胸腰段椎体骨折后路内固定术后伤椎骨缺损的生物力学有限元分析

发布时间：2019-06-17 12:30

【摘要】：目的:对胸腰椎骨折术后出现伤椎终板塌陷的病人,建立有限元模型对该类患者是否适合取出内固定进行生物力学分析。方法:(1)实验对象:招募男性志愿者一名,通过病史询问及X线等影像学检查,脊柱无畸形、无外伤、无肿瘤等其他脊柱病变。(2)资料采集设备:志愿者取自然状态平卧位,自Ti1-I3椎体行水平薄层扫描,获得144张相应节段水平截图。扫描的数据资料以DICOM格式导出,并刻录光盘储存,以便于Mimics15.0医学图像处理软件处理图像数据。(3)建立Ti1-L3的胸腰椎三维有限元模型:将数据导入到Mimics15.0医学图像处理软件中,利用Draw Profile Line及Thresholding功能,将图像阈值调节为462-2676HU,使腰椎各部分的界限更清楚。利用区域增长可将上述蒙版上彼此不相连的分割区域形成一个新的蒙版。利用Region Growing功能可粗略提取感兴趣的腰椎各个节段。利用软件的三维空间建模功能,将经过断层图像处理后的数据进行三维模型建模,建立各个椎体的,独立的三维表面骨骼模型。为了使模型更加真实平滑,对各个模型分别设定适当的参数,从而更加清楚直观的地再现胸腰段椎体骨结构的三维立体形态。由此建立的三维图像,可以在软件中进行垂直压缩、左右平移及旋转,可以对脊柱功能进行全方位的演示。还可根据研究的实际情况,对不需要的功能进行隐藏、删除,增加、合并需要的功能以获得不同的外观和效果。SolidWorks软件包含网格处理向导及曲面生成向导功能,利用这两个功能可以将各椎体的点云文件生成实体零件,处理过程包括对模型进行除噪点、平滑、曲面拟合等,同时使用草图功能绘制钉棒系统的轮廓图,并使用拉伸、旋转等功能获得钉棒系统的实体模型,然后使用工程图精确定位装配模型。将SolidWorks软件中建立的装配体导入HyperMesh软件,利用HyperMesh软件强大的网格制作及剖分功能,将装配体网格化,同时构建皮质骨,设定厚度1mm,四面体网格划分尺寸分别为:腰3-腰5为2mm,骶1为3mm,钉棒系统为1mm。按照解剖部位和形态,补充胸腰段各附属解剖结构,如终板、纤维环、髓核、关节突软骨,用Truss单元模拟椎体间存在的7种不同的韧带结构,包括前纵韧带、后纵韧带、横突间韧带、棘上韧带、棘间韧带、黄韧带、关节囊韧带等结构,以及上下关节突,软骨等结构,获得胸11-腰3的三维有限元模型,该模型具有147064单元和39157个节点组成。(4)验证模型的有效性及精确度:本模型中各项材料赋值是根据国内外医学者公认的文献赋值,并且运算加载的数据参数也是根据最新的研究成果来设定的。本实验采用网格划分功能较强的Hypermesh软件来划分网格,提高了网格的质量,并采用了自适应能力强的C3D4四面体单元,能够在可接受的时间内运算出精确的结果。5、建立伤椎缺损椎体模型:建立5种伤椎上终板的骨缺损模型,缺损体积设定为占伤椎前柱体积的1/5、2/5、3/5、4/5、5/5。分别对装配内固定及取出内固定的5种模型施加各类载荷,对其受力情况进行生物力学分析,统计数据做图表及趋势图分析。结果:从正常椎体受力云图中我们可以发现,垂直状态下椎体前2/3及椎体终板的后部及近椎弓根处是正常椎体的应力集中区,并向后外侧呈放射状分布;很明显皮质骨尤其是椎体前缘所受应力高于松质骨;当椎体前后及侧向屈伸运动时,屈侧及伸侧以及椎弓根附近均出现应力集中现象。在打入钉棒系统的模型中,5种上终板塌陷(缺损体积分别为椎体前柱的1/5、2/5、3/5、4/5、5/5)模型,在垂直、前后屈、侧屈、左右旋转下的应力分布图可以看出,植入内固定后,随着伤椎缺损体积不断增大,应力也相应增大,且随着伤椎上终板塌陷及前柱骨缺损体积逐渐增大,应力逐渐向内固定集中。而取出内固定后,5种上终板塌陷模型的受力图显示随着内固定的取出,失去了内固定的支持后,随着缺损体积的增加,应力逐渐变大。从点线图中可以看出,取出内固定后在应力逐渐增加的趋势下,随着缺损体积的增加,当缺损体积达到伤椎前柱4/5并继续增加时,E组(4/5缺损组→5/5缺损组应力差)伤椎所承受的7种工况的综合应力增加幅度最大。意味着此时伤椎对载荷承载能力显著下降,增加的集中应力将导致伤椎前柱再次骨折。此时取出内固定,塌陷的伤椎不足以维持稳定性,增加的生物力学应力有导致其出现继续压缩甚至再次骨折的风险。结论:通过有限元法模拟伤椎上终板塌陷,计算分析随缺损体积变化的伤椎应力改变,当缺损体积达到伤椎前柱4/5并继续增加时,伤椎所承受的7种工况的综合应力增加幅度最大。意味着此时伤椎对载荷承载能力显著下降,增加的集中应力将导致伤椎前柱再次骨折。此时取出内固定,塌陷的伤椎不足以维持稳定性,增加的生物力学应力有导致其出现继续压缩甚至再次骨折的风险,而当缺损体积达到前柱3/5时,就应慎重考虑内固定的取出,但此现象及临床治疗仍需进一步的研究。
[Abstract]:Objective: To establish a finite element model for the biomechanical analysis of the patients with the collapse of the vertebral endplates after the fracture of the thoracolumbar fracture. Methods: (1) Experimental subjects: one of male volunteers was recruited, including medical history, X-ray and other imaging examinations, and there were no other spinal diseases such as spinal deformity, no trauma, and no tumor. (2) Data acquisition equipment: volunteers take the natural state horizontal position, and scan the horizontal thin layer from the Ti1-I3 vertebral body to obtain the horizontal screenshot of 144 corresponding sections. The scanned data is derived in a dicom format and is recorded on an optical disc for processing the image data in the mmoics15.0 medical image processing software. (3) The three-dimensional finite element model of the thoracic and lumbar spine of Ti1-L3 was established: the data was introduced into the Mimics5.0 medical image processing software, the image threshold was adjusted to 462-2676 HU by the Draw Profile Line and the Thresholding function, and the limit of each part of the lumbar vertebra was more clear. A new mask can be formed using the region growth to form a segmented region on the mask that are not connected to each other. Use the Region Growing feature to roughly extract the various segments of the lumbar region of interest. And the