Synovial osteochondromatosis.

Synovial osteochondromatosis is a benign disorder in which cartilaginous loose bodies develop about the large joints, usually the knee. It is caused by synovial metaplasia of unknown etiology. Symptoms are due either to mechanical problems caused by the loose bodies or to the degenerative arthritis that usually follows in several years. Surgical or arthroscopic removal of the loose bodies appears to be the only effective treatment. Loose bodies may recur, necessitating synovectomy.