Low skeletal muscle mass and radiographic osteoarthritis in knee, hip, and lumbar spine: a cross-sectional study.

Background: Although several studies have shown that low skeletal muscle mass is correlated with knee osteoarthritis, no studies have investigated the correlation between skeletal muscle mass and hip and lumbar spine osteoarthritis (OA).
Aim: This study aimed to delineate the relationship between low skeletal muscle mass and radiographic OA (ROA) of the knee, hip, and lumbar spine.
Methods: This is a cross-sectional study using the public data obtained from the Fifth Korean National Health and Nutrition Examination Survey (2010-2011). We included subjects aged ≥ 50 years who completed the surveys (3813 subjects). ROA was assessed by knee, hip, and lumbar spine radiographs and defined as Kellgren/Lawrence (KL) grade of at least 2 in the knee and lumbar spine, whereas KL grade ≥ 1 in the hip. Multivariate logistic regression analyses were performed to evaluate the effects of low skeletal muscle mass on radiographic joint degeneration.
Results: Appendicular skeletal muscle mass (ASM) was higher in subjects with healthy joints than in subjects with knee and lumbar spine ROA (18.9 ± 0.1 kg vs. 17.1 ± 0.2 kg, P < 0.0001 and 18.6 ± 0.1 kg vs. 17.4 ± 0.2 kg, P < 0.0001, respectively), whereas it was higher in those with ROA than in those with healthy hip (17.9 ± 0.1 kg vs. 19.1 ± 0.2 kg P < 0.0001). On multivariate logistic regression analysis, lower skeletal muscle mass independently associated with knee ROA [odds ratio (OR) 1.348; 95% confidence interval (CI) 1.037-1.752]. However, it was inversely associated with lumbar spine ROA (OR 0.786; 95% CI 0.623-0.991).
Conclusion: Low skeletal muscle mass was independently associated with knee ROA alone, whereas it was inversely associated with lumbar spine ROA. These opposite results might originate from measuring the area of ASM.