Occurrence of radiographic osteoarthritis of the knee and hip among African Americans and whites: a population-based prospective cohort study.

Objective: To compare the incidence and progression of radiographic osteoarthritis (OA) in the knee and hip among African Americans and whites.

Methods: Using the joint as the unit of analysis, we analyzed data from the Johnston County Osteoarthritis Project, a population-based prospective cohort study in rural North Carolina. Baseline and followup assessments were 3-13 years apart. Assessments included standard knee and hip radiographs read for Kellgren/Lawrence (K/L) radiographic grade. Weighted analyses controlled for age, sex, body mass index, level of education, and baseline K/L grade; bootstrap methods adjusted for lack of independence between left and right joints. Time-to-event analysis was used to analyze the data.

Results: For radiographic knee OA, being African American had no association with incidence (adjusted hazard ratio [HRadj ] 0.80, 95% confidence interval [95% CI] 0.53-1.22), but had a positive association with progression (HRadj 1.67, 95% CI 1.05-2.67). For radiographic hip OA, African Americans had a significantly lower incidence (HRadj 0.44, 95% CI 0.27-0.71), whereas the association with progression was positive but nonsignificant (HRadj 1.46, 95% CI 0.53-4.01). In sensitivity analyses, the association with hip OA incidence was robust to a wide range of assumptions.

Conclusion: African Americans are protected against incident hip OA, but may be more susceptible to progressive knee OA.