基于Hangmann骨折的植骨融合钢板内固定术有限元稳定性分析

Hangmann骨折是近年来发病率逐渐上升的上部颈椎损伤之一。植骨融合钢板内固定术作为一种较新的手术方案刚刚开始在国内采用。本文采用基于医学影像的快速自动三维有限元模型的构建方法,建立了上颈椎C2～C4两个运动节段的三维有限元模型,对上颈椎正常状态、植骨融合钢板系统内固定术方案在模拟生理荷载下的三维六自由度的稳定性、内固定器植入后的应力情况进行了计算和比较分析,并通过实验验证了内固定手术对上颈椎的生物力学稳定性和内固定器的力学疗效特征。本文结果显示：对Hangmann骨折治疗,植骨融合钢板系统内固定技术是一个较好的可供选择的措施之一。     

脊柱L3-L5段机械模型的力学特性分析

借助计算机辅助设计软件SolidEdge,根据人体解剖学数据建立了人体脊柱L3-L5段近似三维几何模型,并利用有限元分析软件ANSYS进行赋值,模拟了脊柱L3-L5段的结构特性、材料特性、接触特性。将椎骨划分为皮质骨、松质骨等结构,用接触连接的方法模拟了椎骨与椎间盘之间、小关节之间的连接情况,采用实体单元Solid187对其进行网格划分。对该三维有限元模型进行加载分析,得到其在200N轴向力作用下和100N侧向力作用下的应力和变形数据,该数据可以为脊柱生物力学的研究和侧凸脊柱的病因及矫正提供一定的参考依据。     

腰椎力学分析的数值模拟与实验研究

采用数值模拟和实验测试技术对两种不同内固定法的腰椎模型进行应力和变形分析,基于CT图像建立L4-S1的三维数值模型,经ANSYS计算分析得出五种工况下的终板应力值;在实验中采用了一种薄膜压力测试传感器结合图像处理的方法,提高测试椎间盘压力分布的精度;同时采用数字图像相关技术对腰椎骨上下关节突在承载情况下的空间位移进行了测量,获得了腰椎间盘（L3-L4）在承受轴压、前屈后伸和侧弯情况下的压力分布,以及对应的关节突的位移迹线。结果表明：本研究采用的数值分析技术和实验开发的测试技术可操作性强,精度满足要求,有望在类似的生物力学分析中得到应用。     

基于多孔弹性模型的脊椎关节生物力学特性和体液流动特性研究

建立了L4/L5段人体腰椎关节的非线性多孔弹性有限元模型,并对其施加1000N振动载荷1h,考察在不同的振动频率(1Hz、4Hz、8Hz、11.5Hz、15Hz)下腰椎关节的变形、应力分布和体液流动情况;并对不同频率作用下脊椎组织的生物力学特性进行了对比分析。结果表明,在不同频率振动载荷下,脊椎模型的应力分配、体液流量都呈现与振动载荷不同的周期性波动变化。振动载荷频率等于腰椎关节的固有频率11.5Hz时,椎间盘应力分配和体液流量波动的幅值最短;而振动频率为4Hz、8Hz、15Hz时各项指标波动的幅值比11.5Hz时小。振动过程中,椎间盘内外压力梯度的变化引起体液的流动,振动时间越长,总流失量越大。     

PEEK颈椎融合器的拓扑优化设计

为了提高聚醚醚酮(polyether ether ketone, PEEK)材料颈椎椎间融合器的融合率,本研究利用有限元方法对其进行三维结构的拓扑优化设计。首先建立C3～C7节段的颈椎有限元模型并验证,然后创建C5～C6节段椎间融合器植入和前路钢板内固定的模型。将PEEK融合器设置为椭圆盘型和箱型两种初始设计域。先后进行单工况和多工况下融合器拓扑优化,并结合加权柔度优化。经过两次拓扑优化后,再对融合器的构型提取分析。研究结果表明：PEEK融合器的优化结构为环形,前方缺失,材料集中分布于后部及两侧;当体积分数分别为50%和30%时,融合器优化为多孔径和单一大孔径的形状,前者比后者增加了与终板的接触面积;优化后的融合器通过降低自身应力,增加了内部植骨块所受的应力。本研究通过加权柔度的方法构建的颈椎融合器优化模型,不受初始设计域变化的影响,且可以有效减少应力遮挡,增加植骨块的应力传导,将有助于促进融合。     

