AU2003262694B2 - Intervertebral disc implant - Google Patents

Description

WO 2004/016205 PCTIUS2003/025535 INTERVERTERRAL DISC IMPLANT FrELn OF-t"E INVENTION [001! Theinvention is related to dvics and methods for the treatment of trauma.

anq disasca of the spine, More particularly..the invention relates to intervertebral disc relaceinent.

BACKCGROUNOtOFTHE INVENTION [002) A variety of conditions suchias spondylolysis, disc herniation, compression of spinal cord nerve roots, degenerative dise disease, and trauma are known to cause severe discifort, :requiring medical attention. Among the procedures currently used to alleviate such conditions are spinal fusion, such as intervertebral and posterolateal fusion or srtrodesis. In these procedures, two adjacent vertebral bodies are fused together, The affected intervertebral disc is first excised, And an implant is inserted which accommodates bo growth between the two vertebral bo s to effectively bridge the gap left by the disc removal. A number of different implant mterials and implant designs have been used for fAdion with varying success. Although intervertebral and posterolateral fusion are widely usd;, drawbacks to their use include a reduced physiologic range of motion and other fusion relted complications such as degeneration of adjacent discs and destabilization ofthe fitional spinal unit. As a result, alternative treatments with fewer complications, but sinilar fficacy to fusion, are desirable. One such alternative to spinal fusion is arthroplasty and the use of a prosthetic or artificial disc.

[03] In general, arthroplasty is used in the replacement of diseasedjoints.

Arhroplasty involves a set of procedures ditected to maintaining motion of the joint, thereby praserving its integrity and keeping the adjacent motion segments from deteriorating, as they feid to do after fusion. Depending on the Location and the condition of the affectedjoint, spcific arthroplasty procedures may be used. For example, interpositional reconstruction suijery, which reshapes the joint and adds.aprosthetic disk between the two bones forming theijoint is commonly used on elbow, shoulder, ankle, and finger joints. Total joint replacement, or total joint arthroplasty, replgces the entire diseased joint with an artificial WO 2004/016205 PCT/US2003/025535 prosthesis and, in recent years, has becomethe operation of choice for most knee and hip problems.

i [004] Hip and knee replacements are particularly widespread with nearly 300,000 hip replacements and about as many knee replacements performed in the United States in 2001. With respect to the knee and hip joint replacement surgeries, there are several implants.

or prosthetics available. For the hip prosthetic, in an exemplary design, there are two components, one is a metal ball attached to a metal stem which is fitted into the femur, and the second is a matching plastic socket which is implanted into the pelvis. The metal pieces are generally formed from stainless steel, alloys of cobalt and chrome, titaniumn and alloys of titanium; the plastic pieces are generally fonned from high-density polyethylene. For the knee prosthetics, in an exemplary embodiment, metal and plastic components are again used to replace the damaged bone ends and cartilage. The metal pieces are generally formed from stainless steel, alloys of cobalt and chrome, titanium, and alloys of titanium; the plastic pieces are generally formed from high-density polyethylene.

[005] Although the evolution of spinal arthroplasty and the use ofprosthetics in the .spine has been similar to that of other joints in the body, evolving from fusing the joint to replacing the functional joint, the advent of spinal athroplasty, however, has been slower than arthroplasty in other major joints in the body. A few of the possible reasons why spinal artbroplasty has been delayed are that spinal problems related to disc degeneration are difficult to diagnose, spinal procedures are typically crisis-driven and thus conservative solitions such as fusion are acceptable, and spinal anatomy is complex.

[006] Over the past 40 years spinal:arthroplasty technologies have been under development and in the last 10 years spinalaithroplasty has won the attention of leading surgeons and implant manufacturers. The evolution of spinal arthroplasty essentially began in the 1950's and one of several emerging concepts was the spherical concept of the disc prostheses. The spherical concept is simply the placement of a ball, essentially circumferential, in the cavity of the nucleus pulposus after a discectomy procedure has been performed. The annulus is kept in place and the ball serves as a nucleus replacement device.

Various materials have been experimented with for the spherical concept. For example, in theiearly 19.60's, implants using silicone ball bearings were implanted into the cervical regions of patients, but the outcomes were uncertain. In the mid 1960's, stainless-steel (ball beaking) prostheses were implanted into patients. The results of the procedure were initially

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WO 2004/016205 PCT/US2003/025535 promising bit over time the disc spaces lost height due to subsidence ofthe steel balls into the vertebral bodies. Presently, the concept of a spherical prosthesis continues to be examined using different materials, the latest of which is a modified carbon fiber.

[007] Another emerging concept is the mechanical concept design. The riechanical concept design is essentially a total disc replacement product which is intended to iestore the range of motion of the vertebral motion segment unit. These devices are often comprised of metallic endplates fixed to the adjacent vertebral bodies via a stabilization mechanism and a core formed from polyethylene or other polyineric materials. Alternatively, instead of a core, bearing surfaces can be used, the bearing surface materials being ceramic-on-ceramic; metalon metal; or metal-on-polyethylene. The mechanical design concept is based on the same principles as joint reconstruction products, such as knee and hip replacements, and a variety of mechanical design prostheses concepts have been proposed and continue to be proposed.

[008] Another concept is the physiological concept. The physiological concept uses a hydrogel, elastomer, or polyurethane-based core which is intended to restore the disc function by absorbing and emitting fluid between the patient's vertebral endplates; while also maintaining the natural shock absorbing or cushioning function of the disc. The physiological concept devices are generally considered only a partial solution as they are designed to replace only the nucleus or a portion of the disc.

[009] All.of the approaches to discreplacement are aimed at some or all of the following: alleviating discogenic pain, restoring range of motion, maintaining the iatural shock absorbing function of the disc, restoring normal form or disc height, and restoring physiological kinematics. Generally, four exemplary types of artificial intervertebral discs have been developed for replacing a portion-or all of an excised disc: elastomer/fluid filled discs, ball and socket type discs, mechanical spring discs and hybrid discs.

[0010] Elastomer/fluid filled discs typically include an elastomer cushion or a fluid filled chamber positioned between lower and upper rigid endplates. The cushions and chainbers of these implants advantageously function, in mechanical behavior, similar to the removed intervertebral disc tissue.

[0011] Ball and socket type discs typically incorporate two plate members having cooperating inner ball and socket portions which permit articulating motion of the members during mpvement of the spine.

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[0012] Mechanical spring discs typically incorporate one or more coiled springs disposed between metal endplates. The coiled springs define a cumulative spring constant that is designed to be sufficient to maintain the spaced arrangement of the adjacent vertebrae while allowing normal movement of the vertebrae during flexion and extension of the spine in any "I direction.

[0013] The fourth type of artificial intervertebral disc, the hybrid disc

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incorporates two or more of the aforementioned design principles. For Sexample, one known hybrid disc arrangement includes a ball and socket joint S 10 surrounded by an elastomer ring.

