Using Two Cages With Different Materials In The Treatment Of Lumbar Interbody Fusion By Finite Element Analysis

With the development of the spinal biomechanics,Pedicle screw system with intervertebral cage is widely used in clinical,the use of Intervertebral cage makes unstable parts of the spine fusion and fixation is closer to the normal spine three-dimensional structures and biomechanical properties.The use of intervertebral cage increase the vertebral fusion rate,needs less bone,to restore the original height of the intervertebral disc,improve fusion speed,shorten the operation time,and all of these maks it one of basic technology in spinal surgery.But this method still can appear fusion failure,such like the complications of subsidence,shift of intervertebral cage(about 14%).To solve the problems above,we have done a lot of experimental research about the Pedicle screw system with intervertebral cage in clinical,the research for the pedicle screws are mainly concentrated in equipment fatigue,screw output and screw pull force analysis.For intervertebral cage,the tests are mainly concentrated in tension resistance,shear tolerance and stability.Finite element method can better predict the biomechanical characteristics of screw fixation and intervertebral cage,its has been widely used in design and analysis of pedicle screws and fusion.Objective:Through the finite element analysis method to evaluate pedicle screws combined with two kinds of materialsl of intervertebral cage in biomechanical performance of lumbar fusion.Methods: choose 1 healthy female volunteers,using spiral CT scanning spine L4 ~L5 segment,using Mimics and Geomagic software for 3 d model reconstruction CT images and put them in the finite element analysis software ANSYS12.0 establishing normal three-dimensional finite element model of L4 ~ L5 segments(INT).On this basic,the simulation of two kinds of material model of the fusion combined with pedicle screw fixation,bilateral pedicle screws + Ti(Ti)intervertebral fusion(M1),bilateral pedicle screws + PEEK(poly(ether ether ketone)intervertebral fusion(M2).Give the model 400 n preload,movement additional force for 6 n m.Definite the model constraint and load conditions,lumbar proneness,stretch,left lateralflexion and rotation around six calculation under the condition of L4 ~ L5 segment angular displacement and pedicle screws and fusion of stress.Results: Mod1,Mod2 under various working conditions in the angular displacement of less than an INT.The peak stress experiment,Mod1 cage under various conditions were higher than in Mod2.At the state of stretch,the screw and intervertebral cage peak stress of the Mod1 and Mod2 are smaller than other conditions.Conclusion: pedicle internal fixation can provide enough stability of fusion segments.For fusion segment,in the stability of pedicle screw with the same conditions,the peak stress of PEEK material cage are smaller than Ti material cage,the possibility of settlement and displacement of PEEK material cage are lower than Ti material cage,so its convergence rate is higher.At the state of stretch,stress is smaller,and we can suggest that at the state of stretch,it reach a stable position.