Synovial chondromatosis is a rare cartilaginous neoplasm that most commonly affects the knee joint. Histologically, it presents as a multinodular cartilaginous proliferation showing clusters of chondrocytes. These can be quite atypical, simulating chondrosarcoma. The lesion is usually self-limited but sometimes may exhibit a more aggressive clinical course characterized by multiple local recurrences. Chondrosarcomatous transformation in synovial chondromatosis is exceedingly rare but has been documented.

Until recently, synovial chondromatosis was considered a reactive process. Recent cytogenetic studies have shown recurrent chromosomal abnormalities, especially involving chromosome6, therefore supporting a clonal, neoplastic nature of this intriguing lesion.