胸腰椎三维非线性有限元模型的建立

目的 为胸腰椎的生物力学有限元分析研究建立有效的T11～L3节段的三维非线性有限元模型.方法 将健康成人自T11～L3节段脊柱的CT扫描图像,以DICOM格式导入软件Simpleware2.0,生成三角网格模型.利用软件Geomgic8对模型进行修复和优化后生成实体模型,导入有限元软件Abaqus6.9中,骨性结构均采用C3D8单元;椎间盘由髓核和纤维环组成,髓核由5层8节点实体单元组成,纤维环有8层相互交叉胶原纤维层组成,髓核与纤维环采用C3D8RH单元进行网格划分,胶原纤维采用TRUSS单元;赋予所有韧带1 mm的厚度,通过S4R壳单元模拟了前纵韧带、后纵韧带、黄韧带、棘上韧带、棘间韧带、横突间韧带,采用S3R壳单元模拟小关节囊韧带.赋予椎间盘超弹性、骨性结构弹塑性及韧带黏弹性材料属性.并通过验证模型的几何相似性和椎间盘的载荷-位移变化以及冲击暴力下的应力分布情况,验证模型的有效性.结果 建立了胸腰椎(T11～L3)的三维有限元模型,共包含71 939个节点和78 887个单元.本模型几何相似性好;与体外实验在相同条件下得到的椎间盘载荷-位移曲线图结果非常相近;在动态冲击实验下观察应力云图,椎体皮质骨、后部结构及松质骨的应力分布规律和其他实验一致.结论 建立的具有六面体网格的、非线性模型的完整胸腰椎(T12～L1)有限元模型,可进行冲击实验并进行动态分析,为下一步进行胸腰椎生物力学研究提供了有效的三维有限元模型.

Abstract：

Objective To build an effective nonlinear three-dimensional finite-element (FE) model of T11 - L3 segments for a further biomechanical study of thoracolumbar spine. Methods The CT ( computed tomography) scan images of healthy adult T11 - L3 segments were imported into software Simpleware 2. 0 to generate a triangular mesh model. Using software Geomagic 8 for model repair and optimization, a solid model was generated into the finite element software Abaqus 6. 9. The reasonable element C3D8 was selected for bone structures. Created between bony endplates, the intervertebral disc was subdivided into nucleus pulposus and annulus fibrosus (44% nucleus, 56% annulus). The nucleus was filled with 5 layers of 8-node solid elements and annulus reinforced by 8 crisscross collagenous fiber layers. The nucleus and annulus were meshed by C3D8RH while the collagen fibers meshed by two node-truss elements. The anterior (ALL) and posterior (PLL) longitudinal ligaments, flavum (FL), supraspinous (SSL), interspinous (ISL) and intertransverse (ITL) ligaments were modeled with S4R shell elements while capsular ligament (GL) was modeled with 3-node shell element. All surrounding ligaments were represented by envelops of 1 mm uniform thickness. The discs and bone structures were modeled with hyper-elastic and elasto-plastic material laws respectively while the ligaments governed by visco-elastic material law. The nonlinear three-dimensional finite-element model of T11 - L3 segments was generated and its efficacy verified through validating the geometric similarity and disc load-displacement and stress distribution under the impact of violence. Using ABAQUS/EXPLICIT 6. 9 the explicit dynamic finite element solver, the impact test was simulated in vitro. Results In this study, a 3-demensional, nonlinear FE model including 5 vertebrae, 4 intervertebral discs and 7 ligaments consisted of 78 887 elements and 71 939 nodes. The model had good geometric similarity under the same conditions. The results of FEM intervertebral disc load-displacement curve were similar to those of in vitro test. The stress distribution results of vertebral cortical bone, posterior complex and cancellous bone were similar to those of other static experiments in a dynamic impact test under the observation of stress cloud. Conclusion With the advantages of high geometric and mechanical similarity and complete thoracolumbar, hexahedral meshes, nonlinear finite element model may facilitate the impact loading test for a further dynamic analysis of injury mechanism for thoracolumbar burst fracture.

Building an effective nonlinear three-dimensional finite-element model of human thoracolumbar spine

Objective To build an effective nonlinear three-dimensional finite-element (FE) model of T11 - L3 segments for a further biomechanical study of thoracolumbar spine. Methods The CT ( computed tomography) scan images of healthy adult T11 - L3 segments were imported into software Simpleware 2. 0 to generate a triangular mesh model. Using software Geomagic 8 for model repair and optimization, a solid model was generated into the finite element software Abaqus 6. 9. The reasonable element C3D8 was selected for bone structures. Created between bony endplates, the intervertebral disc was subdivided into nucleus pulposus and annulus fibrosus (44% nucleus, 56% annulus). The nucleus was filled with 5 layers of 8-node solid elements and annulus reinforced by 8 crisscross collagenous fiber layers. The nucleus and annulus were meshed by C3D8RH while the collagen fibers meshed by two node-truss elements. The anterior (ALL) and posterior (PLL) longitudinal ligaments, flavum (FL), supraspinous (SSL), interspinous (ISL) and intertransverse (ITL) ligaments were modeled with S4R shell elements while capsular ligament (GL) was modeled with 3-node shell element. All surrounding ligaments were represented by envelops of 1 mm uniform thickness. The discs and bone structures were modeled with hyper-elastic and elasto-plastic material laws respectively while the ligaments governed by visco-elastic material law. The nonlinear three-dimensional finite-element model of T11 - L3 segments was generated and its efficacy verified through validating the geometric similarity and disc load-displacement and stress distribution under the impact of violence. Using ABAQUS/EXPLICIT 6. 9 the explicit dynamic finite element solver, the impact test was simulated in vitro. Results In this study, a 3-demensional, nonlinear FE model including 5 vertebrae, 4 intervertebral discs and 7 ligaments consisted of 78 887 elements and 71 939 nodes. The model had good geometric similarity under the same conditions. The results of FEM intervertebral disc load-displacement curve were similar to those of in vitro test. The stress distribution results of vertebral cortical bone, posterior complex and cancellous bone were similar to those of other static experiments in a dynamic impact test under the observation of stress cloud. Conclusion With the advantages of high geometric and mechanical similarity and complete thoracolumbar, hexahedral meshes, nonlinear finite element model may facilitate the impact loading test for a further dynamic analysis of injury mechanism for thoracolumbar burst fracture.