CROSS-REFERENCE TO RELATED APPLICATIONS

[0001| Benefit of U.S. Provisional Patent Application Serial Number 80/822,460 tiled 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 anύ inferior eπdpiates, 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 the neural structures of the spinal cord and nerves for protection. 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 vertebra! 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.

[0006] One treatment for spina! 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, It would be desirable to provide an intervertebral disc prosthesis that initially provides relative movement between adjacent vertebrae; and which can be modified after installation to provide fusion of the adjacent vertebrae.

BRIEF SUMMARY OF THE INVENTION

[0006] In accordance with one aspect of the present invention, provided is an intervertebral disc prosthesis for installation in a spinal column. The prosthesis includes a first intervertebral plate for engaging one or both of the inferior vertebral endplate anύ the inferior ring apophysis of a superior vertebral body. A second intervertebral plate engages one or both of the superior vertebral endplate and the superior ring apophysis of an inferior vertebral body. A removable insert core is located between and engages the intervertebral plates. A projection projects from one of the intervertebral plates toward the other intervertebral plate. The removable Insert core at least partially surrounds the projection when installed. The removable insert core is removable from between the intervertebral plates and from around the projection while the intervertebral plates and projection remain installed.

[0007] In accordance with another aspect of the present invention, provided is an intervertebral disc prosthesis for installation in a spinal column. The prosthesis Includes a first intervertebral plate for engaging one or both of the inferior vertebral endplate and the Inferior ring apophysis of a superior vertebral body. The first Intervertebral plate has aperture for permitting bone growth from ϊhe superior vertebral body through the first intervertebral plate, and has a plurality of upwardly projecting teeth. A second intervertebral plate engages one or both of the superior

vertebras endpiate and the superior ring apophysis of an inferior vertebral body. The second intervertebral plate has another aperture for permitting bone growth from the inferior vertebral body through the second intervertebral plate, and has a plurality of downwardly projecting teeth. A removable insert core is located between and engages the intervertebral plates. The removable insert core is a resident core having a generally C-shaped upper and lower profile. The removable insert core permits relative movement between the first intervertebral plate and the second intervertebral plate. A downward projection, having a rounded distal end, projects downward from the first intervertebral plate toward the second intervertebral plate. The second intervertebral plate forms a recessed portion for receiving the rounded distal end of the downward projection. The removable insert core at least partially surrounds the downward projection when installed in the prosthesis. The removable insert core is removable from between the intervertebral plates and from around the downward projection white the Intervertebral plates and projection remain installed,

[0008] In accordance with another aspect of the present invention, provided is an intervertebral disc prosthesis for Installation in a spinal column. The prosthesis includes a first intervertebral plate for engaging the endpiate of a first vertebral body. A second intervertebral plate engages the endpiate of a second vertebral body that is adjacent to the first vertebral body, A projection projects from one of said intervertebral plates toward the other one of said intervertebral plates. A generally C-shaped removable insert core Is located between the intervertebral plates and partially surrounds the projection. The generally C-shaped removable insert core is removable from between the intervertebral plates and from around the projection while the intervertebral plates and projection remain installed.

[0009] In accordance with another aspect of the present invention, provided is an intervertebral disc prosthesis for installation in a spinal column. The prosthesis includes a first intervertebral plate for engaging one or both of the inferior vertebral endpiate and the Inferior ring apophysis of a superior vertebral body. A second intervertebral plate engages one or both of the superior vertebral endpiate and the superior ring apophysis of an Inferior vertebral body. A removable insert core Is located between and engages the intervertebral plates. Upper retaining tabs project downward

from peripheral portions of the first intervertebral plate. Lower retaining tabs project upward from peripheral portions of the second intervertebral plate and correspond to the upper retaining tabs. The removable Insert core is radially positioned along the spinal column between said retaining tabs. The removable insert core is removable from between the intervertebral plates and retaining tabs while the intervertebral plates remain installed.

