Zeng Zhi-Li, Cheng Li-Ming, Zhu Rui, Wang Jian-Jie, Yu Yan
Department of Orthopedic Surgery, Shanghai Tongji Hospital, Tongji University School of Medicine, Shanghai 200065, China.
Zhonghua Yi Xue Za Zhi. 2011 Aug 23;91(31):2176-80.
To build an effective nonlinear three-dimensional finite-element (FE) model of T(11)-L(3) segments for a further biomechanical study of thoracolumbar spine.
The CT (computed tomography) scan images of healthy adult T(11)-L(3) 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 (CL) was modeled with 3-node shell element. All surrounding ligaments were represented by envelope 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 T(11)-L(3) 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.
In this study, a 3-dimensional, 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.
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.
构建有效的T11 - L3节段非线性三维有限元（FE）模型，用于进一步的胸腰椎生物力学研究。
将健康成人T11 - L3节段的CT（计算机断层扫描）扫描图像导入Simpleware 2.0软件以生成三角形网格模型。使用Geomagic 8软件进行模型修复和优化，然后将实体模型导入有限元软件Abaqus 6.9。为骨结构选择合理的C3D8单元。在椎体终板之间创建椎间盘，将其细分为髓核和纤维环（44%为髓核，56%为纤维环）。髓核用5层8节点实体单元填充，纤维环由8层交叉的胶原纤维层加强。髓核和纤维环用C3D8RH单元划分网格，而胶原纤维用两节点桁架单元划分网格。前纵韧带（ALL）、后纵韧带（PLL）、黄韧带（FL）、棘上韧带（SSL）、棘间韧带（ISL）和横突间韧带（ITL）用S4R壳单元建模，而关节囊韧带（CL）用3节点壳单元建模。所有周围韧带均用1 mm均匀厚度的包络表示。椎间盘和骨结构分别用超弹性和弹塑性材料定律建模，而韧带用粘弹性材料定律控制。生成T11 - L3节段的非线性三维有限元模型，并通过验证几何相似性以及暴力冲击下椎间盘的载荷 - 位移和应力分布来验证其有效性。使用ABAQUS/EXPLICIT 6.9显式动态有限元求解器在体外模拟冲击试验。
在本研究中，一个包含5个椎体、4个椎间盘和7条韧带的三维非线性有限元模型由78887个单元和71939个节点组成。该模型在相同条件下具有良好的几何相似性。有限元椎间盘载荷 - 位移曲线结果与体外试验结果相似。在应力云图观察下的动态冲击试验中，椎体皮质骨、后柱复合体和松质骨的应力分布结果与其他静态实验结果相似。
非线性有限元模型具有高几何和力学相似性以及完整的胸腰椎六面体网格等优点，可能有助于进行冲击载荷试验，以进一步动态分析胸腰椎爆裂骨折的损伤机制。
