Case report: Failure of rotating-hinge total knee prosthesis by disengagement of the hinge-post extension.

BACKGROUND: Although modern-generation rotating-hinge knee implants have been modified to mitigate earlier complications related to aseptic loosening with these devices in revision TKAs, there are few, if any, reports of failure related to the hinge mechanism in these prostheses. CASE DESCRIPTION: We present a case of disengagement of the hinge-post extension in a contemporary rotating-hinge knee prosthesis originally implanted during revision surgery for instability and extensor mechanism insufficiency. We hypothesize the screw home kinematics of the knee resulted in a counterclockwise torque, contributing to the hinge post locking screw disengagement in this case. LITERATURE REVIEW: Although some authors have reported complications and failures related to aseptic loosening with rotating-hinge knee prostheses, there have been no reports regarding complications related to the hinge mechanism, which simultaneously links and permits rotation between the femoral and tibial components. CLINICAL RELEVANCE: Arthroplasty surgeons who use rotating-hinge knee prostheses need to be aware of this potential mode of failure. Design modifications, including more secure locking mechanisms and side-specific implants, may avoid this complication.