US20060282165A1 - Intervertebral disc implant - Google Patents

Abstract

An intervertebral disc implant having a body with a greater height than width comprised of a resilient material and an elongate cavity for receiving a key to maintain the spacing between the vertebrae adjacent an intervertebral disc when implanted into the space from which a portion of the disc is removed. To distribute and cushion against compression loads, and to mimic the normal kinematics of the intact, healthy intervertebral disc, the key is removed after the body is implanted into the disc space and a frame that both provides resistance to compression and tension loads and translates the axis of rotation of the spinal column anteriorally and posteriorally as the patient bends and rotates is inserted into the cavity in the implant body. The frame does not extend all the way into the cavity in the body and the portion of the cavity into which the frame does not extend is filled with a hydrogel.

Description

• This application in a continuation-in-part of co-pending applications Ser. No. 11/246,961, filed Oct. 7, 2005, entitled TOTAL ARTIFICIAL INTERVERTEBRAL DISC, Ser. No. 11/195,890, filed Aug. 2, 2005, entitled TOTAL ARTIFICIAL DISC, International Application No. PCT/US2005/009323, filed Mar. 19, 2005, entitled ROTATING, LOCKING, SPRING-LOADED ARTIFICIAL DISK, and Ser. No. 10/804,895, filed Mar. 19, 2004, entitled ROTATING, LOCKING, SPRING-LOADED ARTIFICIAL DISK.
BACKGROUND OF THE INVENTION
• The present invention relates to an intervertebral disc implant for stabilizing two adjacent vertebrae that maintains the functions of the normal, healthy disc. More specifically, the present invention relates to a rectangularly-shaped disc implant that is expanded in the middle portion that is used as an alternative to spinal fusion.
• Treatment of the damaged intervertebral disc, especially in the cervical and/or lumbar region of the spine, continues to be a challenging field of medicine. The classic treatment for a ruptured disc is diskectomy, i.e., removal of the disc from between the vertebrae. In this process, all or a portion of the intervertebral disc is removed, leaving a defect that may bother the patient throughout the rest of their life and compromising the normal interaction between disc and adjacent vertebrae. A procedure that is sometimes used as an alternative to diskectomy is to remove some or all of the disc and then fill the disc space with a bone graft, usually bone chips cut from the patient's iliac crest, or bone plug, bringing about fusion of the vertebrae above and below the disc, eliminating the empty space between the vertebrae.
• Diskectomy with fusion is not ideal because the replaced bone does not have the function of the cartilaginous tissue of the disc, i.e. no cushioning effect, and has complications because of several factors. First, conventional bone plugs used to pack the disc space do not conform to the space of the disc because the disc bulges maximally in the center while the bone plug is generally cylindrically shaped and the disc space is wider in the middle and narrower at its anterior and posterior ends. For this reason, many commercially available bone plugs have just four points at which they contact the bodies of the adjacent vertebrae, i.e. two points at each of the front and back of the disc space. Second, access to the disc is from the side of the dorsal spine of the adjacent vertebrae, leaving a space that is “off-center” relative to the bodies of the adjacent vertebrae such that the stability of the implant is even more problematical than might be apparent from the limited contact resulting from the shape of the intervertebral space. Another complication is the possibility of infection or other conditions that may require removal of the implant. Also, if the bone pieces do not fuse, they may eventually extrude out of the disc space, pressuring the nerve roots. The most significant disadvantages of fusion, however, is that it eliminates all motion at the joint between the two vertebrae as well as the shock-absorbing/cushioning function of the disc.
• Various prosthetic disc plugs, or implants, are disclosed in the art, but all are characterized by limitations of not conforming to the shape of the disc space, lack of stability when inserted off-center, inability to be removed, or other disadvantages. For instance, U.S. Pat. No. 4,863,476 (and its European counterpart, EP-A-0260044) describes an elongate, generally cylindrically-shaped body divided longitudinally into two portions having a cam device between the two portions for increasing the space between the two body portions once inserted into the disc space. However, because that device is cylindrical in shape such that the only contact points between the device and the vertebral bodies are at the front and back of the disc space, creating increased likelihood of instability, that device is generally unsuitable for use after partial diskectomy.
