WO2008022206A2

WO2008022206A2 - Spinal implant

Info

Publication number: WO2008022206A2
Application number: PCT/US2007/076017
Authority: WO
Inventors: Jorge Alexander Ochoa; Brian Hewko
Original assignee: Motionback Llc
Priority date: 2006-08-15
Filing date: 2007-08-15
Publication date: 2008-02-21
Also published as: WO2008022206A3

Abstract

An intervertebral disc prosthesis for installation in a spinal column between upper and lower vertebral surfaces includes a first intervertebral plate and a second intervertebral plate. The first intervertebral plate engages the upper vertebral surface. The second intervertebral plate engages the tower vertebral surface. A nonelastomeric resilient body is installed between and engages said intervertebral plates. The nonelastomeric resilient body comprises a plurality of deformable plates and permits relative movement between the first intervertebral plate and the second intervertebral plate.

Description

SPINAL IMPLANT

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Benefit of U.S. Provisional Patent Application Serial Number 60/822.480 filed August 15, 2006, is hereby claimed and the disclosure incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

[0002] The present invention relates to spinal implants, and, more particularly, to intervertebral disc prostheses.

Description of Related Art

[0003] The spinal column comprises a series of vertebrae stacked on top of each other. There are typically seven cervical (neck), twelve thoracic (chest), and five lumbar (low back) segments. Each vertebra has a cylindrical shaped vertebral body in the anterior portion of the spine with an arch of bone to the posterior, which covers the neural structures. Each vertebral body includes superior and inferior endpfates. which are respectively surrounded by superior and inferior bony rings, called ring apophyses. Between each vertebral body is an intervertebral disc, a cartilaginous cushion to help absorb impact and dampen compressive forces on the spine. To the posterior, the laminar arch covers and protects the neural structures of the spinal cord. At the junction of the arch and anterior vertebral body are articulations to allow movement of the spine.

[0004] Various types of problems can affect the structure and function of the spinal column. These can be based on degenerative conditions of the intervertebral disc or the articulating joints, traumatic disruption of the disc, bone or ligaments supporting the spine, tumor or Infection. In addition congenital or acquired deformities can cause abnormal angulation or slippage of the spine. Slippage (spondylolisthesis) anterior of one vertebral body on another can cause compression of the spinal cord or nerves. Patients who suffer from one of more of these conditions often experience extreme and debilitating pain, and can sustain permanent neurological damage if the conditions are not treated appropriately.

[QOOSJ One treatment for spinal diseases and injuries is the removal and replacement of the intervertebral disc with a prosthetic device. Some intervertebral prosthetic devices provide a degree of pivotal and rotational movement, while others promote fusion of adjacent vertebrae. Typicai non-fusion prosthetic discs, that provide a degree of pivotal and rotational movement, have rigid attachment members for attaching to adjacent vertebrae. The space between the attachment members is usually occupied by a core that generally includes either one or a plurality of elements that move relative to each other or to the fixation elements and can be formed from polymers, ceramic materials, metals and combinations thereof; or a single element such as a solid elastorπeric core located between the attachment members that provides relative motion between the attachment elements due to its material deformation. Some artificial disc cores have been proposed that include mechanical elements or mechanisms such as dashpots, springs, gears, dovetails, hinges, cams and bar linkages. Such prosthetic discs may require complicated assembly steps to assemble the attachment members and the eiastomeric core. Further, metallic, ceramics, mechanical element and eiastomeric cores may not replicate the quality or range of spinal movement to an acceptable degree. H would be desirable to provide a unitary intervertebral disc prosthesis that provides a degree of pivotal, translational and rotational movement, and which does not employ sliding or rolling elements, mechanical linkages or an eiastomeric core,

BRIEF SUMMARY OF THE INVENTiON

[0008] In accordance with one aspect of the present invention, provided is an intervertebral disc prosthesis for installation in a spinal column between upper and lower vertebral surfaces. A first intervertebral plate engages the upper vertebral surface. A second intervertebral plate engages the lower vertebral surface. A noneiasfomeπc resilient body Is installed between and engages said intervertebral plates. The noneiasfomen^'c resilient body comprises a plurality of deformabfe plates and permits relative movement between the first intervertebral plate anύ the second intervertebral plate.