BRIEF DESCRIPTION OF THE DRAWINGS

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

[0011] FlG. 2 is an exploded perspective view of the intervertebral disc prosthesis;

[0012] FIG. 3 is a front elevation view of the intervertebral disc prosthesis;

[0013] FIG. 4 is a side elevation view of the intervertebral disc prosthesis;

[0014] FlG. δ is a rear elevation view of the intervertebral disc prosthesis;

[0015] FlG. δ Is a is a front exploded view of intervertebral disc prosthesis;

[0016] FIG. 7a is a plan view of a first intervertebral piate and assembled removable insert core;

[0017] FiG. 7b is a plan view of a second intervertebral plate;

[0018] FiG. 8 shows the intervertebral disc prostheses installed in a spinal column; and

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

[0020] FIG. 10 is a front elevation view of an example embodiment of an intervertebral disc prosthesis;

[0021] FlG. 11 is a front elevation view of an example embodiment of an intervertebral disc prosthesis;

[0022] FiG, 12 is a perspective view of an example embodiment of an intervertebral disc prosthesis; and

[0023] FiG. 13 Is a top plan view of an aiterπative embodiment of the removable insert core depicted in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention relates to spinal impiaπts. 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 άmwn 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, it 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.

[0025] Example embodiments of an intervertebral disc prosthesis 1 for installation in a spinal column are shown in Figs. 1-12. The intea-'ertebrai disc prosthesis 1 is designed to be inserted anteriorly been adjacent superior (upper) and inferior (lower) vertebral bodies, to replace a removed disc.

[0028] With reference to Figs, 1 anά 2, the intervertebral disc prosthesis 1 includes a first intervertebral plate 11 and a second intervertebral plate 12, During use, as depicted in Fig. 8, the first Intervertebral plate 11 engages a superior vertebral body 19, More specifically, the first intervertebral plate 11 engages one or both of a inferior vertebral endplate of the superior vertebral body 19 and a inferior ring apophysis of the. superior vertebral body 19. The second intervertebral plate 12 engages an adjacent, inferior vertebra! body 20. More specifically, the second intervertebral plate 12 engages

one or both of a superior vertebral endplate of the adjacent inferior vertebral body 20 and the superior ring apophysis of the adjacent inferior vertebral body 20.

|0027] Returning to Figs. 1 and 2, the intervertebral piate 11 has an interior surface 50 and an opposing exterior surface 52 that each extend between a posterior side 54 and an anterior side 58. Opposing surfaces 50 and 52 also extend between opposing lateral sides 56 and 58. A perimeter side wall 62 encircles intea>ertebrøi piate 11 and extends between opposing surfaces 50 and 52. In the depicted embodiment opposing surfaces 50 and 52 are shown having a substantially square or rectangular configuration with rounded corners, in alternative embodiments opposing surfaces 50 and 52 can be circular elliptical or have other polygonal or irregular configurations. Intervertebral plate 11 is also shown have a substantially uniform thickness where opposing surfaces 50 and 52 are substantially planer and are disposed in substantially parallel planes, in alternative embodiments intervertebral plate 11 can be tapered. For example, intervertebral plate 11 can increase in thickness as it extends from posterior side 54 to anterior side 56 so that intervertebral plate 11 has a wedged shaped configuration, it is also appreciated that the intervertebral plate 11 can have a curved shape, to better match the curved end face of a vertebral body. In one embodiment interior surface 50 can be planer while exterior surface 52 is curved or has an other desired configuration.

[0028] The intervertebral piate 12 can have substantially the same configuration and alternatives as discussed above with regard to intervertebral piate 11. Like elements between plates 11 and 12 are designated by the same reference number except that the corresponding reference numbers of piate 12 include a prime '"". in alternative embodiment it is appreciated that the various alternatives for Intervertebral plates 11 and 12 can be mixed and matched so that intervertebral piates 11 and 12 each have a different configuration for a given disc prosthesis.

[0029] As can be seen in Figs, 2 and 4, the exterior surfaces 52, 52' of intervertebral piates 11 , 12 can include a plurality of teeth 13 for anchoring the piates 11 , 12 to their respective vertebral bodies. In an example embodiment, the intervertebral piates 11 , 12 have elongated serrations, which provide a saw-toothed side

B

or front profile, and which allow the plates to dig into and thereby anchor to adjacent vertebral bodies. The plurality of teeth 13 can aiso be in the form of a plurality of spaced apart pointed spikes, teeth, or other types of projections that can engage the vertebral bodies. In alternative embodiments teeth 13 can be eliminated and exterior surfaces 52, 52 ^: can be roughened or smooth and planer.

