and arterial line were placed, and blood was drawn for laboratory analysis. The patient was noted to have clear breath sounds with no obvious rash, and her urine remained clear. Blood gas showed a profound metabolic acidosis, with pH of 7.09, base deficit of 5.9, and lactate of 8.9. The patient was treated with bicarbonate infusion. The patient was noted to ooze significantly during central venous line and arterial line placement, despite apparently normal coagulation during the surgical approach. Coagulation values were consistent with disseminated intravascular coagulation (DIC): prothrombin time, 57 s (international normalized ratio, 6.7); partial thromboplastin time, >200 s; thrombin time, 110 s; D-dimer, >10,000 ng/mL (normal, 0-200 ng/mL); and fibrinogen, <60 mg/dL (normal, 222-475 mg/dL). The patient’s thromboelastogram showed a flat line indicating an absence of clotting. Interestingly, the platelet count remained near the preoperative level at 338×10³/µL. The patient’s blood pressure remained labile and was responsive primarily to epinephrine boluses, of which she received a total of 5 mg. After 1 hour of resuscitation, during which time the patient received a total of 5 L crystalloid and 3 units pRBC, the patient was transferred to the intensive care unit (ICU), intubated, and started on a titrated epinephrine infusion.

Upon arrival in the ICU, the patient quickly stabilized hemodynamically. She was weaned from all inotropic support within 2 hours of arrival. The patient lost 800 mL of blood through wound VAC over the first 12 hours postoperatively and required a total of 11 units of pRBC, 6 units fresh frozen plasma, and 3 units of pooled cryoprecipitate, all of which were compatible. Laboratory values, including arterial pH, lactic acid, and coagulation studies, normalized on the evening of surgery, and, by the next morning, the patient was alert and was extubated without difficulty. Steroids were tapered without hemodynamic compromise while the patient was in the ICU. Cardiology examination revealed no abnormalities. Because of the temporal association of blood transfusion with cardiovascular collapse, pRBC units were retested for antibodies and cultured. Both of these investigations were negative. Wound cultures again were positive for Staphylococcus epidermidis, and blood cultures were negative. The patient was started on daptomycin based on susceptibility profiles. Serum histamine levels taken during initial resuscitation in the operating room were normal. The serum tryptase level obtained at the same time was markedly elevated at >700 ng/mL (normal, <11.5 ng/mL), although this information was not available until several days later.

The patient underwent 2 additional surgeries during the same admission, including the prosthesis removal and tobramycin cement spacer placement, without incident. She was discharged home, again without incident. The patient was later evaluated by an outside allergist and underwent skin puncture and intradermal allergy testing. The results were consistent with a strong IgE-mediated hypersensitivity. Interestingly, she was found not to have a penicillin allergy.

Discussion

Vancomycin hypersensitivity reactions include the anaphylactoid reaction red man syndrome and a true IgE-mediated anaphylactic reaction. Red man syndrome is much more common, with reported rates in infected patients from 3.7% to 47%,^4,5 when vancomycin is given at the suggested  rate of 1 g over 1 hour. The reaction occurs because of histamine release from mast cells and basophils, and does not require previous sensitization.³ The rate of infusion is directly related to the development of symptoms, with 100% of patients developing symptoms in 1 study with rapid infusion (1 g over 10 min).⁶ Red man syndrome can typically be prevented by slowing the rate of infusion or by giving an H₁ blocker.³ Anaphylaxis is more rare but can occur.⁷ Anaphylaxis is mediated by vancomycin-specific IgE, which requires previous exposure, as was the case with our patient. Interestingly, the patient had received vancomycin many times without any signs of a hypersensitivity reaction. Antihistamines are not effective in treating anaphylaxis, and epinephrine is the first-line agent.³ This was clearly demonstrated in this case, as there was a significant hemodynamic response to epinephrine and a negligible response to other vasopressors, specifically norepinephrine and vasopressin.

Most hypersensitivity reactions during the course of a surgical procedure occur with induction of anesthesia, with neuromuscular blocking agents and antibiotics being the most common causes.⁸ In our case, antibiotics were held until after deep cultures were taken. Given the time from induction to the anaphylactic reaction, it is unlikely the reaction resulted from the induction agents or the neuromuscular blocking agent. The possibility of a transfusion reaction was also investigated, since a unit of pRBC was still being transfused when symptoms began. An acute hemolytic transfusion reaction has the classic triad of fever, flank pain, and hemoglobinuria, and can also present as DIC.⁹ Under anesthesia, DIC can often be the presenting sign. In this case, a hemolytic transfusion reaction appeared very unlikely. All of the blood components the patient received were rechecked and found to be compatible, posttransfusion analysis showed no evidence of hemolysis in any sample, and the direct antiglobulin test was negative in all components.

