A method of determining the pedicle base circumference and the pedicle isthmus tofacilitate screw placement in a pedicle of a vertebral body during spinal surgery, comprisingproviding a series of first lines tangential to the outer cortical surface ofthe vertebral body in and near the pedicle on a transverse section from a three-dimensionalimage of the vertebral body, providing a series of second lines extending throughthe vertebral body in and near the pedicle thereof in perpendicular relationto the series of first lines, identifying the pedicle base circumference as theareas of the outer cortical surface where adjacent second lines are at the greatestangle with respect to one another, and identifying the pedicle isthmus as theareas of the outer cortical surface where the second lines that are opposed toeach other are closest to being parallel to one another. The center of the pedicleisthmus is identified from a cross- section thereof as the intersection of twolines derived from the centers of infinitesimal orthogonal second perpendicularlines from the outer cortical surface.