[0030] in an example embodiment, the intervertebral plates 11 , 12 include a plurality of apertures 14 or recessed portions. Apertures 14 can extend ail the way through plates 11 ,12 or can form recesses on exterior surfaces S2, 52'. The apertures

14 or recessed portions permit bone growth from the engaged vertebral bodies into the intervertebral plates 11 , 12. ft is appreciated that each plate 11.12 can have one aperture 14 or recessed portion or any desired number thereof, it is also appreciated that apertures 14 or recessed portions can be eliminated. The intervertebral plates 11, 12 can also be coated with or formed from a porous material, to permit bone growth into the porous material from the engaged vertebral bodies. For example, the intervertebral plates 11 , 12 can include a hydroxyapatite or other conventional implant coating.

[0031] As depicted in Figs 2 and δ,one of the intervertebral plates, for example, the first intervertebral plate 11, Includes a projection 15 which projects from interior surface 50 toward the other intervertebral plate 12. The projection 15 can have a short, generally cylindrical main body 66 that attaches to the intervertebral plate 15 at a proximal enύ. _. and a rounded, generally knobiike or spherical head 68 located at an opposing distal end, as shown in the figures. It is to be appreciated that the projection

15 can take other forms, such as a post, rod or tab _s for example, which typically have a rounded distal end that provides a pivoting surface, and can be provided on either of the intervertebral plates 11 , 12. The projection 15 helps ensure proper axial and radial positioning of the intervertebral plates 11 , 12 within the spinal column.

[0032] The intervertebral plate that lacks the projection 15, such as intervertebral plate 12 can include a recessed portion formed on interior surface 50' or an aperture 16 that extends all the way through plate 12 and thai are configured for receiving the distal enύ of the projection 15. In one alternative, the recessed portion can be formed on the distal enύ of a post or other structure that upstands from interior

surface 50' of intervertebral plate 12. As depicted in Flo. 5, the distal end of the projection 15 rests in the recessed portion or aperture 16 anά can pivot and rotate within the recessed portion or aperture 18, which allows relative movement between the intervertebral plates 11 , 12. As a result, recessed portion or aperture 18 typically has a contour complementary to head 88, such as circular, so that smooth pivoting can be made therebetween. The mating between the projection 15 anά recessed portion or aperture 16 heips ensure proper axial and radial positioning of the intervertebral plates 11 , 12 within the spinal column. The projection 15 also serves to position and retain a removable insert core 17 between the Intervertebral plates 11. 12. In an embodiment, the projection 15 includes a spring (not shown) that permits axial movement between the intervertebral plates 11 , 12 along the spinal column. For example, the projection 15 can be formed from two interconnecting parts where one part freely slides over the other. A spring can be positioned between the two parts to enable the projection to resilieπtly expand and compress along its longitudinal axis. The spring can also be positioned between intervertebral plate 11 and projection 15.

[0033] The kinematics of the spine can be described by a range of rotation around an instant .Axis of Rotation {IAR)/Heiical Axis of Motion (HAM). The projection 15 and aperture 16 can be located along the instant axis of rotation to allow the prosthesis 1 to better replicate the motion of a spinal disc. As can be seen in, for example, Fig. 2, the projection 15 and aperture 16 can be located directly in the center of plates 11, 12 or slightly off center , such as toward the posterior of the prosthesis 1 , in accordance with the instant axis of rotation. That Is, in some embodiments projection 15 and aperture 16 are not located at the center of interior surfaces 50, 50 ^s but toward posterior edges 54, 54'. However it is to be appreciated that the projection 15 and aperture 1β can be located in other positions, such as toward an anterior portion or lateral portion of the prosthesis 1.

[0034] Example materials of construction for the intervertebral plates include metals such as stainless steel, titanium alloys, and cobalt-chrome-molybdenum alloys, or a bio-inert polymer, for example polyefheretherketones, such as the PEEK-GPTilvlA® product, which is commercially available from invibio, Ltd. Other materials have desired properties can also be used.

