Methods and apparatus for intervertebral disc prosthesis insertion
A method for inserting an intervertebral disc prosthesis into a space between two vertebrae involves inserting the prosthesis partway into the space under constraint to prevent endplates of the prosthesis from articulating, releasing the prosthesis from constraint, and inserting the unconstrained prosthesis farther into the space. In some embodiments, the method involves grasping the prosthesis with a grasping device to insert the prosthesis partway under constraint, loosing the grasping device to release the prosthesis from constraint, and pushing the prosthesis farther into the disc space using the grasping device and/or one or more separate pusher devices. A system includes a grasping device, at least one separate pushing device, and optionally a vertebral spreading device and/or a vertebral midline indicator device.
1. A method of inserting an intervertebral prosthesis into a space between two adjacent vertebrae, the method comprising:
inserting the prosthesis partway into the space under constraint to prevent endplates of the prosthesis from articulating;
releasing the prosthesis from constraint; and
inserting the unconstrained prosthesis farther into the space.
2. A method as in claim 1 , wherein the prosthesis comprises a core disposed between the endplates and the endplates of the constrained prosthesis are prevented from articulating about the core of the prosthesis, and wherein the endplates of the unconstrained prosthesis are free to articulate about the core to help the prosthesis conform to the space between the two vertebrae.
3. A method as in claim 1 , wherein inserting the prosthesis partway under constraint comprises:
grasping the endplates with an insertion tool such that they cannot move relative to one another; and
pushing the prosthesis partway into the space using the insertion tool.
4. A method as in claim 3 , wherein releasing the prosthesis from constraint comprises loosening the insertion tool.
5. A method as in claim 4 , wherein inserting the unconstrained prosthesis farther into the space is performed using the loosened insertion tool.
6. A method as in claim 4 , wherein inserting the unconstrained prosthesis farther into the space is performed using a separate pusher tool.
7. A method as in claim 1 , wherein inserting the prosthesis partway comprises inserting the prosthesis less than halfway into the space prior to releasing constraint.
8. A method as in claim 1 , wherein the prosthesis is inserted in approximately an anterior-to-posterior direction.
9. A method as in claim 1 , wherein the prosthesis is inserted in approximately a lateral-to-lateral direction.
10. A method as in claim 1 , wherein the prosthesis is inserted in an anterolateral-to-posterior direction.
11. A method as in claim 1 , wherein inserting the unconstrained prosthesis farther into the space comprises pushing the prosthesis into the space.
12. A method as in claim 11 , wherein pushing the unconstrained prosthesis farther into the space comprises individually pushing upper and lower endplates of the prosthesis.
13. A method as in claim 11 or 12 , wherein pushing the unconstrained prosthesis farther into the space comprises simultaneously pushing upper and lower endplates of the prosthesis.
14. A method as in claim 11 , wherein pushing the unconstrained prosthesis farther into the space comprises positioning a center of rotation of the prosthesis closer to posterior edges of the two vertebrae than to anterior edges of the vertebrae.
15. A method as in claim 1 , further comprising, before inserting the prosthesis partway under constraint:
inserting a vertebral spacing device at least partway into the space; and
manipulating the spacing device to increase a height of the space.
16. A method as in claim 15 , wherein inserting the constrained prosthesis partway into the space comprises sliding the prosthesis between two opposing jaws of the spacing device.
17. A method as in claim 16 , wherein inserting the prosthesis partway into the space comprises sliding at least one fin on at least one outer surface of the endplate(s) through at least one corresponding slot in the opposing jaws.
18. A method as in claim 17 , wherein inserting the unconstrained prosthesis farther into the space comprises sliding the at least one fin into at least one corresponding slot formed in one of the vertebrae.
19. A method as in claim 1 , further comprising, before inserting the prosthesis partway under constraint:
locating a midpoint of at least one of the two vertebrae using a vertebral midpoint indicator device; and
marking the midpoint on one of the two vertebrae.
20. A method as in claim 19 , wherein locating the midpoint comprises:
inserting the vertebral midpoint indicator device into the space between the vertebrae; and
imaging the midpoint indicator device using a radiographic imaging device.
21. A method as in claim 1 , wherein the endplates of the prosthesis are unconnected parts.
22. A method as in claim 21 , wherein when the prosthesis is under constraint the endplates are immovable with respect to one another.
23. A method as in claim 22 , wherein when the prosthesis is unconstrained the endplates are able to articulate with respect to one another.