AU2003262695B2

AU2003262695B2 - Controlled artificial intervertebral disc implant

Info

Publication number: AU2003262695B2
Application number: AU2003262695A
Authority: AU
Inventors: Christopher M. Angelucci; Ii Michael L. Boyer; Justin K. Coppes; David Gerber; David Paul; Pascal Stihl
Original assignee: MICHAEL BOYER II
Current assignee: Synthes GmbH
Priority date: 2002-08-15
Filing date: 2003-08-15
Publication date: 2008-12-04
Anticipated expiration: 2023-08-15
Also published as: CN100560038C; CN1722993A; AU2003262695A1; KR20060056265A

Description

WO 2004/016217 PCT/US2003/025536 CONTROLLED ARTIFICIAL INTERVERTEBRAL DISC IMPLANT FIELD Of THE INVENTION f0001] The invention is related to devices and methods for the treatment of tauma and diseases of the spine. More particularly, the invention relates to intervertebral disc replaceient.

BACKGROUND OF THE INVENTION [0002] A variety of conditions' such as spondylolysis, disc hreniation, pmpression of spinal cord nerve roots, degenerative disc disease, and trauma are known to c use severe discomfort, requiring medical attention. Among the procedures currently used to alleviate such conditions are spinal fusion, such as intervertebral and posterolateral fusion c arthrodesis. In these procedures, two adjacent vertebral bodies are fused together. The a ected intervertebral disc is first excisedi and an implant is inserted which accommodates b ne growth between the two vertebral bodies to effectively bridge the gap left by the disc r moval. A itnber of different implant iaterials and implant designs have been used for f sion with varying success. Although intrvertebral and posterolateral fusion are widely Sed, drawbacks to their use include a rediced physiologic range of motion and other fusion r lated complications such as degeneration of adjacent discs and destabilization of the ft ntional spinal unit. As a result, alternatie'treatments with fewer complications, but si ilar efficacy to fusion, are desirable. One such alternative to spinal fusion is arthroplasty aid theuse ofa prosthetic or artificial disc.

[0003] In general, arthroplastyi used in the replacement of diseased joints.

A throplasy involves a set of procedures directed to maintaining motion of the joint, tbereby preserving its integrity and keepini the adjacent motion segments from.

deteriorating, as they tend to do after fusion. Depending on the location and the condition of the affected joint, specific arthroplasty prcedures may be used. For example, in rpositibnal reconstruction surgery, which reshapes the joint and adds a prosthetic disk between the two bones forming the joint is:commonly used on elbow, shoulder, ankle, and figer joints. Total joint replacement, or total joint arthroplasty, replaces the entire diseased joint with.an artificial prosthesis and, in rec t years, has become the operation of choice fO most knee and hip problems.

[0004] Hip and knee replacements are particularly widespread with-nearly 30(,000O hip replacements and about as many.knee replacements performed in tlie inited WO 2004/016217 PCT/US2003/025536 States in 2001. With respect to the knee and hip joint replacement surgeries,'the are several implants or prosthetics available.: For the hip prosthetic, in an exemplary design, tlore 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.

TIhe 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 pblyethylene, For the knee prosthetics, in ai exemplary embodiment, metal and plastic components are again used to replace the damaged bone ends and cartilage. The metal pieces are generally formed from stainlesisiteel, alloys of cobalt and chrome, titanium, and aloys of titanium; the plastic pieces are geneally fbmied from high-density polyethylene.

S [0005] Although the evolutioi of spinal arthroplasty and the use of prsthetics i4 the spine has been similar to that of other joints in the body, evolving from fusing the jiint to relacing the functional joint, the advent of spinal athroplasty, however, has been slwer than arthroplasty in other major joints in the body. A few of the possible reasons vi y spinal arthroplasty has been delayed:r that spinal problems related to disc degeneration are difficult to diagnose, spinal procedures are typically crisis-drivei aid thus conservative solutions such as fusion are aNceptable, and spinal anatomy is complex.

[0006] Over the past 40 years spinal arthroplasty technologies have been under dvelopment and in the last 10 years spinal arthroplasty has won the attention of leading srgeons aud implant manufacturers. The evolution of spinal arthroplasty essentially began i the 1950's and one of several emerging concepts was the spherical concept ofhe disc polfstheses. The spherical concept is simply the placement of a ball, essentially ciicunferential, in the cavity of the nucleus pulposus after a discectomy procedure has been p formed, The annulus is kept in place anidthe ball serves as a nucleus replacement deivice. Various materials have been experimented with for the spherical concept. For example, in the early 1960's, implants using silicone ball bearings were implanted into the c vical regions of patients, but the outcomes were uncertain. In the mid 1960's, stainlessstiel (ballbearing) prostheses were implanted into patients. The results of the procedure were initially promising but over time the disc spaces lost height due to subsidence of the steel balls into the vertebral bodies. Presently, the concept of a spherical prosthesis copinues to be examined using different riatirials, the latest of which is a modified carbon fit er.

[0007] Another emerging concept is the mechanical concept design. The chanical concept design is essentially a total disc replacem ent product which is itended to restore the range of motion of the vertebral motion segment unit. These devices are often WO 2004/016217 PCT/US2003/025536 cbmptised of metallic endplates fixed to the adjacent vertebral bodies via a stabiihation 4lechanismknd A core formed from polye plene or other polymeric materials.

Alterrnatively, fistead of a core, bearing stirfaces can be used, the bearing surface materials bpingceramic-on-ceramic, metal-on metat or mretal-on-polyethylene. The mechanical design concept is based on the same principles as joint reconstruction products, such as kIee and hip replacements, and a variety f mechanical design prostheses concepts have been proposed and continue to be proposed.

tO08] Another concept is the.physiological concept. The physiological cmncept uses a hydrogel, elastomer, or polyurethane-based care which is intended to restore dise function by absorbing and emittin fluid between the patient's vertebral endplates, while also maintaining the natural shock aisorbing or cushioning function of the disc. The physiological concept devices are generally considered only a partial solution as they are 4signed to replace only the nucleus or a portion of the disc, [0009] All of the approaches t dise replacement are aimed at some or all of the fcjlovwing alleviating discogenic pain, restbring range of motion, maintaining the natural shock absorbing function of the disc, restoing normal form or disc height, and restoring physioogical kinematics. Generally, four kemplery types of artificial intervertebral discs Mve been developed for replacing a portio or all of an excised disc: lastomer/fluid filled dise, ball and socket type discs, mechanical spring discs and hybrid discs.

1 [0010] Elastomer/fluid filled discs typically include an elastomer cushion or a f 4d filled chamber positioned between lower and upper rigid endplartes. The oushions and c abers ofthese implants advantageously function, in mechanical behavior, similar to the rnoved intervertebral disc tissue.

(001.1] Ball and socket type digc typically incorporate two plate members having.cooperating inner ball and socket portions which permit articulating motion of the m nbers during movement of the spine.

.[0012] Mechanical spring discs typically incorporate one or more coiled spngs disposed etween metal endplatesjThe coiled springs define a cumulative.spring constant that is designed to be sufficient to m'aintain the spaced arrangement of the adacent vertebrae while allowing normal movement of the vertebrae during flexion and extension of h.spine in any direction.

[0013] The fourth type of artifit al intervertebral disc, the hybrid dise i orporates two or more of the aforementidned design principles. For example, one known h rid dise arrangement includes a ball and socket joint surrounded by an elastomer ring.

00[0014] While each of the foregoing prostheses addresses some of the Sproblems 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 NOto the vertebrae, permits sufficient mobility to allow the patient an approximate normal Srange of motion, provides for axial compression between adjacent vertebrae, and has shock absorption abilities.

SA reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission or a suggestion that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

SUMMARY OF THE INVENTION [0014A] According to one aspect, the present invention provides an articulating intervertebral implant for implantation between first and second vertebrae, the implant comprising: a first endplate having a first inner surface and a first outer surface for engaging the first vertebra; a second endplate having a second inner surface and a second outer surface for engaging the second vertebra; a cover plate coupled to the first endplate, the cover plate including an inner opening; a first insert member adapted to be received within the inner opening of the cover plate, the first insert member having a first articulating surface operatively associated with the second endplate so that the first and second endplates can articulate with respect to each other; and a spring component located between the first insert member and the first endplate.

4 728749 amend pages 0 [0015] The invention relates 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 compression. Furthermore, the intervertebral disc may be used in the cervical, the thoracic, or the lumbar regions of

ID

C 5 the spine.

[0016] The intervertebral disc includes a body having a footprint that is 0preferably conforming in size and shape with at least a portion of the ends of adjacent C vertebrae. The shapes of the intervertebral disc include, but are not limited to, circular, C oval, ellipsoid, kidney-bean, annular, C-shaped, D-shaped, etc.

[0017] In one embodiment, the intervertebral disc includes an upper endplate, a lower endplate, and an intermediate elastic membrane disposed between the upper and lower endplates. Alternatively, the elastic membrane may surround and encapsulate the endplates. The elastic membrane in combination with the upper and lower endplates defines an interior volume. The interior volume of the disc includes at least one spring element, the spring element being attached to the upper and lower endplates. Preferably, the spring element is attached to the lower endplate within a pocket or groove formed on the inner surface of the lower endplate, while the upper end of the spring element is attached to a hemi-spherical member. The hemi-spherical member is designed to mate with and articulate in a socket formed on the inner surface of the upper endplate.

[0018] Alternatively, the disc may be provided with a plurality of spring elements with each spring element extending from the upper endplate to the lower endplate, and each spring element may have a hemi-spherical members on both ends to mate with corresponding sockets formed on the inner surface of the upper and lower endplates. The disc may also be configured such that the disc generally contains a first spring element surrounded by a plurality of second spring elements uniformly spaced around the first 4a 728749 amend pages WO 2004/016217 PCT/US2003/025536 sprig.elemerit. he first spring element iteferably having a stiffness and'zr sprig' cwtant which is greater than the stiffnes of the periphery spring elements.

[0019] Furthermore, the disc may include a plurality of spring clement, ,hereby only'aportion of the spring elemrtts may be attached to a hemri-spherical member, 4ith the remaining spring elements being attached to the upper and lower endplates, peferably in pockets. In one exemplary embodiment, the first spring element with be' atached to a hemi-spherical member while the surrounding peripheral second spring Ceaments will be attached directly to the pper arid lower endplates.

[0020] The disc may also inclide an elastomeric strut or ring in placof one or al of the spring elements. Furthermore, the disc may incorporate casing members.

[0021] The disc may also include a fluid disposed within the interior volume and a valve forpeitting insertion of and.iemoval of the fluid.

[0022] The upper and lower endplates are preferably formed of metal, such as titanium stainless steel, titanium alloys, cobalt-chromium alloys, or amorphous alloys.

Alteinatively, however, the upper and lower endplates may be formed of ceramics, composites, polymers, such as poly-ether-etier-ketone PEEK) or an ultra high molecularweight polyethylene UHMWPE); bone, including cortical, cancellous, al ograft; autograft, xenograft, demineralized or partially demincralized bone, or aniy other m terials able to serve as load bearing supports. The materials chosen:for the endplates, in .oibination.with the desired fluid, are preferably selected to reduce the amount ofwear, and thusiiicrase the life of the joint.

