枢椎棘突作为第三锚定点枕颈固定的生物力学有限元分析

A finite element analysis of aspinous process screw as a third anchor point in C2 for occipitocervical fixation

目的:通过有限元方法分析枢椎棘突作为第三锚定点枕颈固定的生物力学稳定性。方法:选择一位健康成年人的C0-C3 CT资料,利用Mimics、Hypermesh和Abaqus等软件建立上颈椎有限元模型(完整模型)。模拟寰椎Jefferson骨折后进行枕颈固定,分别为双侧枢椎椎弓根螺钉+枢椎棘突螺钉+枕骨螺钉钉棒固定(第三锚定点枕颈固定组)和双侧枢椎椎弓根螺钉+枕骨螺钉钉棒固定(双侧枢椎椎弓根螺钉枕颈固定组)。在骨折模型前和固定后,分别施加50N垂直载荷,模拟头部重力作用,施加1.5N·m纯扭矩,从而模拟颈椎前后屈伸、左右旋转、左右侧屈6种状态。在动态加载中,计算固定前和后C0/1、C1/2、C2/3关节间在前屈、后伸、左右侧屈和旋转6个方向上的活动度(ROM)。结果:本研究建立的上颈椎(C0-C3)三维非线性有限元模型外形与正常上颈椎解剖结构相符,韧带连接一致,能较好地体现上颈椎的解剖特点。在边界范围和载荷条件相同的情况下,本研究完整模型的ROM在体外标本实验研究参考文献的实验数据范围内,具有很好的关联性。双侧枢椎椎弓根螺钉固定组和第三锚定点固定组在屈伸、侧屈和旋转运动C0-C2 ROM结果均较完整模型组显著降低,其中差异最大的在C1/2旋转活动上。可见,两种固定方法都可以对骨折模型起到较好的稳定作用。除C0/1的侧屈活动外,第三锚定点固定组在其余各个方向上C0-C2固定后ROM均较双侧椎弓根螺钉固定组降低,其中差异最大的在C0/1屈伸活动上。结论:枕颈固定融合中枢椎棘突作为第三锚定点也许可以进一步加强枕颈屈伸的稳定性,减少内固定失败的发生。

Objectives:This study aimed to determine the biomechanical feasibility of aspinous process screw as a third anchor point in C2 for occipitocervical fixation through a finite element analysis.Methods:A models of the upper cervical spine(C0-C3)supplied by an adult were reconstructed using computed tomography images.The images were processed using commercially-available software,such as Mimics,Hypermesh and Abaqus software.A nonlinear finite element model of C0-C3 had been developed and validated.Then the C1 fracture models were simulated and occipitocervical fixation was completed.Two different fixation techniques of occipitocervical fixation were applied.The inferior surface of the C3 vertebra was constrained completely.Vertical load of 50N was applied on the C0 to simulate head weight,and 1.5N·m torque was applied to the C0 to simulate flexion,extension,lateral bending,and axial rotation.The range of motion(ROM)of the C0/1,C1/2 and C2/3 segments of the models was measured for intact and fixation models respectively.Results:A nonlinear finite element model of C0-C3 had been developed and validated with the normal upper cervical spine.Since the boundary and loading conditions in these studies were comparable,we compared the ROM of the C0-C3 segments of the intact finite element models with the results of the in vitro test to validate our model.Compared with the intact model,both the bilateral C2 pedicle screw group and the spinous process screw as a third anchor point group reduced the ROM of C0-C2 in the occipitocervical fixation.Compared with the bilateral C2 pedicle screw group,the spinous process screw as a third anchor point group further reduced the ROM of C0-C2 in the occipitocervical fixation except lateral bending of C0/1.Conclusions:In the occipitocervical fixation,the spinous process screw as a third anchor point group combined with the bilateral C2 pedicle screw fixation may enhance the stability of the occipitocervical joint.