Efficacy Of The Extreme Lateral Transpsoas Approach To The Low-grade Lumbar Spondylolisthesis And A Three Dimensional Finite Element Analysis Of Biomechanical Stability Of Extreme Lateral Lumbar Interbody Fusion

ObjectiveTo evaluate the efficacy of the extreme lateral transpsoas approach to the low-grade lumbar spondylolisthesis and a three dimensional finite element analysis of biomechanical stability of extreme lateral lumbar interbody fusion.Methods1.Experimental part:a healthy male volunteer was scanned to obtain L3-S1 lumbar CT image data.mimics21.0,wrap2017,SolidWorks 2017 and ANSYS 17.0 software were used to construct a three dimensional finite element normal lumbar model.After finite element validation,12 kinds of different finite element models were used to calculate the range of motion and stress.2.Clinical study:70 patients of low-grade lumbar spondylolisthesis who was underwent minimally invasive XLIF procedure from January 2012 to December 2017(16 stand alone,30 lateral fixation,24 bilateral pedicle screw fixation).The disc height(DH),foraminal height(FH),slipping percentage(SP),lumbar lordotic(LL)angle,and segmental lordotic(SL)angle were measured preoperatively,3 days postoperatively,and the last follow-up.Cage subsidence were evaluated the last follow-up.Clinical outcomes were evaluated using Japanese Orthopaedic Association(JOA)and visual analog scale(VAS)scores.The stand alone group,lateral fixation group and bilateral pedicle screw fixation group were compared based on radiologic and clinical outcomes measures using SPSS v23 for statistical analysis.Results1.Experimental part:the three dimensional finite element normal lumbar model was confirmed to be valid.ANSYS 17.0 analysis software results show that 18mm XLIF cage can provide bending and rotation stability,In addition,increased peak endplate stress was found in 18mm stand alone models in flexion/extension,whereas 26mm cage,BPS or UPS fixation provide favorable biomechanical stability.2.Clinical study:The DH,FH,LL angle,SL angle were significantly increased from preoperatively to 3 days postoperatively in stand alone,lateral fixation and bilateral pedicle screw groups.From preoperatively to last follow-up,there were no significant differences in DH in stand alone group,While other imaging parameters were significantly increased.The mean correction of vertebral slippage measured on lateral lumbar X-ray was 40.99%in stand alone group,42.30%in lateral fixation group and 58.42%in bilateral pedicle screw group at 3 days postoperatively.And the mean correction of vertebral slippage was decreased in stand alone and lateral fixation group from 3 days postoperatively to last follow-up.The risk of cage subsidence at last follow-up was similar in all groups.At last follow-up,the VAS and JOA scores were significantly improved in all groups.The fusion rate was satisfactory.Conclusions18mm XLIF cage can provide bending and rotation stability,In addition,increased peak endplate stress was found in 18mm stand alone models in flexion/extension,whereas 26mm cage,BPS or UPS fixation provide favorable biomechanical stability.XLIF is a reliable minimally invasive technique to treat low-grade lumbar spondylolisthesis.