To our knowledge, there are no reported cases of vancomycin-induced anaphylaxis with concomitant DIC. Symptoms of anaphylaxis after exposure to a possible antigen include rapid onset of hypotension or rapid onset of signs in at least 2 organ systems, including cutaneous, gastrointestinal, respiratory, and cardiovascular.¹⁰ Anaphylaxis with DIC is rare after exposure to any substance but has been reported.¹¹ In fact, induction of systemic anaphylaxis in mice is known to cause DIC, with platelet-activating factor suggested as an important common mediator. A similar mechanism is suspected in humans.¹²

Confirmation of, and, certainly, prediction of, a vancomycin hypersensitivity reaction is difficult. Histamine levels can be used as a measure of mast-cell degranulation, but serum levels peak within 5 minutes and quickly return to baseline, limiting its diagnostic usefulness.³ Tryptase is an enzyme found in the secretory granules of mast cells. It has become an accepted marker of acute anaphylaxis, and, in vancomycin hypersensitivity reactions, can also distinguish between anaphylactic and anaphylactoid reactions.¹³ Tryptase levels peak 1 to 2 hours after the reaction, making this easier to measure than histamine, but results may not be available for several days, making it useful only in retrospect, as in our case. Skin testing is probably the best way to confirm a hypersensitivity reaction, although even this has been questioned with vancomycin because some find a high false-positive rate³, while others think the false-negative rate is likely too high.⁷ In this case, we were able to confirm our initial clinical suspicion with both an elevated tryptase level and a positive skin test.

Conclusion

We present a rare case of vancomycin anaphylaxis with DIC after repeated and prolonged previous exposure, which was treated acutely with hemodynamic resuscitation, replacement of blood components, steroids, and, most importantly, repeated boluses of epinephrine. Although several papers have described successful vancomycin desensitization⁷, this was fortunately not necessary in this case because the causative organism was sensitive to other acceptable antibiotics. The patient has been treated with systemic daptomycin and a tobramycin cement spacer without further incident.

Vancomycin is a glycopeptide antibiotic that exhibits bactericidal activity against gram-positive cocci. It is commonly recommended for surgical prophylaxis in cases of suspected bacterial resistance or penicillin allergy.¹ Two main types of hypersensitivity reactions associated with vancomycin can have similar presentations. Red man syndrome is an anaphylactoid reaction caused by direct release of histamine from mast cells via a nonimmunologic mechanism, and is the more common of the 2 reactions. The second type is an anaphylactic reaction, which is an immunoglobulin E (IgE)–mediated systemic event and requires exposure to become sensitized.^2,3

We present a patient who had received vancomycin on at least 12 occasions without incident. On this occasion, however, she developed a true anaphylactic reaction causing acute hemodynamic collapse that she survived after extensive resuscitation. The patient provided written informed consent for print and electronic publication of this case report.

Case Report

A 55-year-old woman had a history of metastatic giant cell tumor of the right proximal tibia. She was originally treated 27 years ago for proximal tibial resection and reconstruction with a custom proximal tibial prosthesis. Four months later, she underwent resection of multiple pulmonary metastases via bilateral thoracotomies in a single surgical setting. After this, the patient had no evidence of recurrent metastatic disease. In subsequent years, the patient underwent multiple revision surgeries for problems such as hardware failure, patellar maltracking, and infection. The patient underwent 19 operations, including several nonorthopedic procedures. Because the patient had a rash after receiving penicillin as a child, she was thought to be allergic to penicillin. Consequently, she received vancomycin as antibiotic prophylaxis for the majority of these procedures. She also received extended courses of vancomycin of at least 6 weeks on 2 separate occasions. During her most recent revision procedure, 6 weeks prior to the procedure under discussion, the patient took vancomycin without incident. She was then found to have a prosthetic infection with Staphylococcus epidermidis, the same organism isolated in her previous infections, and she was advised to undergo a staged revision.

