ZA200501542B - Controlled artificial intervertebral disc implant - Google Patents
Controlled artificial intervertebral disc implant Download PDFInfo
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- ZA200501542B ZA200501542B ZA200501542A ZA200501542A ZA200501542B ZA 200501542 B ZA200501542 B ZA 200501542B ZA 200501542 A ZA200501542 A ZA 200501542A ZA 200501542 A ZA200501542 A ZA 200501542A ZA 200501542 B ZA200501542 B ZA 200501542B
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- South Africa
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- intervertebral disc
- endplate
- disc according
- disc
- leaf spring
- Prior art date
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Description
CONTROLLED ARTIFICIAL v INTERVERTEBRAL DISC IMPLANT
[0001] The invention is related to devices and methods for the treatment of auma and diseases of the spine. More particularly, the invention relates to intervertebral 5 replacement.
[0002] A variety of conditions'such as spondylolysis, disc hemiation, pmpression of spinal cord nerve roots, degenerative disc disease, and trauma are known to
Ei severe discomfort, requiring medical attention. Among the procedures currently used 1¢ alleviate such conditions are spinal fusion, such as intervertebral and posterolateral fusion o arthrodesis. In these procedures, two adjacent vertebral bodies are fused togethef: | The cted intervertebral disc is first excised; and an implant is inserted which accommodates tt ne growth between the two vertebral bodies to effectively bridge the gap left by the disc removal. -A number of different implant materials and implant designs have been used for : sion with varying success. Although intervertebral and posterotateral fusion are widely used, drawbacks to their use include a reduced physiologic range of motion and other fusion ralated complications such as degeneration of adjacent discs and destabilization of the i ional spinal unit. As aresult, alternative treatments with {fewer complications, but i ilar efficacy 10 fusion, are desirable, One such alternative to spinal fusion is arthroplasty ad the use of a prosthetic or artificial disc,
[0603] In general, arthroplasty is used in the replacement of diseased joints,
Arth plasty involves a set of procedures directed to maintaining motion of the joint, eby preserving its integrity and keeping 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 procedures may be used. For example, i ositional 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 ‘ 30 finger joints. Total joint replacement, or total joint arthroplasty, replaces the entire diseased oe with an artificial prosthesis and, in recent years, has become the operation of clivice . for most knee and hip problems. - [0004] Hip and knee replacements are particularly widespread with nearly 300,000 hip replacements and about as many knee replacements performed in thie United
Lo States i02001. With respect to the knee and hip joint replacement surgeries, there are several implants or prosthetics available. : For the hip prosthetic, in an exemplary design, ; . there are two components, one is a metal all 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, oo 8) The metal pieces are generally formed from stainless steel, alloys of cobalt and chrome, titanium, and alloys of titanium; the plastié pieces are generally formed from high-density : pblyethylene, For the knec prosthetics, ian exemplary embodiment, metal and plastic Co components are again used to replace the damaged bone ends and cartilage. The metal ) pieces are generally formed from stainless steel, atloys of cobalt and chrome, titanium, and
C10 alloys of titanium; the plastic pieces are generally formed from high-density polyethylene. oo
[0005] Although the evolution of spinal arthroplasty and the use of prosthetics ~~. ir} the spine has been similar to that of other joints in the body, evolving from fusing the ~~ jdint to replacing the functional joint, the advent of spinal athroplasty, however, has been sower than arthroplasty in other major joints in the body. A few of the possible redsons why spinal arthroplasty has been delayed are that spinal problems related to disc © Co degeneration are difficult to diagnose, spinal procedures are typically crisis-driven and thus © chnservative solutions such as fusion are acceptable, and spinal anatomy is complex. )
[0006] Over the past 40 years spinal arthroplasty technologies have been under . dévelopment and in the last 10 years spinal arthroplasty has won the attention of leading ©20 srgeons and implant manufacturers. The evolution of spinal arthroplasty essentially began inthe 1950’ and one of several emerging concepts was the spherical concept of the disc : prostheses. The spherical concept is simply the placement of a ball, essentially circumferential, In the cavity of the nucleus pulposus afier a discectomy procedure has been -
P ormed, The annulus is kept in place andthe ball serves as a nucleus replacement 7 oe Various materials have been experimented with for the spherical concept, For example, in the early 1960’, implants using silicone ball bearings were implanted into the carvical regions of patients, but the outcomes were uncertain. In the mid 1960°s, stainless- : stiel (ball bearing) prostheses were implanted into patients. The results of the procedure CL were initially promising but over time the disc spaces lost height due to subsidence of the © 30 steel balls into the vertebral bodies. Presently, the concept of a spherical prosthesis . continues to be examined using different materials, the latest of which is a modified carbon - . hger. = : . : {0007} Another emerging concept is the mechanical concept design. “The : mechanical concept design is essentially a total disc replacement product which is intended
I the range of motion of the vertebral motion segment unit. These devices are often :
comprised of metallic endplates fixed to the adjacent vertebra) bodies via a stabilization inp a core formed from polyethylene or other polymeric materials: Co termatively, instead of a core, bearing surfaces can be uscd, the bearing surface materials ' being ceramijc-on-ceramic, metal-on metal; or metal-on-polyethylene. The roechanical : s design concept is based on the same principles as joint reconstruction products, such as’ knee and hip replacements, and a variety of mechanical design prostheses concepts have been proposed and continue to be proposed. :
[0008] Another concept is the physiological concept. The physiological concept uses a hydrogel, elastomer, or polyurethane-based core which is intended:to restore the disc fimction by absorbing and emitting fluid between the patient’s vertebral endplates, thi e also maintaining the natural shock absorbing or cushioning function of the disc. The a corncept devices are generally considered only a partial solution as they are dbsigoed to replace only the nucleus or a portion of the disc. SE - [6609] = All of the approaches £6-dise replacement are aimed at some or all of the following: alleviating discogenic pain, restoring range of motion, maintaining the natural shock: absorbing function of the disc; restoring normal form or disc height, and restoring physiological kinematics. Generally, four exemplary types of artificial intervertebral discs have been developed for replacing a portion or all of an excised disc: €lastomer/fluid filled dipes, ball and socket type discs, mechanical spring discs and hybrid discs. | [0010] Elastomer/fluid filled discs typically include an elastomer cushion ora flnid filled chamber positioned between lower and upper rigid endplates. The cushions and c bers of these implants advantageously function, in mechanical behavior, similar toithe r oved intervertebral disc tissue. EE
[0011] : Ball and socket type discs typically incorporate two plate members ; havi g cooperating irmer ball and socket portions which permit articulating motion of the
F during movement of the spine. : A
[0012] © Mechanical spring discs typically incorporate one or more coiled ; springs disposed between metal endplates, “The coiled springs define a cumulative spring constant that is designed to be sufficient to maintain the spaced arrangement of the adjacent ‘vertebrae while allowing normal movement of the vertebrae during flexion and extension of E : thd spine in any direction. ; : CL oo : [001 3] The fourth type of artificial intervertebral disc, the hybrid disc . ingorporates two or more of the aforementioned design principles. For example, one known hybrid disc arrangement includes a ball and;socket joint surrounded by an elastomer sing.
. 0014] While each of the foregoing prostheses addresses some ui the problems = relating to intervertebral disc replacement; each of the implants presents significant ; - : dfawbaicks. Thus, there is 2 need for an intervertebral implant that accommodates the oo aatomy 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
Co siluplicity in design. More particularly, there is a need for a spinal disc implant which provides stability for supporting the high loads applied to the vertebrae, permits sufficient - mobility to allow the patient an approximate normal range of motion, provides for axial compression between adjacent vertebrae, and has shock absorption abilities. - ] SUMMARY OF THE INVENTION a. [oo1s3 The invention relates to an intervertebral disc that is preferably ddsigned to restore disc height and lordosis; allow for a natural range of motion, absorb shiock and provide resistance to motion and axial compression. Furthermore, the - infervestebral disc may be used in the cervical, the thoracic, or the lumbar regions of the ©! [0016] The intervertebral disc includes a body having a footprint thatis pri ferably conforming in size and shape with at least a poriion of the ends of adjacent vcore ‘The shapes of the intervertebral disc include, but are not limited to, circular, oval, ellipsoid, kidney-bean, annular, C-shaped, D-shaped, ctc. _ | [0017] In one embodiment, the intervertebral disc includes an upper endplate, a lower endplate, and an intermediate clastic membrane disposed between the upper and lower endplates. Alternatively, the elastic membrane may surround and encapsulate the cnliplates. 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
To spring clement being attached to the upper and lower endplates. Preferably, the spring element is attached to the lower endplate within a pocket or groove formed onthe inder 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. : i 30 [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 clement may have a hemi-spherical members on both ends to mate with co nding sockets formed on the inner surface of the upper and lower endplates. The dis may also be configured such that the disc generally contains a first spring element prs a plurality of second spring elements uniformly spaced around the fist
. spring element. The first spring element preferably having a stiffness and/Sr spribg’ ’ - cgristant which is greater than the stiffiess/of the periphery spring elements. : BN
X | 3 [0019] Furthermore, the disc may include a plurality of spring clement, . whereby only a portion of the spring elements may be attached to a herni-spherical tember, with the remaining spring elements being @ttached to the upper and lower endplates, Co preferably in pockets. In one exemplary embodiment, the first spring element wih be’ oo attached to a hemi-spherical member while the surrounding peripheral second spring no - clecents will be attached directly to the upper and lower endplates.