S[00'23] The outer surface of the upper and lower endplates may be substantially Sflt, wedge-shaped, etc. The outer surfaces of the upper and lower endplates may alTotbe Sdoe shiped with their radii defined in th sagittal and coronal planes to generally match thqse of the ends of the adjacent vertebra. The dome shape allows the upper and lower eniplates to better conform with the ends of the adjacent vertebrae for a better fit in situ.

[0024] The intervertebral disc also preferably includes migration-resistait stractures provided on the outer surface of at least one or both of the endplates to impede movement, dislodging, or expulsion of the endplates within and from the ends of the adacent vertebrae. The migration-resistant structures include, but are not limited to, flaps, sp ces, teeth, fins, deployable spikes, deployable teeth, flexible spikes, flexible teeth alt natively shaped teeth, insertable or expadable fins, screws, hooks, serrations, ribs, and tex iured surfaces.

S0025]. Furthermore, the upper and lower endplates also preferably coated with a b n growth inducing or conducting substince to promote bony ingrowth to permanently WO 2004/016217 PCT/US2003/025536 secure the disc Lo.the adjacent vertebrae. Alternatively, the upper and lower endlates may have a roughened surface; a porous surface; laser treated endplate layers; integrate an oste.oconductive/osteoinductive scaffold; gr may be provided with or made from an integral ostepconductive and/or osteoinductive material to promote bony ingrowth. The endplates may further include a membrane.and/or a batrier to limit the amount and/or depth ofbony ingrowth.

[0026] The upper and:lower endplates may also have implant instrumentation attachmnent, guiding, and retainment structures. For example, the endplates may have.holes, 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 slat being configured to receive an implant insertion instrument, a distractor or both, [0027] The upper and lower epdplates may also preferably include articulazng surfaces, thus providing the intervertebraldisc with greater mobility. The articulating surfaces preferably including a surface polish or similar wear reducing finish suchlas diamond finish, TiNi finish, etc. in order to minimize wear, decrease particle generation, and increase disc life.

[0028] In some embodiments, the interior of the disc may include a leaf spring attached on one end to the upper and/or lower endplate but unattached on the othe end.

Disposed between the ends, the leaf spring preferably includes an enlarged convex intermediate section which mates, articulates, and slides with the inner surface of one of'the endplates. Preferably, the unattached end ofthe leaf spring is attached to a roller by means of an axle, the axle allowing the roller to fteely rotate thus permitting the leaf spring to move freely during the flexing of the spring.

[0029] In some embodimcnts,the:interior volume of the disc includes an articulating member which is attached to the upper or lower endplate. The articlating member preferably being attached to one of the endplate by an intermediate shock' absorbing layer. The shock absorbing layer preferably being an elastomer, polymer fibers, polyurethane, silicone, or other suitable elastic material having shock absorbing properties.

[0030] In other embodiments, the disc generally includes an upper endplate, a lower endplate, and a flexible core disposed between the upper and lower endplates, preferably within pockets containing mating :surfaces. The flexible core preferably is either a slotted core, a ring spring, a winged leaf spring, or a leaf spring. The flexible member ms be dimensioned and configured to provide flexion/extension, lateral bending, axial I WO 2004/016217 PCT/US2003/025536 rotation, and/or banslation, depen;ng on the loading conditions imparted on the-' irtervettebral disc.

[0031] The intervertebral discpay be implanted in amodular fashion if pqssible, or may be implanted preassembled. An anterior, anteriolateral, or lateral surgical alproachimay be used for the intervertebral disc. Furthermore, depending on the ii4tervertebral disc to be implanted, a minimnially invasive surgical method and/or a sinultaneous distraction and implantation surgical method may be used. Also depending oh the intervertebral disc to be implanted, the Anterior Longitudinal Ligament may be attached directlyto the disc or to the adjacent vertebral bodies. The Anterior Longitudinal Ligament may be formed from partially deinineralized or deminineralized autdgraft, allograft, or xenograft. Alternatively, the Anterior Longitudinal Ligament may be formed froin biocompetible materials such as elastomer, or braided polymers. To assist with the iilplantation of the intervertebral disc, the iate4vertebral disc may include alignment I [0 1 BRIF DESCMPONy QVTWE D.AWINS [0032] To facilitate an undertnding of and for the purpose of illus&ing the p esent invention, exemplary and preferred features and embodiments are disclosed jn the acompanying drawings, it being understood, however, that the invention is not lizhited to tprecise arrangements and instrumentalides shown, and wherein similar reference caracters denote similar elements throughout the several views, and wherein: [0033] Figure 1 is a perspective view of a first embodiment of an artificial ihtervertebral disc according to the preseiitihvention; [0034] Figure 2 is a cross-sectional view of the artificial intervertebral disc of FiluZC I taken along line A-A; [0035] Figure 2a is an altemrnate cross-sectional view of the artificial iraervertebral disc of Figure 1 taken along line A-A; [0036] Figure 2b is an altena cross-sectional view of the artificial infervtebral dise of Figure 1 taken aldng lne A-A; [0037] Figure 2c is an altcrnali:rbss-sectioa view of the artificial intervertebral disc of Figure 1 taken along line A-A; [0038] Figure 2d is an altenfateross-sectional view of the artificial Sin erveteral disc of Figure 1 taken along line.A-A; I 0039] Figure 3a is a side view of deployable spike according to tib present in 4eion; WO 2004/016217 PCT/US2003/025536 [0040] Figure 3b is a side vid* of another deployable spike according to the presenait inention.

[0.041] Figure 3c is side view ofa flexible spike according to the.presnt.

inv.ntion.

[0042] Figure 3d is a side view. of alternatively shaped teeth according to the piesentinvention.

0043] Figure 3e is a side view:of anchors according to the present invention, 0044] Figure 4 is a cross-sectiobial view of a second embodiment of an a idficial intervertebral disc according to the.present invention; .[0045] Figure 4A is a side vieW.:of the leaf spring and roller of the articial irterrtebral disc.of Figure 4; S [0046] Figure 5 is a cross-sectioal view of a third embodiment of an artificial iretvertebral disc according to the present invention; [0047] Figure 6 is a perspective view of a fourth embodiment of an artificial in tevertel}ral disc according to the present invention; [0048] Figure 7 is a perspective view of a fifth embodiment of an artificial.

Sin eveitebral disc:according to the present invention; [0049] Figure 8 is a perspective view of a sixth embodiment of an artificial in rertebral disc according to the present,invention; :[0050] Figure 9 is a cross sectional view of a seventh embodiment f an.

ar ficial intervertebral disc according to thepresent invention; [0051] Figure 9a is an alternate cross-sectional view of the seventh: embodiment of an artificial intevertebral disc according:to the present invention; S.[0052] Figure 9b is an exploded view of the seventh embodiment shown is Fiuro9a; S [0053] Figure 9c is an exploded view of the seventh embodiment shown is Fi e 9a; and [0054] Figure 10 is schematic view of a eight embodiment of an intervertebral disc according t6 the present invention.

DE'TAILED DESCRIPTION O rTHE PREFERRED EMBODIMENTS [0055] Any of a wide variety of different implant structures can be pepared acording:to the'teachings shown by the illustrative examples of the intervertebral discs dilosed herein. The intervertebral discs of the present invention are preferably:designed WO 2004/016217 PCT/US2003/025536 tci restore the natural spinal curvature (or sagittal balance), disc height, to allow for a natural rnge of motion, absorb shock and to provide resistance to motion and axial compression.

[0056] The intervertebral discs preferably are sized and adapted for use in the cTvical, thoracic, and lumbar regions of the spine, Also, the intervertebral discs can be tdilored for each individual patient allowing for disc characteristics appropriate for the iidividual patient. For example, and artificial disc may be provided having a pair of ezdplates and a core, and the core of the disc can include different assemblies, different components, and/or various types of materials to create the desired dynamic characteristics fr each individual patient.

I [0057]. Furthermore, the intervertebral discs may allow flexion, extenion, lteral bending, rotation, and translation. Flexion is movement that brings two prts 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 aNay.from each other; in the spine, this is a movement in which the spine starts straight and Moyes 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.

Rbtation is a movement that results in a portion of the spine twisting, rotating or turning with respet to the axis of the spinal column. Translation is a limited movement that is generallytransverse to the axis of the spinalcolumn.

[0058] Additionally, similar to a natural intervertebral disc, the artificial ierkvertebral 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 tbs line that does not move. The instantaneous axis of rotation is this line. A moving istantaneous axis of rotation refers to the ability of the instantaneous axis of rotation to m ve translate) as a result of different loading conditions; in other words, the location o the instantaneous axis of rotation moves with respect to the disc. The preferred mean lotiation of the moving instantaneous axis of rotation for the lumbar region of the spine is proferably 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 thoracic region of the spine is pr ferably in the inferior portion of the disc space and proximal to the caudal vertebral body exending posteriorly into the spinal canal, and the preferred mean location of the moving in tanneous axis ofrotation for the cervical region of the spine is preferably in the p terior half of the caudal vertebral body..

I~

WO 2004/016217 PCT/US2003/025536 [0059] Also similar to a natur.l itervertebral disc, the response characteristics ofthe artificial intervertebral disc are preferably non-linear. For example, in response to continiued axial compression, the artificial intervertebral disc preferably undergoes a large initial amount of compression followed by non-linearly decreasing amounts of compression.

[0060] Referring to the acconipanying drawings, preferred embodiments and featuresof the artificial intervertebral disc'"ill be described in detail. It is to be noted however that these descriptions of specific &mbodiments and features are merely illustrative. It is contemplated that one oriiore features or elements of the various embodiments may be combined or used singularly, and that modifications of the various einbodiments, as well as other embodimerits are contemplated and will be apparent to those persons skilled in the art.

S[0061] Referring initially to Figure 1, a perspective view of an exemplary first embodiment of an artificial disc 10 is show. Disc 10, preferably, has a generally kidneybhan shaped footprint which includes an anterior side 11, a posterior side 13, and first and second lateral sides 15, 17, respectively. Anterior side 11 and lateral sides 15, 17 are all substantially convex in shape while posterior side 13 is substantially concave in shape.

Hbwever, the disc 10 may take on other shaes that generally conform geometrically and anatomically with the adjacent vertebral bodies including, but not limited to circular, oval, ellipsoid, annular, D-shaped, C-shaped, etc. i 0062] As shown, disc 10 includes an upper endplate 20, a lower endplate 22, and aanintermediate elastic membrane 24, th elastic membrane 24 generally extending fr6m the upper endplate 20 to the lower enAdlate 24, preferably, proximate the outer periphery of the disc 10. Alternatively, the: lastic membrane 24 may surround and ettapsulate the upper and lower endplates 20, 22. The elastic membrane 24 in combination with thupper and lower endplates 20, 22 defie an interior volume 26, S [0063] The elastic membrane 24 preferably is formed from an elastomer such asipolyurethane, silicone, a braided polymner or any other appropriate elastic material. The elastic membrane 24 may be permeable or semi-permeable to allow fluid to flow into and out of the interior of the disc (as described inmore detail below). Alternatively, the membrane may be non-permeable. Preferably, the elastic membrane 24 may resist translational motion between the upper and lower endplates 12, 14, and may also prevent soh tissue ingrowth between the endplates-12, 14 as well as contain any wear particles gelerated within the interior volume. The elstic membrane 24 may be attached to the WO 2004/016217 PCT/US2003/025536 uper.and lower endplates 12, 14 by any fition method known in the art includig, but not limited to, bonding agents, ultrasonic weldig, screws, nails, mechanical wedging and pins: S [0064] Alternatively, the elastic membrane 24 may be in the form of a bellow, the:bellow assuming an "accordion" or other flexible shape, enabling it to expand and.

contract under the various loading conditi6ns. The bellow may be rigidly attached to the upper and lower endplates 12, 14 by any imthod known in the art including, but not limited td a circular groove formed in each endplate 12, 14, bonding agents, ultrasonic welding, sqrews, nails, mechanical wedging,: and pins. Preferably, the bellow is made from a metal, alough other material such as elastomerstor polymers may be used. In an alternative eAbodiment, membrane 16 may be made of any appropriate non-elastic material known in t art.

