新型后路寰枢椎限制性非融合内固定系统的有限元分析

Finite-element analysis of a novel posterior atlantoaxial restricted non-fusion fixation system

背景:寰枢椎融合是目前治疗寰枢椎脱位的主要修复方式,但是其前提是牺牲寰枢椎活动为代价,特别是旋转功能。限制性非融合内固定是一种既可以维持寰枢椎稳定性,又可保留寰枢椎活动功能的方法,其生物力学特点与传统融合术之间的差异有待进一步研究。目的:通过建立寰枢椎不稳的三维有限元模型并模拟后路寰枢椎限制性非融合内固定系统和后路寰枢椎钉棒内固定系统,验证该新型内固定系统的生物力学特性。方法:选择1名31岁成年健康男性志愿者,采集从枕骨底到第3颈椎(C0-C3)的CT数据,应用Simpleware3.0、Geomagic 8.0、Hypermesh 10.0、Abaqus 6.9、Rhino 4.0软件构建有限元模型。施加1.5 N·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。建立后路寰枢椎限制性非融合内固定系统模型和后路寰枢椎钉棒内固定系统模型,对比两种模型在前屈、后伸、侧弯、旋转等工况下的椎间活动度,记录下限制性非融合内固定系统模型的SMise应力云图。结果与结论:(1)实验建立了健康人的上颈椎(C0-C3)三维非线性有限元模型,模型包括206 747单元,72 500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;(2)限制性非融合内固定系统模型C1-C2节段前屈、后伸工况的活动度与传统钉棒内固定系统模型相似;(3)在左右侧屈工况下,传统钉棒内固定系统模型C1-2间的侧屈活动度明显受限,而限制性非融合内固定系统模型的活动度比寰枢椎脱位模型有所增加,与正常寰枢椎模型基本相同;(4)在左右旋转工况下,传统钉棒内固定系统模型寰枢椎之间的旋转活动度基本消失,而限制性非融合内固定系统模型其活动度虽有所减少,但仍保留大部分旋转活动度;(5)限制性非融合内固定系统模型在螺钉与连接棒、连接杆接触部位出现应力集中;(6)结果表明,后路寰枢椎限制性非融合内固定系统是一种实用、有效的寰枢椎内固定方式,该限制性非融合内固定装置具有限制屈伸活动,并且有效保留寰枢椎轴向旋转和侧弯活动功能的特点。

BACKGROUND： Atlantoaxial fusion is currently the main surgical treatment of atlantoaxial dislocation, but the premise is at the expense of atlantoaxial range of motion, especially the rotation motion. Restricted non-fusion fixation is a method that can maintain the atlantoaxial stability, while retain the atlantoaxial range of motion. Further research should be performed to compare the biomechanical characteristics between the two methods.OBJECTIVE： To develop a three-dimensional finite element model of atlantoaxial instability, compare and determine the biomechanical properties of posterior atlantoaxial restricted non-fusion fixation system and posterior atlantoaxial screw-rod fixation system. METHODS： A verified intact finite element upper cervical（C0-C3） model was established and analyzed by Simpleware 3.0, Geomagic 8.0, Hypermesh 10.0, Abaqus 6.9, and Rhino 4.0 softwares based on the CT data collected from a 31-year-old healthy male volunteer. The moment couple of 1.5 N·m was loaded, which made the model movement in flexion-extension, lateral bending, and rotating direction, respectively. The range of motion was recorded and compared with the in vitro biomechanical experimental data to verify the effectiveness of the model. The ranges of motion of the posterior atlantoaxial restricted non-fusion fixation system model and the posterior atlantoaxial screw-rod fixation system model were analyzed using the finite element method under flexion, extension, lateral bending, and axial rotation; meanwhile, stress nephograms of the posterior atlantoaxial restricted non-fusion fixation system model were observed. RESULTS AND CONCLUSION：（1） There were 206 747 elements and 72 500 nodes in the intact model of upper cervical spine（C0-C3） in this experiment, and the range of motion of intact model validated with the reported cadaveric experimental data.（2） The range of motion of the posterior atlantoaxial restricted non-fusion fixation system group was similar to which of the posterior atlantoaxial screw-rod fixation system group in flexion-extension direction.（3） In lateral bending direction, the range of motion of the posterior atlantoaxial restricted non-fusion fixation system model was obviously limited, respectively. The range of motion of the posterior atlantoaxial restricted non-fusion fixation system model was larger than that of the atlantoaxial dislocation model and basically same as that of the normal atlantoaxial model.（4） As to the rotating direction, the range of motion of the posterior atlantoaxial restricted non-fusion fixation system mainly disappeared at the atlantoaxial segment; by contrast, a majority of rotating motion was still retained in the posterior atlantoaxial restricted non-fusion fixation system group.（5） The stress concentration occurred in the contact part between the screw and the connecting rod in posterior atlantoaxial restricted non-fusion fixation system model.（6） Results suggest that posterior atlantoaxial restricted non-fusion fixation system is effective and useful for atlantoaxial fixation. It not only restricted atlantoaxial flexion-extension, but also preserved axial rotation and lateral bending at the atlantoaxial joint.