A Finite Element Analysis Of Adjacent Segment Of Grade Ⅱ Lumbar Spondylolisthesis After In-situ And Reductive PLIF

Objective: Lumbar spondylolisthesis is a common disease that affects the health and quality of life of middle-aged and old people.Posterior lumbar interbody fusion(PLIF)is a common and effective surgical treatment for lumbar spondylolisthesis.However,there are few biomechanical studies on PLIF for lumbar spondylolisthesis at home and abroad.In this study,to analyze the biomechanical differences of adjacent segments,we developed the three-dimensional finite element models of grade Ⅱ lumbar spondylolisthesis treated with in-situ and reductive PLIF,and verify the validity of the models.Methods: In this study,we selected a patient with grade Ⅱ L4 spondylolisthesis and without severe adjacent segmental lesion to obtain CT images of lumbar vertebrae and saved them in DICOM format.We imported the DICOM file into the Mimics,and extracted the bone of L3-S2 to develop a preliminary3 D model.Then,by using Geomagic and Solidworks,we simulated surgery to remove the bone,polished the preliminary model and construct the curved surface to develop a solid model.And we developed the models of lumbar intervertebral discs,facet joint,fusion cage and nail-rod system used in surgery to develop the three-dimensional finite element models of grade Ⅱ lumbar spondylolisthesis treated with in-situ and reductive PLIF.After developing the model of ligaments with Ansys Workbench,we exerted the follower load of1200 N and 6.0 N·m torque on the models.The compression value of lumbar intervertebral disc and the range of the motion(ROM)were measured and compared with the in vitro biomechanical results recorded in the literature.Finally,we exerted the following load of 400 N and 7.5 N·m torque on the in-situ model and the reductive model to simulate flexion,extension,lateral bending and rotation to simulate flexion,extension,lateral bending and rotation of the lumbar spine,and measured the ROM,the intradiscal pressure(IDP)and the facet joint stress(FJS)of adjacent segments for analysis.Results: We successfully developed the three-dimensional finite element models of grade Ⅱ lumbar spondylolisthesis treated with in-situ and reductive PLIF including adjacent segments.The data of validity verification were consistent with the results of in vitro biomechanical experiments recorded in the literature.There are significant biomechanical differences between the in-situ model and the reductive model on adjacent segments in this study.When simulating flexion and extension,the sum of flexion and extension ROM of the adjacent segments of the reductive model is smaller than that of the in-situ model.When simulating flexion,extension,lateral flexion and rotation,the IDP and FJS of the adjacent segments of reductive model are significantly smaller than those of the in-situ model.Conclusion: In this study,we developed the effective three-dimensional finite element models of grade Ⅱ lumbar spondylolisthesis treated with in-situ and reductive PLIF.The finite element analysis(FEA)data of this study show that,there is a significant biomechanical difference between the adjacent segments of grade Ⅱ lumbar spond ylolisthesis treated with in-situ and reductive PLIF.The reduction of the spondylolisthesis can reduce the load of the intervertebral disc and facet joint of the adjacent segments,make the load distribution more uniform,and reshape the biomechanical effect of the lumbar spine.Therefore,for grade Ⅱ lumbar spondylolisthesis,the reduction of spondylolisthesis during operation has a positive and great effect on slowing down occurrence and progress of the adjacent segment degeneration(ASD).