Fig. 2

A The entire pedicle (green parts) was selected to determine the pedicle axis (blue lines). The pedicle lateral angle (LA) was defined as the angle between the axis and the YZ plane. The pedicle screw length (PSL) was defined as the distance between the entry point (intersection point of the trajectory and lateral mass surface) and intersection point (intersection point of the trajectory and anterior vertebral wall). B The pedicle screw diameter (PSD) was determined by the maximum diameter of the pedicle, which was automatically calculated by the software. The left side of pedicle, illustrating the pedicle was damaged by the simulation screw. C The pedicle sagittal angle (SA) was defined as the angle between the axis and the fitting plane of the lateral mass surface (red plane). D The locations of the entry point (blue point), LN (yellow point) and MP (green points) are illustrated. E The measurement of the lateral notch horizontal distance (LNHD), lateral notch vertical distance (LNVD) and middle point of the inferior edge of the C6 inferior articular process (MP) horizontal distance (MPHD)