青少年坐姿时腰部受力数值模拟

为了定量研究青少年坐姿时腰部受力情况,根据静力学原理,结合人体测量学对青少年坐姿时腰椎各节段所承受的重力矩进行分析,探讨腰椎各节段竖脊肌的肌力大小以及腰椎各椎体所承受的剪切力和挤压力.对腰椎部位进行CT扫描,应用Mimics和Ansys软件对数据进行三维重建并分析.通过分析发现腰椎各节段承载的负荷与躯干前倾角度密切相关,在脊柱前曲逐渐增大时,上位体重对腰椎的压力在竖直方向的分量减小而在水平方向的分量增大,从而引起周围软组织水平方向负荷的增加.躯干前倾角度为30°时,各椎体最大应力自上而下依次分别为:4.01MPa、7.26 MPa、7.29 MPa、11.07 MPa、15.64 MPa,各椎间盘的最大应力自上而下依次分别为:1.3 MPa、1.81 MPa、1.83 MPa、2.19 MPa.有限元法分析结果表明:椎体是承载应力的主要结构,椎间盘起到传递载荷的作用,坐姿时椎体的前下方出现应力集中现象;在坐姿时应尽量减少脊柱的前倾角度,将脊柱的前倾角度控制在30°范围之内,以降低椎体及椎间盘所承受的负荷,从而减少腰椎及其椎间盘损伤的风险.     

基于压力隧洞模型的复合材料横向热残余应力分析

考虑碳纤维横向刚度情况下,将复合材料横向热残余应力问题简化为压力隧洞模型.利用该模型推导出复合材料固化成型过程中形成的横向热残余应力,其中分析得出了单纤维与树脂的接触压力以及该压力传递到纤维和树脂后的分布情况.结果表明接触压力传递到纤维内部后成一固定值,传递到树脂后以正比于r.函数衰减.在其基础上提出场叠加方法,得出纤维之间相互耦合的接触压力与残余应力场.通过有限元模拟,理论模型和数值模拟基本一致.     

瞬态载荷下L4/L5椎间盘内流固耦合效应

中医正脊治疗通过对腰椎施加瞬态拉伸和旋转来治疗腰椎间盘退变, 本文采用考虑流固耦合效应的数值模拟研究其生物力学机制. 通过实验测量和文献调研, 确定了合理的拉伸和旋转的载荷参数; 发展了使用人体断层扫描图像结合解剖学数据建立详细腰椎几何模型的方法; 将松质骨、终板、椎间盘考虑为多孔弹性介质, 其他组织考虑为线性弹性介质, 进而建立了考虑生物组织中流固耦合效应的物理模型; 通过数值模拟得到了不同瞬态载荷及其组合作用下椎间盘内应力?应变与流体流动的变化规律. 研究发现, 瞬态载荷通过改变L4/L5椎间盘基质应力和髓核内外压力梯度, 在髓核中产生流体流动; 拉伸加载引起流体先流出髓核、再流入髓核, 产生含水量变化; 顺时针旋转加载在髓核左右产生相反的流动, 髓核右侧的含水量变化较左侧大. 本研究所采用的方法为流动过程相关的人体椎间盘退变病理生理机制研究提供了新的方法, 为中医正脊研究提供科学化思路, 也为相关的力学-生物学耦合研究和髓核再生的基础研究提供了一个切入点.      

