Artificial intervertebral disc having a bored semispherical bearing with a compression locking post and retaining caps Number:7,393,361 from the United States Patent and Trademark Office (PTO) owispatent An artificial intervertebral disc having a pair of opposing baseplates, for seating against opposing vertebral bone surfaces, uses a semispherical, bored bearing that is secured to the baseplates with compression locking posts and one or more retaining caps. The compression locking posts extend through the bearing bore and baseplate apertures such that the bearing is between the baseplates' inwardly facing surfaces. Retaining caps are attached to the compression locking posts, securing the baseplates to the bearing. Bearing surfaces on the inwardly facing side of each baseplate allow each baseplate to rotate relative to the bearing, however, rotation of each baseplate is limited by the interference of each baseplate and its respective retaining cap. Rotation of the baseplates about the longitudinal axis of the spine can be limited via a notch in the retaining caps and a groove in the baseplates, or vice versa.<H intervertebral, semispherical, Artificial, inte, 7393361.html, Patent, pto, 7393361

Title: Artificial intervertebral disc having a bored semispherical bearing with a compression locking post and retaining caps

Abstract: An artificial intervertebral disc having a pair of opposing baseplates, for seating against opposing vertebral bone surfaces, uses a semispherical, bored bearing that is secured to the baseplates with compression locking posts and one or more retaining caps. The compression locking posts extend through the bearing bore and baseplate apertures such that the bearing is between the baseplates' inwardly facing surfaces. Retaining caps are attached to the compression locking posts, securing the baseplates to the bearing. Bearing surfaces on the inwardly facing side of each baseplate allow each baseplate to rotate relative to the bearing, however, rotation of each baseplate is limited by the interference of each baseplate and its respective retaining cap. Rotation of the baseplates about the longitudinal axis of the spine can be limited via a notch in the retaining caps and a groove in the baseplates, or vice versa.

Patent Number: 7,393,361 Issued on 07/01/2008 to Zubok, et al.

Inventors: Zubok; Rafail (Midland Park, NJ), Dudasik; Michael W. (Nutley, NJ), Errico; Joseph P. (Green Brook, NJ)
Assignee: SpineCore, Inc. (Summit, NJ)

Appl. No.: 10/782,982

Filed: February 20, 2004

Current U.S. Class: 623/17.15

Current International Class: A61F 2/44 (20060101)

Field of Search: 623/17.11-17.16

References Cited [Referenced By]

U.S. Patent Documents


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Foreign Patent Documents


WO-97/10776	Mar., 1997	WO

Primary Examiner: McDermott; Corrine
Assistant Examiner: Miller; Cheryl
Attorney, Agent or Firm: Lerner, David, Littenberg, Krumholz & Mentlik, LLP

Claims

What is claimed is:

1. An artificial intervertebral disc, comprising: a first baseplate having a first baseplate aperture; a second baseplate having a second baseplate aperture; and a bearing mechanism coupled to said first baseplate and said second baseplate, wherein said bearing mechanism comprises a semispherical bearing and a pair of retaining caps connected to each other by compression locking posts; and said semispherical bearing including a first through bore having a first diameter and a second through bore having a second diameter that is smaller than the first diameter, said first and second through bores being aligned with one another; said pair of retaining caps including a first retaining cap having a first post insertible into said first through bore and a second retaining cap having a second post insertible into said second through bore; wherein said first baseplate and said second baseplate rotate relative to said bearing mechanism; and wherein rotation of said first baseplate to at least one angular position relative to said bearing mechanism extends said bearing mechanism through said first baseplate aperture.

2. The artificial intervertebral disc of claim 1, wherein rotation of said second baseplate to said at least one angular position relative to said bearing mechanism extends said bearing mechanism through said second baseplate aperture.

3. The artificial intervertebral disc of claim 1, wherein said rotation has a range defined by at least one of the group consisting of a first distance between said first baseplate and said bearing mechanism, a second distance between said second baseplate and said bearing mechanism, and one or more physical parameters of said bearing mechanism.

