OBJECTIVE: Depressive symptoms are common in patients with knee osteoarthritis (KOA) and reduce energy, motivation, and movement
thus, declines in physical activity (PA) could worsen as clinical disease progresses. The objective was to evaluate the longitudinal relationship between depressive symptoms and self-reported PA over time among persons with KOA. METHODS: The sample included Osteoarthritis Initiative participants (N = 2602) with radiographic disease (Kellgren-Lawrence grade ≥ 2). Depressive symptoms were measured using the Center for Epidemiologic Studies Depression Scale (CES-D
score ≥ 16) at baseline and first 3 follow-up visits. Self-reported PA was assessed with the Physical Activity Scale for the Elderly (PASE) at the first 4 follow-up visits. Marginal structural models controlling for time-invariant and time-varying confounders evaluated the longitudinal relationship between depressive symptoms and PASE RESULTS: Depressive symptoms were associated with lower PA (β -0.09
95% CI -0.20 to 0.01) over time, but the relationship was not statistically significant. When including depressive symptoms-by-time interactions, the relationship was nonlinear from the first to fourth follow-up visit: visit 1 = -0.18 (95% CI -0.33 to -0.02), visit 2 = -0.05 (95% CI -0.22 to 0.11), visit 3 = -0.01 (95% CI -0.19 to 0.16), and visit 4 = -0.11 (95% CI -0.29 to 0.08). However, the interaction terms were not statistically significant. CONCLUSION: Depressive symptoms may contribute to worse self-reported PA levels in persons with KOA. Future research should determine whether lower physical function is a further sequela of decreased PA related to depressive symptoms.