[0065] With reference to Figure 2, the interior 26 of disc 10 is shown..

Peferably, the interior 26 of the disc 10 includes at least one spring element 30, and the s in.g-element 30 may have a longitudinal axis. The spring may be oriented such-that its lo gitudinal axis is oriented substantially perpendicular to the plane formed by each of the uaper and lower endplates 20,22. Altematively, the spring may be oriented such that its: axis .forms an acute angle with at least one,f the upper and lower endplates. The spring el ment may have a first end which contacts the lower endplate 22 within a pocket or gi ove 32 fbrmed on the inner surface 40 of the lower endplate 22. Such a pocket or gr ove may prevent lateral displacement of the spring with respect to the endplate. An i4 per end of the spring element 30 may engage an articulation member 34 having a springeqgaging surface 33 and an opposite substantially spherical surface 35. The spring element may be fixed to the pocket 32 and/or the articulation member 34 using any appropriate fiation method known in the art including, but not limited to bonding agents, ultrasonic wlding screws, nails, press-fit, and pins. Alternatively, the spring element 30 and the ar iulation member 34 may be integrally fdrmed.

1 0066] The spherical surface 35bf articulation member 34 may be configured to ariculate within a correspondingly shapediocket 36 formed on the inner surface 38 of the uper endplate 20. The interface between the articulation member 34 and the socket 36 may approximate a ball and socket type connection, with the spherical articulation:member 34 able tb articulate within the socket 36. The type and amount of articulation desired may distate the curvature and are of the spherical, surface 35 provided on the articulation m< mber 34 and socket 36. For example, ifithe spherical surface 35 has the sameradius as thf socket 36, then the disc 10 may provid6greater support but more constrained WO 2004/016217 PCT/US2003/025536 novement. Alternatively, if the socket 36has a larger radius than the spherical sirface the disc 10 may provide increased articulation and/or translation.

[0067] In an alternative embodiment, the socket 36 may incorporate a flattened portion which may permit the articulationit:ember 34 to translate within the socket, thereby providing translational movement of the upper endplate 20 relative to the lower endplate 22.

By providing for such translation, the disc .10 may provide a moving instantaneous axis of rotation. It-is possible for the articulation-member 34 and socket 36 to have contours other than spherical in order to achieve the desired articulation motion. Such other contours may c6mprise elliptical or egg-shaped, and multiply-spherical shaped in which the articulation niember and the socket each may comprise at least two separate or cojoined spherical segments. Moreover, while the articulatiti member 34 and socket 36 are illustrated as having contours that generally permit mating of their respective surfaces, the correponding surfaces may take on any appropriate shape to achieve the desired articulating mobility b tween the upper and lower endplates 204 22..

[0068] While the disc 10 has been described as having the articulating member 3# associated with the lower endplate 22 aid the socket 36 associated with the upper e.dplate 20, the elements may be reversedso that the socket 36 and articulating element Sae instead associated with the lower and upper endplates, respectively. Furthermore, the scket member may be provided integral with its respective end plate, such as providing a oC-piec end plate with a hollow spherical inner surface. Also, the socket member and aticulating element may comprise any appropriate material known in the art, such as titanium, stainless steel, polymers such as.iltra high molecular weight polyethylene, etc.

Ftrthermore, the articulating surfaces may include a surface polish or similar wear reducing fiish such as diamond finish, TiNi finish,.etc. in order to minimize wear, decrease particle g neration, and increase disc life.

[0069] The spring element 30-nay encompass any appropriate resilient member kown in the art including, but not limited"to, spiral springs, coil springs, plate or leaf springs, etc. Moreover, the spring element 30 may be formed from any appropriate material klaown in the art including, for example, polymers, composites, or metals such as cobaltchtomium alloys, titanium alloys, stainless steel, shape memory alloys, and amorphous alloys.. Likewisethe spring element 30 coprise two or more individual spring elements provided either in series, in parallel, or in a combination of series and parallel .elments, S [0070] The selection of a particular spring element may depend on the needs of thparticular patient, however, the spring or springs selected should mimic the properties of WO 2004/016217 PCT/US2003/025536 tde patienit's normal L-terveebral disc, or should be appropriate as required for the p ~tiulaf procedure. Thus, springs having the appropriate stiffness in axial compression a d in transverse bending should be selected to provide the following ranges: fldxibn/extension from about 0 Newton-meters per degree (Nm/deg) to about 8 Nm/deg); lateral bending from about Nm/deg to about 5 Nm/deg; and compression from about 1) to about 5000 N/mm. Furthermore, the outer diameter of the springs selected may ige from about 5 millimeters (mm) to about 30 mm; and the heights of the springs may range from about 7.5 mm to about 12 rmm. It is noted that the preceding are provided as representative dimensions only, and the springs used may have any size, shape, strength and flexibility appropriate for the particular patient.

[0071] The use of a spring element in combination with an articulating siurface .nay provide a combination of articulation, translation and compression/shock absorption btween the upper and lower endplates 20 22, and thus allowing for a moving i taneous axis of rotation, Articulation maybe provided through the interaction of the aticulating member 35.and the socket 36, and/or by bending of the at least one spring element 30. Compression and shock absoiption may be provided by the spring element apd translation may be provided by bending:of the spring element or through the choice of a socket having a flattened portion such that.the articulating member 36 may translate within the socket i [0072] Referring to Figure 2a, a disc 10 comprising a plurality of intemal s ring elements 30 is illustrated, each spring element 30 may extend from the upper dplate 20 to the lower endplate 22 such.that the longitudinal axis of each spritigelement is oriented substantially perpendicular to the plane formed by each of the end plates 20, 22.

Alternatively, one or more of springs 30 may be oriented so that their longitudinal axis forms an acute angle relative to the plane of one or both of the end plates.

S [0073] The plurality of spring 'lements 30 may be arranged in a configuration propriate to provide uniform shook absoiption, load bearing, and tension/compression r sistance, r the spring elements 30 may be strategically placed to allow for increased resistance to shock and/or compression on one side anterior, posterior) of the disc as compared to the other. Preferably, however, the disc 10 includes at least one central spring eement 30 and at least one peripheral spring element 30 spaced away from the central.

spaig element 30. In the illustrated embodiment, a single central spring element is st irounded by a plurality of peripheral spring elements. The central and peripheral spring eement 30 may have substantially the same stiffness, or their stiffnesses may be different.

P eferably, the central spring element 30 may have a stiffness greater than the stiffness of 13 WO 2004/016217 PCT/US2003/025536 t peripheral spring elements 30. Such an:arrangement may result in a disc hlat iga central spring which provides primary shoak absorption and resistance during tbeinitial stages of an axial compression evolution, and having peripheral spring elements,30 which p oyide secondary shock absorption and resistance during the later phases of axial ccmpression. This provides a desirable non-linear response to compressive loads which qay; closely mimic the response ofthe patint's natural disc. 0074] As shown in Figure 2a; each spring element 30 has first and second ends associated with respective upper and lower end plates 20, 22. The first and second ends of eah spring may have an associated spherical articulation member 34 configured to mate vitI a corresponding spherical socket 36 formed on the inner surface of the uppeand lower endplates 20, 22 as previously described. The combination of spring and articulation nembers permits the upper and lower endplates 20, 22 to move with respect to edch other.

Fb* example, articulation members 34 may articulate within associated sockets 36.so that the pper and lower endplates 20, 22 can articilate with respect to each other without c'eating resistive torsion in spring elements 30 that would be present if the endsof the srings were rigidly connected to the endplates. Alternatively, each spring element 30 may bol be attached to a spherical member 34.bn one end, the other end being attached to the uppr or lower endplate 20, 22 as previous described.

[0075] Referring to Figure 2b; theidis 10 may include a plurality of spring elements 30 where only one end of the first spring element 30 comprises a spheical ticulation member 34, and the opposite end of the first spring element 30 as well as both ends of the second spring elements 30 are disposed within corresponding pockets, or ce sses, in the upper and lower endplates20, 22 (the arrangement and connectioi of these reces .and the associated spring elements being the same as previously described in relation to the embodiment of Figure As shown in Figure 2b, preferably the irst spring e ement 30tis attached to a hemi-spherical.member 34 for mating with a corresponding s cket 36 located in the upper or lower endplate 20, 22. The plurality of second spring elements 30 surrounding the first spring element 30 being attached directly to theupper and tdwer endplates 20, 22 as previously described. In one embodiment, the first spring may be attached to one hemi-spherical member 34,.and the plurality of second spring elements 4a be may be attached to two hemi-spheticalmember 34. As with the previousi.

eijbpdiments, the number, stiffness, and arrangement of the springs, as well as the selection a d lacement of the articulating elements'and sockets 36 maybe made in any combination propriate to provide a disc that mimics as closely as possible the properties of the normal i tervertebral disc, or that provides the properties appropriate to the particular pocedure.

WO 2004/016217 PCT/US2003/025536 [0076]: Referring to Figure- 2, tha disc 10 may include an elastomric stiut 54 located peripherally to a central spring element 30. The strut 54 may have a longitudinal axis and first and second ends, and each end may be associated with an upper or lower endplate 20, 22. The elastomeric strut 54 may be seated in a groove 32 formed:in the associated inner surfaces 38, 40 of the upper and lower endplates 20, 22 to resist displacement. The elastomerio strut 54imay serve essentially the same function as peripheral spring elements 30 previously described, i.e. to provide the disc 10 with c ompression force resistance and shock absorption and to resist motion. The elastomeric strut 54 may be formed from any appropriate material known in the art including, but not limited to, polyurethane or silicone. Any number of individual struts 54 may be provided, iand the struts individual struts may assume various shapes in order to provide the iappropriate stiffness or resistance suppor for the end plates. Thus, the struts 54 may be.

cylindrical, square, rectangular, etc., and-they may have any appropriate cross section, such as circular, triangular, elliptical, etc. The struts may also be provided with continuous or non-continuous cross-sections, and they may be made up of different layers of materials, such as having alternating elastomeric and metallic or polymer layers. The strnts.S4 may also be hollow, or they may be ring-shaped. The ring-shaped struts.54 may be configured to surround at least.a portion of the first spring element 30. As with earlier embodiments, the ends of struts 54 may be connected to the end plates using any appropriate method in the art, including press-fit, bonding agents, etc, One or more struts may also be provided to move within their associated groove or grooves. The arrangement, number and eonfiguration ofthe struts 54 is not critical, but instead may be any combination desired to trovide a disc 10 that mimics the properties of the patient's normal intervertebral disc, or hatprovides the properties appropriate to the particular procedure.

j [0077] The inner surfaces 38; 40 of endplates 20, 22 may be porous to allow the *lastomeric strut 50 to be integrated into the corresponding surfaces of the upper and lower dndplates 20, 22 during manufacture such as.by molding the elastomer to the endplate.: A Shembrane and/or barrier may also be inclided within endplates 20, 22 to limit the depth of impregnation and bony ingrowth respectively.