100351 The removable insert core 17 has a generally C-shaped upper and lower profile and fits around the projection 15. More specifically _: as depicted in Rg. 2, insert core 17 has a top surface 70 and an opposing bottom surface 72 with an encircling perimeter side wall 74 extending therebetween. A slot 76 passes through insert core 1? between top surface 70 and opposing bottom surface 72 and extends from side wall 74 toward the middle insert core 17. In one embodiment, slot 76 passes through the center of insert core 17 and extends slightly therebeyound so that when projection 15 is received within slot 76, insert core 17 be centered between Intervertebral plates 11 and 12. To that extent, the orientation and position of slot 76 depends on the position of projection 15. Insert core 17 can have any of a variety of different configurations but is typically configured so as to be completely covered by plates 11 and 12 as shown ϋn Fig. 1. Opposing top and bottom surfaces 70, 72 can have a substantially square, rectangular, circular, elliptical, or other polygonal or irregular configurations. Insert core 17 Is also shown have a substantially uniform thickness between surfaces 70 and 72 where opposing surfaces 70 and 72 are substantially planer and are disposed in substantially parallel planes, in alternative embodiments insert core 17 can be tapered so as to have a wedged shaped configuration.

[0038] The removable insert core 17 can be removably attached to the projection 15 by elastic and friction forces provided by the removable insert core 17. For example, the slot 78 of removable insert core 17 can be configured to "hug" or frictionally bias against the projection 15 so as to be retained between the intervertebral plates 1 I ₁ 12 by hugging the projection 15. The knoblike heaά 68 at the distal end of the projection 15 can further aid in positioning and retaining the removable insert core 17. Additionally or alternatively, the removably insert core 17 can be secured to the projection 15 or one or both intervertebral plates 11 , 12 via a fastener 18, such as a screw, bolt, pin, or the like.. For example, a passage 78 extends from perimeter side wall 74 of Insert core 17 to the interior end of slot 7β. A bore 80 transversely extends into the side of projection 15 such that when projection 15 is received within slot 76, passage 78 is aligned with bore 80. In one embodiment, bore 80 is threaded or is made from a material that can engage a thread so that fastener 18, having a threaded shaft 82 and an enlarged head 84, can be passed through passage 78 and screwed into bore

80 so as to removably secure insert core 17 to projection 15. in alternative embodiment, bore 80 can be formed on the interior surface of intervertebral plate 11 or 12 and passage 78 can be formed to align with the bore 80. Fastener 16 can then be used to secure Insert core 17 directly to intervertebral plate 11 or 12.

[0037] Depicted in Fig. 13 is another alternative embodiment of an insert core 17', Insert core 17' has substantially the same configuration as insert core 17 and like elements are identified by like reference characters. The primary distinction is that in contrast to insert core 17 where slot 78 has a substantially constant width along its length, insert core 17' has an enlarged opening 82 extending between opposing top ana bottom surfaces 70, 72 into which projection 15 can be received, and a narrow slot 84 extends between perimeter side wall 74 and enlarged opening 82. That is, slot 84 has a width that is narrower than the diameter of enlarged opening 82 and is typically narrower than the diameter of head 88 of projection 15. An outwardly tapered mouth 88 can be formed where slot 84 intersects with perimeter side wail 74. As a result, by pushing mouth 86 against projection 15, slot 84 radially outwardly expands allowing projection 15 to pass therethrough. When projection 15 is received within enlarged opening 82, slot 84 resiiieπtly closes and thereby self-locks insert core 17' about projection 15. In this embodiment, fastener 18 can be used or can be eliminated.

[0038] Returning to Figs. 4-6, the removable insert core 17 is located between and operatively engages the Intervertebral plates 11 12. For example, relative movement between the intervertebral plates 11 , 12 can apply force to the removable insert core 17 _: which resists such relative movement. The removable insert core 17 can directly engage the Intervertebral plates 11 , 12, by direct contact with the plates, or can indirectly engage the plates through, for example, a spacer (not shown).

