Objectives : Assessment of the accuracy and angle of cortical bone trajectory (CBT) screw implantation before and after introduction of preoperative three-dimensional (3D)-simulation.
Methods : Forty-eight screws (24 L4 screws and 24 L5 screws) used in 13 operations for lumbar decompression and fusion performed at our institution were analyzed using postoperative CT. Twenty-four screws used before and after the introduction of 3D-simulation (initial group and later group, respectively) were compared for 1) the number of deviations (Neoʼs criteria), 2) the laterally oriented angle on the axial plane, and 3) the cranially oriented angle on the sagittal plane.
Results : Three out of 24 screws in the initial group deviated medially (grade 1 : one screw, grade 2 : two screws) without clinical symptoms. In the later group, all 24 screws were properly inserted. The laterally oriented angle and cranially oriented angle at the L4 level in the initial group were 17.1°and 31.8°, respectively, whereas those in the later group were 14.5°and 30.6°, respectively. The corresponding angles at the L5 level in the initial group were 13.6°and 30.6°, respectively, and those in the later group were 15.3°and 28.3°, respectively.
Discussion : In conventional pedicle screw implantation, it is easy to correct the insertion point or angle using fluoroscopy. However, in CBT screw implantation, since a screw is inserted obliquely from both the sagittal and axial planes, the correct lateral orientation and screw entry point are difficult to determine from intraoperative fluoroscopy alone. Therefore, it is important to confirm not only the screw angles but also the insertion point and screw size in preoperative 3D-simulation in order to insert the CBT screws properly.