[0078] The disc 10 of this embodiment also may include a membrane. 24 and a vve (not-shown), the valve providing.acess to the interior 26 of disc 10 so that fluid ay b. injected into, or removed from, the inteior 26 of the disc 10. The valve preferably is a one-way valve, as known to those skilled in.the art, so that the fluid, once injected, can not ape from the interior 26 of the disc 10.: Preferably, the valve is disposed through the! e ltic membrane 24, alternatively however,. the valve may be disposed through.the upper WO 2004/016217 PCT/US2003/025536 and/orlower endplates 20, 22. When thf valve is disposed on the upper and/or wer endplates 20, 22, a passageway preferably is included to interconnect the valve with the, Interior 26 ofthe disc [0079] The fluid may be a gas, a liquid, a gel, or any combination thereof, that is sufficient to provide shock absorption during axial compression of the disc 10; while also permitting limited articulation ormovement of the upper endplate 20 and lower endplate 22 with respect to one another. Preferably, the fluid is incompressible, for example, saline or: mineral water. In use, the fluid may beinjected into the interior 26 of the disc 11) before' insertion of the dis 10 between adjacentivertebrae. Alternatively, the fluid may be injected in situ to facilitate insertion of disc 10 and subsequent distraction betwee adjacent vertebrae. The rigidity and distraction capability of the disc 10 may be a function of the amount of fluid injected into the interior 26 of the disc 10. Generally, the more fluid provided in the interior 26 of the disc 10, Ithe more rigid the disc 10, and the greater the distraction .capbility. Furthermore, pliability and increased articulation may be realized by filling only a portion of the interior 26 of the disc 10. Finally, variably filling the interior 26 of the disc 10 with fluid permits the overall height H of the disc 10 to be varied as necessary depending on the needs of the individualpatient.

[0080] Depending on. the lodation of the spine where the disc 10 is implanted, the disc 0pieferably restore height in tht range between about 4 millimeters to:about 26 millimeters. In addition, the disc 10 preferably restore lordosis in the range between about 00 to about 20. The disc 10 preferably also restore stiffness from about 1 Nm/idg to about 11 Nm/deg in axial rotation, about 0 Nm/deg to about 7 Nm/deg in flexion/extension, and about 0 Nm/deg to about 5 Nm/deg in lateral bending. In addition, the disc 10 preferably offers compression stiffness from abouti 100 N/mm to about 5000 N/mm and tension.

stiffness from about 50 N/mm to about 1000 N/mm. Furthermore, depending on the location of the spine where the disc 10 is mplanted, the intervertebral disc 10 preferably allows for a range of motion of about 5°o about 450 in flexion/extension, of about 30 to about 33" in lateral bending, and about 1I to about 600 in axial rotation. The intervertebral: disc 10 preferably also allows for axial eqmpression in the range from about 2 mm to about 2mm.

[0081] Preferably, the upper ind lower endplates 20, 22 are formedof metal, such as titanium, stainless steel, titaninum alloys, cobalt-chromium alloys, shape memory lloys, or amorphous alloys. Alternativly, however, the upper and lower endplates 20,22 may be formed of polymers including rigid-polymers, PEEK or UHMWPE, ceramics, domposites, bone including cortical, cancellous, allograft, autograft, xenograft, WO 2004/016217 PCT/US2003/025536 Sdeneralized or partially demineralizedone, or any other material appropnate to serve as load bearing supports. More preferablythe materials chosen for the endplates :re chosen .so:as to. minimize wear.

[0082] Furthermore, preferinbl, any articulating surfaces in the interrtebral idiscs of the present invention include a siiface polish or similar wear reducingfinish such asidiamond finish, TiNi finish, etc. in order to minimize wear, decrease particle generation, and increase disc life.

[0083]. The outer surface of te.upper and lower endplates 20, 22 may be substantially flat, wedge-shaped, etc. The outer surfaces of the upper and lower endplates 22 may also be dome shaped with thir radii defined in the sagittal and coronal panes to generally match.the shape of the ends ofihe adjacent vertebral, thereby providing a better fitin situ.

[0084] In addition, as shown- in Figure 1, the disc 10 may include migration resistant features, such as, for example, s.ike-like structures 18 on the outer surfaces of the upper and lower endplates 20, 22. The migration resistant features may facilitate engagement of the disc 10 with the endso the adjacent vertebra by providing. mechanical intelockas a result of penetration and/o4:deformation of the ends of the adjacent vertebrae.

The initial, mechanical stability afforded by spikes 18, for example, minimizes tei, risk of Spost-opetive instability, movement, dislodging or expulsion of the disc 10. Other migration resistant features may include,:vithout limitation, flaps, teeth, deployahle teeth, deployable spikes, flexible spikes, flexible teeth, fins, insertable or expandable fins, anchors, screws, ridges, serrations, or other similar texturing on the upper and lower enlates 20, 22, As shown in Figure 3a deployable spikes 41 may be provided, and a cam echanism 43 may be used to deploy tha spikes. Alternatively, as shown in Figuie 3b, the deployable spikes may be configured to-be deployed by an instrument (not show). As shown in Figures 30 through 3e, respectively, examples of flexible spikes 44, shaped teth and anchors 46 are shown. Alternatively or in addition, bonding agents may also be .sed to secure the disc 10 to adjacent vertebra.

[0085] Furthermore, the uppe and lower endplates 20, 22 may also be coated with a bone growth inducing substance, such as hydroxyapatite, to promote bony ingrowtli t permanently secure the disc 10 to the adjacent vertebrae. Alternatively, the uppr and lower endplates 20, 22 may have a roughied or porous surface to facilitate bony ingrowth.

lternatively, the upper and lower endplates,20, 22 may have laser treated endplate layers t create a porous structure, or may integrate an osteoconductive/osteoinductive scaffold.

heeandplatcs 20, 22 may also be made fibm an osteoconductive and/or osteoinductive 17 WO 2004/016217 PCT/US2003/025536 material to promote bony ingrowth. Th endplates 20, 22 may further include awiembrane Sand/orbarrier to.limit the depth of bony ingrowth permitted.

i [0086] The upper and lowertendplates 20, 22 may also have implaht' instrumentation attachment, guiding, and retaining structures. For example, the endplates 22 may have holes, slots, threads, or a dovetail for accepting a tool used to implant Sd/or distract the vertebrae. For example, the disc may include a slot formed in the upper ni/or lower endplates 20, 22, the slot configured to receive an implant insertion :ns tnmnent, a distractor or both.

S [0087] As a result of the material and structural components used, the disd an allow flexion/extension, lateral bending, axial rotation, and translation, depending on ihe loading imparted on the intervertebrl .disc. In addition, under various spinal loading conditions resulting from spinal movements, the spring element 30 can compress, tilt, articulate and/or bend varying amounts. [0088] With reference to Figures 4 and 4a, a second exemplary embodiment of an intervertebral disc 100 is shown. Similar to the previous embodiments described, the .xternal configuration of disc 100 may take on any shape that generally conforms geometrically and anatomically with th:eadjacent vertebral bodies including, but not limited to circular, oval, ellipsoid, annular, kidney-bean, D-shaped, C-shaped, etc, As shown, disc.

100 includes an upper endplate 102, a lower endplate 104, and an intermediate elastic inembrane 106, the elastic membrane 106 in combination with the upper and lower ndplates 102, 104 defining an interior volume 108. The endplates 102, 104 atd elastic Snemnbrane 106 are similar to those endplates and elastic membrane described previously in elation to other embodiments. The disc 100 may also include a valve (not shown), the valve providing access to the interior 108:ofthe disc 100 for permitting the insertion of, or emoval of, a fluid as previously described in relations to other embodiments. Disc 100 may also include migration resistant featres, permanent fixation means and/or implant instrumentation attachment, guiding, and retaining structures as previously described in relation to Figures 3a 3e and previous embodiments.

[0089] Disc 100 further may include a leaf spring 110 having a first end 112 :and second end 114. The first end 112 may be attached to the upper endplate 102, while the second end 114 of leaf spring 110 may comprise a roller 130 capable of rolling on the inner aurface of the upper end plate 102. The leaf spring may have a central portion 116 disposed etwveen the first and second end 112, 114, aid this central portion 116 may comprise a concavo-convex shape. The convex surface may generally face the lower endplate 24 and te concave surface generally facing the upper endplate 24. Lower end plate 104 may WO 2004/016217 PCT/US2003/025536 q: codrise a surface configured to. accept intermediate section 116 which itself is.. cnfigured to maie, articulate, slide and pivot.with the inner surface like a ball in a socket. While the leaf spring 110 is described herein as attahhed to the upper endplate, it may altematively be jattached to.the lower endplate 104 so that its concavo-convex intermediate section 116 Jinteraots with the inner surface of the upper end plate 102. It is noted that although the articulating surface of leaf spring 110 isillustrated as being disposed near the center of the leaf spring,.the articulating surface may be located at any point along the length .and/or iwidth of the leaf spring, as appropriate tp provide the desired articulation.

[0090] The second unattachid end 114 of leaf spring 110 may be provided with aroller 130 on an axle 132, the roller 130being freely rotatable about the axle 132. .he.

Isecond end 114 of leaf spring 110 may slide or roll along the inner surface of the upper iendplate 102 during axial loading or compression and during axial unloading or tension..

SThe leaf spring of this embodiment is thus allowed to translate as it is flexed, providing a Igreathe raige of flexibility compared to leaf springs constrained at both ends. In an laltenative embodiment, the leaf spring i1T may have a rounded end instead of a roller 130 !for sliding directly along the inner surface of the upper endplate 102.

0091] The lower endplate 14 may comprise a pocket 106 for receiving a pad [120. The pad 120 may have a lower surface for engaging the lower endplate 104,and an upper Surface comprising a concave section 122 configured and dimensioned to mate with the larged intermediate convex section116 of leaf spring 110. The type and amount of cjulation provided by the spring and pad may be adjusted by controlling the curvature rovided on the intermediate section 116:and concave section 122. Where the intermediate :section 116 has the same radius as the concave section 122, the disc 100 may provide egratr support but more constraited movement. Alternatively, where the concave section X22 has a larger radius of curvature than'the intermediate section 116, the disc may provide ncreased articulation.

[0092] The intermediate meiber 116 and concave section 122 may also take on other.contours to achieve the desired articulation. The concave section 122 of ite pad 120 may be convex to mate with a concave intermediate section 116. Moreover, while the concave section 122 and intermediate member 116 are shown with contours that:generally 4 tmit mating of their surfaces, non-mating contours may be provided to achieve the lesired articulation.

[0093] Furthermore, the compression and sliding of leaf spring 110 may varyilepeding on the area.or areas of loading. For example, loading one end of disc100 may iesult in greater compression of disc 100 when compared with an opposing end of disc 100.

WO 2004/016217 PCT/US2003/025536 Additionally, the pad 120 and the pocket106 may be configured to allow the p to t.aislate within the pocket 106. The varying movements, i.e. compression, of leaf spring :110and translationof leaf spring 110 with respect to the pocket 106 may allow a moving iinstantaneous axis of rotation.

0094] Leaf spring 110 may be formed from any appropriate material known in ithe art including, for example, polyrers,;ceramics, composites and metals, such as cobiltchromium alloys, titanium alloys, stainless steel, shape memory alloys, and amorphous alloys, The pad 120 may likewise be formed of similar materials.

