People who develop knee pain associated with osteoarthritis often subsequently develop pain in other joints, according to a study of two observational, community-based cohorts that could not discern any pattern of new pain sites.
In the “first investigation of the association of knee pain with pain in multiple other sites,” David T. Felson, MD, of Boston University and his colleagues reported that the regions where pain developed after first appearing in the knee varied from person to person and occurred in both upper and lower extremities, which goes against the hypothesis that adjacent joints are most often affected by knee pain.
The study involved patients from the MOST (Multicenter Osteoarthritis Study) trial, including 281 with knee pain at the index visit (168 unilaterally) and 852 without, as well as patients from OAI (the Osteoarthritis Initiative), including 412 with knee pain at the index visit (241 unilaterally), and 1,941 without. The investigators assessed the patients’ data for 14 total joints outside of the knees: 2 each of feet, ankles, hips, hands, wrists, elbows, and shoulders (Arthritis Rheumatol. 2016 Sep 2. doi: 10.1002/art.39848).
Patients with new-onset knee pain at the index visit reported a mean of 2.3 painful joints outside the knee, compared with a significantly lower number of 1.3 reported by those without knee pain. The mean number of nonknee joints with pain was higher among patients with bilateral knee pain, compared with unilateral knee pain. The percentage of patients who reported pain outside the knee rose with the number of painful knees: 80% for two, 64% for one, and 50% for none.
The patients who developed new unilateral knee pain at the index visit also experienced an increase in prevalent joint pain in multiple joints in upper- and lower-extremity sites. In particular, the investigators noted that ipsilateral prevalent hip joint pain, which they characterized as pain in the groin or front of the thigh, was more than twice as likely to occur among those with new unilateral knee pain at the index visit, but the odds for contralateral hip joint pain did not reach statistical significance. The comparisons were adjusted for age, sex, body mass index, depression at the index visit, study (MOST or OAI), and count of painful upper and lower limb joints at the index visit (excluding knees).
When examining only patients with new-onset joint pain outside of the knee, the odds of patients with new knee pain to later develop new-onset joint pain outside the knee were 30% higher than for those without knee pain. Patients with new knee pain had a mean 2.6 new painful joints out of 12.1 eligible joints, compared with 2.0 new painful joints in those without knee pain out of 12.7 eligible joints. (Joint regions with prevalent symptoms at the index visit were excluded as incident painful sites.) Patients with knee pain also had a consistently higher rate of new-onset pain in nonknee joints when compared with patients without knee pain in at least half of the follow-up visits over the course of the MOST and OAI studies. Sensitivity analyses indicated that the association between knee pain and subsequent pain in other joints was not driven by the inclusion of patients with widespread pain.
“There was no clear-cut predilection for pain in any specific lower-extremity joint region,” the investigators wrote.
The investigators noted that other researchers have suggested that patients with knee pain may be at higher risk for lower-extremity joint pain because of changes to their gait that gradually cause damage to other joints, but evidence in this study doesn’t “necessarily support the argument that in persons with knee pain, aberrant loading by altered movement patterns induces pain in only nearby joints. Our findings suggest that the sites affected are more than just hip and ankle and that there is no special predilection for pain in these locations.”
While the investigators cannot differentiate underlying mechanisms for their study’s finding of multiple co-occurring sites of joint pain in people with new-onset knee pain, they suggested that it “supports either a predilection for osteoarthritic changes at multiple joint sites and/or raises the possibility that nervous system–driven pain sensitization increases the risk not only of widespread pain but even of regional pain. Since symptomatic OA is unusual in some of these painful sites (e.g., elbow, shoulder, ankle), pain sensitization would seem a more likely explanation.”
Some of the study’s limitations described by the investigators included the uncertainty surrounding whether new-onset knee pain was truly new onset or whether it was a reoccurrence, and also the fact that most of the people in the two cohorts had multiple sites of joint pain at both the baseline and the index visit and there were too few people with no sites of pain outside the knee to carry out subanalyses in that group, which “speaks to the high prevalence of multiple joint pains in older adult cohorts.”