Systematic evaluation of the biomechanical characteristics of PFNA, PFBN, and InterTan fixation for intertrochanteric fractures under gradient variations of proximal femoral lateral wall thickness and delineation of optimal fixation domains.

backgroundThe proximal femoral lateral wall serves as a critical "lateral pillar" in the mechanical stability of intertrochanteric fractures, and variations in its thickness may profoundly influence the biomechanical behavior of different intramedullary fixation systems. However, previous studies have largely assessed the lateral wall in a binary manner, lacking systematic evidence based on continuous gradients. This study aimed to elucidate the biomechanical coupling between lateral wall thickness and three mainstream intramedullary fixation systems (PFNA, PFBN, and InterTan) using high-resolution finite element models, and to delineate the optimal lateral wall domains for each system.

methodsSixteen continuous gradient models of the lateral wall, ranging from + 35 mm to - 20 mm, were constructed and implanted with PFNA, PFBN, or InterTan. Under three typical loading conditions-standing, slow walking, and fast walking-the maximum equivalent stress of the lag screw/main nail, overall displacement fields, and the mechanical response trajectories and instability trends of each fixation system during lateral wall thinning were analyzed and compared.

resultsLateral wall thickness significantly affected the overall mechanical stability of intertrochanteric fractures. With progressive thinning, all three fixation systems exhibited increasing stress concentration and displacement. This relationship was nonlinear, with accelerated deterioration observed once the lateral wall was reduced below specific thresholds. Among the devices, PFBN maintained more uniform load distribution across the full gradient range, sustaining relatively low implant stress and minimal fracture gap displacement even with weak or absent lateral walls. InterTan demonstrated intermediate stability between PFBN and PFNA, with stress and displacement changes occurring more gradually during wall thinning. In contrast, PFNA was more sensitive to lateral wall deficiency, showing pronounced displacement increases under extremely thin wall conditions.

conclusionFinite element analysis indicates that lateral wall thickness is a decisive factor for the fixation stability of intertrochanteric fractures. Progressive thinning leads to marked increases in stress and displacement for all intramedullary devices, accompanied by characteristic mechanical critical points. PFBN provides superior stability under weak or absent lateral wall conditions, whereas PFNA and InterTan are more sensitive to lateral wall structural variations. These findings suggest that lateral wall thickness should be a core parameter in selecting fixation methods and formulating postoperative weight-bearing strategies, providing critical biomechanical evidence for individualized management of unstable intertrochanteric fractures.