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.     

有限元分析法研究颈椎内固定物的生物力学特点

有限元分析法是用于结构分析的矩阵方法,将一个由无限个质点构成并且有限个自由度的连续体划分成有限个小单元体所组成的集合体。应用有限元分析法对颈椎在生理及病理情况下的生物力学特性进行分析,及不同术式、内固定器械对颈椎生物力学的影响,展望了有限元法应用于颈椎生物力学研究的前景,由于所建立的有限元模型其形态结构与人体实际存在差异,计算结果范围较为狭小和固定,随着计算机及软件的进一步发展,有限元分析法将成为脊柱生物力学研究的热点。     

人工颈椎间盘置换对下颈椎活动影响的三维有限元分析

建立人工椎间盘置入后下颈椎C_(3~7) 的三维模型,分析颈椎人工椎间盘置换后下颈椎运动情况.根据1例人工椎间盘置入患者术后6个月CT片,应用有限元方法建立其包含Bryan~(TM)人工颈椎间盘假体的下颈椎三维有限元模型,导入Ansys 9.0中,对椎体皮质骨、松质骨、椎间盘用三维十节点四面体结构实体单元进行网格划分后进行分析.对模型加载2 N·m的力矩,观察其在前屈/后伸、侧屈及旋转几种状态下的运动情况,了解其运动特性.通过与以往的研究结果比较,试验结果基本符合或趋势基本一致.结果提示,颈椎间盘置换后能基本保证下颈椎运动稳定性.     

Less invasive anterior fusion of the cervical spine

Summary

Trauma, degenerative and inflammatory diseases, or tumours may destabilise and deform the cervical spine, causing compression of the spinal cord and/or the nerve roots. The goals of surgical therapy are decompression of the neurostructures and restoration of the physiological alignment, along with stabilisation by fusion and fixation of the affected vertebrae. ‘Minimally invasive’ defines an effective surgical treatment with the least morbidity for the patient. The combined use of computed tomography (CT) and MRI, microsurgical techniques, intra-operative fluoroscopy and devices for internal fixation (plates and screws) has significantly improved the outcome. Nowadays bone graft substitutes, endoscopy and image-guided navigation are being introduced for clinical use, in order to reduce the surgical morbidity even further. Benefits of this evolution are: surgical procedures tailored for different pathologies; early mobilisation and rehabilitation, especially of elderly patients. Disadvantages are: a rapidly increasing number of operative procedures with a demanding learning curve, which have to be performed at specially qualified centres; and increasing sophistication (as a potential source of error) of the surgical equipment. A more balanced cooperation between industry and clinicians, along with an ethical agreement on how much surgery should be done, has become mandatory.     

颈椎骨折行前路手术39例围术期护理

目的:探讨颈椎骨折患者行前路手术围术期的护理方法。方法:对39例颈椎骨折行前路手术患者做好术前心理护理、气管推移训练、体位适应训练、呼吸功能训练,术后体位护理、呼吸道护理、引流管护理、病情观察、康复训练指导。结果:本组随访6个月~2年,FranrelA级1例,术后肢体功能无明显改善,B级2例恢复至C级,均未发生严重并发症。结论:对颈椎骨折行前路手术患者,加强围术期护理,可有效预防并发症发生,促进术后康复。     

下颈椎脱位小关节突交锁复位后前路稳定手术效果观察

目的探讨下颈椎小关节突交锁牵引复位后前路稳定手术的治疗效果。方法下颈椎小关节突交锁患者29例先行牵引复位，然后再行前路椎间植骨融合固定。结果牵引复位成功26例，3例复位未成功者均伴有小关节骨折先行后路切开复位。本组病例前路手术后均获得骨性融合，未出现内固定松动、断裂、脱落。结论下颈椎小关节交锁颅骨牵引、闭合复位安全可靠，颈前路植骨融合固定，骨愈合可靠，生物强度高，足以维持颈椎稳定性。     

颈前路显微椎间孔减压术对颈椎静态稳定性的影响

目的:评价颈前路显微椎间孔减压术对颈椎静态稳定性的影响。方法:6例成人新鲜颈椎标本,选择C4～7为实验节段。将标本分为5种状态,A:单节段完整状态,B:多节段完整状态,C:单间隙钩突切除,D:三间隙钩突切除,E:单间隙钩突切除联合椎体部分切除。应用脊柱三维运动分析仪测试在上述5种状态下标本在6个方向上三维运动范围(ROM)的改变,将5种状态分为单节段和多节段两组,分别进行统计学分析。结果:①单节段组两种手术状态在前屈轴向与完整状态差异具有非常显著性意义(P<0.01),在后伸轴向差异具有显著性意义(P<0.05),在侧屈和轴向旋转方向无差异,两种手术状态间差异无显著性意义。②多节段组任一运动方向上手术状态与完整状态ROM的改变差异无显著性意义(P>0.05),在运动范围总和上,两种状态差异具有非常显著性意义(P<0.01)。结论:颈前路椎间孔显微减压术将导致颈椎静态稳定性的轻度下降。     

