Application of an asymmetric finite element model of the C2-T1 cervical spine for evaluating the role of soft tissues in stability

Different finite element models of the cervical spine have been suggested for evaluating the roles of ligaments, facet joints, and disks in the stability of cervical spine under sagittal moments. However, no comprehensive study on the response of the full cervical spine that has used a detailed finite element (FE) model (C2-T1) that considers the asymmetry about the mid-sagittal plane has been reported. The aims of this study were to consider asymmetry in a FE model of the full cervical spine and to investigate the influences of ligaments, facet joints, and disk nucleus on the stability of the asymmetric model during flexion and extension. The model was validated against various published in vitro studies and FE studies for the three main loading planes. Next, the C4-C5 level was modified to simulate different cases to investigate the role of the soft tissues in segmental stability. The FE model predicted that excluding the interspinous ligament (ISL) from the index level would cause excessive instability during flexion and that excluding the posterior longitudinal ligament (PLL) or the ligamentum flavum (LF) would not affect segmental rotation. During extension, motion increased when the facet joints were excluded. The model without disk nucleus was unstable compared to the intact model at lower loads and exhibited a similar rotation response at higher loads.     

Finite element modeling of the cervical spine: role of intervertebral disc under axial and eccentric loads

An anatomically accurate, three-dimensional, nonlinear finite element model of the human cervical spine was developed using computed tomography images and cryomicrotome sections. The detailed model included the cortical bone, cancellous core, endplate, lamina, pedicle, transverse processes and spinous processes of the vertebrae; the annulus fibrosus and nucleus pulposus of the intervertebral discs; the uncovertebral joints; the articular cartilage, the synovial fluid and synovial membrane of the facet joints; and the anterior and posterior longitudinal ligaments, interspinous ligaments, capsular ligaments and ligamentum flavum. The finite element model was validated with experimental results: force–displacement and localized strain responses of the vertebral body and lateral masses under pure compression, and varying eccentric anterior-compression and posterior-compression loading modes. This experimentally validated finite element model was used to study the biomechanics of the cervical spine intervertebral disc by quantifying the internal axial and shear forces resisted by the ventral, middle, and dorsal regions of the disc under the above axial and eccentric loading modes. Results indicated that higher axial forces (compared to shear forces) were transmitted through different regions of the disc under all loading modes. While the ventral region of the disc resisted higher variations in axial force, the dorsal region transmitted higher shear forces under all loading modes. These findings may offer an insight to better understand the biomechanical role of the human cervical spine intervertebral disc.     

Finite element modeling of multi-level cervical spinal segments (C3-C6) and biomechanical analysis of an elastomer-type prosthetic disc

A three-dimensional finite element (FE) model for the multi-level lower cervical spinal segment C3-C6 has been developed using computed tomography (CT) data, and applied to study of the effects of the fusion and the artificial disc prosthesis on the biomechanical behavior of the lower cervical spine. The NURBS computer adided dedsig (CAD) data used in this study for modeling the vertebrae facilitate adding surface patch layouts for seamless attachment of the soft tissues, such as intervertebral discs onto the vertebrae. A FE model was completed by generating mesh out of this geometry. Its accuracy was validated by comparing with previously published experimental and numerical results for the flexion-extension, axial rotation, and lateral bending moments. An implantation of an elastomer-type disc prosthesis or fused graft between C4-C5 vertebrae was considered in the FE model by modifying the intact disc. It is shown that the fusion reduced the mobility at its level by about 50-70% for the considered loading cases. It is numerically demonstrated that an elastomer with Young's modulus of 5.9 MPa for the artificial disc prosthesis well restores the biomechanical behavior of the intact spine.     

聚醚醚酮/羟基磷灰石/碳纤维复合材料的生物力学分析

目的利用有限元分析法比较聚醚醚酮/羟基磷灰石/碳纤维复合材料（75PEEK/10HA/15CF）与钛合金的生物力学。方法建立C4～C6有限元模型,于C5～C6间植入75PEEK/10HA/15CF或钛合金人工椎间盘和椎间融合器,计算在前屈、后伸、侧弯和旋转时临近椎体、椎间盘的wonMises应力变化和C5～C6节段的活动度及植入物上的应力分布。结果在正常情况下,钛合金人工椎间盘置换模型在前屈时C5椎体、C4~5椎间盘平均won Mises应力改变率分别为75PEEK/10HA/15CF人工椎间盘模型的1.50倍和1.67倍;在侧弯时C6椎体的平均won Mises应力改变率为75PEEK/10HA/15CF人工椎间盘置换模型的1.33倍。融合器模型,在前屈时C5椎体、C4~5椎间盘应力改变率前者为后者的1.48倍和1.87倍;在侧弯时C6椎体应力改变率,前者为后者的1.67倍。钛合金植入物的最大应力为75PEEK/10HA/15CF的4.5倍,并出现应力集中。结论与钛合金相比,75PEEK/10HA/15CF能更好地将负荷传递,增加融合率,能有效地减少临近椎体的应力,减少植入物沉降的发生。     

