A Novel Case of Tenosynovial Giant Cell Tumor at 4 Years After Total Knee Arthroplasty for Medial Osteoarthritis With Synovial Osteochondromatosis.

We report an unusual case of a tenosynovial giant cell tumor (TGCT) in a patient who received a total knee arthroplasty (TKA) for medial knee osteoarthritis with synovial osteochondromatosis (SO). A 72-year-old woman underwent conventional jig-based simultaneous bilateral bicruciate-stabilized TKA. Four years after the surgery, she came to our hospital with a chief complaint of persistent pain in the right knee only, with recurrent spontaneous hemarthrosis. We performed a synovectomy with open excisional debridement and a polyethylene exchange. Histologic analysis of synovial samples was consistent with TGCT. We present the imaging and pathological details of the first case of de novo TGCT that occurred in the background of SO after TKA.