Study On Three-dimensional Finite Element Of The Instrumentation Growing Rods Of Sliding Pedicle Screw System

Objective To establish an effective L3-L5three-dimensional finite element model，andstudy the biomechanics of the instrumentation growing rods of sliding pedicle screwsystem and the rationality of it.Methods On the basis of CT scan,establish a normal lumbar spine(L3-L5)model usingreverse-engineering software Mimics,solidworks PATRAN and verify its effectveness,establish the instrumentation growing rods of sliding pedicle screw system and instrumentation traditional pedicle screw system of the geometric model by Solidworks softwareand simulate the process of assembly dynamic internal fixation system into the lumbarspine;import the geometric model into the Patran software and conducted meshing,get thefinite element mesh model.According to the gray value of the CT lumbar model andmaterial properties of internal fixation,import the assignment model into PATRANsoftware and obtain the final finite element model.Imposed on the model of axialcompression of500N and15N.m torque pre-load and make the model produceflexion,extension,lateral bending,rotation. Using the NASTRAN software,complete theinstrumentation growing rods of sliding pedicle screw system and instrumentationtraditional pedicle screw system of internal stress distribution and the size of thecalculation and analysis in four kinds of operating conditions.On the Hyperview finiteelement analysis software,show the results and calculate the angle and displacementtransfer movement in four kinds of operating conditions and compare the established finiteelement model to evaluate the biomechanical properties.Results1.A lumbar spine (L3-L5) three-dimensional finite element was establishedsuccessfully which was non-discrimination with the model literature reported. The lumbarspine finite element model assembled the instrumentation growing rods of sliding pedicle screw system compared with instrumentation traditional pedicle screw system havesome differences in results of the angle of its movement and displacemen.2. In a simulated different pressure, the stress of the instrumentation growing rodsof sliding pedicle screw system was significantly higher than the locking group inanteflexion and postexion,but significantly lower in rotary situation,and the stress of thescrew-bone interface was increased in different degree under various working conditions.The maximum stress value of the titanium bars and screw was577.8Mpa but the ultimatestrength of titanium alloy was785-1100Mpa. The maximum stress value of the screw-boneinterface was13.42Mpa but the ultimate strength of the normal vertebrae was500Mpa.Conclusion1. A effective normal lumbar spine (L3-L5) three-dimensional finiteelement model was established.2. The instrumentation growing rods of sliding pedicle screw systemhave a much better moving range compareing with the instrumentation traditionalpedic lescrew system, the maximum stress value of titanium bars,screw,crew-boneinterface, normal vertebrae is less than the ultimate strength, and the system has a betterbiomechanical characteristics.