Source: https://patents.google.com/patent/US7585326B2/en
Timestamp: 2019-04-25 12:43:17+00:00

Document:
In an attempt to treat disc related pain without fusion, an alternative approach has been developed, in which a movable, implantable, artificial intervertebral disc (or “disc prosthesis”) is inserted between two vertebrae. A number of different intervertebral disc prostheses are currently being developed. For example, the inventors of the present invention have developed disc prostheses described in U.S. patent application Ser. Nos. 10/855,817 and 10/855,253, previously incorporated by reference. Other examples of intervertebral disc prostheses are the LINK SB CHARITÉ™ disc prosthesis (provided by DePuy Spine, Inc.) the MOBIDISK™ disc prosthesis (provided by LDR Medical, the BRYAN™ cervical disc prosthesis (provided by Medtronic Sofamor Danek, Inc.), the PRODISC™ disc prosthesis or PRODISC-C™ disc prosthesis (from Synthes Stratec, Inc.), and the PCM™ disc prosthesis (provided by Cervitech, Inc.).
A number of exemplary intervertebral disc prostheses are listed above. Published U.S. patent applications 2002/0035400A1 and 2002/0128715A1 describe disc implants which comprise opposing plates with a core between them over which the plates can slide. The core receives one or more central posts, which are carried by the plates and which locate in opposite ends of a central opening in the core. Such arrangements limit the load bearing area available between the plates and core.
In some embodiments, the method also includes inserting a vertebral spacing device at least partway into the space and manipulating the spacing device to increase a height of the space. An example of such a spacing device is described by the assignees of the present application in PCT Patent Application No. 2004/000171, filed Jan. 26, 2004, the full disclosure of which is hereby incorporated by reference. The spacing step is typically performed before inserting the constrained prosthesis partway into the intervertebral space. In some embodiments, inserting the constrained prosthesis partway into the intervertebral space comprises sliding the prosthesis between two opposing jaws of the spacing device. In such an embodiment, inserting the constrained prosthesis partway into the space may optionally further involve sliding at least one fin on at least one outer surface of the endplates through at least one corresponding slot in the opposing jaws. In one embodiment, such a fin (or fins) may then be slid into a corresponding slot formed in one of the vertebrae.
Some embodiments also involve using a vertebral midpoint indicator device to locate a midpoint of at least one of the two vertebrae, and marking the midpoint on one or both of the two vertebrae. An example of a midline indicator device is described by the assignees of the present application in PCT Patent Application No. 2004/000170, filed Jan. 26, 2004, the full disclosure of which is hereby incorporated by reference. Midline finding and marking are typically performed before inserting the constrained prosthesis partway into the intervertebral space. In some embodiments, locating the midpoint involves inserting the vertebral midpoint indicator device into the space between the vertebrae and imaging the midpoint indicator device using a radiographic imaging device.
In some embodiments, the system further includes a vertebral spacing device for increasing a height of the space between the two vertebrae. An example of such a spacing device is described in PCT Patent Application No. 2004/000171, which was previously incorporated by reference. In such embodiments, the grasping member is adapted to slide through the vertebral spacing device disposed between two adjacent vertebrae. Optionally, the pusher device may also be adapted to slide through the spacing device.
The system may optionally further include a vertebral body midline indicator device for locating a midline on a vertebral body of at least one of the two vertebrae. An example of a midline indicator device is described in PCT Patent Application No. 2004/000170, which was previously incorporated by reference.
In various embodiments, the method just described may include fewer steps or additional steps. For example, in one embodiment, a spreader device is inserted between the two vertebrae V to spread them apart before inserting the constrained prosthesis 104. An example of such a spacing device is described in PCT Patent Application No. 2004/000171, previously incorporated by reference. In such embodiments, the insertion device 102 is typically sized to fit between opposing jaws of the spreader device. When the prosthesis 104 is partially inserted, the spreader device is removed from the intervertebral space IS, and the prosthesis 104 is released from constraint and inserted the rest of the way into the space IS. Also in some embodiments, a midline indicator device may be used to facilitate the location of a midline on one or both of the two adjacent vertebrae V. An example of such a midline indicator device is described in PCT Patent Application No. 2004/000170, previously incorporated by reference. Typically, the midline indicator is used before the disc prosthesis 104 is inserted. These and other steps or features may be included in various embodiments of the method without departing from the scope of the invention.