4. The artificial intervertebral disc of claim 1, wherein said first baseplate aperture has a tapered edge, such that an outwardly facing surface of said tapered edge has a larger diameter than an inwardly facing surface of said tapered edge, thereby increasing an angle of rotation of said first baseplate relative to said bearing mechanism in which said bearing mechanism does not physically contact said tapered edge.

5. The artificial intervertebral disc of claim 1, wherein at least one of said baseplates has an internal semispherical contour.

6. The artificial intervertebral disc of claim 1, wherein at least one of said baseplates has an outwardly facing, domed, vertebral body contact surface.

7. An artificial intervertebral disc, comprising: a bearing mechanism, wherein said bearing mechanism comprises a semispherical bearing and a pair of retaining caps connected to each other by locking posts, said pair of retaining caps being connectable to said semispherical bearing; said pair of retaining caps including a first retaining cap having a monolithic first locking post having a first diameter, said first locking post having an axial opening extending therethrough, and a second retaining cap having a second locking post having a second diameter that is smaller than the first diameter of said first locking post, said second locking post being insertible into the axial opening of said first locking post; a first baseplate coupled to said bearing mechanism and having a first baseplate aperture and a first internal bearing surface shaped to conform with a first contour of said bearing mechanism; and a second baseplate coupled to said bearing mechanism and having a second baseplate aperture and a second internal bearing surface shaped to conform with a second contour of said bearing mechanism; wherein said first baseplate and said second baseplate rotate relative to said bearing mechanism; wherein said bearing mechanism is seatable in said first internal bearing surface and said second internal bearing surface; and wherein said rotation has a range defined by at least one of the group consisting of a first distance between said first baseplate and said bearing mechanism, a second distance between said second baseplate and said bearing mechanism, and one or more physical parameters of said bearing mechanism.

8. The artificial intervertebral disc of claim 7, wherein rotation of said first baseplate to at least one angular position relative to said bearing mechanism extends said bearing mechanism through said first baseplate aperture.

9. The artificial intervertebral disc of claim 7, wherein rotation of said second baseplate to at least one angular position relative to said bearing mechanism extends said bearing mechanism through said second baseplate aperture.

10. The artificial intervertebral disc of claim 7, wherein said first baseplate aperture has a tapered edge, such that an outwardly facing surface of said tapered edge has a larger diameter than an inwardly facing surface of said tapered edge, thereby increasing an angle of rotation of said first baseplate relative to said bearing mechanism in which said bearing mechanism does not physically contact said tapered edge.

11. The artificial intervertebral disc of claim 7, wherein a portion of said bearing mechanism is semispherical, said first and second internal bearing surfaces are substantially identical, and said first and second internal bearing surfaces have a semispherical contour.

12. The artificial intervertebral disc of claim 7, wherein at least one of said baseplates has an outwardly facing, domed, vertebral body contact surface.

13. An artificial intervertebral disc, comprising: a first baseplate, having a first baseplate outwardly facing surface, a first baseplate inwardly facing surface, and a first baseplate aperture, said first baseplate inwardly facing surface having a first baseplate bearing surface along an inward perimeter of said first baseplate aperture; a second baseplate, having a second baseplate outwardly facing surface, a second baseplate inwardly facing surface, and a second baseplate aperture, said second baseplate inwardly facing surface having a second baseplate bearing surface along an inward perimeter of said second baseplate aperture; a bearing defining a spherical contour, said bearing having a bearing bore; a first retaining cap having an axial bore and passing through said first baseplate aperture and into said bearing bore; and a second retaining cap passing through said second baseplate aperture, said bearing bore, said first baseplate aperture, and into said axial bore in said first retaining cap; wherein said first retaining cap is secured to said bearing bore and said second retaining cap, thereby securing said first baseplate and said second baseplate to said bearing; wherein said bearing is seatable in said first baseplate bearing surface and said second baseplate bearing surface; wherein said first baseplate and said second baseplate rotate relative to said bearing, and wherein rotation of said first baseplate to at least one angular position relative to said bearing extends said bearing through said first baseplate aperture.

14. The artificial intervertebral disc of claim 13, wherein said rotation of said first baseplate is limited by interference between said first retaining cap and said first baseplate aperture, and wherein said rotation of said second baseplate is limited by interference between said second retaining cap and said second baseplate aperture.

