Characterization of lag screw migration under cyclic loading in an intertrochanteric fracture model

摘要

The rapidly increasing number of hip fractures is posing one of the most severe orthopaedic challenges in the new millennium. The high incidence of over 250,000 proximal femur fractures per year in the USA is considered epidemic and is directly linked to the continuously increasing mean population age. Therefore renewed attention should be paid to evaluate and improve the performance and longevity of orthopaedic interventions aimed at stabilizing trochanteric fractures. Lag screws constitute a key component of implants for intertrochanteric fracture fixation of the femur. Despite widespread use, these implants exhibit a disturbingly high complication rate of up to 23%. The most common failure mechanism is migration of the femoral head into varus, which often leads to cut-out of the lag screw from the femoral head. There exists a wide variety of screw designs, each posing theoretical advantages to resist screw cut-out. Early lag screw designs have undergone extensive biomechanical evaluation, in the 1970's and 80's. More recent laboratory studies were aimed directly at investigating the lag screw cut-out phenomena. However, a major shortcoming of these studies is that lag screw cut-out has been induced under quasi-static loading conditions. A laboratory model evaluating implant performance under dynamic loading conditions is virtually non-existent. Therefore we developed a surrogate trochanteric fracture model to simulate for the first time implant fixation failure under cyclic loading conditions.