Synovial osteochondromatosis (SOC) (synonyms include synovial chondromatosis, primary synovial chondromatosis, synovial chondrometaplasia) is a rare disease that creates a benign change or proliferation in the synovium or joint-lining tissue, which changes to form bone-forming cartilage. In most occurrences, there is only one joint affected, either the knee, the hip, or the elbow. Rarely involves the TMJ.The cause is unknown. In this condition, cartilaginous metaplasia takes place within the synovial membrane of the joint. Metaplastic synovium organizes into nodules. With minor trauma, nodules are shed as small bodies into the joint space. In some patients, the disease process may involve tendon sheaths and bursal sacs. Cartilaginous intra-articular bodies float freely within the synovial fluid, which they require for nutrition and growth. Progressive enlargement and ossification occur with time. If they remain free, they continue to grow larger and more calcified. In severe cases, they may occupy the entire joint space or penetrate to adjacent tissues. Also, they can deposit in the synovial lining, reestablish a blood supply, and become replaced by bone. On occasion, synovial reattachment can lead to complete reabsorption of the cartilage fragment. Signs and symptoms
Chronic, progressive pain and swelling of the affected joint are exacerbated by physical activity. Joint effusion and limited range of motion are common associated features. It affects primarily large joints, including knee (>50% of cases), elbow, hip, and shoulder. SOC is twice as common in men as women. Some patients have intra-articular bodies resting in stable positions within joint recesses or bursae.
Partly calcified intra-articular bodies demonstrate foci of absent signal on all pulse sequences. Like CT arthrography, MR with gadolinium may be used to detect intra-articular bodies that have not yet calcified. Pathology
Cartilaginous bodies or osteocartilaginous bodies with central ossification may be noted. They are typically spherical in shape. Sizes range from several millimeters to several centimeters in diameter. The synovium of the involved joint demonstrates villous hyperplasia, which imparts a wrinkled appearance on gross examination. There may be cartilaginous bodies attached to the synovium. Synovial involvement may be focal or diffuse in nature. Differential diagnosis
Trauma-related:
Fracture with avulsed fragment
Fragmentation of meniscus with calcification
Degenerative joint disease related:
Degenerative joint disease with detached spur
Synovial proliferation:
Pigmented villonodular synovitis
Neoplastic:
Synovial chondrosarcoma
Other:
Osteochondritis dissecans
Sequestrum from osteomyelitis
Neuropathic (Charcot) jointIntra-articular bodies in SOC typically have popcorn calcification, with a dense sclerotic border with radiolucent central region. This distinct radiographic appearance sets it apart from other causes of intra-articular bodies. Number and size of intra-articular bodies can prove helpful as well. SOC typically presents as multiple intra-articular bodies. Few or isolated intra-articular bodies are more consistent with trauma or osteoarthritis. Classification
Classification is divided into primary versus secondary SOC. Primary SOC occurs in an otherwise normal joint. It is suggested by monoarticular involvement in a patient in the third to fifth decades of life. Secondary SOC occurs in older patients in joints previously affected by joint disease such as osteoarthritis. This pattern is suggested by bilateral involvement with multiple joint intra-articular bodies. Treatment
Asymptomatic patients do not require therapy. Symptomatic patients should undergo arthroscopic or surgical removal of intra-articular bodies.