Giant cell tumor of the tendon sheath extending around the patellar tendon and invading the knee joint and tibia: A case report.

The current report presents the case of a 41-year-old male exhibiting a giant cell tumor of the tendon sheath (GCT-TS) arising from the patellar tendon sheath. Plain radiography and magnetic resonance imaging revealed a well-localized mass that wrapped around the patellar tendon, and extended from the subcutis into the infrapatellar fat pad and tibia. Following histopathological determination of the diagnosis, a piecemeal resection was performed. Nodular-type GCT-TS occurs less frequently in large joints compared with the small joints of the fingers and toes. The current report presents the unique features of a case of GCT-TS extending around the patellar tendon, and invading into the knee joint and proximal tibia bone.