基于Simpleware全颈椎三维有限元模型的构建与分析

目的 利用Simpleware软件构建全颈椎三维有限元模型,并对模型进行验证和分析,为探讨颈椎损伤机制提供可靠模型。方法 基于CT断层扫描图像,利用医学图像处理软件Simpleware、逆向工程软件Geomagic建立C1~7全颈椎三维实体模型,导入Hypermesh进行颈椎网格划分、添加韧带并引入小关节突接触关系等,建立C1~7全颈椎有限元模型,在ANSYS中模拟前屈、后伸、侧弯和轴向旋转工况下颈椎的生物力学性能。结果 建立的模型准确可靠,在前屈、后伸、侧弯和轴向旋转时,活动范围与文献中离体实验和有限元分析结果相近。椎间盘应力集中在椎体受压侧,C4/5最易产生应力集中。结论 建立的C1~7全颈椎有限元模型能够有效模拟颈椎的生物力学特性,为后续颈椎挥鞭样损伤的生物力学研究奠定良好的基础。     

侧卧位枕高与颈椎间盘应力关系的三维有限元分析

目的 采用三维有限元法分析人体侧卧位状态下枕高与颈椎间盘应力的关系,为合理用枕提供依据.方法 对1名正常男性志愿者进行颈椎薄层CT扫描,联用医学图像处理软件Mimics、逆向工程软件Geomagic Studio、有限元软件MSC.Patran建立人体侧卧位枕高分别为10 cm(冠状面颈椎左侧屈)、17 cm(冠状面颈椎中立)、25 cm(冠状面颈椎右侧屈)3种条件下的全颈椎三维有限元模型,并进行分析运算.结果 冠状面颈椎近似中立位模型(枕高17 cm)的等效应力、最大主应力、最大剪应力均明显低于左侧屈或右侧区模型.结论 颈椎冠状面处于中立位可使颈椎间盘获得最佳应力分布状态.人体侧卧睡眠时,合理的枕高应是颈椎在冠状面处于中立位.     

Development and Validation of a 10-Year-Old Child Ligamentous Cervical Spine Finite Element Model

Although a number of finite element (FE) adult cervical spine models have been developed to understand the injury mechanisms of the neck in automotive related crash scenarios, there have been fewer efforts to develop a child neck model. In this study, a 10-year-old ligamentous cervical spine FE model was developed for application in the improvement of pediatric safety related to motor vehicle crashes. The model geometry was obtained from medical scans and meshed using a multi-block approach. Appropriate properties based on review of literature in conjunction with scaling were assigned to different parts of the model. Child tensile force–deformation data in three segments, Occipital-C2 (C0–C2), C4–C5 and C6–C7, were used to validate the cervical spine model and predict failure forces and displacements. Design of computer experiments was performed to determine failure properties for intervertebral discs and ligaments needed to set up the FE model. The model-predicted ultimate displacements and forces were within the experimental range. The cervical spine FE model was validated in flexion and extension against the child experimental data in three segments, C0–C2, C4–C5 and C6–C7. Other model predictions were found to be consistent with the experimental responses scaled from adult data. The whole cervical spine model was also validated in tension, flexion and extension against the child experimental data. This study provided methods for developing a child ligamentous cervical spine FE model and to predict soft tissue failures in tension.     