Co [0020] The disc may also include an elastomeric strut or ring in place of one or : : 10° al of the spring elements. Furthermore, the disc may incorporate casing members. : - i [0021] The disc may also include a fluid disposed within the interior volume . and a valve for permitting insertion of and removal of the fluid. , : oo | [0022] "The upper and lower enidplates are preferably formed of metal, such as titanium, stainless steel, titanium alloys, cobalt-chromium alloys, or amorphous alloys; :
Alternatively, however, the upper and lower endplates may be formed of ceramics, : ios polymers, such as poly-cther-tlier-ketone (i.e., PEEK) or an ultra high ST oi m lecular weight polyethylene (i.e., UHMWPE), bone, including cortical, cancellous, : + ‘aljograft; autograft, xenograft, demineralized or partially demincralized bone, or atiy other ei able to serve as load bearing supports. The materials chosen for the endplates, in eofubination with the desired fluid, are proferably selected to reduce the amount of wear, -and thus-increase the life of the joint. a SE : . | a [0023] : The outer surface of the upper and lower endplates may be substantially © At wedge-shaped, etc. The outer surfacesof the upper and lower endplates may; also'be : : ie shaped with their radii defined in the sagittal and coronal planes to generally match se of the ends of the adjacent vertebra. The dome shape allows the upper and lower en plates to better conform with the ends of the adjacent vertebrae for a better fit in situ,
[0024] The intervertebral disc also preferably includes migration-rosistant oo strhctures 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 - © adjacent vertebrae. The migration-resistant structures include, but are not limited 0; flaps, . ken teeth, fins, deployable spikes, deployable teeth, flexible spikes, flexible teeth, al atively shaped teeth, insertable or expandable fins, screws, hooks, serrations, ribs; and . textured surfaces. oo BE :
HEE . [0025] Furthermore, the upper and lower endplates also preferably coated with
Ti inducing or conducting substance to promote bony ingrowth to permanently
Co secure the disc (0 the adjacent vertebrae, Alternatively, the upper and lower eridplates may have a roughened surface; a porous surface; laser treated endplate layers; integrate an osteoconductive/osteoinductive scaffold; or may be provided with or made from an integral ) osteoconduptive 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 of bony ingrown | . (RT on - [0026] The upper and lower endplates may also have implant instrumentation attachment,’ guiding, and retainment structures. For example, the endplates may have holes, slots, treads, or a dovetail for implanting the implant and/or distracting the adjacent : vertebrae. For example, the disc may include a slot formed in the upper and/or lower : endplates, the slot being configured to receive an implant insertion instrument, a distragtor orboth, | . : : aE ; [0027] The upper and lower endplates may also preferably include articulating surfaces, thus providing the intervertcbral disc with greater mobility. The articilating - surfaces preferably including a surface polish or similar wear reducing finish suchas oo diamond finish, TiNi finish, etc. in order to minimize wear, decrease particle generation, : and increase disc life. 2 IE no [0028] In some embodiments, the interior of the disc may include a feaf spring oo attached on one end to the upper and/or lower endplate but unattached on the other end. oo
Disposed between the ends, the leaf spring preferably includes an enlarged convex - intermediatd section which mates, articulates, and slides with the inner surface of one of the endplates. Preferably, the unattached end of the leaf spring is attached to a roller by means of an axle, the axle allowing the roller to freely rotate thus permitting the leaf spring to” - move freely during the flexing of the spring! Cee bo [0029] In some embodiments, the interior volume of the disc includes’an “ articulating member which is attached to the ‘upper or lower endplate. The articulating CL member preferably being attached to one of the endplate by an intermediate shock” Co absorbing layer. The shock absorbing layer preferably being an elastomer, polymer fibers, - : polyurcthane, 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 . may be dimensioned and configured to provide flexion/extension, lateral bending, axial’
Lo To
. ' Tgtation, and/or translation, depending on the loading conditions imparted on the intervertebral disc. © [06031] The intervertebral disc thay be implanted in a modular fashion, if + : possible, or may be implanted preassembled. ‘An anterior, anteriolateral, or lateral surgical
Ss approach may be used for the intervertebral disc. Furthermore, depending on the itftervertebral disc to be implanted, a minimally invasive surgical method andfora’ . © simultaneous distraction and implantation Surgical method may be used. Also depending on the intervertebral disc te be implanted, the Anterior Longitudinal Ligament may be attached directly to the disc or to the adjacent ‘vertebral bodies. The Anterior Longitudinal
Ligament may be formed from partially demineralized or demineralized autograft, allograft, of xenograft. Alternatively, the Anterior Longitudinal Ligament may be formed from biocompatible materials such as elastomers, or braided polymers. To assist with the : itiplantation of the intervertebral disc, the intervertebral disc may include alignment :
[0032] To facilitate an understanding of and for the purpose of illustrating the present invention, exemplary and preferredifeatures and embodiments are disclosed in the. . adcomparying drawings, it being understood, however, that the invention is not firhited to thie precise arrangements and instrumentalities shown, and wherein similar reference characters denote similar elements throughout the several views, and wherein: - ; [0033] Figure lisa perspective view of a first embodiment of an artificial : : infervertebral disc according to the preserit jivention; REA © | | [0034] Figure 2is a cross-sectional view of the artificial intervertebral disc of ripe 1 taken along line A-A; ; A : : 4 [0035] Figure 2a is an alternate cross-sectional view of the artificial . intervertebral disc of Figure | taken along line A-A; 1 [0036] Tigre 2bisan alternate cross-sectional view of the artificial intervertebral disc of Figure 1 taken along line A-A;
[0037] Figure 2c is an alternats éross-sectional view of the artificial 30° intervertebral disc of Figure 1 taken along line A-A; . | [0038] Figure 2d is an alternate, cross-sectional view of the artificial
N intervertebral disc of Figure 1 taken along line A-A; . i [0039] Figure 3ais a side view of a deployable spike according to the present inyention.” - Ci - ,
. [0040] . + * Figure 3b is a side viéw. of another deployable spike according to. the © present invention. Co SE n [0041] Figure 3¢ is side view ofa flexible spike according to the present. nyention. Go
C5 | - [0042] Figure 3d is a side view of alternatively shaped teeth according to the + preséntinvention. A Cn i | [0043] . . Figure 3e is a side view of anchors according to the present invention. } ) [0044] Figure disa cross-sectional view of a second embodiment ofan oo . - artificial intervertebral disc according to the present invention; El © [0045] © Figure 4A isa side view ‘of the leaf spring and roller of the artificial intervertebral disc of Figure 4; | : | So : . [0046] Figure 5 is a cross-sectional view of a third embodiment of an artificial intervertebral disc according to the present invention; : So : [0047] "- Figure 6is a perspective view of a fourth embodiment of an artificial intetverteliral disc according to the present invention; Ce i 3 [0048] ) Figure 7is a perspective view of a fifth embodiment of an artificial intervertetiral disc according to the present irivention; a. : ¢ [0049] Figure 8is a perspective view of a sixth embodiment of an artificial Ce intervertebral disc according to the present invention; x : oo E i a [0050] Figure 9is a cross sectional view of a seventh embodiment of an. artificial intervertebral disc according to the present invention; - ’ }
[0051] Figure 9a is an alternate cross-sectional view of the seventl embodiment of an artificial intervertebral disc according to the present invention; 1 , [0852] - Figure 9b isan exploded view of the seventh embodiment shown is
Figure 9a; : te ol o [0053] Figure Sc is an exploded view of the seventh embodiment shown is - bese + mm " [0054] ~ Figure 10 is schematic view of a eight embodiment of an intervertebral diso according to the present invention. . 30 © DETAILED DESCRIPTION 05 THE PREFERRED EMBODIMENTS : Co
[0055] Any of a wide variety of different implant structures can be prepared . according to the teachings shown by the illustrative examples of the intervertebral discs ailtosed herein. The intervertebral discs of the present invention arc preferably designed ta restore the natural spinal curvature (or sagittal balance), disc height, to allow for a natural ’ range 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 ’ cervical, thoracic, and lumbar regions of the spine. Also, the intervertebral discs canbe 5s tailored for each individual patient allowing for disc characteristics appropriate for the iE iridividual patient. For example, and artificial disc may be provided having 2 pair of endplates 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. cn I i ~ {0057 Furthermore, the intervertebral discs may allow flexion, extension, feral bending, rotation, and translation. Flexion is movement that brings two parts ofa jdint 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 Co . away from each other; in the spine, this is a movement in which the spine starts straight and. moves into backward bending. Lateral bending is a bending movement toward a lateral side; in the spine, this movement generally; involves bending (lateral) and coupled rotation. : Rbtation is a movement that results in a portion of the spine twisting, rotating or turning with respect to the axis of the spinal column. Translation is a limited movement thatis generally iransverse to the axis of the spinal column. | o
[0058] Additionally, similar toa natural intervertebral disc, the artificial ~~ } infervertebral 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 . thie lize that does not move. The instantarieous axis of rotation is this line. A moving . instantaneous axis of rotation refers to the ability of the instantancous axis of rotation to ve (i.e, translate) as 3 result of different loading conditions; in other words, the location of] the instantaneous axis of rotation moves with respect to the disc. The preferred mean loation of the moving instantaneous axis of rotation for the lumbar region of the spine is preferably in the posterior half of the disc space or proximal to an adjacent (superior or inferior) endplate, preferably proximal to the inferior/caudal endplate, the preferred mean logation of the moving instantaneous axis of rotation for the thoracic region of the spine is ¢ preferably in the inferior portion of the disc space and proximal to the candal vertebral body extending posteriorly into the spinal canal, and the preferred mean location of the movihg a instantaneous axis of rotation for the cervical region of the spine is preferably in the oo half of the caudal vertebral body. -
oo [0059] Also similarto a naturdlintervertebral disc, the response characteristics of the artificial intervertebral disc are preferably non-linear. For example, in response to continized axial compression, the artificial intervertebral disc preferably undergoes a large initial amount of compression followed by rion-lincarly decreasing amounts of .$ compression. si + [0060] Referring to the accompanying drawings, preferred embodiments and features of the artificial intervertebral disc:vill be described in detail. It is to be noted however that these descriptions of specific émbodiments and features are merely : illustrative. It is contemplated that one or more features or elements of the various embodiments may be combined or used singularly, and that modifications of the various embodiments, as well as other embodiments are contemplated and will be apparent to those persons skilled in the art. i [0061] Referring initially to Figire 1, a perspective view of an exemplary first embodiment of an artificial disc 10 is show. Disc 10, preferably, has a generally kidney- bean shaped footprint which includes an anterior side 11, a posterior side 13, and first and ’ second lateral sides 185, 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.
