Unusual Case of Failure of Tibial Polyethylene Insert Locking Mechanism in a Design of Cruciate Retaining Total Knee Arthroplasty - A Case Report.

Introduction: Bilateral total knee arthroplasty (TKA) with a cruciate-retaining (CR) design is a widely performed procedure, but complications involving the prosthesis's locking mechanism are rare. We present a case of locking clip dislodgement in a Zimmer Biomet Vanguard prosthesis, highlighting a rare cause of post-operative swelling and hardware impingement. Case Report: A patient, 1 year after undergoing bilateral TKA, presented with a four-month history of medially prominent knee swelling. Clinical examination and radiographs revealed impinging hardware and confirmed the failure of the locking mechanism, with the locking clip visible as a dislodged entity. Following a negative work-up for infection, the patient was taken for revision surgery. The locking clip was found in the subcutaneous tissue, having buttonholed through the retinaculum. To facilitate access, the posterior cruciate ligament was released, a quadriceps snip was performed, and the anterior superficial medial collateral ligament was subperiosteally released. The original polyethylene liner was replaced with a new anterior stabilized (AS) polyethylene liner of the same thickness and secured with a new locking clip. Intraoperative cultures were negative. The post-operative course was uneventful, with the patient achieving full range of motion within 1 week. Conclusion: This case report underscores that locking mechanism failure should be considered in the differential diagnosis of post-TKA knee swelling and pain. The use of an AS polyethylene liner with a new locking clip proved to be a successful revision strategy, leading to a favorable functional outcome.