Finite Element Stress Analysis Of Adjacent Segments After Long Segment Internal Fixation For Degenerative Lumbar Scoliosis

Objective CT imaging data of patients with degenerative lumbar scoliosis were obtained by continuous spiral CT scan.Computer-aided engineering software was used for image processing analysis to establish a three-dimensional finite element model.Material properties were added according to finite element model materials.Different surgical procedures on the established model.To explore the stress distribution of vertebral body,intervertebral disc and nail rod system in patients with degenerative lumbar scoliosis,and to provide evidence for the study of adjacent segment degeneration.Methods A case of degenerative lumbar scoliosis was collected and the complete Dicom format CT images were obtained successfully.The images scanned by CT are input into Mimics software to get clear skeletal outline.After mask skin processing,the skeletal outline is exported in STL format.The STL file is read into Geomagic,and a series of image processing is carried out on the three-dimensional model.Then the surface patches are distributed on the model.Finally,the solid surface is encapsulated and the IGES file format of the three-dimensional graphics is generated.After the outline of each bone is built,the structure of annulus fibrosus and nucleus pulposus is established by Solidworks,and then imported into Workbench.The ligaments are connected by lines according to their physiological position.The complete T1-S1 model is established,and the T9-L5 model is selected as the research data.On the basis of the established finite element model,the T10-T11 intervertebral disc was excised and the interbody cage was implanted to establish a scoliosis correction model including the nail rod internal fixation system and the cage.Constraining all 6 degrees of freedom of the end plate under L5,applying a torque of 10 Nm on the top of T9,the model produces six conditions of flexion and extension,left and right side bending,and left and right rotation.To study the stress effects of different surgical procedures on adjacent segments of vertebral body,intervertebral disc and screw rod system.Results This study established a finite element model of degenerative lumbar scoliosis in patients with pedicle screw internal fixation system,interbody fusion cage,thoracolumbar vertebral body,intervertebral disc and corresponding ligament structure.No interbody fusion cage model: 338,690 units and 559,489 nodes.Interbody fusion cage model: 341,868 unitsand 566,573 nodes.According to the two surgical procedures,the stress of each segment of the pedicle screw,connecting rod,vertebral body and intervertebral disc under the same load was measured.The comparison of the overall displacement between the group with fusion cage and the group without fusion cage showed that the overall stiffness increased after the implantation of the interbody fusion cage,and the displacement decreased under the six directions of load,that is,the actual activity decreased,and the difference was statistically significant.Compared with the non-fused group,the maximum stress of the vertebral body in the fused group increased after the implantation of the intervertebral fusion device,and the difference was statistically significant.The maximum stress of the vertebral body in the fused group was concentrated in the T11 vertebral body.Compared with the fusing group and the non-fusing group,the maximum stress value of the intervertebral disc was all concentrated in the t9-t10 intervertebral disc.After the fusion device was implanted,the stress of the intervertebral disc in the adjacent segment changed,and the stress decreased under left-right rotation and increased in other load directions,with no statistical significance.Compared with the fusing group and the non-fusing group,the maximum stress value of the screw rod was concentrated at T10,and the stress of the screw rod decreased in the anterior flexion,posterior extension and left and right rotation,while the difference in left and right lateral bending was not significant,with no statistical significance.Conclusion 1.After long segment internal fixation and fusion,the overall stiffness increases and the actual activity decreases,which can accelerate the degeneration of adjacent segments;2.After long segment internal fixation and fusion,the stress concentration of intervertebral disc and screw rod internal fixation system in adjacent segments can be concentrated,which can accelerate the degeneration of adjacent segments;3.For degenerative lumbar scoliosis patients,long segment internal fixation and fusion can be performed without the need to implant intervertebral fusion device in the upper segment;4.Finite element method can accurately and intuitively study degenerative lumbar scoliosis,which has important reference value for individualized treatment of different patients.