Methods: We used data from the OAI, a U.S. multicenter, longitudinal, observational study of knee OA. We selected knees with radiographic, symptomatic OA at baseline (KL 2+, WOMAC Pain at least 1). We determined the TKA incidence rate as the ratio of number of TKAs in a specific subgroup over time at risk for TKA. Time at risk was defined from time of enrollment to time of TKA or to the last available visit date for those without TKA. We computed incidence rate per person-year and used repeated measures Poisson regression to identify the independent contribution of sex, age and race to the incidence of TKA.

Results: We used data from 2,630 knees (1,915 subjects) with radiographic, symptomatic knee OA at baseline. 1,488 (57%) were KL2, 871 (33%) were KL3, and 271 (10%) were KL4. There were 281 TKAs over 84 months of follow-up, for an overall annual incidence rate of 1.7% (95% CI: 1.5 – 2.0). The annual incidence rate of TKA among Whites was estimated at 2.0% (1.8 – 2.3) compared to 1.1% (0.8 – 1.5) in non-Whites. The annual incidence rate of TKA among those who were younger than 65 years was estimated at 1.5% (1.2 – 1.8) compared to 2.1% (1.8 – 2.6) among older persons. In adjusted analysis, higher incidence of TKA was significantly associated with White race and female sex (Table). After adjusting for income and health insurance status, Whites had 1.7 times the rate of TKA compared to non-Whites. Whites were more likely to earn more than $50k annually compared to non-Whites (62% vs. 38%); in income-stratified analysis the racial disparity in TKA incidence persisted: Whites had 1.5 (1.0 – 2.3) times the rate of TKA vs. non-Whites among subjects earning less than $50k and 2.2 (1.2 – 3.8) times the rate among subjects earning more than $50k.

Conclusion: We used a large longitudinal cohort of persons with diagnosed knee OA to determine the incidence of TKA in specific demographic subgroups. This approach overcomes prior estimates from population-based samples that could not distinguish risk factors for OA from risk factors for TKA. In this cohort, with adjustment for age, sex, radiographic severity, income and insurance status, Whites had 1.7 times the TKA incidence of non-Whites. These data confirm the racial disparity suggested by population-based estimates and underscore the need for interventions to address the disparity.