Fig. 4

a Schematic diagram for measurement of axial angle α of the CBT screw and axial angle β of the TPT screw: α is the angle between the axis of the CBT screw and the midline of the vertebral body in the axial view; β is the angle between the axis of the TPT screw and the midline of the vertebral body in the axial view. b Schematic diagram for measurement of sagittal angle γ of the CBT screw and sagittal angle δ of the TPT screw: γ is the angle between the axis of the CBT screw and the upper endplate of the vertebral body on the sagittal plane; δ is the angle between the axis of the TPT screw and the upper endplate of the vertebral body on the sagittal plane