颈枕部三维非线性有限元模型的有效性验证

背景：人体组织属性主要表现为非线性，颈枕部的生物力学特点更易受软组织材料属性变化的影响，因此建立非线性有限元模型与人体真实属性更接近。目的：构建正常成人颈枕部三维非线性有限元模型并验证其有效性。方法：利用MarConi MX8000多层螺旋CT对健康成人进行颅底-C₃段扫描，获取二维图像。直接读入Dicom格式原始图像，图像分割，数据光顺，三维重建后生成颅底-C₃节段脊柱三维实体模型；将此模型导入ScanFE模块，进行体网格划分；在ANSYS 10.0软件中直接导入以上三维模型，构建颅底-C₃段内韧带单元，模拟韧带力-位移曲线，建立完成颅底-C3段的三维非线性有限元模型。垂直向下方向施加40 N预载荷，1.5 N•m力矩模拟前屈、后伸、侧屈及旋转运动，对比分析实验结果，判断模型应力分布与临床相符度。结果与结论：构建的三维非线性有限元模型包括663 551个单元，178 247个节点。施加预载荷及1.5 N•m力矩后，寰枕关节运动范围为前屈13.3°、后伸11.9°、侧屈4.3°、旋转8.7°；寰枢关节运动范围为前屈15.5°、后伸12.6°，侧屈6.4°、旋转30.8°，与尸体标本实验结果相符。从整个模型的纵向应力分布看，在任何相对位置状态下，枢椎齿状突后方的应力均较高，后伸位时应力增高区域加大。上颈椎的应力主要集中于椎管周围，寰椎侧块两端及枢椎横突的应力则较小。对比研究发现，在不同相对工况下前屈、后伸、侧屈、旋转时C₂-C₃小关节应力均大于钩椎关节，颈枕部三维非线性有限元模型的应力分布特点符合临床实际情况。结果提示应用多层螺旋CT扫描得到的二维图像及simple ware、Ansys10.0软件，建立的颈枕部三维非线性有限元模型符合人体真实的运动规律，可以很好地模拟颈枕部的生物力学特性。

Effectivity of cervical three-dimensional nonlinear finite element model

BACKGROUND:The human tissue exhibits nonlinear property, and the cervical biomechanical characteristics are closely related with the changes of soft tissue material properties. So it is important to establish the nonlinear finite element model that close to the actual property of the human body. OBJECTIVE:To establish cervical three-dimensional nonlinear finite element model and to verify the effectivity of the model.              METHODS:The C₀-C₃ spine was scanned by MarConi MX8000 multislice spiral CT machine to obtain the two-dimensional image. The images were read with Dicom format, and then the accurate C₀-C₃ cervical three-dimensional model was established after image segmentation, data fairing and three-dimensional reconstruction. The model was imported to the ScanFE mode for meshing. Then the model was imported into the ANSYS 10.0 software directly to construct the C₀-C₃ cervical ligament elements and simulate the force-displacement curve, and thus the cervical three-dimensional nonlinear finite element model was established. After model establishment, 40 N preload was loaded on the vertically downward direction, and the flexion, extension, lateral bending and rotational motions were simulated with 1.5 N•m torque. The experimental results were compared to examine the stress distribution and clinical consistent degree. RESULTS AND CONCLUSION:The three-dimensional nonlinear finite element model included 663 551 elements and 178 247 nodes. After loaded with preload and 1.5 N•m torque, the range of motion for occipitoatlantal joint was flexion 13.3°, extension 11.9°, lateral bending 4.3° and rotation 8.7°, the range of motion of atlantoaxial joint was flexion 15.5°, extension 12.6°, lateral bending 6.4° and rotation 30.8°, which consistent with the experimental results of cadaver specimens. Observed from the longitudinal stress distribution of the model, the stress on the backside odontoid process of axis was higher in any condition, and when extension, the region for stress increasing was increased. The upper cervical spine stress distribution mainly located around the vertebral tunnel, while the stress distribution on both end of the lateral mass and the axial transverse process was lower. Comparative study showed that the stresses on C₂-C₃ joint in flexion, extension, lateral bending and rotation conditions were greater than those on the uncovertebral joint, and the stress distribution of three-dimensional nonlinear finite element model was consistent with the clinical condition. The cervical three-dimensional nonlinear finite element model established with the two-dimensional images, the simple ware and Ansys10.0 software that obtained through multislice spiral CT scan are consistent with the motion law of the human body.