Synovial Osteochondromatosis

A 44-year-old man with a history of grand mal seizures experienced knee pain while walking. The pain was more severe in the left than in the right knee. The patient had a history of trauma to his left knee caused by falling during seizures.

The left knee was held in a flexed position of approximately 5 degrees; crepitus and swelling of the joint were noted. An x-ray film demonstrated bilateral ossification posterior to the proximal tibia region (arrow) and minor degenerative changes with spurring of the tibial spine and the patellofemoral joint. These findings were confirmed on an MRI scan, which also revealed meniscal tears on the right and effusions that were greater in the left than the right joint. The radiologist noted that the appearance was not typical of myositis ossificans and the pathology did not appear to involve the underlying bone or muscle. Synovial osteochondromatosis was diagnosed after consultation with the radiologist, a rheumatologist, and an orthopedist.

Dr Kofi Clarke of Pittsburgh writes that synovial osteochondromatosis is usually a monoarticular disorder of unknown origin that occurs in large joints. It affects men 2 to 4 times more often than women. The typical patient is between the ages of 20 and 40 years.¹ Characteristically, proliferation and metaplasia of the synovium occurs; eventually fragments break off into the joint space and may grow, calcify, or ossify. The differential diagnosis includes pigmented villonodular synovitis, broken-off osteophytes, synovial hemangiomas, and rice bodies of rheumatoid arthritis. Roentgenography and MRI scanning are the mainstays of diagnosis.

The knee is most commonly involved; elbows, shoulders, and hips also can be affected. Occasionally, the disorder may involve multiple joints.

Classic symptoms of this essentially benign condition are pain, swelling, and limitation of movement. Associated degenerative joint disease and radiographic changes can occur. Rare cases of malignant transformation have been described. The treatment of choice is synovectomy, since recurrence is common after surgical excision of the hypertrophied synovium.

Initially, this patient refused surgery and opted for NSAIDs to control his pain and swelling. The medical therapy failed to allow him to resume activities of daily living; he underwent arthroscopic surgery and regained significant knee function. The cause and duration of this patient's joint disease is unknown; the role of his knee trauma is uncertain.

REFERENCE:1. Monu J, Oka M. Synovial osteochondromatosis. 2002. Available at: http://www.emedicine.com. Accessed November 4, 2002.