• The art also discloses intervertebral disc prostheses such as are shown in U.S. Pat. Nos. 3,867,728, 4,309,777, 4,863,477, 4,932,969, Applicant's own Pat. No. 5,123,926, and French Patent Application No. 8816184 that may have more general contact with the adjacent discs, and spinal joint prostheses as described in U.S. Pat. No. 4,759,769, but which are not intended for use in fusion of the discs. The utility of such devices is also limited by a number of disadvantages, in particular, the same lack of cushioning described above in connection with prior art disc plugs and implants. Further, those implants and prostheses that attempt to address this cushioning problem have generally failed because they are not capable of supporting the load imposed upon them by the active post-surgical patient. Further, many prior implants and prostheses require removal of the disc. Removing the disc is not totally undesirable because removing the intervertebral disc does help prevent problems from recurrent disc herniation through the opening into the intervertebral disc space. However, as with all surgical procedures, it is desirable to utilize as much existing structure as possible and to minimize invasiveness. One reason it is desirable to retain as much of the original disc as possible is that if an implant subsequently fails, or if further surgical intervention is indicated for reasons such as infection, the only alternative that is generally available after removal of the intervertebral disc is fusion.
• There is, therefore, a need for a device capable of stabilizing the vertebrae adjacent an intervertebral disc that overcomes the various disadvantages and limitations of known spinal fusion procedures and the disc plugs and implants that are used in such procedures, and it is an object of the present invention to provide apparatus and methods for meeting that need.
• There is also a need for a device that can be implanted into the disc space in a procedure that decreases the likelihood of recurrent disc herniation and it is also an object of the present invention to provide apparatus and methods for meeting that need.
• There is also a need for a device that mimics the function of the disc, in part by retaining as much of the undamaged disc as possible, that cooperates with the remaining portion of the disc to function in a manner similar to the normal, intact disc to provide the cushioning effect of the disc, and it is an object of the present invention to provide apparatus and methods for meeting that need.
• There is also a need for a device that not only functions to provide the cushioning effect of the intervertebral disc but that also provides the opportunity for repairing the remaining portion of the disc, and it is an object of the present invention to provide apparatus and methods for meeting that need.
• Another need that is apparent from the limitations and disadvantages of prior procedures, disc plugs, and prostheses is the need for a device that maintains the function of the healthy, intact intervertebral disc when implanted between adjacent vertebrae, is capable of being implanted in a surgical procedure that is minimally invasive, and that does not require removal of the entire intervertebral disc, and it is therefore also an object of the present invention to provide apparatus and methods for meeting that need.
• Another need that is apparent from the limitations and disadvantages of prior procedures, disc plugs, and prostheses is the need for a device that works with the structure of the intervertebral disc space to maintain as much of the normal function of the disc as possible, and it is also an object of the present invention to provide apparatus and methods that combine the properties of cushioning (by utilizing the remaining portion of the disc), stability (by utilizing a monolithic, biconvex implant), shock absorption (by providing different cushioning characteristics in different portions of the disc space), and provide the opportunity to help reconstruct and/or prevent recurrent herniation of the remaining portion of the disc (by utilizing a hydrogel to fill gaps in the disc space and using known surgical repair techniques) thereby meeting that need.
• Another need that is apparent is the need for a device that is capable of supporting the load imposed upon it when implanted in the disc space while also providing the cushioning function of the natural intervertebral disc and it is also an object of the present invention to provide apparatus and methods for meeting that need.
• Another need that is apparent is a need for a frame for an intervertebral disc implant comprised of two spaced apart, substantially parallel arms, a bridge connecting the arms at one end, a “U”-shaped ear extending at approximately a right angle from the end of one of the arms opposite the bridge and having a hole formed therein for receiving a screw, and a “Y”-shaped ear extending at approximately a right angle from the end of one of the arms opposite the bridge having holes formed in both forks of the Y-shaped ear for receiving screws, the frame being comprised of a material that tends to return to its original shape after the frame is subjected to either a compression or tension load object of the present invention is to provide a frame for meeting that need.
