小关节角矢状化、椎间盘退变对退变性腰椎滑移作用的有限元研究

目的探讨小关节矢状化与椎间盘退变间的关系及其对退变性腰椎滑移的作用和意义。方法采用一种新型CAD方法精确构建65°小关节角、45°小关节角、25°小关节角与正常椎间盘、轻度退变椎间盘、重度退变椎间盘相组配的9种腰椎L4-L5活动节段有限元模型。生理压缩载荷下,分别对9种有限元模型的生物力学参数进行测试。结果与小关节角45°和25°有限元模型相比,小关节角65°有限元模型的矢状方向椎体前移位增加,关节突、峡部等效应力和关节突水平方向接触力明显增加;小关节角65°有限元模型的终板膨出减小,纤维环基质应力增加。与正常有限元模型相比,椎间盘轻度退变有限元模型刚度下降,小关节突及峡部应力轻度增加。9种有限元模型中,轻度退变椎间盘结合小关节角65°有限元模型的抗前剪力能力最差。结论小关节角矢状化既是退变性腰椎滑移的原发诱因,又是局部应力变化导致关节突再塑形的继发病理改变,矢状型小关节腰椎活动节段矢状方向内在不稳定性受椎间盘退变程度的影响,椎间盘退变对小关节角矢状化无明显促进作用。     

椎间盘高度降低及退变对腰椎生物力学影响的有限元分析

目的：分析椎间盘高度降低及退变对腰椎活动节段生物力学的影响。方法：首先采用一种新型CAD方法精确构建腰椎L4-5，活动节段正常高度椎间盘（NHD）、单纯高度降低椎间盘（PHDD）、椎间盘高度降低合并严重退变（DHDD）三种有限元模型。垂直压缩载荷下，分别对3种有限元模型的生物力学参数进行测试。结果：椎间盘高度降低及退变对腰椎活动节段轴向移位、后外侧椎间盘膨出、纤维环纤维应力最大值有明显的影响，DHDD模型的椎体一终板界面应力分布与NHD和PHDD模型明显不同。结论：高度降低后椎间盘刚度明显增加，DHDD最不易发生内层纤维环纤维破裂，关节突关节间隙与轴向移位比值是决定椎间盘承载力大小的关键因素，退变椎间盘对压缩应力有明显分散传递作用。     

腰椎间盘退变对软骨终板生物力学特性影响的有限元分析

目的　研究腰椎终板不同位点的压应力分布规律,分析腰椎间盘退变对软骨终板压应力的影响。 方法　选取一青壮年男性新鲜尸体的腰椎运动节段标本,螺旋CT机对腰椎运动节段进行连续CT扫描,利用有限元分析方法,建立L4/5运动节段有限元分析模型,在此基础上建立椎间盘退变模型。模拟椎间盘正常状态和椎间盘退变状态,在L4、L5椎体终板上选择具有代表性的结点,分别代表椎体终板正中部、左右侧边缘、后中部和前中部,对上下软骨终板压应力分布进行有限元分析。 结果　椎间盘退变组较正常组的终板压应力均显著增大,上下终板在轴向加载、前屈、后伸、左旋和右旋加载时椎间盘退变组较正常状态时应力分布均显著增大,具有统计学意义（P<0.05）。 结论　腰椎椎间盘退变因素对终板的应力分布有明显影响, 随着椎间盘退变,椎间盘软骨终板应力显著增大。     

椎板不同切除范围对腰椎生物力学影响的有限元分析

建立全腰椎有限元模型,模拟三种后路手术方式,分析不同椎板切除范围对腰椎生物力学的影响。综合利用三维重建自编软件和Hyper Mesh软件,建立腰椎(L1-L5)有限元模型并与前人所作体外实验数据比较,验证本模型的有效性。在此基础上模拟全椎板切除、半椎板切除及椎板开窗减压术,比较减压节段的运动范围及相应椎间盘的应力改变。L3-4、L4-5节段后部结构切除后,腰椎运动范围与椎板切除大小成正比,纤维环应力最大变化发生在前屈、后伸和左右旋转运动时,而在侧屈运动时无明显的变化。腰椎运动范围的增加与腰椎后部结构的切除程度有关。在彻底减压的同时,最大程度的保留腰椎后部结构,可以减小术后椎间盘应力,减轻关节突等结构的进一步退变。     

