Knee joint synovial cyst following total knee arthroplasty with bone allograft

Allograft has been shown to be highly successful for managing large osseous defects in total knee arthroplasty. We report a 68-year-old woman in whom a bone allograft had been used during total knee arthroplasty owing to a massive segmental medial tibia plateau defect 4 years earlier. Eighteen months after surgery, a 10 × 10 cm knee synovial cyst was detected by computed tomography scanning on the anteromedial side of the tibial plateau, and an en-bloc surgical excision was performed. At 36-month follow-up, a 16 × 12 cm cyst was found. Excision was again performed with removal of the allograft and application of an autologous iliac graft. After allograft removal, clinically and radiologically satisfactory results were achieved at the final follow-up.