[0007] In accordance with another aspect of the present invention, provided is an intervertebral disc prosthesis for installation in a spinal column between upper anύ lower vertebral surfaces. A first intervertebral plate engages the upper vertebral surface. A second intervertebral plate engages the lower vertebral surface, A nonβiastomeric resilient body is installed between and engages said intervertebral plates. The πoπelastomeric resilient body comprises a plurality of deformable parallel beams and permits relative movement between the first intervertebral plate and the second intervertebral plate.

[0008] In accordance with another aspect of the present invention, provided is an intervertebral disc prosthesis for installation in a spinal column between upper and lower vertebral surfaces. A first intervertebral plate engages the upper vertebral surface. A second intervertebral plate engages the lower vertebral surface. A nonelastomeric resilient body is installed between and engages said intervertebral plates. The nonelastomeric resilient body comprises a plurality of compliant trusses and permits relative movement between the first intervertebral plate and the second intervertebral plate.

^}} in accordance with another aspect of the present invention, provided is an intervertebral disc prosthesis for installation in a spinal column between upper and lower vertebral surfaces. A first intervertebral plate engages the upper vertebral surface. A second intervertebral plate engages the lower vertebral surface. A noneiastomeric resilient body is installed between and engages said intervertebral piates. The nonelastomeric resilient body comprises a plurality of structural members forming an Irregular honeycomb and permits relative movement between the first intervertebral plate and the second intervertebral plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a perspective view of an example embodiment of an intervertebral disc prosthesis;

[0011] FIG, 2A is a section view of an example embodiment of an intervertebral disc prosthesis;

[0012] FIG. 2B is a section view of an example embodiment of an intervertebral disc prosthesis;

13] FIG. 3 is a perspective view of an example embodiment of an intervertebral disc prosthesis;

[0014] FIG. 4 is a front eievation view of the intervertebral disc prosthesis of

Fig- 1;

[0015] FIG. 5 is a side elevation view of the intervertebral disc prosthesis of Fig. 1 ;

[0016] FIG. 8 is a posterior elevation view of an installed intervertebral discprosthesis:

[0017] FIG. 7 is a perspective view of an example embodiment of an intervertebral disc prosthesis;

[0018] FlG. 8 is a perspective view of an example embodiment of an intervertebral disc prosthesis;

[0019] FIG. 9 is a perspective view of an example embodiment of an intervertebral disc prosthesis;

[0020] FlG. 10 shows a structural polygon for an intervertebral disc prosthesis resilient body:

[0021] FlG. 11 is a perspective view of an intervertebral disc prosthesis resilient

)22] FlG. 12 shows a structural polygon for an intervertebral disc prosthesis resilient body; [0023] RG. 13 shows an irregular structural shape for an intervertebral disc prosthesis ressiient body; and

[0024] FlG. 14 shows an irregular structural shape for an intervertebral disc prosthesis resilient body.

DETAILED DESCRIPTION OF THE INVENTiOM

[0025] The present invention relates to spinal implants, such as intervertebral disc prostheses implanted via posterior, anterior or lateral approaches. The present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout, It is to be appreciated that the various drawings are not necessarily drawn to scale from one figure to another nor inside a given figure, and in particular that the size of the components are arbitrarily- drawn for facilitating the understanding of the drawings. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. Ii may be evident, however, that the present invention can be practiced without these specific details. Additionally, other embodiments of the invention are possible and the invention Is capable of being practiced and carried out in ways other than as described. The terminology and phraseology used in describing the invention is employed for the purpose of promoting an understanding of the invention and should not be taken as limiting.

[0026] An example embodiment of an intervertebral disc prosthesis 1 for installation in a spinal column is shown in perspective in Fig. 1 and in front and side elevation in Figs. 4 and 5, respectively. The intervertebral disc prosthesis 1 is designed to be inserted posteriorly between adjacent superior (upper) and inferior (lower) vertebral surfaces, to replace a removed disc. However, it is to be appreciated that the disc prosthesis could also be inserted anteriorly or laterally if desired.