[0014] While each of the foregoing prostheses addresses some of the problems relating to intervertebral disc replacement, each of the implants presents significant drawbacks. Thus, there is a need for an intervertebral implant that accommodates the anatomy and geometry of the intervertebral space sought to be filled as well as the anatomy and geometry of the ends of adjacent vertebral bodies, while providing reliability and simplicity in design.

More particularly, there is a need for a spinal disc implant which provides stability for supporting the high loads applied to the vertebrae, permits sufficient mobility to allow the patient an approximate normal range of motion, provides for axial compression between adjacent vertebrae, and has shock absorption abilities.

SUMMARY OF THE INVENTION A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was, in Australia, known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

The invention includes an intervertebral disc for placement between first and second vertebrae, the intervertebral disc including: an upper surface for contacting the first vertebra; a lower surface for contacting the second vertebra; an exterior wall having an inner surface and an outer surface, the exterior wall extending between the upper and lower surfaces; and 00 S. an interior volume defined between the upper and lower surfaces and 0^ the inner surface of the exterior wall, the interior volume including a central chamber surrounded by a plurality of interconnected peripheral chambers.

en, [0015] The invention may relate to an intervertebral disc that is preferably designed to restore disc height and lordosis, allow for a natural range of motion, absorb shock and provide resistance to motion and axial NO compression. Furthermore, the intervertebral disc may be used in the cervical, I(N the thoracic, or the lumbar regions of the spine.

[0016] The intervertebral disc includes a body having a footprint that is c- 10 preferably conforming in size and shape with at least a portion of the ends of adjacent vertebrae. The shapes of the intervertebral disc include, but are not limited to, circular, oval, ellipsoid, kidney-bean, annular, C-shaped, D-shaped, etc.

[0017] In one embodiment, the body of the intervertebral disc includes an upper endplate, a lower endplate, and an elastic membrane disposed between the upper and lower endplates. Alternatively, the elastic membrane may surround and encapsulate the endplates. The elastic membrane defines an interior that is at least partially filled with a fluid. Preferably, the fluid is selected from the group consisting of gas, a liquid, a gel or any WO 2004/016205 PCTIUS2003/025535 coijbination thereof In addition, the fluid iiay be compressible, and may be selected from thd group consisting of, for example, gas, lidi, or hydrogel, or may be incompressible, and mdy be selected from the group consisting of,ifor example, saline.

18 The disc also preferably incti es a valve for permitting insertion of fluid to the interior of the intervertebral disc. The valve may be disposed on the elastic membrane, alternatively, however the valve can.be located in the upper and lower endplates of the disc.: [0 19] The upper and lower endplates are preferably formed of metal, such as titdnium, stainless steel, titanium alloys, colblt-chromium alloys, or amorphous alloys.

Alternatively, however, the upper and lower endplates may be formed of ceramics, coaposites, polymers, such as poly-ether-eth~r-ketone PEEK) or an ultra high molecular wight polyethylene UHMWPE), bone, including cortical, cancellous, allograft, apograft, xenograft, demineralized or partily demineralized bone, or any other materials able to serve as load bearing supports. The:materials chosen for the endplates, in.

combination with the desired fluid, are preferbTly selected to reduce the amount of wear, and this increa.e the life of the joint.

[0920] The outer surface of the upper and lower endplates may be substantially:flat,,.

wedge-shaped, etc. The outer surfaces of the upper and lower endplates also maybe dome shped with their radii defined in the sagittal aid coronal planes to generally match those of the ends of the adjacent vertebra. The dome shape allows the upper and lower endplates to better conform with the ends of the adjacen vertebrae for a better fit in situ.

[0921] The intervertebral disc also jeferably includes migration-resistant structures prbvided on the outer surface of at least one or both of the endplates to impede miovement, dislodging, or expulsion of the endplates within and from the ends of the adjacent vertebrae.

Th migration-resistant structures include, but are not limited to, flaps, spikes, teeth, fins, deloyablespikes, deployable teeth, flexible sikes, flexible teeth, alternatively shaped teeth, instable or expandable fins, screws, hooks, serrations, ribs, and textured surfaces.

[0422] Furthermore, the upper and lower endplates also preferably coated with a bone gro wh inducing or conducting substance toqpromote bony ingrowth to permanently secure the disc to the adjacent vertebrae. Alternatively, the upper and lower endplates may have a ro hened surface; a porous surface; laser teated endplate layers; integrate an ost oonductive/ostoinductive scaffold; or ay be provided with or made from an integral osot onductive and/or osteoinductive matial to promote bony ingrowth. The endplates WO 2004/016205 PCT/US2003/025535 may fArther include a membrane and/or a baier to limit the amount and/or depth f bony ingowth.

[0023] The upper and lower ehdplatesmay also have implant instrument tion attachment, guiding, and retainment structures. For example, the endplates may have loles, slots, threads, or a dovetail for implanting the implant and/or distracting the adjacent vertebrae. For example, the disc may include a slot formed in the upper'and/or lower endplates, the slot being configured to receiee an implant insertion instrument a.distractor or both.

[O024] The upper and lower endplatbs:may also preferably include articlating surfaces, thus providing the intervertebral disc with greater mobility. The articulating surfaces preferably including a surface polish or similar wear reducing finish such as diamond. fiish, TiNi finish, etc. in order to .minimize wear, decrease particle generation, and increase disc life.

[0025] In some embodiments, in addition to the fluid or in place of the fluid, additional structures may be included to proyvde additional stiffness. The structures include, but are not limited to, springs, elastomers, bellow, balloons, closed reservoirs, h6llow bodies, biocompatible fibers, and cables.

[0026] In some embodiments, the intevertebral dise also preferably has an articulating mechanism to allow the endplaieto pivot with respect to one another such that associated portions of the endplates may come closer together under compressio while different associated portions of the endplates may separate under tension. The atticulation mechanism may be in the form of a center lpivot axis or fulcrum. Preferably, thea' intervertebal disc also allows and provides.a mechanism, or is configured to all9w the location of the pivot axis within the disc toldhange in response to the loading conditions, thus providing a moving instantaneous axis of rotation. The intervertebral disc also preferably comprises a mechanism, such as providing. afluid, an elastomer, a spring, a cable, etc. to absorb axial compression forces and to provide a shock absorbing effect.

