Teaching Case

Swelling of the right ankle of several months duration. Joint pain and locking, tenderness and limited range of motion.

The patient, without relevant past medical history presented with swelling of the right ankle of several months duration. She also suffered from joint pain and locking. Physical examination of the swollen ankle demonstrates tenderness and limited range of motion.

The first description of synovial osteochondromatosis (SOC) was presented by Ambroise Paré in 1558 when discussing loose cartilage bodies in the joints. SOC is more frequently seen in males and often diagnosed during 3rd to 5th decades of life. Large joints, in decreasing order of frequency: knee, elbow and ankle joint, are involved. Bilateral or even polyarticular distribution may be observed. It is generally believed that primary SOC is caused by hyperplastic chondrometaplasia of the synovium with subsequent endochondral bone formation and formation of calcified loose bodies within the joint space. Three phases of primary SOC are described. Synovial metaplasia without loose bodies, metaplasia with development of loose bodies, and an inactive phase, with loose bodies but without synovial metaplasia. The etiology of SOC remains unknown. Patients with SOC usually present with chronic pain, stiffness, swelling and limitation of motion. The radiological diagnosis of SOC is based on the demonstration of cartilaginous loose bodies of variable number that are enclosed by a thickened synovial joint capsule. Subsequently, these nodules may calcify and ossify to a variable extent. In long standing disease, cortical scalloping and bony erosions may develop secondary to pressure changes. Differential diagnosis of SOC includes synovial sarcoma, i.e. soft tissue sarcoma with calcification, intraarticular loose bodies secondary to osteoarthritis, peripheral chondrosarcoma and unusual conditions, such as synovial hemangioma or hemangiosarcoma. SOC may be complicated by degenerative osteoarthritis or, more seldomly, by malignant transformation into chondrosarcoma. Treatment of SOC consists of surgical removal of the loose bodies and complete synovectomy of the involved joint. Recurrence rates of 11% are reported following therapy.