Mechanical effect of different implant caput-collum-diaphyseal angles on the fracture surface after fixation of an unstable intertrochanteric fracture: A finite element analysis

Abstract

Background/Objective: The choice of implant is one of the most easily controllable factors affecting the outcome of intertrochanteric fractures. While most of the caputcollum-diaphysis (CCD) angles of the femur are within the range of 125 degrees and 130 degrees, there is a shortage of data on whether 125 degrees or 130 degrees implants are preferable. Thus, the present finite element analysis (FEA) aimed to compare the biomechanical effects on the fracture surface when using implants with different CCD angles where the anatomical CCD angle of the femur was between 125 degrees and 130 degrees. Methods: After establishing a finite element model of an unstable intertrochanteric fracture from the femur with a native CCD angle of 127.3 degrees, proximal femoral nail antirotation (PFNA) models with CCD angles of 125 degrees and 130 degrees were virtually implanted to have the same position of screw tip, respectively. Results: In the one-leg stance during walking, when the implant with 130 degrees CCD angle was used, the magnitude of compressive stress (1.61 and 2.12 MPa in the 130 degrees and 125 degrees model, respectively) was lower and the area of the fracture surface under tensile stress (55% and 5% in 130 degrees and 125 degrees model, respectively), the interfragmentary movements (40.9% more movement in 130 degrees model), and the magnitude of bone deformation (23.5% more deformation in 130 degrees model) were more than those of the 125 degrees model. Conclusion: The intertrochanteric fracture fixed with PFNA with a 125 degrees CCD angle revealed less interfragmentary movement on the fracture surface when the native CCD was an in-between angle in the FEA. (C) 2019 Asian Surgical Association and Taiwan Robotic Surgery Association. Publishing services by Elsevier B.V.