下颈椎前路椎弓根螺钉固定系统的有限元法生物力学研究

Three-dimensional finite-element study on anterior transpedicular screw fixation system of the subaxial cervical spine

目的 比较下颈椎前路椎弓根螺钉内固定系统（ACTPS）和颈椎前路椎体螺钉钛板系统（ACLP）重建两节椎体次全切后的生物力学特性.方法 选择一名28岁成年健康男性志愿者,采集颈椎（C1 -T1）的CT数据,应用Mimics 10.0、Rapidform XOR3、Hypermesh10.0、CATIA5 V19、ANSYS14.0软件建立下颈椎三维非线性的（C3-C7）完整模型.在C3上分别施加75 N的轴向压力和1N·m的纯力偶矩,使模型在屈伸、侧弯、旋转方向上运动.将模型的椎间活动度与文献报道的体外生物力学实验数据相比进行验证.建立ACTPS模型和ACLP模型,利用ANSYS计算两种模型在前屈、后伸、侧弯、旋转等工况下的椎间活动度.记录下ACTPS模型组和ACLP模型组的Von Mises应力云图及最大应力值,将ACTPS固定模型、ACLP固定模型的椎间活动度与完整模型进行比较.结果 本次实验建立了健康人的下颈椎（C3-C7）三维非线性有限元模型,模型包括85 832个单元,23 612个节点,其外形逼真,椎间活动度与文献报道的体外生物力学实验结果吻合.ACTPS模型组应力分布的相对比较均匀,ACLP模型组在螺钉与钛板接触部位出现应力集中.两组模型的最大应力值相比差异较明显.ACTPS组固定节段与ACLP组相比,椎间活动度更小,邻近节段椎间活动度相比差异不明显;与完整组比较,ACTPS组和ACLP组整体椎间活动度在屈伸、侧屈、旋转方向上分别减小约25°、20°和8°,相应的邻近C3-4节段的椎间活动度代偿性的变化约0.3°、3°和0.1°.结论 ACTPS的生物力学稳定性优于ACLP,适用于2节段及以上颈椎前路减压后稳定性重建.与ACLP相比,ACTPS的断裂风险更低.

Objeetive To evaluate the biomechanical effects of the anterior cervical transpedicularscrew system （ACTPS）, compared to the anterior cervical screw plate system （ACLP）, in the subaxial cervical spine after 2-level corpectomy.Methods A verified intact finite element subaxial cervical （C3-C7） model was established and analyzed by Mimics 10.0, Rapidform XOR3, Hypermesh 10.0, CATIA5V19, ANSYS 14.0 softwares based on the CT data（C1-T1） was collected from a 28 years old male volunteer.The axial force of 75 N and moment couple of 1N·m was loaded on the upper surface of C3 , which made the model movement in flexion extension, lateral bending, rotating direction, respectively.Then, recorded the range of motion, and compared the results with the in vitro biomechanical experimental data to verify the effectiveness of the model.The ACTPS model and the ACLP model were analyzed using the finite element method.The range of motion at the operation segments （C4-C7） , the range of motion at the adjacent segment （C3-C4） and stress distribution under flexion, extension, lateral bending, and axial rotation were calculated, and compared the range of motion with intact model.Results There were 85 832 elements and 23 612 nodes in the intact model of subaxial cervical spine（C3-C7） in this experiment, and the range of motion of intact model validated with the reported cadaveric experimental data.In ACTPS group the stress was been well-distributed, but the stress concentrated on the interface between screw and the titanium plate in ACLP group.There were obvious differences of the maximum stress value between the two groups.The range of motion of fixed segments in ACTPS group was smaller than ACLP group, however adjacent segment range of motion showed no significant difference.Compared with the intact group, the range of motion in flexion extension, lateral flexion, rotation direction was decreased respectively about 25°, 20° and 8°, the range of motion at adjacent segment （C3-C4）was correspondingly compensated about 0.3°, 3° and 0.1°.Conclusions ACTPS is better than ACLP in terms of biomechanical properties.It offers rigid stability, and may be more suitable for reconstruction stability of 2-level and more than 2 levels corpectomy in the subaxial cervical spine.Meanwhile, the risk of fracture of ACTPS system is lower than that of the ACLP system.