Abstract
<title>Abstract</title> <p> The lateral femoral wall concept was developed primarily for DHS fixation. Given the distinct biomechanics of PFNA, we propose the concept of the "effective lateral wall" to define its functional extent and biomechanical significance in PFNA fixation. DIC mechanical testing was performed to analyze strain distribution and subsidence displacement on the proximal femoral cortex under simulated loading. Seventy-nine patients with AO/OTA A1 and A2 intertrochanteric fractures underwent 3D-CT reconstruction with virtual reduction to measure effective lateral wall parameters. DIC confirmed that the cortical region bounded by the 130-degree oblique plane (the helical blade trajectory) and the fracture line—the "effective lateral wall"—is the strain concentration zone. Medial support deficiency significantly increased strain on this region. Additional lateral wall defect further increased subsidence displacement by 19.2% despite existing medial wall deficiency (p < 0.0001). CT measurements showed that effective lateral wall area progressively decreased with advancing AO/OTA classification, with A2 fractures measuring only 43.52% of A1 (p < 0.001). The "effective lateral wall" is a biomechanical functional region in PFNA fixation that differs from the traditional lateral wall, providing objective guidance for preoperative assessment, implant positioning, and postoperative rehabilitation. <bold>Level of Evidence:</bold> Diagnostic Level III. </p>