幼儿半椎体所致脊柱侧凸后路矫形三维有限元分析

发布时间：2018-08-04 19:40

【摘要】：目的：先天性脊柱侧凸是一种发病率高、严重影响患儿身心健康的疾病。尤其小年龄组脊柱侧凸畸形患儿胸廓发育差、心肺功能不全，具有畸形复杂严重、手术并发症发生率高、手术麻醉风险大的特点，一直是脊柱侧凸治疗领域的难题。这种畸形需要早期手术矫治，但又需最大程度地减少对脊柱生长发育的影响。所以矫形方式和椎体融合节段的选择是影响疗效和预后的关键因素。目前后路半椎体切除椎弓根螺钉内固定是主要的治疗方式。但是，因患儿畸形复杂、个体之间畸形变化差异很大，在矫形过程中，固定节段的选择主要根据医生的临床经验，其生物力学研究证据不足。所以易导致矫形欠佳、不满意或术后出现脊柱失代偿等并发症。基于此，本研究利用建立的幼儿半椎体所致脊柱侧凸（Congenital scoliosis）三维有限元模型（finite element model，FEM）模拟后路半椎体切除、椎弓根螺钉固定矫形手术，并比较选择不同固定节段的生物力学特点，从而为临床提供理论依据。方法： 1、获取图像：选取1名幼儿半椎体所致脊柱侧凸患儿，男性，2岁9个月，胸12为半椎体，体重14kg，身高90cm。取平卧位，行西门子64排螺旋CT从第二颈椎上缘至骶骨扫描，层厚1.25mm，层间距0mm，，扫描范围包括全部骨性结构及椎间盘。获得Dicom格式CT平扫图像470张，实际建模采用中间有效部位148张。 2、建立三维几何模型：将获得的Dicom格式图像，倒入逆向工程软件Mimics14.0中，对原始图像进行蒙版、分割、光滑等步骤生成胸椎、腰椎、椎间盘的初级三维模型。将模型的正侧位视图与临床正侧位X线片对比，并在模型上测量半椎体大小、体积、Cobb角等。 3、模拟后路矫形手术：对模型进行简易处理后导入3-Matic5.1处理软件中，进行模拟后路半椎体切除椎弓根螺钉内固定手术。术中先行打入椎弓根螺钉，再行切除十二胸椎半椎体，安装矫形棒，逐渐闭合T11和L1椎间隙，达到侧凸畸形的矫正。与术后X线相比矫形效果满意。 4、建立三维有限元模型：在3-Matic5.1中,将椎弓根螺钉和矫形棒以及椎骨、椎间盘装配，装配后整体进行网格划分。划分好后再次将先天性脊柱侧凸模型导入Mimics14.0中，设置模型各个组件的弹性模量、柏松比等相关参数，得到先天性脊柱侧凸三维有限元模型。 5、进行有限元分析：将已赋好材料属性、划分好网格的幼儿半椎体所致脊柱侧凸模型导入有限元分析软件ANSYS13.0中，对模型进行约束（于四组模型的底部进行约束，限定各个方向位移）、加载（最上面椎体上表面凹侧施加垂直向下的压力100N、200N、300N、400N、500、600N，凸侧施加垂直向上的压力100N、200N、300N、400N、500、600N）、求解，得到不同固定节段的等效应力云图和位移云图，并比较不同固定节段的应力和位移变化。结果： 1建立了幼儿半椎体所致脊柱侧凸三维有限元模型，包括胸椎、腰椎、椎间盘。共有105252个单元，185849个节点，其中胸椎模型2块，单元31576个、节点56105个；腰椎模型2块，单元37890个、节点67281个，椎间盘模型（髓核+纤维环）5块，单元11577个、节点21163个。 2幼儿半椎体所致脊柱侧凸有限元模型逼真的描绘了患儿脊柱的特点：幼儿脊柱椎体宽、略呈卵圆形；椎体高度明显高于椎间盘厚度；椎体滋养孔多，孔径较大；松质骨与密质骨相互包容，难以界定。模型于临床大体像、X线片脊柱曲线吻合。胸12半椎体体积为3793mm3，最大长径31.27mm，最大高度为15.13mm，术前Cobb角为40.2°。 3顺利完成后路半椎体切除、椎弓根螺钉内固定手术模拟。根据固定节段的不同，进行个体化分组，有T_(10)~L_1组(凹凸侧各3枚螺钉)，T_(11)~L_1组（凹凸侧各2枚螺钉）、T_(11)~L_2组（凹凸侧各3枚螺钉）、T_(10)~L_2组（凹凸侧各4枚螺钉），术后矫形效果均达到100%。 4软件ANSYS13.0分析得出四种固定方案下模型的等效应力（Equivalent Stress）分布图、位移云图和安全系数云图。从图中看出，随着加载力值的逐渐增加(10~4N)，模型的位移云图图形、应力云图图形基本无变化，而各云图区域所代表的值，呈线性增长。四组固定方案的等效应力云图显示，最大等效应力主要集中在椎弓根螺钉钉头与螺钉体、椎弓根螺钉与矫形杆、椎弓根螺钉与椎弓根交界处。四组固定方案的位移云图显示，其最大位移均在每一组的最上面椎体，并向下呈依次减小趋势。 5在四组模型顶部凹侧施加垂直向下的压力300N，凸侧施加垂直向上的压力300N时，四组矫形方案T_(10)~L_1组、T_(11)~L_1组、T_(10)~L_2组、T_(11)~L_2组的最大等效应力值分别为：52.552Mpa、59.422Mpa、55.215Mpa、59.624Mpa；四组脊柱模型凸侧所受的等效应力明显大于凹侧，约3-6倍；模型凸侧的最上面和最下面椎体所受作用力较大，中间作用力相对较小。在四组矫形方案中，T_(11)~L_1组椎弓根螺钉所受作用力最大，向头端或尾端各延长一个固定节段，椎弓根螺钉的受力降低，如T_(10)~L_1组、T_(11)~L_2组。但向头端或尾端再延长一个固定节段，如T_(10)~L_2组，对椎弓根螺钉的受力无明显影响。在四组矫形方案的安全系数云图中，T_(11)~L_1组凸侧矫形杆最小安全系数的图像范围是其他三组的4-8倍，而最小安全系数的区域越大越易造成疲劳破坏。总之，T_(10)~L_1、T_(11)~L_2两组可作为较好的手术方案选择。结论： 1应用先进的计算机辅助工程软件Mimics14.0及ANSYS13.0，根据患儿CT图像，可成功建立幼儿半椎体所致脊柱侧凸三维有限元模型。应用该模型可成功的模拟脊柱侧凸的后路半椎体切除椎弓根螺钉内固定三维矫形手术。 2幼儿半椎体所致脊柱侧凸三维有限元模型可以在各种条件下进行应力变化分析和模拟手术研究，为幼儿半椎体所致脊柱侧凸疾病提供了良好的相关生物力学理论和临床研究，为制定脊柱侧凸患儿个性化手术方案提供了良好的生物力学研究基础。