[0027] In some embodiments:the imterertebral disc includes an upper end a lower eid, and an outer sidewall disposed therebetween. The disc may have an interior volume defined between the upper and lower ends and the outer sidewall, with the interior volume preferably including a center pivot and at leIst one chamber, the chamber being peripheral to and surrounding the center pivot. Preferably, the center pivot includes a central wall defining !6 WO 2004/016205 PCTIUS2003/025535 a central cbamnber, and the at least one periph chamber is disposed between th ater sidowall and the central wail, A first fluid may be disposed in the at least one peripheral chamber. A second fluid may be disposed in the central chamber. The first and second fluids mayor may hot be the same. The intervertebi4a disc may include additional periphtoal chambers wihich may or may not be in fluid communication with the central chambor and,.

eaqih other. Further, the sidewall may be formied of a first material while the ceitr wall may be formed of a second material, with the firs material having a different stiffness tk h the second material. Preferably, the center pivot and/or central chamber may permit th upper and lowers ends to pivot with respect to eachbother, and may include a resilient eleient such asa spring.: [008] in -another embodiment, the inervertebral disc includes a body havin an upper surface spaced from and opposing a lower surface. The spacing between the pper suriface and the lower surface may be selectable. The body further includes an oute sidewall fotiing an outer wall and a thru-hole forming an inner wall, with the inner wall de ing an opening. TIrther, the body may be substantially C-shaped. A chamber may also bjIdisposed within the.body. In addition, there may be at least one portion extending from the lkdy for cointactini avertebrae, with the portion defining a hole for receiving a fastener.

[0029] 'The intervertebral disc may lS implanted in a modular fashion, if possible, or it may be implanted preassembled. An antexir,- anteriolateral, or lateral surgicd approach may be used to implant the intervertebral disc Furthermore, depending on the intvertebral disc.to be implanted, a minimally invasive surgical method or a simultaneous distrttion and I I im lantation surgical method may be used, Also depending on the intervertebral duo to be implante the Anterior Longitudinal Ligament may be attached directly to the disc to the adjacentyertebral bodies. The Anterior Loigitudinal Ligament may be formed fro partially deineralized or demineralized autograft, alograft, or xenograft. Alternatively, thAntedior Logitudinal Ligament may be formed from biocompatible materials such as elastioers, or braided polymers. To assist with the implantation of the intervertebral disc, the intervtebral disc may include aliganment markers.

BRIEF DESCIUPTiN op TrE DRAWINOS [0030 To facilitate an understandin bf and for the purpose of illustrating the preient inv ntion, exemplary and preferred features end embodiments are disclosed in the 7 00 Saccompanying drawings, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, and wherein similar reference characters denote similar elements throughout the several views, and wherein: [0031] Figure 1 is a perspective view of a first embodiment of an artificial intervertebral disc; [0032] Figure 2 is a cross-sectional view of the artificial intervertebral IDdisc of Figure 1 taken along line A-A; [0033] Figure 2a is an alternate cross-sectional view of the artificial intervertebral disc of Figure 1 taken along line A-A; [0034] Figure 3a is a side view of a deployable spike according to a form of the invention.

[0035] Figure 3b is a side view of another deployable spike according to a form of the invention.

[0036] Figure 3c is a side view of a flexible spike according to a form of the invention.

[0037] Figure 3d is a side view of alternatively shaped teeth according to a form of the invention.

[0038] Figure 3e is a side view of anchors according to a form of the invention.

[0039] Figure 4 is a perspective view of a second embodiment of an intervertebral disc; [0040] Figure 5 is a cross-sectional view of the intervertebral disc of Figure 4 taken along line B-B.

[0041] Figure 6 is a perspective view of an alternative embodiment of the intervertebral disc of Figure 4; [0042] Figure 7 is a perspective view of a third embodiment of an intervertebral disc according to the present invention; [0043] Figure 8 is a cross-sectional view of the intervertebral disc of Figure 7 taken along line C-C; 00

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[0044] Figure 9 is a cross-sectional view of an alternative embodiment of the intervertebral disc of Figure 7 taken along line D-D; [0045] Figure 10 is a perspective view of a fourth embodiment of an intervertebral disc.

[0046] Figure 11 is a side view of the fourth embodiment of the intervertebral disc of Figure [0047] Figure 12 is schematic view of a fifth embodiment of an Iintervertebral disc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0048] Any of a wide variety of different implant structures can be prepared according to the teachings shown by the illustrative examples of the intervertebral discs disclosed herein. The intervertebral discs of the present invention are preferably designed to restore spinal lordosis, disc height, to allow for a natural range of motion, absorb shock and to provide resistance to motion and axial compression.

[0049] The intervertebral discs preferably are sized and adapted for use in the cervical, thoracic, and lumbar regions of the spine. Also, the intervertebral discs can be tailored for each individual patient allowing for disc characteristics appropriate for the individual patient. For example, the core of the disc can include different assemblies, different components, and/or various types of materials to create the desired characteristics for each individual patient.

[0050] Furthermore, the intervertebral discs may allow flexion, extension, lateral bending, rotation, and translation. Flexion is movement that brings two parts of a joint or body into a bent position; in the spine, this is a movement in which the spine starts straight and moves into forward bending.

Extension is a movement that draws two parts away from each other; in the spine, this is a movement in which the spine starts straight and moves into backward bending. Lateral bending is a bending movement toward a lateral side; in the spine, this movement generally involves bending (lateral) and coupled rotation. Rotation is a movement that results in a portion of the spine twisting, rotating or turning with respect to the axis of the spinal column.

9a 00 O Translation is a limited movement that is generally transverse to the axis of the spinal column.

[0051] Additionally, similar to a natural intervertebral disc, the artificial intervertebral discs preferably allow for a moving instantaneous axis of rotation. At every instant for a body in plane motion there is a line in the body or a hypothetical extension of this line that does not move. The instantaneous NO axis of rotation is this line. A moving instantaneous axis of rotation refers to Sthe ability of the instantaneous axis of rotation to move translate) as WO 2004/016205 PCT/US2003/025535 a result of different loading conditions; in othr words, the location of the instantaneous axis of rotation moves with respect to the disc. The preferred mean location of the moving instantaneous axis of rotation for the lumbar region of the spine is preferably in the posterior half of the disc space or proximal to an adjacent (superior or inferior) endplate, preferably proximal to the inferior/caudal endplate, the preferred mean location of the moving instantaneous axis of rotation for the thoracicregion of the spine is preferably in the inferior portion of the disc space and proximal to the caudal vertebral body extending posteriorly into the. spinal canal, and the preferred mean location of the moving instantaneous axis of rotation for the ceivical region of the spine is preferably in the posterior half of the caudal vertebral body.

[0052] Also similar to a natural intetrertebral disc, the response characteristics of the artificial intervertebral disc are preferably non-linear, For example, in response to continued axial compression, the artificial intervertebral disc preferably undergoes a large initial amount of compression followed by non-linearly decreasing amounts of compression.

