Safety Of Cortical Bone Trajectory Screw Placement And Related Risk Factors In Lower Lumbar Vertebrae

Objective:To investigate the accuracy of cortical bone trajectory（CBT）screw placement and the rate of proximal facet joint violation（FJV）in the lower lumbar vertebrae,and analyze the related risk factors that lead to the malposition of CBT screw and the violation of proximal facet joint.Methods:Thirty-six patients that received CBT screw placement from March 2019 to February 2021 were retrospectively included.The main indexes were accuracy of CBT screw placement and the rate of proximal FJV.The complications due to the malposition were observed intraoperatively and postoperatively.Moreover,the related risk factors leading to the malposition of CBT screw and the proximal FJV were assessed with univariate analysis and Logistic regression analysis.Results Thirty-six patients totally received 140 CBT screws.According to the Gertzbin-Robbins criteria,there were 127 screws（90.7%）graded A,11 screws（7.9%）graded B,2 screws（1.4%）graded C,and no screws graded D and E.Among the 13 screws that caused damage to the pedicle cortex,5（38.4%）damaged the outer cortex,4（30.8%）damaged the inner cortex,and 4（30.8%）damaged the inferior cortex.According to Babu criteria,20（19.6%）of the 102 CBT screws resulted in proximal FJV.82（80.39%）facet joints were intact and rated as grade 0.Besides,14（13.73%）,1（0.98%）and 5（4.90%）facet joints were grade 1,2 and 3,respectively.Among the 20 proximal FJV,1（5.0%）was caused by the screw shaft and the remaining 19（95.0%）were caused by the screw head.Among 36 patients,one patient underwent intraoperative revision due to malposition.In addition,there were no cases of postoperative revisions,postoperative neurological symptoms and wound infections due to malposition.Univariate analysis showed that gender（χ2=4.382,P=0.036）,L5 segment placement（χ2=4.388,P=0.036）and the angle of screw and endplate（χ2=2.221,P=0.029）are the factors affecting the rate of proximal FJV.Logistic regression analysis found that L5 segment placement（adjusted OR 3.285,95%CI 1.036-10.421;P=0.043）and the angle of screw and endplate<19°（adjusted OR 6.403,95%CI 2.096-19.558;P=0.001）are the independent risk factors leading to the proximal FJV.Conclusion:CBT screw placement has a high accuracy of screw placement and promising protection of proximal FJV.Meanwhile,the incidence of complications due to malposition is low.Therefore,CBT placement is a safe and reliable supplement for traditional pedicle screw placement in clinical practice.In addition,L5 segment placement and the angle of screw and endplate<19° are independent risk factors leading to the proximal FJV.