[0039] The removable insert core 17 can be solid or generally hollow or have hollow and solid portions. For example, removable Insert core 17 can have one or more openings passing therethrough or can have one more cavities formed therein, The removable insert core 17 can be constructed from a resilient, generally flexible material or a rigid, generally inflexible material. A resilient removable insert core 17 will allow relative movement between the intervertebral plates 11 , 12. However, such relative

movement can be constrained by the insert 17. based on the physical properties of the insert 17. An example materia! of construction for a resilient removable insert core 17 is an eiastorneric material, such as silicon or polyethylene. The removable insert core 17 could also be constructed from a variety of different polymers having desired resilient properties, such as the PEEK-OPTIMA© product, which is commercially available from Invibio, Ltd. A rigid removable insert core 17 wii! prevent relative movement between the intervertebral ^' plates 11, 12, and will provide fusion between vertebrae. A rigid removable insert core 17 can include one or more passageways, to allow bone growth through the passageways. Example materials of construction for a rigid removable insert core 17 include metals, such as stainless steel, titanium alloys, and cobalt- chrome-molybdenum alloys, ceramics, and polymers, such as the PEEK-OPTIMA® product, which is commercially available from Invibio, Ltd.

[0040] The removable insert core 17 is removable from between the intervertebral plates 11, 12 and from around the projection 15. The removable insert core 17 is removable white the intervertebral plates 11 , 12 remain Installed In a spinal column. In the embodiments of Figs. 1-9 and 12, the removable insert core 17 is removed by first withdrawing the fastener 18, then pulling the insert 17 away from the projection 15. The projection 15 maintains proper spacing between the Intervertebral plates 11. 12 while the removable insert core 17 is removed. Additional temporary bracing can be provided to prevent undesirable relative movement between the intervertebral plates 11, 12 while the removable insert core 17 is removed. A new removable insert core 17 with similar or different properties when compared to the initial removed insert core 17 can be installed between the intervertebral plates 11. 12. For example, a resilient removable Insert core 17 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 a fusion-type prosthesis.

[0041] Fig, 8 shows the intervertebral disc prosthesis 1 installed between adjacent superior 19 and inferior 20 vertebral bodies. The prosthesis is installed by first removing a diseased or otherwise damaged disc. Then the intervertebral plates 11, 12 are respectively pressed into the superior 19 and inferior 20 vertebral bodies. The teeth 13 on the intervertebral plates help secure the plates 11 , 12 to the vertebra! bodies, by

digging into the vertebral endplates and/or the ring apophyses. A removable insert core 17 having, for example, a desired rigidity or flexibility is chosen and is inserted between the intervertebral plates 11 , 12 and around the projection 15. it is to be appreciated that a suitable removable insert core 17 can be selected based on additional criteria, such as durability, compatibility with the intervertebral plates 11 , 12, ability to adhere to the intervertebral plates H ₁ 12 anόio? the projection 15, etc. As discussed above, the removable insert core 17 can have a generally C-shaped upper and lower profile. It may be desirable to temporarily stretch open or widen the C-shaped profile, to facilitate the placement of the removable insert core 17 around the projection 15. A suitable tool can be used for this purpose. After the removable insert core is inserted between the intervertebral plates 11, 12, the fastening device is applied to secure the removable insert core to the projection 15, Alternatively, the removable Insert core 17 can be secured directly to the intervertebral plates 11 , 12 themselves. If desired, the installed removable insert core 17 can be removed and replaced with another core, while the intervertebral plates 11 , 12 remain attached to their respective vertebral bodies.

|0042] Turning to Fig. 8, in an example embodiment, the intervertebral disc prosthesis 1 includes means for selectively preventing relative movement between the intervertebral plates 11 , 12. As discussed above, when a resilient removable insert core 17 is installed in the prosthesis 1, relative 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 insert core with a rigid insert core. Another method of preventing such relative movement is by activating a selectively deployabie blocking mechanism, to block relative movement in certain directions between the intervertebral plates 11 , 12. For example, the blocking mechanism can include deployabie pivot arms 21 that block relative movement between the Intervertebral plates 11 , 12. The pivot arms 21 are selectively deployabie. and can be activated when needed. In an embodiment, the pivot arms 21 are spring-biased in the deployed, generally vertical, position, and can be held in a retained, generally horizontal, position. When a trigger, such as a lever or switch, Is activated, the spring- biased pivot arms 21 are released to the deployed position. The deployed pivot arms 21 prevent relative movement between the intervertebral plates. If desired, the pivot

arms 21 can be rotated back to and locked m the retained position, for later redeployment If desired. It is to be appreciated that the pivot arms 21 can be located on either intervertebral plate 1 I ₁ 12 and need not be spring-biased.