[0053]. Referring to the accompanying drawings, preferred embodiments and features of the artificial intervertebral disc will be described in detail. It is to be noted however that these descriptions of specific embodiments and features are merely illustrative. It is contemplated that one or more features or elemnents of the various embodiments may be combined or used singularly, and that modifications of the various embodiments, as well as other embodiments are contemplated and will be apparent to those persons skilled.ih the art.- [0054]. Referring initially to Figures 1.and 2, a perspective view of an exemplary first .embodiment of an artificial intervertebral disc 10 is shown. As shown, the disc 10 has a generally kidney-bean shaped footprint which includes an anterior side 11, a posterior side 13, and first and second lateral sides 15, 17,respectively. The anterior side 11 and lateral sides. 15, 17 are all substantially convex in shape while the posterior side 13 is substantially concave in.shape. However, the disc 10 may take on other shapes that preferably conform geometrically and anatomically with the adjacent vertebral bodies including, but not limited to. circular, oval, ellipsoid, annular, D-shaped, C-shaped, etc.

[0055] As shown, the intervertebral disc 10 includes an upper endplate 12,.a lower endplate 14 and an elastic membrane 16, the elastic membrane 16 generally extending from the upper endplate 12 to the lower endplate 14 and is located, preferably, proximate to the outer periphery of the diso 10. Alternatively, the elastic membrane 16 may surround and/or WO 2004/016205 PCT/US2003/025535 endapulat the upper and lower endplates 12, 14. The elastic membrane 16 in combination with the upper-and lower endplates 12, 14 may define an interior volume that may.beat least patially filled with a fluid 22. The elastic membrane 16 preferably is formed from an elastomer such as polyurethane, silicone, abraided polymer, or any other appropriate elastic material known'in the art. The elastic membrane may be non-permeable. Alternatively the elastic membrane 16 may be permeable or semi-permeable to allow fluid to flow into and out of the interior of the dise (as described in more detail below). Preferably, the elastic mebane. i6 may resist translational motion.between the upper and lower endplates 12,14, and may also prevent soft tissue ingrowth between the endplates 12, 14 as well as contain any wear particles generated within the interior volume. The elastic membrane 16 may be attched to-the upper and lower endplates 12 14 by any fixation method known in the art including, but not limited to, bonding agents fltrasonic welding, screws, nails, mechanical weging, and pins.

[0056] Alternatively, the elastic meibrane 16 may be in the form of a bellow, the below assuming an "accordion" shape, enabling it to expand and contract under the various loading conditions. The bellow maybe rigily attached to the upper and lower endplates 12, 14 by any method known in the art including, but not limited to a circular groove formed in each endplate 12, 14, bonding agents, ultrasonic welding, screws, nails, mechanicialwedging, and pins. Preferably, the bellow is made from a metal, although other material such as elatomers .or polymers may be used.

057] The disc 10 also may includea valve 20, the valve 20 providing access to the interior 19 of disc 10 so that fluid may be injected into, or removed from, the interior 19 of theidisc 10. The valve 20 preferably is a one-way valve, as known to those skilled in the art, so iat the fluid, once injected, can not escape from the interior 19 of the disc 10. As shown in Fig.res 1 and 2, the valve 20 preferably is disposed within the elastic membrane 16, alteatively however, the valve 20 may be disposed within the upper and/or lower endplates 12,14. as shown inFigure 2a. When the vafve is disposed on the upper and/or lower en dlates 12, 14, a passageway 30 preferablyis included to interconnect the valve 20 with the int4ior 19 of the disc [00Jj: The fluid 22 provided in the interior volume may be a gas, a liquid, a. gel, or anu combination thereof. Where a gas is prgvided as the fill media for the interior volume, or where a combination of gas and liquid or gel is provided, the ultimate gas pressure within the WO 2004/016205 PCT/US2003/025535 S intrior volume should be selected to provide adequate shock absorptioti during axial comipression of the disc 10. The fluid may.also permit limited articulation or movement of the.upper epdplate 12 and lower endplate 14 with respect to one another. Preferably, the fluid is an incompressible liquid, for example, a saline solution. In use, the fluid 22 may-be injected into the interior 19 of the disc 10 before insertion of the disc 10. between adjacent vertebrae. 'Alternatively, the fluid 22 maybe injected in situ to facilitate insertion of disc and subsequent distraction between adjacent:vertebrae. The rigidity and distraction capabilities.of the disc 10 may be a function of the amount of fluid 22 injected into the interior 19 6f the disc 10 and/or the elastic nature of the membrane 16. Generally, the more fluid 22 provided in the interior 19 of the diic 10, the more rigid the disc 10, and the greater the distraction capability. Furthermore, pliability and increased articulation may be realized by filling only a portion of the interior volume 19 of the disc 10. finally, variably filling the interior 19 of.the disc 10 with fluid 22 permits the overall height H of the disc 10 to. be varied as necessary depending on the needs of the individual patient.

[0059] As shown in Figure 2a, the upper endplate 12 may have an inner surface provided with an arcuate socket 32, while the lower endplate 14 may have an inner surface provided with an arcuate protrusion 34, or vice versa. The socket 32 and protrusion 34 are configured'and dimensioned to mate, or to crrespond generally with each other. The typeand.aimount of articulation desired may dictate the curvature of the socket 32 and protrusion 34 provided. For example, if the protrusionrr4 has the same radius as the socket 32, then the disp 10 may provide greater support but more constrained movement, Alternatively, if the socket 32 has a larger radius than the protru sin 34, the disc will provide incr6ased articulation Furthermore, the protrusion 34 and/or socket 32 may also incorporate a flattened poition: which may allow translational movement of the upper endplate 12 with respect to the lower endplate 14. By allowing translation, the disc 10 may provide a moving instantaneous axis of rotation as previously explained.

[060] It is also possible for the socket 32 and protrusion 34 to take on contours other than those described above in order to achieve a desired articulation. Moreover, while the socket 32 and protrusion 34 are shown with contours that generally permit mating of their sm.ces, it is possible to provide non-mating contours for the socket 32 .and protrusion 34 to aceve a desired articulation.

WO 2004/016205 PCT/US2003/025535 [0061]. The use of a fluid filled interior volume 19 in combination with an articulatig surface may permit the socket 32 and protrsion 34 to translate more easily with respect to each other by reducing friction between the sliding surfaces.

[0062] Alternatively, where the fluiis a compressed gas, the articulation surfaces may not be constantly engaged, but may only become engaged when sufficient compressive force is placed in the disc by the adjacent vertebrae. Thus, the disc of this embodiment would have a dual performance aspect, under one loading scenario performing like a fluid-filled diso, and under a second scenario performing like a mechanical protrusion/socket articulatiig dis [0063] Depending on the location inthe spine where the disc 10 is implantbd,: the disc 10 referably may restore height in the rang: from about 4 millimeters (mm) to about 26 mm.

In addition, the disc 10 preferably may restorlordosis in the range between about 0° to about 204. The disc 10 preferably may also restore stiffness in the range from about 1 Newtonmcter per degree (Nm/deg) to about 11 Nm/deg in axial rotation, about 0 Nm/deg to about 7 Nii/deg in flexioniextension, and about 0 Nm/deg to about 5 Nm/deg in lateral bending. Ir addition, the disc 10 preferably provides a dcmpression stiffness from about 100 N/mm to ab ut 5000 N/mm and tension stiffness from about 50 N/mm to about 1000 N/mm.

