腰椎弹性内固定与刚性内固定的应力对比研究

目的:通过有限元的方法评价自行研制的腰椎"U"型弹性内固定器的力学特性,并与传统的刚性内固定器进行比较.方法:选择一名成年患者腰椎标本,以L4～5节段为研究对象,采用64排螺旋CT对其进行层厚1.0 mm的连续水平扫描,将所得图像进行轮廓提取和阈值分割后,借助三维重建软件Mimics11.1、Simpleware和有限元软件Abaqus 6.51软件,建立L4～5节段三维非线性有限元模型.同时根据椎弓根螺钉、连接棒的几何尺寸,力学参数,分别建立两种不同内固定器的有限元模型.然后分别施加压缩、前屈、后伸、侧屈及旋转等各种生理载荷,观察各模型不同载荷下螺钉、连接棒的应力分布.结果:两种内固定器的椎弓根螺钉前、中部的应力差异无统计学意义(P>0.05);刚性固定的椎弓根螺钉与棒连接处是应立集中的部位,该部位的应力远大于弹性固定器,而弹性内固定应力集中的部位均匀的分布于整个U型连接棒上,两模型固定节段螺钉及棒的最大有效应力均出现于前屈时.结论:在加载相同的纵向载荷条件下,刚性内固定器应力主要集中在螺钉与棒交界处,容易易发生螺钉断裂,U型弹性内固定器的应力均匀分布在U型连接棒上,可以减少断钉的现象发生.

Biomechanic comparision between the "U" shape lumbar dynamic fixation system and traditional fixation system

Objective: To compare biomechanical features between the new "U" shape lumbar dynamic fixation system and traditional rigid fixation system. Methods: Finite element analysis of the two fixation systems were performed on the basis of a three-dimensional model reconstructed from the images of CT scanning of an adult cadaveric lumbar with the interval of 1 mm. The stress and displacement of every nodule and element in the course of deformation of the internal fixation were tested and analyzed. Results: In the same shearing load of 500 N,The force of the dynamic fixation system concentrated on the "U" shape elastic zone,however,the force of the rigid fixation system concentrated on the posterior 1/3 of the lower screw. Conclusions: This study demonstrates the new "U" shape lumbar dynamic fixation system has a totally different biomechanical properties comparing to that of traditional rigid fixation system. This dynamic fixation system may be a choice to replace the rigid fixation system for the treatment of the lumbar degenerative disease.