C_4～C_6颈椎有限元模型的建立和多点力学加载方法

背景：人体颈椎运动是多节段之间相互力学及位移关系的变化,建立多节段有限元模型及多点力学加载方法可以为颈椎生物力学研究提供高精度的模型和科学的计算分析方法。目的：建立人体C4~C6颈椎三维有限元模型,并在此基础上提出多点力学加载方法。方法：以正常人C4~C6颈椎CT图像作为数据源,利用Mimics10.0、Ansys11.0有限元分析软件建立三维有限元模型,对其进行多点力学加载测试,模拟生理状态时颈椎的轴向、屈曲、后伸、侧弯、扭转运动,分析各运动状态下C4~C6颈椎关节突和椎间盘的应力和位移改变。结果与结论：建立的C4~C6颈椎有限元模型几何形态逼真,重现了C4~C6颈椎节段解剖结构外形,整体显示直观,表面无过多简化,建成后的三维有限元模型与实体组织具有良好的几何相似性。应力Se、Sz在不同加载工况时,前屈/后伸〉侧弯〉轴向加载。轴向加载载荷明显小,导致应力位移水平低。提示应用正常人体原始资料构建的C4~C6颈椎有限元模型以及多点力学加载分析的方法科学有效,为颈椎的生物力学研究提供了高精度模型和科学的计算分析方法。     

正常人体下颈椎有限元模型的建立及验证

目的建立解剖结构较为精确的下颈椎三维有限元模型并验证其有效性。方法采用正常成人颈椎CT图像建立C4-C5-C6有限元模型。在屈伸、侧弯、轴向旋转加载条件下绘制模型的力矩-位移曲线,计算曲线在实验生物力学模型所建立的力矩-位移标准差范围中所占的百分比。结果和结论建立了正常颈椎C4-C5-C6节段有限元模型,力矩-位移曲线在标准差范围中所占的百分比平均为90%。     

Hangman骨折相关三维有限元模型的建立和验证

背景:目前有关上颈椎多节段有限元模型的相关文献很少,尚无建立Hangman骨折有限元模型的报道。目的:建立C2~4节段正常颈椎及不同程度Hangman骨折的三维有限元模型,并对各模型进行模拟及加载验证。方法:选择一健康成年男性志愿者进行C2~4节段CT扫描,以CT扫描图像为基础,在计算机工作站利用ANSYS等有限元分析软件,建立C2~4节段颈椎三维有限元模型,模型包括椎体和椎弓、椎间盘、韧带成分,在此模型基础上逐步模拟切断双侧C2椎弓峡部、切除C2~3前纵韧带和部分椎间盘的Hangman骨折模型,分别计算正常颈椎、不同Hangman骨折模型在模拟施加50N载荷下,C2~3,C3~4节段三维六自由度的角位移(ROM)。结果与结论:C2~3节段Hangman骨折加韧带椎间盘切除模型在各个方向上均较正常和固定模型ROM增大,在屈伸运动时增大最明显,而在旋转和侧屈时与正常标本相差不多。C3~4节段各组间的ROM相差不超过0.16°。各种三维有限元模型的位移和应力验证结果与实验生物力学结果基本相符,提示建立的三维有限元模型可以模拟颈椎生物力学实验。     

人工椎间盘置换对腰椎小关节应力影响的三维有限元分析

背景:近年来随着对脊柱生物力学研究的深入,人工椎间盘被认为是治疗腰椎退行性变较理想的方法,但目前对人工腰椎间盘的生物力学研究还非常有限.目的:建立腰椎运动节段人工椎间盘置换的三维有限元模型并进行生物力学分析,观察人工椎间盘置换对腰椎小关节应力的影响.方法:在已建立的正常腰椎运动节段三维有限元模型的基础上去除L4～5椎间盘、上下终板的有限元单元,加入SB-Chaite Ⅲ型人工椎间盘的有限元模型,保留L4～5椎间隙的纤维环及相关韧带,形成L4～5运动节段人工椎间盘置换的三维有限元模型.对三维有限元模型在垂直压缩、前屈、后伸、侧弯等不同载荷下进行生物力学分析,记录小关节的应力,并与正常运动节段三维有限元模型相应部位的应力进行对比.结果与结论:生物力学分析结果显示,人工椎间盘置换后:①垂直压缩时上下椎体、双侧小关节内应力与正常节段相比差异无显著性意义(P > 0.01).②前屈、后伸时上下椎体前、后方及双侧小关节内应力与正常节段相比差异无显著性意义(P > 0.01).③侧弯时上下椎体左右两侧及双侧小关节内应力与正常节段相比差异无显著性意义(P > 0.01).提示人工腰椎间盘置换后小关节应力可保持在正常运动节段的水平,人工腰椎间盘置换可以达到腰椎生物力学性能重建的目的.     

