Muscle weakness in osteoarthritis.

Muscle has an integral role in the structure and function of joints. Evidence for muscle weakness in osteoarthritis of the knee exists and is not fully explained by the effects of aging. Weakness is associated with pain and disability. The temporal relationship requires further study, but preliminary evidence for a causative role is emerging. Muscle weakness can be assessed in various ways. Voluntary measures of strength are affected by degree of effort. In osteoarthritic patients, as in other patient groups, effort may be influenced by pain and psychologic outlook. Techniques to estimate muscle activation are available but have yet to be fully explored in osteoarthritis. Quadriceps exercises increases strength and may have beneficial effects on pain and function. The long-term benefits of exercise for therapy and possible prevention of osteoarthritis are not yet known. This is an exciting area of research, and it is anticipated that more findings will emerge in the near future.