Background Leg muscle mass is related to development and progression of knee OA, and some studies suggested low leg muscle mass quantified by cross-sectional images of CT or MRI was related to knee symptoms [1,2]. However, this direct method of quantification is hard to apply to clinical practices, and it can be affected by total body mass which can confound the relationship of leg muscle mass and knee symptoms.

Objectives We sought to examine if the ratio of leg to whole body muscle or fat mass by DXA relates to knee symptoms in radiographic knee OA.

Methods We performed a cross-sectional study using data from the Fifth Korean National Health and Nutrition Examination Survey. We included subjects with radiographic knee OA (Kellgren-Lawrence grade≥2) and obtained degree of symptoms, body composition of both legs and the whole body using DXA and calculated the ratios of leg to whole body for muscle and fat mass. Analysis of covariance and multivariable logistic regression models were used to examine the associations of leg to whole body mass with knee symptoms adjusting for possible confounders.

Results 1664 subjects were eligible for analysis. The ratio of leg to whole body muscle mass (LTWBM) was significantly lower in the group with knee pain or stiffness (30.27±0.10 vs. 30.92±0.08, p<0.0001) (Table 1). There was a significant inverse trend between degree of knee pain and LTWBM (p for trend<0.01). LTWBM was 0.86 fold lower in subjects with severe pain (p=0.012, 95% CI 0.79 to 0.94) 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) (Table 1).

Conclusions Symptomatic knee OA was associated with reduced leg muscle mass. Local sarcopenia indicated by low leg to whole body muscle mass could be an important and useful clinical marker for symptomatic knee OA. Strategies to increase leg muscle mass might counteract having symptomatic knee OA.

References

1. Sattler, M., et al., Side differences of thigh muscle cross-sectional areas and maximal isometric muscle force in bilateral knees with the same radiographic disease stage, but unilateral frequent pain - data from the osteoarthritis initiative. Osteoarthritis Cartilage, 2012. 20(6): p. 532-40.

2. Wang, Y., et al., Increase in vastus medialis cross-sectional area is associated with reduced pain, cartilage loss, and joint replacement risk in knee osteoarthritis. Arthritis Rheum, 2012. 64(12): p. 3917-25.

Disclosure of Interest : None declared

DOI 10.1136/annrheumdis-2014-eular.2422