人体腰椎生物力学的某些基本问题

本文就人体腰段脊柱生物力学的某些基本问题的研究现状与进展进行述评。介绍了腰椎各组成部分包括椎体、椎间盘、椎弓、韧带以及脊髓的力学性能,对其运动学和运动力学进行了讨论,最后就腰椎的力学模型主要是有限元模型的研究作了简单的回顾。      

低频振动作用下人体椎间盘多孔弹性单元的研究

建立了 L4/L5段人体腰椎关节的非线性多孔弹性单元有限元模型，并对该模型进行了轴向静力（0Hz)和低频(0.01 Hz、0.1 Hz、0.5 Hz、1 Hz)振动作用各1小时的仿真研究，对比了在不同频率振动作用下人体脊椎组织的多孔弹性单元力学特性。结果表明：在相同振幅和时间内，与低频(0.01Hz、0.1Hz)相比，相对较高频率(0.5 Hz、1 Hz)作用下的椎间盘组织产生的轴向位移较大，髓核和纤维环的孔压应力均呈现逐渐上升的趋势；与此同时，髓核的有效应力逐渐增加，而纤维环的有效应力却逐渐减少；在相对较低频率(0.01Hz、0.1Hz)作用下的各项力学特性指标与静力作用下的相比，差值均在3%以下；加载时间超过600s 后，振动频率的增加更容易使椎间盘轴向位移增大；相对较高频率(0.5 Hz、1 Hz)振动作用下髓核和纤维环内的孔压值逐渐升高，而静力压缩和相对较低频率(0.01 Hz、0.1 Hz)振动作用下孔压值却逐渐降低；不断增加的孔压应力使椎间盘内的体液流失速率变大，导致椎间盘退化。     

Biomechanical analysis of lumbar interbody fusion with an anisotropic hyperelastic model for annulus fibrosis

Based on computed tomography scanning images, this paper developed a detailed finite element model for the human L2–L4 lumbar spine segment with or without L3–L4 fusion. The model included vertebrae, intervertebral disc, facet articulating surfaces and various ligaments. A previously developed hyperelastic fibre-reinforced constitutive model was used to characterize the material property of annulus fibrosus. Numerical results of L3–L4 motion unit such as load–displacement curves and nucleus pressure were compared with experimental data to validate the FE model. The normal and fused lumbar spine segments under various loading conditions, such as flexion, extension and axial rotation, were analysed. The motion range and stress distribution of the L2–L4 models under different loading conditions were then obtained to investigate the effect of lumbar fusion operation. It was shown that under the same loading condition, the fused model had a much smaller body motion range. Interbody fusion brought out obviously different stress distribution in adjacent intervertebral disc annulus fibrosus. And it also increased the intradiscal pressure of adjacent intervertebral disc significantly.     

Development and validation of a viscoelastic finite element model of an L2/L3 motion segment

The prediction of the time dependent response of the spine to dynamic loading conditions is essential in understanding the injury mechanisms leading to occupationally related low back disorders (OLBD). Many previous finite element (FE) models of the lumbar spine have over-simplified the geometry and the material properties of their elements, yielding results limited generalizability. This study reports on the development and validation of a nonlinear viscoelastic FE model that can quantify the mechanical responses of the L2/L3 motion segment to time varying external loads. This model was developed by consideration of the intrinsic material properties of its individual constituents. A piecewise parameter identification method was adopted due to the inherent complexity in determining the role and contribution of each element to the overall behavior of the motion segment. The results of simulation of four loading conditions (quasistatic, constant loading rate, creep and cyclic relaxation) showed a satisfactory agreement with experimental observations in the literature. The detailed estimates of the state of stress/strain of this validated FE model can be used to test the role of epidemiological risk factors such as prolonged awkward posture, speed of lift (strain rate effect) and complex repetitive loading in OLBD.     

