What is the diagnosis?

Synovial Osteochondromatosis

• Pearl: Synovial osteochondromatosis is a rare, benign condition, involving an abnormal growth of synovium which can become calcified and potentially break off causing damage to the smooth articular joint surface as a loose body [1].

What is the mechanism of injury?

Cartilaginous metaplasia can spontaneously occur in any joint. The knee is most commonly affected. It typically occurs only in one joint but occasionally is present in multiple joints. Incidence is two times higher in men, most commonly ages 30 - 50 years old [1,4].

What physical exam findings are expected?

On examination, you will note moderate to large effusion, crepitus, and may see a limited range of motion [1].

Which imaging modalities can be used?

Plain radiographs of the joint will show an effusion and possible loose bodies in the joint space. Early synovial osteochondromas may not be calcified and will not show up on x-ray. Recommend outpatient MRI or CT scan if symptomatic and not improving with conservative management [1,2]. 

Image 2. MRI that demonstrates extensive degenerative changes associated with multiple intra-articular osteochondral bodies in the joint with a large knee effusion and baker's cyst. 

E - effusion, D - degenerative change, B - baker’s cyst, O - osteochondral body. Case courtesy of Frank Gaillard, Radiopaedia.org, rID: 5651, annotations by WD.

What is the management in the ED?

These patients should be counseled that this a benign condition and treatment depends on severity of symptoms. Conservative management with NSAIDs and discharge with orthopedic follow up is appropriate. Do not limit motion. Compression sleeves can help reduce swelling [1,3]. 

• Pearl: Symptomatic management and orthopedic follow up without limitation of mobility is key.

When do you consult Orthopedics?

Orthopedics should be consulted for severe symptoms and limited mobility for open vs arthroscopic synovectomy and loose body resection. Surgical resection can help prevent degenerative joint destruction [3].