• Other objects, and the many advantages of the present invention, will be made clear to those skilled in the art in the following detailed description of several preferred embodiments of the present invention and the drawings appended hereto. Those skilled in the art will recognize, however, that the embodiments of the invention described herein are only examples provided for the purpose of describing the making and using of the present invention and that they are not the only embodiments of artificial discs that are constructed in accordance with the teachings of the present invention.
SUMMARY OF THE INVENTION
• The present invention addresses the above-described problem by providing an intervertebral disc implant comprising an elongate body comprised of a resilient material having a cavity extending longitudinally into the body, the height of the body being greater than the width of the body, and a frame received within the cavity in the body comprised of two spaced apart, substantially parallel arms and a bridge connecting the arms at one end, the frame being comprised of a material that tends to return to its original shape after the frame is subjected to either a compression or tension load, the frame extending only part way into the cavity of the body in which it is received.
• In another aspect, the present invention provides a method of mimicking the function of the intervertebral disc of the intact spinal column after removal of a portion or all of the intervertebral disc from between the two adjacent vertebrae comprising the steps of inserting a resilient body having a height greater than its width and a cavity formed therein with a key received in the cavity into the intervertebral disc space with the height of the body oriented substantially parallel to the longitudinal axis of the spinal column, removing the key from the cavity in the body after the body is inserted into the intervertebral disc space, and inserting a frame part way into the cavity in the body, the frame comprising first and second arms arms connected by a bridge at one end for providing resistance to flexion and/or extension of the spinal column, and filling the portion of the cavity in the body into which the frame does not extend with a hydrogel.
BRIEF DESCRIPTION OF THE DRAWINGS
• Referring now to the figures,FIG. 1 shows a side elevational view of a presently preferred embodiment of an intervertebral disc implant constructed in accordance with the teachings of the present invention showing the key assembled to the implant for implantation in the intervertebral disc space.
• FIG. 2 is an end view of the intervertebral disc implant ofFIG. 1.
• FIG. 3 is a perspective view of the intervertebral disc implant ofFIG. 1 after removal of the key from the cavity in the body of the implant and insertion of the frame into the cavity.
• FIG. 4 is a side elevational view of the invertebral disc implant ofFIG. 3.
• FIG. 5 is an end view of the intervertebral disc implant ofFIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
• In more detail,FIG. 1 shows a presently preferred embodiment of an intervertebral disc implant constructed in accordance with the teachings of the present invention atreference numeral10.Disc implant10 is comprised of three components, each described in more detail below,implant body12,key14, andframe16.Body12 is preferably molded from a resilient, polymeric material. Although not limited to these materials, in the preferred embodiment,body12 is molded from a biocompatible, viscoelastic polymer such as silicone, a urethane such as a polycarbonate urethane, or a polyurethane. As shown inFIGS. 1, 2, and3, thebody12 is molded with a profile that approximates the shape of the normal intervertebral disc space with a height H greater than the width W (seeFIG. 2); the top andbottom surfaces36 ofbody12 are arched so that the height ofbody12 is greater in the center than at its ends. This shape ofbody12 is referred to as being biconvex, e.g., both the top andbottom surfaces36 ofbody12 are convex in the anterior-posterior direction. Although shown in the figures as being configured for the use of theintervertebral disc implant10 vertebrae in the lumbar region of the spine, those skilled in the art will recognize from this description that, with appropriate changes in size and configuration, the intervertebral disc implant of the present invention can also be utilized to advantage for replacement of a portion of a disc located in other portions of the spine.