15. The artificial intervertebral disc of claim 13, wherein said first retaining cap is compression lockable to said bearing and said second retaining cap.

16. The artificial intervertebral disc of claim 13, wherein said first baseplate aperture has a tapered edge, such that an outwardly facing surface of said tapered edge has a larger diameter than an inwardly facing surface of said tapered edge, thereby increasing an angle of rotation of said first baseplate relative to said bearing in which said first retaining cap does not physically contact said tapered edge.

17. The artificial intervertebral disc of claim 13, wherein at least one of said first baseplate and said second baseplate has an internal semispherical contour.

18. The artificial intervertebral disc of claim 13, wherein at least one of said first baseplate and said second baseplate has an outwardly facing, domed, vertebral body contact surface.

19. The artificial intervertebral disc of claim 13, wherein said first baseplate aperture extends from said first baseplate outwardly facing surface to said first baseplate inwardly facing surface.

20. The artificial intervertebral disc of claim 13, wherein said second baseplate aperture extends from said second baseplate outwardly facing surface to said first baseplate inwardly facing surface.

Description

FIELD OF THE INVENTION

This invention relates generally to a device for implantation into an intervertebral space to simultaneously stabilize the adjacent vertebral bodies and permit proper anatomical motion at the segment. Specifically, the present invention relates to such a device having upper and lower baseplates that articulate about a central, bored semispherical bearing. The present invention maximizes the strength (i.e., compression and tension load capabilities) of such a device by allowing the semispherical bearing to have a larger diameter without increasing the height of the device.

BACKGROUND OF THE INVENTION

The bones and connective tissue of an adult human spinal column consist of more than twenty discrete bones coupled sequentially to one another by a tri-joint complex, which consists of an anterior disc and two posterior facet joints, the anterior discs of adjacent bones being cushioned by cartilage spacers referred to as intervertebral discs. These more than twenty bones are anatomically categorized as being members of one of four classifications: cervical, thoracic, lumbar, or sacral. The cervical portion of the spine, which comprises the top of the spine up to the base of the skull, includes the first seven vertebrae. The intermediate twelve bones are the thoracic vertebrae, and connect to the lower spine comprising the five lumbar vertebrae. The base of the spine comprises the sacral bones (including the coccyx). The component bones of the cervical spine are generally smaller than those of the thoracic spine, which are in turn smaller than those of the lumbar region. The sacral region connects laterally to the pelvis.

The spinal column is highly complex in that it includes these more than twenty bones coupled to one another, housing and protecting critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these complications, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.

Genetic or developmental irregularities, trauma, chronic stress, tumors, and degenerative wear are a few of the causes that can result in spinal pathologies for which surgical intervention may be necessary. A variety of systems have been disclosed in the art that achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. The region of the back that needs to be immobilized, as well as the individual variations in anatomy, determine the appropriate surgical protocol and implantation assembly. With respect to the failure of the intervertebral disc, the interbody fusion cage has generated substantial interest because it can be implanted laparoscopically into the anterior of the spine, thus reducing operating room time, patient recovery time, and scarification.

Referring now to FIGS. 2-3, in which a side perspective view of an intervertebral body cage and an anterior perspective view of a post implantation spinal column are shown, respectively, a more complete description of these devices of the prior art is herein provided. These cages 1 generally comprise tubular metal body 2 having an external surface threading 3. They are inserted transverse to the axis of the spine 4, into preformed cylindrical holes at the junction of adjacent vertebral bodies (in FIG. 3 the pair of cages 1 are inserted between the fifth lumbar vertebra (L5) and the top of the sacrum (S1)). Two cages 1 are generally inserted side by side with the external surface threading 3 tapping into the lower surface of the vertebral bone above (L5), and the upper surface of the vertebral bone (S1) below. The cages 1 include holes 5 through which the adjacent bones are to grow. Additional materials, for example autogenous bone graft materials, may be inserted into the hollow interior 6 of the cage 1 to incite or accelerate the growth of the bone into the cage. End caps (not shown) are often utilized to hold the bone graft material within the cage 1.

