Magnetic resonance imaging-assessed vastus medialis muscle fat content and risk for knee osteoarthritis progression: relevance from a clinical trial
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Objective Studies have proposed vastus medialis (VM) muscle cross-sectional area change as a variable associated with cartilage volume loss in knee osteoarthritis (OA). However, the VM also includes fat ( Fat), which may influence knee function. This study analyzed the VM area and Fat data, separately and in combination, to predict symptoms, cartilage volume loss, and bone marrow lesion (BML) change in knee OA. Methods This study included the according-to-protocol population (n = 143) of a 2-year knee OA randomized clinical trial having magnetic resonance imaging at baseline and 2 years. Correlations used multivariate analyses. Results Greater baseline value for VM area and Fat were significantly associated with sex (male, area; female, Fat), higher body mass index (BMI), and Western Ontario and McMaster Universities Osteoarthritis Index stiffness, function, and total scores (better, high area; worse, high Fat). Moreover, a VM Fat increase of 1 at 2 years was associated with worsening of cartilage volume loss in the global knee (P = 0.015) and some subregions (P = 0.030), and with an increment of BML global score change (P <0.001). A 1 decrease in VM area at 2 years was associated with worsening of knee pain score (P = 0.048). Importantly, the concurrent presence of low VM area, high VM Fat, and high BMI identified a subgroup of patients with greater cartilage volume loss in the medial femur (P = 0.028) than the rest of the cohort. Conclusion These data demonstrated, for the first time, that VM fat content is a strong predictor of cartilage volume loss and the occurrence and progression of BML. Importantly, the combined data of VM area, VM Fat, and BMI identified patients at higher risk for OA progression.