腰椎间盘突出症力学特征的仿真计算方法

目的建立腰椎间盘突出症力学特征的数值计算分析模型,为腰椎间盘突出症的力学机理提供一种检测评估方法。方法利用健康成人L4～5腰椎运动节段CT影像,采用Mimics 10.01医学图像处理软件和Geomagic10.0逆向工程软件分别建立L4～5腰椎运动节段的椎骨和椎间盘,并在Ansys软件中附加腰椎相关韧带及通过改变椎间盘突出后对应的材料属性,建立腰椎L4～5运动节段有限元模型,构建正常模型和腰椎间盘突出模型;运用有限元方法模拟正常椎间盘和突出椎间盘在轴向压力、前弯、侧弯、旋转和后伸5种载荷下的生物力学特征参数。结果椎间盘突出后,椎间盘的应力分布及传递载荷的能力改变,应力集中于纤维环后外侧;在相同的载荷情况下,突出的椎间盘的最大形变量比正常椎间盘的大;椎间盘突出模型的小关节突接触力比正常模型的小关节突接触力大。结论椎间盘突出后,椎间盘的承载功能下降,关节突的应力水平升高,小关节的负荷增加,从而导致腰椎稳度下降。     

髓核摘除术对腰椎生物力学特性影响的有限元研究

目的　采用三维有限元模型分析方法,探讨腰椎间盘突出症髓核摘除术对腰椎生物力学特性的影响。 方法 采用新型CAD方法精确建立腰椎L4～5活动节段有限元模型,构建正常模型、退变模型、髓核摘除模型和疤痕长入模型分别模拟正常椎间盘、退变椎间盘、髓核摘除后即刻和术后中长期时的椎间盘;并比较其生物力学特征。 结果　(1)髓核摘除模型的刚度较退变模型减小,但较正常模型提高;　(2)疤痕长入模型腰椎节段刚度大幅回升并超过退变模型;(3)髓核摘除后即刻小关节突接触力减小,而疤痕长入模型则表现为小关节突接触力增加。 结论　腰椎间盘髓核摘除术后即刻对腰椎稳定性和后部结构应力影响较小,而髓核摘除中长期后则可有腰椎运动节段变硬和关节突的应力增加。     

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。     

不同单节段颈椎前路椎间融合系统对邻近节段的生物力学影响

目的对比Zero-P零切迹颈椎前路椎间融合固定系统和Cage-Plate融合系统对相邻节段的生物力学影响,为单节段颈椎病的治疗远期临床疗效提供参考。方法选择正常人CT扫描数据建立颈椎C1~7有限元模型,在验证模型的有效性后,分别建立在颈椎C5~6植入Zero-P和Cage-Plate融合系统的有限元模型。分别加载1.5 N·m扭矩模拟颈椎前屈、后伸、侧弯和旋转运动,对比正常情况下颈椎和分别植入Zero-P与Cage-Plate融合系统后相邻节段活动范围(range of motion,ROM)变化和椎间盘髓核、纤维环、终板及小关节上的应力。结果两种颈椎融合器植入后,C4~5椎间ROM增大20%,但C6~7椎间ROM增大120%,C4~5、C6~7髓核上的应力分别增大78%、110%,相邻节段终板和纤维环上的应力均有所增大。结论 Cage-Plate和Zero-P融合系统植入后均会引起相邻节段ROM增大,以及相邻椎间盘髓核、纤维环和小关节上应力增大,长远上会引起邻近节段的病变。但Cage-Plate和Zero-P融合系统对邻近节段的生物力学影响没有本质区别。     

