Lower leg muscle mass relates to knee pain in patients with knee osteoarthritis

Aim This study aimed to investigate the relationship between leg muscle mass measured by dual-energy X-ray absorptiometry (DEXA) and knee pain/stiffness in patients with radiographic knee osteoarthritis (OA). Methods We performed a cross-sectional study using data from the Fifth Korean National Health and Nutrition Examination Survey. We included participants with radiographic knee OA (Kellgren–Lawrence grade ≥ 2) and obtained the degree of knee pain/stiffness and body composition of both legs and the whole body using DEXA. We calculated the ratios of legs to whole body in terms of muscle and fat mass. Analysis of covariance and multivariable logistic regression models were used to examine the associations of leg to whole body mass in patients with knee symptoms, adjusting for possible confounders. Results We analyzed data for 1664 individuals. The ratio of leg to whole body muscle mass (LTWMM) was significantly lower in the group with knee pain or stiffness (30.27 ± 0.10 vs. 30.92 ± 0.08%, P < 0.0001). We found a significant inverse trend between the degree of knee pain and LTWMM (P for trend < 0.01). LTWMM was 14% lower in persons with severe pain (P = 0.012) when adjusted for age and sex. Leg to whole body fat mass was higher in the group with knee pain or stiffness (28.65 ± 0.22 vs. 27.95 ± 0.17%, P = 0.009). Conclusion DEXA-measured leg muscle mass was significantly associated with knee pain in people with radiographic knee OA. Low leg muscle mass is a useful clinical indicator for symptomatic knee OA, and DEXA is potentially an excellent tool to quickly assess leg mass in patients with knee OA.