• Not only are the top andbottom surfaces36 ofbody12 convex in the anterior-posterior and side-to-side directions, but they are also provided with anintegral metal strip20 that may be textured or provided with a grooved surface to facilitate the ingrowth of bone onto thesurfaces36. In the preferred embodiment shown, themetal strips20 are provided with structure for resisting anterior-posterior movement ofbody12 once inserted into the disc space in the form ofprongs22 for biting into the cortical bone on the bearing surface of the adjacent vertebrae (not shown). In a second embodiment, themetal strips20 affixed to thesurfaces36 ofbody12 are covered with a porous or roughened titanium coating and perhaps even a layer of calcium phosphate for this purpose; other suitable coatings/surfaces are known in the art and include titanium wire mesh, plasma-sprayed titanium, porous cobalt-chromium and bioactive materials such as hydroxyapatite and the aforementioned calcium phosphate. This component of theartificial disc10 of the present invention functions in a manner similar to the function of the cartilage of the normal, healthy disc to facilitate ingrowth of bone on thesurfaces36.
• Theimplant body12 is provided with anelongate cavity18 for receiving a key14 therein. In the preferred embodiment shown, thecavity18 is formed with a portion near the opening intobody12 that is rectangularly-shaped (when viewed in cross-section) with dimensions that approximate the rectangular shape ofkey14 and an enlarged portion deeper intobody12, both for a purpose described below. Because thebody12 is comprised of a resilient material that can be compressed, the key14 is comprised of a relatively incompressible material such as stainless steel, titanium, or a polymer such as nylon or polycarbonate (or any other relatively imcompressible biocompatible material) to maintain the shape of thebody12 when inserted into the intervertebral disc space after removal of a portion of the intervertebral disc. Although not limited to this use, theintervertebral implant10 of the present invention is optimally placed in the space from which a portion of the intervertebral disc has been removed at the centerline of the spinal column.
• Frame16 is shown inFIGS. 3, 4, and5, and by reference to those figures, it can be seen thatframe16 is comprised of two spaced apart arms24 connected at one end by a bridge26. One or both of theends25 of the arms24 opposite bridge26 are provided with ears28 having one ormore holes30 formed therein for receiving one or more screws (not shown) for securingframe16 to the bodies of the vertebrae (not shown) adjacent the intervertebral disc space into whichdisc implant10 is inserted. In the preferred embodiment shown, both ends of arms24 are provided with ears28, theear28A on the end of one arm24A being shaped in the form of a Y” and having twoholes30 formed therein, the portion ofear28A between theholes30 being cutout at32 to form the arms of the “U”-shapedear28A, and theear28B on the end of the other arm24B being shaped in the form of an inverted “U” and having asingle hole30 therein. This arrangement of “Y” and inverted “U”-shapedears28A and28B allows the use of thedisc implant10 of the present invention in the intervertebral disc spaces of successive segments of the spinal column. When secured to the body of the adjacent vertebra, the inverted “U”-shapedear28B of one artificial disc extends into thecutout portion32 of the “Y”-shapedear28A secured to the body of that same vertebra.
• As best shown inFIG. 4, when inserted into thecavity18 inbody12 after the key14 has been removed therefrom,frame16 does not extend all the way intocavity18. In other words, the bridge26 offrame16 is positioned only about half way into thecavity18 indisc implant12. As noted above,cavity18 is formed of a portion near the opening into the cavity with a shape that approximates the rectangular cross-sectional shape ofkey14, and as best shown inFIG. 4,frame16 resides in that portion of the cavity near the opening intocavity18. The dimensions of the portion offrame16 that includes the arms24 and bridge26 are preferably approximately the same as the internal dimensions of this portion of cavity18 (and coincidentally, the rectangular cross-sectional shape of key14), although in one preferred embodiment, the dimensions of the portion ofcavity18 near the opening intocavity18 is slightly smaller than the dimensions of the portion offrame16 that includes the arms24 and bridge26 so as to help retain theframe16 therein. In otherwords, it may be advantageous for the relative dimensions of theframe16 and the opening intocavity18 to be sized so that theframe16 slightly stretches or expands the resilient material comprisingimplant body12 whenframe16 is inserted intocavity18. Similarly, the arms24 offrame16 may be angled slightly outwardly, or apart from each other, so that once theframe16 is inserted into thecavity18 inbody12, the resilience of thematerial comprising body12, which may be stretched or expanded by insertion of theframe16, tends to retainframe16 in the opening intocavity18. This slight angle of the arms24 offrame16, which is preferably less than about 5% from parallel, is exaggerated in the figures for purposes of illustration; in actual practice, the angle is small enough that it is appropriate to refer to the arms24 as being substantially parallel to each other.
