Primary synovial osteochondromatosis in the ankle: a case report.

Primary synovial osteochondromatosis results from the metaplasia of synovial tissue into cartilaginous tissue. This cartilaginous tissue then undergoes calcification and ossification, producing multiple osteochondral nodules. The cause of the metaplasia is unknown. Primary synovial osteochondromatosis is relatively rare and less common than secondary synovial osteochondromatosis. The primary form of the disease arises from the articular or tendon sheath synovium, whereas the secondary form is fragmented articular cartilage within the joint space. Primary synovial osteochondromatosis most commonly occurs in people aged 30 to 40 years and is more prevalent in men. Symptoms include pain, swelling, and decreased range of motion. Because of their abundance of synovial tissue, larger joints are more likely to be affected than smaller joints. Knees are the most commonly affected joints, followed by, in no specific order, shoulders, hips, and elbows. The ankle and the joints of the hand are seldomly involved. In the early stage of the disease, only active synovitis is present, and radiographs are negative. In the late stage, loose bodies can be detected on radiographs. Grossly, these bodies are consistent with ossified nodules. Microscopically, the nodules are composed of cartilaginous material lined by synovial tissue with a central area of calcification.