Effect Of Monoaxial Or Polyaxial Pedicle Screws On Adjacent Segmental Degeneration In Lumbar Posterior Fusion

Objective:to analyze the effect of monoaxial pedicle screw or polyaxial pedicle screw on adjacent segment degeneration in posterior lumbar fusion。Methods:Data of patients who underwent lumbar posterior fusion in our hospital from2014 to 2019 were collected.According to the type of intraoperative pedicle screws,the patients were divided into two groups: monoaxial pedicle screw group(21cases)and polyaxial pedicle screw group(19cases).The clinical effect was evaluated by visual analog scale(VAS).Imaging degeneration was evaluated at 3 to 6 months after surgery,1 year after surgery,and 2 years after surgery by lumbar X-ray at 3 different time periods.Use Mimics,Geomagic Studio,Solid Works,Hyper Mesh software to build two groups of models.Finally,the finite element analysis was carried out with ABAQUS software.Results:Follow-up data of all enrolled patients were complete.There were no significant differences in gender,age,BMI,smoking history and drinking history between 2groups(P > 0.05).Clinical results: There was no significant difference in visual analog scale(VAS)between the two groups preoperatively and postoperatively(P > 0.05),and the postoperative VAS of the two groups decreased significantly compared with the preoperative comparison,showing a statistical difference.(P < 0.05).Imaging adjacent segment degeneration results:3-6 months after surgery,4 cases(19%)of the monoaxial pedicle screw group and 1 case(5.3%)of the polyaxial pedicle screw group showed no significant difference between the two groups(P > 0.05).One year after surgery,9 cases(42.9%)of the monoaxial pedicle screw group and 2 cases(10.5%)of the polyaxial pedicle screw group showed statistically significant difference between the two groups(P < 0.05).Two years after surgery,10 cases(47.6%)of the monoaxial pedicle screw group and 3 cases(15.8%)of the polyaxial pedicle screw group showed statistically significant differences between the two groups(P <0.05).In terms of postoperative complications,only one patient in the monoaxial screw group was suspected of infection.The range of motion of adjacent segments in the monoaxial pedicle screw group was higher than that in the polyaxial pedicle screw group.The stress of the adjacent segments of the intervertebral disc in the monoaxial screw group was larger than that in the polyaxial screw group(except for the extension of the L5-S1 segments,the stress in the polyaxial screw group was slightly greater than that in the monoaxial screw group).Conclusion:monoaxial pedicle screw and polyaxial pedicle screw can achieve similar clinical effects,and the postoperative complications of the two groups are also similar.However,the monoaxial screw has a greater influence on the degeneration of the adjacent segments,and the influence of the head end is greater than that of the caudal end.