Synovial chondromatosis (also known as osteochondromatosis) is an uncommon condition characterized by cartilage formation within the synovium.
Primary synovial osteochondromatosis usually presents with monoarticular pain and swelling, as well as limitation of motion.

Locking of the joint will be present in some cases, but is relatively uncommon.
Synovial osteochondromatosis can occur in any synovial tissue, including bursae and tendon sheaths, but it is by far most usual within joint cavities.

The knee is the most commonly affected joint, in more than 50% of cases, followed by the hip and elbow.

On arthrotomy or arthroscopy, the soft tissues of the joints are markedly thickened and the joint cavity is filled with a large number of small, very irregular, cartilaginous nodules. It is characteristic to find some secondary osteoarthritic changes on the side of the joint surface and this is most common in long-standing cases, particularly in weight-bearing joints.

The differential diagnosis includes
Osteoarthritis.
Rheumatoid arthritis.
Osteochondral fractures.
Tumoral calcinosis.
Calcium pyrophosphate disease.

The three stages of synovial osteochondromatosis

Stage I – intrasynovial bodies.

Stage II – cartilaginous bodies partially attached to the synovium.

Stage III – loose bodies floating within the joint space. In most cases, all three stages coexist.

The treatment of synovial osteochondromatosis is controversial.

Some authors advocate observation while others postulate that the disease will progress to osteoarthritis and should be aggressively treated with removal of the loose bodies and complete synovectomy. This is the accepted procedure.

The question of whether a patient will need a knee replacement depends on the damage to the natural cartilage - i.e. - the degree of osteoarthritis in the knee.

I would frequently suggest an arthroscopy examination - removal of the cartilage loose fragments and a synovectomy. I would then put in a cortisone injection and take the patient off weight bearing exercises for at least 6-8 wks and review.