• In the preferred embodiment,frame16 is comprised of a material that tends to return to its original shape after the frame is subjected to either a compression or tension load. Materials that are characterized by this spring-like function when formed into theframe16 include, but are not limited to stainless steel, titanium and titanium alloys, cobalt-chrome (Co—Cr) alloys, cobalt-chromium-molybdenum (Co—Cr—Mo), and medical grade (inert) polymeric plastics such as polyethylene, all as known in the art. In other words, when theimplant body12 is inserted into the intervertebral disc space and key14 is removed and replaced byframe16,body12 is subjected to both compression and tension loads as the spine flexes and extends and as the patient moves during his/her normal daily routine. When subjected to these compression and tension loads,frame16 deforms. Under compression, the ends25 of the arms24 opposite bridge26 tend to move closer to each other and when in tension, the ends25 of the arms24 opposite bridge26 tend to move further apart; in other words, the arms24 offrame16 deviate from their original spaced apart position (in the preferred embodiment shown, the two arms are substantially parallel, but those skilled in the art who have the benefit of this disclosure will recognize that the invention is not limited to a frame having parallel arms) when under compression or tension force. When the respective compression or tension force is relieved, theframe16 tends to return to its original shape, i.e., the ends25 of arms24 opposite bridge26 return to their original spaced relationship, and the arms therefore assume their original, spaced apart relationship. When subjected to loads in this manner, frame16 acts as both a “backbone” and as a spring to help both bear compression loads and relieve tension loads in a manner that mimics normal disc function.
• Note also that when theimplant body12 is inserted into the intervertebral disc space, the bridge26 offrame16 is positioned posteriorally relative to theends25 of arms24 opposite bridge26. The spring function offrame16 is advantageous because, as the patient bends forward, the ends of arms24 opposite bridge26 are subjected to compression loads, and the further the patient bends, the more thematerial comprising frame16 tends to resist the compression load, providing the spring function discussed above. As best shown inFIG. 4, the bridge26 offrame16 is provided with aprojection34 that extends between the arms24 that functions to limit the bending of the arms24, thereby limiting the flexure of the spinal column at the vertebrae adjacent theimplant body12. Further, biomechanical studies of normal, healthy spines have shown that the axis of rotation (the weight-bearing center of the intervertebral disc) translates anteriorally and posteriorally as the spine flexes and extends, and the variable resistance provided by this configuration and placement offrame16 in the intervertebral disc space helps provide this normal front-to-back shift in the axis of rotation so that the disc implant of the present invention replicates that shifting in the axis of rotation.
• As noted above,implant body12 is provided with acavity18 and after positioning theimplant body12 in the space from which a portion of the intervertebral disc has been removed and removing the key14 fromcavity18, theframe16 is inserted into the cavity in place of the key. As is best shown inFIG. 4,frame16 does not extend all of the way into theelongate cavity18, leaving a space that in the preferred embodiment is at least partially filled with a hydrogel such as a polyvinyl alcohol (PVA), synthetic silk-elastin copolymers, polymethyl- or polyethylmethacrylate, polyethylene or polyacrylonitrile that absorbs water and increases in volume upon absorption of water, thereby functioning to maintain disc height in a manner similar to the manner in which the healthy disc maintains proper spacing between adjacent vertebrae. As best shown inFIGS. 3-5, thecentral projection34 of the bridge26 ofbody12 is provided with aport38 through which hydrogel is added (or removed) from the portion of thecavity18 that is not occupied byframe16.Port38 is comprised of a channel that extends through thecentral projection34 into thecavity18 and the surgeon injects the hydrogel (or uses a syringe to remove hydrogel) as needed to confer the desired amount of initial disc height to the implantedbody12. Once the desired disc height is obtained, theport38 is capped or plugged to prevent extrusion of the hydrogel contained withincavity18. In an alternative embodiment, a one-way valve of a type known in the art may be utilized for this purpose. As described above, thecavity18 is provided with a portion having expanded dimensions (as compared to the dimensions of the portion ofcavity18 proximate the opening into the cavity) for the purpose of allowing the injection of increased amounts of hydrogel for extra adjustability in obtaining the desired disc height. Some or all of theprongs22 used to resist anterior-posterior movement of theimplant body12 in the disc space are provided withchannels40 communicating withcavity18 for the purpose of allowing ingress and egress of fluid into and out of the hydrogel contained incavity18.
