后路C2-3固定治疗不稳定Hangman骨折术后不同复位程度的生物力学有限元分析

Biomechanical finite element analysis of different reduction degrees after posterior C2-3 fixation for unstable Hangman′s fractures

中文关键词:  Hangman骨折  有限元方法  生物力学  稳定性  复位程度

英文关键词:Hangman′s fracture  Finite element method  Stability  Biomechanical  Degree of reduction

中文摘要:

  【摘要】 目的：评估后路C2-3固定治疗不稳定Hangman骨折术后不同复位程度的生物力学稳定性，从而为临床治疗方案的选择提供理论支持。方法：选择1位27岁健康男性志愿者，采用256排薄层螺旋CT扫描对全头颅、全颈椎节段进行层厚0.25mm的薄层扫描，利用Mimics 19.0、Geomagic 2013、Hypermesh 2019以及Abaqus 2019软件，建立正常颈椎C0-3节段有限元模型，通过测量模型每个运动节段的活动度（range of motion，ROM）并与既往有限元分析和体外生物力学实验数据进行对比验证其有效性。通过重新分割、删除、弱化网格单元强度等方法模拟术后不同复位程度的典型Hangman骨折模型，包括术后残余骨折线间隙为0mm、1mm、2mm、3mm的四种模型，并在上述模型置入后路C2-3椎弓根钉棒系统获得术后不同复位程度的内固定模型；在模型枕骨髁部施加75N垂直向下的力模拟头颅重力，施加1.5N·m力矩模拟前屈、后伸、侧屈、旋转四种工况实际生活中的情况，比较这四种模型在不同工况下C2-3之间螺钉的应力大小分布和沿C2椎体骨折断端节点的位移大小变化，判断其稳定性。结果：建立的正常颈椎模型在各工况下的ROM与既往文献数据基本吻合，模型验证有效。有限元生物力学分析结果表明，在前屈后伸时，螺钉的应力随着骨折间隙的增加而增加，螺钉的最大应力出现在骨折间隙为3mm的模型中，前屈最大应力为85.34MPa，后伸最大应力为46.34MPa，主要集中在连接棒和螺钉的尾部；而侧屈和旋转时，螺钉最大应力出现在骨折间隙为2mm的模型中，侧屈最大应力为57.26MPa，旋转为59.78MPa，其应力主要集中在螺钉的连接棒以及C2螺钉的中后段。当骨折间隙为0mm时，在前屈、侧屈、旋转工况枢椎椎体骨折端节点路径上各节点的绝对位移较其他三种模型节点位移小，固定C2骨折端位移方面效果最好。当后伸时，四种模型的位移数值相差不大。结论：Hangman骨折C2-3固定复位后骨折间隙3mm时前屈后伸螺钉所受应力最大，骨折间隙2mm时侧屈旋转螺钉所受应力最大；当骨折间隙为0mm时，骨折端节点路径上的位移最小，限制骨折位移效果好。

英文摘要:

  【Abstract】 Objectives: To evaluate the biomechanical stability of different reduction degrees after posterior C2-3 fixation for unstable Hangman′s fracture, and provide theoretical support for the selection of clinical treatment options. Methods: A 27-year-old healthy male volunteer was selected, and a 256-slice thin-slice spiral CT scan was performed on the entire head and cervical spine segments with a slice thickness of 0.25mm. A finite element model of the C0-3 segment of the normal cervical spine was established by Mimics 19.0, Geomagic 2013, Hypermesh 2019 and Abaqus 2019 software, and its effectiveness was verified comparing the range of motion(ROM) of each segment with the previous finite element analysis and in vitro biomechanical experimental data. Typical Hangman′s fracture models with different degrees of postoperative reduction were simulated by re-segmenting, deleting, and weakening the strength of the grid elements, including four models with postoperative residual fracture lines of 0mm, 1mm, 2mm, and 3mm. And the posterior C2-3 pedicle screw rod system was implanted in the above models to obtain internal fixation models with different degrees of postoperative reduction. A vertical downward force of 75N was applied to the occipital condyle of those models to simulate the gravity of the skull, and a torque of 1.5N·m was applied to simulate the four working conditions of flexion, extension, lateral bending and rotation in real life, and the stress distribution of the screws between C2-3 and the displacement changes of the fractured end node along the C2 vertebral body were compared between these four models under different working conditions to judge its stability. Results: The ROM of the established normal cervical spine model under various working conditions was basically consistent with the data in previous literature, therefore the model was verified to be effective. Finite element analysis results indicated that during flexion and extension, the maximum stress of the screw appeared in the model with a fracture gap of 3mm. The maximum stress in forward flexion was 85.34MPa and in posterior extension was 46.34MPa. As the fracture gap increased, the maximum stress was increasing, mainly concentrated in the tail of the connecting rod and screw. During lateral bending and rotation, the maximum stress of the screw appeared in the model with a fracture gap of 2mm, the maximum stress of lateral bending was 57.26MPa, and the maximum stress of rotation was 59.78MPa. The stress was mainly concentrated in the connecting rod of the screw and the middle and rear section of the C2 screw. When the fracture gap was 0mm, the absolute displacement of each node on the fracture end node path of the axis vertebral body in flexion, lateral bending, and rotation was smaller than the node displacement of the other three models, and it was the most effective in limiting and fixing the displacement of the C2 fracture end. In extension condition, the displacement values of the four models were not much different. Conclusions: After fixation and reduction of Hangman fracture C2-3, the greatest stress on the screw is under flexion and extension when the fracture gap is 3mm, and it appears under lateral flexion and rotation when the fracture gap is 2mm. When the fracture gap is 0mm, the displacement along the fracture end node path is the smallest, and the effect of restricting fracture displacement is good.