有限元法分析不同侧方跌倒角度下股骨颈骨折裂纹扩展的断裂力学特征

A finite element analysis on crack extension on femoral neck simulated by multi-axial sideways fall based on fracture mechanics

背景:目前骨折发生机制的分析主要通过分析静态受力分布(Von Mises应力云图)来判断应力集中部位,预测骨折发生的起始点。然而骨骼是各向异性的弹塑性材料,传统准静态有限元分析无法给出具体断裂起始点及骨折发生发展过程。因此,在骨科有限元研究领域引入断裂力学的概念是具有实际意义的。目的:模拟不同侧方跌倒角度对股骨颈骨折裂纹扩展的影响。方法:选取1名健康志愿者的股骨原始CT数据,导入Mimics 19.0软件,经区域增长、编辑笼罩、光滑、包裹等重建股骨近端三维有限元模型,并在Hypermesh 14.0中进行网格划分、定义材料属性、设定边界条件、加载载荷,模拟股骨中立位0°、内旋30°、外旋30°、内收30°跌倒状态等前处理,将生成的K文件导入LS-DYNA求解器中运算。结果与结论:(1)股骨内收模型最早发生股骨颈断裂失效,外旋模型最迟;(2)4种模型的应力集中及骨质断裂均最早出现在股骨颈外上侧,内下侧继而出现裂纹并与之相融合,形成GardenⅡ型骨折;(3)股骨颈骨折Linton角以内收模型最小,外旋模型其次,中立位模型与内旋模型差异无显著性意义(P=0.387);(4)股骨颈外上侧为压力侧,内下侧为张力侧;除内收模型,其余模型的股骨颈内下侧可出现压力向张力转换的应力分布;(5)提示不同侧方跌倒角度在时间和空间上会影响股骨颈骨折裂纹扩展行为。

BACKGROUND: The pathogenesis of fractures is mainly investigated by Von Mises stress nephogram to assess the stress centration region, and further predict the start part of fracture. Bone is an anisotropic elastoplastic material, so traditional static finite element analysis cannot confirm the specific start part and occurrence progress of fracture. Thereafter, fracture mechanics applied in bone finite element analysis is of great significance. OBJECTIVE: To simulate the crack extension on femoral neck induced by multi-axial sideways fall. METHODS: CT image data of a healthy volunteer’s femur were collected and imported to Mimics 19.0 software. After region growing, cavity filling, editing, smoothing and wrapping, a three-dimensional finite element model of proximal femur was established. The primary model was imported in Hypermesh 14.0 for meshing, defining material properties, failure parameters, interfacial properties. Load and force boundary constraints simulating multi-axial sideways fall were also simulated. The multi-axial sideways fall was set as rotation 0°, internal rotation 30°, external rotation 30° and adduction 30°. The integrated K files were finally calculated in LS-DYNA. RESULTS AND CONCLUSION:(1) Adducent femur was the earliest to crack on femoral neck while the external rotation femur was the latest.(2) Garden type II fractures were simulated in all objects on which crack occurred firstly on the superior of femoral neck fusing with the inferior breakage.(3) The neutral femur showed no significance with internal rotation femur (P=0.387) in Linton angle, while adducent femur showed the smallest Linton angle, followed by external rotation femur.(4) Tensile and compressive stresses, respectively, were found on the inferior and superior of femoral neck in Von Mises distribution, whereas the state of stress was convertible from tensile to compressive at the beginning of impact in all femurs except adducent femur on the inferior of femoral neck.(5) To conclude, different axial loadings on femoral head during sideways fall influence the crack extension behavior on femoral neck.