[0043] in an embodiment, the resilient insert core is constructed from a material such that the properties of the resilient insert core can be changed via piezoelectric stimulation. For example, the resiilent insert core can be made rigid via piezoelectric stimulation. This mitigates the need to remove and replace the insert core, should s change to e fusion-type prosthesis be desired. Electronics can be provided within the prosthesis itself, which are activated from outside the body, to provide the piezoelectric stimulation necessary to change the properties of the insert core.

[0044] Turning to Fig. 10, In an example embodiment, the intervertebral disc prosthesis 1 includes a first removable insert core 22, a second removable insert core 23, and a stabilizer piate 24 located between the first anά second removable insert cores 22, 22. The stabilizer plate 24 can be a generally planar metallic piate. Together, the removable insert cores 22, 23 and the stabilizer piate 24 can form a stack having a generally C-shaped upper and lower profile, as discussed above with respect to the removable insert core 17 of Figs. 1-8. Any one or more of the first removable insert core 22, the second removable insert core 23, and the stabilizer piate 24 can be removed and replace, as desired. The stabilizer piate 24 adds additional rigidity to the removable insert cores 22, 22.

[0045] Turning to Fig. 1 I ₁ In an example embodiment, an intervertebral disc prosthesis 31 includes a first intervertebral plate 32, a second intervertebral plate 33, anά a removable insert core 34 located between the intervertebral plates 32, 33. in the embodiment of Fig, 11 , the removable insert core 34 need not be generally C-shaped,. although it can be generally C-shaped, or some other shape, such as a circular or elliptical cylinder. Further, the projection discussed above neeά not be included, although It can be included. The first intervertebral plate 32 includes upper retaining tabs 35 that project downward from peripheral portions of the first intervertebral plate 32. The second intervertebral plate 33 includes corresponding lower retaining tabs 38 that project upward from peripheral portions of the second intervertebral piate 33. The

retaining tabs 35, 36 radially position and retain the removable insert core 34 along the spina! column and between the intervertebral plates 32, 38. The intervertebral plates 32, 33 can each include one large retaining tab or a plurality of smaller retaining tabs.

[0048] In an embodiment, the lower retaining tabs 36 include a channel 37 for receiving a distal portion of the upper retaining tab 35. The channel 37 helps to limit relative movement between the intervertebral plates 32, 33. Further, means for selectively preventing relative movement between the intervertebral plates 32, 33 can be provided, such as the deployable blocking mechanism discussed above.

[0047] Like the above-discussed embodiments, the embodiment of FIg. 11 can include either a resilient or rigid removable insert core 34, A rigid removable insert core 34 can include one or more passageways, to allow bone growth through the passageways. Further, the intervertebral plates 32, 33 can include apertures for permitting bone growth from the vertebral bodies into and through the apertures.

[0048] In an example embodiment depicted in Fig, 12, the second Intervertebral plate 12 includes an inwardly projecting raised lip 41 and the removable insert core 17 includes a corresponding groove 42. When the removable insert core 17 is pressed into the second intervertebral plate 12, the inwardly projecting raised lip 41 locks into the groove 42, which locks the intervertebral plates 11 , 12 and removable insert core together. The prosthesis can initially be provided with a slightly oversized resilient removable Insert core, which rests on top of the raised Hp 41 on the second intervertebral plate 12. When it is desired to change to a fusion-type prosthesis, the oversized resilient core can be removed and a rigid insert core having the groove 42 can be installed. The Hp and groove system, along with the rigid insert core, locks the prosthesis firmly together.

[0049] The embodiments described above can preferably be used to support adjacent cervical vertebrae in the anterior region of the vertebrae, However persons skilled In the art would recognize that the disclosed embodiments may be utilized to support adjoining thoracic and lumbar vertebrae in the anterior, lateral or posterior regions of the vertebrae. Further, the disclosed embodiments can be used to join other pieces of bone in other parts of the body.

[0050] 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,