DEVICE FOR STABILIZING A VERTEBRAL JOINT AND METHOD FOR ANTERIOR INSERTION THEREOF

Abstract

A prosthetic device can be used as a prosthesis following a discectomy or a corpectomy. The prosthetic device includes two endplates with staggered motion limiting members. The device can be configured to allow six degrees of motion when comparing one endplate relative to the other. The endplates can be configured to fix the joint by changing the body held within the device and by adding a locking plate and fasteners. A method teaches how to insert a device to an intervertebral space via an anterior incision.

Claims

1. A method for stabilizing a first vertebra relative to a second vertebra, the method comprising: contacting a superior endplate of a stabilizing device to the first vertebra, the superior endplate having an inferior surface and a motion limiting member, said motion limiting member extending downward below said inferior surface; contacting an inferior endplate of the device to the second vertebra, the inferior endplate having a superior surface and a motion limiting member, said motion limiting member extending upward above said superior surface; and attaching a locking plate having a superior screw anchoring member to the first vertebra and an inferior screw anchoring member configured to the second vertebra, said locking plate overlying said superior endplate and said inferior endplate, wherein the device further includes a compressible and flexible body having a superior surface and an inferior surface, said superior surface of said body facing said inferior surface of said superior endplate, said inferior surface of said body facing said superior surface of said inferior endplate, said body being held in contact with and laterally between said superior endplate and said inferior endplate by said motion limiting members.

2. The method of claim 1, wherein said motion limiting member on said superior endplate and said motion limiting member on said inferior endplate are staggered with regard to each other.

3. The method of claim 1, wherein: said body has a height; and said motion limiting member on said superior endplate is shorter than said height of said body.

4. The method of claim 1, wherein: said body has a side; and said motion limiting member on said superior endplate and said motion limiting member on said inferior endplate both support said body along said side.

5. The method of claim 1, wherein: said body has a first side and a second side opposing said second side; said motion limiting member disposed on said superior endplate supports said body along said first side of said body; and said motion limiting member disposed on said inferior endplate supports said body along said second side of said body.

6. The method of claim 5, further comprising a further motion limiting member disposed on said superior endplate, said further motion limiting member supporting said body along said second side of said body.

7. The method of claim 1, wherein at least one of said endplates is shaped substantially like a quadrilateral.

8. The method of claim 1, wherein at least one of said endplates complements a contact surface of a body of a vertebra to be supported by said at least one of said endplates.

9. The method of claim 1, wherein at least one of said endplates has bone growth bore formed therein.

10. The method of claim 1, further comprising a superior screw anchoring member extending superiorly from said superior endplate, said superior screw anchoring member being configured to be fastened to a superior vertebra.

11. The method of claim 10, further comprising an inferior screw anchoring member extending inferiorly from said inferior endplate, said inferior screw anchoring member being configured to be fastened to an inferior vertebra.

12. The method of claim 1, further comprising an inferior screw anchoring member extending inferiorly from said inferior endplate, said inferior screw anchoring member being configured to be fastened to an inferior vertebra.

13. The method of claim 10, further comprising a fastener connected to said superior screw anchoring member, said fastener being configured to secure said superior screw anchoring member to the superior vertebra.

14. The method of claim 12, further comprising a fastener connected to said inferior screw anchoring member, said fastener being configured to secure said inferior screw anchoring member to the inferior vertebra.

15. A method for stabilizing a first vertebra relative to a second vertebra, the method comprising: inserting a stabilization device between the first vertebra and a second vertebra; attaching a locking plate to the stabilization device; and securing the locking plate to the first vertebra and the second vertebra, wherein the locking plate further includes a superior screw anchoring member configured to connect to the first vertebra and an inferior screw anchoring member configured to connect to the second vertebra, wherein the stabilization device further comprises: a superior endplate having an inferior surface and a motion limiting member, said motion limiting member extending downward below said inferior surface; an inferior endplate having a superior surface and a motion limiting member, said motion limiting member extending upward above said superior surface; and a compressible and flexible body having a superior surface and an inferior surface, said superior surface of said body facing said inferior surface of said superior endplate, said inferior surface of said body facing said superior surface of said inferior endplate, said body being held in contact with and laterally between said superior endplate and said inferior endplate by said motion limiting members.

16. The method of claim 15, wherein said motion limiting member on said superior endplate and said motion limiting member on said inferior endplate are staggered with regard to each other.

17. The method of claim 15, wherein: said body has a height; and said motion limiting member on said superior endplate is shorter than said height of said body.

