Application Of Modified S2 Screw Fixation Technique In L5 Spondylolisthesis Surgery

Background: Spinal deformity is more common in the clinic and is one of the important reasons for surgical treatment of spinal diseases.Lumbar spondylolisthesis often requires surgical orthopedic reduction and internal fixation,while severe lumbar spondylolisthesis often needs to be fixed to the humerus and even the pelvis to achieve orthopedic and stability requirements.Traditional spine and pelvic fixation techniques often face a series of complications such as internal fixation loosening,broken nails,pseudoarticular formation and pain.The use of tibial screws and S2 Alar Iliac Screws(S2AI)has greatly reduced the complications associated with internal fixation,but has also reported clinical problems such as sacroiliac joint degeneration and sacroiliitis.In addition,in order to achieve precise placement of the spine pelvis,timely guidance of related tools such as C-arm(X-ray)or O-arm(CT)is often required during surgery,which also increases the operation time and additional radiation.In addition,the neurovascular injury caused by the deviation of the tibia and sacroiliac joint is also one of the issues that need to be highly valued.Objective: Exploring the imaging nail data of modified S2 screws in Chinese people,and simulating the biomechanical data of modified S2 screws compared with traditional lumbar spondylolisthesis under simulated flexion,extension,rotation and lateral bending conditions,and retrospectively obtained the biomechanical data of modified S2 screws.To analyze the therapeutic effect and complications of modified S2 screw surgery and traditional screw surgery in the treatment of lumbar spondylolisthesis,it is proved that the improved S2 screw can provide sufficient holding force to achieve strong stability of distal fixation.Methods: In this study,the CT scan of the lumbosacral pelvis structure of 60 normal Chinese adults was used to reconstruct the three-dimensional image.The Minics software was used to explore the optimal bone trajectory of the modified S2 screw.The length of the screw,the angle of the declination,the offset of the nail insertion point and other related data were measured and evaluated to achieve the imaging evaluation of the modified S2 screw.Secondly,a three-dimensional reconstruction model of the lumbosacral pelvis of an adult man was selected,modeled by Mimics 10.0 and Geomagic 9.0 software,and the three-dimensional finite element analysis pre-processing was completed by Hypermesh 11.0 software.We compared the changes in spine mobility between the normal spine and the four different surgical procedures((1)L5-S1 fusion fixation;(2)L4-L5-S1 fusion fixation;(3)L5-S1-S2AI;(4)L5-S1-modified S2 fixation scheme).The stress distribution and pull-out resistance of the distal fixation screws of the four different nailing schemes under flexion and extension,rotation and side bending were evaluated.Finally,a retrospective study was performed on the modified S2 screw.Patients with L5 spondylolisthesis were treated with L5-S1-modified S2 and conventional L5-S1 and L4-L5-S1.The SF-36 scale and preoperative and postoperative and the last follow-up imaging data were in comparison to analyze its clinical efficacy and complications,and to improve the clinical evaluation of modified S2 screw stability.Results:(1)The ideal screw path data of modified S2 screw were obtained by CT measurements of 60 Chinese normal lumbosacral vertebrae.The average screw path of male was 50.4±2.4 mm,the screw-rod angle was 41.2±2.8°,the right screw-rod angle was 50.7±1.8mm,the screw-rod angle was 42.3±2.2°,the lumbosacral relative angle was 35.4±13.6°;The average screw path of female was 48.2±2.1mm,the screw-rod angle was 42.4±2.5° and the right screw-rod angle was 48.9±2.6mm and the screw-rod angle was 42.2±2.7°,the lumbosacral relative angle was 39.5±17.2°.The data shows that the modified S2 screw channel is long enough,and the safety of placing the pedicle screw and installing the connecting rod is controllable.There was a statistical difference between male and female in screw length,sagittal declination,and relative angle of lumbosacral.The safety of placing the pedicle screw and installing the connecting rod is controllable.There was a statistical difference between male and female in screw length,sagittal declination,and relative angle of lumbosacral.(2)Modified S2 screw for moderate to severe L5 spondylolisthesis has little effect on spinal mobility.Similar to other surgical procedures,the comparison of surgical methods suggests that the modified S2 screw has uniform stress distribution during flexion,extension,rotation and lateral bending,and has strong resistance to pullout.It can achieve the purpose of strong fixation at the distal end.(3)60 patients in 3 groups were followed up for 12-20 months.In the L4-L5-S1 group,two patients had lumbosacral pain about 3 months after operation.The review showed that the S1 screw was loose.Complete recovery after bed rest and anti-osteoporosis treatment.In the L5-S1 reduction and internal fixation group,1 patient had S1 loosening,L5/S1 pseudoarticular formation in 5 months after operation and revision surgery.The follow-up results were good.There was no obvious complications in the L5-S1-modified S2 group occur.Conclusions:(1)The modified S2 screw designed by us has a maximum off-angle of 45°,which can find the ideal screw path in the sacrum.The screw length and declination meet the clinical requirements,and the clinical application is feasible.(2)Modified S2 screw for moderate to severe lumbar spondylolisthesis has little effect on spinal mobility.Similar to other surgical procedures,the comparison of surgical methods suggests that the modified S2 screw has uniform stress distribution during flexion,extension,rotation and lateral bending,and has good resistance to pullout.Ability to achieve remote fixation enhancement.(3)Clinical retrospective analysis showed that the modified S2 screw was stable in internal fixation and less complications in the treatment of severe lumbar spondylolisthesis.It can be applied to the distal fixation of long segmental spinal deformity after accumulating certain clinical experience.