Biomechanical Effect Of Cage Position Combined With Bilateral Pedicle Screw Fixation In The Osteoporotic Lumbar Spine Of Oblique Lumbar Interbody Fusion: A Finite Element Analysis

Objective:To study the biomechanical effects of different cage positions with stand-alone(SA)methods and bilateral pedicle screw fixation(BPSF)in osteoporotic lumbar spine undergoing oblique lumbar interbody fusion(OLIF)by using finite element analysis.Methods:CT scan data of lumbar spine in DICOM format of an adult male volunteer were obtained,and L3-L5 normal three-dimensional finite element model(N)was established by using Mimics,Geomagic,Solidworks and ANSYS software.After validation,an osteoporosis(OP)model was constructed by adjusting material properties.SA models(S1,S2,S3)and BPSF models(M1,M2,M3)in which a cage was placed in the anterior,middle and posterior third of the L5 superior endplate(SEP)were constructed at the L4-L5 segment of the OP.A 400 N compression force and a 10 N·m moment were applied to the superior surface of L3 to simulate 6 different physiological motions:flexion/extension,left/right lateral bending and left/right axial rotation.The range of motion(ROM)of L4-L5,the maximum stress of the L5 SEP,the maximum stress of the cage and the maximum stress of the fixation were recorded and compared among the different models.Results:According to the degree of ROM of L4-L5,the stress of the L5 SEP and the stress of the cage for most physiological motions,the SA and BPSF models were ranked as follows: S2<S1<S3,M2<M1<M3.In M2,the stress of fixation was minimal,except during flexion and extension.At the same cage position,the ROM of L4-L5,the stress of the L5 SEP and the stress of the cage in the BPSF models were significantly reduced compared with those in SA models.Compared with S1,M1 had a maximum reduction of89.37%,71.98% and 78.38% in these parameters,respectively.Compared with S2,M2 had a maximum reduction of 83.24%,70.71% and 73.52% in these parameters,respectively.Compared with S3,M3 had a maximum reduction of 74.28%,53.13% and54.16% in these parameters,respectively.Conclusion:Placing the cage in the middle third of the L5 SEP for OLIF could reduce the maximum stresses of the L5 SEP,the cage and the fixation,which may reduce the risk of postoperative cage subsidence,endplate collapse and fixation fracture in the osteoporotic lumbar spine.Compared with SA OLIF,BPSF could provide sufficient stability for the surgical segment and may reduce the incidence of the aforementioned complications.