18. The method of claim 15, wherein: said body has a side; and said motion limiting member on said superior endplate and said motion limiting member on said inferior endplate both support said body along said side.

19. The method of claim 15, wherein: said body has a first side and a second side opposing said second side; said motion limiting member disposed on said superior endplate supports said body along said first side of said body; and said motion limiting member disposed on said inferior endplate supports said body along said second side of said body

20. A method for stabilizing a superior vertebra relative to an inferior vertebra following a discectomy or a corpectomy, the method comprising: inserting a stabilization device between the superior vertebra and the inferior vertebra; and attaching the stabilization device to the superior vertebra and the inferior vertebra, wherein the stabilization device comprises: a superior endplate having an anterior edge, a posterior edge, a right edge, a left edge, an inferior surface, a textured superior surface, and motion limiting members extending inferiorly from said inferior surface, said superior endplate having a bone growth bore formed therein; an inferior endplate having an anterior edge, a posterior edge, a right edge, a left edge, a superior surface, a textured inferior surface, and motion limiting members, one of said motion limiting members extending superiorly said inferior endplate having a bone growth bore formed therein; a compressible and flexible body having a superior surface, an inferior surface, and a height defined between said superior surface and said inferior surface, said superior surface of said body facing said inferior surface of said superior endplate, said inferior surface of said body facing said superior surface of said inferior endplate, said body being held in contact and laterally between said superior endplate and said inferior endplate by said motion limiting members; a superior screw anchoring member extending superiorly from said anterior edge of said superior endplate, said superior screw anchoring member being configured to connect to the superior vertebra; an inferior screw anchoring member extending inferiorly from said anterior face of said inferior endplate, said inferior screw anchoring member being staggered from said superior screw anchor and configured to connect to the inferior vertebra; and a locking plate having a superior screw anchoring member configured to connect to the superior vertebra and an inferior screw anchoring member configured to connect to the inferior vertebra, said locking plate overlying said superior endplate and said inferior endplate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 is a diagrammatic top side view of a device according to the invention.

[0044] FIG. 2 is a front side view of the device shown in FIG. 1.

[0045] FIG. 3 is a left side view of the device shown in FIG. 1.

[0046] FIG. 4 is a right side view of the device shown in FIG. 1.

[0047] FIG. 5 is a rear side view of the device shown in FIG. 1.

[0048] FIG. 6 is a bottom side view of the device shown in FIG. 1.

[0049] FIG. 7 is a front side view of a locking plate according to the invention.

[0050] FIG. 8 is a perspective view of the locking plate shown in FIG. 7.

[0051] FIG. 9 is a front side view of the device shown in FIG. 2 with the locking plate shown in FIG. 7 installed.

[0052] FIG. 10 is a perspective view of a screw according to the invention.

[0053] FIG. 11 is a side view of a first embodiment of a body that is homogeneous.

[0054] FIG. 12 is a side view of a second embodiment of a body having three layers.

[0055] FIG. 13 is a perspective view of a self-standing expanding cage.

[0056] FIG. 14 is a perspective view of a self-standing single body cage.

[0057] FIG. 15 is a left side view of a device being inserted anteriorly in a corpectomy.

[0058] FIG. 16 is a top side view of the device shown in FIG. 15 installed after a corpectomy.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[0059] Referring now to the figures of the drawing in detail and first, particularly, to FIGS. 1-6 thereof, there is seen a device 20 for stabilizing a first bone of a joint relative to a second bone of a joint. In particular, the device 20 is useful for stabilizing a first vertebra relative to a second vertebra following discectomies or corpectomies. The device 20 includes a superior endplate 1 and inferior endplate 11. As shown in FIG. 15, the superior endplate 1 is configured to support a superior vertebra 101. The inferior endplate 11 is configured to support an inferior vertebra 111. In one embodiment, a superior surface 8 of the superior endplate 1 is textured to increase friction between the superior vertebra 101 and the superior endplate 1. Likewise, the inferior surface 18 of the inferior endplate 11 is textured. The textured surface can include teeth, ridges, and/or grooves. These protrusions extend from a bone engaging surface of the device and engage bone of the joint to reduce or prevent movement of the surface relative to the bone. The superior surface 8 and inferior surface 18 either directly contact the superior vertebra 101 or inferior vertebra 111, respectively, or intervening layers and bodies, which are not shown, can be inserted therebetween.

[0060] In the embodiment shown in FIG. 1, the superior endplate 1 has a bone growth bore 4 formed therein. Multiple bores 4 are formed in the embodiment of the inferior endplate shown in FIG. 6. Bone tissue from an adjacent bone can grow into bone growth bore 4. Growing bone into the bone growth bore 4 forms a strong connection between the bone and the device 20.

