Hinge-Knee Megaprostheses Components Wear and Corrode: A Retrospective Study of 40 Devices.

INTRODUCTION: Hinge-knee megaprostheses are frequently used in complex revision surgeries and are known to have higher complication and revision rates than primary total knee arthroplasties. However, the in vivo damage to the metal and polymer components of megaprostheses remains poorly understood. We, therefore, investigated the damage modes, their severity, and how they varied by implant manufacturer. METHOD: Forty megaprostheses and associated clinical data were collected from an institutional review board-exempt retrieval program, including implants from three manufacturers. We semiquantitatively scored the in vivo damage modes on polymer and metal megaprostheses components using the Kahlenberg method. The Goldberg score was used to classify corrosion for metal-on-metal interfaces. We then analyzed the differences between damage types and device manufacturers using nonparametric statistics. RESULTS: We identified and classified scratching, pitting, and burnishing as major damage modes on polyethylene inserts and abrasion, delamination, surface deformation, and embedded debris as minor damage modes. Minor damage modes markedly differed between implant cohorts (P < 0.001), whereas major damage modes did not (P > 0.05). On metal components, scratching was more prevalent than burnishing and discoloration (P < 0.001). Damage to metal tibial components differed by manufacturer (P < 0.01) and corrosion was present in varying degrees across cohorts. CONCLUSION: In vivo damage occurred on both metal and polyethylene megaprostheses components. Within modular taper junctions, mechanics combined with chemically based processes generated corrosion. We found minimal differences between manufacturers, except for minor polyethylene damage and tibial component damage. The rotating hinge may release metal debris when unprotected by a polyethylene bumper evidenced by burnishing.