[Abstract]:Objective: congenital scoliosis is a disease with high incidence and serious physical and mental health, especially in children with scoliosis, especially in children with scoliosis deformity, poor cardiopulmonary function, complex and serious malformation, high incidence of surgical complications and high risk of anesthesia, which has always been a difficult problem in the field of scoliosis treatment. Malformation requires early surgical correction, but it needs to minimize the effect on the growth and development of the spine. Therefore, the choice of orthopedic and vertebral fusion segments is the key factor affecting the curative effect and prognosis. In the process of orthopedics, the selection of fixed segments is mainly based on the clinical experience of doctors, and the evidence of biomechanics is insufficient. Therefore, it is easy to lead to poor correction, dissatisfaction, or postoperative complications such as spinal decompensation. Based on this, this study uses the established Congenital scol of the established children's hemivertebra. Iosis) the three-dimensional finite element model (finite element model, FEM) is used to simulate posterior hemi vertebral resection, pedicle screw fixation, and compare the biomechanical characteristics of different fixed segments, so as to provide a theoretical basis for clinical practice.
Method:
1, obtain images: 1 children with hemivertebra caused scoliosis, male, 2 years and 9 months, 12 hemivertebra, body weight 14kg, height 90cm. horizontal position, SIEMENS 64 row spiral CT from second cervical spine to sacral scan, thickness 1.25mm, interlayer space 0mm, scan range including all bone structure and intervertebral disc. Obtain Dicom format CT flat. 470 images were swept, and 148 effective parts were used in actual modeling.
2, a three-dimensional geometric model is established: the obtained Dicom format image is inverted into the reverse engineering software Mimics14.0, and the primary three-dimensional model of the thoracic vertebra, the lumbar vertebra and the intervertebral disc is generated by the mask, segmentation, and smoothness of the original image. The model's positive side view is compared with the clinical positive lateral X ray, and the size of the hemi vertebral body is measured on the model. Product, Cobb angle, etc.
3, simulated posterior orthopedic surgery: after simple treatment of the model, the 3-Matic5.1 treatment software was introduced into the simulated posterior hemivertebra resection with pedicle screw fixation. The pedicle screws were inserted before the operation, the twelve thoracic vertebrae were resected, the orthopedics was installed, the T11 and L1 intervertebral space were gradually closed, and the correction of scoliosis deformity was achieved. The orthopedic effect was satisfactory compared with the postoperative X-ray.
