Pigmented villonodular synovitis: an unusual complication of Oxford unicompartmental knee replacement leading to failure and revision. Two case reports and review of the literature

Background  Pigmented villonodular synovitis (PVNS) is a rare disease of the synovial membrane. Its relationship to unicompartmental arthroplasty is unknown and it has never been reported as a complication of this procedure. Methods  Retrospective review of two cases who presented with this rare condition after Oxford unicompartmental arthroplasty (Biomet, UK). We present their cases and discuss the difficulties we faced in their management. Discussion  These cases are remarkably similar in their presentation. The diagnosis was confirmed histologically in both cases. We mainly focus on the diagnostic difficulties and our treatment strategies in both cases. We also review the current literature on this unusual disease.