Fuithefnore, depending on the location of the spine where the disc 10 is implanted, the intervertebral disc 10 preferably allows for a range of motion of from about 5° to about 450 in fle:ion/extension, from about 30 to about 33. in lateral bending, and from about 1 "to about 60' in axial rotation. The intervertebral disc 10 preferably also allows for axial compression in 1 ie range from about 0.2 mm to about 2 mm.

[O 64] Preferably, the upper and lower endplates 12, 14 are formed of metal, such as tita ium, stainless steel, titanium alloys, coialt-chromium alloys, or amorphous alloys.

Allernatively, however, the upper and lower endplates 12, 14 may be formed of ceramics, co posites, polymers, such as PEEK or UIIMWPE, bone, including cortical, cancellous, alldgraft, autograft xenograft, demineralized or partially demineralized bone, or any other ma erials.appropriate to serve as load bearing supports. More preferably, the materials chc sen for the endplates, in combination with the fluid, may be chosen so as to minimize we Ir.

[0055] Furthermore, preferably, anyiarticulating surfaces in the intervertebral discs of the present inventi6n includes a surface polish or similar wear reducing finish such.as WO 2004/016205 PCT/US2003/025535 diamond finish, TiNi finish, etc. in order to iniimize wear, decrease particle genertion, and inciease disc life.

[C066] The outer surface of the uppt:and lower endplates may be substantially flat, wedge-shaped, etc. The outer surfaces of th~upper and lower endplates 12, 14 also-may be dome shaped with their radii defined in the sagittal and coronal planes to generally match the shapp of the ends of the adjacent vertebral, thereby providing a better fit in situ.

[0067] In addition, as shown in Figures 1 through 2a, the disc 10 may include migration resistant features, such as, for example, spike-like structures 18 on the outer surfaces of te upper and lower endplates 12, 14. The migration resistant features may facilitate eigagement of the disc 10. with the ends of the adjacent vertebra byproviding a me&hanical interlock as a result of penetratin 'and/or deformation of the ends of the. adjacent vertebrae. The initial mechanical stability afforded by spikes 18, for example, minimizes the risk.of postoperative instability, movement, dislodging or expulsion of the disc 10,. Other migration resistant features may include, without limitation, flaps, teeth, deployable teeth, de loyable spikes, flexible spikes, flexible teeth, fins, insertable or expandable fins, anchors, screws, ridges, serrations, or other similar texturing on the outer surfaces of the upper and loWer endplates 12,14. As shown in Figure 3a, deployable spikes 21 may be provided,.and a ca* mechanism 23 may be used to deploy the.spikes 21. Alternatively, as shown in Figure 3ban instrument may be used to deploy the spikes 21. As shown in Figures 3c through 3e, respetively, examples of flexible spikes 24. shaped teeth 25, and anchors 26 are shown.

Alternatively or in addition, bonding agents such as calcium phosphate cements, etc. may also.be used to secure the disc 10 to adjacent vertebra.

OQSi Furthermore, the upper and lower endplates 12, 14 may also be coated with a boe i growth inducing substance, such as hydroxyapatite, to promote bony ingrowth to pemanently sectre the disc 10 to the adjacent vertebrae. Alternatively, the upper and lower en plates 12, 14 may have a roughened or porous surface to facilitate bony ingrowth.

Alternatively, the upper and lower endplates 12,14 may have laser treated endplate layers. to create a porous structure, or may integrate an osteoconductive/osteoinductive scaffold. The endplates 12, 14 may also be made from an bsteoconductive and/or osteoinductive material to pmroote boy ingrowth. The endplates 12,-14 may further include a membrane and/or barrier to iJmit the de4th of bony ingrowth permitted.

WO 2004/016205 PCT/US2003/025535 [009] The upper and lower endplates 12, 14 may also have implant instmmentatlon attacnment,:guiding, and retaining structures,. For example, the endplates 12, 14 may have holes, slots, threads, or a dovetail for accepting a tool used to implant the disc 10 and/or to distract the vertebrae. For example, the discmay include a slot formed in the upper and/or lower endplates 12, 14, the slot configured to receive an implant insertion instrumeht, a distractor r both.

[0070]; As a result of the material and structural components used, the disc 1 can allow flexion/extension, lateral bending, axial rotation, and translation, depending on the loadig imparted on the intervertebral disc. In addition, under the various spinal loading conditions sesulting from spinal movements, the fluid 22 may move within the inteior .volume, either compressing (in the case of a.gas), or moving radially outward as.the membrane exparnds, allowing the end plates .to move with respect to each other. This varying movement or displacement of fluid 22 provides a moving instantaneous axis of rotation.

[0071] As shown in Figures 4 and 5, a second exemplary embodiment of a. artificial disc is provided. Disc 100 generally has an:annular shape and includes an upper surface 102,.

alower surface 104, an outer sidewall 106 foming an outer wall, and an inner sidewall 107 defining an.opening 108 a thru-hole). However, the disc 100 may take on other shapes that preferably conform geometrically and anatomically with adjacent vertebral bodies, including, but not limited to, kidney-bean shape, circular, oval, ellipsoid, C-shape, D-shape etc The disc 100. is preferably made from an elastomeric material that forms a closed resprvoir having an interior volume 103. The disc 100 may further include avalve118 for introducing or withdrawing fluid 120 fromthe interior volume 103 of disc 100 as previously described. Preferably, the valve 11& comprises a one-way valve and is located on the outer sidbwall 106, as shown in Figure 5, however, the valve 118 may also be located on the upper surface 102, the lower surface 104, or on th inner wall 107.

:[0072]. As best shown in Figure 5, the disc 100 may further include a metalmesh 105 mqlded onto or otherwise secured to the upper surface 102 and/or lower surface 104. The metal mesh 105 may impart additional streigth and rigidity to the disc 100. The metal mesh 105 may also be flexible so as to adapt to the concavity of the ends of the adjacent vertebral bodies to thereby facilitate a high degree ofSurface contact with the disc. The metal mesh 105 may also be textured, its surface may be porous, and it may be used'in conjunction with WO 2004/016205 PCT/US2003/025535 boec growth inducing or conducting substances to further enhance engagement and fsiqn with the adjacent vertebral elements.

[0073] Preferably, the througi-hole 108 may be filled with an elastomeric material (no shown). The elastomeric material may hav a stiffness different from that of the disc l0O. Preferably, the elastomeric material ha. a higher stifftess than the stiffness of dise 100 thereby allowing the through hole 108 to beiaore rigid and thus to act as a center pivot or oeter strut about which the upper and lower surfaces 102, 104 may articulate. The center piv t may allow one portion or side of the disc 100 to compress while at the same time peittng another portion of the disc 100 tq expand. In an alternative embodiment, the elastomeric material may have a lower stiffiess than the stiffness of disc 100. Alternatively, th through-hole 108 may be filled with a hyrdogel.