Referring now to FIG. 3, in some embodiments a separate pusher device 150 may be used to push an unconstrained prosthesis 140 farther into an intervertebral space. The pusher device 150 is typically constructed of stainless steel or other suitable metal and suitably includes an elongate shaft 152, a pusher member 154 at the distal end of the shaft 152, and a handle 158 at the proximal end of the shaft 152. The pusher member 154 includes a concave inner portion 156 for pushing against the inner rims 144 of endplates 142 of the prosthesis 140. The concave portion 156 may be tapered and/or rounded to facilitate pushing against upper and lower endplates 142 individually while also allowing for simultaneous pushing against both endplates 142. In alternative embodiments, the pusher device 150 may have any of a number of alternative configurations, shapes, sizes and the like. In some embodiments, multiple pusher devices 150 of different configurations and/or sizes are provided to allow a physician to select one or more desired devices 150.
Referring now to FIGS. 4A-4E, a spreader device 10 for spreading adjacent vertebrae to facilitate intervertebral disc prosthesis 30 insertion is shown. Again, the device 10 is described in greater detail in PCT Patent Application No. 2004/000171, which was previously incorporated by reference. The spreader device 10 generally includes distally located opposable jaws 12, a slidable pusher member 45 and an actuator 15. The opposable jaws 12 are carried by arms 14 which form part of a scissors-type mechanism having a single hinge point 15. Handles 16 on the proximal end of the device are used to manipulate the opposable jaws 12. When the handles 16 are actuated, arms 14 translate the actuation motion to the single hinge point scissors type mechanism 15. This causes the opposable jaws 12 to open or close. The jaws 12 have opposing surfaces 18 formed with ribs 20 and transverse slots 22 which extend for the height of the jaws as seen in FIG. 4B. At their free ends, the jaws 12 are provided with relatively sharp tips or blades 24 having curved extremities 26.
FIGS. 4A and 4B illustrate how the handles 14 are inclined relative to the jaws 12. Manipulation of the handles 16 by moving them causes the jaws 12 to open or close. Other embodiments include a double hinge instead of the single hinge 15 which would pivot the jaws apart from one another when the handles 16 are displaced towards one another.
A method of inserting the intervertebral prosthesis is illustrated in FIGS. 4D and 5. In order to place the prosthesis 30, the vertebrae 38 are distracted by a distance sufficient for at least partial insertion of the prosthesis 30. To achieve this, the tips 24 of the opposable jaws 12 are inserted between the vertebrae 38 with the slots 22 in the opposable jaws 12 aligned with the slots in the vertebrae 40. The handles 16 are then manipulated to force the opposable jaws 12 apart which also forces the vertebrae 38 apart from one another, creating a gap. The prosthesis 30 is then inserted into the gap 42 between the opposable jaws 12 where it is held therein with fins 36 engaged with the corresponding slots 22. The prosthesis 30 is then slipped distally in the gap while being guided by the fins 36 cooperating with the slots 22. The prosthesis 30 is moved through the inter-jaw gap and past the jaw tips 24 in order to locate the prosthesis 30 between the vertebrae 38 with fins 36 in the vertebral cut slots 40. The slots 22 in the opposable jaws 12 help to guide the fins 36 into the vertebral cut slots 40.
FIGS. 6A-6D show another optional device for use in the insertion methods of the present invention. As mentioned above, a midline indicator device 210 such as the one shown is described in greater detail in PCT Patent Application No. 2004/000170, which was previously incorporated by reference. The midline indicator 210 suitably includes an elongate shaft 212 and a body 214 coupled with one end of the shaft 212. The shaft 212 may be made of one or more radiopaque materials, such as but not limited to stainless steel, titanium or the like. Alternatively, the shaft 212 may be radiolucent. The body 214 is made of one or more radiolucent materials, such as a polymer, so that it is not visible on radiographs. Embedded in the body 214 are two elongate radiopaque markers 216, also made of any suitable radiopaque material(s). The markers 216 are parallel to the shaft 212 and are located on opposite sides and equidistant from the shaft 212.
Additionally, if the shaft 212 and markers 216 are properly aligned in the A-P direction, they will appear as dots on the radiograph. If the midline indicator 210 is turned, however, as is demonstrated by the dotted lines in FIG. 7B, the shaft 212 and markers 216 will show up as lines or stretched-out dots on the radiograph. The A-P direction of the radiograph is shown by 224, with misalignment of the indicator 210 shown by angles θ. By consulting one or more radiographs and manipulating the indicator 210, the surgeon positions the handle 212 of the indicator 210 at the vertebral midline 222. The surgeon may then make a mark 226 in one or more vertebrae 218, 220 to indicate the midline 222. The mark 226 may be made by any suitable means, such as by burning with an electrocautery device, marking with a marking pen, inserting a pin, or the like. After one or more midline marks 226 are made, the midline indicator 210 is removed and the disc prosthesis (not shown) is inserted. Again, the midline finding step is optional.
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.
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.
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.
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.
marking the midpoint on one of the two vertebrae.
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.

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