颈椎病患者前路手术围手术期健康指导

目的：探讨颈椎病患者前路手术围手术期健康指导。方法：选取颈椎病前路手术患者40例,随机分为实验组和对照组各20例,实验组进行个性化护理,对照组进行常规护理。采用自行设计的调查问卷进行调查,比较两组的护理效果。结果：实验组与对照组比较效果显著,具有显著性差异（P〈0.01）。结论：个性化健康指导更有利于患者对疾病知识的理解和掌握。     

上颌前牙区非埋入式种植体不同角度基台的三维有限元分析

背景:研究发现,在上颌前牙区的角度基台增加到25°时,种植体应力增加18%,当种植体的应力增大到其所能承受的范围之外时必然会导致种植失败率的增加,因此角度基台角度肯定不是越大越好.那么到底使用最大多少角度的角度基台不会影响种植的成功率呢?以往的研究并未给予明确的答案.目的:观察上颌前牙区种植体连接不同角度基台时的应力应变情况,分析种植体的安全系数,确定上颌种植时能用的基台角度.方法:通过建立三维模型,利用有限元软件计算种植体连接不同角度的角度基台时,种植体及周围骨质的应力分布.结果与结论:种植体连接不同角度基台时,随基台角度的增大,种植体的最大von-mises应力值逐渐增大,受力部位逐渐向种植体颈部转移,各模型组相互比较,差异具有显著性意义(P<0.05).提示上颌前牙区种植为了远期成功率建议最大不要超过25°的角度基台;使用大于25°角度基台时应适当减少其所受(牙合)力.     

颈椎前路撑开钛板固定治疗下颈椎骨折脱位患者的护理

笔者总结了69例颈椎前路撑开钛板固定治疗下颈椎骨折脱位患者的护理。认为术前心理护理、牵引制动是手术成功的前提；术后正确的体位、观察呼吸变化、做好切121护理、并发症的预防及康复护理是促进患者康复的关键。     

Biomechanical analysis on of anterior transpedicular screw-fixation after two-level cervical corpectomy using finite element method

BackgroundAnterior cervical trans-pedicle screw fixation was introduced to overcome some of the disadvantages associated with anterior cervical corpectomy and fusion. In vitro biomechanical studies on the trans-pedicle screw fixation have shown excellent pull-out strength and favorable stability. Comprehensive biomechanical performance studies on the trans-pedicle screw fixation, however, are lacking.MethodsThe control computed tomography images (C2-T2) were obtained from a 22-year-old male volunteer. A three dimensional computational model of lower cervical spine (C3-T1) was developed using computed tomography scans from a 22 year old human subject. The models of intact C3-T1 (intact group), anterior cervical trans-pedicle screw fixation (trans-pedicle group), and anterior cervical corpectomy and fusion (traditional group) were analyzed with using a finite element software. A moment of 1 N·m and a compressive load of 73.6 N were loaded on the upper surface and upper facet joint surfaces of C3. Under six conditions, four parameters such as the range of motion, titanium mesh plant stress, end-plate stress, and bone-screw stress were measured and compared on two treatment groups.FindingsCompared with the intact model, the range of motions for treatment groups were decreased. Compared with cervical corpectomy and fusion, the titanium plant, C4 upper end-plate and C7 lower end-plate stresses in trans-pedicle group were reduced. No significant difference was discovered on bone-screw stress between the two groups for lateral flexion and rotation, but bone-screw stress is smaller in trans-pedicle group when compared with traditional group. With exception of individual difference, trans-pedicle group had better biomechanical results than traditional group in range of motions, titanium mesh plant stress, end-plate stress and bone-screw stress.InterpretationThe trans-pedicle method has better biomechanical properties than the anterior cervical corpectomy and fusion making it a viable alternative for cervical fixations.     

睡姿和枕高对颈椎应力影响的三维有限元分析

背景:目前睡姿和枕高的研究主要集中在临床方面,多采用统计调查、测量及影像学相结合的方法。但采用三维有限元法分析睡姿和枕高对颈椎应力影响的研究至今鲜见报道。目的:采用数学仿真的方法探讨睡姿及枕高对颈椎应力的影响。方法:以正常人体头颈CT图像为原始数据,依次经过Mimics 10.0、Geomagic Studio 11.0及Hypermesh 10.0软件建立全颈椎的三维有限元模型,利用Abaqus 6.10软件仿真分析仰卧状态与侧卧状态不同枕高下颈椎的应力特性。结果与结论:睡姿和枕高对颈椎应力均有影响。枕高相同时,仰卧位椎间盘应力的最大值大于侧卧位。同样睡姿下,颈椎椎体及椎间盘的应力值均随枕高的增加而增大。从颈椎应力的生物力学角度看,侧卧比仰卧更有利于颈椎的健康,且仰卧位枕高应低于侧卧位。     

