Mode of Fixation Failures of Dynamic Hip Screw with TSP in the Treatment of Unstable Proximal Femur Fracture: Biomechanical Analysis and a Report of 3 Cases

There are few reports of the failure mode of a dynamic hip screw with a trochanteric stabilizing plate (TSP) in the treatment of unstable proximal femur fractures. We present 3 cases of fixation failure of a TSP used to treat unstable intertrochanteric fractures. All cases had the same type of failure mode, which represented a fatigue fracture of the distal screw at the junction of a plate and screw. Non-union occurred in 2 cases, and one case was an incidental finding 4 years after union. Biomechanical analysis and SEM (scanning electron micrograph) examination was also performed. Adding TSP to the plate might increase the level of shear stress and slip motion in the distal screw followed by a fatigue fracture. SEM of the surface of the broken screw revealed a multiple cycle and low stress fatigue fracture. Recommendations are made regarding the implant design and surgical technique.