Fig. 1

Measurement of pedicle screw planning trajectory. A Axial view of the vertebra. Draw a guideline (green straight line) through the midline of the vertebra. Measure the vertical distance d from the entry point to the midline and the angle θ between the long axis of the screw and d. B Sagittal view of the vertebra. Draw a guideline (green straight line) along the lower endplate of the vertebral body. Measure the vertical distance d’ between the entry point of the screw and the guideline and the angle θ’ between the long axis of the screw and d’