Finite Element Analysis Of Two-level Vertebrae Barbed Axial Internal Fixation Device

Objective: To establish a three-dimensional finite element model of normal adult lumbosacral vertebrae(L1-S2) and verify its effectiveness.The screw was placed simulatively in the L4-S1 vertebra by software,and the spinal motion was simulated under physiological load and ultimate load.Observe and analyze the stress distribution and displacement of the internal fixation,and provide a theoretical basis for further improvement and clinical application.Methods: CT scan was used to obtain the imaging data of normal adult male lumbosacral vertebrae.The complete lumbosacral three-dimensional finite element model was constructed by Mimics 20.0,Geomagic 12.0,ansys workbench 18.0,and its validity was verified.According to CAD drawings,the three-dimensional model of the L4-S1 vertebral barbed axial internal fixation was established by Solidworks2015 software with the stretching,rotation,and stretching function,the internal fixation was implanted into the designated site to complete the lumbosacral vertebra model with the internal fixation.The model was subjected to finite element analysis,and the physiological load(verticalcompression 1500 N,flexion and extension 25N·m,rotation 15N·m) and ultimate load(vertical compression 10000 N,flexion and extension 91N·m,rotation 88N·m) were designed to simulate the vertical compression,flexion and extension,lateral bending,and axial rotation of the lumbosacral vertebrae.Ansys workbench 18.0 software was used to calculate the stress distribution and displacement of the L4-S1 barbed axial internal fixation under various working conditions.So we can evaluate the biomechanical property of the internal fixation through observing its stress concentration and displacement.Results: An effective lumbosacral vertebrae(L1-S2) model for finite element analysis had been established successfully,and simulated the implantation of the L4-S1 vertebral barbed axial internal fixation,and established a lumbosacral vertebrae model with internal fixation.The data of stress distribution and displacement change in 21 cases were obtained:under the physiological load,the internal fixation screw showed no obvious displacement,and the stress on each part was much less than the yield stress(1034Mpa).Under the ultimate load,the internal fixation screw locally exhibited stress concentration and over the yield stress,but without yield displacement in general.Conclusions: The stiffness and strength of the L4-S1 vertebral barbed axial internal fixation can meet the requirement of human physiological conditions.Local stress concentration occured under theapplication of ultimate load.In subsequent improvements,the shape of the thread and the poke structure could be changed.The contact area of the main screw and the pokes could be increased to disperse stress.