However, the disc 10 may take on other shiapes that generally conform geometrically and anatomically with the adjacent vertebral bodies including, but not limited to circular, oval, : .20 ellipsoid, annular, D-shaped, C-shaped, etc. : ° : oo :[0062] As shown, disc 10 inclsdes an upper endplate 20, a lower endplate 22, and an intermediate elastic membrane 24, the elastic membrane 24 generally extending from the. upper endplate 20 to the lower endplate 24, preferably, proximate the outer ‘periphery of the disc 10. Altematively, the elastic membrane 24 may surround and éncapsulate the upper and lower endplates 20, 22. The elastic membrane 24 in cornbination with the-upper and lower endplates 20, 22 define an interior volume 26, [00631 The elastic membrane 24'preferably is formed from an elastomer such asipolyurethane, silicone, a braided polymer; or any other appropriate clastic material. The elastic membrane 24 may be permeable or s¢mi-permeable to allow fluid to flow into and out of the interior of the disc (as described in more 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
N soft tissue ingrowth between the endplates 12, 14 as well as contain any wear particles geherated within the interior volume. The elastic membrane 24 may be attached to the ubper and lower endplates 12, 14 by any fixation method known in the art including, but not : limited to, bonding agents, ultrasonic welding, screws, nails, mechanical wedging, and pins. - | [0064) Alternatively, the clasti membrane 24 may be in the form of abellow, . . : tHe bellow assuming an “accordion” or other flexible shape, enabling it to expand and. contract under the various loading conditions. The bellow may be rigidly attached to the
Co pper and lower endplates 12, 14 by any method known in the art including, but not limited da circular groove formed in each endplate 12, 14, bonding agents, ultrasonic welding, : screws, nails, mechanical wedging, and pins. Preferably, the bellow is made from a metal, : although other material such as elastomnersor polymers may be used, In an altemative embodiment, membrane 16 may be made of any appropriate non-elastic material known in the art. . | i Ll 1. [0065] With reference to Figuré 2, the interior 26 of disc 10 is shown.
Pleferably, the interior 26 of the disc 10 includes at least one spring element 30; and the spring element 30 may have a longitudinal axis. The spring may be oriented such:that its loigitudioal axis is oriented substantially perpendicular to the plane formed by each of the
SL per and lower endplates 20, 22. Alternatively, the spring may be oriented such that its. : axis forms an acute angle with at least one.of the upper and lower endplates. The spring : elpment may have a first end which contacts the lower endplate 22 within 2 packet or gipove 32 formed on the inner surface 40 of the lower endplate 22. Such a pocket.or . 20 grpove may prevent lateral displacement of'the spring with respect to the endplate: An upper end of the spring element 30 may engage an articulation member 34 havinga spring- enigaging surface 33 and an opposite substantially spherical surface 35 . The spring element 30 may be fixed to the pocket 32 and/or the articulation member 34 using any appropriate fikarion method known in the art including, but not limited to bonding agents, ultrasonic : welding, screws, nails, press-fit, and pins. - Alternatively, the spring element 30 and the culation member 34 may be integrally formed. SA
[0066] The spherical surface 38of articulation member 34 may be configured to ficulate within a correspondingly shaped socket 36 formed on the inner surface a3 of the upper endplate 20. The interface between the articulation member 34 and the socket 36 may approximate a ball and socket type contection, with the spherical articulation member ! 34 able to ‘articulate within the socket 36. The type and amount of articulation desired may didtate the curvature and arc of the spherical surface 35 provided on the articulation “ m | er 34 and socket 36. For example, ifthe spherical surface 35 has the same radius as of ccs then the disc 10 may provide greater support but more constrained movement. Alternatively, if the socket 36has a larger radius than the spherical girface 38, oo ’ the disc $0 may provide increased articulafion and/or translation. | :
[0067] In an alternative embodiment, the socket 36 may iricorporate a flattened portion which may pemnit the articulation‘tmember 34 to wranslate 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 asticulation member 34 and socket 36 to have contours other than spherical in order to achieve the desired articulation motion. Such other contours may comprise elliptical or egg-shaped, and multiply-spherical shaped in which theiarticulation member and the socket each may comprise at least two separate or cojoined spherical segments. Moreover, while the articulation member 34 and socket 36 are illustrated as having contours that generally permit mating of their respective surfaces, the corresponding surfaces may take on any appropriate shape to achieve the desired articulating mobility between the upper and lower endplates 20,22. : ° | [0068] While the disc 10 has been described as having the articulating member 34 associated with the lower endplate 22 aid the socket 36 associated with the upper endplate 20, the elements may be reversed 50 that the socket 36 and articulating element 35 : ae instead associated with the lower and upper endplates, respectively, Furthermore, the socket member may be provided integral with its respective end plate, such as providing a one-piece end plate with a hollow spherical‘inner surface. Also, the socket member and articulating element may comprise any appropriate material known in the art, such as titanium, stainless steel, polymers such as iiltra high molecular weight polyethylene, etc. - :
Furthermore, the articulating surfaces may include a surface polish or similar weat reducing : finish such as diamond finish, TiNi finish, etc. in order to minimize wear, decrease particle ‘generation, and increase disc life. Co : To
[0069] The spring element 30.may encompass any appropriate resilient member : known: 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 known in the art including, for example, polymers, composites, or metals such as.cobalt- chromium alloys, titanium alloys, stainless steel, shape memory alloys, and amorphous ~~ : alloys. Likewise, the spring clement 30 may.comprise two or more individual spring elements provided either in series, in parallel, or in a combination of series and parallel . eloments. B .
[0070] The selection of a particular spring element may depend on the needs of - at particular patient, however, the spring or springs selected should mimic the properties of tHe patient's normal izterve.iebral disc, or should be appropriate as required for the oo partiéular procedure. Thus, springs having the appropriate stiffness in axial compression 2p in transverse bending should be selected to provide the following ranges: ‘flexion/extension - from about 0 Newton-meters per degree (Nm/deg) to about 8 Nm/deg);
Jateral bending - from about - Nm/deg to about 5 Nmv/deg; and compression - from about 1p0 to about 5000 N/mm. Furthermore, the outer diameter of the springs selected may rgoge 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 mm. It is noted thai the preceding are provided as representative dimensions only, and the springs used may have any size, shape, strength and 10° Sexibilic appropriate for the particular patient. : [0071] The use of a spring element in combination with an articulating surface ; y provide a combination of articulation, translation and compression/shock absorption ehwoen the upper and lower endplates 20; 22, and thus allowing for a moving irlsta taneous axis of rotation, Articulation may be provided through the interaction of the licens member 35 and the socket 36, and/or by bending of the at least one spring . clement 30. Compression and shock absorption may be provided by the spring element 30, ahd 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 : te socket. | | [0072] - = Referring to Figure 2a, disc 10 comprising a plurality of internal ring elements 30 is illustrated, each spring element 30 may extend from the upper apn 20 to the lower endplate 22 such that the longitudinal axis of each spring element ig oriented substantially perpendicular to the plane formed by each of the end plates 20, 22.
Alternatively, one or more of springs 30 may be oricnted so that their longitudinal axis forms an acute angle relative to the plane of one or both of the end plates.
[0073] The plurality of spring elements 30 may be arranged in a configuration ‘appropriate to provide uniform shock absorption, load bearing, and tension/compression
Te or the spring elements 30 may be strategically placed to allow for increased resistance to shock and/or compression on one side (i.e. anterior, posterior) of the disc as cémparedto the other. Preferably, however, the disc 10 includes at least one central spring ’ lrnent 30 and at least one peripheral spring element 30 spaced away from the central spring element 30. In the illustrated embodiment, a single central spring element is surrounded by a plurality of peripheral spring elements. The central and peripheral spring element 30 may have substantially the same stiffness, or their stiffnesses may be different. eferably, the central spring element 30 may have a stiffness greater than the stiffness of -
C13 - .
Co the peripheral spring elements 30. Such an drrangement may result in a disc haking a B central spring which provides primary shock absorption and resistance during the initial stages of an axial compression evolution, and having peripheral spring elements 30 which oo provide secondary shock absorption. and resistance during the later phases of axial oo compression. This provides a desirable non-linear response to compressive loads;which may. closely mimic the response of the patint’s natural disc. i g ;
Co ' hi 10074] As shown in Figure 24: each spring element 30 has first and second ends’ } aisociated with respective upper and lower end plates 20, 22. The first and second ends of each spring may have an associated spherical articulation member 34 configured to mate with a comesponding spherical socket 36 formed on the inner surface of the upperiand lower endplates 20, 22 as previously described. The combination of spring and articulation - members permits the upper and lower endplates 20, 22 to move with respect to each other.
For example, articulation members 34 may articulate within associated sockets 3650 that the upper and lower endplates 20, 22 can articulate with respect to each other without =~ ‘Cheating resistive torsion in spring elements 30 that would be present if the endsiof the springs were rigidly connected to the endplates. Alternatively, each spring elemint 30may ohly be attached to a spherical member 346m one end, the other end being attached tothe upper ar lower endplate 20, 22 as previous described. ; a | | [0075] Referring to Figure 2b; theidisc 10 may include a plurality of spring SE elements 30 where only one end of the first spring clement 30 comprises a spherical : articulation member 34, and the opposite end of the first spring element 30 as weil as both ends of the second spring clements 30 are disposed within corresponding pockets, or recesses, in the upper and lower endplates. 20, 22 (the arrangement and connection of these - recesses and the associated spring elements being the same as previously described in relation to the embodiment of Figure 2). As shown in Figure 2b, preferably the frst spring - olement 39:is attached to a hemi-spherical' member 34 for mating with a corresponding oo : socket 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 the:upper and tower 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 30 way be may be attached to two hemi-spherical: member 34. As with the previo’ E embodiments, the number, stiffness, and arrangement of the springs, as well as the selection and placement of the articulating elements and sockets 36 may be made in any combination — to provide a disc that mimics as closely as possible the properties of the normal i : ertebral disc, or that provides the properties appropriate to the particular procedure.
© [0076]: Referring to Figure 2c, the disc 10 may include an elastomeric stiut 54 Co located peripherally 10 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 oo displacement. The elastomeric strut 54'thiay serve essentially the same function as peripheral spring elements 30 previously described, i.e. to provide the disc 10 with: * . ,compression force resistance and shock, absorption and to resist motion. The elastomeric 1 strut 54 may be formed from any appropriate material known in the art including, butnot 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 - . appropriate stiffness or resistance support for the end plates. Thus, the struts 54 may be. ‘cylindrical, square, rectangular, etc., and they may have any appropriate cross séction; such ’ ‘as circular, tnangular, 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 struts 54 may also be hollow, or they may be ring-shapéd. The ring-shaped struts. 54 may be configured ) to surround at least a pottion 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, numberand - configuration of the struts 54 is not critical, but instead may be any combination desired to provide a disc 10 that mimics the properties ‘of the patient’s normal intervertebral disc, or. that provides the properties appropriate to, the particular procedure.
