Emergency Medical

Medical Students

Teaching Cases

Learning Resources


A 39-year-old man presents with a 6-month history of pain in his right ankle. The pain has been insidious and is accompanied by stiffness and swelling of the ankle joint. The patient cannot move his ankle well. He cannot perform his daily activities despite using a crutch.

The patient has no history of trauma. He does not have fever, other joint involvement, or back pain. He has no history of sexually transmitted diseases, and his family history is negative for arthritis.

On physical examination, the patient has normal vital signs, including temperature. Cardiac findings are negative for murmurs or rubs. No rash or penile discharge is observed. Examination of the right ankle elicits discomfort and reveals physical limitation with inversion and eversion and especially with flexion and extension. On palpation, the patient has mild tenderness, and the swelling feels firm. No warmth or redness is found over the joint. The remainder of the physical examination yields unremarkable results.

A plain radiograph of the ankle is obtained. What is the diagnosis?


Synovial osteochondromatosis (SOC): SOC, also called synovial chondromatosis, is typically a benign, monoarticular proliferation of the synovial lining of a joint, bursa, or tendon sheath with cartilaginous metaplasia. Proliferation of the synovium produces small nodules that break off and migrate toward the joint cavity. After it becomes intra-articular, metaplasia transforms the nodules into cartilaginous bodies, which enlarge and which typically undergo central necrosis. The necrotic portion becomes calcified and eventually ossified to various degrees. Large joints, such as the knee, hip, elbow, and shoulder, are most commonly affected. However, as this case illustrates, the disease process can involve other joints. In fact, any synovial surface, including extra-articular bursae, may be affected.

As the condition progresses, the joint becomes painfully distended with many such bodies, which may number in the hundreds and which result in mechanical symptoms of restricted motion with eventual joint destruction and secondary osteoarthritis.

The incidence of the disease is 2-4 times higher in men with an age range of 20-50 years than in the general population. SOC usually results in several years of joint pain and swelling. At the time of presentation, the affected joint often has limited range of motion. The patient may also have a history of the joint locking up. Malignant transformation into chondrosarcoma is rarely reported and usually occurs after repeated partial synovectomy procedures.

Plain radiographs are commonly diagnostic, demonstrating several ossified intra-articular loose bodies. Features of osteoarthritis may be seen. In the absence of ossified loose bodies, soft tissue swelling may be appreciated; if so, a differential diagnosis of pigmented villonodular synovitis may be considered. CT scanning, if performed, shows the same findings as radiography does, but CT scans may reveal the nonossified loose bodies. MRI is the modality of choice for demonstrating effusion, synovial changes (which are hyperintense on T2-weighted images with enhancement after the administration of gadolinium-based contrast agent), and loose bodies (which are isointense to hypointense on T1-weighted images and which have signal voids if they are ossified).

Treatment is synovectomy, though recurrences are frequent unless total synovectomy is performed. The patient in this case underwent partial synovectomy with extraction of the loose intra-articular bodies. He remained symptom-free at the time of this writing several months after the procedure.

  • Crotty JM, Monu JU, Pope TL Jr. Synovial osteochondromatosis. Radiol Clin North Am. 1996 Mar;34(2):327-42, xi.
  • Pendse NA, Diwan A, Menghani V. Synovial osteochondromatosis. Ind J Radiol Imag. 2003;13(3):281-3.
  • Resnick D: Diagnosis of Bone and Joint Disorders. Philadelphia, Pa: W.B. Saunders Company. 4th ed. 2002.

Link to further Information on:

For more information on SOC, see the eMedicine article Synovial Osteochondromatosis (within the Radiology specialty).