不同运动状态下模拟人体腰椎结构特征变化的有限元分析

目的比较不同运动状态下正常与退变腰椎节段三维有限元模型的应力变化特点及量效关系,分析中医推拿手法对退变腰椎节段力学调衡作用机制。方法建立完整、真实人体脊柱退变腰椎节段(L4~5)三维有限元模型,模拟腰椎节段前屈与后伸的生理活动。在加载外力即中医推拿手法作用下,分析退变腰椎节段的应力变化特点以及外加载荷逐渐递增过程中退变腰椎节段的应力变化,并与正常腰椎节段在不同运动状态下的应力、应变改变趋势进行对比。结果在不同运动状态下,人体腰椎节段椎间盘内应力分布、髓核、纤维环等结构的弹性模量随着腰椎退变程度的增加呈逐渐增大的趋势。中医推拿手法作用后能改变椎间盘内的应力分布,一定程度地增大椎管内的空间,使神经根所受的应力减小,椎体、小关节应力、椎弓根应力后伸位大于前屈位;椎间盘内部应力前屈位大于后伸位;且均由上至下呈逐渐增大的趋势。结论中医推拿手法对人体退变腰椎节段力学环境的调衡起到改善和治疗腰椎间盘病变的目的。同时,与人体正常腰椎节段三维有限元模型对比,从生物力学环境与特性改变角度研究腰椎退变的过程,能够为中医推拿手法在临床中预防和治疗脊柱退行性疾病的推广应用提供科学依据,也为中医推拿手法有效地预防和治疗脊柱腰椎节段病损的生物力学机制的研究提供新研究思路。     

人体腰椎L_(4~5)节段有限元建模及分析

本文基于CT图像数据结合图像处理软件建立人体腰椎L4~5节段有限元模型,进行前屈、后伸、侧弯和轴向旋转工况下的生物力学特性分析。首先,选择一名正常志愿者腰椎L4~5节段的CT图像数据建立三维模型,模型包括椎体、椎间盘、软骨终板、连接韧带和小关节突关节等部分,在前屈、后伸、侧弯和轴向旋转工况加载下进行生物力学性能的分析。结果表明,建立的腰椎模型几何形态逼真且验证有效,在500、1 000、1 500和2 000N分布压力下,腰椎L4~5有限元模型的轴向位移分别为0.23、0.47、0.76、1.02mm,与前人在相同条件下离体实验和有限元分析的研究相近,几种情况下腰椎整体及椎间盘的应力分布符合腰椎的生物力学特性。因此,本文所建立的腰椎L4~5节段有限元模型能有效地模拟腰椎的生物力学特性,为后续腰椎植入物的生物力学性能研究奠定良好的基础。     

Biomechanical analysis of the lumbar spine with anterior interbody fusion on the different locations of the bone grafts

The anterior lumbar interbody fusion is the common procedure in the management of the degenerated disc in the lumbar spine, but the biomechanical behavior of the fused segment would be changed because of the implantation of bone graft at the different locations. To investigate the biomechanical alteration, the study applied the finite element model to undergo the stress analysis.A three-dimensional finite element model of the lumbar spine was established, and modified to the three fusion models consisted of the bone graft at the anterior site, the middle site and the posterior site, respectively. The 12 N m flexion and the 10 N m torsion with pre-load 150 N were imposed on the L1 vertebral body.The results of the finite element model indicated that placing bone graft at anterior site could effectively resist flexion moment, and decreased the tensile force of the posterior ligaments about 15% above. Placing bone graft at posterior site could resist torsional moment, and also led to none of contact force of the facet joint in the fused segment. However, wherever the bone grafts were placed, stress slightly increased on the disc adjacent to interbody fusion about 5% below.     

Finite element analysis of the spondylolysis in lumbar spine

Spondylolysis is a fracture of the bone lamina in the pars interarticularis and has a high risk of developing spondylolisthesis, as well as traction on the spinal cord and nerve root, leading to spinal disorders or low back pain when the lumbar spine is subjected to high external forces. Previous studies mostly investigated the mechanical changes of the endplate in spondylolysis. However, little attention has been focused on the entire structural changes that occur in spondylolysis. Therefore, the purpose of this study was to evaluate the biomechanical changes in posterior ligaments, disc, endplate, and pars interarticularis between the intact lumbar spine and spondylolysis. A total of three finite element models, namely the intact L2-L4 lumbar spine, lumbar spine with unilateral pars defect and with bilateral pars defect were established using a software ANSYS 6.0. A loading of 10 N.m in flexion, extension, left torsion, right torsion, left lateral bending, and right lateral bending respectively were imposed on the superior surface of the L2 body. The bottom of the L4 vertebral body was completely constrained. The finite element models estimated that the lumbar spine with a unilateral pars defect was able to maintain spinal stability as the intact lumbar spine, but the contralateral pars experienced greater stress. For the lumbar spine with a bilateral pars defect, the rotation angle, the vertebral body displacement, the disc stress, and the endplate stress, was increased more when compared to the intact lumbar spine under extension or torsion.     