[0027] The intervertebral disc prosthesis 1 includes a first intervertebral plate 11 and a second intervertebral plate 12. The first intervertebral plate 11 engages the upper vertebral surface. More specifically, the first intervertebral plate 11 engages one or both of the inferior vertebral endplate of the upper vertebral body and the inferior ring apophysis of the upper vertebral body. It is to be appreciated that the first intervertebral plate 11 could engage other portions of the upper vertebra, such as a pedicle or spinous process, for example. The second intervertebral plate 12 engages a surface of an adjacent lower vertebral body. More specifically, the second intervertebral plate 12 engages one or both of the superior vertebrai endpiate of the lower vertebral body and the superior ring apophysis of the lower vertebral body. It is to be appreciated that the second intervertebral plate 12 could engage other portions of the lower vertebra, such as a pedicle or spinous process, for example,

[0028] The intervertebral plates 11 , 12 can have a generally planar shape. Alternatively, the intervertebral plates 11, 12 can also have a curved shape, to better match the contour of the vertebra to which they are attached.

[0029] As can be seen in Figs. 1 and 5, the intervertebral plates 11, 12 include a plurality of teeth 13 for anchoring the plates 11 , 12 to their respective vertebrae. In an example embodiment the intervertebral plates 11 , 12 have serrations, which provide a saw-toothed side or front profile, and which allow the plates to dig into and thereby anchor to adjacent vertebrae. The plurality of teeth 13 can also be in the form of a plurality of pointed spikes.

[0030] in an example embodiment, the intervertebral plates 11 , 12 include a plurality of apertures 14 or recessed portions. The apertures 14 or recessed portions permit bone growth from a vertebrai surface into the intervertebral piates 11 , 12, The intervertebral plates 11, 12 can also be coated with a porous material, to permit bone growth into the porous material from a vertebrai surface. For example, the intervertebral piates 11 , 12 can Include a hydroxyapatite coating.

[0031] Example materials of construction for the intervertebral plates 11. 12 include metals such as stainless steel, titanium alloys, for example ΪI6AI4V, cobalt aiioys/superailoys, or cobalt-chrome-molybdenum alloys,, shape memory alloys (SIVIA). such as πitiπoi, and bio-inert polymers, for example, carbon reinforced polymers and poiyetheretherketones (PEEK), such as the PEEK-OPTIfviAΦ product, which is commercially available from Invibio, Ltd. [0032] The intervertebral disc prosthesis 1 includes a resilient body 15. The resilient body 15 is located between and operativeiy engages the first intervertebral plate 11 and the second intervertebral plate 12, The resilient body 15 can directly engage tha intervertebral plates 11 12 by direct contact with the plates, or can indirectly engage the plates through, for example, a spacer (not shown). The resilient body 15 is elasticaiiy deformable. which allows for relative movement between the intervertebral plates 11. 12 and compression of the resilient body 15. When installed in a spinal column, the resilient body is compressed by the intervertebral plates 11, 12. Relative movement between the intervertebral plates 11 , 12 can apply additional forces to the removable body 15, which resists such relative movement. The resilient body 15 can be designed to accurately reproduce or, alternatively, specifically alter, the physiological, nonlinear load displacement profiles (e.g., range of motion, kinematic signatures, etc.) of a healthy spinal disc.

[0033] The resilient body 15 is preferably nonelastomeπc, and its resilience is due to the inclusion of a so-called compliant mechanism. A compliant mechanism is a jointless, monolithic, flexible mechanism for transferring or transforming motion, force, energy, etc. A compliant mechanism is different from a rigid-body mechanism, which transfers or transforms motion, force, energy, etc. using rigid links and movable joints. A compliant mechanism relies on the deflection of flexible members, rather than rigid links and movable joints. The flexible members undergo elastic deflection when moving. The load-displacement behavior of the compliant mechanism can be made to be nonlinear, to better mimic the behavior of a spinal disc in flexion/extension, lateral bending, axial rotation, etc. Because a compliant mechanism is jointless and monolithic, it does not experience internal friction and backlash, like a traditional rigid- body mechanism. Further, because a compliant mechanism is monolithic and lacks a plurality of separate rigid links, its associated assembly costs may be less than a comparable traditional rigid-body mechanism.