S 0095] Depending on the location of the spine where the disc 100 is implanted, i0 the disc 100 preferably restores height, natural spinal curve (or sagittal balance), stiffness, joffes compression stiffness, and allows a range of motion similar to that described in i :relation to previous: embodiments.

[0096] With reference to Figure 5, a third exemplary embodiment of an intervertebral disc 50 is shown. Similar to the previous embodiments described, disc 150 may take on any shape that generally conforms geometrically and anatomically with the ;adjacent vertebral bodies including, but not limited to circular, oval, ellipsoid, annular, jkidney-bean, D-shaped, C-shaped, etc. As shown, disc 150 includes an upper endplate 152, Sa lower endplate 154, and an intermediate elastic membrane 156, the elastic membrane.156 iin combination with the upper and lowerr;oadplates 152, 154 defining an interior volume 158. The endplates 152, 154 and elastic membrane 156 are similar to those previously ;described in relation to other embodiments. The disc 150 may also include a valve (not shown), the valve providing access to the interior 158 of the disc 150 for permitting the.

insertion of, or removal of, a fluid as previously described in relations to other embodiments. Disc 150 may also include migration resistant features, permanent fixation eans and/or implant instrumentation attachment, guiding, and retaining struct-res as previously described in relation to Figures 3a-3e and the previous embodiments.

[0097] Disc 150 may further include a medial articulating member 160 attached to one of the upper or lower endplates 152, 154, preferably the lower endplate 152. The articulating member 160 may have a convex lower surface 162 that is configured and dimensioned to articulate with respect to concave surface 164 formed on the ijier surface pfone ofthe lower endplate 154. The curvature of the corresponding articulating surfaces 162, 164 may be manipulated as necessary to provide the desired amount of articulation-and aslation between the endplates 152, 154, as has already been described in relation to ther embodiments.

WO 2004/016217 PCT/US2003/025536 F0098] Alternatively, the artic lating member 162 may comprise a.-ricave.

lower surface coifigured and dimensione to mate and articulate with rcspect t a convex' surface formed on the inner surface of the opposing endplates 152, 154. Furthermore, the concave surface 164 may be integrally formed on the inner surface of one of the endplates 152 154 or it may be separately formed and mounted thereon. Mounting the coecave surface 164 onto the inner surface of one!of the endplates 152, 154 permits the concave urface 164 to be made from a material different from that of the associated endplate, for p xample, polyethylene or other polymeri.r a shock absorbing material may be provided, as S 'escribedinmore detail later.

[0099] The articulating member 160 may be attached to one of the endplates .1152, 154 by any fixation method known in the art including, but not limited to bonding: agents, ultrasonic welding, screws, nails, mechanical wedging, and pins. Preferably,.

however, the articulating member 160 may be attached to one of the endplate 150, 152 via an intermediate shock absorbing layer 170. The shock absorbing layer 170 may be an elastomner, molded or bound polymer fibers, polyurethane, silicone, or any other suitable lastic material having the appropriate shock absorbing properties. Articulating member 160:imay be fabricated from a metals, polymers, composites, ceramics, or any combination thereof S 010010] The disc 150 may also include an additional elastic membrane 1172 onfigaued to confine and/or secure the aticulating member 160 to one ofthe endplates 152 154, and/or to encapsulate the shock.absorbing layer 170. The additional elastic membrane may be a bellow which may provide shock absorption, compression resistance, land .dded stability for the articulating nember 160 in shear.

S[00101] Depending on the location of the spine where the disc 150 is implanted, ithe disc !50 preferably restores height, natural spinal curve (or sagittal balance), stiffness; offers compression stiffness, and allows a range of motion similar to that described in relation to previous embodiments.

S 0.0102] As a result of the maerials, geometry, and compofnents used, disc 150 jan allow flexion/extension, lateral bending, axial rotation, and translation, depending on the loading conditions imparted on the intervertebral disc, In addition, under various spinal loadingonditions, the shock-absorbing lyer disposed between the articulating member j160 and.one of the endplates 152, 154 caincompress and/or bend varying amounts, iepending on the location of the compressed and/or bent area with respect to the area or areas.of loading Furthermore, disc 150 permits different regions of the disc 150 to mpress varying amounts.

WO 2004/016217 PCT/US2003/025536 [00103] With reference to Figue 6, a fourth exemplary embodimeit of an intervertebral disc 200 is shown. Disc 20 has a generally circular shape with an upper endplate 202, a lower endplate 204, and a slotted core 206 having an upper curved surface anda lower flat surface. The disc 200 may take on any other shape that appropriately conforms geometrically and anatomically with adjacent vertebral bodies, including, but not limited to, kidney-bean shape, oval, annular, ellipsoid, C-shape, D-shape etc. Other features described previously with respect to the other embodiments, such as the migration resistant structures, permanent fixation features and/or implant instrument attachment, guiding, and Sretaining structures may be included on endplates 202,204. Furthermore, the outer surfaces .ofthe upper and lower endplates 202, 204 may be substantially flat, wedge-shaped, etc.

.The outer surfaces of the upper and lower endplates 202, 204 also may be dome shaped with their radii defined in the sagittal ana coronal planes to generally match the shape of the :ends of the adjacent vertebrae, thereby providing a better fit in situ. Preferably, the upper: .and lower endplates 202, 204 may be made from metal. However, the upperand lower endplate 202, 204 may alternatively be made from any of the endplate materials previously idescribedin relation to earlier embodiments.

[00104] As shown, the lowerendplate 204 preferably includes apocket 208 located on its inner surface, the pocket 2d8 designed to receive the lower flat strface of slotted core 206. Alternatively, the slottd core 206 and lower endplate 204 may be formed as an integral piece. Where the core is fTrmed as a separate piece, it may comprise a Idifferent material from the end plate 204 thus, a metal end plate may be provided having, ffor example, a polymer mating feature core 206.

[00105] Where the core 206 ad endplate 204 are formed separately, the disc i200 may also include a c-ring (not show or similar structure, such as a lip or ring locaied within or adjacent to pocket 208, to retain the core 206 within the endplate pocket 208.

!Such a ring may be configured to prevent the core from translating with respect to the endplate 204, or it may allow translation of the core in one or more directions, Alternatively, the core 206 may be retained in pocket 208 by means such as welding, pressfitting, staking, or bonding a cap (not shown) to the lower endplate 204, the cap covering a portion ofthe core 206.

S [001061 Although pocket 208is shown as having a circular shape, the pocket may take on any other appropriate shapeincluding, but not limited to oval, elliptical, kidney-bean shaped, rectangular, etc. Where the core and endplate are formed as separate pieces, pocket 208 may be wider or longer than slotted core 206, thus allowingthe core 206 to translate within the pocket 208 during;:operation. Alternatively, the pocket 208 may 22 WO 2004/016217 PCT/US2003/025536 assume various ;dimensional configurati0is necessary to allow translation of tz core 206 within the pocket only along specific diiwetions. Thus, the pocket may be pro yied with a same general width as the core in all directions but one, the pocket being wider than the core in that one direction the anterior posterior direction). Thus, a pocket that is wider than the core along the anterior-posterior axis may allow the core to translate in the anterior-posterior direction during use. borresponding modifications to the pocket geometry may be made to allow translation in other directions, such as medial-lateral translation.

[00107o The inner surface of the iupper endplate 202 may have a coneave mating feature 210 configured to accept the uper curved surface 212 of theslotted core 206.

Preferably, the mating feature 210 allows the upper end plate 202 to articulate with respect to the slotted core 206. This mating featu e 210 may be integral to the upper efd plate 202; or it may be formed as a separate piece, it to the end plate. Where the mating feature is formed as a separate piece, it may comp$se a different material from the end plate 202.

Thus, a metal end plate may be provided having, for example, a polymer mating feature 21Q.

:[00108]1 As previously described in relation to other embodiments; the articulating surfaces may be reversed, fat is, mating feature 210 may be provided in convex form, arid the slotted core mayb' provided with a concave surface. Furthermore, the type and amount of articulation and/or translation provided by the disc of this embodiment may likewise be adjusted'by adjusting the curvature of the convexand concave surfaces as previously described in relation to other embodiments. By allowing articulating and translational movement between th~-endplates, a moving instantaneous axis of rotation is allowed that approximates the motion!of a natural intervertebral disc.

[00109] The slotted core 206 jmay be resilient, allowing it to compress under axial loading,. thereby providing shock absorption. Thus the core 206 may have;at least one slot 216 cut into its periphery. Slots 216 may be straight or curved and may extend horizontally, veitically, or obliquely. Slots 216 may also vary in length and width and may.

be provided at various depths through the core. The slots 216 may increase thei compressibility of slotted core 206 and thus give additional shock absorbing qualities to the disc 200. The arrangement and configu tion of the slots provided in the core 206 may be -of any combination appropriate to provide.the desired degree of compressibility.

[00110] Although shown as having a round footprint, the slotted core 206 may be.:any other shape including oval, recta gular, elliptical, and kidney-bean. Preferably the shape.of the slotted core 206 matches wi4h the shape of the pocket 208 formed on the inner 23 WO 2004/016217 PCT/US2003/025536 surface of the lower endplate 204. Slotted core 206 may be formed from materials including, for example, ceramics, compsites, polymers, or metals such as cobalt-chromium alloys, stainless steel, and titanium alloys Alternatively, slotted core 206 may be made up: of two components (not shown) of differing materials. Also, as previously stated, the !slotted core 206 may be made integral with the lower endplate 204, i '00111] Disc 200 may also include stiffness restoration features suchi as an [elastic methbrane, an elastomer ring, bellow, springs, or fluid as previously discussed in [relations to other embodiments. Disc 200 .may also incorporate additional shock absorbing features as previously discussed in relations to other embodiments.

I [00112] The disc 200 endplates.may have migration-resistant structures provided +on the outer surface of at least one or both of the endplates to impede movement, idislbdging, or expulsion of the endplates within and from the ends of the adjacent vertebrae.

|The migration-resistant structures include, but are not limited to, flaps, spikes, teeth, fms, ideployable spikes, deployable teeth, flexible spikes, flexible teeth, alternatively shaped teeth, insertable or expandable fins, screws, hooks, serratiors, ribs, and textured surfaces.

S [00113] Furthermore, the upper and lower endplates of disc 200 also may be coated with a bone growth inducing or conducting substance to promote bony ingrowth to permanently secure the disco o theadjacent vertebrae. Alternatively, the upper and lower iendplates may have a roughened surface; a porous surface; laser treated endplate layers; ,integrate an osteoconductiveostpoinductive scaffold; or may be provided with or made Ifrom an integral osteoconductive and/or osteoinductive material to promote bony ingrowth.

[00114] Depending on the loation of the spine where the disc 200 is implanted, Ithe disc 200 may restore height, lordosis, stiffness, offer compression stiffness, and allow a range of motion intended to mimic that of the natural intervertebral disc, or as required for Ithe particular procedure.

00115] In addition, preferably, as discussed with previous embodiments, the articulating surfaces of disc 200 include asurface polish or similar wear reducing finish such as diamond finish, TiNi finish, etc. in order to minimize wear, decrease particle gncration, and increase disc life.

[0016] As a result of the materials, geometry, and components used; disc 200 can allow flexion/extension, lateral bending, axial rotation, and translation, depending on ie loading conditions imparted on the intervertebral disc. In addition, under various spinal loading conditions, the slotted core 206 can variably compress and allow for different regions of the slotted core 206 to compress in different amounts, depending on.the location adtype of spinal loading, thus allowing.different regions of the endplates 02, 204 to be WO 2004/016217 PCT/US2003/025536 compressed different amounts. This varbl compression of slotted core 206 allows ifor a moving instantaneous axis of rotati"4.

