【作者】 李劲松；

【导师】 张宏其；

【作者基本信息】 中南大学 ， 临床医学， 2013， 博士

【摘要】 本研究应用CAE (Computer aid engineering)软件建立了腰椎运动节段的有限元模型,通过3组模型各种工况结果的对比,探索出最佳建模方案；运用最佳建模方案建立了6例Lenkel型特发性脊柱侧凸有限元模型,并对模型有效性进行了验证；在证实仿真有效的6例有限元模型上模拟了后路侧凸矫形脊柱,并对每一椎弓根螺钉应力分布进行了测算；通过对椎弓根应力分布分析推算出“关键椎”节段,二次建模后模拟了“关键椎”置钉方案的后路矫形,并与实际手术结果进行了对比研究。第一章有限元单元类型和局部形态对脊柱模型生物力学仿真度的影响目的应用CAE软件建立了3组L4-5运动节段三维有限元模型,通过各种工况模拟探索较优的建模方式。方法一例Lenkel型特发性脊柱侧凸患者作为研究对象,取其L4-5节段CT图像,以Dicom格式输入Mimics10.01,建立包括椎间盘、所有附属韧带在内的腰椎运动单元(FSU, Function spinal unit)。在此基础上作前屈、后伸、扭转、侧弯、压缩以及拉伸等工况模拟,所得结果与经典体外实验数据对比,分析得出最佳建模方式。结果成功建立3组L4-5脊柱FSU,每组有限元模型包括两个椎体、一个椎间盘以及所有韧带组织。分析各种工况模拟位移云图、力-位移曲线和力矩-角度曲线发现模型A与体外实验数据吻合度最高。结论分别采用四面体单元构建椎体和六面体单元构建椎间盘结构的有限元模型仿真模拟人体脊柱运动单元生物力学特性较佳,此方法可以用于后续脊柱侧凸有限元模型的建立。第二章青少年特发性脊柱侧凸有限元模型的建立和有效性验证目的建立青少年特发性脊柱侧凸有限元模型并对其有效性进行验证方法选择1例青少年特发性脊柱侧凸志愿者作为研究对象。仰卧位下进行CT从C7至尾骨的连续扫描,获得Dicom格式CT图像616张。导入逆向工程软件MIMICS10.01,建立完整的有限元几何模型。经过几何清理、网格划分、材料赋值生成三维有限元模型。分别进行分段加载验证和整体活动验证。分段验证：取T10-T11, T11-L1以及L1-S1三个节段,分别参照体外实验对模型进行加载模拟,并与体外实验结果比对验证模型的有效性；整体验证：模拟悬吊位、仰卧左右Bending位、支点加压位,测量测量各椎体质心与骶骨中垂线的距离,并与X线片测量结果对照以验证模型有效性。结果建立了完整的LenkelBN型特发性脊柱侧凸有限元模型。共采用5种单元类型。14种材料属性,共划分节点214429个,建立Combin单元7778个；Shell单元259226个；四面体单元749910个,六面体单元16306个。分段加载验证：10-T11,T11-L1以及L1-S1三个节段与体外实验结果基本吻合。整体验证：悬吊位、左右Bending位以及支点加压位有限元模型与X线片侧凸角度测量值误差率为8.1%。有限元模型模拟悬吊位、左右Bending位以及支点加压位与X线片椎体质心与CSVL距离无显著性差异。结论从有限元模型的几何外形、分段验证试验、悬吊位、左右Bending位以及支点加压位等整体验证实验,验证了建模的可靠性和有效性。为后续建立多例脊柱侧凸有限元模型及矫形模拟奠定了基础。第三章有限元法模拟脊柱后路矫形技术及椎弓根螺钉应力分布研究目的利用前述方法建立6例青少年脊柱侧凸有限元模型,模拟后路矫形手术并测算椎弓根钉应力分布。方法采用第二章所用方法建立了6例Lenke1型青少年特发性脊柱侧凸有限元模型。应用建立的有限元模型进行脊柱侧凸全节段置钉方案后路矫形模拟,并分析了椎弓根螺钉应力分布情况。结果6例模型均顺利完成了模拟矫形。上固端定椎均为T4,2例以L3为下端固定椎,3例以L2为下固定椎,1例以L1为下固定椎。冠状面上胸弯平均Cobb角由22.8°矫正至8°；主胸弯由41.6°矫正至10°；腰弯由28.5°矫正至8.5°,平均矫形率分别为：64.9%、75.9%、70.1%°矫形术后胸椎后凸由平均19.7°增大21.8°；术前腰椎前凸角由平均34.3°减小32.8°。矫形后椎弓螺根应力分布特点为：两端椎区域和顶椎区域螺钉应力最大,顶椎区域凸侧螺钉应力较凹侧大结论有限元法能有效模拟脊柱侧凸后路矫形手术过程。通过分析矫形椎弓根螺钉应力分布特点,为下一步探索选择性置钉方案提供了有效途径。第四章有限元法应力分析选择关键椎在脊柱侧凸矫形手术中的应用目的探讨有限元法应力分析选择关键椎置钉方案在脊柱侧凸矫形策略制定的有效性。方法通过分析全节段置钉方案矫形后椎弓根螺钉应力分布特点,将表面应力最大值小于1Gpa的椎弓根螺钉予以去除后二次建模,重新建立6例“关键椎”置钉的侧凸有限元模型并重新模拟前述后路矫形过程。测量“全节段”置钉方案与“关键椎”置钉方案的侧凸参数。比较“关键椎”置钉方案与实际手术置钉方案之间差异。比较两种有限元模拟矫形效果与实际手术效果。结果“关键椎”置钉方案矫形效果与“全节段置钉”矫形效果无明显差异。“关键椎”置钉方案矫形效果与实际术后矫形效果对比同样无明显差异。有限元模型应力分析得出的“关键椎”置钉方案内固定使用总体数量少于实际手术方案。结论有限元法分析选择关键椎置钉方案辅助制定脊柱侧凸矫形策略是一种新型有效的方法,可为外科医生制定和优化脊柱侧凸矫形策略提供指导意见。更多还原

