Neuromuscular mechanisms of exercise therapy in knee osteoarthritis

Objectives. Although exercise therapy is an effective treatment for reducing pain and activity limitations in knee osteoarthritis (OA), underlying mechanisms are unclear. The aim of this study is to evaluate whether improvement in upper leg muscle strength and knee joint proprioception are longitudinally associated with reductions in pain and activity limitations in patients with knee OA treated with exercise therapy. Design. Secondary analyses from a randomized controlled trial on exercise therapy. Setting. Outpatient rehabilitation center. Participants. One hundred fifty nine participants diagnosed with knee OA. Intervention. Two supervised exercise programs of 12 weeks. Main outcome measures. Changes in pain and in self-reported and observed activity limitations during the 38-week follow-up period. Results. Improved upper leg muscle strength was significantly associated (P<0.001) with reductions in pain (B (95% CI)=-2.5 (-3.7,-1.4) and in self-reported (B (95% CI)=-8.8 (-13.4, 4.2) and observed activity limitations (B (95% CI)=-1.7 (-2.4, 1.0)). Improved knee proprioception was not related with better outcome of exercise therapy. Conclusions. This study provides evidence that upper leg muscle strengthening is one of the mechanisms underlying the beneficial effects of exercise therapy in knee OA.