下颈椎前路椎弓根螺钉人工椎体系统的有限元研究

FINITE ELEMENT STUDY ON ANTERIOR TRANSPEDICULAR SCREW-ARTIFICIAL VERTEBRAL BODY FIXATION IN LOWER CERVICAL SPINE

目的利用有限元研究方法，比较下颈椎前路椎弓根螺钉人工椎体系统（anterior transpedicular screw-artificial vertebral body, AVB）与传统颈椎前路钉板系统的生物力学性能。方法采集1名38岁正常女性志愿者颈椎（CJ-TJ）CT数据，应用Mimics 14．0、Geomagic Studio 2013、ANSYS14．0软件建立下颈椎（C3～7）完整模型、颈椎前路钛板椎体钉（anterior screw plate system，AP）固定模型、AVB固定模型。在C3上分别施加74N轴向压力及1N·m纯力偶矩，使模型产生前屈、后伸、左侧弯、右侧弯、左旋和右旋运动，记录AP组及AVB组VonMises应力云图及最大应力值，计算并比较3组椎间活动度（range of motion，ROM）。结果实验建立了正常人下颈椎（C3～7）有限元模型，模型包括286382个单元，414522个节点，其椎间ROM与Panjabi等及Kallemeyn等实验数据吻合度较好。AP组在钉板连接部位出现应力集中，AVB组应力分布较均匀。在74N轴向压力、前屈、后伸、左旋、右旋工况下，AP组与AVB组最大应力值差异明显。与AP组相比，AVB组固定节段ROM更小，邻近节段ROM相对较大；与完整组相比，AP组与AVB组的整体ROM减小约3°，但邻近C3、4及C6、7节段的ROM代偿增加约5°。结论AVB作为一种新型固定技术，其稳定性优于AP，且固定系统断裂的风险显著低于AP。

Objective To compare the biomechanical properties of the anterior transpedicular screw- artificial vertebral body （AVB） and conventional anterior screw plate system （AP） in lower cervical spine by finite element study. Methods CT images （G-T0 were obtained from a 38-year-old female volunteer. The models of intact C34 （intact group）, AP fixation （AP group）, and AVB fixation （AVB group） were established and analyzed by Mimics 14.0, Geomagic Studio 2013, and ANSYS 14.0 softwares. The axial force of 74 N and moment couple of 1 N＇m were loaded on the upper surface and upper facet joint surfaces of C3. Under conditions of flexion, extension, lateral bending, and rotation, the Von Mises stress distribution regularity and maximum equivalent stree of AP and AVB groups were recorded, and the range of motion （ROM） was also analyzed of 3 groups. Results The intact model of lower cervical spine （C3-7） was established, consisting of 286 382 elements and 414 522 nodes, and it was successfully validated with the previously reported cadaveric experimental data of Panjabi and Kallemeyn. The stress concentrated on the connection between plate and screw in AP group, while it distributed evenly in AVB group. Between AP and AVB groups, there was significant difference in maximum equivalent stress values under conditions of 74 N axial force, flexion, extension, and rotation. AVB group had smaller ROM of fixed segments and larger ROM of adjacent segments than AP group. Compared with intact group, whole ROM of the lower cervical spine decreased about 3°, but ROM of C3. 4 and C6. 7 segments increased nearly 5° in both AP and AVB groups. Conclusion As a new reconstruction method of lower cervical spine, AVB fixation provides better stability and lower risk of failure than AP fixation.