[O074] It addition, the upper and kloer surfaces 102, 104 of disc 100 may iieclude mi.' rtion resistant features, permanent fixation means and/or implant instrumentation att chment, guiding, and retaining structures as previously described in regards to the disc of Figures 1 through 3. Preferably, disc 100 may be provided with at least one securing feaure flap) 110 to facilitate engagement of the disc 100 with the vertebral bodies of the adjacent vertebra, As shown in Figure 4, preferably two flaps 110 are provided, one flap 110 foi the upper surface 102 and one flap 110 or the lower surface 104. Flaps 110 maybe p 'vided as one piece which extends beyond the upper and lower surfaces 102, 104, or flaps 110 may be provided as two or more pieces: Flaps 110 preferably extend above and below s 1 faces 102, 104, respectively, fromilateral side 106, and are sized to abut a portion of the ex erior surface of the vertebral bodies of the adjacent vertebrae, Flaps 110 may, include thL Bugh-hoes. 114 for receiving fasteners such as, for example, fixation screws (not shown).

Th fixation screws can be used to secure disc 100 to the vertebral bodies of the adjacent veltebrae. [0075] Alternatively, as shown in Figure 6, disc 100 may further include agap 126 in its circumference, producing opposed end faces 122, 124 which give the disc 100 a general shaped appearance. Preferably, end faces 122, 124 are configured to be resiliently biased apart however; end faces 122, 124 may be naturally disposed apart from each other, without resilient biasing. The gap 126 formed between end faces 122, 124 provide the disq 100 with in reased flexibility thus facilitating insertion and placement of the disc 100 between v ebrae. The gap 126 permits the diamctr of disc 100 to be decreased by pressing ends WO 2004/016205 PCT/US2003/025535 122, 124 together. The gap 126 also may aow the disc to be unfolded by pullig ends 122, 124 apart. thus, the gap 126, allows the dis 100 to be configured to have at leastbne smialer outer dimension as compared.to its.est state, which in turn may allow the disc 100 to be inserted into an anatomical region through-a cavity or other opening that is smaller than the uncompressed at rest) size of disc lO0, thus making posterior insertion possible.

[0076]. I Depending on the location ofthe spine where the disc 100 is implanted, the disc li preferably restores height, lordosis, siiffiess, offers compression stiffness, and allows a range of motion similar to that desribed in relation to previous embodiments.

[0077] As a result of the materials geometry, and components used, disc 100 can allow flexitn/extension, lateral bending, axial rotation, and translation, depending on the loading imparted on the intervertebral disc..Similar to the embodiment of Figures. 1 through 2aJ uider various spinal loading conditions iresulting from spinal movements, the fluid 22 may move .Wvithin the interior volume, either.compressing (in the case of a gas), or moving radially outward as the membrane expands; allowing the end plates to move with respect to each other; This varying movement or displacement of fluid 22 provides a moving instantaneous.axis of rotation.

0'78] With reference to Figures 7 through 9, a third exemplary embodiment of an artificial di~o will be described. Preferably disc 150 has a generally cylindrical shape with a circulai footprint and has an upper end 1521 lower end 154, and an outer sidewall 156 disposed terboetween. The disc further includes an interior volume as defined between the upper and tower ends 152, 154 and the outer sidewall 156. Although illustrated as a cylinder, the disc 150 may take on any other shape iat preferably conform geometrically and anatomicaly with adjacent vertebral bodies, including, but not limited to, kidney-bean sh'ped.a tular, oval, ellipsoid, D-shaped, 9Cshaped, etc.

[00791 The disc 150 may be made from any material lnown in the art capable of serving as a load bearing support including, but not limited to, elastomers, polymers, ceamics,.composites, etc. The disc 150 may frther include a valve (not shown) for introducing fluid 158 into the interior of disc as previously described in relation to other embodimehts.

[080J j The disc 150 may further inlude upper and lower end plates (not shown) as previouslydescribed with regards to other ibodiments. Alternatively, the disc 150 may inblude a metal mesh molded onto or othe ri*e secured to the upper surface 152 and/or lower WO 2004/016205 PCT/US2003/025535 surface.154 as previously described in relation to other embodiments, In addition,,;the disc 150 may further include migration resistant'features, permanent fixation means and/or implant instrumentation attachment, guiding iand retaining structures as previously described in relation to other embodiments.

[0081] Depending on the location ofthe spine where the disc 150 is implanted, the disc 150 preferably restores height, lordosi sitiffness, offers compression stiffness, and allows a range of motion similar to that described in relation to previous embodiments.

[0082] With reference to Figure 8,.the interior of disc 150 is shown. Preferably the interior of disc 150 includes a plurality of interconnected peripheral chambers 16. and a separate central chamber 162. The multi-ciambered interior of disc 150 permits controlled fluid flow within the intervertebral disc 150 so that under loading, controlled articulation or motion is permitted. The peripheral chambers 160 may be in fluid communicatio:iwith the central chamber. 162 by way of an open passageway, a porous central wall 165,:an.smotic membrane, etc. Preferably, however, the peripheral chambers 160 are in fluid communication with the central chamber 162iby way of a baffle and/or valve. More preferably, the baffle and/or valve is configured to provide for selective exchange f fluid such that the fluid 158 from the peripheral .hambers 160 may flow more easily orquickly into the central chamber 162 than the fluid 158 would flow out of the central chamber 162.

Alternatively, the central chamber 162 may:bb sealed with respect to the periphera chambers 160 In this case, the peripheral chamber 1.60 and central chamber 162 may be filled with the.

same or different fluids.

[0083] The peripheral chambers 16, are defied by walls 163, while the cntral chamber 162 is separated from the peripherl! chambers 160 by a central wall 165 In addition to defining the geometry of chambers 160, 162, walls 163, 165 also serveas supports between surfaces 152, 154 by resisting loads acting upon the disc 150 when in use.

[0084] Preferably the central chamber 162 and outer periphery chambers 1 0 are arranged so that the central chamber 162 is more rigid than the outer peripheral chambers 160 (suchas by completely filling with incompressible fluid), thus enabling the central chamber 162.to act as a center pivot or center strut about which the upper and lower surfaces 152, 154: may articulate. The center pivot allows one portion or side of the disc 150 to conipress while at the same time permitting another portion of the disc 150 to expand. The walls 163 of the peripheral chambers 160 may be formed of a'material having a lower stiffness tha the WO 2004/016205 PCT/US2003/025535 mteral.used to produce the central wall 16, thereby allowing the central chambe1162 to be moe rigid and act as a center pivot, Altemrnively, the walls 163 of the peripheral chambers 160 may be formed of the same material as ie central wall 165, but with a geometry that provides a lower stiffness than the geometry of the central wall 165 of central chamber 162 tereby allowing the central chamber 162 tjact as a center pivot for disc 150. Furthermore, a combination of material and geometric obar cteristics of the chamber walls 163, 165 may be selected t inake the central chamber 162 mre rigid than the peripheral chambers 160 so that the central chamber 162 may act as a cente ivot about which the disc 150 pivot.

