Solitary synovial osteochondroma of the knee: mimicking a giant loose body

Abstract

Solitary synovial osteochondromas are rarely seen. Usually arising from the juxta-articular soft tissues without attaching to the bone, these lesions can be large and show clinical and radiological features of a malignant process. This report is about a 64-year-old woman with no history of trauma. She had a history of dull pain and a progressive limited range of motion that had been ongoing for 3 years. An unusual presentation of an uncommon disease that is not widely known by orthopedic surgeons is reported.

Keywords: arthroscopy; knee joint; loose body; solitary synovial osteochondroma; synovial chondromatosis.

Figure 1

The (A) plain radiograph and (B) computed tomography scan shows unexpectedly large sized, bony structured (radiodense) loose bodies (black arrow and blue arrows) at the lateral compartment of the knee. (C) Magnetic resonance imaging examination shows osteocartilaginous structures (unusual large sized loose bodies, two small and one large) joining with the lateral meniscus. Note: The lateral meniscus has lost its healthy appearance and has been overshadowed (orange arrows) by osteocartilaginous structures.

Figure 2

A histologic preparation of a synovial solitary osteochondroma (H&E, × 10 obj) revealed the characteristic pattern of an osteochondroma covered by a thick cartilaginous cap formed with columnar arrangement of chondrocytes typical for osteochondroma (black arrows [A]). The fibrous capsule was adjacent to the fibrocartilaginous meniscus tissue (yellow arrows [B]). At the chondro-osseous junction, an osteoid matrix with osteocytes forming bony trabecula is apparent at the base of the cap (blue arrows [C]).