Intervertebral disc replacement and associated instrumentation
An endplate for an intervertebral prosthesis includes an inner domed region and a peripheral rim wherein the inner domed region has a non-circular plan and has an area that is at least 50% of the area of the endplate. A surgical instrument for milling a recess in a vertebral endplate includes a cutting tool having a drive shaft with a positioning collar, a guard frame, and a pair of guide plates attached to the guard frame and spaced to confine the positioning collar and having guide slots for the drive shaft.
1. Apparatus for milling a recess in a vertebral endplate comprising:
a surgical cutting tool including a surgical cutter and a drive shaft attached thereto, said drive shaft having a guide collar; and
a guide frame for positioning and guiding said surgical cutter in an intervertebral space between two vertebrae adjacent along a spinal axis for milling an endplate of at least one of said vertebrae,
said guide frame including:
a first guide plate adapted to be fixed to at least one of said vertebrae, said guide plate having a first generally central aperture sized for admitting said drive shaft and at least one guide slot communicating with said central aperture adapted to guide said drive shaft in a predetermined path, and
a second guide plate having a second generally central aperture sized for admitting said drive shaft and at least one guide slot communicating with said second aperture and adapted to guide said drive shaft in said predetermined path, said second guide plate being adapted to be oriented parallel to said first guide plate and spaced anteriorly therefrom by a distance selected such that said guide collar can be received between said first and second guide plates in sliding contact therewith.
2. The apparatus of claim 1 , wherein said first guide plate is adapted to be fixed to both of said adjacent vertebrae.
3. The apparatus of claim 1 , wherein said first generally central aperture is sized to admit said surgical cutter.
4. The apparatus of claim 1 , wherein said drive shaft of said guide collar is generally cylindrical.
5. The apparatus of claim 1 , wherein said first generally central aperture is sized to admit said surgical cutter but not said guide collar.
6. The apparatus of claim 1 , wherein said first generally central aperture is sized to admit said surgical cutter but not said guide collar, and said second generally central aperture is sized to admit said guide collar.
7. The apparatus of claim 1 , additionally comprising a guard structure extending from at least one of said guide plates adapted to extend into said intervertebral space and having a dimension parallel to said spinal axis greater than a dimension of said surgical cutter parallel to said spinal axis.
8. The apparatus of claim 7 , wherein both of said first and second guide plates are attached to said guard structure.
9. The apparatus of claim 7 , wherein said guard structure defines a protective space around said cutter.
10. The apparatus of claim 8 , wherein said guard structure defines a protective space around said cutter.
11. A guide frame for positioning and guiding a surgical cutter in an intervertebral space between two adjacent vertebrae along a spinal axis for milling an endplate of a vertebra, said guide frame comprising:
a generally U-shaped guard rail adapted to be inserted into said intervertebral space, said guard rail including:
a base portion adapted to be positioned within said intervertebral space generally adjacent a posterior margin of said vertebra and having a dimension parallel with said spinal axis greater than a dimension of said surgical cutter in a direction parallel to said spinal axis, said base portion having a pair of opposite ends spaced generally a distance corresponding to a transverse diameter of said vertebra, and
a pair of support arms extending anteriorly from said base portion, each of said support arms extending from one of said opposite ends of said base portion and terminating in a terminal end portion;
a posterior guide plate supported on said support arms and extending between said support arms, said posterior guide plate being provided with a posterior guide plate cutter insertion aperture and at least one posterior guide plate guide channel for guiding said surgical cutter; and
an anterior guide plate supported on said support arms and spaced anteriorly from said posterior guide plate, said anterior guide plate being provided with an anterior guide plate cutter insertion aperture and at least one anterior guide plate guide channel for guiding said surgical cutter, said posterior guide plate being spaced from said base portion of said guard rail such that said posterior guide plate is positioned generally adjacent to an anterior margin of said vertebra when said base portion of said guard rail is positioned generally adjacent said posterior margin of said vertebra.