建立正常人C2～7的三维有限元模型

背景：随着计算机技术的发展,颈椎生物力学研究不再局限于动物或人体尸体实验,计算机模型可以进行更准确的生物力学研究。目的：在已有研究的基础上,建立人体C2～7三维有限元模型,以期为颈椎前路分节段减压融合的生物力学研究提供参考数据。方法：选择1名28岁健康男性志愿者为观察对象,无明显的颈椎病史,扫描前先拍摄颈椎正侧位、斜位、过伸过屈位X射线片以排除颈椎病变。首先根据志愿者CT扫描图片,采用计算机辅助设计数据处理技术,输入相关的材料特性,构建C2～7三维有限元模型。模型重建采用先进的Geomagics系统,可以准确模拟颈椎结构,有限元部分则采用广泛使用的ANSYS系统。其次在1.8N？m作用力下,观察节段运动与力-位移反应,并与国外的实验结果对比,在前屈、后伸、侧弯和旋转等4种工况（载荷状态）下对模型进行验证。结果与结论：整个模型包括C2～7六个椎体、C2/3～6/7五个椎间盘以及后部结构与主要韧带,共有23348个节点和215749个单元。在模拟外力的作用下,模型前屈、后伸、侧弯和旋转工况下的颈椎活动度与以往实验模型结果数据基本吻合。提示所建立的颈椎有限元模型可以模拟颈椎生物力学实验,进行生物力学分析。     

建立正常人C_(2～7)的三维有限元模型

背景:随着计算机技术的发展,颈椎生物力学研究不再局限于动物或人体尸体实验,计算机模型可以进行更准确的生物力学研究.目的:存已有研究的基础上,建立人体C2～7三维有限元模型,以期为颈椎前路分节段减压融合的生物力学研究提供参考数据.方法:选择1名28岁健康男性志愿者为观察对象,无明显的颈椎病史,扫描前先拍摄颈椎正侧位、斜位、过伸过屈位X射线片以排除颈椎病变.首先根据志愿者CT扫描图片,采用计算机辅助设计数据处理技术,输入相关的材料特性,构建C2～7三维有限元模型.模型重建采用先进的Geomagics系统,可以准确模拟颈椎结构,有限元部分则采用广泛使用的ANSYS系统.其次在1.8 N·m作用力下,观察节段运动与力-位移反应,并与国外的实验结果对比,在前屈、后伸、侧弯和旋转等4种工况(载荷状态)下对模型进行验证.结果与结论:整个模型包括C2～7六个椎体、C2/3～6/7五个椎间盘以及后部结构与主要韧带,共有23 348个节点和215 749个单元.在模拟外力的作用下,模型前屈、后伸、侧弯和旋转工况下的颈椎活动度与以往实验模型结果数据基本吻合.提示所建立的颈椎有限元模型可以模拟颈椎生物力学实验,进行生物力学分析.     