A non-linear finite element model of human L4-L5 lumbar spinal segment with three-dimensional solid element ligaments

This paper establishes a non-linear finite element model (NFEM) of L4-L5 lumbar spinal segment with accurate three-dimensional solid ligaments and intervertebral disc. For the purpose, the intervertebral disc and surrounding ligaments are modeled with four-nodal three-dimensional tetrahedral elements with hyper-elastic material properties. Pure moment of 10 N·m without preload is applied to the upper vertebral body under the loading conditions of lateral bending, backward extension, torsion, and forward flexion, respectively. The simulate relationship curves between generalized forces and generalized displacement of the NFEM are compared with the in vitro experimental result curves to verify NFEM. The verified results show that: (1) The range of simulated motion is a good agreement with the in vitro experimental data; (2) The NFEM can more effectively reflect the actual mechanical properties than the FE model using cable and spring elements ligaments; (3) The NFEM can be used as the basis for further research on lumbar degenerative diseases.     

Deduction of Spinal Loading from Vertebral Body Surface Strain Measurements

The lumbar intervertebral disc, the apparent nexus of low back pain, undergoes biomechanical changes during its degeneration which are as yet poorly understood. In an effort to ultimately examine in vivo daily activity loads across intervertebral discs, we engaged in the following methodological study. The aim of this research was to correlate vertebral body surface strains with the loads across a lumbar spine segment. Rosette strain gages were affixed anterolaterally on L4 and L5 in a macaque monkey model. These tissues were loaded axially and with sagittal plane moments and the principal strains were compared with the applied loads. Predictable axial and sagittal plane loading profiles were found for similar strain measurements and the system was found to be robust through freezing and thawing. These results support future research aimed at quantifying the in vivo disc mechanics of healthy and degenerate tissues in an attempt to develop prevention or intervention strategies to ease those afflicted with low back pain.     

基于贝叶斯信息融合的岸桥有限元模型修正研究

为建立精确的岸桥有限元模型,研究了基于贝叶斯信息融合的模型修正方法．通过方差分析,确定待修正参数,利用中心复合试验设计获取样本点,根据有限元计算结果与实测的结果残差为目标函数获得响应样本．拟合样本点和响应样本值构建二阶多项式响应面模型,并检验响应面模型的精度．基于贝叶斯理论更新融合系数来优化响应面参数,从而获得修正模型．以宁波大榭3号岸桥为工程背景,对比修正后的模态频率和实测频率,最大频率相对误差不超过5%,进而验证了基于贝叶斯信息融合的动力学有限元模型修正方法的有效性．修正后的有限元模型可进一步应用于岸桥的健康监测和安全评估．     

An Experimental–Numerical Methodology for a Rapid Prototyped Application Combined with Finite Element Models in Vertebral Trabecular Bone

In the present study, a novel evaluation method involving rapid prototyped (RP) technology and finite element (FE) analysis was used to study the elastic mechanical characteristics of human vertebral trabecular bone. Three-dimensional (3D) geometries of the RP and FE models were obtained from the central area of vertebral bones of female cadavers, age 70 and 85. RP and FE models were generated from the same high-resolution micro-computed tomography (μCT) scan data. We utilized RP technology along with FE analysis based on μCT for high-resolution vertebral trabecular bone specimens. RP models were used to fabricate complex 3D objects of vertebral trabecular bone that were created in a fused deposition modeling machine. RP models of vertebral trabecular bone are advantageous, particularly considering the repetition, risks, and ethical issues involved in using real bone from cadaveric specimens. A cubic specimen with a side length of 6.5 mm or a cylindrical specimen with a 7 mm diameter and 5 mm length proved better than a universal cubic specimen with a side length of 4 mm for the evaluation of elastic mechanical characteristics of vertebral trabecular bones through experimental and simulated compression tests. The results from the experimental compression tests of RP models closely matched those predicted by the FE models, and thus provided substantive corroboration of all three approaches (experimental tests using RP models and simulated tests using FE models with ABS and trabecular bone material properties). The RP technique combined with FE analysis has potential for widespread biomechanical use, such as the fabrication of dummy human skeleton systems for the investigation of elastic mechanical characteristics of various bones.