CT scan showing that the diameter and the length of thoracic CBT screws: (1) the screw diameter; (2) maximal screw length; (3) screw insertion point; (4) the red line was horizontal axis, which can be used to calibrate the axial plane; (5) the blue line represents the sagittal axis, which can adjust the sagittal plane. CBT = cortical bone trajectory, CT = computed tomography.