4, establish a three-dimensional finite element model: in 3-Matic5.1, the pedicle screws and orthopedics, vertebrae, and intervertebral discs are assembled, and the whole mesh is meshed. Then the model of congenital scoliosis is introduced into Mimics14.0 again, and the modulus of elasticity of each component of the model is set, and the related parameters such as pines ratio are obtained, and the congenital scoliosis is obtained. A convex three-dimensional finite element model.
5, the finite element analysis is carried out: the model of the scoliosis caused by the children's semi vertebral body is introduced into the finite element analysis software ANSYS13.0. The model is constrained (the bottom of the four groups of models is constrained, the displacement is limited in all directions), and the vertical downward pressure is imposed on the upper surface of the upper body (10). 0N, 200N, 300N, 400N, 500600N, the vertical upward pressure 100N, 200N, 300N, 400N, 500600N) are applied. The equivalent stress and displacement clouds of different fixed segments are obtained, and the stress and displacement changes of different fixed segments are compared.
Result:
1 a three-dimensional finite element model of scoliosis caused by children's hemivertebra was established, including the thoracic vertebra, the lumbar vertebra, and the intervertebral disc. There were 105252 units and 185849 nodes, including the thoracic vertebra model 2, the unit 31576, the node 56105, the lumbar model 2, the unit 37890, the node 67281, the disc model (nucleus pulposus + ring) 5, the unit 11577, node 21163. One.
2 the finite element model of scoliosis caused by the hemivertebra of young children vividly depicts the characteristics of the children's spine: the children's spine is wide and slightly oval; the height of the vertebral body is obviously higher than the thickness of the intervertebral disc; the vertebral foramen is more and the pore size is larger; the cancellous bone and the dense bone are mutually inclusive and difficult to define. The model is in the clinical general image, the X-ray curve of the spine curve. The volume of the chest 12 semi vertebral body is 3793mm3, the maximum length 31.27mm, the maximum height is 15.13mm, the preoperative Cobb angle is 40.2 degrees.
3 successfully completed posterior hemi vertebral resection and pedicle screw internal fixation. According to the different segments, individual groups were divided into group T_ (10) ~L_1 (3 screws on the concave and convex sides), T_ (11) ~L_1 group (2 screws in concave and convex sides), T_ (11) ~L_2 group (3 screws in concave and convex sides), and T_ (10) ~L_2 group (4 screws in concave and convex sides), and the postoperative orthopedic effect was all Reach 100%.
4 software ANSYS13.0 analysis obtained the equivalent stress (Equivalent Stress) distribution diagram, displacement cloud map and safety coefficient cloud chart under four fixed schemes. As we can see, as the loading force increases gradually (10~4N), the displacement cloud graph of the model, the base of the stress cloud graph are not changed, and the values represented by each cloud map are linearly increasing. The equivalent stress cloud chart of the four groups of fixed schemes showed that the maximum equivalent stress was mainly concentrated on the Shiumi Ne screw head and screw body, the Shiumi Ne screw and the orthopedics, the Shiumi Ne screw and Shiumi Ne junction. The displacement cloud chart of the four groups of fixed schemes showed that the maximum displacement was in the top vertebral body of each group, and the downward trend decreased in turn. Potential.
5 at the top concave side of the four groups, the vertical downward pressure 300N was applied and the vertical upward pressure was applied on the convex side. The four groups of orthopedic schemes T_ (10) ~L_1, T_ (11) ~L_1, T_ (10) ~L_2, and T_ (11) ~L_2 group were the equivalent stress of the 52.552Mpa, 59.422Mpa, and four spinal models. In the four groups of orthopedic schemes, the force of the T_ (11) ~L_1 pedicle screws was the largest, the head or tail was extended a fixed segment, and the force of the pedicle screw was reduced, such as the T_ (10) ~L_1 group, T_ (11) ~ (11). L_2 group. But a further extension of a fixed segment to the head or tail, such as the T_ (10) ~L_2 group, has no obvious effect on the force of the pedicle screw. In the safety factor cloud of the four groups of orthopedics, the image range of the minimum safety factor of the T_ (11) ~L_1 group is 4-8 times that of the other three groups, and the greater the area of the minimum safety factor, the more vulnerable to fatigue. In conclusion, T_ (10) ~L_1, T_ (11) ~L_2 two can be used as a better surgical option.
Conclusion:
1 with advanced computer aided engineering software Mimics14.0 and ANSYS13.0, a three-dimensional finite element model of scoliosis caused by children's hemivertebra can be successfully established according to the CT images of children. The model can be successfully used to simulate the posterior hemivertebra resection of the vertebral pedicle screw for three-dimensional orthopedic surgery.
2 the three-dimensional finite element model of scoliosis caused by children's hemivertebra can be analyzed and simulated under various conditions. It provides a good biomechanical theory and clinical study for the scoliosis caused by hemivertebra in children, and provides good biology for the formulation of the individualized operation scheme for scoliosis patients. The foundation of mechanics research.
【学位授予单位】：河北医科大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R726.8

【参考文献】