three-dimensional space modeling function of the software is utilized, and the data subjected to the fault image processing is modeled by a three-dimensional model, and the independent three-dimensional surface skeleton model of each vertebral body is established. In order to make the model more real and smooth, the appropriate parameters are set for each model, so that the three-dimensional three-dimensional shape of the bone structure of the thoracolumbar vertebral body is more clearly and intuitively reproduced. The three-dimensional image thus established can be vertically compressed in the software, the left and right translation and the rotation can be performed in a comprehensive manner on the functions of the spine. It is also possible to hide, delete, add, and merge the required functions to obtain different appearance and effect according to the actual situation of the study. The SolidWorks software includes a grid processing wizard and a surface generation wizard function, and the two functions can be used to generate a solid part of a point cloud file of each vertebral body. The processing method comprises the following steps of: performing noise elimination, smoothing, surface fitting and the like on the model, and simultaneously using a sketch function to draw a contour map of the nail rod system, And using the functions of stretching, rotation and the like to obtain the solid model of the nail rod system, and then using the engineering drawing to accurately position the assembly model. The assembly body established in the SolidWorks software is introduced into the HyperMesh software, and the assembly body is meshed with the powerful mesh generation and division function of the HyperMesh software, and the cortical bone is constructed at the same time, the thickness is 1mm, and the division sizes of the tetrahedron mesh are respectively: the waist 3-waist 5 is 2 mm, the thickness 1 is 3 mm, and the nail rod system is 1 mm. According to the anatomical location and morphology, the accessory anatomical structures of the thoracolumbar segment, such as the endplates, the fiber rings, the nucleus pulposus and the articular cartilage, are used to simulate the 7 different ligament structures present between the vertebral bodies, including the anterior longitudinal ligament, the posterior longitudinal ligament, the transverse interspinous ligament, the spinous ligament, the interspinous ligament, The structure of the ligamentum flavum, the joint capsule and the like, as well as the structure of the upper and lower articular processes, the cartilage and the like, is used to obtain a three-dimensional finite element model of the chest 11-waist 3, and the model is composed of a 147064 cell and a 39157 nodes. (4) The effectiveness and accuracy of the verification model: the assignment of the materials in the model is based on the document assignment accepted by the Chinese and foreign medical personnel, and the data parameters for operation and loading are also set according to the latest research results. In this experiment, the mesh is divided by the Hypermesh software with strong grid division function, the quality of the grid is improved, and the C3D4 tetrahedral unit with strong self-adaptive capacity is adopted, and the accurate result can be calculated in the acceptable time. The defect volume was set to 1/5,2/5,3/5,4/5,5/5 of the volume of the prevertebral column. All kinds of loads are applied to the five models fixed and removed