• The positioning offrame16 only part way into thecavity18 inbody12 serves an additional purpose. The spring function offrame16 provides resistance to compression and tension loads, but it also functions to allow anterior-posterior translation of the axis of rotation as the spine flexes so as to mimic the kinematics of the healthy disc. First, because of the resilient nature of thematerial comprising body12, the portion of thematerial comprising body12 that is positioned between the arms24 offrame16 and the bearing surfaces of the vertebral bodies of the adjacent vertebrae provides additional cushioning and resistance to the deformation of theframe16 under extraordinary compression load. Second, because it extends only part way into thecavity18 ofbody12, thebody12 having theframe16 positioned therein provides different amounts of resistance to compression load as the patient bends. The resistance to compression provided by the location offrame16 part way intocavity18 is greater as spinal flexion increases compared to the resistance to compression provided by the portion ofimplant body12 in which the resistance to compression is provided by thematerial comprising body12 and the hydrogel located in the portion ofcavity18 into whichframe16 does not extend. Of course the surgeon has the opportunity to fine-tune the amount of resistance as the spine flexes and/or extends by utilizing a frame with arms24 of greater or shorter length so as to provide less or more resistance to flexure, respectively, and by adding or removing hydrogel in the portion of thecavity18 into whichframe16 does not extend.
• The healthy intervertebral disc includes three parts, the nucleus pulposus, annulus fibrosus, and cartilagenous endplate, each with separate functions, and all of which cooperate to provide motion, load bearing characteristics, and the other functions of the intact spinal column. Theintervertebral disc implant10 of the present invention provides corresponding parts, with their corresponding contribution to function, in the form of theimplant body12, which functions in a manner similar to the annulus fibrosus to maintain disc height, the frame-filled and hydrogel-filledcavity18 which functions in a manner similar to the nucleus pulposus to distribute load and resist compression and tension, and the roughened surface of the metal strips20 onsurfaces36, which functions in a manner similar to the cartilagenous endplate by providing a surface that facilitates ingrowth of the bone, thereby making the intervertebral implant of the present invention an integral part of the spinal column. As noted above, the surfaces of the metal strips20 may be provided withprongs22 or other structure for engaging the adjacent vertebrae to resist anterior-posterior movement of theimplant10 in the intervertebral disc space, but ingrowth of bone, facilitated by the roughened surface and/or surface coating onstrips20, is particularly advantageous in retaining theimplant10 in the disc space.
• Those skilled in the art who have the benefit of this disclosure will recognize that certain changes can be made to the component parts of the apparatus of the present invention without changing the manner in which those parts function and/or interact to achieve their intended result. By way of example, those skilled in the art who have the benefit of this disclosure will recognize that the amount of resistance to compression and/or tension load provided by theframe16 depends on such factors as the length of the arms24 and the material comprising theframe16 and that although it may be appropriate to implant an artificial disc constructed in accordance with the teachings of the present invention having a frame with a certain level of resistance to compression/tension load, it may be that an intervertebral disc including a frame with a different level of resistance to compression/tension load is better suited for implantation in another patient. It will also be recognized by those skilled in the art that to obtain desirable load resistance properties, it may be advantageous to increase the thickness of thecentral projection34 so as to limit movement of the arms24 toward each other under compression load or to make theimplant body12 from a combination of materials, with an embedded layer of material that is relatively incompressible or having a second set of resilience and/or load-bearing characteristics, or as a laminated “sandwich” of polyurethane and other material(s), each material adding a unique component to the load bearing characteristics of theimplant body12. All such changes, and others that will be clear to those skilled in the art from this description of the preferred embodiments of the invention, are intended to fall within the scope of the following, non-limiting claims.