腰椎滑脱不同融合术式的三维有限元研究

目的通过建立腰椎后路椎间（PLIF）和后外侧（PLF）两种融合术的三维有限元模型,比较并判断融合后融合节段的稳定性以椎弓根螺钉和融合器上的应力及椎体位移有无显著性差异。方法利用健康志愿者L1～L5CT扫描的DICOM数据,通过计算机软件重建腰椎模型,进行有限单元网格划分,在腰4／腰5间置入椎弓根钉内固定系统,然后分别在椎间置入融合器生成腰椎后路椎间融合术式三维有限元模型,在横突间植入自体骨生成腰椎后外侧融合术式三维有限元模型。通过对模型进行轴向加压、前屈,后伸、侧弯及轴向扭转五种加载方法进行实验。结果建立L4／L5腰椎滑脱模型及后路腰椎椎间融合及腰椎后外侧融合的有限元模型,①观察对模型分别施加轴向压缩、侧弯、前屈、后伸、旋转载荷,PLF应力多集中在椎弓根钉与钛棒连接处、PLIF内固定系统应力为Cage所分散,未见明显应力集中;②对比在五种载荷下两种不同内固定位移PLIF组均小于PLF,P〈0．05。结论①建立了L4／L5滑脱不同后路融合术式的三维有限元模型。②在前屈、后伸、压缩、侧弯及扭转载荷下,相比PLF,PLIF位移更小,证实椎体间融合的稳定性优于和椎弓根螺钉内固定加后外侧植骨融合;③PLF应力多集中在椎弓根钉与钛棒连接处、PLIF内固定系统应力为Cage所分散,未见明显应力集中。     

腰椎滑脱不同融合术式的三维有限元研究

目的通过建立腰椎后路椎间(PLIF)和后外侧(PLF)两种融合术的三维有限元模型,比较并判断融合后融合节段的稳定性以椎弓根螺钉和融合器上的应力及椎体位移有无显著性差异。方法利用健康志愿者L1～L5CT扫描的DICOM数据,通过计算机软件重建腰椎模型,进行有限单元网格划分,在腰4/腰5间置入椎弓根钉内固定系统,然后分别在椎间置入融合器生成腰椎后路椎间融合术式三维有限元模型,在横突间植入自体骨生成腰椎后外侧融合术式三维有限元模型。通过对模型进行轴向加压、前屈,后伸、侧弯及轴向扭转五种加载方法进行实验。结果建立L4/L5腰椎滑脱模型及后路腰椎椎间融合及腰椎后外侧融合的有限元模型,①观察对模型分别施加轴向压缩、侧弯、前屈、后伸、旋转载荷,PLF应力多集中在椎弓根钉与钛棒连接处、PLIF内固定系统应力为Cage所分散,未见明显应力集中;②对比在五种载荷下两种不同内固定位移PLIF组均小于PLF,P0.05。结论①建立了L4/L5滑脱不同后路融合术式的三维有限元模型。②在前屈、后伸、压缩、侧弯及扭转载荷下,相比PLF,PLIF位移更小,证实椎体间融合的稳定性优于和椎弓根螺钉内固定加后外侧植骨融合;③PLF应力多集中在椎弓根钉与钛棒连接处、PLIF内固定系统应力为Cage所分散,未见明显应力集中。     

人类腰段脊柱三维有限元模型的建立

目的为研究人类腰段脊柱生物力学,提供三维有限元含肌肉整体力学模型。方法通过对尸体腰段脊柱表面各节点的三维坐标值测量,运用超级空间有限元电算程序(SUPER-SAPⅤ)将腰段脊柱按空间有限离散的原则,在计算器上建立三维空间坐标系,仿真完整脊柱腰段力学模型。运用横截面积肌力计算法,测量尸体腰椎周围肌肉:腰大肌、腰方肌、竖脊肌、腹内外斜肌、腹横肌的解剖横断面积及其与腰段脊柱纵轴的中心数据值,求得力矩值。再根据力矩等价换算公式得出加载于模型体表各点的肌力值。通过对本模型重力及肌力的加载,使其更接近于正常人体腰段力学状态。结果建立L1～5脊柱三维有限元模型,形成8节点6面体单元496个,共1006个节点,按不同材料参数仿真脊柱各部结构,并仿真腰段活动进行加载。结论建立完整脊柱腰段三维有限元模型,能够分析脊柱前屈、后伸、侧屈、旋转等多种情况下各部的应力分布及位移量,以探讨腰段脊柱损伤应力的病理机制。     

