Obesity is an important risk factor for knee OA. Evidence suggests that fat and muscle have differential effects on the pathogenesis of disease. The aim of this study was to examine the relationship between body composition and knee structure, including knee cartilage volume, defects and bone marrow lesions (BMLs).
A total of 153 subjects aged 25-60 years, 81% females, were recruited across a range of BMI (18-55 kg/m2) for a study examining the relationship between obesity and musculoskeletal disease. MRI was performed of the dominant knee. Cartilage volume, defects and BMLs were measured using validated methods. Body composition was measured using dual X-ray absorptiometry.
There was an 81 (95% CI: 69, 94) mm3 increase in cartilage volume for every 1 kg increase in skeletal muscle mass. Fat mass was not significantly associated with cartilage volume. Fat mass, but not skeletal muscle mass, was a risk factor for cartilage defects and BMLs. For every 1 kg increase in total body fat there was an increased risk of cartilage defects (OR=1.31, 95% CI: 1.04, 1.64) and BMLs (OR=1.09, 95% CI: 1.01, 1.18).
In this relatively healthy population, fat mass was associated with increased cartilage defects and BMLs, which are features of early knee OA. In contrast, skeletal muscle mass was positively associated with cartilage volume, which may be due to coinheritance, a commonality of environmental factors associated with cartilage accrual or a protective effect of increased muscle.