Internal fixation with proximal femoral nail anti-rotation for intertrochanteric fracture involving lateral wall: a finite element analysis

Abstract

Objective To study the biomechanical performance of proximal femoral nailing anti- rotation (PFNA) in the treatment of femoral intertrochanteric fracture involving the lateral wall using finite element analysis and the significance of the lateral wall. Methods A healthy senior volunteer, male, 80 years of age, was recruited for this study.The CT data of his proximal femur were used to establish a three-dimensional finite element model of proximal femur by software Mimics17.0 and Geomagic Stusio. After the intertrochanteric fracture of AO-type 31-A1.2 was simulated together with coronal displacement of the lateral wall fracture, it was assembled with PFNA into the three-dimensional finite element model. Finite element analysis was performed on the femoral head, neck, fracture ends, lateral wall, and internal components of the model to observe the stress values of various parts of the model under the same load, with different degrees of fracture reduction (no displacement, anterior displacement of 5%, 10%, 15% and 20%, posterior displacement of 5%, 10%, 15% and 20%) and with or without the lateral wall. Results The stress values for internal components at the femoral head, neck, fracture ends, main nail with anatomical reduction of fracture ends and integrity of the lateral wall were 0.40 MPa, 30.05 MPa, 74.35 MPa and 121.68 MPa, respectively. The respective stress values of the above with lateral wall fracture were 0.82 MPa, 47.32 MPa, 151.92 MPa and 266.88 MPa, increased by about 100%. With every horizontal reduction loss increased by 5% forward or backward, the stress exerting on the corresponding spots would see a 10% progressive growth, plus 20% lateral wall fracture and reduction loss. The stress of the main nail (468.43 MPa) was thrice that (121.68 MPa) of the stress posing on the complete lateral wall with the fracture ends 100% reduced. Conclusions When PFNA is used in the treatment of femoral intertrochanteric fractures involving the lateral wall, stresses on the internal components may be doubled. Loss of coronal reduction may lead to the most significant increase in stress on the bonding site between the main nail and screw blade. Key words: Hip fractures; Fracture fixation, intramedullary; Bone nails; Finite element analysis; Lateral wall