[00117] With reference to Figre: 7, a fifth exemplary embodiment of an iintervertebral disc 250 is shown. Disc 250 has a generally circular shape with an upper iedplate 252, a lower endplate 254, a cap 256 and a ring spring 258, Disc 250, however, imay take on other shapes that preferably confoon geometrically and anatomically with adjacent vertebral bodies, including, but not limited to, kidney-bean shape, oval, annular, ellipsoid, C-shape, D-shape etc, S[00118] As shown, the lower endplate 254 preferably includes a pocket 260 located on its irmer surface, the pocket 260 is designed to receive a ring spring 2SS having a tapered outer surface, and a cylindrical irner surface. Preferably, the pocket 260 has a itapered inner surface for mating with the tapered outer surface of the ring spring 258.

'Although pocket 260 is shown as having a circular or conical shape, the pocket 260 may 'take on any other shape including, but ndt limited to oval, elliptical, kidney-bean, or .'rectangular.

[00119] Pocket 260 may be lager in dimension than the rng ring pi258 to.allow the ring spring.258 to translate within tht pocket 260. As with the pocket of the previous embodiment, pocket 260 may be specifically dimensioned to allow limited translation of the ring spring 258 in one direction. By allowing translational movement, a moving instantaneous axis of rotation is created.:; This moving instantaneous axis of rotation more naturally replicates the motion of a natural intervertebral disc.

[.00120] The disc 250 may also include a c-ring (not shown) or similar type Sstructure,, such as a lip or a ring located Within or adjacent to the pocket 260, to: retain the Iring spring 258 in the pocket 260. Alternatively, the ring spring 258 may be retained in pocket 260 by any means known in the art including, but not limited to, welding, press- Sfitting staking, or bonding. As previously stated, the ring spring 258 is maintained in the Jpolet 260 in a manner permitting the ring spring 258 to translate within pocket 260. In !one embodiment, the ring spring and cap may be retained in the pocket 260 by a lid that engages the lower endplate 254 and thatbovers at least a portion of the ring spring 258 and/or the cap 256.

[00121] The ring spring 258 is preferably a spring-like element that compresses under axial loading to provide shock absorption, flex and compression resistance.] Although Ishown ashaving a general shape with a circular footprint, the ring spring 258 may be any other shape including oval, rectangular, elliptical, and kidney-bean. Preferably the shape of the ring spring 258 matches with the shape of the pocket 260 formed on the inner WO 2004/016217 PCT/US2003/025536 surface of the lower endplate 254.. The ring spring 258 may be formed of any ropriate material known in the art including, for example, ceramics, composites, polynjers or metals, such as cobalt-chromium alloys, stainless steel and titanium alloys.

[00122] As shown, the ring spring 258 has a top surface 264, a bottom surface 266, an outer surface,268 and an inner surface 270 defining a central bore 272 for mating with a shank 276 formed on the cap 256.: :Preferably, the outer surface 268 of he 'ring spring.258 is tapered to mate and. engage with the inner surface ofthe pocket 26; In addition, the ring spring 258 may include at least one slot 262 formed and/or dut into its periphery. The slot 262 may be straight or curved and may extend horizontally, vertically, or obliquely. The slot 262 may also vary:in length and width. Preferably, as shown, the ring spring 258 includes one vertical slot 262 extending from the top surface 64 the bottom surface 266 of the ring spring 258, and extending from the outer surface 268 t the inner surface 270 of the ring spring 258. The inclusion of this slot 262 increases the compressibility of the ring spring 258 and thus provides additional shock absorbing ualities to the disc 250. [00123] In an alternative embodiment, the ring spring 258 may incorporate a plurality of slots 262-(not shown) running from the top and/or bottom surface 264, 266 part way through the thickness of the ring spring 258 to provide desired compressive characteristics of the disc.

[00124] The disc 250 may al~t ipclude a cap 256 having an enlarged body section 274 and a shank 276. Thejuncture between the enlarged body sectioni 274 and the shank 276 may form a shoulder 278, the shank 276 e configured, and dimensidned to be received within the central bore 272 of the ring spring 258, and the shoulder configured to Sengage the top surface 264 of the ring spring so that the cap 256 may sit on to' of the ring spring 258 when the two pieces are assembled. In one embodiment, the central bore 272 is larger than the shank 276 thus permitting compression of the ring spring 258 via closure of Sthe gap created by the at least one slot 262 when a compressive force is placed on the disc 250. Also, providing a central bore 272 which is larger than the shank 276 miy permit the cap 256 to translate with respect to the ringspring 258.

[00125] As previously described, the shoulder 278 of cap 256 contscts the top surface 264 of the ring spring 258. Thus, axial loads applied to the cap 256 may be transmitted directly to the ring spring 258, pressing it down into the pocket 260B As the ring spring 258 is pressed into the pocket 260, the. tapered outside surface 268 ofthe ring spring S710 engages the tapered surface of the pocket 260, in the process compressing the at least one slots 262. This elastic compression of ring spring 258 under axial loading provides the WO 2004/016217 PCT/US2003/025536 desired:shock absorption and compression resistance. The size of and number :f.slots provided in the ring spring may be selectd as appropriate to provide the desired compressive characteristics of the disc. [00126] The axial displacemnit of the ring spring 258 may be limtite by decreasing the depth of the pocket 260, by decreasing the width of the slot 262;,by .increasing the thickness and/or length o the shank 276, or by a combination of ny or all of these options. Alternatively, a coil springor elastic layer (both not shown) may be supplied in the pocket 260 to provide an upward bias to the ring spring 258.

[00127] The disc 250, as previously stated, also includes an upper endplate 252.

Preferably, the inner surface of the upper.endplate 252 includes a mating surface 280 which is dimensioned and configured to mate with the top surface of the enlarged body section 214 of the cap 256. Preferably, the mating surface 280 on the upper endplate 252 has a concave surface configured to articulate with a convex surface formed on the top surface of the cap 256. Alternatively, the mating suface 280 may comprise a convex surface and the top surface ofthe cap 256 may be concave. As previously described in relation to other embodiments,.the degree of curvature may be adjusted for either or both surfaces in order to provide the desired articulation and/or translation between the upper endplate and the cap .256.

[00128] In an alternative embodiment, the mating surface 280 is provided as a separate piece from the upper endplato. 52. The mating surface 280 in such a case may comprise a material different from that of the endplate 252 (for example, the erid:plate may i betitanium while the mating surface maybe a UHMWPE), The articulating surfaces of Sdisc 250 may also include a surface polish or similar wear reducing finish such as diamond Sfinish, TiNi finish, etc. in order to minirize wear, decrease particle generation, and increase ;dise li.

I[00129] In an alternative emidiment, the separate cap 256 may be elimiated, and the ring spring 256 may incorporatea' convex upper surface 264 configured to articulate Swithin the mating surface 280 of the upper endplate 252.

[00130] The disc 250 of this. mbodiment may comprise the additional features described previously with respect to the:ther embodiments, such as migration tesistant structures, permanent fixation features such as porous surfaces or coated surfaces, and/or implant instrument attachment, guiding,.and retaining structures may be included on Sendplates 252, 254. Furthermore, the outer surfaces of the upper and lower endplates 252, 254may be substantially flat, wedge-shaped, etc. The outer surfaces of the upper and lowvir j endplates 252; 254 may also be dome shaped with their radii defined in the sagttal and WO 2004/016217 PCT/US2003/025536 coronal planes to generally match the shape of the ends of the adjacent vertebra, thereby prviding a better fit in situ. The outer:irfaces may further comprise at east twe groove, slot, or other features appropriate to allow.the disc to be engaged by an insertion instrument.

Preferably, the.upper and lower endplates 252,254 are made from metal. However, the upper.and lower endplate 252,254 may ilternativelybe made from other materials as .prviously described.

S 00131] Disc 250 may also include stiffness restoration features such as an elastic membrane, an elastomer ring, bellow, springs, or fluid as previously discussed in; relations to other embodiments. Disc 250 may also incorporate any of the shock absorbing .feetures previously discussed in relatio. to other embodiments.

(00132] Depending on the location of the spine where the. disc 250 is implanted.

the disc 250 preferably restores height, lordosis, stiffness, offers compression stiffiess, and allows a range of motion similar to that described in relation to previous embodiments.

[00133] As a result of the materials, geometry, and components used, disc 250 can allow flexion/extension, lateral bending, axial rotation, and translation, depending oi the loading conditions. In addition under various spinal loading conditions the ring spring 258 can compress varying amounts. Tis varying compression of ring spring 258 allows for a moving instantaneous axis of rotation. In addition, the ring spring 258:pennits different regions of the disc 250 to compress varying amounts.

[00134] With reference to Figure 8, a sixth exemplary embodiment of an intervertebral disc 300 is shown. Disc 300 has a generally circular shape with an upper endplate 302, a lower endplate 304, and, awinged leaf spring 306 having lateral ends 310.

The disc 300, however, may take on oth r shapes that preferably conform geometrically and anatomically with adjacent vertebral bodies, including, but not limited to, kidney-bean shape, oval, annular, ellipsoid, C-shape, D-shape etc. Other features described previously with respect to the other embodiments, such as migration resistant structures, permanent: fixation features and/or implant instrument attachment, guiding, and retainingstructures may also be included on the outer surfaces of endplates 302, 304. Furthermore, the outer surfaces of the endplates 302, 304 may be substantially flat, wedge-shaped, etc. The outer surfaces of the upper and lower endplates 302, 304 may also 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 in situ. Preferably,.the.upper and lower endplates 302, 304 are made from metal.: However, the upper and lower endplate 302,304 my alternatively be made from other materials as already described.

WO 2004/016217 PCT/US2003/025536 [00135] As shown, the lower efdplate 304 preferably includes a cuitiou308 apoc':: on its inner surface,, the cut-dut 308 configured to receive at least a center portion of winged leaf spring 306. The lower endplate 304 may support the winged leaf :spring 306 along at least a portion of its lateral ends 310, and the center portion 314 of the leaf spring 306 sits within the cut-out 308, there being a gap between the bottom surface of the leaf spring 306 and the bottom surface of the cut-out 308. Thus, when the leaf spring is subjected to an axial compressive load, the lateral ends 110 may flex, allowing the center portion 14 of the leaf spring to be pressed down into the cut-out 308 until the bottom surfaceof the center portion contacts the bottom surface of the out-out 308. The size of the initial gap between the leaf spring and th:ecutout may be selected, along with the stiffhess 'of the lateral ends 310, to achieve a desired compressive stiffness, as well as a maximum axial compression, of the disc 300. The lateral ends may have stiffnesses that are .substantially equivalent, or their stiffness may be substantially different. Likewise, the Sbottom of the cut-out 308 may be substantially flat, or it may be angled to allow greater deflection of the center portion of the leaf spring in a desired direction. The stifXesses and gaps may be selected as appropriate to mimic the properties of the patient's nornal intervertebral disc, or as appropriate for the particular procedure.

