The Biomechanical Properties Of Different Surgical Types For L5-S1 Single-segment Isthmic Spondylolisthesis With A Completely Collapsed Disc Space And The Evaluation Of Clinical Outcome For Reduction

Part 1:A study of the biomechanical properties of different surgical methods for L5 spondylolysis with complete intervertebral space collapse:a finite element analysis[Objective]Currently,there are many surgical methods for lumbar spondylolysis,and the efficacy of these surgeries has always been controversial.Posterolateral fusion(PLF)in situ,PLF with reduction or posterior lumbar interbody fusion(PLIF)with reduction are typical surgical methods at present.The aim of the research was to analyze the postoperative biomechanics of isthmic spondylolisthesis(IS)with complete intervertebral space collapse and provide more information to surgeons for the surgical plan.[Methods]Five volunteers of single segmental L5 IS with a completely collapsed disc space were selected,X-ray and Computer Tomography(CT)examinations were performed to exclude other lumbar diseases.CT was used to scan the corresponding segments from the lumbar spine to the sacral vertebra to obtain the Digital Imaging and Communications in Medicine(DICOM)data.Mimics19.0;3-Maticl2.0,Geomagic12.0,Pro/Engineer5.0,Hypermesh 12.0,ANSYS and other software were used to build postoperative FE models.A vertical pressure of 500N was applied to the superior endplate on L5,and the movement of forward bending,backward extension,left and right bend and left-right rotation were simulated with 10Nm.The bottom of S1 was fixed.The magnitude and distribution of the stress and the range of motion(ROM)were calculated and analyzed by computer.The significance was set at 0.05.[Results]The L5-S1 FE models established in this study were verified by comparing the ROM in L5-S1 functional units with the classical sample model and previous FEA research,which proved to be effective for analysis.The FE model of PLIF with reduction had the least ROM,the FE model of PLF in situ had the ROM close to the PLIF model,except for the left rotation movement.The ROM of PLF with reduction model was much greater than the other two surgical models,even greater than the intact model.As the load on internal fixation system,the stress on PLF in situ model was greater than PLIF with reduction,and less than the stress on the PLF with reduction.The maximum stress in PLF with reduction model reached 2008.60±556.61MPa。[Conclusion]The FE model established by software was effective and can be used as a basic model to simulate the FE models of different surgical interventions.The postoperative stress distribution of different models on the instrumentation was similar,but the magnitude of the stress was different.The stress on internal fixation system in the PLF with reduction model was much greater than that of PLF in situ,and the load in the latter model was greater than PLIF with reduction model.The stability of PLF in situ model was close to the PLIF with reduction model,which was most stable in the 3 operative models.The PLF with reduction model was more unstable than the intact model.Part 2:The impact of different surgical interventions on biomechanics at the adjacent intervertebral space in L5 isthmic spondylolisthesis with a completely collapsed disc space:a finite element analysis[Objective]Though the load on the internal fixation in posterior lumbar interbody fusion(PLIF)with reduction model was greater than Posterolateral fusion(PLF)in situ model,there were no significant differences in stability between two operative models.The study was going to evaluate the possibility of the adjacent segmental disease(ASD)after different surgical interventions for L5-S1 IS with a completely collapsed disc space.[Methods]With the computer tomography(CT)data of the volunteers in part one,finite element(FE)models of L4-S1 established.Three different FE models were used to simulate PLIF with reduction(rectangle or wedge)and PLF in situ.A vertical pressure of 500N was applied to the superior endplate on L4,and the activities of forward bending,backward extension,left and right bend and left-right rotation are realized through 10Nm.FE models were fixed at S1 bottom.The stress in L4-5 disk and articular process were calculated with software.Distribution and magnitude of the stress on the instrumentation was analyzed with computer.The significance level was set at 0.05.