人类腰段脊柱三维有限元模型的建立

目的 为研究人类腰段脊柱生物力学，提供三维有限元含肌肉整体力学模型。方法 通过对尸体腰段脊柱表面各节点的三维坐标值测量，运用超级空间有限远电算程序（SUPER－SAP Ⅴ）将腰段脊柱按空间有限离散的原则，在计算器上建立一维空间坐标系，仿真守整脊柱腰段力学模型，运用横截面积肌力计算法，测量尸体腰椎周围肌肉：腰大肌、腰方肌、竖脊肌、腹内外斜肌、腹横肌的解剖横断面积及其与腰段脊柱纵轴的中心数据值，求得力矩值，再根据力矩等价换算公式得出加载于模型体表各点的肌力值，通过对本模型重力及肌力的加戴，使其更接近于正常人体腰段力学状态。结果 建立L1－5脊柱三维有限元模型，形成8节点6面体单元496个，共1006个节点，按不同材料参数仿真脊柱各部结构，并仿真腰段活动进行加载。结论 建立完整脊柱腰段三维有限元模型，能够分析脊柱前屈、后伸、侧屈、旋转等多种情况下各部的应力分布及位移量，以探讨腰段脊柱损伤应力的病理机制。     

A comprehensive finite element model of surgical treatment for cervical myelopathy

BackgroundCervical myelopathy is a common and debilitating chronic spinal cord dysfunction. Treatment includes anterior and/or posterior surgical intervention to decompress the spinal cord and stabilize the spine, but no consensus has been made as to the preferable surgical intervention. The objective of this study was to develop an finite element model of the healthy and myelopathic C2-T1 cervical spine and common anterior and posterior decompression techniques to determine how spinal cord stress and strain is altered in healthy and diseased states.MethodsA finite element model of the C2-T1 cervical spine, spinal cord, pia, dura, cerebral spinal fluid, and neural ligaments was developed and validated against in vivo human displacement data. To model cervical myelopathy, disc herniation and osteophytes were created at the C4-C6 levels. Three common surgical interventions were then incorporated at these levels.FindingsThe finite element model accurately predicted healthy and myelopathic spinal cord displacement compared to motions observed in vivo. Spinal cord strain increased during extension in the cervical myelopathy finite element model. All surgical techniques affected spinal cord stress and strain. Specifically, adjacent levels had increased stress and strain, especially in the anterior cervical discectomy and fusion case.InterpretationsThis model is the first biomechanically validated, finite element model of the healthy and myelopathic C2-T1 cervical spine and spinal cord which predicts spinal cord displacement, stress, and strain during physiologic motion. Our findings show surgical intervention can cause increased strain in the adjacent levels of the spinal cord which is particularly worse following anterior cervical discectomy and fusion.     

Finite element analysis of the cervical spine: a material property sensitivity study

OBJECTIVE: The study determined the effect of variations in the material properties of the cervical spinal components on the output of the finite element analysis (external and internal responses of the cervical spine) under physiologic load vectors. DESIGN: A three-dimensional (3D) anatomically accurate finite element model comprising of the C4-C5-C6 cervical spine unit including the three vertebrae, two interconnecting intervertebral discs, and the anterior and posterior ligament complex is used. BACKGROUND: The effect of material property variations of spinal components on the human lumbar spine biomechanics is extensively studied. However, a similar investigation of the cervical spine is lacking. METHODS: Parametric studies on the variations in the material properties of all the cervical spine components including the cortical shell, cancellous core, endplates, intervertebral disc, posterior elements and ligaments were conducted by exercising the 3D finite element model under flexion, extension, lateral bending and axial torsion loading modes. Low, basic and high material property cases for each of the six components under all the four physiologic loading modes were considered in the finite element analysis. A total of 432 results were evaluated to analyze the external angular rotation, and the internal stresses in the middle vertebral body, the superior and inferior endplates and the two intervertebral discs. RESULTS: Variations in the material properties of the different cervical spinal components produced dissimilar changes in the external and internal responses. Variations in the material properties of the cancellous core, cortical shell, endplates and posterior element structures representing the hard tissues did not affect the external angular motion, and the internal stresses of the inferior and superior intervertebral discs under all four loading modes. In contrast, variations in the material properties of the intervertebral disc and ligament structures representing the soft tissues significantly altered the angular motion, and the stresses in the inferior and superior intervertebral discs of the cervical spine. CONCLUSION: The material properties of the soft tissue structures have a preponderant effect on the external and internal responses of the cervical spine compared with the changes in the material properties of the hard tissue structures. RELEVANCE: Bone remodeling (e.g., osteophyte) secondary to degeneration of the human cervical joints may be explained by a change in the material property of the soft tissues, coupled with an increase in stress (due to these material property variations) in the spinal components. Consequently, to accurately predict the biomedical effects of cervical spine degeneration, it is critical to accurately determine the material property of these components.     

