System and methods for improved access to vertebral bodies for kyphoplasty, vertebroplasty, vertebral body biopsy or screw placement

A method of determining the size and/or placement of screws or other instruments in pedicles during surgery in a selected spinal area, comprising:

• using a computer to generate a dimensionally 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 with cortical wall thicknesses selected by a surgeon performing the surgery such that the individual vertebra can be visualized as a structure that has been hollowed out with the remaining vertebral body being highlighted throughout its walls;
• using a computer to determine the narrowest diameter or isthmus within each pedicle based on the surgeon's selected pedicle cortical wall thickness;
• using a computer to generate a straight line starting at the center of the isthmus and extending inwardly to a point centered within the anterior cortex that is equidistant from superior and inferior endplates so that it is positioned concentrically within the pedicle without touching the highlighted walls thereof, the line terminating inside the vertebral body a predetermined distance from the anterior inner cortical wall and extending outwardly in the opposite direction to penetrate the posterior pedicle cortex;
• using a computer to expand the line concentrically to a diameter that does not exceed the isthmus diameter based on the surgeon's selected pedicle cortical wall thickness. the line being expanded into a cylinder that stops growing when any portion thereof contacts the highlighted inner cortical wall of the vertebral body with the exception of the posterior pedicle cortex.
• using a computer to determine the length of the cylinder from its innermost end spaced from the anterior inner cortical wall to a point at which the outer end thereof contacts the posterior pedicle cortex, and
• using a computer to calculate an ideal pedicle screw or instrument diameter, length and/or trajectory based on dimensions and a trajectory of the cylinder generated for each pedicle.