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Tumors rarely affect joints unless the joints are near a bone or soft-tissue tumor. However, two conditions—synovial chondromatosis and pigmented villonodular synovitis—occur in the lining (synovium) of joints. These tumors are noncancerous (benign) but aggressive. Both conditions usually affect one joint, most often the knee and then the hip, and can cause pain and an accumulation of fluid. Treatment for both requires surgical removal of the abnormal synovium (synovectomy).
Synovial chondromatosis (previously called synovial osteochondromatosis) is a condition in which cells in the lining of the joint turn into cartilage-producing cells. These converted cells can form clumps of cartilage, which then shed into the space around the joint, forming loose bodies, each of which may be no larger than a grain of rice, and cause pain and swelling. This condition rarely becomes cancerous (malignant). Recurrence is common.
Pigmented villonodular synovitis causes the lining of the joint to become swollen and grow. This growth harms the cartilage and bone around the joint. The lining also produces extra fluid that can cause pain and swelling. The process often causes bloody fluid to appear in the joint. It usually affects one joint. A total joint replacement may be needed if the condition recurs. On rare occasions after several synovectomies, radiation therapy can be used.
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