Methods for determining pedicle base circumference, pedicle isthmus and center of the pedicle isthmus for pedicle screw or instrument placement in spinal surgery
A method of determining the pedicle base circumference and the pedicle isthmus to facilitate screw placement in a pedicle of a vertebral body during spinal surgery, comprising providing a series of first lines tangential to the outer cortical surface of the vertebral body in and near the pedicle on a transverse section from a three-dimensional image of the vertebral body, providing a series of second lines extending through the vertebral body in and near the pedicle thereof in perpendicular relation to the series of first lines, identifying the pedicle base circumference as the areas of the outer cortical surface where adjacent second lines are at the greatest angle with respect to one another, and identifying the pedicle isthmus as the areas of the outer cortical surface where the second lines that are opposed to each other are closest to being parallel to one another.
1. A method of determining the pedicle base circumference and the pedicle isthmus for enabling optimum screw or instrument placement in a pedicle of a vertebral body during spinal surgery, comprising:
using computer imaging apparatus to create a three-dimensional image of the vertebral body,
using computer imaging apparatus to create an image of the outer cortical shell of the vertebral body by taking a section of the three-dimensional image in a transverse plane;
using computer imaging apparatus to provide on the transverse section a series of first lines tangential to the outer cortical surface of the vertebral body in and near the pedicle;
using computer imaging apparatus to provide a series of second lines substantially perpendicular to the series of first lines, said second lines extending through the vertebral body in and near the pedicle thereof;
using computer imaging apparatus to identify the pedicle base circumference as the areas of the outer cortical surface where adjacent second lines are of the greatest angle with respect to one another; and
using computer imaging apparatus to identify the pedicle isthmus as the areas of the outer cortical surface where said second lines that are opposed to each other are closest to being parallel to one another.
2. The method of claim 1 wherein infinitesimal points are utilized on the outer cortical surface for the placement of said first lines and said second lines.
3. The method of claim 2 wherein anatomical three-dimensional locations of the pedicle base circumference and pedicle isthmus are determined by collating infinite transverse sections defining the pedicle base circumference and pedicle isthmus.
4. The method of claim 1 further comprising identifying a center of the pedicle isthmus from a cross-section thereof as the intersection of two lines derived from the centers of infinitesimal orthogonal second lines extending from the outer cortical surface.