A Rare Case of Posterior Dislocation of Hinge Knee Prosthesis due to Wear of Anti-Luxation Device: A Case Report.

Introduction: Hinge knee joint prosthesis are utilized in a variety of surgical scenarios, including complex primary, revision, salvage surgeries, and radical resection of tumor's. Link's Endo-model Hinged Knee Prosthesis is a newer design that includes ramped tibial components for controlled pivot point motion during flexion and an anti-dislocation feature to prevent prosthesis dislocation.. The re-design of the hinge prosthesis has resulted in less force transfer along the implant bone junction. However, despite the improved design, complications can still arise. This report presents a rare complication of posterior dislocation due to polythene wear of the anti-dislocation device in a patient with a rotating hinge knee prosthesis.

Case Report: After 4 years, a 42-year-old patient who had undergone multiple total knee replacements (TKRs) with a history of pain, swelling, and difficulty walking for the previous 2 months presented to us. Radiographs from the initial presentation revealed aseptic loosening, for which a revision TKR using a Link-Waldemier non-modular (rotational) joint endo-model with an anti-dislocation mechanism was performed. Three years later, the patient began experiencing episodes of instability, and a radiograph revealed posterior dislocation of the hinge knee prosthesis. As a result, a decision was made to perform revision surgery, during which the worn-out polyethylene was replaced with a new polyethylene insert, and stability was confirmed intraoperatively. Four weeks after surgery, the patient's knee range of motion was 0-120°, and all discomfort had completely subsided. At a year's follow-up, the patient's Knee Society score had improved from 40 before surgery to 90 after surgery.

Conclusion: Interference in the normal framework of knee anatomy distorts its intrinsic stability. This interference can be in variable form such as bone deficiency, infection, multiple revision surgeries, and ligamentous laxity. Restoration of intrinsic stability in today's world has been made possible by a highly constraint, hinged knee prosthesis. An anti-dislocation mechanism on the rotating hinge prosthesis guards against dislocation brought on by distracted engagement. In our instance, the anti-dislocation mechanism had aseptically loosened, increasing flexion laxity and permitting severe distraction. The anti-dislocation mechanism will eventually relax, but its lifespan can be increased by proper gap balancing, which offers inherent stability and increases the anti-dislocation mechanism's stability.