基于有限元法的下颈椎弓根螺钉人工椎体系统研究

Research on Artificial Vertebral Bodies System of Lower Cervical Pedicle Screws Based on Finite Element Method

本实验利用有限元法对下颈椎前路椎弓根螺钉人工椎体系统进行研究,采用有限元法对构建下颈椎的生物力学稳定性及应力情况进行分析,进而对椎弓根螺钉进行优化设计,为临床医用提供进一步的理论。通过对患者的下颈椎处进行CT扫描,获得DICOM数据导入Mimics中,根据不同HU值范围构建下颈椎参数,并运用蒙板编辑、阈值选取、三维增长等工具建立颈椎结构区域的三维模型。采用ANSYS对建立构建的三维下颈椎模型进行有限元分析。构建人体下颈椎有限元模型,对皮质骨、软骨终板等椎间韧带结构进行模拟,设计的下颈椎模型单元有276 382个,节点有413 522个。研究表明,下颈椎在侧弯、屈伸、旋转等六个工况下的ROM椎间值与Panjabi及Kallemeyn等实验研究进行对比,实验数值与Panjabi的实验很近似,且都处于有效区间内,进而证实了实验模型的可行性与有效性。对设计的模型进行网格划分,AVB组设置273 347个单元,378 746个节点,AP组设置265 634个单元,374 593个节点。AP组相较于AVB组的应力峰值明显有增大趋势,但是AVB组的应力情况呈现均匀分布,最大应力主要分布在螺钉尾部及L形钛板与人工椎体接触部位;AP组的最大应力分布在前路钛板的钛网、中上部、螺钉钉杆尾端以及上下椎体接触部位,在钉板连接部位AP组出现应力集中现象。

In this research, the artificial vertebral bodies system of lower cervical pedicle screws was studied by finite element method. The finite element method was used to analyze the construction of the cervical spine biomechanics stability and stress situation, and then the pedicle screw design was optimized, aiming to provide further theoretical basis for clinical medicine. CT scan was carried out on the lower cervical spine of the patient and the obtained DICOM data were imported into Mimics. The parameters of lower cervical spine were constructed according to the range of HU values, and the 3D model of cervical structure area was established by mask editor, threshold selection, and three-dimensional growth tools. ANSYS was adopted to carry out finite element analysis on the established 3D model of lower cervical spine. A finite element model of the lower cervical spine was set up to simulate the structures of the cortex, cartilage, endplate and other ligaments. The designed lower cervical vertebra model unit had 276 382 units with 413 522 nodes. The results showed that the ROM intervertebral value of the lower cervical spine under lateral bending, flexion and extension, rotation and other six conditions was compared with the experimental study of Panjabi and Kallemeyn, and the experimental values were very similar to those of Panjabi and all were within the effective range, which proved the feasibility and validity of the experimental model. The designed model was meshed, with 73 347 units, 378 746 nodes setting in AVB group,and 265 634 units, 374 593 nodes in AP group. Compared with AVB group, there was an obvious increasing trend in the peak stress of the AP group, but the stress distribution of AVB group was even distribution, and the maximum stress was mainly distributed at the tail of the screw and the contact area between the L shaped titanium plate and the artificial vertebral body; the maximum stress in the AP group was found in the titanium mesh, middle and upper part of the titanium plate, the tail end of the screw rod and the contact area between the upper and lower vertebral bodies, and the stress concentration occurred in the AP group at the nail plate connection site.