Finite element simulation of cut-out failure of proximal femoral nail anti-rotation for intertrochanteric fracture

doi:10.3969/j.issn.2095-4344.1896

Abstract

Abstract:

BACKGROUND: Spiral blade cut-out is the main failure in proximal femoral nail anti-rotation. Generally, it is based on Von Mises stress to evaluate the fixation failure risk and the primary zone in finite element analysis with a disadvantage that cannot directly demonstrate the development of failure. Element erosion method is designed to show the crack propagation in component in engineering which will have an important role in studying internal fixation failure.

OBJECTIVE: To simulate biomechanical process of cut-out failure of proximal femoral nail anti-rotation for intertrochanteric fracture.

METHODS: CT data of femur from a healthy volunteer were collected and imported to Mimics 19.0 software. After region growing, editing, smoothing and wrapping, a three-dimensional finite element model of proximal femur was created and polished in Geomagic Studio. Proximal femoral nail anti-rotation model was created in SolidWorks based on the specification and matched with the polished femoral according to the surgical protocol. Component including proximal femoral nail anti-rotation and femur was imported in Hypermesh for tetrahedron meshing and fracture constructing as AO31-A2.1. After setting material content and friction coefficient, K file was finally solved in LS-DYNA.

RESULTS AND CONCLUSION: (1) Femoral neck fragment slid to shaft and lesser trochanter until medial cortical contact, breakdown of cancellous bone surrounding helical blade causing varus and rotational movement of femoral head. The varus was translated faster than rotational movement with a positive support of lesser trochanter, while conversely with a negative support of lesser trochanter. Finally, these led to internal fixation failure. (2) When failure began, stress distributed on the lateral wall and under lesser trochanter, and then stress increased on lesser trochanter and dispersed over intertrochanteric region. (3) Failure strain mainly concentrated on the contact surface between helical blade and lateral wall, femoral neck and lesser trochanter, lesser trochanter and femoral shaft. (4) Femoral neck and lesser trochanter were the unstable part with the most significant displacement, especially on the posterior of femoral head. (5) Results indicate that failure of AO31-A2.1 fracture fixed by proximal femoral nail anti-rotation is compound, including crispation, varus and rotation.

Key words: intertrochanteric fracture, proximal femoral nail anti-rotation, internal fixation failure, spiral blade, biomechanics, finite element, National Natural Science Foundation of China

CLC Number:

R459.9|R318|R445

Zheng Liqin, Chen Xinmin, Zhang Biao, Li Musheng, Liang Ziyi, Zheng Yongze, Lin Ziling. Finite element simulation of cut-out failure of proximal femoral nail anti-rotation for intertrochanteric fracture[J]. Chinese Journal of Tissue Engineering Research, 2019, 23(36): 5794-5799.

Figures/Tables 5

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