[0077] The inner surfaces 38,'40 of endplates 20, 22 may be porous to allow the . elastomeric strut 50 to be integrated into the corresponding surfaces of the upper and lower endplates 20, 22 during manufacture suchas by molding the elastomer to the endplate. A thembrane and/or barrier may also be included within endplates 20, 22 to limit the depth of impregnation and bony ingrowth respectively. 30 . : [0078] The disc 10 of this embodiment also may include a membrane 24 and a valve (not shown), the valve providing acéess to the interior 26 of disc 10 so that fluid may be injected into, or removed from, the intetior 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 cleapo from the interior 26 of the disc 10. Preferably, the valve is disposed through the: elpstic membrane 24, altematively however the valve may be disposed through the upper and/or lower endplates 20, 22. When the valve is disposed on the upper and/or Tower ’ endplates 20, 22, a passageway preferably is inclnded to interconnect the valve with the . inferior 26 of the disc 10, I RE ’ a [0079] The fluid may bea gas, a liquid, a gel, or any combination thereof, that is siifficient t6 provide shock absorption during axial compression of the disc 19; while also permitting limited articulation or movement of the upper endplate 20 and lower éndplate 22 with respect to one another. Preferably, the fluid is incompressible, for example, saline or , tineral water. In use, the fluid may be injected into the interior 26 of the disc 10 before: insertion of the disc 10 between adjacerit vertebrae . Alternatively, the fluid maybe injected in situ to facilitate insertion of disc 10 and subsequent distraction betwega 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, the more rigid the disc 10, and the greater the . distraction capability. Furthermore, pliability and increased articulation may be realized by filling only a portion of the interior 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 individual patient. SE
SERRE [0080): Depending on.the location of the spinc where the disc 10 is implanted,
K the disc 10 preferably restore height in the range between about 4 millimeters to about 26 . ¢. millimeters. In addition, the disc 10 preferably restore lordosis in the range between about . 0°to about 20°. The disc 10 preferably also restore stiffness from about 1 Nm/deg to about’ 11 Nm/deg in axial rotation, about O Nm/deg to about 7 Nmv/deg in flexion/extension, and about 0 Nm/deg to about 5 Nmy/deg in literal bending. In addition, the disc 10 preferably
Offers compression stiffness from about! 100 N/mm to about 5000 N/mm and tension. 25. stiffness from about 50 N/mm to about 1000 N/mm. Furthermore, depending on the location of the spine where the disc 10 is implanted, the intervertebral disc 10 preferably allows for 2 range of motion of about 5° to about 45° in flexion/extension, of abot 3°to about 33° in Jateral bending, and about 1° to about 60° in axial rotation. The intervertebsal : disc 10 preferably also allows for axial compression in the range from about .2 mm to about 2mm. PE : fo [0081] Preferably, the upper énd lower endplates 20, 22 are formed of metal, such as titanium, stainless steel, titanium alloys, cobalt-chromium alloys, shape memory : slloys, or amorphous alloys. Altematively, however, the upper and lower endplates 20, 22 : thay be formed of polymers including rigid polymers, PEEK or UHMWPE, ceraiiics, oo composites, bone including cortical, cancéllous, allograft, autograft, xenograft, =
- demineralized or partially demineralized’bone, or any other material appropnafe to serve as _ load bearing supports. More preferably; the materials chosen for the endplates are chosen’ “soias to. minimize wear. ih 8 Co : : {0082] Furthermore, preferably, any articulating surfaces in the intervertebral discs of the present invention include a siirface 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. E SA
SNTIRE [0083] The outer surface of the upper and lower endplates 20, 22 hay be substantially flat, wedge-shaped, etc. The outer surfaces of the upper and lower endplates 20,22 may also be dome shaped with their radii defined in the sagittal and coronal planesto generally match the shape of the ends of fhe adjacent vertebral, thereby providing'a better © : § [0084] In addition, as shown:in Figure 1, the disc 10 may include migration oo . resistant features, such as, for example, spike-like structures 18 on the outer surfaces of the 15 . ‘upper and lower endplates 20, 22. The migration resistant features may facilitate oo : engagement of the disc 10 with the ends of the adjacent vertebra by providing a mechanical : : : interlock as a result of penetration and/ot deformation of the ends of the adj acent vertebra.
Thi initial mechanical stability afforded by spikes 18, for example, minimizes the, risk of : i post-operative instability, movement, dislodging or expulsion of the disc 10. Other migration resistant features may include, without limitation, flaps, teeth, deployable 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 endplates 20, 22. As shown in Figure 3ai deployable spikes 41 may be provided, and a cam
LL mechanism 43 may be used to deploy the spikes. Alternatively, as shown in Figure 3b, the deployable spikes may be configured tobe deployed by an instrument (not shown). As shown in Figures 3c through 3e, respectively, examples of flexible spikes 44, shaped teeth 45, and anchors 46 ate shown. Altematively or in addition, bonding agents may also be used to secure the disc 10 to adjacent vertebra. B -
Co LC [0085] Furthermore, the upperand lower endplates 20, 22 may also be coated with a bone growth inducing substance, stich as hydroxyapatite, to promote bony ingrowth to permanently secure the disc 10 to the adjacent vertebrae. Alternatively, the upper and lower endplates 20, 22 may have a roughened or porous surface to facilitate bony ingrowth. . . Alternatively, the upper and lower endplates. 20, 22 may have laser treated endplate layers 10 create a porous structure, or may integrate an ostcoconductive/osteoinductive scaffold.
The endplates 20, 22 may also be made from an osteoconductive and/or osteoinductive
: ‘material to promote bony ingrowth. The:endplates 20, 22 may further include membrane : ~~ !iand/lor barrier to limit the depth of bony ingrowth permitted. HE.
[0086] The upper and lower endplates 20, 22 may also have implant’ oo ‘instrumentation attachment, guiding, and retaining structures. For example, the endplates - 5: 20, 22 may have holes, slots, threads, ora dovetail for accepting a tool used to implant i and/or distract the vertebrae. For example, the disc may include a slot formed in the upper : oo and/or lower endplates 20, 22, the slot configured to receive an implant insertion Co instrument, a distractor or both. : . LL 1 oo [0087] As a result of the material and striictural components used, the disc 10 “10 can allow flexion/extension, lateral bending, axial rotation, and translation, depending on - the loading imparted on the intervertebral disc. In addition, under various spinal loading - conditions resulting from spinal mavements, the spring element 30 can compress, tlt, CL
Co articulate and/or bend varying amounts. B i ’ . 2 [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 external configuration of disc 100 may take on any shape that generally conforms geometrically and anatomically with the adjacent vertebral bodies including, but not limited : Co to circular, oval, ellipsoid, annular, kidnsy-bean, D-shaped, C-shaped, etc, As shown, disc. oo 100 includes an upper endplate 102, a lower endplate 104, and an intermediate elastic membrane 106, the elastic membrane 106 in combination with the upper and lower SE . endplates 102, 104 defining an interior volume 108. The endplates 102, 104 and élastic ~ - inémbrane 106 are similar to those endplates and clastic membrane described previously in relation to other embodiments. The disc 100 may also include a valve (not shown), the - B
Ce | valve providing access to the interior 108.0f the disc 100 for permitting the insertion of, or ‘remioval of, a fluid as previously described in relations to other embodiments. Disc 100 - - ‘ay also include migration resistant feariires, permanent fixation means and/or implant oo 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 : gecond end 114 of leaf spring 110 may comprise a roller 130 capable of rolling on the inner surface of the upper end plate 102. The leaf spring may have a central portion 116 disposed . between the first and second end 112, 114, and this central portion 116 may comprise a loncavo-convex shape. The convex surface may generally face the lower endplate 24 and B
To surface generally facing the upper endplate 24. Lower end plate 104 may
Lo comprise a surface configured to accept intermediate section 116 which itself is configured ’ | } ito mate, articulate, slide and pivot with the inner surface like a ballin a socket. While the leaf spring 110 is described herein as attached to the upper endplate, it may altematively be ] oo attached to the Tower endplate 104 so that its concavo-convex intermediate section 116 {interacts with the inner surface of the upper end plate 102. Jt is noted that although the ‘articulating surface of leaf spring 110 is {tustrated as being disposed near the center of the ‘leaf spring, the articulating surface may be located at any point along the length and/or width of the leaf spring, as appropriate to provide the desired articulation. oo oo oo ! [0090] The second unattached end 114 of leaf spring 110 may be provided with 10° ‘a roller 130 on an axle 132, the roller 130 being freely rotatable about the axle 132. The ‘second end 114 of leaf spring 110 may slide or roll along the inner surface of the upper ‘endplate 102 during axial loading. or compression and during axial unloading or tension.
The leaf spring. of this embodiment is thus allowed to translate as it is flexed, providing a lgreater range of flexibility compared to Teaf springs constrained at both ends. In an Co alternative embodiment, the leaf spring 110 may have a rounded end instead of a roller 130 lfor sliding directly along the inner surface of the upper endplate 102. 2 i [0091] The lower endplate 104 may comprise a packet 106 for receiving a pad oo 1120. The pad 120 may have a lower surface for engaging the lower endplate 104, and an’
R upper surface comprising a concave section 122 configured and dimensioned to mate with the enlarged intermediate convex section 116 of leaf spring 110. The type and amount of larticuliition provided by the spring and pad may be adjusted by controlling the curvature provided 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 greater support but more constrained movement. Alternatively, where the concave section 122 has. larger radius of curvature than the intermediate scction 116, the disc may provide
B increased articulation. ; : Lo . oo : | Lo [0092] The intermediate member 116 and concave section 122 may also take on : bther contours to achieve the desired articulation. The concave section 122 of the pad 120 busy 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 . a permit misting of their surfaces, non-mating contours may be provided to achieve the desired articulation. - £ : 7 [0093] Furthermore, the compression and sliding of leaf spring 110 may vary epending on the area or areas of loading; For example, loading one end of disc 100 may a compression of disc 100 when compared with an opposing end of disc 100.