Claims (14)

1. An intervertebral disc implant comprising an elongate body comprised of a resilient material having a cavity extending longitudinally into said body and a frame received within the cavity in said body comprised of two spaced apart arms with a bridge connecting the arms at one end, said frame being comprised of a material that tends to return to its original shape after said frame is subjected to either a compression or tension load, said frame extending only part way into the cavity of said body in which it is received.

2. The intervertebral disc implant ofclaim 1 wherein said frame is provided with a port for receiving an injection of hydrogel therein.

3. The intervertebral disc implant ofclaim 2 wherein said port is positioned so that the hydrogel injected into said port fills the portion of the cavity into which said frame does not extend.

4. The intervertebral disc implant ofclaim 1 additionally comprising a metal strip attached to at least a portion of the surfaces of said body that bear against adjacent vertebrae when implanted into the intervertebral disc space, said metal strip being provided with structure for contacting the adjacent vertebrae to resist movement of said body relative to the adjacent vertebrae.

5. The intervertebral disc implant ofclaim 4 wherein at least a portion of said metal strip is provided with a coating of or comprises porous or roughened titanium, calcium phosphate, titanium wire mesh, plasma-sprayed titanium, porous cobalt-chromium, or hydroxyapatite.

6. The intervertebral disc implant ofclaim 1 additionally comprising a key positioned in the cavity in said body and extending substantially all the way into the cavity, said key being withdrawn from the cavity after said body is implanted into the space between two adjacent vertebrae and before said frame is inserted into the cavity in place of said key.

7. The intervertebral disc implant ofclaim 1 additionally comprising a “U”-shaped ear extending at approximately a right angle from the end of one of the arms opposite the bridge and having a hole formed therein for receiving a screw for attaching said frame to a first adjacent vertebra and a “Y”-shaped ear extending at approximately a right angle from the end of the other arm opposite the bridge having holes formed in both forks of the Y-shaped ear for receiving screws for attaching said frame to a second adjacent vertebra.

8. The intervertebral disc implant ofclaim 1 additionally comprising a projection extending from the bridge between the arms of said frame.

9. The intervertebral disc implant ofclaim 1 wherein the arms of said frame are angled apart from each other.

10. A method of mimicking the function of the intervertebral disc of the intact spinal column after removal of some or all of the intervertebral disc from between two adjacent vertebrae comprising the steps of:

inserting a first resilient body having a cavity formed therein and a key received in the cavity into the intervertebral disc space with the height of the body oriented substantially parallel to the longitudinal axis of the spinal column;

removing the key from the cavity after the body is inserted into the intervertebral disc space;

inserting a frame part way into the cavity in the body, the frame comprising first and second arms spaced apart arms connected by a bridge at one end for providing resistance to flexion and/or extension of the spinal column; and

filling the portion of the cavity in the body into which the frame does not extend with a hydrogel.

11. The method ofclaim 10 additionally comprising attaching the frame to the adjacent first and second vertebrae.

12. The method ofclaim 10 additionally comprising resisting anterior or posterior movement of the body in the intervertebral disc space.

13. The method ofclaim 10 additionally comprising limiting the movement of the arms of the frame as the spinal column flexes.

14. The method ofclaim 10 additionally comprising resisting relative movement between the frame and the implant body.

Images