Optimisation strategies for intramedullary nailing parameters in subtrochanteric fractures of the femur: a multimodal assessment based on finite element and biomechanical experiments.

Abstract

<h4>Background</h4>Subtrochanteric femur fractures account for 40 % of proximal femur fractures, and intramedullary nailing (IMN) is the treatment of choice, but there is a lack of uniformity in the selection of models. The challenge of individualized adaptation of diameter and length needs to be resolved, as too large or too small may lead to a lack of stability or increased surgical risk.<h4>Objective</h4>To establish a parametric selection model by analyzing the biomechanical properties of IMNs of different specifications to provide a basis for the clinical optimization of implantation strategies.<h4>Methods</h4>Finite element analysis combined with in vitro biomechanical experiments was used to construct a three-dimensional model based on femur CT data from healthy volunteers to assess the stress distribution and displacement characteristics of 15 sets of IMN (10/11/12 mm in diameter and 280-360 mm in length); a Sawbone artificial bone was used to simulate the Seinsheimer II C fracture, and the strain under axial compression was tested, ultimate load and failure mode.<h4>Result</h4>The 12 mm diameter IMN performed optimally biomechanically, with lower displacement and stress peaks than the smaller diameter group, but may exacerbate the femoral neck stress masking effect. Nail length had no significant effect on stress. Re-fracture around the locking screws occurred in all groups at a load of 5 kN, suggesting a mechanically weak zone near the fracture line.<h4>Conclusion</h4>For patients with Seinsheimer type IIC subtrochanteric femoral fractures who have good bone quality and a femoral neck anteversion angle ≤15°, this study proposes a personalized selection strategy using CT-based 3D reconstruction of the narrowest medullary cavity diameter, recommending an anatomically matched intramedullary nail (320 mm length) to optimize both mechanical stability and biological healing. The results provide important theoretical support for clinical precision treatment.