坐位旋转手法对腰椎内在应力的实时监测

目的：研究坐位旋转手法时对腰椎内在应力分布的特点。方法：使用L4-5腰椎CT片，以Mimics软件系统逐层重建，建立L4-5三维有限元模型。根据手法原理，将坐位腰椎旋转手法进行分解，把各项力学参数代入三维有限元模型进行计算分析。即时显示手法作用时腰椎间盘的位移和内在应力的变化。结果：正常腰椎在旋转手法作用时应力主要集中在椎体、终板和椎间盘处。退变腰椎在手法作用时应力主要集中在L4小关节的下关节突和椎弓，且应力分布集中。结论：(1)坐位腰椎旋转手法时，对于正常腰椎应力主要作用于椎体、终板和椎间盘等前部结构。(2)对于退变腰椎，应力主要作用于后部结构，并且所受应力分布集中，易损伤小关节、椎弓。     

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.     

腰椎间盘退变及腰椎融合的有限元研究进展

退变椎间盘腰椎有限元模型即通过椎间盘材料特性及形态结构的改变模拟椎间盘退变的病理过程。椎间盘退变后椎间盘刚度的增加对腰椎应力分布有明显的影响。椎体融合器植入后椎体的应力变化与融合器的形态、材料特性以及松质骨、终板的密度密切相关。     

椎体成形术后相邻椎体终板应力变化的有限元分析

目的：利用有限元方法分析椎体成形术对相邻椎体终板应力变化的影响。方法：在已建立的胸腰段骨质疏松性椎体压缩性骨折三维有限元模型上，模拟经皮穿刺椎体成形术(PVP)过程在胸12椎体中置入骨水泥，分析轴向压缩、前屈和后伸3种加载状态下手术前后相邻椎体终板的应力变化。结果：胸11下位终板和腰1上位终板手术前后总体应力变化不大。但两终板中间部分的应力在各种状态下术后较术前均有增加。结论：注入较小剂量(胸124．0ml)骨水泥，PVP不足以引起由于应力集中而造成相邻椎体骨折可能性增加。PVP中较小剂量的骨水泥注入是安全有效的。     

Inhibition of vertebral endplate perfusion results in decreased intervertebral disc intranuclear diffusive transport

Impaired nutrition of the intervertebral disc has been hypothesized to be one of the causes of disc degeneration. However, no causal relationship between decreased endplate perfusion and limited nutrient transport has been demonstrated to support this pathogenic mechanism. To determine the importance of endplate perfusion on solute diffusion into the nucleus pulposus and to show causality of endplate perfusion on intranuclear diffusion in large animal lumbar intervertebral discs, diffusive transport into ovine lumbar intervertebral discs was evaluated after inhibiting adjacent vertebral endplate perfusion. Partial perfusion blocks were created in vertebrae close and parallel to both endplates of lumbar discs of anaesthetized sheep. To assess diffusivity of small molecules through the endplate, N2O was introduced into the inhalation gas mixture and concentrations of intranuclear N2O were measured for 35 min thereafter. Post mortem, procion red was infused through the spinal vasculature and perfusion through the endplate was assessed by quantifying the density of dye-perfused endplate vascular buds in histology sections. Perfusion of the endplates overlying the nucleus pulposus was inhibited by almost 50% in the partially blocked discs relative to the control discs. There was also a nine-fold decreased transport rate of intranuclear N2O in partially blocked discs compared with control discs. The density of perfused endplate vascular buds correlated significantly to the amount of transported intranuclear N2O (r2 = 0.52, P = 0.008). The vertebral endplate was demonstrated to be the main route of intravascular solute transport into the nucleus pulposus of intervertebral discs, and inhibition of endplate perfusion can cause inhibited solute transport into the disc intranuclear tissue.