Finite Element Analysis And Biomechanical Evaluation Of Different Posterior Endoscopic Canal Decompression For Lumbar Spinal Stenosis

Background and Objective: With the innovation of spinal canal decompression technology and the development of surgical instruments and optical equipment,spinal endoscopy technology is increasingly widely used in the treatment of lumbar spinal stenosis(LSS).Percutaneous endoscopic interlaminar discectomy(PEID)Procedures such as endoscopic fenestration decompression(Endo-LOVE)and endoscopic unilateral laminotomy for bilateral decompression(Endo-ULBD)have achieved good clinical results and are gradually being accepted by spinal surgeons.However,based on clinical observations of a large number of cases,there are still limitations to the current PEID technique.Endo-ULBD often results in insufficient decompression of the central spinal canal and contralateral recess,while in bilateral Endo-LOVE,the central spinal canal may not be fully decompressed.Furthermore,in order to achieve an ideal decompression range,it is sometimes inevitable to excessively remove the facet joints,even the facet joint is severed,increasing the incidence of iatrogenic segmental instability.Against this background,this study explores the use of a modified PEID technique(Cross-Overtop decompression,Cross-Overtop)to treat LSS,which achieves relatively sufficient decompression of the lumbar spinal canal through full-endoscopic interlaminar decompression without excessively removing the facet joints or compromising the integrity of the posterior ligament complex(PLC).The study intends to systematically evaluate the effects of different PEID techniques on surgical segment stability through finite element simulation analysis and biomechanical evaluation of various lumbar decompression procedures such as Endo-LOVE,Endo-ULBD,and Cross-Overtop.The aim is to verify the clinical feasibility of endoscopic spinal decompression for LSS and provide biomechanical evidence for the clinical application and promotion of modified PEID techniques.Part Ⅰ Finite element analysis and biomechanical evaluation of endoscopic fenestration decompression and endoscopic unilateral laminotomy for bilateral decompression for lumbar spinal stenosisObjective: To analyze the effects of Endo-LOVE and Endo-ULBD on the biomechanics of the responsible segment after the treatment of lumbar spinal stenosis,and to evaluate the effect of the two surgical methods on the stability of the lumbar spine.Provide biomechanical basis and theoretical framework for its clinical application and promotion.Methods: The finite element model M0 of normal lumbar L4-L5 segment was established by Mimics,Geomagic,Solidworks and ANSYS software.On this basis,the Endo-LOVE model M1 and the Endo-ULBD model M2 were established respectively.The same stress was applied to the upper surface of L4 vertebral body in the three models.During simulation,the bottom of the L5 vertebral body was fixed completely.The total range of motion and the Von Mises stress extreme value of the annulus fibrosus were analyzed under six working conditions: flexion,extension,left lateral bending,left rotation,right lateral bending,and right rotation.Results:(1)Compared with model M0,the range of motion of model M1 under flexion,extension,left lateral bending,left rotation,right lateral bending and right rotation increased by 8.24 %,12.17 %,0.77 %,1.60 %,1.86 % and 6.85 %,respectively.The ROM of model M2 increased by 8.24 %,12.17 %,0.77 %,1.60 %,2.17 % and 6.85 % respectively in six cases.Compared with model M1,model M2 showed a slight increase in ROM during right lateral bending,but no significant increase or change in trend was observed in other conditions.(2)Compared with the model M0,the Von Mises stress extremum of the annulus fibrosus of the model M1 in the six cases increased by 4.65%,16.09%,0.21 %,0.77 %,0.25 %,1.51 %,respectively,and the model M2 increased by 4.58 %,16.15 %,0.20 %,0.80 %,0.23 %,1.52 %,respectively.The trend of annulus fibrosus Von Mises stress maximum values under different conditions for models M1 and M2 was not significantly different.Conclusion: After the treatment of LSS with Endo-LOVE and Endo-ULBD,the stability of the responsible lumbar spinal segment was good without a significant increase in joint mobility or sudden changes in stress on the intervertebral disc’s fibrous ring.Therefore,these surgical techniques can effectively maintain the stability of the responsible spinal segment.Part Ⅱ Finite element analysis and biomechanical evaluation of modified endoscopic posterior decompression for severe lumbar spinal stenosisObjective: Using finite element analysis,evaluate and compare the biomechanical characteristics of three PEID surgical models: Endo-ULBD,bilateral Endo-LOVE,and Cross-Overtop.Explore the feasibility and rationality of the Cross-Overtop surgery from a biomechanical perspective,and provide theoretical and practical evidence for the decision-making of severe LSS surgery,as well as a biomechanical foundation and theoretical basis for the clinical application and promotion of Cross-Overtop.Methods: A finite element model M0 of the L4-L5 standard motion segment was established based on computed tomography images of the ordinary human body.Firstly, the validity of the FE model(M0)of the lumbar spine was verified by comparing it with the results of previous studies.And then,the Endo-ULBD model(M1),Endo-LOVE model(M2)and Cross-Overtop model(M3)were also established based on M0 following the experimental protocol.Perform a biomechanical evaluation of the lumbar spinal segment’s ROM and the Von Mises stress of the intervertebral disc for the L4-L5 segment in models M1,M2,and M3.Results: The comparison between the parameters resulted from the established virtual FE lumbar model and the previous research showed that the ROM of the M0 model was consistent with the other scholars’ research results,indicating the validity of the FE model in this study.In terms of ROM value,M1 increased by 2.05 %,7.54 %,0.19 %,0.10 %,0.51 % and 9.36 % respectively compared with M0 under six working conditions.Compared with M0,M2 increased by 7.43 %,11.56 %,0.89 %,0.38 %,3.80 % and 9.36 % respectively.Compared with M0,M3 increased by 7.20 %,8.55 %,0.33 %,0.71 %,3.66 % and 4.13 % respectively.In terms of the extreme value of intervertebral disc stress,M1 increased by 8.20 %,12.57 %,0.00 %,0.96 %,0.70 % and 15.75 % respectively compared with M0 under 6 working conditions.Compared with M0,M2 increased by 8.74 %,9.29 %,0.75 %,0.96 %,2.11 % and 15.75 % respectively.Compared with M0,M3 increased by 8.20 %,13.11 %,0.75 %,1.44 %,1.41 % and 8.90 % respectively.All the ROM values in the surgical models were less than 10 o,compared with the M0 model,the growth rate of ROM ranged from 0.10% to 11.56%,while those of disc stress ranged from 0% to 15.75%.Verifying the stability of the affected segment after Cross-Overtop operation.Conclusion: Cross-Overtop can achieve the goal of full decompression of the entire spinal canal by fully expanding the volume of the central vertebral canal and the lateral recess,while maximizing the protection of the integrity of the facet joint and posterior ligament complex.As an improved technique of endoscopic PEID,although it may increase the segmental range of motion and disc stress compared to the preoperative state,it can be controlled within a stable range close to Endo-ULBD and Endo-LOVE.The study suggests that the biomechanical characteristics of the responsible lumbar segments after Cross-Overtop decompression surgery have no significant changes.Therefore,it can be considered as an effective method for endoscopic treatment of severe LSS.