[0061] As shown in FIGS. 1 and 6, the endplates 1 and 11 have a cross section that is similar to the cross section of the vertebrae being supported. Generally, this shape is substantially trapezoidal. With respect to the shape, substantially means that the shape is interpreted as generally trapezoidal but the sides may be curvilinear. The larger base of the trapezoid shape is to be the anterior edge (i.e. front edge).

[0062] Motion limiting members 5 extend downward (i.e. inferiorly) from the superior endplate 1. The motion limiting members 5 are spaced apart from each other. In the preferred embodiment, the motion limiting members are rectangular cuboids. The edges can be rounded.

[0063] Motion limiting members 15 extend upward (i.e. superiorly) from the inferior endplate 11. The motion limiting members 15 are spaced apart from each other. In the preferred embodiments, the motion limiting elements 15 are rectangular cuboids. The edges can be rounded.

[0064] When the endplate 1 and the endplate 11 are brought together, the motion limiting members 5 and 15 seat between each other. Space can remain between the motion limiting members 5 and 15 to allow the endplates 1 and 11 to move relative to each other. The relative movement is subject to the compressive and elastic qualities of a body 10; the body 10 is described in detail below. However, when the endplates 1 and 11 move too far laterally from each other, a given motion limiting members 5 and 15 contact a neighboring motion limiting member 5 or 15 to limit how far the endplates 1 and 11 can shift relative to each other. The amount of lateral movement allowed can match a typical range of motion before the implantation or can match an amount that the device 20 is safe to allow. In the preferred embodiment, the motion limiting members 5 and 15 alternate between a motion limiting member 5 on the superior endplate 1 and a motion limiting member 15 on the inferior endplate 11.

[0065] The motion limiting members 5 and 15 are distributed about the perimeter of the respective endplate 5 and 15. In an exemplary embodiment, a motion limiting member 5 is located at each corner of the superior endplate 1. A motion limiting member 15 is located in the middle of each edge of the inferior endplate 11.

[0066] A body 10 is placed between the superior endplate 1 and the inferior endplate 11. The body 10 is placed in the center in the middle of the motion limiting members 5 and 15, which are disposed about the perimeter of the endplates 1 and 11. Embodiments of the body 10 are discussed later in the specification. The body 10 has a height that is sized so that the overall height of the device (i.e. the height of the endplates 1 and 11 plus the height of the body 10) is substantially equal to the space in which the device is being inserted. For example, if the device were to replace an intervertebral disc, the height of the device would be equal to the height of the intervertebral disc. If the device were replacing a vertebra, the height of the device when installed would be equal to the height of the vertebra. The combined height is said to be substantially equal because often the anatomy being replaced has degenerated and is compressed so the height of the replacement may be slightly larger to provide a replacement of what the height should be.

[0067] In one embodiment, the motion limiting members 5 and 15 have a height from the face of the endplate that is less than the height of the body 10. In this way, the body 10 can compress axially and the motion limiting members 5 and 15 will not contact the opposing endplate.

[0068] In the preferred embodiment, the motion limiting members 5 and 15 have a height at least as high as the expected amount of axial expansion. In this way, the motion limiting members 5 and 15 will remain in contact with the body 10 even when the spine is at its greatest length. Accordingly, the motion limiting members 5 and 15 never become disengaged from the body 10.

[0069] The space between a given limiting member 5 or 15 with neighboring motion limiting members 15 or 5, respectively, should be great enough to allow the intended range of motion. The space between should not be so great to exceed a safe amount of twisting.

[0070] A screw anchor member 4 extends superiorly (i.e. upward) from the superior endplate 1. The screw anchor member 4 is a rectangular tab, although other shapes are possible. The screw anchor member 2 extends upward from an anterior edge 7 of the endplate 1. The screw anchor member 2 is disposed above the motion limiting member 5 on the anterior edge 7. A socket 3 is formed in the screw anchor member 2. The socket 3 is preferably threaded and counter sunk. In an alternate embodiment, the socket 3 is not threaded and not counter sunk. A bone screw 30 is screwed though the socket 3 into the underlying body of the vertebra.

[0071] The bone screw 30 includes a head 31. The head 31 cannot pass through the socket 3. The head and socket 3 may be polyaxially matable to facilitate secure attachment of the screw to bone, for example, cortical bone. The head 31 has a socket 32 formed therein. The bone screw includes a thread 33.