Additionally, the pad 120 and the pocket 146 may be configured to allow the pad to translate within the pocket 106. The varying movements, i.e. compresston, of leaf spring 110:and translation .of leaf spring 110 with respect to the pocket 106 may allow'a moving ) y instantaneous axis of rotation. ; ’
[0094] Leaf spring 110 may be formed from any appropriate material known in. oo the art including, for example, polymers, ceramics, composites and metals, such as cobilt- : ‘chromium alloys, titanium alloys, stainless steel, shape memory alloys, and amorphous.’ alloys. The pad 120 may likewise be formed of similar materials. oo
[0095] Depending on the location of the spire where the disc 100 is implanted, ‘the disc 100 preferably restores height, natural spinal curve (or sagittal balance), stiffness, : ‘offers compression stiffness, and allows a range of motion similar to that described in Po : § relation to previous embodiments. : : ) : . [0096] With reference to Figuie §, a third exemplary embodiment of an : a intervertebral disc 150 is shown. Similar to the previous embodiments described, disc 150 15: may take on any shape that generally conforms geometrically and anatomically with the ‘adjacent vertebral bodies including, but riot limited to circular, oval, ellipsoid, annular, ° ~ kidney-bean, D-shaped, C-shaped, etc. As shown, disc 150 includes an upper endplate 152, a lower endplate 154, and an intermediate elastic membrane 156, the elastic membrarie 156 in combination with the upper and lower-endplates 152, 154 defining an interior volume 20° 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 oo shown); the valve providing access to the interior 158 of the disc 150 for permitting the. oo 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 25. incans and/or implant instrumentation attachment, guiding, and retaining structiires as ‘previously described in relation to Figures 3a-3¢ and the previous embodiments. : [0097] Disc 150 may further include a medial articulating member 160 attached w 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 30 dimensioned to articulate with respect to concave surface 164 formed on the infer surface of one of the lower endplate 154. The cuivature of the corresponding articulating surfaces 162, 164 may be manipulated as necessary to provide the desired amount of articulation and . . translation between the endplates 152, 154, as has already been described in relation to ; . ener embodiments. -
So [0098] ~ Altematively, the articulating member 162 may comprise a coricave. lower surface configured and dimensioned to mate and articulate with respect to 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 concave surface 164 onto the inner surface of one:of the endplates 152, 154 permits the concave ; Co oo surface 164 to be made from a material different from that of the associated endplate, for. ; oo ‘example, polyethylene or other polymer, or a shock absorbing material may be provided; as oo described in more detail later. - EE 4 oo (0099) The articulating member 160 may be attached to one of the endplates : 182, 154 by any fixation method known in the art including, but not limited to bonding a agents, ultrasonic welding, screws, nails, mechanical wedging, and pins.
Preferably, oo 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 bean elastomer, molded or bound polymer fibers, polyurethane, silicone, or any other suitable - elastic material having the appropriate shock absorbing properties.
Articulating member 160'may be fabricated from a metals, polymers, composites, ceramics, or any combination ©! [00100] The disc 150 may also include an additional elastic membrane 172 configured to confine and/or secure the siticulating member 160 to one of the 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 added stability for the articulating member 160 in shear.
E Co ’ [001 01] Depending on the loéation of the spine where the disc 150 is implanted, the disc:150 preferably restores height, natural spinal curve (or sagittal balance), stiffness; a offers cortipression stiffness, and allows a range of motion similar to that described in ~ - relation to previous embodiments. 5 : } oo © [00102] Asaresult of the materials, geometry, and comporients used, disc 150 : can allow flexion/extension, lateral bending, axjal rotation, and translation, depending on the loading conditions imparted on the intervertebral disc.
In addition, under various spinal : joading conditions, the shock-absorbing layer disposed between the articulating member 160.and:one of the endplates 152, 154 cin compress and/or bend varying amounts, . i epending on the location of the compressed and/or bent area with respect to the area or : : eas of loading.
Furthermore, disc 150 permits different regions of the disc 150 to 35. — varying amounts. 3 IE
© [00103] With reference to Figuie 6, a fourth exemplary embodiment of an’ © intervertebral disc 200 is shown. Disc 200 hes a generally circular shape with an upper “endplate 202, a lower endplate 204, and a slotted core 206 having an upper curved surface and a lower flat surface. The disc 200 niay take on any other shape that appropriately ‘conforms geometrically and anatomically with adjacent vertcbral 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 “retaining structures may be included on endplates 202, 204. Furthermore, the outer surfaces of the upper and lower endplates 202, 204.may be substantially flat, wedge-shaped, ete.” ) The outer surfaces of the upper and lower endplates 202, 204 also may be dome shaped with their radii defined in the sagittal and coronal planes to generally match the shape of the ‘ends of the adjacent vertebrae, thereby providing a better fit in situ. Preferably, the upper. -and lower endplates 202, 204 may be made from metal. However, the upper and lower ‘endplate 202, 204 may alternatively be rhade from any of the endplate materials previously idescribed’in relation to earlier embodiments. ; :
[00104] As shown, thé loweriendplate 204 preferably includes a pocket 208 located on its inner surface, the pocket 208 designed to receive the lower flat surface of slotted core 206. Alternatively, the slotted core 206 and lower endplate 204 may be formed ‘as an integral piece. Where the core is formed as a separate piece, it may comprise a different material from the end plate 204, thus, a metal end plate may be provided having, for example, a polymer mating feature core 206. . i [00105] Where the core 206 4nd endplate 204 are formed separately, the disc ‘200 may also include a c-ring (not showk) or similar structure, such as a lip or ring located ‘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 corc in onc or more directions, © ‘Alternatively, the core 206 may be retained in pocket 208 by means such as welding, press- © fitting, staking, or bonding a cap (not shown) to the lower endplate 204, the cap covering a portion of the core 206. : : ) Co ] [00106] Although pocket 208}is shown as having a circular shape, the pocket may take on any other appropriate shape’including, 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 allowing the core 206 fo translate within the pocket 208 during operation. Alternatively, the pocket 208 may
Lo 22
‘assume various dimensional configurations necessary lo allow translation of tiie:core 200 ‘within the pocket only along spccific ditgctions. Thus, the pocket may be provided with a same general width as the core in all directions but one, the pocket being wider than the } ‘core in that one. direction (e.g. the anterior posterior direction). Thus, a pocketithat is wider
S tban the core along the antevior-posterio axis may allow the core to translate in the .anterior-posterior direction during use. Corresponding modifications to the pocket :
N geometry may be made to allow translation in other directions, such as medial-lateral Co : - [00107] The inner surface ofthe upper endplate 202 may have a concave mating feature 210 configured to accept the upper curved surface 212 of the slotted core 206. _ : Preferably, the mating feature 210 allows the upper end plate 202 to articulate with respect a to the slotted core 206. This mating featiife 210 may be integral to the upper hd plate 202, ort may be formed as a separate piece, fit to the end plate. Where the mating feature is : formed as a separate piece, it may comprise a different material from the end plate 202.
Thus, ametal end plate may be provided having, for example, a polymer mating. feature 210. I | he oo
Co © [00108], As previously described in relation to other embodiments; the :
Co articulating surfaces may be reversed, that is, mating feature 210 may be provided in convex form, and the slotted core may bp provided with a concave surface. Furthermore, : the type and amount of articulation and/or translation provided by the disc of this oo embodiment may likewise be adjusted By adjusting the curvature of the convex and concave surfaces as previously described in relation to other embodiments. By allowing articulating .-and translational movement between the endplates, a moving instantaneous axis of rotation ‘is allowed that approximates the motioniof a natural intervertebral disc. : : oo [00109] The slotted core 206 may 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, vetically, 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 the : : ‘comprossibility of slotted core 206 and thus give additional shock absorbing qualities to the : disc 200. The arrangement and configuration of the slots provided in the core 206 maybe of any combination appropriate to provide the desired degree of compressibility. . : foo110] Although shown as Having a round footprint, the slotted core 206 may be any other shape including oval, rectangular, elliptical, and kidney-bean. Preferably the shape of the slotted core 206 matches with the shape of the pocket 208 formed on the. inner
C23 isurface of the lower endplate 204. - Slottéd core 206 may be formed from materials 8 . including, for example, ceramics, composites, polymers, or metals such as dobalt-chromium ‘alloys, stainless steel, and titanium alloys, Alternatively, slotted core 206 may be made up: ) lof two components (not shown) of differing materials. Also, as previously stated, the islotted coré 206 may be made integral with the lower endplate 204. : : 100111] Disc 200 may also include stiffness restoration features suchiesan ~~ ielastic membrane, an elastomer ring, bellow, springs, or fluid as previously discussed in : irelations to other embodiments. ‘Disc 200;may also incorporate additional shock absorbing } \features as previously discussed in relations to other embodiments. iE E i . [001 12] The disc 200 endplates may have migration-resistant structires provided ) : ‘on the outer surface of at least one or both of the endplates to impede movement, Co dislodging, 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, fins, : deployable spikes, deployable teeth, flexible spikes, flexible teeth, alternatively shaped ‘teeth, insertable or expandable fins, STEWS, hooks, serrations, ribs, and textured surfaces. [001 13] Furthermore, the upper and lower endplates of disc 200 also may be icoated with a bone growth inducing or conducting substance to promote bony ingrowth to:
Cn {permanently secure the disc to the adjacent vericbrae. Alternatively, the upperand lower © endplates may have a roughened surface; a porous surface; laser treated endplste layers; © © 20 qintegrate an osteoconductive/osteoinductive scaffold; or may be provided with or made . - [from an integral osteoconductive and/or steoinductive material to promote bony ingrowth.
