Finite element analysis on the position of the spiral blade in the femoral head of internal fixation for intertrochanteric fractures

Background: Intramedullary fixation is the preferred treatment for AO type 31A2.2-3.3 intertrochanteric fractures. However, the planting position of the spiral blade into the femoral head is controversial, and relative biomechanical studies are sparse. This article aims to investigate the influence of different position of spiral blade on fixation of intertrochanteric fracture. Methods: A three-dimensional (3D) finite element model of a femoral intertrochanteric fracture with proximal femoral nail antirotation (PFNA) fixation was developed in which the collum femoris was divided into three parts based on the length of the spiral blades. Subsequently, we measured the displacement and stress both the intertrochanteric fracture model and the spiral blade in nine fixation modalities. Results: When the spiral blade was placed in the middle position of the femoral neck, the displacement was the lowest (2.68 mm) and the stress was the least (180.77 Mpa), followed by the lower position of femoral neck, while the displacement and the stress of the upper position of the femoral neck were the largest. The stress decreased stepwise from the tip of the spiral blade to the distal end of the intramedullary nail. Conclusion: The upper spiral blade position produced the largest displacement of the finite element model. A medium-length spiral blade located in the middle of the femoral neck can achieve a stable fixation, and reduce the cutting effect on the femoral head, which is recommended for the treatment of intertrochanteric fractures.