These cages of the prior art have enjoyed medical success in promoting fusion and grossly approximating proper disc height. It is, however, important to note that the fusion of the adjacent bones is an incomplete solution to the underlying pathology as it does not cure the ailment, but rather simply masks the pathology under a stabilizing bridge of bone. This bone fusion limits the overall flexibility of the spinal column and artificially constrains the normal motion of the patient. This constraint can cause collateral injury to the patient's spine as additional stresses of motion, normally borne by the now-fused joint, are transferred onto the nearby facet joints and intervertebral discs. It would therefore, be a considerable advance in the art to provide an implant assembly which does not promote fusion, but, rather, which mimics the biomechanical action of the natural disc cartilage, thereby permitting continued normal motion and stress distribution.

It is, therefore, an object of the invention to provide an intervertebral spacer that stabilizes the spine without promoting a bone fusion across the intervertebral space.

It is further an object of the invention to provide an implant device that stabilizes the spine while still permitting normal motion.

It is further an object of the invention to provide a device for implantation into the intervertebral space that does not promote the abnormal distribution of biomechanical stresses on the patient's spine.

It is further an object of the invention to provide an artificial intervertebral disc that supports compression loads.

It is further an object of the invention to provide an artificial intervertebral disc that supports tension loads.

It is further an object of the invention to provide an artificial intervertebral disc that prevents lateral translation of the baseplates relative to one another.

It is further an object of the invention to provide an artificial intervertebral disc that provides a centroid of motion centrally located within the intervertebral space.

It is further an object of the invention to provide artificial intervetebral disc that provides maximized strength without increasing the height of the disc.

Other objects of the invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.

SUMMARY OF THE INVENTION

The preceding objects are achieved by the invention, which is an artificial intervertebral disc or intervertebral spacer device, comprising a pair of support members (e.g., spaced apart baseplates), each with an outwardly facing surface. Because the artificial disc is to be positioned between the facing endplates of adjacent vertebral bodies, the baseplates are arranged in a substantially parallel planar alignment (or slightly offset relative to one another in accordance with proper lordotic angulation) with the outwardly facing surfaces directed away from one another. The baseplates are to mate with the vertebral bodies so as to not rotate relative thereto, but rather to permit the spinal segments to bend or axially compress relative to one another in manners that mimic the natural motion of the spinal segment. This natural motion is permitted by the performance of a bearing disposed between the secured baseplates, and the securing of the baseplates to the vertebral bone is preferably achieved through the use of a vertebral body contact element attached to, or a surface feature of, the outwardly facing surface of each baseplate.

Preferable body contact elements include, but are not limited to, a convex mesh (of any shape or contour, but preferably domed) and one or more spikes. These vertebral body contact elements are disclosed in greater detail in application Ser. No. 10/256,160 ("the '160 application") and application Ser. No. 10/642,258 ("the '258 application"), which are incorporated herein by reference.

To enhance the securing of the baseplates to the vertebral bones, each baseplate preferably further comprises a surface feature that permits the long-term ingrowth of vertebral bone into the baseplates. A preferred surface feature is a porous area, which at least extends in a ring around the lateral rim of each outwardly facing surface. The porous area may be, for example, a sprayed deposition layer, an adhesive applied beaded metal layer, or another suitable porous coating known in the art. The porous ring permits the long-term ingrowth of vertebral bone into the baseplates, thus permanently securing the prosthesis within the intervertebral space.

The semispherical bearing disposed between the baseplates permits rotation and angulation of the two baseplates relative to one another and to the bearing, which establishes a centroid of motion (for this rotation and angulation) centrally between the baseplates. The semispherical bearing is captured between the baseplates by first and second retaining caps which are connected together by engagement of compression locking posts. Further, the capturing prevents separation and/or disassembly of the device under tension loading, and prevents lateral translation of the baseplates, during the rotation and angulation.