颈枕部三维非线性有限元模型的有效性验证

背景：人体组织属性主要表现为非线性,颈枕部的生物力学特点更易受软组织材料属性变化的影响,因此建立非线性有限元模型与人体真实属性更接近. 目的：构建正常成人颈枕部三维非线性有限元模型并验证其有效性. 方法：利用MarConi MX8000多层螺旋CT对健康成人进行颅底-C3段扫描,获取二维图像.直接读入Dicom格式原始图像,图像分割,数据光顺,三维重建后生成颅底-C3节段脊柱三维实体模型;将此模型导入ScanFE模块,进行体网格划分;在ANSYS 10.0软件中直接导入以上三维模型,构建颅底-C3段内韧带单元,模拟韧带力-位移曲线,建立完成颅底-C3段的三维非线性有限元模型.垂直向下方向施加40 N预载荷,1.5 N？m力矩模拟前屈、后伸、侧屈及旋转运动,对比分析实验结果,判断模型应力分布与临床相符度. 结果与结论：构建的三维非线性有限元模型包括663551个单元,178247个节点.施加预载荷及1.5 N？m力矩后,寰枕关节运动范围为前屈13.3°、后伸11.9°、侧屈4.3°、旋转8.7°;寰枢关节运动范围为前屈15.5°、后伸12.6°,侧屈6.4°、旋转30.8°,与尸体标本实验结果相符.从整个模型的纵向应力分布看,在任何相对位置状态下,枢椎齿状突后方的应力均较高,后伸位时应力增高区域加大.上颈椎的应力主要集中于椎管周围,寰椎侧块两端及枢椎横突的应力则较小.对比研究发现,在不同相对工况下前屈、后伸、侧屈、旋转时C2-C3小关节应力均大于钩椎关节,颈枕部三维非线性有限元模型的应力分布特点符合临床实际情况.结果提示应用多层螺旋CT扫描得到的二维图像及simple ware、Ansys10.0软件,建立的颈枕部三维非线性有限元模型符合人体真实的运动规律,可以很好地模拟颈枕部的生物力学特性.     

基于CT图像和逆向工程方法建立正常人体腰椎三维有限元模型

背景：利用有限元法可以分析静止及活动时正常脊柱的生物力学,并预测应力时的风险。目的：建立腰椎L3~L5三维有限元模型。方法：选取一名健康30岁男性志愿者L3~L5薄层CT扫描图像,使用工具软件Geomagic和Ansys,应用逆向工程原理构建三维有限元模型,设定边界条件进行加载,记录角位移及应力集中部位,计算模型的平均刚度。结果与结论：建立L3~L5椎体三维有限元模型,包括椎体、韧带、椎间盘、纤维环和小关节,模型总单元数51905个,通过定量和定性两方面验证模型有效。说明所建立的L3~L5椎体三维有限元模型符合脊柱生物力学特征,可用于进一步脊柱生物力学研究。     

基于CT图像和逆向工程方法建立正常人体腰椎三维有限元模型

背景:利用有限元法可以分析静止及活动时正常脊柱的生物力学,并预测应力时的风险。目的:建立腰椎L3~L5三维有限元模型。方法:选取一名健康30岁男性志愿者L3~L5薄层CT扫描图像,使用工具软件Geomagic和Ansys,应用逆向工程原理构建三维有限元模型,设定边界条件进行加载,记录角位移及应力集中部位,计算模型的平均刚度。结果与结论:建立L3~L5椎体三维有限元模型,包括椎体、韧带、椎间盘、纤维环和小关节,模型总单元数51905个,通过定量和定性两方面验证模型有效。说明所建立的L3~L5椎体三维有限元模型符合脊柱生物力学特征,可用于进一步脊柱生物力学研究。     

The influence of the axial,antero-posterior and lateral positions of the center of rotation of a ball-and-socket disc prosthesis on the cervical spine biomechanics

Background

Previous studies documented the importance of the positioning and the design parameters of the prosthesis in determining the biomechanics of the implanted spine. However, a comprehensive biomechanical evaluation of the significance of these parameters is still lacking. Therefore, the paper is aimed to the quantification of their influence on the flexibility of the implanted spine and the force transmitted through the facet joints.

