Background/Purpose:   Pain and disability from knee osteoarthritis (KOA) has been reported to be greater among African-Americans (AAs) than Whites (WHs), though progression in KOA-related symptoms by race has not been described. Our objective is to compare self-reported pain and disability between AAs and WHs, with or at high-risk of KOA, over 9 years of follow-up.

Methods:   The Osteoarthritis Initiative is a longitudinal cohort study of participants with or at risk of KOA, with up to 9 years of annual self-reported pain and disability assessments including WOMAC pain, pain severity in the past 30 days using a numerical rating scale (NRS), and WOMAC disability. Mixed models for repeated measures were used to estimate race group means and change in group means during follow-up, adjusted for age, sex, education, marital status, body mass index, and depression. Generalized linear mixed models for multinomial logistic regression were used to estimate the relative odds of reporting clinical improvement and worsening, based on established clinically important differences [CID], for AAs compared to WHs. The referent outcome was no CID, and 2 knees per participant were accounted for with random intercepts.

Results:   A total of 3790 WH and 874 AA subjects were included, with baseline mean WOMAC pain subscale scores of 1.9 (SD 2.8) and 4.4 (SD 4.4), respectively. During the first year follow-up, there was a significantly greater decline in mean WOMAC pain among AAs compared to WHs (-0.64 [95% CI: -0.78 to -0.50] vs. -0.15 [95% CI: -0.21 to -0.08]; p<0.0001), while mean pain levels remained stable between the 1 year and 9 year follow-up visits. Pain severity and WOMAC disability had similar patterns, with a significantly greater decline among AAs from baseline to first year follow-up, followed by relatively stable group means. However, AAs had significantly increased odds of reporting clinically important worsening and improvement in pain and disability among nearly all consecutive annual clinic visits, and across all three outcome measures, compared to WHs (Table 1).

Conclusion:   Race-specific group means suggest that AAs report a precipitous drop in KOA-related symptoms between first administration at baseline and second administration 1 year later, followed by stable average pain and disability. Closer examination revealed that AAs were more likely than WHs to report CID, both worsening and improvement, in KOA pain and disability, revealing substantial within-person variance among AAs. Whether the increased variability in responses from AAs reflects fluctuations in actual pain and disability experienced or lack of cross-cultural instrument validity is unknown. Self-reported measures of symptoms are accepted as primary endpoints in randomized controlled trials (RCTs). RCTs that rely on changes in these measures to demonstrate drug efficacy may suffer from obscured treatment effects among AAs.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/racial-differences-in-self-reported-pain-and-disability-a-longitudinal-study-of-knee-osteoarthritis/