[0034] Because the resilient body 15 owes its resilience to the Inclusion of a compliant mechanism. It need not made of an eiastomeric material. For example, the resilient body 15 may be formed from a hard synthetic polymeric material, such as high density polyethylene (HDPE), cross-linked ultra-high molecular weight polyethylene (UHMWPE), nylon, reinforced polymers, or pofyetheretherketones (PEEK), such as the PEEK-OPTIMA® product. Hard synthetic materials would normally provide a more rigid body, given the apparent size of the body. However, the resilient body 15 includes a plurality of voids 16 that permit the body to deform and provide a surprising degree of resilience. Further, the resilient body 15 includes thick, more rigid constraining portions 17, and thin, more flexible deformable portions 18. The thicker constraining portions 17 can limit the movements of the resilient body 15 and, more specifically, the deformable portions 18.

[0035] The resilient body 15 may be formed from non brittle, flexible biocompatible metals such as titanium and its alloys suoh as T18AL4V, stainless steel, cobalt and its alloys such as cobalt-chrome-molybdenum alloys, and biocompatible shape memory alloys (SMA) such as nitinol. Shape memory alloys have a memory, which allows a former shape to be recovered when the alloy is heated.

[0038] In an embodiment, and as shown in the section view of Fig. 2A, the resilient body 15 can include a plurality of flexible deformable plates 19. The deformable plates 19 can bend and twist to allow relative movement between the first intervertebral plate 11 and the second intervertebral plate 12. In an embodiment, the deformable plates 19 are parallel plates, which are separated by voids in the resilient body 15. The parallel plates can be horizontal, vertical or at some other orientation. The resilient body 15 can include a plurality of non-parallel plates and a combination of parallel and non-parallel plates, as desired.

[0037] in an embodiment, and as shown in Fig. 28_; the resilient body 15 includes a plurality of flexible deformable beams 20. The deformable beams 20 bend to allow relative movement between the first intervertebral plate 11 and the second intervertebral plate 12. In an embodiment, the deformable beams 20 are parallel beams, which are separated by voids in the resilient body 15. The parallel beams can be horizontal, vertical or at some other orientation. The resilient body 15 can include a plurality of non-parallel beams and a combination of parallel and non-parallel beams, as desired. The resilient body 15 can further include a combination of deformable plates 19 and deformable beams 20, Further, individual beams of the resilient body may have thicker and thinner portions, for example notched portions, which form flexible hinges to allow bending at desired positions along the beam.

[OD 38] In an embodiment, and as shown In Fig. 3, the resilient body 15 includes a plurality of compliant deformable trusses 21. The trusses 21 are formed by deformable beams. The deformable beams are provided in a triangular or quasi- triangular configuration. Each beam forming the truss may have differing compliant properties For example, each beam in the truss may have a different thickness, to allow certain beams to bend more easily than other beams. Also, individual beams may have thicker and thinner portions, for example notched portions 22, to allow bending at desired positions along the beam. The trusses may include an opening at a corner of the truss's triangle, to allow relative movement between beams at the corner. Additionally or alternatively, the trusses may include an opening in the center of a beam, The openings allow for movement of the beams and facilitate deformation of the truss.

[0039] As can be seen In the figures, the resilient body 15 can have a tapered central portion 23, which allows the resilient body 15 to bend and twist at the tapered central portion. As shown in Fig. 1 , the resilient body 15 can be tapered at each of four sides, so as to form an upper portion having an inverted pyramidal shape and a lower portion having a pyramidal shape. Alternative, the resilient body 15 can have a rounded, hourglass shape. As shown In Fig. 3, the resilient body 15 can be tapered at two sides, for example, lateral sides, while the anterior and posterior sides of the resilient body 15 have little or no tapering.

