Abstract: Intramedullary nail fixation of the fracture surface is the primary method of hip fracture treatment, and its mechanical reliability is key to ensuring treatment success. In this study, a finite element model of an intramedullary fixation system (IFS) for intertrochanteric fractures was constructed. This model considers the layered structure of the femur and muscle forces. The mechanical response of the IFS was simulated under slow walking conditions. The concept of a safety factor was proposed to quantitatively evaluate the mechanical reliability of the IFS. Based on this concept, the influence of the positioning parameters of a lag screw on the reliability of the IFS was systematically investigated. Severe stress concentrations are found at the contact regions between the femur and the lag screw, between the trochanteric nail and the lag screw, and between the trochanteric nail and the locking screw. These stress concentration regions play an important role in determining the mechanical reliability of the IFS. This study also showed that the IFS has good mechanical reliability. Reducing the lag screw height improves the mechanical reliability of the system, whereas the effect of the proximal nail angle on the reliability is negligible.

Key words: femoral fracture, intramedullary ?xation system, mechanical reliability, structural optimization, ?nite element method