[00114] Depending on the location of the spine where the disc 200 is implanted, ithe disc 200 may restore height, lordosis, stiffness, offer compression stiffness, and allow a ivange of motion intended to mimic that of the natural intervertebral disc, or as required for - , 25 ithe particular procedure. ; ER a. [00] 15] In addition, preferably, as discussed with previous embodiments, the. laxticulating surfaces of disc 200 include’a surface polish ot similar wear reducing finish jsuch as diamond finish, TiNi finish, etc. in order to minimize wear, decrease particle ‘|generation, and increase disc life. - | : 1001 16] As aresult of the materials, geometry, and components used, disc 200 ’ ican allow flexion/extension, lateral bending, axial rotation, and translation, depending on oe loading conditions imparted on the intervertebral disc. In addition, under various spinal . loading conditions, the slotted core 206 can vanably compress and allow for different regions of the slotted core 206 to compress in different amounts, depending on the location nd type of spinal loading, thus allowing different regions of the endplates 202, 204 to be compressed different amounts. This variable compression of slotted core 206 also allows : for a moving instantaneous axis of rotation. | : EE 4 [oot 17) With reference to Figure 7, a fifth exemplary embodiment of an : ‘intervertebral disc 250 is shown. Disc 250 has a generally circular shape with an upper endplate 252, a lower endplate 254, a cap 256 and a ring spring 258. Disc 250, however, imay 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. I
[00118] As shown, the lower endplate 254 preferably includes a pocket 260 10° located on its immer surface, the pocket 260 is designed to receive a ring spring 258 having a . ‘tapered outer surface, and a cylindrical inner surface. Preferably, the pocket 260 has a tapered 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 261, limited to oval, elliptical, kidney-bean, or : ‘15 rectangular. PT - [00119] Pocket 260 may be larger in dimension than the ring spring 258 to aliow the ring spring 258 to translate within thé 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 oo instantaneous axis of rotation is created... This moving instantaneous axis of rotation mare ‘naturally replicates the motion of a natural intervertebral disc.
[00120] The disc 250 may algo include a c-ring (not shown) or similar type structure, such as a lip or a ring located within or adjacent to the pocket 260, to retain the : Ting 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- : fitting, staking, or bonding. As previously stated, the ring spring 258 is maintained in the : | pocket 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 bya lid that engages the lower endplate 254 and that covers at least a portion of the ring spring 258 and/or the cap 256. ; ’ [00121] The ring spring 258 i preferably a spring-like element that compresses [under axial loading to provide shock absorption, flex and compression resistance. Although : shown as having a general “C” shape with. a circular footprint, the ting spring 258 may be ary other shape including oval, rectangular, elliptical, and kidney-bean. Preferably the = he the ring spring 258 matches with the shape of the pocket 260 formed on the inner :
.. surface of the lower endplate 254. . The ring spring 258 may be formed of any gppropriate : material known in the art including, for example, ceramics, Composites, polymers or metals, such as cobalt-chromium alloys, stainless steel and titanium alloys. - {00122} As shown, the ting spring 258 has a top surface 264, a bottom surface 266, anouter 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 the ting ‘spring 258 is tapered to mate and engage with the inner surface of the pocket 260. In ‘addition, the ring spring 258 may include at least one slot 262 formed and/or cht 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 264 the bottom ‘surface 266 of the ring spring 258, and extending from the outer surface 268 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 qualities to the disc 250. - Po ©. [00123] In an altemative embodiment, the fing spring 258 may incorporate a. plurality of slots 262 (not shown) rurming from the top and/or bottom surfaces 264, 266 part way through the thickness of the ring spring 258 to provide desired compressive : characteristics of the disc. SE © © [00124]. The disc 250 may also include a cap 256 having an enlarged body section 274 and a shank 276. The juncture between the enlarged body section 274 andthe shank 276 may form a shoulder 278, the shank 276 e configured and dimensioned to be : received within the central bore 272 of the Ting spring 258, and the shoulder configured to : engage the top surface 264 of the ring spring so that the cap 256 may sit on top of the ring 25 . 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 ‘the 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 may permit the ‘cap 256 to translate with respect to the ringispring 258.
[00125] As previously described, the shoulder 278 of cap 256 contacts 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 260. As the ring . spring 258 is pressed into the pocket 260, the tapered outside surface 268 of the ring spring 1710 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
-desired shock absorption and compression: resistance. The size of and number df slots - provided in the ring spring may be selected as appropriate to provide the desired to compressive characteristics of the disc. . EE : Co [00126] The axial displacement of the ring spring 258 may be limited by decreasing the depth of the pocket 260, by decreasing the width of the slot 262, by Co .increasing the thickness and/or length of the shank 276, or by a combination of any orall of these options. Alternatively, a coil spring or 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 eddplate 252. 10 . Preferably, the inner surface of the upper. endplate 252 includes a mating surface 280 which ‘is dimensioned and configured to mate with the op surface of the enlarged body section | co 274 of the cap 256. Preferably, the mating surface 280 on the upper endplate 252 hasa concave surface configured to articulate with a convex surface formed on the top surface of oo _the cap 256. Alternatively, the mating surface 280 may comprise a convex surface and the top surface of the cap 256 may be concave. As previously described in relation’to other ~~ + embodiments, the degree of curvature miay be-adjusted for either or both surfaces in order to : provide the desired articulation and/or translation between the upper endplate and the cap oo : 256. Le SCTE
[00128] In an altemative embodiment, the mating surface 280 is provided asa. sepamte piece from the upper endplate 252. ‘The mating surface 280 in such a case may =. comprise a material different from that of the endplate 252 (for example, the end plate may be titanium while the mating surface may be a UHMWPE). The articulating, surfaces of : disc 250 may also include a surface polish or similar wear reducing finish suchas diamond finish, TiNi finish, ete. in order to minirnize wear, decrease particle generation, and increase . disc life. SE : Co © [00129] In an alternative embodiment, the separate cap 256 may be eliminated, a . and the ring spring 256 may incorporate’a convex upper surface 264 configured to articulate -. within the mating surface 280 of the upper endplate 252. Co : [00130] The disc 250 of this embodiment may comprise the additional features © 30. . described previously with respect to the other embodiments, such as migration ‘resistant - . : structures, permanent fixation features sich as porous surfaces or coated surfuces, and/or implant instrument attachment, guiding, and retaining structures may-be included on . ; endplates 252, 254. Furthermore, the outer surfaces of the upper and lower endplates 252, 254 may be substantially flat, wedge-shaped, etc. The outer surfaces of the upper and lower endplates 252, 254 may also be dome shaped with their radii defined in the sagittal and corpnal planes to generally match the shape of the ends of the adjacent vertebral, thereby ) providing a better fit in site. The outer sirfaces may further comprise »t east vile groove, : no lo, or other features appropriate wo 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 alternatively be made from other materials as : previously described. | Co ST 1001 31] Disc 250 may also ificlude stiffness restoration features suchas 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 10. features previously discussed in relations to other embodiments. -
B [00132] Depending on the location of the spine where the disc 250 is implanted, Co the disc 250 preferably restores height, Iidosis, stiffness, offers compression stiffness, 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 on . the loading conditions. In addition under various spinal loading conditions the ring spring - 258: can compress varying amounts. This varying compression of ring spring 258 allows : for a moving instantaneous axis of rotation. In addition, the ring spring 258 permits ! different regions of the disc 250 ta compress varying amounts. ] [00134] With reference to Figure 8, a sixth exemplary embodiment ofan ‘intervertebral disc 300 is shown. Disc 300 has a generally circular shape with an upper: ; endplate 302, a lower endplate 304, and a winged leaf spring 306 having lateral ends-310. : The disc 300, however, may take on other shapes that preferably conform geometrically and anatomically with adjacent vertebral bodies, including, but ot limited to, kidney-bean shape, oval, annular, ellipsoid, C-shape, D-shape etc. Other features described previously with respect to the other embodiments, sich as migration resistant structures, permanent: fixation features and/or implant instrument attachment, guiding, and retaining structures nL ‘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 may alternatively be made from other materials as already described. EE
[00135] As shown, the lower ehdplate 304 preferably includes a cutout 308° ; [2 e., A,poct:::) on its inner surface, the cot-cut 308 configured to receive at least 2 Genter "portion of winged leaf spring 306. The l6Wwer endplate 304 may support the winged leaf . pring 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 centér : ) ‘portion 314 of the leaf spring to be pressed down into the cut-out 308 until the bottom : Ek : surface of the center portion contacts the bottom surface of thc cut-out 308. The size of the inital gap between the Jeaf spring and the cutout may be selected, along with the stiffness’ 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 ate. ~~ substantially equivalent, or their stiffnesses may be substantially different. Likewise, thie bottom: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 stiffnesses and } . gaps may be selected as appropriate to mimic the properties of the patient's normal’ intervertebral disc, or as appropriate for the particular procedure. B oo 100136] 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-out. 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 aud = . 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 cut- "out 308 may take on any other shape including, but not limited to circular, oval, elliptical, . kidney-bean, or rectangular. The cut-out 308 may be larger in dimension than the central " body portion 314 of winged leaf spring 306 thus allowing for translational mévement of the. winged leaf spring 306 within the cut-out. ‘By allowing translational movement, amoving =. instantaneous axis of rotation is created. which more naturally replicates the motion of a - . natural intervertebral disc. a : " ; [00138] The disc 300 may inclyde an upper endplate 302 having in inner surface oo . 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. Alternatively, however, the mating surface may havea convex profile, and the mating surface 316 of the upper endplate 302 may be convex; and the articulaung surface 312 of the central body 314 may be concave. As discussed Po previously in relation to other embodiments, the degree of curvature of the concave/convex ) sutfaces 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. ; : Co oo [00139] In an alternative embodiment the lateral ends 310 of the winged leaf
Co spring 306 may have a constant thickness, length and width. Alternatively, the lateral ends 310'may have a variable thickness, length, and/or width. The transition from the lateral ends 310 to the central body 314 may be gradual such that the thickness gradually iricreases from the outer periphery of the lateral eilge 310 toward the articulating surface 312 or it oo 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 having 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 308 formed on the inner surface of the lower endplate 304. The winged leaf spring 306 is preferably oo formed. from materials including, for example, ceramics, composites, polymers or metals, such ag cobalt-chromium alloys, stainless steel and titanium alloys. Co
[00141] Altematively, the disc 300, may include a lid or ring member (not shown), configured to retain the winged leaf spring 306 in the cutout 308, thus preventing the spring 306 from dislodging. In this instance, the lid or ring member may bé 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 25. kaown'in the art including, but not limited to pins, screws, welding, bonding, press-fit, etc. ol [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
Co absorbing features as previously described in relation to other embodiments, for example, © manufacturing portions of the disc frond elastomeric material, etc. oo . : © [00143] In addition, the articulating surfaces of disc 300 may bé provided with a surface polish or similar wear reducing finish such as diamond finish, TiNi finish, gic. in : order to minimize wear, decrease particle generation, and increase disc life. : ‘
[00144] . Depending on the location of the spine where the disc 300 is jmplanted, the disc 300 preferably restores height, siatural spine curve (or sagittal balance), stiffness,