[0085] The geometry of chambers 10, 162, the geometry and material of the walls 163, 165, along with the fluid(s) disposed iterein can be selected to obtain the desired characteristics of the disc, including the desired'stiffness, height, pliability, and preferably the relative.stiffiess of the central chamber 1621 with respect to the peripheral chambers 160 to provide the desired articulation between the pper and lower ends 152, 154. Thusthe disc :;159 will move, deform or extend in flexion extension, lateral bending, axial rotation, and translation depending on the loadings impaied on the intervertebral disc since undr various .spial loading conditions, the fluid can trlate between the peripheral chambers 160 and/or .th.central chamber 162. This movement ofthe chambers with respect to each other, as well as he movement of the fluid within and be reen the chambers allows for a moving intantatiedus axis of rotation of the disc 15b. It should be noted that the central chamber 162 ne*dn't be located in the center of the disc, jbut rather may be positioned in any other location within the disc appropriate to produce the dsired movement of the endplates relative to. each other.

[0086] Alternatively, as shown in Figure 9, the central chamber 162 may house a sp ing 167. The spring 167 serves as additinal support for disc 150 further enabling the central chamber 162 to act as a center pivot and/or strut. When a spring 167 is provided in the central chamber 162, fluid may or may hot also be provided. The spring 167 may be fomed from any material known in the artIfor example, cobalt-chromium alloys, titanium alloys, stainless steel, amorphous alloys, pdlymers, or composites.

[Ob87] Alternatively, the central chl ber 162 may house a bladder (not shown). The bladder may be integrally formed with, or connected to, ends 152, 154. Alternatively, the bldder may be separate from the ends 152; 154. This bladder may articulate, coripress, ad/or translate within the central chamber l!62, providing the disc with a moving WO 2004/016205 PCT/US2003/025535 instantaneous axis of rotation, which under various loading conditions, may allow for a greater degree of articulation or movement of disc 150. In addition, the central bladder may serve as additional support for disc 150 so that the central chamber 162 may act a center pivot and also permit the desired motion.

[0 88] With reference to Figures 10 and 11, a fourth embodiment of an artificial intrvertebral disc will be described. Disc 250, has a generally kidney-bean shapedifootprint with an upper endplate 252, a lower endplate 254, and at least one cable element 256, 258.

Although disc 250 is shown as having a kidney-bean shaped footprint, the disc 250 may take oniany other shape that generally conformsigeometrically and anatomically with adjacent vertebral bodies, including, but not limited to, circular, annular, oval, ellipsoidal, D-shaped, C-haped, etc. In addition, the endplates 252, 254 preferably include migration resistant f&tures, permanent fixation means and/or iiplant instrumentation attachment, guiding, and retining structures as previously described in relation to previous embodiments.

[0089J Preferably, the.upper and lower endplates 252, 254 are formed of metal, such astitanium, stainless steel, titanium alloys, cobalt-chromium alloys, or amorphous alloys.

Alternatively, the upper and lower endplates 252, 254 may be formed of ceramics: cociposites, polymers, such as PEEK or UAIWPE, bone, including cortical, cancellous, lgraft, autograf, xenograft, demineralizd or partially demineralized bone, or any other mterials appropriate to serve as load hearilg supports.

[090] The outer surface of the ur and lower endplates may be substantiallyflat, wedge-shaped, etc. Alternatively, the outersurfaces of the upper and lower endplates 252, 254 may be dome shaped with their radii defined in the sagittal and coronal planes to generally match the shape of the ends of the:adjacent vertebral, thereby providing a better fit insuit.

[0991] The disc 250 may also. inclide an elastic membrane, the elastic membrane generally extending from the upper endplate 252 to the lower endplate 254 as previously dsolfibed in relations to previous embodiments. The disc 250 may also include a alve, the vlve providing access to the interior of the disc 250 so that a fluid may be at least partially inected into the interior ofthe disc as descrbed in relation to previous embodiments.

[092] Depending on the location of the spine where the disc 250 is implanted, the dihc 250 preferably restores height, lordos., stiffness, offers compression stiffless, and allows a range of motion similar to that described in relation to previous embodiments.

WO 2004/016205 PCT/US2003/025535 [0093]. As shown, dise 250 includes a.plurality of peripheral cable elements .26 and a central cable element 258. The peripheral cable elements 256 may be located near the perimeter of disc 250, while the center cable element 258 is preferably located near the center of the disc. The peripheral cable elements 256and the center cable element 258 are attached to the upper and lower endplates 252, 254 by any fixation means know in the artincluding, but not limited to, bonding agents, ultrasonic Welding, screws, nails, mechanical wedging and pins. Preferably, however, the cable elements 256, 258 engage the upper and lower endplates 252, 254 via boreholes 260 formed on the upper and lower endplates 252, 254. The ends of cable elements 256, 258 are crimped where tliy penetrate the outer surface of the upper and lower endplates 252, 254. This permits surgeons to appropri ately size the disc 250 just prior to implantation by means of crimping/attaching appropriately sized cables to the endplates.

The peripheral cable elements 256 and central cable element 258 may be made from metals, polymers, composites, or any other appropriate material known in the art.

[0094] In one embodiment, the center cable element 258 is shorter than the peripheral cable elements 256. This causes the periphal elements 256 to assume a curved orbowed shape between the endplates 252,254. As aresult, the length of the central cable-element 258 determines the maximum distance between the upper and lower endplates 252,254 under tension. Furthermore, as a result of the peripheral cable elements 256 being longer than the central cable element 258, the shorter central cable element 258 causes the longer peripheral cable elements 256 to be held in compression.! The resilience of the bowed peripheral cable elements 256 provides shock absorption, axial compression and articulation characteristics to the disc 450.

[0095] As a result of the materials, geometry, and components used, disc 250can .allowflexion/extension, lateral bending, axialmrotation, and translation, depending on the loding conditions. In addition, under various spinal loading conditions resulting from spinal movements, the peripheral cable elements 256 can bend or compress varying amounts. Such variable bending/compression provides the. desired moving instantaneous axis of rotation.

