Chair stand performance and symptomatic knee osteoarthritis onset: a prospective cohort study.

Chair stand performance is a simple measure of lower-extremity physical function, but its association with incident structural and symptomatic knee osteoarthritis (KOA) in time-to-event analyses remains unclear. This study investigated the association between chair stand performance and the risk and timing of structural and symptomatic KOA onset. This prospective cohort study used data from the Osteoarthritis Initiative and included 1,003 participants (2,006 knees) aged 45-79 years at increased risk of KOA without radiographic KOA (Kellgren-Lawrence grade 0) at baseline. Structural KOA was defined as incident Kellgren-Lawrence grade ≥ 2, and symptomatic KOA as a Western Ontario and McMaster Universities Osteoarthritis Index pain score ≥ 6 with an increase of ≥ 2 points from baseline. The exposure was time to complete five repeated chair stands. Associations were examined using Cox proportional hazards models and Weibull accelerated failure time models. During follow-up, 69 knees (3.4%) developed structural KOA and 214 knees (10.7%) developed symptomatic KOA. Chair stand time was not associated with structural KOA onset (hazard ratio [HR] 0.96 per second, 95% confidence interval [CI] 0.78-1.05), but was associated with symptomatic KOA onset (HR 1.07 per second, 95% CI 1.03-1.12). Longer chair stand time was also associated with shorter time to any KOA onset (time ratio 0.96 per second, 95% CI 0.93-0.99). Poorer chair stand performance was associated with symptomatic KOA onset and earlier KOA-related onset, but showed no clear association with structural KOA onset.