Biomechanical comparison of femoral neck system and cannulated screws coupled with medial plate for treating Pauwels III femoral neck fractures

BACKGROUND: The femoral neck system (FNS) has been considered as a novel strategy for femoral neck fracture. The diversity of internal fixation creates difficulties in choosing an effective option for Pauwels III type femoral neck fractures. Therefore, it is significant to investigate the biomechanical effects of FNS versus conventional approaches on bones. OBJECTIVE: To evaluate the biomechanical characteristics of FNS versus cannulated screws coupled with medial plate (CSS+MP) for the treatment of Pauwels III type femoral neck fractures. METHODS: Through three-dimensional computer software (Minics, Geomagic - Warp), the proximal femur model was rebuilt. Based on the present clinical characteristics, models of internal fixation were reconstructed in SolidWorks, including cannulated screws (CSS), medial plate (MP) and FNS. After parameter setting and meshing, boundary conditions and loads were set up for the final mechanical calculation in Ansys Software. Under identical experimental conditions, such as the same Pauwels angle and force loading, the peak values of displacement, shear stress and equivalent (von Mises) stress were recorded. RESULTS: This study showed that the displacement of the models was CSS, CSS+MP, and FNS in descending order of magnitude. The shear stress and equivalent stress of the models was CSS +MP, FNS, and CSS in descending order. The principal shear stress of CSS+MP was concentrated on the medial plate. The equivalent stress of FNS was more dispersed and distributed from the proximal main nail to the distal locking screw. CONCLUSION: CSS+MP and FNS exhibited better initial stability compared to CSS. However, the MP was subjected to more shear stress, which could increase the risk of internal fixation failure. Due to its unique design, FNS may be a good choice for the treatment of Pauwels III type femoral neck fractures.