Three-dimensional Finite Element Analysis Of Unilateral Pedicle Screw Fixation In Oblique Lumbar Interbody Fusion

Objective Application of three-dimensional finite element method to verify whether OLIF-assisted unilateral pedicle screw-rod fixation can provide adequate interbody stability for corresponding fusion segments after intervertebral fusion.Methods On the basis of CT scan data of normal L3-S1 segments,a three-dimensional finite element model(M0)of normal L3-S1 segments was established by using Mimics,Geomagic 3-matic software,Freeform and other software.On this basis,I set up OLIF Stand alone model(M1),OLIF with unilateral pedicle screw-rod fixation(Wiltse approach)model(M2),OLIF with bilateral pedicle screw-rod fixation(Wiltse approach)model(M3)and PLIF with bilateral pedicle screw-rod fixation model(M4)and MTLIF with bilateral pedicle screw-rod fixation model(M5).MSC.Patran/Nastran finite element software was used to set upper and lower vertebral endplates as intervertebral fusion and apply 500 N preload on the upper surface of L3 and 10N·m moment was applied to simulate the physiological activities of lumbar spine such as flexion,extension,lateral flexion and rotation.The L4-L5 segment range of motion(ROM),stress distribution of cage and pedicle screw was observed under different working conditions.Results 1,The ROM values of 6 groups of finite element models in each movement state were ranked from small to large: M0,M3,M4,M2,M5,M1.Among them,M1 ROM was the closest to M0.M2 ROM was significantly reduced compared to M0,and M3 ROM was the smallest in all models.Compared with M0 and M1,M2 showed better stability in flexion and extension.Compared with M5,M2 showed better stability in extension and left rotation.M3 showed better stability in flexion and extension.M4 showed better stability inextension and right lateral bending.M2 and M0 showed similar stability in right lateral bending and right rotation.M2 and M1 and M3 showed similar stability in left and right rotation.M2 and M4 showed similar stability in flexion and left lateral bending.M2 and M5 showed similar stability in left and right lateral bending.Although the ROM of M2 in various motion states was larger than the two groups of M3 and M4 models,the variation range of M2 compared with M0 ROM was much larger than that between M2 and M3,M2 and M4 ROM.2,In terms of the peak stress of the cage,in addition to upright,the peak stress of M2 was slightly higher than that of M1.In other states of motion,the peak stress of the cage in each OLIF group showed a certain decrease trend with the increase of the number of additional pedicle screw and rod system.This trend was most evident when retroextension.The peak stress of M1 cage was greater than M4 when retroextension,and the stress peak difference between M2 and M4 decreased significantly after the additional unilateral pedicle screw system was fixed.After the addition of bilateral pedicle screw fixation,the stress peak of M3 cage was lower than that of M4.In addition to retroextension,the peak stress of M2 cage was significantly less than that of M4 and M5.Although the peak stress of the M3 cage was also smaller than that of M2,this difference between M2 and M3 was not as significant as the stress difference between M2 and M4,M2 and M5.3,In terms of the peak stress of the screw system,in addition to the peak stress of M2 which was slightly higher than that of M5 when upright and higher than that of M4 when retroextension,in other states of motion,the peak stress of M2 was significantly reduced compared to M4 and M5.The peak stress of M2 screw system was significantly lower than that of the M3 in right lateral flexion state,and slightly lower than that of the M3 in the left lateral bending.In other states of motion,the peak stress of the screw system of M2 was higher than that of the M3,but this stress difference was more obvious in the right lateral bending and retroextension.However,the stress difference between M2 and M4,M2 and M5 was significantly greater than that between M2 and M3,except the right lateral bending and extension.4,The stress peaks of the five surgery groups of model screws and cage were farfrom their yield strength.Conclusion 1,A three-dimensional finite element model of normal L3-S1 segments was established.In this study,the validity of the model was verified by comparing with the results of previous studies,which proved that the model was effective and qualified for further research.2,The surgical segment stability of OLIF with unilateral pedicle screw fixation model was better than that of OLIF Stand alone,MTLIF with unilateral pedicle screw fixation model,and slightly worse than that of OLIF with bilateral pedicle screw fixation model and PLIF with bilateral pedicle screw fixation model.3,The model of OLIF with unilateral pedicle screw and rod fixation model can provide sufficient intervertebral stability for the corresponding fusion fixation segment.