More specifically, the two baseplates of the present invention each include an aperture and each is secured to a bored central bearing in the following manner. The first and second baseplates are disposed such that their outwardly facing surfaces face away from one another, and their inwardly facing surfaces are directed toward one another. The second baseplate aperture is then passed over the compression locking post of second retaining cap and integral second retaining cap such that the compression locking post passes through the outwardly facing surface first and the inwardly facing surface second. A circumferential protrusion in the second baseplate aperture wall (i.e., the axially inwardly directed surface of the second baseplate) will rest upon the inwardly facing surface of the second retaining cap. Next, the bore of the central bearing is passed over the compression locking post and into the second baseplate aperture until a portion of the bearing having a smaller diameter contacts the inwardly facing surface of the second retaining cap and a portion of the bearing having a larger diameter contacts the inwardly facing surface of the circumferential protrusion in the wall of the second baseplate aperture. Then, the first baseplate aperture is passed over the compression locking post until the circumferential protrusion in the first baseplate aperture wall (i.e., the axially inwardly directed surface of the first baseplate) rests upon the bearing. Finally, compression locking post of the first retaining cap is pressed into the bearing bore and over the compression locking post of the second retaining cap under a force sufficient to compression lock the two compression locking posts, its integral retaining caps, and the bearing. At this point, the two retaining caps, compression locking posts, and bearing become one stationary unit (i.e., the retaining caps, compression locking posts, and bearing do not rotate or otherwise move relative to each other). The baseplates are free to rotate and articulate about the bearing and its firmly affixed retaining caps and post).

After assembly, as described above, the inwardly facing surfaces of the baseplate aperture walls (i.e., the surfaces extending from the circumferential protrusion in each aperture wall to the inward edge of each aperture wall) provide bearing surfaces, within which the bearing is captured, thereby facilitating limited angulation of the baseplates relative to the bearing. These bearing surfaces are preferably contoured to closely accommodate the spherical contour defined by the bearing, such that the bearing may easily contact and slide against the bearing surfaces. In this manner, the baseplate bearing surfaces, and therefore the baseplates, may angulate with limitation about the bearing.

As noted above, angulation of the baseplates relative to the bearing is limited. The outwardly facing surfaces of the baseplate aperture walls (i.e., the surfaces extending from the circumferential protrusion in each aperture wall to the outward edge of each aperture wall) are tapered to a larger diameter toward the baseplate's outwardly facing surfaces. Additionally, and preferably, the conformation of the taper matches the contour defined by the inwardly facing surface of the respective retaining cap. Because the retaining caps and posts are stationary with respect to the bearing, such tapering and conformation of the baseplate aperture wall permits the baseplates to angulate (about the centroid of motion at the center of the bearing) with respect to the bearing until the point at which the baseplate interferes with, or contacts, the respective retaining cap. Therefore, the taper, diameter, and conformation of this articulation (i.e., the space between the retaining cap and its respective baseplate) limit the angular movement of the respective baseplate relative to the bearing. Preferably, the taper, diameter, and conformation of the taper accommodate rotation of the respective baseplate relative to the bearing at least until the inwardly facing surfaces of the baseplates meet.

Furthermore, in the preferred embodiment of the present invention, the axial rotation of each baseplate is limited, preferably to between 7 and 10 degrees. This limitation may be created using a variety of methods. For example, this can be realized by a notch and groove, wherein notches are formed in each retaining cap and grooves are formed in each baseplate. Alternatively, the grooves may be formed in the retaining caps and the notches may be formed in the baseplates.

Accordingly, the baseplates rotate with limitation relative to the bearing. Because the bearing is secured to the baseplates with the compression locking posts and retaining caps as discussed above, the artificial intervertebral disc of the present invention can withstand tension loading of the baseplates, and the assembly does not come apart under normally experienced tension loads. Thus, in combination with the securing of the baseplates to the adjacent vertebral bones, the disc assembly has an integrity similar to the tension-bearing integrity of a healthy natural intervertebral disc. Also because the bearing is laterally captured between the bearing surfaces, lateral translation of the baseplates relative to one another is prevented during rotation and angulation, similar to the performance of a healthy natural intervertebral disc. The baseplates are designed to rotate relative to the bearing, therefore, the disc assembly provides a centroid of motion within the bearing. Accordingly, the centroid of motion of the disc asse