-[00136] Further, the depth of the cut-out 308 may be preferably deep enough to allow the winged leaf spring 306 to flex however, it is more preferable that the depth of the cut-aut 308 is not so deep as to prevent failure of the flexing portions of the winged leaf spring 306 as flexing of the winged leaf spring 306 provides shock absorption and compression resistance which is preferably designed in disc 300 to mimic the compression .resistance and shock absorption characteristics of the natural intervertebral disc, or that provides the compression resistance appropriate to the particular procedure,.

[00137] Although cut-out 308 is.shown as having a rectangular shape, the cutout 308 may take on any other shape including, but not limited to circular, oval, elliptical, kidney-bean, or rectangular. The cut-fot 308 may be larger in dimension than the central bodyportion 314 of winged leaf spring 306 thus allowing for translational moirement of the winged leaf spring 306 within the cut-out. By allowing translational movement, a moving instantaneous axis of rotation is created which more naturally replicates the motion.of a natural intervertebral disc.

[00138] The disc 300 may inclqde an upper endplate 302 having in inner surface comprising a mating surface 316 which is dimensioned and configured to mate with the articulating surface 312 on the central body 314 of the winged leaf spring 306.: Preferably, the mating surface 316 is concave. Alterntively, however, the mating surface may have a WO 2004/016217 PCT/US2003/025536 convex profile, and the mating surface 3;.6 of the upper endplate 302 may be convexi and the articull$ak g suface 312 of the central body 314 may be concave. As discused previously in relation to other embodimbnts, the degree of curvature of the concave/convex surfaces may be selected to provide the desired amount of articulation to mimic the properties of the normal intervertebral disc, or may be as required for the particular procedure.

[00139] In an alternative embodiment the lateral ends 310 of the winged leaf spring 306 may have a constant thickness, length and width. Alternatively, the lateral ends 310 may have a variable thickness, lengh and/or width. The transition from the lateral: ends 310 to the central body 314 may be gradual such that the thickness gradually ifcreases from the outer periphery of the lateral edge 310 toward the articulating surface 312 Or it may be fairly abrupt. In addition, the winged leaf spring 306 may include one or more slots or grooves in either the lateral ends (not shown) to further increase the spring's flexibility.

[00140] Although shown as laving a rectangular shape, the winged leaf spring 306 may be any other shape including oval, circular, elliptical, kidney-bean, etc. Preferably the shape of the winged leaf spring 306 matches with the shape of the cut-out 30.8 fbnned on the inner surface of the lower endplate 304. The winged leaf spring 306 is ireferably formed from materials including, for example, ceramics, composites, polymers or metals, such as cobalt-chromium alloys, stainless steel and titanium alloys.

[001413 Alternatively, the disc 300, may include a lid or ring member (not Sshown), configured to retain the winged leaf spring 306 in the cutout 308, thus preventing the spring 306.from dislodging. In thisiinstance, the lid or ring member may be attached to the lower endplate 304 after the winged leaf spring 306 is placed within the.cut-out 308.

The lid or ring member may be attached to the lower endplate 304 by any fixation means known in the art including, but not limited to pins, screws, welding, bonding, press-fit, etc.

[00142] Disc 300 may also include stiffness restoration features such as an elastic membrane, an elastomer ring, bellow, springs, or fluid as previously discussed in relation to various other embodiments.: Disc 300 may also incorporate additional shock Sabsorbing features as previously described in relation to other embodiments, for example, manufacturing portions of the disc fron elastomeric material, etc.

[00143] In addition, the articulating surfaces of disc 300 may be provided with a surface polish or similar wear reducingflnish such as diamond finish, TiNi finish, etc. in order to minimize wear, decrease particle generation, and increase disc life.

[00144] Depending on the l.cation of the spine where the disc 300 is implanted, the dise 300:preferably restores height,:. atural spine curve (or sagittal balance), stiffiess, WO 2004/016217 PCT/US2003/025536 offers compression stiffness, and allows.a range of motion similar to that described in relation to previous embodiments.

[00145] As a result of the maerials, geometry, and components used, disc 300 can allow flexion/extension, lateral bending, axial rotation, and translation, depending on the loading conditions imparted on the intervertebral disc- [00146] With reference to Figure 9, a seventh exemplaryembodiment of an i intervertebral disc 350 is shown. Disc 350 has a generally circular shape with an upper, endplate 352, a lower endplate 354, a leaf spring 356 and an articulating cap 358. However, the disc 350 may take on other shapes that preferably conform geometrically and anatomically with adjacent vertebral bodies, including, but not limited to, kidney-bean shape, oval, annular, ellipsoid, C-shape, D-shape etc. Other features described previously with respect to other embodiments, such as migration resistant structures, permanent fixation features and/or implant ifistrument attachment, guiding, and retaining structures may be included on endplates 352, 354. Furthermore, the outer surfaces of the upper and lower endplates 352, 354 may be substaitially flat, wedge-shaped, etc. The outer surfaces of the upper and lower endplates 352, 34may also be dome shaped with their radii defined in the sagittal and coronal planes to generally match the shape of the ends of the adjacent vertebra, thereby providing a better fit in situ. Preferably, the upper and lower endplates 352,354 are made from metal. However, the upper and lower endplate 352,354 may altematively be made from other materils, as previously described.

[00147] As shown, the lower endplate 354 may comprise a first recess 362 defined by a pair of first shoulder members 364. These shoulder members 364 are configured to support leaf spring 356 along a bottom surface of the.leaf spring near its outer perimeter, creating an axial gap between the leaf spring 356 and the recess 362. Thus, when an axial load is applied to the top surface of the leaf spring it may flex toward and into the recess. The pair of first shoulder members 364 may be integrally fortmed -with the lower endplate 354 or they may comprise separate pieces.

[00148] The lower endplate:354 further may have a pair of second shoulder; members 365 located axially above and radially outward from the first shoulder members 364. The second shoulder members 365 are configured to engage the perimeter edge of the leaf spring 356, to retain the spring laterally translationally) to ensure that the leaf spring remains centered with respect to.the first shoulder members 364 and the.recess 362, Sthus assuring appropriate spring flexion. The second shoulder members 365 may-be configured to restrain the leaf spring so as to prevent all translational movement.

Alternatively, however, the second shoulder members 365 may be laterally offset fromn the WO 2004/016217 PCT/US2003/025536 Sleaf sping in at least one direction, thus.allowing the leaf spring to translate in. e at least one direction. By allowing such translafna.movement, a moving instantaneous axis of rotation is created, which more naturally replicates the motion of a natural intervertebral :disc,.

.[00149} A cover plate 360 maybe provided to cover the leaf spring,preventing -the leaf spring from moving axially out .f engagement with the pairs of first and second shoulder members 364- In this embodiment, the cover plate 360 may be attached to the top surface of the pair of second shoulder members 365. The cover plate 360 may.be attached to the second shoulder members 365 hyny fixation means known in the art including, but :not limited to press-fit, welding, pins, screws, bonding, etc. The cover plate 360 may have San outer perimeter sized to approximate the outer perimeter of the lower endplte 354, and an inner opening 369 sized to accept an. aticulation element (to be discussed in more detail below). The cover plate 360 inner opening may include an upwardly extendinginner edge 367 that may act in combination with a.'orresponding surface on the upper endplate 352 to limit articulation of the dise 350. The co:er plate may also be configured to accept a disc insertion instrument. The embodiment poFigure 9 illustrates the leaf spring 356 as aseparate element from the lower endplate 354, however, in an alternative embodiment shown in.Figure 9a, the leaf spring 356 nay be integrally formed with the lower endplate 354.

[00150] The leaf spring 356:iay be a spring-like element that flexes under axial loading to provide shock absorption, flexion and compression resistance. Tholeaf spring 356 imay haves uniform thickness, or its thickness may vary. In the embodiment illustrated Sin Figure 9 the leaf spring has a greater thickness in the center than:at its ends; in the Sembodiment illustrated in Figure 9a, the leaf spring is thicker at the center and:the ends, and has thinner segments between the ends1and the center, rendering the leaf spring with a :waved shape when viewed in cross section. The leaf spring may have any thickness appropriate to provide the required shock absorption, flexion and compressionriesistance.

[00151] The leaf spring 356 iay be formed from any appropriate material knowi in the art, including, for example,;ceramics, composites, polymers, or metals such as cobaltchromium alloys, stainless steel Oad titanium alloys.

[00152] Articulating cap 3S!iay be provided with a convex uppec articulation surface 368 and with a lower, leaf spring-engaging, protrusion 370. The articlation surface 368 inay be configured to mate and articulate with a mating surface 371 formed on the inner surfice of the upper endplate 352. Theinating surface 371 may comprise a concave surface corresponding to the convex surface of the articulating cap 358. Altematively, the WO 2004/016217 PCT/US2003/025536 upper endplate mating surface 371 may e: convex and the top surface of the articilating cap 358 may be concave. The curvatures of .ie respective articulation surface 368 and mating surface 371 may be selected to provide te appropriate type and amount of articulation and/or translation to mimic the movement of the patient's natural disc, or as required for the .particular procedure.

(00153] The mating surface 371 of the upper endplate 352 may be integral with the endplate, or as illustrated in Figure 9a it may be formed as a separate piece and attached to the endplate using any appropriate fixation method known in the art, and as previously described for other embodiments. When formed as a separate piece, the mating surface 371 may comprise a material different from that of the endplate, such as the various materials described as appropriate for articulation surfaces in relation to other embodiments. The mating surface 371 may be recessed into.a raised portion 372 of endplate 352, which may allow the endplate 352 to be relatively thin without limiting the radius of curvature that may be provided for the concave mating surface 371 and/or requiring the mating surface to be :too shallow.

I[00154] The raised portion.372 of the upper endplate 352 may comprise a raised face 374 having a raised face height "Lq. The raised face 374 may be configured to engage the upwardly extending inner edge 367;.f the leaf spring cover plate 360 to limit articulation of the disc 350 in at least one direction. Alternatively, the raised face 374 and the upwardly extending inner edge 367Taay be configured to limit articulation.ofthe disc in all directions. In one embodiment, the .raised face 374 and inner edge 367 may be configured to limit articulation of the disc in a single plane only, the medial-lateral plane). The raised, face 374 and inner idge 367 may comprise any dombination of configurations appropriate to provide the disc 350 with the desired range of articulation in all planes. Thus, the raised face 374 height may be different at different locations about the disc, for example, the height tI" may be smaller on the anterior and posterior sides of the disc 350 and greater on the lateral sides of the disc, thus controlling the degree of articulation in the anterior-posteriordirection. Alternatively, the raised face 374 and inner edge 367 may comprise mating surfaces, such as flat faces, correspondingly curved surfaces, angled faces, stepped faces, etc;, to control the degree of articulation of the disc in the desired direction.

[00155] The bottom surface of the articulating cap 358 may further comprise a protrusion 370 which is dimensioned' an configured to mate with a groove 366 formed on the upper surface of the leaf spring 356.. Thus, the cap 358 may be at least partially restrained within groove 366. In one embodiment, groove 366 may be sized the same or WO 2004/016217 PCT/US2003/025536 :only slightly larger than the protrusion 370, thereby rendering the cap restrained transversely. In an alternative embodi nt, the groove may be larger than theprotrusion in at least one direction along the anteior-posterior axis), thus allowing the cap 358 to Smove transversely translate) in that ;irection during operation. By allowing translational movement, a moving instataneous axis of rotation is provided. This moving instantaneous axis of rotation may more naturally replicate the motion of a natural interv erebral disc.

[00156] Alternatively, the protrusion 370 may be rigidly secured within the groove'366, thus permitting no translatipual movement.