Three-Dimensional Finite Element Models of the Human Pubic Symphysis with Viscohyperelastic Soft Tissues

Three-dimensional finite element (FE) models of human pubic symphyses were constructed from computed tomography image data of one male and one female cadaver pelvis. The pubic bones, interpubic fibrocartilaginous disc and four pubic ligaments were segmented semi-automatically and meshed with hexahedral elements using automatic mesh generation schemes. A two-term viscoelastic Prony series, determined by curve fitting results of compressive creep experiments, was used to model the rate-dependent effects of the interpubic disc and the pubic ligaments. Three-parameter Mooney-Rivlin material coefficients were calculated for the discs using a heuristic FE approach based on average experimental joint compression data. Similarly, a transversely isotropic hyperelastic material model was applied to the ligaments to capture average tensile responses. Linear elastic isotropic properties were assigned to bone. The applicability of the resulting models was tested in bending simulations in four directions and in tensile tests of varying load rates. The model-predicted results correlated reasonably with the joint bending stiffnesses and rate-dependent tensile responses measured in experiments, supporting the validity of the estimated material coefficients and overall modeling approach. This study represents an important and necessary step in the eventual development of biofidelic pelvis models to investigate symphysis response under high-energy impact conditions, such as motor vehicle collisions.     

Cervical spine response in frontal crash

Predicting neck response and injury resulting from motor vehicle accidents is essential to improving occupant protection. A detailed human cervical spine finite element model has been developed, with material properties and geometry determined a priori of any validation, for the evaluation of global kinematics and tissue-level response. Model validation was based on flexion/extension response at the segment level, tension response of the whole ligamentous cervical spine, head kinematic response from volunteer frontal impacts, and soft tissue response from cadaveric whole cervical spine frontal impacts. The validation responses were rated as 0.79, assessed using advanced cross-correlation analysis, indicating the model exhibits good biofidelity. The model was then used to evaluate soft tissue response in frontal impact scenarios ranging from 8G to 22G in severity. Disc strains were highest in the C4–C5–C6 segments, and ligament strains were greatest in the ISL and LF ligaments. Both ligament and disc fiber strain levels exceeded the failure tolerances in the 22G case, in agreement with existing data. This study demonstrated that a cervical spine model can be developed at the tissue level and provide accurate biofidelic kinematic and local tissue response, leading to injury prediction in automotive crash scenarios.     

颈椎椎体次全切除，钛网植骨钢板固定三维有限元模型的建立

目的 探讨利用螺旋 CT建立颈椎椎体次全切除减压植骨固定的三维有限元模型的高度数字化方法,为研究颈椎减压手术的生物力学实验提供标准模型。方法 对健康成年男性志愿者进行CT 扫描,获得C4～C7节段的断层图片,将数据保存为Dicom格式,导入Mimics 9.1 软件进行三维几何模型重建,形成三维图像,利用Freeform 软件进行模型修改和表面划分,以IGES格式转入有限元软件Ansys 9.0完成颈椎骨性模型的建立。利用有限元软件Ansys 9.0,在颈椎骨性模型的基础上,补建终板、补充建立终板、 椎间盘、 髓核、 前纵韧带、 后纵韧带、 黄韧带、 棘间韧带、 棘上韧带等结构。然后模拟颈椎椎体次全切除,将C5椎体、前纵韧带、上下椎间盘切除,将建立的钛网、钢板实体模型添加到减压区。采用合适的材料性质和实体单元类型对模型进行有限元网格划分。结果 颈椎脊柱三维模型有限元网格划分结果：利用三维重建软件Mimics 和有限元软件Ansys 9.0 , 成功进行椎体次全切除减压钛网植骨钢板固定三维模型有限元网格划分。整个模型共有138995个节点和94039个单元,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。结论 建立的椎体次全切除植骨固定手术三维有限元模型接近真实的生物力学标本,可以进行临床和实验研究。     

基于CAD技术的个体化退变腰椎有限元模型库的建立

目的根据退变腰椎的形态特征,采用计算机辅助设计（computer aided design,CAD）方法精确建立不同形态改变的退变腰椎L4-L5运动节段三维有限元模型。方法采用改良的“非种子区域分割”以及非平行“最佳切割平面”等一系列新型CAD方法精确建立包括终板凹陷角、椎间盘高度、腰椎小关节角及椎间盘前凸角改变的L4-L5节段表面模型基本“结构模块”,表面模型数据导入ANSYS获得各“结构模块”有限元模型后,通过界面间的拼接粘贴构建不同形态改变的退变腰椎有限元模型并进行充分加载验证。结果所构建的有限元模型包含L4-L5节段所有重要解剖结构,正常和退变腰椎有限元模型预测结果与体外实验生物力学研究结果相符合。结论基于CT数据的新型CAD方法实现了个体化退变腰椎有限元模型库的建立。     

Effect of bilateral facetectomy of thoracolumbar spine T11–L1 on spinal stability