_ offers compression stiffness, and allows a range of motion similar to that described in relation to previous embodiments: M Lo x oo [00145] As a result of the materials, 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. ; no i (00146) With reference to Figure 9, a seventh exemplary embodimerit ofan: = - . ; 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, suck as migration resistant structures, permanent fixation features and/ot implant ihstrument 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 substantially flat, wedge-shaped, etc. The outer surfaces * of the upper and lower endplates 352, 34: 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 vertebra, thereby providing a better fit # situ. Preferably, the upper and lower endplates 382, 354 are made from metal. However, the upper and lower endplate 352, 354 may alternatively be made from other materials 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 ae : 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, 25 . 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 formed withthe © oo } lower endplate 354 or they may comprise separate pieces. oo Co . [oo 148] 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 (i.e. translationally) to ensure that the leaf spring remains centered with respect to the first shoulder members 364 and the recess 362, . . thus 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 from the
SE. leaf spring in at least one direction, thus allowing the leaf spring to translate in the at least : © one dircetion. By allowing such wanslatiopal movement, a moving instantaneous axis of rotation is created, which more naturally replicates the motion of a natural intervertcbral : | [00149] A cover plate 360 may be provided to cover the leaf spring, preventing ‘the \eaf spring from moving axially out of 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 mémbers 365. The cover plate 360 may be attached . iothe second shoulder members 365 byagy fixation means known ini the art including, but not limited to press-fit, welding, pins, screws, bonding, etc. The cover plate 360 may have _ an outer perimeter sized to approximate the outer perimeter of the lower endplate 354, and an inner opening 369 sized to accept an articulation element (to be discussed ini more detail below): The cover plate 360 inner opening may include an upwardly extending inner edge 367 that may act in combination with acomesponding surface on the upper endplate 352 to 15. Limit articulation of the disc 350. The cover plate may also be configured to accept a disc inseition instrument. The embodiment of Figure 9 illustrates the leaf spring 3%6 asa
Lo separate element from the lower endplate 354, however, in an alternative embodiment shown in Figure 9a, the leaf spring 356 iay be integrally formed with the lower endplate 354. LE © [00150] The leaf sprinig 356:may be a spring-like element that flexes under axial a. loading to provide shock absorption, flexion and compression resistance. The leaf spring . 356 may have a uniform thickness, or its thickness may vary. In the embodiment illustrated in Figure 9, the leaf spring has a greater thickness in the center than at its ends; in the + embodiment illustrated in Figure 9a, the Teaf spring is thicker at the center and the ends, and i has thinner segments between the ends and the center, rendering the leaf spring with a “waved shape when viewed in cross sectiol The leaf spring may have any thickness appropriate to provide the required shock absorption, flexion and compression resistance. {001511 The leaf spring 356 may be formed from any appropriate material
Co ‘known in the art, including, for example, ‘ceramics, composites, polymers, or metals such as 'cobalt:chromium alloys, stainless steel and titanium alloys. A oo ) oo [00152] Articulating cap 358imay be provided with a convex upper articulation - surface 368 and with a lower, leaf spring-engaging, protrusion 370. The articulation surface } 368 may be configured to mate and articulate with a mating surface an formed on the inner ‘surface of the upper endplate 352, The mating surface 371 may comprise a concave : surface corresponding to the convex surface of the articulating cap 358. Alternatively, the 32 tv : i upper endplate mating surface 371 may be convex and the top surface of the articulating cap ’ ‘358 shay be concave. The curvatures of the respective articulation surface 368 and mating : surface 371 may be selected to provide the appropriate type and amount of articulation : and/or translation to mimic the movement of the patient’s natural disc, or as required for the *S° particular procedure. ; A
[00153] The mating surface mn of the upper endplate 352 may be iritegral with . ‘the endplate, or as illustrated in Figure 9ait may be formed as a separate piece and attached : to the 0% dpla te 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 articulations 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 © 15 too shallow. oo : : [00154] The raised portion 372 of the upper endplate 352 may comprise araised ~ face 374 having a raised face height oY The raised face 374 may be configured to engage the upwardly extending inner edge 367.0f the leaf spring cover plate 360 to Limit oo . : articulation of the disc 350 in at least one direction. Alternatively, the raised face 374 and 20. the upwardly extending inner edge 367 may be configured to limit articulation of thediscin 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, (e.g. the medial-lateral plane). The raised face 374 and inner ¢dge 367 may comprise any combination of . configurations appropriate to provide the disc 350 with the desired range of articulation in
C25 all planes. Thus, the raised face 374 height “R* may be different at different locations - about the disc, for example, the height wh» 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-posterior direction. 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. CC © [00155] The bottom surface of the articulating cap 358 may further comprise a. . protrusion 370 which is dimensi oned and 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 oo restrained within groove 366. In one embodiment, groove 366 may be sized the same or
‘only slightly larger than the protrusion 3770, thereby rendering the cap restrained _- : ‘transversely. In an alternative embodiment, the groove may be larger than the protrusion in .at least one direction (e.g. along the antérior-posterior axis), thus allowing the cap 358 to . .nove transversely (7.e. translate) in that direction during operation. By allowing translational movement, a moving instantaneous axis of rotation is provided. This moving : instantaneous axis of rotation may more naturally replicate the motion of a natural © , intérvertebral disc. ) : RE : © [00156] Alternatively, the protrusion 370 may be rigidly secured within the oo ~: groove:366, thus permitting no translatipnal movement. : {001 57] It is noted that although the groove and protrusion are illustrated as J having substantially corresponding rectangular shapes, the protrusion 370 end groove 366 may take on any other appropriate shapé known in the art including, but not limited to circular, oval, ellipsoidal, etc., to provide the requisite translational freedom. i.
[00158] In an alternative embodiment, shown in Figures 9a through Sc, the leaf spdng 356 may comprise a post 380 anlithe 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 fo the lower endplate 354 in at least one direction. ‘When the groove 366 and post 380 arc configured to allow translation of the cap 358,the cover plate 360 also must be configured 50 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, oo ) [00159] The upper endplate 352 may include a recess 384 for receiving am articulating insert 386, the insert having 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 the articulating surfaces while not affecting the = material of the endplates 352, or otherwiss affecting the design or installation of the other components of the disc 350. Thus the insert 384 may be formed of any appropriate material known in the art including but not limited to polymers including rigid polymers, such as "30 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 configured to retain the insert 386, The recess may comprise a radial ridge configured to fit within a corresponding radial groove in the insert such that the insert may be snapped into) the recess. Alternatively, the insert may be. : attached to the recess via a press fit, by using a bonding agent, or any combination thereof,
Co [00161] In an alternative embodiment, disc 350 may also include stiffness ’ restoration features such as an elastic membrane, an elastomer Ting, bellow, springs, or fluid as previously discussed in relations to other embodiments. Disc 350 may also incorporate ’ additional shock absorbing features as previously discussed in rclations to other - [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. : 10 . [00163] The disc 350 endplates may have migration-resistant structires 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 adjacent vertebrae. : The migration-resistant structures inclide, but are not limited to, flaps, spikes, teeth, fins, oo deployable spikes, deployable teeth, flexible spikcs, flexible teeth, alternatively shaped 15 . 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 surface; a porous surface; laser treated endplate layers; integrate an osteoconductive/osteoinductive scaffold; or may be provided with or made : from an integral osteoconductive and/or osteoinductive material to promote bony ingrowth.
[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. Po
[00166] As a result of the materials, 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. 3 . + [00167] With reference to Figure 10, an exemplary installation procedure will be 30. described. Generally speaking the disc 400 may include an upper endplate 402, a lower . endplate 404 and a core mechanism 406, 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 example, the endplates 402, 404 of disc 400 may be inserted into the intervertebral cavity ‘35 using instruments such asa distractor and/or holder instrument. The intervertebral disc space may then be distracted using a standard spinal distractor which engages ‘the endplates : : 402, 404, Trial spacers may then be used to determine the appropriate size cf the ere ‘mechanism 406 to be inserted in the resulting disc space. Inan exemplary embodiment, the : . ‘core mechanism, 406 is inserted and attached to endplates 402, 404 through the use ofa Co © 5 dovetail, slot, or similar connection. This modular insertion technique may avold over- distracting the intervertebral space, which may damage surrounding tissue and/or blood . : “vessels, : : :
Co ) oo [00168] Altematively, the infervertebral disc 400 may be inserted preassembled no “with the use of particular insertion tools. For example, an endplate holding clip may be. 10 . used that allows the endplates 402, 404 to be held and locked in a parallel and spaced Co 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 removed from the intervertebral space. In addition, the disc 400 may be implanted in a compressed state
Co fo prevent over-distraction. The introduction of the disc 400 in a compressed state may be accomplished via a surgical insertion instrument or by an internal mechanism located in the © disc400. § J EE - [00169] An anterior, lateral, or anterolateral surgical approach maybe used for the intervertebral disc 400. F urthermore, 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 surface of the endplates = © 402,404 to guide the implant down the distractor during implantation. Also, depending on. + the intervertebral disc to be implanted, anartificial Anterior Longitudinal Ligament or the
SR natural Anterior Longitudinal Ligament may be attached directly to the disc oF tothe = ~ 25 | adjacent vertebral bodies. Attachment of the Anterior Longitudinal Ligament may assist im "preventing movement, dislodging or expulsion of the implant. To assist with the "implantation of the intervertebral discs; the intervertebral discs may include alignroent ~.. markers. Lo : . : | [00170] ~~ While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in combination . thereof. Therefore, this invention is not to be limited to the specific preferred embodiments depicted herein. . a i [00171] Further, it should be understood 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 heréin may be
: formed of bone, such as allografts, autografts, and xenografts, which may be partially or fully dermuneralized. In addition, some irtiplants may include bone material or other bone ‘growth inducing material in their interiors or onfin their endplates. Such substances in the + interiors may be permitted to interact withthe surrounding anatomy, as with channels or
S ; 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 : intervertebral discs can be made rigid ify situations where fusion is necessary. The intervertebral discs may be made rigid by, for example, allowing fusion between. the - endplates, inserting spacers between the,éndplates, or by injecting a solidifying liquid between the endplates. Accordingly, all- expedient modifications readily attainable by one versed in the art from the disclosure set forth herein, that are within the scope and spirit of the present invention are to be included’as further embodiments of the present invention. :
The scope of the present invention is accordingly defined as set forth in the appended awws. To
Claims (41)
1. An intervertebral disc for placement between first and second vertebrae comprising: a first endplate having a first inner surface and a first outer surface, the first outer surface contacting the first vertebra; a second endplate having a second inner surface and a second outer surface, the second outer surface contacting the second vertebra; a leaf spring having first and second resilient ends, configured to engage the second endplate, and a length, the leaf spring further comprising a central body having first and second surfaces, the first surface comprising an articulating surface.