[0072] A screw anchor member 14 extends inferiorly (i.e. downward) from the inferior endplate 11. The screw anchor member 14 is a rectangular tab. The screw anchor member 12 extends downward from an anterior edge 17 of the endplate 11. The screw anchor member 12 is disposed below the motion limiting member 15 on the anterior edge 17. A socket 13 is formed in the screw anchor member 12. The socket 13 is preferably threaded and counter sunk. In an alternate embodiment, the socket 13 is not threaded and not counter sunk. A bone screw 30 or compatible fastener is screwed though the socket 3 into the underlying body of the vertebra.

[0073] In the preferred embodiment, the device 20 allows six degrees of motion in the joint. In the X-axis, the device 20 allows flexion/extension and lateral slip. In the Y-axis, the device 20 allows left/right axial rotation and anterior/posterior slip. In the Z-axis, the device 20 allows left/right lateral bending and axial tension/compression.

[0074] FIGS. 7-9 show a preferred embodiment of locking plate 40. The locking plate 40 has a horizontal plate 42. A superior screw anchoring member extends superiorly (i.e. upwardly) from said horizontal plate 42. The superior screw anchoring member 41 is a rectangular tab. The superior screw anchoring member 41 has a socket 43 formed therein. The socket 43 is threaded and countersunk. An inferior screw anchoring member 45 extends inferiorly (i.e. downwardly) from said horizontal plate 42. The inferior screw anchoring member 45 may also have a socket 43 formed therein. The socket 43 is threaded and countersunk. In other embodiments, the socket is unthreaded or not countersunk. The locking plate 40 is configured to be tall enough so that the superior screw anchoring member 41 overlies a superior vertebra while the inferior screw anchoring member 45 overlies an inferior vertebra. Screws 30 are screwed into each screw anchoring member 41 and 45 and underlying bone to fasten the locking member 40 to the vertebrae. When installed, the vertebrae are no longer able to move relative to each other.

[0075] The locking plate 40 is placed over the anterior face of the device 20. The horizontal plate 42 overlies the superior endplate 1 and the inferior endplate 11. The superior screw anchoring member 41 of the locking plate 40 is adjacent the superior screw anchoring member 12 of the superior endplate 1. The inferior anchoring member 45 of the locking plate 40 is adjacent the superior screw anchoring member 22 of the inferior endplate 11. The superior anchoring member 41 of the locking plate 40 is inline vertically with the inferior anchoring member 12 of the inferior endplate 11. The inferior anchoring member 41 of the locking plate 40 is inline vertically with the superior anchoring member 2 of the superior endplate 1.

[0076] The screw anchoring members 41 and 45 of the locking plate 40 abut the screw anchoring members 2 and 12 of the endplates 1 and 11. Each of the screw anchoring members 41 and 45 has a medial contact surface 46 and 47, respectively. The screw anchoring member 2 has a medial contact surface 9. The screw anchoring member 12 has a medial contact surface 19. When the locking plate 40 is installed, the contact surface 46 abuts the contact surface 9 and the contact surface 47 abuts the contact surface 19. While it is preferred that the contact surfaces directly contact each other, intervening objects can be placed between them.

[0077] The device 20 and locking plate 40 are made of a biocompatible material. Preferably, the device 20 and locking plate 40 are made of a biocompatible metal or polymer.

[0078] In one embodiment shown in FIGS. 2-4, the device 20 allows for movement. In this embodiment, the body 10 is flexible and resilient. A suitable material allows for temporary motion of the endplate 1 relative to the endplate 11 and then helps to return the endplates 1 and 11 to their original position. The body 10 is sandwiched between the superior endplate 1 and the inferior endplate 11. The body 10 is surrounded by and retained by the motion limiting members 5 and 15. The body 10 is compressible and flexible to allow one endplate 1 to move relative to the other endplate 11. As the body 10 compresses and flexes, the motion limiting members 5 of the superior endplate 1 intermesh with the motion limiting members 15 of the inferior endplate 11.

[0079] In the embodiment shown in FIG. 11, the body 10 is made of a single material and is homogeneous. In the embodiment shown in FIG. 12, the body 10 is made of different materials. The body 10 has three layers 61 and 62. The outer layers 61 are made of a first material. The inner layer 62 is made of a second material. The first material has different mechanical properties (i.e. flexibility, resiliency, durability, etc.) than the second material. The material or materials of the body 10 are selected to match a desired flexibility of the device 20. The body 10 can be made to flex like the original anatomy or within the mechanical limits of the device 20.

