Synovial osteochondromatosis

Malignant transformation to synovial chondrosarcoma. This is a very rare complication occurring in chronic cases. Treatment entails synovial excision and total joint replacement.

Clicking, grating, or locking may result from acute mechanical problems due to intra-articular bodies within the affected joint. Locking may destroy articular cartilage, resulting in secondary osteoarthritis. Symptoms such as joint stiffness and aching are the result of osteoarthritis that sets in after years of persistent joint irritation.[2]

Typical finding is of multiple, smooth, oval-shaped calcified masses within the joint space or bursa. They have a characteristic popcorn-ball appearance of calcified cartilage. With serial imaging, masses may be found to change in size, disappear, or migrate to recessed areas of the joint. They may pass from the main joint cavity into a neighboring synovial cyst. For this reason, a mass may not be appreciated within the actual joint space itself.

Additional radiographic findings include joint effusion and degenerative changes such as joint space narrowing, subchondral sclerosis, and osteophyte formation.

CT is best utilized in earlier stages of the disease process before cartilaginous bodies have calcified (become filled with calcium). CT can effectively detect non-calcified masses or those with only minimal calcification, which allows the radiologist to distinguish this condition from a simple joint effusion.

MR appearance depends on the composition of the intra-articular body. Entirely cartilaginous bodies will appear isointense to muscle on T1 and hyperintense to muscle on T2 weighted images. 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.

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.[3]

• 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) joint

Intra-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 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.