下颈椎全椎板切除后侧块螺钉内固定系统重建稳定性的有限元模型构建及其临床意义

目的:建立下颈椎(C3～7)全椎板切除后侧块螺钉内固定系统重建稳定性的有限元模型,为颈椎手术技术的生物力学研究提供一套通用的内固定手术有限元建模方法。方法:采集1例正常男性下颈椎(C3～7)CT数据集,应用Mimics10.01、Geomagic studio10.0、HyperMesh10.0、Abaqus6.9.1等软件建立下颈椎三节段全椎板切除后侧块螺钉内固定系统重建稳定性的有限元模型。模拟施加75N头颅预载荷和1.0Nm运动附加力,使模型产生前屈、后伸、侧屈和旋转运动,分析重建后侧块螺钉内固定系统的应力分布。结果:建立了颈椎三节段全椎板切除后侧块螺钉内固定系统重建稳定性的有限元模型。侧块螺钉内固定系统重建时,钛棒与螺钉接合部易发生应力集中。结论:本有限元模型的力学分析结果能直观地反映临床上侧块螺钉内固定系统易断钉的部位及其原因;有限元模型可作为颈椎生物力学研究的工具。     

颈椎前路手术患者翻身的舒适护理

舒适护理是使患者在生理、心理、灵性、社会上达到最愉快的状态或缩短、降低其不愉快的程度。颈椎前路手术患者术后强迫去枕卧位、颈部制动、活动受限、翻身困难、姿势不当、颈部疼痛是不舒适的重要原因之一。为患者提供舒适的翻身护理,是护理颈椎前路手术患者的重要内容。     

334例颈椎片X线表现分析

目的探讨颈椎病早期X线表现,并分析相关因素。方法回顾性研究2004年至2006年3月共334例有临床症状疑似颈椎病进行颈椎拍片的病例。结果颈椎生理曲度改变与侧弯是最早出现也是最常见的颈椎病影像学表现,颈椎骨质增生、椎间隙狭窄与颈椎旋转的X线表现出现略晚。颈椎生理曲度改变、侧弯及颈段旋转的颈椎病表现,只能在颈部X线片上完全显示出来。结论颈椎病在X线片上的早期改变及诊断的价值,是目前CT、MRI不可替代的诊断指标。     

三维有限元法重建全椎板切除后颈椎三维模型

背景：颈椎后凸畸形是常见的医源性颈椎曲度异常，是一种进行性发展的颈椎畸形，其影响儿童和成人正常的颈椎生理功能。目的：以三维有限元法观察颈椎全椎板切除对颈椎曲度的影响，以及颈椎椎间盘、韧带结构对维持颈椎生理曲度的作用。设计、时间及地点：三维有限元分析，实验于2003—01／2004-01在解放军第二军医大学长征医院完成。材料：实验中高分辨率、层面间隔为1mm的颈椎横断面解剖图来自美国虚拟人计划中男性颈椎横断面解剖图，从The Visible Human Project网站免费下载。方法：采用高分辨率的颈椎横断面解剖图作为颈椎三维结构重建的数据源，重建全椎板切除后颈椎三维模型包括颅底至第1胸椎中上部所有颈椎结构，模型不包括C2～C7椎板、棘突、黄韧带、棘间韧带和棘上韧带。根据文献报道定义替代颈椎各结构的有限元单元类型和材质参数，如弹性模量。使用全椎板切除后颈椎模型，应用ansys6．1有限元分析软件，分析椎板切除后颈椎椎间盘和韧带结构对颈椎生理曲度的影响。主要观察指标：颈椎椎间盘、韧带结构（前纵韧带、后纵韧带）弹性模量变化对颈椎曲度的影响。结果：①全椎板切除后颈椎在多次反复加载负荷下，颈椎生理性前凸曲度减小，多次加载负荷后，颈椎上段生理性前凸消失，出现轻度后凸曲度。②颈椎椎间盘和韧带结构（前纵韧带、后纵韧带）弹性模量减小将加剧全椎板切除后颈椎后凸曲度，随着颈椎椎间盘、韧带结构弹性模量的增大，颈椎后凸曲度逐渐消失，并恢复正常生理性前凸曲度。结论：三维有限元分析显示，全椎板切除明显改变颈椎前凸曲度，使颈椎正常生理性前凸转变为后凸；颈椎椎间盘、韧带弹性模量增加将抑制全椎板切除后颈椎后凸曲度形成。     

距骨缺血性坏死的有限元分析(英文)

背景:对距骨缺血性坏死的具体临床治疗,目前仍有很大争议。目的:观察不同程度距骨坏死时,距骨滑车关节面上的应力及其分布变化。方法:利用8具踝关节标本建立踝关节三维有限元模型,通过改变各模型距骨坏死的体积分析距骨滑车关节面压应力与其分布的变化规律,计算出距骨缺血性坏死可能诱发踝足创伤性关节炎或出现距骨塌陷的临界坏死体积。结果与结论:实验成功建立了踝关节三维有限元模型。分析发现距骨内、外侧坏死程度比较小时,距骨滑车关节面应力分布变化不大;当内侧距骨坏死体积达到(26.6±1.5)%,外侧距骨坏死体积达到(35.0±2.5)%时,距骨坏死组织与正常骨组织边界区域出现应力集中的现象,其应力区域呈不规则形,提示,此时诱发踝足创伤性关节炎或发生距骨体塌陷的危险性很高,应手术治疗。