[0040] It is to be appreciated that a resilient body 15 having a compliant mechanism can Include various combinations of deforrnabie plates, beams and/or trusses. The deformable plates, beams and/or trusses can be applied in geometrically consistent symmetrical configurations, as shown in Figs. 1-7, or in inconsistent or nonsymmetrical configurations. In addition to trusses, the resilient body 15 can include other geometric polygonal structural shapes, such as quadrilateral or hexagonal structural shapes. Structural polygons 31 , 33 for a resilient body can be seen in Figs. 10 and 12 , respectively. A resilient body 32 having serpentine bands and generally vertical posts can be seen in FIg. 11. It is to be appreciated that within a resilient body 15, plates, beams, structural polygons, serpentine bands, etc, of various shapes and sizes can be provided. Instead of or in addition to generally geometric structural shapes, the resilient body can include irregular "organic" structural shapes 34, 35, as shown in Figs, 13 and 14. The irregular "organic" structural shapes 34, 35 can have a spongy appearance, or appear as an irregular honeycomb, as shown in Fig. 14. The irregular honeycomb includes a plurality of nonsymmetrical structural shapes, which may be six-sided, or have more than or fewer than six sides. Irregular structural shapes can be biomimetic, that is, mimicking live structures such as cancellous bone.

[0041] The intervertebral plates 11 , 12 and resilient body can be formed as one piece, or separate pieces. A one-piece disc prosthesis can be created by molding, casting, three-dimensional printing, or laser curing of polymeric fSuidized/powder beds of polymers, for example, A one-piece disc prosthesis can also be created by conventional machining, for example, by selectively removing material from an initial base piece of material. A one-piece disc prosthesis does not require the intervertebral plates 11 , 12 to be assembled to the resilient body 15.

[0042] In an embodiment, the resilient body 15 is removable from between the intervertebral plates 11 , 12. The resilient body 15 is removable while the intervertebral plates 11 , 12 remain installed in a spinal column, if present, fasteners can be removed to free the resilient body 15 from the intervertebral plates 11 , 12. The resilient body 15 is then slid from between the intervertebral plates 11 , 12. Additional temporary bracing can be provided to prevent undesirable relative movement between the intervertebral plates 11 , 12 while the resilient body 15 is removed. A new resilient body 15 with similar or different properties as compared to the removed resilient body can be Installed between the intervertebral plates 11, 12. For example, a resilient body 15 can be removed from a previously installed disc prosthesis, and replaced with a rigid insert. Such a change will modify a flexible prosthesis so that it becomes s fusion-type prosthesis.

[0043] Fig. 6 shows a posterior spinal implant that utilizes two intervertebral disc prostheses 1 Installed between adjacent superior 24 inferior 25 vertebrae. The prostheses 1 are not interconnected, but could be interconnected by a tying member, for example, to better coordinate their movements. Each prosthesis is installed by first removing a diseased or otherwise damaged disc. 11 the prosthesis is not formed as one piece nor preassernbled, the intervertebral plates 11 , 12 are respectively pressed into the upper and lower vertebral surfaces. The teeth on the Intervertebral plates 11. 12 help secure the plates to the vertebral surfaces, by digging into the vertebral endplates and/or the ring apophyses, for example. A resilient body having desired mechanical properties (e.g., rigidity, flexibility, etc.) is compressed and inserted between the intervertebral plates 11, 12. It Is to be appreciated that a suitable resilient body can be selected based on additional criteria, such as durability, compatibility with the intervertebral plates 11 , 12, etc. If desired, the resilient body can be removed and replaced with another body, such as a rigid insert, while the intervertebral plates 11 , 12 remain attached to their respective vertebral bodies. If the prosthesis 1 is formed as one piece_: then the prosthesis can be compressed and inserted between the adjacent superior 24 and inferior 25 vertebrae. Unlike traditional prostheses, the disclosed prosthesis 1 can be installed without having to mechanically pull the adjacent vertebrae apart. The prosthesis 1 can be compressed prior to installation, so that it fits between the adjacent superior 24 and inferior 25 vertebrae. Therefore, the prosthesis 1 can be Installed without having to hyperextend the spine or intervertebral space. In an embodiment, the resilient body Includes a shape memory alloy that, upon application of heat, will expand and engage adjacent vertebrae after being compressed prior to installation:. Although the implant of Fig. δ utilizes two prostheses 1 , it is to be appreciated that a single, centrally located prosthesis can be Installed, such as in anterior or lateral Implants, for example.

