Novel Placement Of Cortical Bone Trajectory Screws In The Lumbar Spine:A Radiographic And Cadaveric Study

Study Design A radiographic and cadaveric study.Objective The aim of this study was to conduct a detailed comparison about the parameters between the ideal cortical bone trajectory(CBT)and the practical CBT screw.Summary of Background Data Pedicle screw fixation system has been widely used in spinal surgery because of its superior biomechanical strength.However,complications such as screw loosening,pullout and broken,often lead to the loss of surgical construct stability.Particularly in patients with poor bone quality,screw loosening is a well-known complication.Recently,cortical bone trajectory screws have been becoming popular in spine surgery because of obtaining improved fixation while minimizing soft tissue dissection.However,to our knowledge,there has been no report conduct a detailed comparison about the parameters between the ideal cortical bone trajectory(CBT)and the practical CBT screw.Methods The three-dimensional computed tomography(3D-CT)scans of 126 spinal vertebrae separated from 40 lumbar spines were studied.After the CBT was determined,the maximal screw length(MSL),the maximal screw diameter(MSD),the lateral angle(LA),and the cephalad angle(CA)were measured.Thereafter,these cadaveric lumbar spines were used in inserting the CBT screw.Subsequently,the LAs and CAs of the screws were measured using 3D-CT.Results As for the CBT,the MSL gradually increased from L1(32.0 mm)to L4(35.3 mm),then decreased at L5(34.8mm).The MSD increased from L1(4.5 mm)to L5(7.5mm).The LA from L1 to L5 were 9.2°,9.4°,9.9°,11.2°,and 12.0°,respectively.The CA from L1 to L5 was25.8°,25.8°,26.3°,26.8°,and 26.0°,respectively.As for the CBT screw,the LAs from L1 to L5 were 12.7°,14.1°,13.2°,12.4°,and13.0°,respectively.The CAs from L1 to L5 were 25.4°,27.5°,29.2°,30.1°,and 30.5°,respectively.A significant difference was observed between the angles of ideal trajectory and the actual screw.Conclusions The parameters of the CBT screw are slightly larger than the measurements of the optimal trajectory.The CAs and LAs are approximately 25°–30°and 10°–16°,respectively.L1 and L2 should be given consider able attention when using the CBT technique.Trajectory measurements can only be used as a guide in clinical practice.