Positive or Negative Anteromedial Cortical Support of Unstable Pertrochanteric Femoral Fractures: A Finite Element Analysis Study

Objective: To explore the mechanical stability of unstable pertrochanteric fractures with proximal femoral nail anti-rotation (PFNA-II) fixation under different anteromedial cortical support reduction patterns. Methods: A 65-year-old healthy male volunteer with no history of hip or systemic disease was recruited. Highresolution computed tomography images with a slice thickness of 0.67 mm of his right femur were obtained. These images were used to establish three-dimensional (3D) models. The lesser trochanter and lateral femoral wall were cut off to create an AO Foundation/Orthopaedic Trauma Association type 31-A2 unstable pertrochanteric fracture model. PFNA-II was used to simulate fixation. Nine different fracture reduction patterns, which included positive-positive, positive-neutral, positive-negative, neutral-positive, neutral-neutral, neutralnegative, negative-positive, negative-neutral, and negative-negative cortical support reductions, were simulated. A load of 700 N was applied to simulate a 70 kg elderly patient standing on one leg. The models were subjected to finite element analysis. The displacement and von Mises stress distributions were analyzed. Results: The positive-positive cortical support reduction pattern showed minimal stress and the negative-negative reduction pattern showed maximal stress on the intramedullary nail. The stress was mainly concentrated at the junction of the helical blade and the main nail and at the site of the lateral aspect of the insertion point of the nail in the great trochanter. The positive cortical support reduction patterns seemed to have smaller maximum displacements of the entire fragment-implant assembly and relative displacements between the head-neck and shaft fragments. Meanwhile, the negative reduction patterns seemed to have larger displacements. Conclusion: The positive-positive support reduction pattern showed better mechanical stability for unstable pertrochanteric fractures. The negative-negative support reduction pattern was prone to fixation failure and should be avoided during an operation.