[0044] FIg. 7 shows an intervertebral disc prosthesis that utilizes two resilient bodies 15 between common intervertebral plates 11, 12. That is, the intervertebral plates 11 , 12 are common to two resilient bodies 15. The intervertebral plates 11 , 12 act as tying members to coordinate the movements of the resilient bodies 15. The resilient bodies 15 in Fig. 7 include a plurality of compliant deforrnabiβ trusses. However, it is to be appreciated that resilient bodies having a plurality of deformable plates or beams could also be provided between common intervertebral plates 11 , 12. Further, the intervertebral plates 11 , 12 are shown as having a generally square or rectangular shape. However, it is to be appreciated that the intervertebral plates 11. 12 can have other shapes. For example the intervertebral plates 11 12 could have rounded corners, as shown in Fig. 8.

[0045] Further, the embodiment of Fig. 7 includes means for selectively preventing relative movement between the intervertebral plates 11, 12. As discussed above, with the resilient body 15 instaiied in the prosthesis, reiative movement between the intervertebral plates 11, 12 can occur, One method of preventing such relative movement, for example, when fusion is desired, is by replacing the resilient body 15 with a rigid body. Another method of preventing such reiative movement is by activating a selectively deployable blocking mechanism, to block reiative movement in certain directions between the intervertebral plates 11, 12. For example, the blocking mechanism can include one or more employable pivot arms 26 to block relative movement between the intervertebral plates 11 , 12. The pivot arm 28 is selectively deployable, and can be activated when needed. In an embodiment, the pivot arm 28 is spring-biased in the deployed, generally vertical, position, and can be held in a retained, generally horizontal, position. When a trigger, such as a [ever or switch, is activated, the spring-biased pivot arm 26 is released to the deployed position. The deployed pivot arm 26 prevents relative movement between the intervertebral plates. If desired, the pivot arm 26 can be rotated back to and locked in the retained position, for later redeployment. It Is to be appreciated that the pivot arm 28 can be located on either intervertebral plate 11, 12 and neeύ not be spring-biased. Another method of preventing relative movement between the intervertebral plates 11 , 12 Is to deliver a liquid curable material into the voids 16 (Fig. 1) of the resilient body 15 and/or around the resilient body 15. The curable material would harden to prevent relative movement between the intervertebral plates 11 , 12. Example curable materials include Po!y(melhyi rnethacryiate) (PMMA) bone cement, or other self-curing, thermo-curing, or photo-curing materials.

[0048] FIg. 8, like Fig, 7, shows a spinal implant that utilizes common intervertebral plates 11, 12 that act as tying members for multiple resilient bodies (not shown). However, in the example embodiment of Fig. 8, the intervertebral plates 11 , 12 have rounded corners and a sheathing 27 extending between the intervertebral plates 11 12 to cover the resilient bodies. The sheathing 27 wraps around the impiant along a periphera^l portion of the iπtervertebrai plates 11 12 to protect the resilient bodies located between the intervertebral plates 11, 12 and prevent the Ingrowth of biological material or tissues that could alter or prevent the desired mechanical function of the resilient bodies. The sheathing 27 can be formed from a flexible material and may or may not be load bearing. The intervertebral plates 11 12 include a plurality of teeth 13 for anchoring the plates 11 , 12 to their respective vertebrae and a plurality of apertures 14 or recessed portions that permit bone growth from a vertebral surface into the intervertebral plates 11, 12,

[0047] Fig. 9 shows an example spinal implant that is similar to the embodiment of Fig. 8, but which is formed in two lateral halves 28. 29. Each lateral half includes a resilient body (not shown) which is covered by a sheathing 27 that extends between the intervertebral plates 11 , 12 of each lateral half. If desired, the lateral halves 28, 28 can be connected by a rigid or resilient tying member, to coordinate the movements of each half 28, 29. Further, the halves 28, 29 can be installed with a small gap between the halves, or with no gap between the halves. Although the implant is shown as having lateral halves 28, 29_: it is to be appreciated that the impiant could alternatively include other halves, such as posterior and anterior halves, for example.

