Abstract / Summary
Abstract Background Women carry more osteoarthritis burden than men, but aggregate estimates may obscure differences across joints and measures. We examined female–male age trajectories for overall osteoarthritis and four anatomical sites. Methods We examined 1990–2021 sex- and age-specific Global Burden of Disease (GBD) 2021 disability-adjusted life-year (DALY) rates. The primary measure, the mean annual log female-to-male rate ratio, described proportional disparity. The secondary measure, the female-minus-male rate difference, described absolute disparity. We compared linear, searched-changepoint, natural-spline, cubic-polynomial and generalized additive model (GAM) representations using information criteria, cross-validation and changepoint-location stability. Results Age trajectories differed across joints. At ages 50–54 years, hand osteoarthritis had the largest proportional disparity (rate ratio 1.88). Knee produced a larger absolute female excess (120.0 versus 80.0 DALYs per 100,000), while point estimates for hip and other-site osteoarthritis favoured males. At this age, the two measures ranked joints differently, and the direction of sex disparity varied across joints. Across ten category-by-measure curves, a five-model comparison did not establish any searched changepoint age over smoother alternatives: nine curves favoured a non-changepoint representation and one (hand, proportional scale) gave mixed evidence. Marginal uncertainty envelopes crossed the null for all curves. Conclusions Female–male osteoarthritis burden varied by joint, age and scale, but none of the selected changepoint ages was supported as a preferred change point. This does not prove that boundaries are absent. Studies should report joint-specific relative and absolute contrasts together, without treating age-specific curve features as individual biological transitions or treatment windows.