Biomechanical Evaluation Of Endoscopic Minimally Invasive Lumbar Interbody Fusion Through Kambin's Triangle:A Finite Element Study

BackgroundMinimally invasive lumbar interbody fusion(LIF)can achieved clinical efficacy in some open surgery cases.LIF through Kambin triangle has many advantages,such as no invasion of abdominal organs and vessels,no damage to the structure of posterior collateral ligament complex,no need to expose the dura and the nerve root and there will be no epidural scar and so on.However,there are still problems to achieve LIF under full endoscopy.Due to the limitations of the working-tube,surgical procedures and placement of the cage in a small vision and narrow space are with high risk and technical difficulty.The smaller the cage,the clearer vision in the channel and the more convenient the conduction space.Obviously,the small cage is one of the methods to achieve minimally invasive LIF.However,whether the small cage is able to meet the biomechanical requirements of the human lumbar spine in daily life is still a question.After the minimally invasive LIF using a small cage,the stress on the screw will increase,and the stability requirements for the FSU of the screws-rods system must be improved.Which method has the best stability of lumbar spine maintenance is also a problem that needs to be solved.Objective1.Establish a lumbar finite element(FE)model and validate it.2.Design a novel narrow-face cage and analyze the biomechanical properties of the narrow-face cage under full-endoscopic LIF with FE method.3.The FE biomechanical analysis was performed on the three kinds of screws-rods fixation methods to find out the best optimal one,including transvertebral screws-rods system(TVS),the cortical bone trajectory screws-rods system(CBTS)and the transpedicle screws-rods system(TPS).Materials and Methods:1.Modeling:Five computer software was used to establish a full lumbar finite element model(L1?L5).Validation:Six activities of lumbar were simulated and the results were compared with those of foreign literature.2.Narrow face cage was designed to match the endoscopic surgery with widths of 7,8 and 9 mm,respectively.Endoscopic lumbar interbody fusion through Kambin's Triangle was simulated and FE studied.3.L4-L5 FSU was took form the validated lumbar spine model assenbleing with an 8 mm novel narrow-surface cage.Respectively,the model was assembled with percutaneous transverterbral screws fixation(PTVS),percutaneous cortical bone trajectory screws fixation(PCBTS),and a percutaneous pedicle screws fixation(PPS).And FE analysis was performed and compared.Results:1.The results of the FE model of the whole lumbar were similar to those of the in vitro test reported in literatures.The trend between two results were the same.2.In all models conditions,the highest stress of the cage was between 59 MPa and 72 MPa,both less than their yield strength 98 MPa.3.The maximum displacement of the vertebral body and the cage in the other five motion directions except for the extension activity of the PTVS model was the smallest among the three models.Conclusions1.The FE model of the whole lumbar spine established by this study can be used for analysis and prediction of lumbar spine biomechanics.2.The new narrow-faced cage designed has sufficient strength to meet the lumbar motion of the human body.3.The stability of lumbar was the highest with PTVS.The novel narrow face cage with PTVS may be a better choice f-or the full-endoscopic LIF through Kambin's triangle.