[Results]The range of motion(ROM)at L4-5 intervertebral disk space was consistent with previous authoritative studies,which verified the efficacy of the FE models in the study.The L4-5 ROM of the PLF in situ FE models was much greater than PLIF with reduction FE models(rectangle or wedge),which was most unstable.PLIF with wedged cage FE model possessed the smallest ROM,especially at the flexion movement.Stress in L4-5 disk of PLIF with wedged cage was less than PLIF with rectangle cage.The stress in the L4-5 intervertebral disk of PLF in situ model was the greatest.The stress on L4-5 articular process was very close between the two PLIF FE models,which was much less than the stress in PLF in situ models.[Conclusion]For L5 IS with a completely collapsed disc space,according to the change of biomechanics,the possibility of ASD after interbody fusion(IF)was lower than PLF in situ.The distribution of stress in L4-5 intervertebral disk was concentrate at frontier part and two back corners,which may lead to protrusion of the nucleus pulposus.Restoration of segmental lordosis(SL)may reduce the pressure in the adjacent disk.IF operation may reduce the stress on the L4-5 articular process than operation of PLF in situ.Part 3:Surgical reduction of grade Ⅱ or Ⅲ L5 single-segment isthmic spondylolisthesis with a completely collapsed disc space[Objective]As a common subtype of the isthmic spondylolisthesis(IS),the surgical types for grade Ⅱ or Ⅲ spondylolisthesis were still controversial.Grade Ⅱ or Ⅲspondylolisthesis with a completely collapsed disc space was a special type,the study focused on the feasibility and efficiency of surgical reduction in the improvement of sagittal alignment as well as clinical outcomes.[Methods]A retrospective review of the radiographic and clinical results from the surgical reduction of grade II or III single segment L5 IS with a completely collapsed disc space in our hospital from 2013 to 2018.According to the inclusion criteria,35 consecutive patients received posterior lumbar interbody fusion(PLIF).The 35 patients were divided into two groups based on preoperative pelvic tilt(PT)and sacral slope(SS):lumbosacral balanced group and imbalanced group.Following parameters were collected:(1)pelvic incidence(PI),(2)SS,(3)PT,(4)lumbar lodorsis(LL),(5)slip percent(SP),(6)slip angle(SA),(7)slip reduction(SR),(8)L1-5 lordosis(L1-5L),(9)L5-S1 lordosis(L5-S1L),(10)visual analogue scale(VAS),(11)Oswestry Disability Index(ODI).The clinical and radiographic outcomes were retrospectively reviewed preoperatively,1 month and 2 years postoperatively.All the parameters were analyzed with Statistical Product and Service Solutions(SPSS)and the Statistical significance level was set at 0.05.[Results]There were no significant differences in sex,age,body mass index(BMI),duration of symptoms and follow-up period between the balanced and imbalanced group.There were 18 grade Ⅱ patients and 7 grade Ⅲ patients in balanced group,4 grade Ⅱ patients and 6 grade Ⅲ patients in imbalanced group.The slipped degree was different in the two groups(p<0.01).The SP was 51.5± 11.3%before the surgery and 10.3±5.6%after the operation(p<0.01).Surgical reduction and fusion corrected the spino-pelvic parameters to a more balanced condition,especially for an unbalanced pelvic group.6 patients with imbalanced pelvis turned into balanced pelvis after the operation.There existed a remarkable decrease in the leg and lumbar VAS and ODI scores.By the 2 years’ of following up,vertebral slippage reduction was effectively maintained.The imbalanced group had a higher SP.PT decreased in both groups,while SS and LL increased.No difference can be found in VAS and ODI score between the balanced and imbalanced group.[Conclusion]Clinic outcomes and radiographic parameters significantly improved after PLIF with slippage reduction for grade II or III single segment L5 IS with a collapsed disc space.The results of this study gave a more specific conclusion that PLIF with slippage reduction was an effective surgical procedure for this particular type of IS.As this a retrospective study with small sample,prospective study with big sample size needs to be performed in the future.