After a preoperative medical evaluation by her primary care physician, the patient was taken to the operating room for prosthesis removal and antibiotic spacer placement. She was anemic with a hemoglobin level of 8.8 g/dL; her erythrocyte sedimentation rate (ESR) was 102 mm/h (normal, <22 mm/h) and her C-reactive protein (CRP) was 38 mg/L (normal, <3 mg/L), but, otherwise, her laboratory values were normal, including a white blood cell count (WBC) of 8100/µL. Her electrocardiogram showed a normal sinus rhythm with nonspecific ST- and T-wave changes. Antibiotics were held until after cultures were taken. General endotracheal tube anesthesia was induced with 2 mg midazolam, 100 µg fentanyl, 180 mg propofol, and 140 mg succinylcholine, followed by 10 mg vecuronium, and maintained with desflurane. A tourniquet was not used per the surgeon’s routine. Dissection was carried down to the prosthesis and showed a small amount of purulent fluid. Transfusion of 1 unit of packed red blood cells (pRBC) was started during the approach owing to relatively low preoperative hemoglobin and significant blood loss. Approximately 500 mL of blood was lost during the approach secondary to the extensive dissection and the local inflammatory response from infection and recent surgery. After cultures were taken, and approximately 10 minutes after blood transfusion began, infusion of 1 g vancomycin in 250 mL normal saline was started via an infusion pump to run over 1 hour.

After infusion of 5 mL vancomycin, the patient’s blood pressure dropped from 117/63 mm Hg to 63/30 mm Hg; her pulse concurrently dropped from 90 to 50 beats/min. Vancomycin infusion was immediately stopped, anesthesia gasses were turned off, and patient received a bolus of normal saline with a second unit of pRBC. Patient received boluses of 0.5 mg to 1.0 mg epinephrine and 100 µg phenylephrine without sustained increase in blood pressure, which had dropped to 54/24 mm Hg, although the patient became tachycardic to ~120 beats/min after epinephrine. A sudden drop in end-tidal CO₂ from 40s mm Hg to 20s mm Hg was also noted, indicating continuous but significantly decreased perfusion of the lungs.

We elected to abort the procedure, and a vacuum-assisted closure (VAC) dressing was applied to the open wound. After 15 minutes, the patient’s pulses, which had been faint, became impalpable, and cardiopulmonary resuscitation was initiated for about 7 minutes. The patient received 40 units vasopressin with repeated boluses of 0.5 mg epinephrine; a norepinephrine continuous infusion was started with the return of pulses. The patient also received 50 mg diphenhydramine, 125 mg methylprednisolone, and 20 mg famotidine for suspected anaphylaxis. A central venous line and arterial line were placed, and blood was drawn for laboratory analysis. The patient was noted to have clear breath sounds with no obvious rash, and her urine remained clear. Blood gas showed a profound metabolic acidosis, with pH of 7.09, base deficit of 5.9, and lactate of 8.9. The patient was treated with bicarbonate infusion. The patient was noted to ooze significantly during central venous line and arterial line placement, despite apparently normal coagulation during the surgical approach. Coagulation values were consistent with disseminated intravascular coagulation (DIC): prothrombin time, 57 s (international normalized ratio, 6.7); partial thromboplastin time, >200 s; thrombin time, 110 s; D-dimer, >10,000 ng/mL (normal, 0-200 ng/mL); and fibrinogen, <60 mg/dL (normal, 222-475 mg/dL). The patient’s thromboelastogram showed a flat line indicating an absence of clotting. Interestingly, the platelet count remained near the preoperative level at 338×10³/µL. The patient’s blood pressure remained labile and was responsive primarily to epinephrine boluses, of which she received a total of 5 mg. After 1 hour of resuscitation, during which time the patient received a total of 5 L crystalloid and 3 units pRBC, the patient was transferred to the intensive care unit (ICU), intubated, and started on a titrated epinephrine infusion.

Upon arrival in the ICU, the patient quickly stabilized hemodynamically. She was weaned from all inotropic support within 2 hours of arrival. The patient lost 800 mL of blood through wound VAC over the first 12 hours postoperatively and required a total of 11 units of pRBC, 6 units fresh frozen plasma, and 3 units of pooled cryoprecipitate, all of which were compatible. Laboratory values, including arterial pH, lactic acid, and coagulation studies, normalized on the evening of surgery, and, by the next morning, the patient was alert and was extubated without difficulty. Steroids were tapered without hemodynamic compromise while the patient was in the ICU. Cardiology examination revealed no abnormalities. Because of the temporal association of blood transfusion with cardiovascular collapse, pRBC units were retested for antibodies and cultured. Both of these investigations were negative. Wound cultures again were positive for Staphylococcus epidermidis, and blood cultures were negative. The patient was started on daptomycin based on susceptibility profiles. Serum histamine levels taken during initial resuscitation in the operating room were normal. The serum tryptase level obtained at the same time was markedly elevated at >700 ng/mL (normal, <11.5 ng/mL), although this information was not available until several days later.