Spinal stenosis can be found in any part of the spine, though it is most commonly located on the lumbar and cervical areas. It has been documented in the literature that bilateral facetectomy in a lumbar motion segment to increase the space induces an increase in flexibility at the level at which the surgery was performed. However, the result of bilateral facetectomy on the stability of the thoracolumbar spine has not been studied. A nonlinear three-dimensional finite element (FE) model of thoracolumbar T11–L1 was built to explore the influence of bilateral facetectomy. The FE model of T11–L1 was validated against published experimental results under various physiological loadings. The FE model with bilateral facetectomy was evaluated under flexion, extension, lateral bending and axial rotation to determine alterations in kinematics. Results show that bilateral facetectomy causes increase in motion, considerable increase in axial rotation and least increase in lateral bending. Removal of facets did not result in significant change in the sagittal motion in flexion and extension.     

颈椎人工椎间盘置换有限元分析

目的　建立C4~5节段PrestigeTM-LP颈椎人工椎间盘植入后的三维有限元模型,进行手术节段的运动分析。 方法 采用对成年男性的新鲜尸体的颈椎标本进行CT三维扫描方法建立C4~5节段和PrestigeTM-LP人工间盘有限元,模拟完成C4~5人工椎间盘置换手术。测量生理加载下手术节段前屈/后伸、侧弯及轴向旋转运动角度。结果 有限元模型对颈椎的结构,包括椎体间韧带、颈椎关节突关节、钩椎关节等均进行了精确的重建,并较好地模拟手术操作进行PrestigeTM-LP人工间盘植入。运动加载后运动角度,前屈5.7°,后伸3.5°,侧弯5.0°,旋转11.3°,与文献报道结果较为接近。 结论　有限元模型具有精确度高,手术模拟真实的特点,可作为颈椎人工椎间盘生物力学研究的一种较好途径。PrestigeTM-LP颈椎人工椎间盘置换可较好地保留手术节段的运动功能。     

下颈椎三节段全椎板切除与侧块螺钉内固定三维有限元模型的建立

背景：随着颈椎后路手术技术的日益完善,侧块螺钉内固定技术已被广泛应用于颈椎的重建稳定性手术之中。然而,当前对于侧块螺钉内固定系统重建颈椎稳定性的有限元研究却很少。 目的：建立精细下颈椎(C3-C7)及三节段全椎板切除后应用侧块螺钉内固定重建的三维有限元模型,对重建后的下颈椎及内固定进行生物力学分析。 方法：采集1例30岁正常女性志愿者行全颈椎CT,得到Dicom数据集。应用Mimics 10.01、Geomagic Studio12.0、Solidworks2012、HyperMesh10.1、Abaqus 6.12软件建立下颈椎(C3-C7)完整模型、全椎板切除模型以及侧块螺钉内固定系统重建模型。分析重建模型在前屈、后伸、侧弯和旋转运动状态下的应力变化情况。 结果与结论：所建下颈椎有限元模型结构精细,外形逼真,共包含503 911个四面体单元,93 390个节点,并通过有效性验证。在软件中完成模拟手术过程,最终得到侧块螺钉内固定重建模型。侧块螺钉内固定系统对全椎板切除模型具有良好的稳定性,重建后颈椎的活动度远低于完整模型,且后伸时侧块螺钉内固定系统的应力最为集中。中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程全文链接：     

基于CT数据的人体L3-L4腰椎节段的三维有限元建模和分析

目的 建立一个精确的人体L3-L4腰椎节段有限元模型,用于腰椎生物力学的研究.方法 基于可视人计划(visible human project,VHP)男性冷冻CT数据,通过Marchingcubes算法三维重建L3和L4椎骨的几何模型并转换为有限元网格,然后结合椎间盘和韧带的网格建立L3-L4节段的有限元网格.根据CT值设定材料特性建立有限元模型,施加压缩的边界条件进行有限元分析,并和参考模型的结果比较分析.结果 基于CT的L3-L4节段有限元模型比参考模型更符合腰椎的解剖结构.结论 基于CT的L3-L4节段有限元模型能够精确的描述腰椎解剖结构,保证有限元分析的准确性.     

