Kinetic MRI Analysis Of Lumbar Spinal Stenosis And Finite Element Analysis Of Lumbar Surgical Model

Objective:Investigating the change rules of dural sac,lateral recess associated with postural changes in LSS patients;And explaining the "separation phenomenon" of LSS.To establish the finite element model of lumbar spine;Comparing the stress distribution and the influence on the range of motion between laminectomy and laminectomy plus pedicle screw fixation;Making out the effect of decompression surgery on lumbar stability and the necessary of pedicle screw fixation.Methods:Randomly selecting the LSS patients in Tianjin Hospital between July 2016 and January 2017 underwent kinetic MRI examination.Mimics 17.0 was used to measure the spinal canal cross-sectional area,sagittal diameter and other parameters.Based on the CT data of a patient in the part I,Mimics10.01,Rhino5.0,Abaqus6.12 and other software were used to establish the model of lumbar spine and verify the validity of it.At the same time,the L3 vertebral body was used as the main operative segment and build the laminectomy model and internal fixation model.In solving,constrained S1 and imposed 400 N on the L1,then applied 8N·m,6N·m,4N·m moment to simulate the flexion-extension and rotation movement.Results:8 patients(5 females and 3 males)were examined.After measurement and analysis,we found that 1)BAP doesn't change significantly with position;DAP and DAP/BAP were maximum in flexion and minimum in extension.2)BCA doesn't change significantly with position;DSCA and DSCA/BCA were maximum in flexion and minimum in extension.3)The left and right disk-flavum ligamentum space were significantly increased in flexion,especially the lower lumbar;the L/R ratio were about 1.0,which had no obvious regularity.The results of finite elements analysis:1)The experimental data of the normal model were larger than the vitro data in extension,and rotation,but it had no significant difference and no effect on the analysis.2)The ROM and average stress of the intervertebral disc of the total laminectomy model increased significantly compared with the preoperative condition,especially in the operation segment and flexion-extension,rotation movement.3)The ROM and average stress of the intervertebral disc of the internal fixation model decreased compared with preoperative condition,especially in the operation segment and flexion-extension,lateral flexion movement.4)The ROM of laminectomy model increased in different degrees compared with the internal fixation model,especially in flexion.The mean stress of the intervertebral disc of laminectomy model was significantly higher than internal fixation group,especially the surgical segment.5)As to the non-operation segment of two surgical model,ROM had no obvious changes and the stress of inter-vertebral disc increased significantly,especially the L5S1 segment.Conclusions:1)DAP,DSCA,DS showed maximum in flexion and minimum in extension.2)The changes of soft tissue spinal canal were related to the intervertebral disc,epidural fat and others.3)The diameters of bony canal didn't change with positions.4)LSS was a dynamic narrowing of the intervertebral foramen,which occured on the basis of lumbar spine degeneration.5)Total laminectomy decompression led to the increase of ROM,increase of the stress in intervertebral disc,and the decrease of lum bar stab ility,even lumbar segment instability.6)Pedicle screw fixation can increase the stability of lumbar spine,but can cause stress con centration in ad jacent seg ments,and ASD.7)We should consider the compensatory and repair ability of human being in clinical,and analysis strictly the fusion segment and indications to prevent ASD.