Synovial chondromatosis is a type of non-cancerous tumor that arises in the lining of a joint. The knee is most commonly affected, however it can affect any joint. The tumors begin as small nodules of cartilage. These nodules can separate and become loose within the joint. Some tumors may be no larger than a grain of rice. Synovial chondromatosis most commonly occurs in adults ages 20 to 50. Signs and symptoms may include pain, swelling, a decreased range of motion, and locking of the joint. The exact underlying cause of the condition is unknown. Treatment may involve surgery to remove the tumor. Recurrence of the condition is common.

Synovial chondromatosis can reportedly occur as either a primary or secondary form. Primary synovial chondromatosis, which is more rare, occurs spontaneously and does not appear to relate to any pre-existing conditions. Secondary synovial chondromatosis is the more common form and often occurs when there is pre-existent osteoarthritis, rheumatoid arthritis, osteonecrosis, osteochondritis dissecans, neuropathic osteoarthropathy (which often occurs in diabetic individuals), tuberculosis, or osteochondral fractures (torn cartilage covering the end of a bone in a joint) in the affected individual.

The long-term outlook (prognosis) for individuals with synovial chondromatosis varies depending on the joint affected, the amount of damage to the joint and whether the condition recurs after treatment. Follow-up examinations are usually required to monitor for recurrence and any progression of osteoarthritis. Sometimes, a second surgery is necessary. The amount of damage that the condition has already done to the joint will influence the chance of arthritis developing. Affected individuals may need physical therapy after treatment to preserve normal functioning of the affected joint.