Biomechanical comparison of dynamic hip screw and Gamma nail for the treatment of unstable trochanteric fractures: a finite element study

Objectives: To investigate the biomechanical behavior of the femur with two different implant configurations, namely dynamic hip screw and Gamma nail, in the treatment of two types of unstable intertrochanteric femoral fracture. Methods: A 3D finite element model of the intact proximal femur was constructed, from which two types of fractured models (AO classification 31-A2 and 31-A3) were produced. Then the fracture models were loaded with the peak force during a single gait cycle. The effect of stress and displacement of femurs with three different implant configurations were recorded and analyzed. Results: The stress induced on the two different implants demonstrated a similar pattern; stress concentration was mainly located in the intersection area between lag screw and the nail or between lag screw and the lateral plate. Gamma nail in both types of fractures shared the smaller displacement. The displacement of femurs fixed by Gamma nail showed smaller displacement. The stress in the calcar region which was the main load-bearing area of the intact femoral neck was decreased markedly in all of the models, especially in model fixed with Gamma nail. Conclusions: In conclusion, for the 31-A3 fracture, DHS may be not suitable because it failed to maintain the integrity of the calcar region and showed larger displacement of fractured fragment. Generally, the Gamma nail has mechanical superiority over DHS, but the shielding effect accompanied may increase the risk of intra-operative and later fracture around or below the implant. When the integrity of the calcar region fails to maintain, the Gamma nail is preferred.