[00157] It is noted that although the groove and protrusion are illustrated as haying substantially corresponding rect gular shapes, the protrusion 370 and groove:366 may take on any other appropriate shapeik'nown in the art including, but not limited to circulars oval, ellipsoidal, etc., to provide the requisite translational freedom.

[00158] In an alternative embodiment, shown in Figures 9a through 9c, the leaf spring 356 may comprise a post 380 a!the cap 358 may have a groove 382 for receiving the post 380. The groove 366 and post 380 may be sized and configured to allow translation of the cap 358 with respect ia the lower endplate 354 in at least one direction.

When the groove 366 and post 380 are ionfigured to allow translation of the cap 358; the cover plate 360 also must be configured so that the translating cap 360 does not interfere with the cover plate center opening 369, Thus, in such a case, the center opening may be elongated or rectangular in the direction of translation.

[00159] The upper endplate352 may include a recess 384 for receiving an articulating insert 386, the insert having a concave surface 385 configured to articulate with the convex articulating surface 368 of the cap 358. As previously described, providing a concave articulating insert 384 may provide the surgeon with greater flexibility in selecting the appropriate material to comprise th articulating surfaces while not affecting the material of the endplates 352, or otherwse affecting the design or installation of the other components of the disc 350. Thus the nsert 384 may be formed of any appropriate material known in the art including but not limited to polymers including rigid polymers, such.as PEEK or UHMWPE, ceramics, composites or any combinations thereof.

[00160] When an articulating insert 386 is provided, the recess 384 in the upper endplate 352 may comprise a surface cbdfigured to retain the insert 386. The recess may comprise a radial ridge configured to fit viithin a corresponding radial groove in the insert suci that the insert may be snapped intdi the recess. Alternatively, the insert may be.

attached to the recess via a press fit, by using a bonding agent, or any combination thereof.

34 WO 2004/016217 PCT/US2003/025536 [00161]. In an alternative embodiment, disc 350 may also include stiffness restoration features such as an elastic membraie, an elastomer ring, bellow, springs, or fluid as previously discussed in relations to other embodiments. Disc 350 may also incorporate 'additional sho.cF absorbing features as previously discussed in relations to other embodiments..

[00162] In addition, as discussed with previous embodiments, the articulating surfaces of disc 350 may include a surface polish or similar wear reducing finish such as diamond finish, TiNi finish, etc. in order to minimize wear, decrease particle generation, and increase disc life.

[.00163] The disc 350 endplates may have migration-resistant structures provided on the outer surface of at least one or both ofthe endplates to impede movement, dislodging, or expulsion of the endplates within and from the ends of the adjacent vertebrae.

The migration-resistant structures inclhde, but are not limited to, flaps, spikes, teeth, fins, Sdeployable spikes, deployable teeth, flexible spikes, flexible teeth, alternatively shaped teeth, insertable or expandable fins, screws, hooks, serrations, ribs, and textured surfaces.

[00164] Furthermore, the upper and lower endplates of disc 350 also may be coated with a bone growth inducing or conducting substance to promote bony ingrowth to permanently secure the disc to the adjacent vertebrae. Alternatively, the upper and lower endplates may have a roughened surfade; a porous surface; laser treated endplate layers; integrate an osteoconductive/osteoinduptive scaffold; or may be provided with or made from an integral osteoconductive and/or osteoinductive material to promote bony inigrowth.

[00165] Depending on the location of the spine where the disc 350 is implanted, the disc 350 may restore height, lordosis, stiffness, offer compression stiffness, and allow a range of motion intended to mimic that of the natural intervertebral disc, or as required for :the particular procedure.

[00166] As a result of the nmterials, geometry, and components used, disc 350 can allow flexion/extension, lateral bending, axial rotation, and translation, depending on the loading conditions imparted on the intervertebral disc.

[00167] With reference to Figure 10, an exemplary installation procedure will be described. Generally speaking the disq 400 may include an upper endplate 402, a lower endplate 404 and a core mechanism 4.6, the core mechanism being any spring, slotted core, ring spring, leaf spring, coil spring, elastomer, fluid filled or articulating disc previously described herein. The intervertebral disc 400 may be implanted in a modular fashion, for Sexample, the endplates 402, 404 of disc 400 may be inserted into the intervertebral cavity using instruments such as a distractor and/or holder instrument. The intervertebral disc WO 2004/016217 PCT/US2003/025536 space may then.be distracted using a standard spinal distractor which engages tie endplates 402, 404. Trial spacers may then be used to determine the appropriate size o the r-re .mechanism 406 to be inserted in the resulting disc space. In an exemplary.emtodiment, the core mechanism, 406 is inserted and attached tb endplates 402, 404 through the use of a dovetail, slot, dr similar connection. This modular insertion technique may avoid overdistracting the intervertebral space, whidh may damage surrounding tissue and/or blood -vessels, [00168] Alternatively, the inervertebral disc 400 may be inserted preassembled with the use of particular insertion tools. For example, an endplate holding clip may be used that allows the endplates 402, 404 to be held and locked in a parallel and spaced relationship as they are inserted into the intervertebral space. Once implanted, the clip may be unlocked and removed from the endplates 402,404. The clip may then be i=emoved from the intervertebral space. In addition, the disc 400 may be implanted in a compressed state to prevent over-distraction. The introduction of the disc 400 in a compressed state may be accomplished via a surgical insertion instrument or by an interal mechanism located in the disc 400.

[00169] An anterior, lateral,.ar:anterolateral surgical approach maybe used for the intervertebral disc 400. Furthermore,-depending on the intervertebral disc 400 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 suiface of the endplates 402, 404 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 hatural Anterior Longitudinal Ligament may be attached directly to the disc of to the adjacent vertebral bodies. Attachment ofthe Anterior Longitudinal Ligamentimay 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.

[00170] While various descriptions of the present invention are decribed 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.

[00171] Further, it should be inderstood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains. For example, some portions of the implants disclosed her.inmay be WO 2004/016217 PCT/US2003/025536 foimed of bone, such as allografts, autografts, and xenografts, which may be partially or fidly demmeralized. In addition, some implants may include bone ms:erial or other bone growth inducing material in their interiors or on/in their endplates. Such substances in the interiors may be permitted to interact with-the surrounding anatomy, as with channels or other holes formed in the implant walls. Also, intra and post-operative alignment markers may be used to assist with implantation of the intervertebral discs. Furthermore, the interyertebral 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 theendplates, 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 -rth herein that are within the scope and spirit of the present invention are to be inoluded'as further embodiments of the present invention.

The scope of the present invention is aecordingly defined as set forth in the appended claims.

Claims

1. An articulating intervertebral implant for implantation between first and second Svertebrae, the implant comprising: IND a first endplate having a first inner surface and a first outer surface for engaging the first vertebra; t a second endplate having a second inner surface and a second outer surface for NO engaging the second vertebra; r a cover plate coupled to the first endplate, the cover plate including an inner opening; a first insert member adapted to be received within the inner opening of the cover plate, the first insert member having a first articulating surface operatively associated with the second endplate so that the first and second endplates can articulate with respect to each other; and a spring component located between the first insert member and the first endplate.

2. The articulating implant of claim 1, wherein the spring component is a leaf spring.

3. The articulating implant of claim 2, wherein the leaf spring has first and second resilient ends configured to engage the first endplate, and a length.

4. The articulating implant of claim 3, wherein the first endplate further comprises a recess having a length smaller than the length of the leaf spring so that when the leaf spring engages the first endplate, the first and second resilient ends are supported on the inner surface of the first endplate.

The articulating implant of claim 4, wherein the leaf spring further comprises a central portion, the central portion of the leaf spring being axially spaced from the first inner surface of the first endplate.

6. The articulating implant of claim 5, wherein the first endplate and leaf spring are configured so that the leaf spring can translate in at least one direction with respect to the first endplate. 38 728749 amend pages

007. The articulating implant of any one of claims 2 to 6, wherein the first endplate Sfurther comprises a pair of first shoulder members for supporting the leaf spring on either end thereof so that a bottom surface of the leaf spring is axially spaced from the first inner surface of the first endplate.

8. The articulating implant of claim 7, wherein the first endplate further comprises t a pair of second shoulder members located axially above and radially outward from the Spair of first shoulder members, the second shoulder members contacting a perimeter IDedge of the leaf spring so that the leaf spring is laterally retained.

9. The articulating implant of claim 8, wherein the pair of second shoulder S 10 members is configured to prevent all translational movement of the leaf spring.

The articulating implant of claim 8 or 9, wherein the pair of second shoulder members is configured to enable the leaf spring to translate in at least one direction.

11. The articulating implant of any one of claims 2 to 10, wherein the leaf spring includes a first surface and a second surface, the first surface being associated with the first endplate, the second surface being associated with first insert member.

12. The articulating implant of claim 11, wherein the first endplate further comprises a recess formed in the first inner surface, the leaf spring having a length sufficient to span the recess so that at least opposite ends of the leaf spring are supported by the first inner surface and a central portion of the leaf spring is positioned over the recess so that the central portion moves into the recess when a compressive force is applied to the second surface of the leaf spring.

13. The articulating implant of claim 11 or 12, wherein the first endplate further comprises a perimeter edge configured to allow the leaf spring to translate with respect to the first endplate in at least one direction.

14. The articulating implant of claim 11 or 12, wherein the first endplate further comprises a perimeter edge configured to prevent the leaf spring from translating in at least one direction. 39 728749 amend OOaes 00

15. The articulating implant of any one of claims 2 to 14 wherein the leaf spring further comprises a top surface, the top surface of the leaf spring including a recess to accept a projection formed on the first insert member. NO

16. The articulating implant of claim 15, wherein the recess and projection enable the first insert member to translate in at least one direction relative to the leaf spring.

17. The articulating implant of any one of claims 2 to 16, wherein the cover plate NI engages at least a portion of the first endplate and covers at least a portion of the leaf N spring to prevent the leaf spring from axially disengaging from the first endplate. t'q

18. The articulating implant of claim 17, wherein the cover plate further comprises at least one raised ridge to contact at least one raised ridge associated with the second endplate to limit articulation between the endplates in at least one direction.

19. The articulating implant of claim 18, wherein the raised ridges have corresponding flat surface profiles.

The articulating implant of claim 18, wherein the raised ridges have correspondingly angled surfaces.

21. The articulating implant of any one of the preceding claims, wherein the first and second endplates are formed from a material selected from the group consisting of metal, polymer, ceramic and composite.

22. The articulating implant of any one of the preceding claims, wherein the first and second endplates are formed of bone material selected from the group consisting of cortical, cancellous, allograft, autograft, xenograft, demineralized and partially demineralized bone.

23. The articulating implant of any one of claims 2 to 22, wherein the leaf spring is integral with the first endplate.

24. The articulating implant of any one of claism 2 to 23, wherein the leaf spring further comprises a top surface, the top surface of the leaf spring includes a post and the first insert member includes a groove, the post being receivable in the groove. 728749 amed pages 00

25. The articulating implant of claim 24, wherein the post and groove enable the first insert member to translate in at least one direction relative to the leaf spring.

26. The articulating implant of any one of the preceding claims, further comprising IDO a second insert member located between the second endplate and the first insert member, the second insert member having a second articulating surface for contacting tt' the first articulating surface formed on the first insert member. N\ CI

27. An articulating intervertebral implant substantially as hereinbefore described CI with reference to Figures 9 to 9c. 41 728749 amend pages