Tumors rarely affect joints, apart from the direct extension of an adjacent bone or soft tissue tumor in the joint. However, two changes occur in the synovium: synovial Condromatose and the pigmented villonodular synovitis. Both changes are benign but locally aggressive. Both usually involve a joint, usually the knee and the second most hip and can cause pain and effusion. Both are treated by synovectomy and removal of intra-articular loose bodies. Synovial Chondromatosis The synovial Chondromatosis (formerly known as synovial osteochondromatosis) is considered metaplastically. It is characterized by a variety of calcified cartilage Gelenkkörperchen in the synovium, which dissolve often. Each of which is not greater than a grain of rice in a swollen, painful joint. A malignant change is very rare. Recurrences are common. Diagnosis is made by imaging methods, usually CT or MRI. The treatment may be symptomatic, but when mechanical symptoms are predominant, an arthroscopic or open removal of the bodies or the synovium is justified. Pigmented villonodular synovitis Pigmented villonodular synovitis is considered to be neoplastic. The synovium thickened and contains hemosiderin, which gives the fabric its blood-stained appearance and characteristic appearance on MRI. The fabric tends to invasive growth in the adjacent bone with the following cystic destruction and damage of cartilage. The pigmented villonodular synovitis is monartikulär normally, but can also occur polyarticular. A late treatment, especially after relapse can make a total joint replacement necessary. After several synovectomy radiation therapy is rarely occasionally used.