[0048] In an embodiment, the resilient body is constructed from a material wherein the properties of the resilient body can be changed via external stimulation, such as the application of heat to a shape memory alloy, piezoelectric stimulation or the application of an electrical current. The resilient body can be constructed from a material that can change properties such as shape, rigidity, etc. based on an electrically induced strain when exposed to an electrical current. The spinal implant could further include an actuator, such as a piezoelectric actuator, to cause it to change shape, rigidity, etc. This mitigates the neeά to remove and replace the resilient body, should a change to or from a fusion-type prosthesis be desired.

[0049] The kinematics of the spine can be described by a range of rotation around an instantaneous axis of rotation (IAR)/heiical axis of motion (HAM). Compliant mechanisms for inclusion in a resilient body of a spinal Implant can be designed io provide a specific, predetermined spinal IAR/HAM during topological and dimensional synthesis. Such compliant mechanisms can be designed to accurately reproduce or specifically alter the physiological, nonlinear load displacement profiles (e.g., range of motion, kinematic signatures, etc.) of a spinal disc. A resilient body that includes such a compliant mechanism can, therefore, be designed to custom match the quality and limits of motion as well as the IAR of an individual patient.

[0050] The spinal implants described above can be provided in various shapes and sizes, to best fit an individual patient's anatomy. For example, different patients may have different intervertebral heights, widths, etc. .A spinal implant kit having cornbinable intervertebral plates and resilient bodies of various sizes and physical properties can be provided, to allow customized spinal implants for a number of individual patients. Further, the spinal implant kit can include a plurality of resilient bodies of differing rigidity, kinematic attributes such as IAR locations, limits of motion and kinematic signature of motions.

[0051] The embodiments described above can preferably be used to support adjacent vertebrae In the posterior region of the vertebrae. However, persons skilled in the art would recognize that the disclosed embodiments may be utilized to support adjoining vertebrae in the anterior or lateral regions of the vertebrae. The disclosed embodiments can be used between vertebrae in any region of the spine, cervical through lumbar. Further, the disclosed embodiments can be used to join other pieces of bone in other parts of the body.

[0052] It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.

Claims

CLAIMSWhat is claimed is;

1. An intervertebral disc prosthesis for installation in a spinal column between upper and lower vertebral surfaces, comprising: a first intervertebral plate for engaging the upper vertebral surface; a second intervertebral plate for engaging the lower vertebral surface; and a nαneiastomeric resilient body installed between and engaging said intervertebral plates, wherein the noneiastomeric resilient body comprises a plurality of deforrnable plates, and wherein the noneiastomeric resilient body permits relative movement between the first intervertebral plate and the second intervertebral plate.

2« The intervertebral disc prosthesis of claim 1 , wherein the plurality of deforrnable plates includes a plurality of parallel plates.

3. The intervertebral disc prosthesis of claim 2, wherein the noneiastomeric resilient body includes a tapered central portion.

4. The intervertebral disc prosthesis of claim 1, wherein the noneiastomeric resilient body comprises a shape memory alloy.

5. The intervertebral disc prosthesis of claim 1 , wherein the first intervertebral plate, the second intervertebral plate, and the noneiastomeric resilient body are formed as one piece.

6. The intervertebral disc prosthesis of claim 5_: wherein the noneiastomeric resilient body includes a tapered central portion.

7. The intervertebral disc prosthesis of claim 6, wherein the noneiastomeric resilient body includes an upper portion having an inverted pyramidal shape and a lower portion having a pyramidal shape.

8. The intervβrtebrai disc prosthesis of claim 1 , wherein the πoneiastomeric resilient body is removable from between the intervertebral plates while the intervertebral plates remain installed.

9. The intervertebral disc prosthesis of claim 1, further comprising means for selectively preventing said relative movement between the first intervertebral plate and the second intervertebral plate.

10. The intervertebral disc prosthesis of claim 1 wherein the intervertebral disc prosthesis is adapted for installation without hyperextension of the spine.

11. The intervertebral disc prosthesis of claim 1 , wherein the πoneiastomeric resilient body is adapted to replicate a spinai instantaneous axis of rotation.

