下胸段单钉T11~12镍钛合金弹性内固定系统有限元分析及临床意义

The finite element analysis of NI-TI anterior screw elasticity fixation on lower thoracic vertebrae

目的 建立T11~12前路病灶清除植骨＋单钉单棒镍钛合金弹性固定系统三维有限元模型，分析弹性固定系统所受应力对其进行改进。方法对一名成年男性进行螺旋CT扫描，将所得数据导入计算机，通过Mimics13.0软件和Ansys11.0有限元软件建立T11~12前路病灶清除植骨＋单钉单棒镍钛合金弹性固定系统三维有限元模型，并在椎体上表面施加500 N压力和10 Nm的力矩模拟腰椎前屈、后伸、侧屈和旋转4种生理载荷，观察不同载荷下固定器械的应力分布，并对其进行比较。结果 单钉单棒弹性固定系统在用于侧前方固定时，其下位螺钉根部与“U”形棒中段承受应力始终较大，而螺钉的中部与“U”形棒的上部则较小。螺钉根部在4种运动状态下，旋转运动加载的应力最大，而侧弯运动时最小，“U”型棒中部在4种运动状态下应力均较大。但均小于镍钛合金的屈服强度。结论T11~12运动节段前路椎间植骨单钉单棒弹性固定患者在正常运动状态下不会由于定械某部位应力过高而导致断钉断棒。

Objective To develop a 3-D finite element（FE） model of NI-TI anterior screw elasticity fixation on lower thoracic vertebrae and evaluate the stress of screw,stick stress. Methods The geometrical model was created by Mimics13.0 based on CT data of T11～12 motion segments from a male patient , which was imported into the Ansys11.0 in order to establish the 3-D FE of anterior screw fixation on lower thoracic vertebrae. The 3D FE models were imported into Ansys11.0 with 500N pressure and 10 Nm moments loaded on the upper surface of T11 to simulate thoracic axial compression,anteroflexion, extension, lateral bending and rotation. The Von mises stress of screws and stick was recorded and input to SPSS11.0 to analyze the difference of different stress distribution of the screws and sticks. Results It was obvious that the Von mises of the screw concentrated on the tail of screws and ＂U＂ segment with inferior bearing larger load than superior surface;the lower segment of stick depressed was larger stress. Rotation mayresult in the Von mises concentration on tails of screw and＂U＂segment,but were lower than yield strength. Conclusions NI-TI anterior screw elasticity fixation on lower thoracic vertebra would not break on usual motion.