in the assembly, and the mechanical analysis, the statistical data and the trend chart of the five models are analyzed. Results: From the stress cloud of the normal vertebral body, we can find that the anterior 2/3 of the vertebral body and the posterior and proximal pedicle of the vertebral endplates of the vertebral body in the vertical state are the stress concentration area of the normal vertebral body, and are radially distributed to the posterior lateral side; the stress of the cortical bone, especially the leading edge of the vertebral body, is higher than that of the cancellous bone; There was a stress concentration around the flexion and extension side as well as the pedicle of the vertebral body when the vertebral body and the lateral flexion and extension movement. In the model of driving the nail rod system,5 upper end plates collapsed (1/5,2/5,3/5,4/5,5/5) of the anterior column of the vertebral body respectively, and the stress distribution in the vertical, anterior and posterior flexion, lateral flexion and left and right rotation can be seen. The stress is also increased correspondingly, and as the vertebral endplates collapse and the volume of the bone defect of the anterior column gradually increases, the stress is gradually concentrated to the inner fixation. After taking out the internal fixation, the stress of the five upper end-plate collapse models showed that with the removal of the internal fixation, the stress was gradually increased with the increase of the volume of the defect. it can be seen from the point chart that, with the increasing of the volume of the defect after the internal fixation is taken out, as the volume of the defect reaches 4/5 of the pre-vertebral column and continues to increase, In group E (4/5 defect group,5/5 defect group, the stress difference of 5/5 defect group) was the largest in 7 working conditions. This means that the load carrying capacity of the injured vertebra is significantly reduced at this time, and the increased concentrated stress will result in the fracture of the anterior column of the injured vertebra. In this case, the internal fixation, the collapse of the injured vertebra is not sufficient to maintain stability, and the increased biomechanical stress has the risk of continued compression or even further fracture. Conclusion: The deformation of the upper end plate of the injured vertebral body is simulated by the finite element method, and the stress change of the injured vertebral body with the change of the volume of the defect is calculated. When the volume of the defect reaches 4/5 of the prevertebral column and continues to increase, the combined stress of the 7 working conditions that the injured vertebra is subjected to is the largest. This means that the load carrying capacity of the injured vertebra is significantly reduced at this time, and the increased concentrated stress will result in the fracture of the anterior column of the injured vertebra. At this time, the internal fixation is taken out, the collapsed injured vertebra is not enough to maintain the stability, the increased biomechanical stress can lead to the risk of continuing to compress or even fracture again, and when the defect volume reaches 3/5 of the front column, the taking out of the internal fixation should be carefully considered, However, this phenomenon and clinical treatment still need to be further studied.
【学位授予单位】：扬州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：R687.3

【参考文献】