Malignant transformation in synovial chondromatosis of the knee?

Although it has been reported, malignant transformation of synovial chondromatosis is rare. We report a case of malignant transformation of synovial chondromatosis in a knee to a low-grade chondrosarcoma, which was treated with synovial excision and total knee replacement. We also present a literature review of the subject. The case illustrates that malignant transformation should be suspected in chronic cases with a sudden exacerbation of symptoms and that interpretation of histology in cartilage lesions is difficult. It also demonstrates that even when guided biopsy techniques are used, the sampling error of a needle biopsy in any large lesion is unavoidable.