Extraosseous intra-articular osteochondroma.

Background. Conventional osteochondromas are common bone lesions developing in the metaphyseal region of growing skeleton. Marginal excision is the treatment of choice for such tumours. Extraosseous cartilaginous tumours are rare and their biological potential is poorly characterized. Case Presentation. A-52-year old woman presented with 3-year history of fullness and dull pain and inability to flex her left knee, sit cross-legged, or squat. Clinical and imaging studies revealed a nodular mineralised mass in the anterior portion of the knee displacing the patellar tendon laterally. Excision biopsy confirmed the diagnosis of extraosseous osteochondroma-like soft tissue mass. There is no recurrence at two-year followup. Conclusion. An integrated clinicopathological diagnosis helps to clarify the nature of extraosseous cartilaginous tumour that can arise at an unusual anatomic site. Complete surgical excision is the treatment of choice.