Methods

A finite element model of the C5–C6 spine unit including a ball-and-socket disc prosthesis was built. Three probabilistic variables were considered: the axial, antero-posterior and lateral positions of the center of rotation. Randomized input parameters were generated with the Monte Carlo method. Pure moments of 1.6 Nm in flexion, extension, lateral bending and axial rotation were imposed to the upper endplate of C5; 100 simulations were conducted for the each of the considered loading conditions.

Findings

Axial position of the center of rotation influenced the spine flexibility in all loading conditions and the facet force in extension, lateral bending and axial rotation. The antero-posterior position was found to influence the spine flexibility in flexion and extension, and the facet force in lateral bending and axial rotation. The lateral position was not significant.

Interpretation

The effects of the positioning of a cervical disc prosthesis were estimated. A wide range of mechanical behaviors can be obtained by the manufacturers by appropriately manipulating the position of the center of rotation. A proper positioning of the artificial disc during the surgery, in particular in the antero-posterior direction, was found to be of critical importance.     

Biomechanics of anterior plating failure in treating distractive flexion injury in the caudal subaxial cervical spine

BackgroundOperative level is a potential biomechanical risk factor for construct failure during anterior fixation for distractive flexion injury. No biomechanical study of this concept has been reported, although it is important in clinical management.MethodsTo explore the mechanism of this concept, a previously validated three-dimensional C2-T1 finite element model was modified to simulate surgical procedure via the anterior approach for treating single-level distractive flexion injury, from C2-C3 to C7-T1. Four loading conditions were used including no-compression, follower load, axial load, and combined load. Construct stability at the operative level was assessed.FindingsUnder these loading conditions with the head's weight simulated, segmental stability decreases when the operative level shifts cephalocaudally, especially at C6-C7 and C7-T1, the stress of screw-bone interface increases cephalocaudally, and in the same operative level, the caudal screws always carries more load than the cephalad ones. All these predicted results are consistent with failure patterns observed in clinical reports. In the contrast, under other loading conditions without the weight of head, no obvious segmental divergence was predicted.InterpretationThis study supports that the biomechanical mechanism of this phenomenon includes eccentric load from head weight during sagittal movements and difference of moment arms. Our study suggests that anterior fixation is not recommended for treating distractive flexion injury at the caudal segments of the subaxial cervical spine, especially at C6-C7 and C7-T1, because of the intrinsic instability in these segments. Combined posterior rigid fixation with anterior fixation should be considered for these segments.     

Strain behavior of malaligned cervical spine implanted with metal-on-polyethylene,metal-on-metal,and elastomeric artificial disc prostheses – A finite element analysis

BackgroundPostoperative alterations in cervical spine curvature (i.e. loss of lordotic angle) are frequently observed following total disc replacement surgery. However, it remains unclear whether such changes in lordotic angle are due to preoperative spinal deformities and/or prostheses design limitations. The objective of the study is to investigate strain and segmental biomechanics of the malaligned cervical spine following total disc replacement.MethodsThree disc prostheses were chosen, namely a metal-on-polyethylene, a metal-on-metal, and an elastomeric prosthesis, which feature different geometrical and material design characteristics. All discs were modelled and implanted into multi-segmental cervical spine finite element model (C3-C7) with normal, straight and kyphotic alignments. Comparative analyses were performed by using a hybrid protocol.FindingsThe results indicated that as the spine loses lordotic alignment, the prosthesis with elastomeric core tends to produce significantly larger flexion range of motion (difference up to 6.1°) than metal-on-polyethylene and metal-on-metal prostheses. In contrast, when the treated spine had normal lordotic alignment, the range of motion behaviors of different prostheses are rather similar (difference within 1.9°). Large localized strains up to 84.8% were found with the elastomeric prosthesis, causing a collapsed anterior disc space under flexion loads.InterpretationChanges in cervical spinal alignments could significantly affect the surgical-level range of motion behaviors following disc arthroplasty; the in situ performance was largely dependent on the designs of the artificial disc devices in particular to the material properties.