2. The intervertebral disc according to claim 1, wherein the second endplate further comprises a recess having a length smaller than the leaf spring length, wherein when the leaf spring engages the second endplate so that the first and second resilient ends are supported on the inner surface of the endplate and the central body is positioned over the endplate recess, at least a portion of the central body may move into the recess when a compressive force is applied to the leaf spring first surface allowing the second surface to contact the recess surface.
3. The intervertebral disc according to claim 2, the recess further comprising a recess surface, the leaf spring second surface and the recess surface configured to define a gap therebetween so that when a predetermined compressive force is applied to the leaf spring first surface the leaf spring second surface contacts at least a portion of the recess surface.
4. The intervertebral disc according to claim 2, wherein the central body and the recess are configured so that the leaf spring may translate in at least one direction with respect to the second end plate. 38 Amended 26 February 2007
5. The intervertebral disc according to claim 1, wherein the first endplate further comprises an inner surface having an articulating surface configured to correspond with the leaf spring articulating surface.
6. The intervertebral disc according to claim 5, wherein the articulating surfaces are configured to allow the leaf spring to articulate, and to translate, relative to the first endplate.
7. The intervertebral disc according to claim 1, further comprising a membrane disposed between the first and second endplates.
8. The intervertebral disc according to claim 7, further comprising a membrane disposed between the upper and lower endplates, the membrane encapsulating at least the leaf spring.
9. The intervertebral disc according to claim 7, wherein the membrane encapsulates the first and second endplates.
10. The intervertebral disc according to claim 7, wherein the membrane is formed of an elastomeric material.
11. The intervertebral disc according to claim 7, wherein the membrane comprises a bellow.
12. The intervertebral disc according to claim 7, wherein the endplates and membrane define an interior volume, the volume being at least partially filled afluid.
13. The intervertebral disc according to claim 12, further comprising a valve in communication with the volume for at least partially filling the volume with the fluid.
14. The intervertebral disc according to claim 12, wherein the fluid is incompressible. 39 Amended 26 February 2007
15. The intervertebral disc according to claim 1, wherein at least one of the endplates is formed from a material selected from the group consisting of metal, polymer, ceramic and composite.
16. The intervertebral disc according to claim 1, wherein at least one of the endplates is formed of bone material selected from the group consisting of cortical, cancellous, allograft, autograft, xenograft, demineralized or partially demineralized bone.
17. The intervertebral disc according to claim 1, further comprising migration-resistant structures disposed on at least one of the first and second outer surfaces.
18. The intervertebral disc according to claim 1, further comprising permanent fixation means disposed on at least one of the first and second outer surfaces.
19. The intervertebral disc according to claim 1, further comprising implant instrumentation attachment, guiding, or retaining structures disposed on at least one of the first and second inner or outer surfaces.
20. An intervertebral disc for placement between first and second vertebrae comprising: a first endplate having a first inner surface and a first outer surface, the first outer surface configured for contacting the first vertebra; a second endplate having a second inner surface and a second outer surface, the second outer surface configured for contacting the second vertebra; a first articulation member having a first surface associated with the first endplate, a lcaf spring having at least a first surface associated with the second endplate and a second surface associated with a second surface of the first articulation member; wherein the first articulation member is configured to allow the first and second endplates to articulate with respect to each other, and the leaf spring is configured 40 : Amended 26 February 2007 to allow the end plates to approach one another in response to a compressive force applied to at least one of the end plates.
21. The intervertebral disc according to claim 20, wherein at least one of the first endplate inner surface and the first articulation member first surface comprises a concave surface, the other surface being convex, the surfaces configured to allow the articulation member to articulate with respect the first endplate.
22. The intervertebral disc according to claim 20, wherein the first endplate inner surface comprises a concave shape, and the first articulation member comprises a corresponding convex shape.
23. The intervertebral disc according to claim 20, further comprising a second articulation member having a first surface associated with the first endplate inner surface and a second surface associated with the first articulation member first surface.
24. The intervertebral disc according to claim 23, wherein the second articulation member second surface is concave and configured to correspond to a convex first surface of the first articulation member.
25. The intervertebral disc according to claim 24, wherein the concave and convex surfaces are configured to allow both articulation and translation between the articulation members.
26. The intervertebral disc according to claim 23, wherein at least one of the articulation members comprises a material that is different from the material of one of the first or second endplates.
27. The intervertebral disc according to claim 20, wherein the first endplate inner surface and the articulation member first surface are further configured to allow the articulation member to translate relative to the first endplate. 41 Amended 26 February 2007
28. The intervertebral disc according to claim 20, the second endplate further comprising a recess in the second 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 inner surface and a central portion of the leaf spring is positioned over the recess, wherein when the central portion may move into the recess when a compressive force is applied to a second surface of the leaf spring.
29. The intervertebral disc according to claim 28, the second endplate further comprising a perimeter edge sized and configured to allow the leaf spring to translate with respect to the second endplate in at least one direction.
30. The intervertebral disc according to claim 28, the second endplate further comprising a perimeter edge sized and configured to prevent the leaf spring from translating in at least one other direction.
31. The intervertebral disc according to claim 27, the leaf spring second surface further comprising a recess configured to accept a projection 15S formed on a second surface of the articulation member.
32. The intervertebral disc according to claim 31, wherein the recess and projection are sized and configured to allow the articulation member to translate in at least one direction relative to the leaf spring.
33. The intervertebral disc according to claim 29, further comprising a cap member configured to engage at least a portion of the second endplate, and to cover at least a portion of the leaf spring to prevent the leaf spring from axially disengaging from the second endplate.
34. The intervertebral disc according to claim 28, the cap member further comprising at least one raised ridge configured to contact at least one raised ridge associated with the first endplate to limit articulation between the endplates in at least one direction.
35. The intervertebral disc according to claim 34, wherein the raised ridges have corresponding flat surface profiles. 42 Amended 26 February 2007
36. The intervertebral disc according to claim 34, wherein the raised ridges have correspondingly angled surfaces.
37. The intervertebral disc according to claim 20, wherein at least one of the endplates is formed from a material selected from the group consisting of metal, polymer, ceramic and composite.
38. The intervertebral disc according to claim 20, wherein at least one of the endplates is formed of bone material selected from the group consisting of cortical, cancellous, allograft, autograft, xenograft, demineralized or partially demineralized bone.
39. The intervertebral disc according to claim 20, further comprising migration-resistant structures disposed on at least one of the first and second outer surfaces.
40. The intervertebral disc according to claim 20, further comprising permanent fixation means disposed on at least one of the first and second outer surfaces.
41. The intervertebral disc according to claim 20, further comprising implant instrumentation attachment, guiding, or retaining structures disposed on at least one of the first and second inner or outer surfaces. 43 Amended 26 February 2007
Applications Claiming Priority (1)
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| US40335602P | 2002-08-15 | 2002-08-15 |
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| ZA200501543A ZA200501543B (en) | 2002-08-15 | 2003-08-15 | Invertebral disc implant |
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| US20080195210A1 (en) * | 2005-03-01 | 2008-08-14 | Columna Pty Ltd | Intervertebral Disc Restoration |
| US20100268340A1 (en) * | 2009-04-16 | 2010-10-21 | Warsaw Orthopedic, Inc. | Minimally Invasive Expandable Contained Vertebral Implant and Method |
| US8123808B2 (en) * | 2009-04-16 | 2012-02-28 | Warsaw Orthopedic, Inc. | Vertebral endplate connection implant and method |
| CN105147420B (en) * | 2014-06-03 | 2017-07-28 | 深圳兰度生物材料有限公司 | Artificial intervertebral disk and preparation method thereof |
| CN105877878B (en) * | 2016-05-20 | 2018-10-23 | 北京爱康宜诚医疗器材有限公司 | Low displacement artificial intervertebral disk |
| CN106388982B (en) * | 2016-11-29 | 2018-10-26 | 河南科技大学 | A kind of Invasive lumbar fusion device |
| CN108836580A (en) * | 2018-07-06 | 2018-11-20 | 北京爱康宜诚医疗器材有限公司 | Artificial intervertebral disk frame body |
| CN109602466B (en) * | 2018-12-17 | 2024-02-06 | 南昌市第一医院 | Cervical vertebra facet joint fusion device |
| CN111281610B (en) * | 2019-12-30 | 2023-08-18 | 雅博尼西医疗科技(苏州)有限公司 | Porous structure and connection structure of substrate |
| CN112535556B (en) * | 2020-11-02 | 2022-04-08 | 淮阴工学院 | Air bag type artificial cervical intervertebral disc prosthesis |
| CN112451182B (en) * | 2020-11-27 | 2022-12-06 | 汕头大学医学院第二附属医院 | XJ bionic artificial intervertebral joint |
| CN115998491B (en) * | 2023-03-24 | 2023-07-28 | 北京爱康宜诚医疗器材有限公司 | Intervertebral fusion device |
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| CH671691A5 (en) * | 1987-01-08 | 1989-09-29 | Sulzer Ag | |
| FR2723841B1 (en) * | 1994-08-23 | 1998-11-06 | Fabien Gauchet | INTERVERTEBRAL DISK PROSTHESIS. |
| FR2751202B1 (en) * | 1996-07-22 | 2001-03-16 | Zacouto Fred | SKELETAL IMPLANT |
| ATE336952T1 (en) * | 1999-12-01 | 2006-09-15 | Henry Graf | DEVICE FOR INTERVERBEL STABILIZATION |
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- 2003-08-15 AU AU2003262694A patent/AU2003262694B2/en not_active Ceased
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| CN100577123C (en) | 2010-01-06 |
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| AU2003262694A1 (en) | 2004-03-03 |
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