The patient underwent 2 additional surgeries during the same admission, including the prosthesis removal and tobramycin cement spacer placement, without incident. She was discharged home, again without incident. The patient was later evaluated by an outside allergist and underwent skin puncture and intradermal allergy testing. The results were consistent with a strong IgE-mediated hypersensitivity. Interestingly, she was found not to have a penicillin allergy.

Discussion

Vancomycin hypersensitivity reactions include the anaphylactoid reaction red man syndrome and a true IgE-mediated anaphylactic reaction. Red man syndrome is much more common, with reported rates in infected patients from 3.7% to 47%,^4,5 when vancomycin is given at the suggested  rate of 1 g over 1 hour. The reaction occurs because of histamine release from mast cells and basophils, and does not require previous sensitization.³ The rate of infusion is directly related to the development of symptoms, with 100% of patients developing symptoms in 1 study with rapid infusion (1 g over 10 min).⁶ Red man syndrome can typically be prevented by slowing the rate of infusion or by giving an H₁ blocker.³ Anaphylaxis is more rare but can occur.⁷ Anaphylaxis is mediated by vancomycin-specific IgE, which requires previous exposure, as was the case with our patient. Interestingly, the patient had received vancomycin many times without any signs of a hypersensitivity reaction. Antihistamines are not effective in treating anaphylaxis, and epinephrine is the first-line agent.³ This was clearly demonstrated in this case, as there was a significant hemodynamic response to epinephrine and a negligible response to other vasopressors, specifically norepinephrine and vasopressin.

Most hypersensitivity reactions during the course of a surgical procedure occur with induction of anesthesia, with neuromuscular blocking agents and antibiotics being the most common causes.⁸ In our case, antibiotics were held until after deep cultures were taken. Given the time from induction to the anaphylactic reaction, it is unlikely the reaction resulted from the induction agents or the neuromuscular blocking agent. The possibility of a transfusion reaction was also investigated, since a unit of pRBC was still being transfused when symptoms began. An acute hemolytic transfusion reaction has the classic triad of fever, flank pain, and hemoglobinuria, and can also present as DIC.⁹ Under anesthesia, DIC can often be the presenting sign. In this case, a hemolytic transfusion reaction appeared very unlikely. All of the blood components the patient received were rechecked and found to be compatible, posttransfusion analysis showed no evidence of hemolysis in any sample, and the direct antiglobulin test was negative in all components.

To our knowledge, there are no reported cases of vancomycin-induced anaphylaxis with concomitant DIC. Symptoms of anaphylaxis after exposure to a possible antigen include rapid onset of hypotension or rapid onset of signs in at least 2 organ systems, including cutaneous, gastrointestinal, respiratory, and cardiovascular.¹⁰ Anaphylaxis with DIC is rare after exposure to any substance but has been reported.¹¹ In fact, induction of systemic anaphylaxis in mice is known to cause DIC, with platelet-activating factor suggested as an important common mediator. A similar mechanism is suspected in humans.¹²

Confirmation of, and, certainly, prediction of, a vancomycin hypersensitivity reaction is difficult. Histamine levels can be used as a measure of mast-cell degranulation, but serum levels peak within 5 minutes and quickly return to baseline, limiting its diagnostic usefulness.³ Tryptase is an enzyme found in the secretory granules of mast cells. It has become an accepted marker of acute anaphylaxis, and, in vancomycin hypersensitivity reactions, can also distinguish between anaphylactic and anaphylactoid reactions.¹³ Tryptase levels peak 1 to 2 hours after the reaction, making this easier to measure than histamine, but results may not be available for several days, making it useful only in retrospect, as in our case. Skin testing is probably the best way to confirm a hypersensitivity reaction, although even this has been questioned with vancomycin because some find a high false-positive rate³, while others think the false-negative rate is likely too high.⁷ In this case, we were able to confirm our initial clinical suspicion with both an elevated tryptase level and a positive skin test.

Conclusion

We present a rare case of vancomycin anaphylaxis with DIC after repeated and prolonged previous exposure, which was treated acutely with hemodynamic resuscitation, replacement of blood components, steroids, and, most importantly, repeated boluses of epinephrine. Although several papers have described successful vancomycin desensitization⁷, this was fortunately not necessary in this case because the causative organism was sensitive to other acceptable antibiotics. The patient has been treated with systemic daptomycin and a tobramycin cement spacer without further incident.