Magnetic Resonance Imaging–Assessed Vastus Medialis Muscle Fat Content and Risk for Knee Osteoarthritis Progression: Relevance From a Clinical Trial

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.