Synovial osteochondromatosis: What causes it?

Synovial osteochondromatosis is an uncommon joint disorder in which cartilage forms in the lining of the joint (synovium). This disorder generally involves a single joint — most commonly the knee, hip or elbow. Synovial osteochondromatosis occurs most often in young to middle-aged adults. Causes include:

• Abnormal changes (metaplasia) in the cells in the synovium. This is called primary synovial osteochondromatosis. In this type, cells in the joint lining convert to cartilage-producing cells (chondrocytes). Cartilage "nests" enlarge, break off into the joint space and calcify, forming loose bodies.
• Injury or osteoarthritis. Doctors refer to this as secondary synovial osteochondromatosis.

Signs and symptoms of synovial osteochondromatosis may include:

• Pain, swelling, limited motion of the affected joint
• Locking of the joint

A doctor may diagnose synovial osteochondromatosis by an imaging scan of the affected joint. Treatment typically is surgical removal of the affected synovium and loose bodies. The disorder can recur.