Method of improving pedicle screw placement in spinal surgery

• US 20050192575A1
• Filed: 02/18/2005
• Published: 09/01/2005
• Est. Priority Date: 02/20/2004
• Status: Active Grant

• Current Assignee: Leucadia 6, LLC
• Original Assignee: Hector O. Pacheco
• Inventors: Pacheco, Hector O.
• Granted Patent: US 7,235,076 B2
• Time in Patent Office: Days
• US Class Current: 606/86.00A
• CPC Class Codes: A61B 17/1604 Chisels; Rongeurs; Punches; Stamps
• CPC Class Codes: A61B 17/1615 Drill bits, i.e. rotating tools extending from a handpiece to contact the worked material
• CPC Class Codes: A61B 17/1671 for the spine
• CPC Class Codes: A61B 17/1757 for the spine
• CPC Class Codes: A61B 2090/376 using X-rays, e.g. fluoroscopy
• CPC Class Codes: A61B 34/10 Computer-aided planning, simulation or modelling of surgical operations

Abstract

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 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; 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, 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 and radially to a cross sectional size that is less than that of the isthmus, the line being expanded into a cylinder that stops growing when any portion thereof contacts the inner cortical wall of the hollowed out vertebral body, with the exception of the posterior pedicle cortex; 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.

Claims

1. 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 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 in opposite directions 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 the point at which the outer end thereof contacts the posterior pedicle cortex, 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.

2. The method of claim 1 wherein two-dimensional images of the selected spinal area are first generated, and then the computer is used to generate the three-dimensional image.

3. The method of claim 2 wherein the two-dimensional images are created by computed tomography scanning (CT), magnetic resonance imaging (MRI), fluoroscopy or similar imaging studies.

4. The method of claim 2 wherein the two-dimensional images are thin cut sections for greater accuracy and detail.

5. The method of claim 1 wherein the center of the isthmus is the fulcrum point for the generated line.

6. The method of claim 1 wherein a computer generates a data summary table which displays the ideal pedicle screw length, diameter and trajectory for each vertebra.

7. The method of claim 6 wherein the trajectory is measured as an angle with respect to the transverse and sagittal planes with corresponding superior end plate as a reference plane for each vertebra pedicle.

8. The method of claim 6 wherein a computer generates a schematic drawing displaying the idealized pedicle screw length, diameter and trajectory for each vertebra.

9. The method of claim 6 wherein a computer is used to determine screw sizes based on screws that are available for use.

10. The method of claim 1 further comprising the identification of the pedicle base circumference at the junction between the pedicle base with its vertebral body to enable a fluoroscopic AP image scan intraoperatively to correlate with the preoperative three-dimensional image generated by the computer for determining pedicle screw placement and measurements based on the outline of the pedicle base circumference.

11. The method of claim 10 further comprising the projection of the outline of the pedicle base circumference outwardly to the posterior pedicle cortex in accordance with the predetermined screw trajectory to identify the starting point for the screw on the posterior cortex.

12. The method of claim 10 wherein a circle is created to correspond with the pedicle base circumference in the intraoperative fluoroscopic image and a pedicle screw pilot hole is determined by viewing where it lies with respect to the circle and the posterior cortex.

13. The method of claim 12 wherein real time intraoperative fluoroscopy is used for registration with the three-dimensional image for each vertebra.

14. The method of claim 12 wherein the pedicle screw pilot hole is offset for eccentric screw placement by rotation of the ideal cylinder trajectory tangentially with the pivot axis being the innermost end of the cylinder adjacent to the anterior inner cortical wall.

15. The method of claim 1 wherein a portion of the generated line and cylinder extending beyond the posterior pedicle cortex is used to facilitate automated intraoperative pedicle screw placement.

16. The method of claim 15 wherein the generated line and cylinder extending beyond the posterior pedicle cortex are intercepted by and extend through a pair of spaced collinear rings that are mounted on a frame supported by a patient'"'"'s bed or other support, one of said rings being located near the posterior pedicle cortex and the other of said rings being spaced outwardly from the one ring, said rings having an inner diameter that is approximately the same as the diameter of the generated cylinder extending therethrough, said rings providing a guide for a drilling cannula or the like to form a pilot screw hole in the pedicle corresponding to the generated cylinder and for the insertion of a pedicle screw.

17. The method of claim 16 wherein said rings are movably mounted on said frame.

18. The method of claim 16 wherein said rings are removably mounted on said frame.

19. The method of claim 16 wherein each of said rings is adjustable to vary the inner diameter thereof.

20. The method of claim 16 wherein a drilling cannula is inserted through said rings and is provided with a central longitudinal opening for the movable support of a drilling member.

21. The method of claim 20 wherein said drilling cannula is mounted on a patient'"'"'s bed or other support and comprises an inner cannula member for movable support of the drilling member.

22. The method of claim 21 wherein said inner cannula member comprises spaced, parallel, longitudinally extending and movable pins which define the central opening for the drilling member, said pins being extendable beyond the inner end of the drilling cannula to provide stable support thereof on uneven surfaces.

23. The method of claim 20 wherein said rings are removably mounted on said frame and, after the drilling of the pilot screw hole in the pedicle and removal of the drilling cannula, a second cannula having a longitudinal slot therethrough is mounted on the exterior of the said rings and is secured to said frame so that the longitudinal axis thereof corresponds to the longitudinal axis of the generated cylinder extending through said rings, said second cannula serving as a guide for the insertion of a screw into the pedicle after said rings are removed from said second cannula.

24. An adjustable awl for forming a hole for the insertion of a screw or other device in a pedicle or other body part, said awl comprising an elongated housing having an open end, and an elongated awl member movably mounted in said housing and being extendable beyond said open end to vary the length of the awl, said awl comprising means for locking said awl member in a selected position relative to said housing, said awl member being provided with markings thereon to indicate its position relative to said housing.

25. The adjustable awl of claim 24 wherein said housing is radiolucent and said awl member is radiopaque.

26. The adjustable awl of claim 24 wherein said markings on said awl member are color banded for easy viewing.

27. The adjustable awl of claim 24 wherein said housing has a window to enable the viewing of said markings on said awl member.

28. The adjustable awl of claim 24 wherein said housing has a solid head at the end thereof opposite to said open end, said head being constructed to be struck by a suitable tool to form a hole in the pedicle or other body part.

29. The adjustable awl of claim 24 wherein said awl member has a central longitudinally extending opening therethrough, said housing has an opening in the end thereof opposite to said open end, said housing opening being longitudinally aligned with said awl member opening, and a guide wire extends through said awl member and housing openings to the outer end of said awl member, thereby enabling said guide wire to be left in the hole formed by the awl after it is removed therefrom to facilitate the identification of the hole for insertion of a screw or other device therein.

30. A method of determining the size and placement of screws in pedicles during surgery in a selected spinal area, comprising:

generating a dimensionally true three-dimensional image of the bony spine in the selected spinal area;

hollowing 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;

determining the narrowest diameter or isthmus within each pedicle based on a surgeon'"'"'s selected pedicle cortical wall thickness;

generating a straight line starting at the center of the isthmus and extending in opposite directions so that it is positional 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;

expanding 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;

determining the length of the cylinder from its innermost end spaced from the anterior inner cortical wall to the point at which the outer end thereof contacts the posterior pedicle cortex; and

calculating the ideal pedicle screw diameter, length and trajectory based on the dimensions and trajectory of the cylinder generated for each pedicle.