[0096] With reference to Figure 12, an exemplary installation procedure will be described.: Generally speaking the disc 300 includes an upper endplate 302, a lower endplate 304 and a core mechanism 306, the core mechanism being any cable, elastomer, fiber, or fl id filled disc previously described. The intbrvertebral discs 300 may be implanted in a modular fashion, for example, the endplates 302, 304 of disc 300 are inserted into the WO 2004/016205 PCT/US2003/025535 intervertebral cavity using instruments such.as a distractor and/or holder instrument. The intervertebral disc space may be distracted using a standard spinal distractor which engages the endplates 302, 304. Trial spacers are then preferably used to determine the appropriate size of the core mechanism 306 to be inserted in the resulting disc space. In an exemplary embodiment, the core mechanism, 306 is inserted and attached to endplates 302, 304 through the use of a dovetail, slot, or similar connection. This modular insertion technique avoids over-distracting the intervertebral space, which may damage surrounding tissue and/or blood vessels.

[00971 Alternatively, the intervertebral disc 300 may be inserted preassembled with the use of particular insertion tools. For example, an cndplate holding clip may beused that allows the endplates 302,304 to be held andilocked in a parallel and spaced relationship as they are inserted into the intervertebral space. Once implanted, the clip may be unlpoked and removed from the endplates 302,304. The clip may then be removed from the intervertebral space- In addition, the disc 300 may be implanted in a compressed state to prevent overdistraciQ. The introduction of the disc 300 in a compressed state may be accomplished via a surgical insertion instrument or by an internal mechanism located in the disc 300.

[0098] An anterior, lateral, or anterolateral surgical approach may be used for the intervertcbral disc 300. Furthermore, depening on the intcrvertebral disc 300 to be implanted, a minimally invasive surgical method or a simultaneous distraction and implantation surgical method may be used. Simultaneous distraction and implantation may be accomplished, for example, by using slots formed on the outer surface of the endplates 302, 304 to guide the implant down the distractor during implantation. Also, depending on the intervertebral disc to be implanted, an artificial Anterior Longitudinal Ligament or the natural Anterior Longitudinal Ligament may be attached directly to the disc or to:the adjacent vertebral bodies. Attachment of the Anterior Longitudinal Ligament may assist in preventing movement, dislodging or expulsion of the implant To assist with the implantation of the intervertebral discs, the intervertebral discs may include alignment markers.

[0099] While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in combination thereof Therefore, this invention is not to be limited to the specific preferred embodiments depicted herein.

WO 2004/016205 PCT/US2003/025535 [00100] Further, it should be understodi!that variations and modifications within the spiit and.scope of the invention may occur to those skilled in the art to which the invention pertains. For example, some portions oftheinplants disclosed herein may be formed of bone, such as allografts, autografts, and xenografts, which may be partially or fully demineraiized. In addition, some implants may include bone material or other bone growth inducing material in their interiors or on/in their endplates. Such substances in the interiors may be pemnitted to interact with the surrounding anatomy, as with channels or other holes formed in fte implant walls. Also, intra and:post-operative alignment markers may be used to assist wiih implantation of the intervertelbal discs. Furthermore, the intervertebral discs can be made rigid in situations where fusion is necessary. The intervertebral discs may be made rigid by, for example, allowing fusion between the endplates, inserting spacers between the endplates, or by injecting a solidifying liquid between the endplates. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as.

further embodiments of the present invention.. The scope of the present invention is accordingly defined as set forth in the appended claims.

Claims (25)

1. An intervertebral disc for placement between first and second vertebrae, the intervertebral disc including: an upper surface for contacting the first vertebra; a lower surface for contacting the second vertebra; an exterior wall having an inner surface and an outer surface, the exterior wall extending between the upper and lower surfaces; and an interior volume defined between the upper and lower surfaces and the inner surface of the exterior wall, the interior volume including a central S 10 chamber surrounded by a plurality of interconnected peripheral chambers.

2. The intervertebral disc of claim 1, wherein the plurality of interconnected peripheral chambers are sealed from the central chamber.

3. The intervertebral disc of claim 2, wherein the central chamber has a first fluid disposed therein and the plurality of interconnected peripheral chambers have a second fluid disposed therein.

4. The intervertebral disc of claim 3, further including: a valve in communication with the plurality of interconnected peripheral chambers for at least partially filling the plurality of interconnected peripheral chambers with the second fluid.

5. The intervertebral disc of claim 4, wherein at least a portion of the valve is disposed within the exterior wall.

6. The intervertebral disc of claim 5, further including: a second valve in communication with the central chamber for at least partially filling the central chamber with the first fluid.

7. The intervertebral disc of claim 6, wherein at least a portion of the second valve is disposed within the exterior wall.

8. The intervertebral disc of any one of the preceding claims wherein the central chamber is defined by a first wall, and the plurality of peripheral chambers are disposed between the exterior wall and the first wall.

9. The intervertebral disc of claim 8, wherein the first wall is formed of a first material having a first stiffness and the exterior wall is formed of a second material having a second stiffness, the first and second stiffnesses being substantially unequal. 00 O

10. The intervertebral disc of claim 8, wherein the first wall has a first e configuration with a first stiffness and the exterior wall has a second C. configuration with a second stiffness, the first and second stiffness being Ssubstantially unequal.

11. The intervertebral disc of any one of the preceding claims, wherein the central chamber has a stiffness, and the plurality of peripheral chambers has a O stiffness less than the stiffness of the central chamber. (N

12. The intervertebral disc of any one of the preceding claims, wherein the central chamber has a resilient element disposed therein.

13. The intervertebral disc of claim 12, wherein the disc has a stiffness and the resilient element is a spring.

14. The intervertebral disc of any one of the preceding claims, wherein the central chamber has a bladder disposed therein.

The intervertebral disc of any one of the preceding claims, wherein the disc is constructed of a material selected from the group consisting of an elastomer, a polymer, a ceramic, a composite and a metal mesh.

16. The intervertebral disc of any one of the preceding claims, further including: a metal mesh secured to the upper and lower surfaces.

17. The intervertebral disc of any one of the preceding claims, further including: an upper endplate secured to the upper surface and a lower endplate secured to the lower surface.

18. The intervertebral disc of claim 17, further including: migration-resistant structures disposed on the upper and lower endplates.

19. The intervertebral disc of claim 17, further including: permanent fixation means disposed on the upper and lower endplates.

The intervertebral disc of claim 17, further including: implant instrumentation attachment, guiding, or retaining structures disposed on at least one of the upper and lower endplates.

21. The intervertebral disc of any one of the preceding claims, further including: 26 00 O Smigration-resistant structures disposed on at least one of the surfaces. C

22. The intervertebral disc of any one of the preceding claims, wherein the plurality of interconnected peripheral chambers are in fluid communication with n the central chamber.

23. The intervertebral disc of claim 22 further including: one of a baffle and a valve that permits fluid communication between Sthe central chamber and the plurality of peripheral chambers. (N I

24. The intervertebral disc of claim 22 further including: a porous central wall that defines the central chamber. c- 10

25. An intervertebral disc, substantially as hereinbefore described with reference to any one of the drawings.