A three-dimensional finite element model of the cervical spine: an investigation of whiplash injury

Very few finite element models of the cervical spine have been developed to investigate internal stress on the soft tissues under whiplash loading situation. In the present work, an approach was used to generate a finite element model of the head (C0), the vertebrae (C1–T1) and their soft tissues. The global acceleration and displacement, the neck injury criterion (NIC), segmental angulations and stress of soft tissues from the model were investigated and compared with published data under whiplash loading. The calculated acceleration and displacement agreed well with the volunteer experimental data. The peak NIC was lower than the proposed threshold. The cervical S- and C-shaped curves were predicted based on the rotational angles. The highest segmental angle and maximum stress of discs mainly occurred at C7–T1. Greater stress was located in the anterior and posterior regions of the discs. For the ligaments, peak stress was at anterior longitudinal ligaments. Each level of soft tissues experienced the greatest stress at the time of cervical S- and C-shaped curves. The cervical spine was likely at risk of hyperextension injuries during whiplash loading. The model included more anatomical details compared to previous studies and provided an understanding of whiplash injuries.     

颈椎半椎板切除后小关节部位的应力分析

根据CT数据建立了颈椎C4-C6功能节段的三维非线性有限元完整模型,并在此模型基础上建立了椎板切除模型。考察了椎板半切除术对小关节的生物力学影响。将C6椎体下表面固定作为边界条件,采用三种加载模式,即于C4椎体上表面施加1.8Nm分别沿矢状面、冠状面、轴面方向的纯弯矩。通过计算得到了C5半椎板切除后小关节部位的应力变化。结果表明,半椎板切除手术对各加载模式下小关节面的Von Mises应力有较大的影响,应力变化最大处应力上升了187.5%。评价颈椎半椎板切除术不能忽视手术对小关节的影响。     

使用有限元法模拟枕寰枢复合体的中性区

目的为枕颈部中性区（NZ）的研究建立有效的数学模型。方法本研究基于可视人数据库建立了枕寰枢复合体的非线性有限元模型,通过细致的轮廓提取和准确的材料特性定义,以提升上颈椎有限元模型的精确性。模型模拟了在静态生理载荷作用下复合体轴向旋转、前屈、后伸和侧弯运动。结果模型预测的运动范围（ROM）和NZ与实验数据相吻合。模型的力矩-转动关系呈明显的非线性关系,最大旋转发生在水平面,其次是正中矢状面和冠状面,且轴向旋转与侧弯相互耦合。模型总体表现出较大的ROM和较高比例的NZ。结论现有文献中尚未见到能同时成功验证ROM和NZ的上颈椎有限元模型。此模型可为枕颈部病变与创伤中出现的异常NZ的研究提供有力的辅助。     

汽车后碰撞时人体头颈部的动力学响应及损伤分析

目的建立基于人体解剖学结构的精细化头颈部有限元模型,研究不同后碰撞速度下颈部损伤。方法该模型以人体头颈部CT扫描图像为基础,利用Mimics进行三维骨重建,通过Hyper Mesh完善颈部三维实体韧带、小关节等组织,并进行网格划分。生成的模型包括头部、8节椎骨(C1～T1)、6个椎间盘(包括纤维环、髓核和上下软骨终板)、小关节(包括软骨和关节囊韧带)、韧带、肌肉等结构,最后在有限元后处理软件中完成模型验证与后碰撞计算。结果分别对模型进行轴向冲击、前后屈伸和侧屈模拟并与实验数据对比,验证模型的有效性,并进行速度为20、40、60、80 km/h后碰撞计算。在20 km/h速度下,颈部无损伤出现,在40、60、80 km/h速度下,最早出现损伤的都是韧带。随着速度增加,颈部各组织受力不断增大。速度为80 km/h时,颈椎的密质骨、松质骨和纤维环最大应力分别为226. 4、11. 5、162. 8 MPa,当韧带应变达到极限时,开始出现撕裂。结论所建头颈部有限元模型具有较高的生物仿真度和有效性,可用于交通事故中颈部损伤分析的研究,在一定程度上有助于颈椎损伤的诊断、治疗和预防。     

颈椎有限元模型的应用进展

有限元分析法（FEA）是一种在生物力学领域广泛应用的研究方法.近年来,颈椎有限元模型已被广泛应用于研究颈椎损伤、颈椎退变及模拟各种颈椎手术,已日趋完善.回顾了颈椎有限元模型的发展,介绍了颈椎有限元建模与分析在颈椎损伤、人工椎间盘置换、椎间植骨融合、颈椎退变及颈椎失稳等方面的应用进展,展望了未来的发展趋势.