12. An intervertebral disc prosthesis for installation in a spinal column between upper and lower vertebral surfaces, comprising: a first intervertebral plate for engaging the upper vertebral surface; a second intervertebral plate for engaging the lower vertebral surface: and a πoneiastomeric resilient body installed between and engaging said intervertebral plates, wherein the nonelastomeric resilient body comprises a plurality of deformable parallel beams, anό wherein the nonelastomeric resilient body permits relative movement between the first intervertebral plate and the second intervertebral plate.

13. The intervertebral disc prosthesis of claim 12, wherein the first intervertebral plate, the second intervertebral plate, and the noneiastomerlc resilient body are formed as one piece.

14. The intervertebral disc prosthesis of claim 13, wherein the noneiastomerlc resilient body includes a tapered central portion,

15. The intervertebral disc prosthesis of claim 14. wherein the πoneiastomeric resilient body includes an upper portion having an inverted pyramidal shape and a tower portion having a pyramidal shape.

16. The intervertebral disc prosthesis of claim 12, wherein the noneiastomeric resilient body is removable from between the intervertebral plates while the intervertebral plates remain installed.

17. The intervertebral disc prosthesis of claim 12, further comprising means for selectively preventing said relative movement between the first intervertebral plate and the second intervertebral plate.

18. The intervertebral disc prosthesis of claim 12, wherein the noneiastomeric resilient body comprises a shape memory alloy.

19. The intervertebral disc prosthesis of claim 12. wherein the noneiastomeric resilient body includes a tapered central portion,

20. The intervertebral disc prosthesis of claim 19, wherein the noneiastomeric resilient body includes an upper portion having an inverted pyramidal shape and a lower portion having a pyramidal shape.

21. The intervertebral disc prosthesis of claim 12, wherein the intervertebral disc prosthesis is adapted for installation without hyperextension of the spine.

22. The intervertebral disc prosthesis of claim 12, wherein the noneiastomeric resilient body is adapted to replicate a spinal instantaneous axis of rotation.

23. An intervertebral disc prosthesis for installation in a spinal column between upper and lower vertebral surfaces, comprising: a first intervertebral plate for engaging the upper vertebral surface: a second intervertebral plate for engaging the lower vertebral surface: and a πoneiastomeric resilient body installed between and engaging said intervertebral ρ!a!es_: wherein the nonelastomeric resilient body comprises a plurality of compliant trusses, and wherein the noneiastomeric resilient body permits relative movement between the first intervertebral plate and the second intervertebral plate.

24. The intervertebral disc prosthesis of claim 23« wherein the first intervertebral plate, the second intervertebral plate, and the nonelastomeric resilient body are formed as one piece.

25. The intervertebral disc prosthesis of claim 23, wherein the nonelastomeric resilient body is removable from between the intervertebral plates while the intervertebral plates remain installed.

28. The intervertebral disc prosthesis of claim 23. further comprising means for selectively preventing said relative movement between the first intervertebral plate and the second intervertebral piate.

27. The intervertebral disc prosthesis of claim 23, wherein the nonelastomeric resilient body comprises a shape memory alloy.

28. The intervertebral disc prosthesis of claim 23, further comprising an additional resilient body installed between and engaging said intervertebral plates.

29. The intervertebral disc prosthesis of claim 23, wherein at least one of the plurality of compliant trusses includes a beam of varying thickness.

30. The intervertebral disc prosthesis of claim 23, wherein at least one of the plurality of compliant trusses includes a first beam having a first thickness and a second beam having a second thickness.

31. The intervertebral disc prosthesis of claim 23, wherein the intervertebral disc prosthesis is adapted for Installation without hyperextension of the spine.

32. The intervertebral disc prosthesis of claim 23_: wherein the πoπelastomeric resilient body is adapted to replicate a spinal instantaneous axis of rotation,

33. An intervertebral disc prosthesis for installation in a spinal column between upper and lower vertebral surfaces, comprising: a first intervertebral plate for engaging the upper vertebral surface; a second intervertebral plate for engaging the lower vertebral surface; and a πonelastorneπc resilient body installed between and engaging said intervertebral plates, wherein the nonelastomeric resilient body comprises a plurality of structural members forming an irregular honeycomb, and wherein the nonelastomeric resilient body permits relative movement between the first intervertebral plate and the second intervertebral plate.