A method of determining the size and placement of screws in pedicles during surgery in a selected spinal area, comprising using a computer to generate a true three-dimensional image of the bony spine in the selected spinal area using a computer to hollow out the vertebra in the three-dimensional image, using a computer to determine the narrowest cross section (isthmus) within each pedicle using a computer to generate a straight line starting at the center of the isthmus and extending in opposite directions so that it is positioned concentrically within the pedicle without touching the walls thereof, using a computer to expand the line concentrically and radially to a cross sectional size that is less than that of the isthmus, and using a computer to calculate the ideal pedicle screw diameter, length and trajectory based on the dimensions and trajectory of the cylinder generated for each pedicle.
