Finite Element Analysis Of Self-developed Dynamic Pedicle Screw For Lumbar Internal Fixation

Objective:With the help of finite element method,the influence of selfdeveloped lumbar dynamic pedicle screw on the stability of spine and the load of intervertebral disc as well as its internal stress distribution and screw displacement are studied.It is determined whether the system has excellent dynamic fixation,load sharing effect and sufficient fixation strength in comparison with the ordinary lumbar interbody fusion system and Dynesys system.The study can provide experimental data to help others design novel instrument that can prevent the degeneration of adjacent segments.Method:1、The three-dimensional finite element model of normal lumbar(L1-L4)was established.Spiral CT was used to scan the lumbar vertebrae of a healthy volunteer.The image data were imported into the Mimics19.0software to establish the three dimensional model of lumbar vertebrae(L1-L4).Then the reconstructed 3D model was imported into 3-Matic software to reduce the triangular surface and other optimization process,and then imported into Geomagic studio 21.0 software and Hyper Mesh 14.0software for finite element preprocess.Finally,the three dimensional finite element model was built in Abaqus 6.12 software,and its validity was verified.2、The three-dimensional finite element models of common lumbar interbody fusion system,Dynesys system and self-developed dynamic pedicle screw implantation were established and analyzed under different conditions.First of all,the three lumbar internal fixation systems were drawn by using UG10.0 software,which was imported into Mimics19.0software,assembled with the established three-dimensional model of the lumbar spine,and finally imported into Abaqus6.12 software to assign values to the nail bar and other materials,set the boundary conditions and load.The intervertebral activity,disc stress,facet joint stress,internal fixation device stress and screw displacement of the fixed segment(L2-L3)and the low adjacent segment(L3-L4)were calculated under the conditions of flexion,extension,lateral bending and rotation,and were compared with each other.Results:1.The three dimensional finite element models of normal lumbar spine(L1-L4),common lumbar fusion system,Dynesys system and self-developed dynamic pedicle screw were established.2.Under the condition of flexion and extension,the ROM of the fixed segment after the operation of the ordinary lumbar fusion system is about23% and 26% of the complete lumbar ROM,the ROM of the fixed segment after the operation of Dynesys system is about 61% and 57% of the complete lumbar ROM,the ROM of the fixed segment after the operation of SDPS is about73% and 45% of the complete lumbar ROM respectively.In addition,the ROM of the lower adjacent segment after the operation of the ordinary lumbar fusion system is about 118% and 120% of the complete lumbar ROM,the ROM of the lower adjacent segment after the operation of Dynesys system is about 108% and 111% of the complete lumbar ROM respectively,and the ROM of the lower adjacent segment after the operation of the SDPS system is about 104% and 112% of the complete lumbar ROM respectively.3.The stress peak value of the intervertebral disc in the adjacentsegment of the common lumbar fusion system is the largest under various conditions.In comparision with Dynesys system,the stress peak value of the SDPS’s adjacent intervertebral disc is smaller in flexion and larger in extension.4.The comparison of the maximum stress value of the little facet joint of the lower adjacent segment after fixation of each lumbar internal fixation system during the extension: ordinary fusion > SDPS > Dynesys.5.Comparison of the internal maximum stress values of each lumbar internal fixation system under the conditions of flexion,extension,lateral bending and rotation: ordinary fusion > SDPS > Dynesys.6.Comparison of the maximum screw displacement of each lumbar internal fixation system under flexion,extension,lateral bending and rotation: Dynesys > ordinary fusion > SDPS.Conclusion:The self-developed lumbar dynamic pedicle screw has a good dynamic fixation effect on the fixed segment when flexing forward,and has little effect on the adjacent segment mobility and intervertebral disc.In addition,the self-developed dynamic pedicle screw has better fixation strength,but its fatigue performance may be general.The experimental data can provide a practical reference for the design of internal fixation instruments which prevent the degeneration of adjacent segments.