Intra-articular calcifying synovial sarcoma mimicking synovial chondromatosis

A case of intra-articular calcifying synovial sarcoma of the right knee joint in a 27-year-old man is reported. Prior to admission the patient had been suffering pain in the right knee for 5 years. Plain radiographs showed multiple calcified densities in the anterior aspect of the right knee closely mimicking synovial chondromatosis. Histological examination revealed that the lesion was a synovial sarcoma with extensive calcification subjacent to the synovial surface. Although intra-articular calcifying synovial sarcoma is very rare, it is important to be aware of the fact that synovial sarcoma, as well as synovial chondromatosis, can be present as a calcified lesion in the joint cavity.