Torsional Stability of the Femoral Neck System for Pauwels Type III Femoral Neck Fracture Fixation: A Finite-element Analysis

Abstract

INTRODUCTION: Femoral neck fracture fixation remains challenging, particularly for Pauwels type III fractures that require robust implants to withstand vertical shear forces. The femoral neck system (FNS) offers greater stiffness and more stable load sharing than multiple screw fixation; however, it has a lower load-to-failure than plate systems. We evaluated the torsional stability of the FNS using finite-element analysis. METHODS: We analyzed a transcervical Pauwels type III femoral neck fracture without a fracture gap, fixed with one of three constructs: multiple screw fixation, a dynamic hip screw (DHS) with an antirotation screw, or an FNS. Finite-element simulations incorporated muscle forces during the leg-swing phase, with constraints applied at the fovea capitis. Cortical-cancellous interfaces were fully bonded, except at the reduced fracture interface where relative translation was allowed. RESULTS: The DHS with an antirotation screw had the highest equivalent von Mises stress and strain energy density (SED) (1130.11 MPa/1,000) and the greatest fragment displacement (0.44 mm). Multiple screw fixation produced the lowest SED (151.73 MPa/1,000), and the FNS showed similar displacement with an intermediate SED (201.96 MPa/1,000). In the FNS, peak stress localized near the lateral cortex of the proximal femur, with reduced stress at the barrel-screw interface. CONCLUSIONS: The FNS provides rotational stability for Pauwels type III fractures comparable with multiple screw fixation and reduces stress at the fracture site. The DHS with an antirotation screw was less stable during hip rotation. Given its greater compressive strength than multiple screw fixation, the FNS is the preferred fixation option.