[0080] In the embodiments shown in FIGS. 13 and 14, a fixed bone spacer is used as the core. The fixed bone spacer is not flexible. Accordingly, the endplates 1 and 11 do not move relative to each other when the fixed bone spacer is used as the body 10. FIG. 13 shows an embodiment with a standing expanding cage as the core. An example of a standing expandable cage is taught in U.S. Pat. No. 7,384,431, which is incorporated by reference herein. FIG. 14 shows an embodiment in which a standing single body cage is used as the body 10. Screws 30 are inserted through the body 10 into the pedicle of the vertebra to fix the body to the vertebra. The device 20 provides a device that can be used for an anterior installation with greater stability than an expanding cage alone.

[0081] A preferred embodiment of the invention includes a method of stabilizing a first vertebra relative to a second vertebra after a discectomy. An incision is made to an anterior aspect of an intervertebral disc of the spine. Next, the intervertebral disc is removed via the anterior incision. If a prosthesis had been inserted previously to replace an intervertebral disc, the prosthesis can be removed via the incision. Next, the device is inserted into the intervertebral space from which the disc was removed. The joint can be expanded or the device compressed to help insert the device 20 into the intervertebral space. To compress the device 20, the superior endplate 1 can be pressed toward the inferior endplate 11 to compress the body 10. When inserting the device 20, the anterior edge 117 is aligned along the anterior of the spine. When the device 20 is inserted, the superior surface 8 of the superior endplate 1 presses against the superior vertebra. Likewise, the inferior surface 18 of the inferior endplate presses against the inferior vertebra. To fix the device 20 to the vertebra, a screw is inserted through the socket 3 of the screw anchor member 2 into the anterior face of the body of the superior vertebra. Likewise, a screw 30 is inserted through the socket 13 of the screw anchor member 12 into the anterior face of the body of the inferior vertebra. Next, the incision is closed.

[0082] When the superior endplate 1 is connected to the superior vertebra and the inferior endplate 11 is connected to the inferior vertebra, the device 20 preserves movement along six degrees of freedom: X-axis: flexion/extension, lateral slip; Y-axis: Left/Right Axial Rotation; Anterior/Posterior Slip; Z-Axis: Left/Right Lateral Bending, Axial tension/compression. A practitioner can determine a permissible range of motion by configuring the body 10 and the spacing and size of the motion limiting members 5 and 15.

[0083] A preferred embodiment of a method for providing soft stabilization utilizes a locking plate 40. The device 20 is installed as described previously. Next, a locking plate 40 is placed over the device 20. The horizontal plate 42 is placed to overly the endplates 1 and 11. The superior screw anchor member 41 is placed on the anterior face of the superior vertebra. The superior screw anchor member 41 is aligned vertically above the anterior motion limiting member 15 on the inferior endplate 11. The superior screw anchor member 41 is placed so a medial contact surface 46 abuts a medial contact surface 9 of the superior screw anchor member 2 of the superior endplate 1. Likewise, the inferior screw anchor member 45 is placed so its medial contact surface 47 abuts a medial contact surface 19 of the inferior screw anchor member 12 of the inferior endplate 11. The locking plate 40 limits the motion of the first endplate 1 with respect to the second endplate 11. However, depending on the qualities of the body 10, some motion still may be provided even when the locking plate 40 is installed.

[0084] A preferred embodiment of a method for stabilizing a vertebra with respect to another vertebra following a corpectomy utilizes the device 20. An incision is made to an anterior surface of a vertebra. The body of the vertebra is removed during the corpectomy. The device 20 is delivered to the site where the body of the vertebra was removed via the anterior incision. In the preferred embodiment, the body 10 is not flexible and has a height so the overall height of the device 20 including the superior endplate 1, body 10, and inferior endplate 11 is substantially equal to the height of the vertebra being replaced. Substantially is used to denote that the height may not be exactly the same as the vertebra being replaced. For example, if the vertebra being replaced was damaged, or compressed, the device 20 might need a height slightly greater or less than the vertebra being replaced. The body 10 can be a rigid homogenous piece of material or have layers of different stiffness. In a preferred embodiment, the body 10 is a self-standing expanding cage. The expanding cage is operated to adjust a height of the self-standing expanding cage to match the height of the vertebra being replaced. In another embodiment, the body 10 is a self-standing single body cage. Screws are inserted from an anterior side into the pedicle of the vertebrae that has had its body removed. In one embodiment, the body 10 is fastened to each of the superior endplate 1 and inferior endplate 11 with respective screws 30.

[0085] While it is apparent that the invention disclosed herein is well calculated to fulfill the objects stated above, it will be appreciated that numerous modifications and embodiments may be devised by those skilled in the art.