Background Manifestations and severity of knee osteoarthritis (KOA) vary across racial groups. Characterizing this variability allows identification of vulnerable groups and customizing interventions accordingly. Pain and functional limitations tend to be greater among African-Americans (AAs) than Whites (WHs) with KOA. Differential progression in KOA symptoms by race has not been well-described.
Objectives To compare progression over 9 years in reported pain, disability and other symptoms of AAs and WHs with or at high-risk of KOA
Methods Data from baseline to 108 months were gathered from the Osteoarthritis Initiative (OAI). The study rationale and inclusion criteria for OAI (people ages 45–79 with symptoms of and/or radiographic KOA, or with risk factors for developing KOA) have been described (http://oai.epi-ucsf.org/datarelease/). All AA and WH subjects were included in the study. Knee pain, disability and other OA symptom trajectories were based on: 1) WOMAC pain subscale score [range: 0–20], 2) Knee pain severity in the past 30 days based on a numerical rating scale (NRS) [range: 0–10], 3) WOMAC disability subscale score [range: 0–68], and 4) Knee Injury and Osteoarthritis Outcome (KOOS) other symptoms score [range: 0–100]. Higher scores indicate greater OA-related pain/disability in all measures, except for KOOS symptoms score. Mixed effect models for repeated measures were used to test for racial differences in mean values and mean change during follow-up. All models were adjusted for age, sex, body mass index [BMI], and education.
Results A total of 3790 WH and 874 AA OI participants were included, and the majority (58.4%) were female. Mean (SD) age at baseline was 61.2 (9.2) years, and mean (SD) BMI was 28.7 (4.9) kg/m2. Baseline WOMAC pain subscale score was higher in AAs (mean 3.90 [95% CI: 3.72 to 4.08]) in comparison to WHs (mean 2.09 [95% CI: 2.00 to 2.18]) (p≤0.0001). After the second administration of the questionnaires 1-year post-baseline, there was a significantly greater decline in mean WOMAC pain score among AAs compared to WHs (-0.64 [95% CI: -0.79 to -0.50] vs. -0.15 [95% CI: -0.22 to -0.08]; p<0.0001), while the mean pain levels remained relatively stable between the 1 year and 9 year follow-up visits (Figure 1).
Trajectories of mean pain severity measured with a NRS, WOMAC disability, and KOOS symptom score had similar patterns, with a significantly greater decline among AAs from baseline to the first year of follow-up, followed by relatively stable group means. Change in mean scores over the first year of follow-up for AAs, in comparison to WHs, were as follows: pain severity (-0.70 [95% CI: -0.83 to -0.56] vs. -0.14 [95% CI: -0.20 to -0.08]; p<0.0001), WOMAC disability score (-1.70 [95% CI: -2.15 to -1.25] vs. -0.79 [95% CI: -0.99 to -0.58]; p=0.0003) and KOOS other symptoms score (2.16 [95% CI: 1.52 to 2.80] vs. 1.18 [95% CI: 0.89 to 1.48]; p=0.0064).
Conclusions The results suggest that AAs report a precipitous drop in KOA-related symptoms between first administration at baseline and second administration 1 year later. Self-reported measures of symptoms are accepted as primary endpoints in randomized controlled trials (RCTs) and commonly used in observational studies. The implications for RCTs that rely on changes in these measures to demonstrate drug efficacy include obscured treatment effects among AAs, as well as biased selection for trial eligibility.
Disclosure of Interest None declared