Race, sex, and risk factors in radiographic worsening of knee osteoarthritis.

OBJECTIVES: Characterize radiographic worsening in knee osteoarthritis (KOA) by race and sex over 4 years and evaluate the role of established risk factors in observed race/sex differences. METHODS: Whites (WHs) (694 males and 929 females) and African-Americans (AAs) (92 males and 167 females) at risk for radiographic KOA were eligible. Cox shared frailty models were used to estimate race and sex group differences in radiographic worsening, defined by Kellgren-Lawrence (K-L) and OARSI joint space narrowing (JSN). Mixed effect models for repeated measures were used to estimate race- and sex-specific mean medial and lateral fixed joint space width (fJSW) over 4 years of follow-up, as well as annual loss of fJSW. RESULTS: Risk of OARSI medial JSN grade worsening was higher among AA males than WH females [HR = 2.28, (95% CI: 1.14-4.57)], though adjustment for KOA risk factors attenuated the association. Compared to WH females, WH males had lower risk of K-L grade worsening [adjusted HR = 0.75 (95% CI: 0.58-0.96)]. Mean baseline medial fJSW (mm) was 6.49 in WH and AA males, 5.42 in WH females, and 5.41 in AA females. Annual change in mean medial fJSW was greater in AA males (-0.19mm/year) than in other subgroups (-0.09 WH males, -0.07 WH females, -0.10 AA females, p < 0.0001). Compared to WHs, AAs had less lateral fJSW at baseline and throughout follow-up. CONCLUSIONS: Compared to WHs and AA females, AA males experienced higher risk of medial joint space loss. Controlling for established risk factors attenuated associations between race/sex and disease worsening, suggesting that risk factors such as obesity, history of knee injury, and bony finger joint enlargements largely explain race/sex variations in rates of KOA development and progression.