【Abstract】 In this study, computer aid engineering (CAE) soft was used to establish finite element model(FEM) of the lumbar function spinal unite (FSU), and compared three different models under several behaviour of the FSU to find out the best modeling method. Then use the optimized modeling method to construct six FEMs of the adolescent idiopathic scoliosis (AIS) and validated the final model. On the basis, we simulated the main steps of the posterior correction surgery using the FEMs and An inverse method based on Finite Element Analysis was used to apply forces to the implant screw model such that it was deformed the same after surgery. Then compared the effective of the Key-segmental instrumentation techniques and all segmental pedicle screws strategy.Chapter One Influence of Element Type and Geometry on the Biomechanical Behavior of a Functional Spinal UnitObjective The CAE soft was used to construct3a functional spinal unit (FSU) L4-L5using a specimen-specific finite element model. The aim of this study was to determine the better element type for each anatomical structure.Methods A female adolescent idiopathic scoliosis patient was includes as object of the study. CT imagines of the L4-L5were imported into MIMICS10.01to create the FEMs.3different types of FEMS was performed using reported in vitro data on the mechanical response of an intact lumbar functional unit and its successive reduced stages after the dissection of ligaments, facet joints, vertebral arch and nucleus pulposus. The loading conditions in the study were pure moments in flexion, extension, lateral bending and axial rotation.Results An intact lumbar functional unit was built successfully in three different modeling methods which named model A, B and C. All of the models were subjected to pure moments and forces in the three anatomical planes. For each of the loading scenarios, with and without vertical and follower preload, the presented model A provides results in closest agreement with the most accepted literature. Conclusions Tetrahedron element to build the vertebrae and hexahedral element to create the intervertebral disk was the best modeling method.Chapter Two Establishment and Validation Study of Finite Element Model of Adolescent Idiopathic ScoliosisObjective To build three-dimensional finite element model of adolescent idiopathic scoliosis and to validate the model.Methods In this study, a patient with adolescent idiopathic scoliosis was included as a volunteer. CT transverse scanning was done in supine position from C7to caudal end, and obtained616CT Dicom images. All CT images were imported into Mimics10.01to form qualified three-dimensional geometry model after geometry clean, initial division of shell, mesh partition and assignment of material parameters. To verify the validity of the model, the view of the model ande linieal X-ray films were being compared, and spinal segments (TI0-T11, T11-L1and L1-S1) extracted from the whole finite element model were constrained and loaded respectively referring to historical specimen biomechanical in vitro studies. Compare the results of simulation of the model with the hanging posterior-anterior X-ray, lateral flexion X-ray and fulcrum bending X-ray. Comparing the vertical distance between each barycenter and CSVL of model and X-ray for biomechanical validation.Results A finite element model of Lenkel1BN adolescent idiopathic scoliosis was built, using five mesh types and14kinds of material parameters, in consist of214429nodes,7778combin element,259226shell elements,749910tetrahedron elements and hexahedron elements. The segmental simulations were similar to their references respectively. Though the parameter comparing, we got the individual FEM whose simulation results had no significant statistical difference to the dates of clinical radiographic film (P>0.05).Conclusions The finite element model was built and well validated by geometry appearance, segmental validation and hanging test, lateral bending test, and fulcrum bending test validation which provided an effective way for further biomechanical research. Chapter Three Finite Element Model Simulation of Posterior Surgical Correction of Adolescent Idiopathic Scoliosis and Analysis of Corrective Force of the ImplantObjective Using the method stated above to create six FEMs of adolescent idiopathic scoliosis, and to simulate posterior correction surgery and investigate the corrective force of the pedicle screw.Methods Six FEMs were built to simulate the posterior correction surgery with all-segmental instrumentation strategy. Then the corrective force of each screw was analysised by CAE soft.Results Six FEMs successfully completed the simulation of posterior correction surgery. The upper instrumentation vertebra was selected to T4in all of the FEMs, and the lowest instrumentation vertebra was to L3in2models, L2in3models and L1in one model. The mean Cobb’s angles of proximal curve, main thoracic curve, lumbar cure, T5-12sagittal kyphosis and L1-5lordosis pro-correction and post-correction simulation were22.8°to8,41.6°to10°,28.5°to8.5°,19.7°to21.8°,34.3°to32.8°, respectively. The corrective force located at the convex and the end instrumentation segment were significant greater than the rest concave area.Conclusions The FEMs can effectively simulate the correction procedure and provide a new way to optimize the fixation strategy by corrective force analysis.Chapter Four Application of Finite element analysis of corrective force in the determination of Key-segment for Surgical Correction of Adolescent Idiopathic ScoliosisObjective To investigate the effective of finite element analysis of corrective force in the determination of Key-segment for surgical correction of adolescent idiopathic scoliosis.Methods Wipe out the pedicle screw which force under lGpa thought the finite element analysis and recreate six FEMs with Key-segment fixation. Simulated the posterior surgical correction again with the secondary finite element models. Measured the Cobb angles and compare the parameter with postoperative X-ray.Results The correction rate of the Key-segment fixation strategy has no significant difference with the all-segment instrumentation strategy, and there was no significant difference when compare to the practical postoperative X-ray. The mount of implants were less than the clinical date.Conclusions The finite element analysis is an effective method in determination of Key-segmental instrumentation. In the future, it can offer an essential guide to assist surgeons during preoperative planning of surgical instrumentation in adolescent idiopathic scoliosis.更多还原