动态载荷下松质骨对骨质疏松性股骨颈骨折断裂力学影响的有限元分析

Effect of cancellous bone on the biomechanics of osteoporotic femoral head fracture under dynamic loading: a finite element analysis

背景:目前髋部骨折有限元模型亦多简化为实心的、线性或非线性的各向同性材料,对髋部骨折的有限元分析多基于静态载荷下的应力分布来预测骨折发生的部位,然而在静态下,骨折发生的确切起点及骨质断裂过程仍然无法客观模拟及观测。目的:探究动态载荷下松质骨对股骨颈骨折的影响及生物力学机制。方法:选取1名健康志愿者的原始股骨CT数据,在Mimics创建三维模型后在Hypermesh中重建为简化的实心模型、仅包含皮质骨的空心模型、含松质骨及主要应力骨小梁的仿真股骨近端模型,并分别赋予材料属性、参数,设置载荷时间函数为F=2 500 t,t≤2 s(单位:MPa),方向与冠状面、矢状面、水平面均呈30°,边界条件设置为大转子与股骨干固定,导出求解文件并在LS-DYNA运算,在Hyperview中观察骨折过程并记录裂纹起始点、时间、应力变化等结果。结果与结论:(1)实心模型的起始裂纹在股骨颈后外侧,空心模型与仿真模型则起始于股骨颈内下方,仿真模型的起始裂纹小于实心模型、空心模型;(2)3种模型皮质骨断裂时的最大应力均分布在股骨颈后外侧,空心模型与仿真模型的应力分布较实心模型更广泛分布于转子间区域;(3)实心模型起始裂纹靠近最大应力区的中央,而空心模型与仿真模型的起始裂纹位于最大应力区的边缘,靠近股骨颈的内下方;(4)3种骨折模型均发生了嵌插,其中实心模型的骨折线较单一且平整,空心模型与仿真模型的骨折线较粗糙,并延伸至转子间,且骨折成角较实心模型大;(5)各模型在断裂时刻的应力最大,后下降,最大值见于实心模型,仿真模型的最大应力下降趋势最平缓及压力与张力侧的波动最对称;(6)结果提示,在抵抗骨折裂纹扩展中松质骨与皮质骨可能起协同作用。

BACKGROUND:The finite element model of hip fracture is simplified into a solid,linear or nonlinear isotropic material.The finite element analysis of hip fracture is based on the stress distribution under static load to predict the location of the fracture,but the exact starting point of the fracture and the process of bone fracture are still not objectively simulated and observed.OBJECTIVE:To investigate the role of cancellous bone in hip fracture and the biomechanical mechanism under dynamic load.METHODS:CT image data of a healthy volunteer’s femur were collected and imported to Mimics software to construct the three-dimensional model.The primary model was imported in Hypermesh to reconstruct a simplified solid model consisting of cortex,cancellous bone,stress trabecular and models were assigned with material property parameters.A load function was set as F=2 500 t,t≤2 s(MPa),the angulation between loading and coronal plane,sagittal plane and horizontal plane was 30°,respectively.Greater trochanter and shaft were constrained.Then,the solver file was exported to LS-DYNA for calculation.The location and moment of initial crack,time-stress curves were recorded in Hyperview.RESULTS AND CONCLUSION:(1)Crack extension started at the posterior of femoral neck in solid model,while at the inferior in hollow and simulation models.The initial crack of the simulation model was smaller than that of solid and hollow model.(2)The Von Mises of each model distributed on the posterolateral side of the femoral neck,and the hollow and simulation models distributed around intertrochanteric region.(3)Initial crack developed at the middle of Von Mises part in solid model,while others developed at the edge of the Von Mises part beneath the femoral neck.(4)All models simulated an impaction of fracture fragments with a wider angle in hollow and solid models.A flat fracture line extended on femoral neck in solid model,on the contrary,hollow and simulation model showed a more rough fracture line both on femoral neck and intertrochanteric region.(5)The stress maximized at the moment of the initial damage and then declined at different rates in all models;the solid one was the highest and steepest,and simulation model showed the most gentle decrease and symmetric stress of compression and tension in time-stress curves.(6)To conclude,the cancellous bone may demonstrate a synergistic effect with cortex during the hip fracture.