Abstract:
An implant stabilizes two adjacent bones of a joint, while enabling a natural kinematic relative movement of the bones. Support components are connected to each bone of the joint, and a flexible core is interposed between them. The core and at least one of the support components are provided with a smooth sliding surface upon which the core and support component may slide relative to each other, enabling a corresponding movement of the bones. The surfaces may have a mating curvature, to mimic a natural movement of the joint. The core is resilient, and may bend or compress, enabling the bones to move towards each other, and or to bend relative to each other.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 13/033,404 filed on Feb. 23, 2011, which is incorporated herein by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to stabilizing adjacent vertebrae of the spine, after surgery or trauma, while preserving a natural kinematic signature. 
     BACKGROUND OF THE INVENTION 
     Intervertebral devices are used to address diseases or disorders of the spine, or to address damage due to trauma. These devices operate, for example, to stabilize, guide, or limit movement of adjacent vertebrae, while bearing weight. 
     The spinal disc may be displaced or damaged due to trauma, disease, degenerative defects, or wear over an extended period. A disc herniation occurs when the annulus fibers are weakened or torn and the inner tissue of the nucleus becomes permanently bulged, distended, or extruded out of its normal, internal annulus confines. The mass of a herniated or “slipped” nucleus tissue can compress a spinal nerve, resulting in leg pain, loss of muscle control, or even paralysis. Alternatively, with discal degeneration, the nucleus loses its water binding ability and deflates, as though the air had been let out of a tire. Subsequently, the height of the nucleus decreases causing the annulus to buckle in areas where the laminated plies are loosely bonded. As these overlapping laminated plies of the annulus begin to buckle and separate, either circumferential or radial annular tears may occur, which may contribute to persistent or disabling back pain. Adjacent, ancillary spinal facet joints will also be forced into an overriding position, which may create additional back pain. 
     Whenever the nucleus tissue is herniated or removed by surgery, the disc space will narrow and may lose much of its normal stability. In many cases, to alleviate back pain from degenerated or herniated discs, the nucleus is removed and the two adjacent vertebrae are surgically fused together. While this treatment alleviates the pain, all discal motion is lost in the fused segment. Ultimately, this procedure places a greater stress on the discs adjacent to the fused segment as they compensate for lack of motion, perhaps leading to premature degeneration of those adjacent disc. 
     As an alternative to vertebral fusion, various prosthetic discs have been developed. The first prosthetics embodied a wide variety of ideas, such as ball bearings, springs, metal spikes and other perceived aids. These prosthetics are all made to replace the entire intervertebral disc space and are large and rigid. Many of the current designs for prosthetic discs are large and inflexible. In addition, prosthetic disc sizes and other parameters limit the approach a surgeon may take to implant the devices. 
     There is a need for a novel spinal disc that mimics the motion of the natural spinal disc. 
     SUMMARY OF THE INVENTION 
     An implant in accordance with the invention includes a flexible core, a first support component, operative to contact a first engaging surface of the core, and a second support component, operative to contact a second, opposing engaging surface of the core. 
     The implant of the invention is operative, when positioned between adjacent bones of a joint, such as adjacent vertebrae, to stabilize the joint. The implant further enables a natural kinematic movement of the joint, while limiting movement beyond a therapeutic range of motion. 
     A flexible core is provided with an inflection region of greater flexibility, which enables a displacement or changed orientation of opposed engaging surfaces of the core. In one embodiment, the core tapers at one end to form the inflection region, and which may deform or buckle to enable a relative angular displacement of engaging surfaces. 
     In addition, the core may compress to reduce a distance between portions of first and second engaging surfaces. Compression may include an expansion of material outwards relative to an interior of the core, or material of the core may collapse into an interior. 
     A tether, or lanyard may be provided, operative to limit a maximum displacement of the core and one or both of the first and second support components. The lanyard is affixed to two of either core and one or both support components. The lanyard is formed of a flexible material which does not prevent movement within an intended range of motion of the implant, and may advantageously be formed of a resilient material, to avoid an abrupt relative cessation of movement at a limit of travel. 
     Each support component includes an engagement plate having a core engaging surface and a bone engaging surface. A keel or other projection extends from the bone engaging surface, and is operative to engage a bony surface, for example, an interior portion of a vertebra. The projection may include a bone ingrowth surface, region, or spaces, to further secure the plate into engagement with the bone. Core engaging surfaces of the first and second support component are advantageously formed with a lubricious material relative to a surface material of the engaging surfaces of the core, if sliding or rotating relative to the core is intended. 
     In one embodiment, an inflection region of the core is most flexible at a point proximate an engaging surface. A hollow interior may be included, operative to provide a space into which material forming the inflection region may deflect. A core engaging surface is provided with a smooth surface, upon which a second engaging surface of the flexible core may slide. 
     Relative motion of bones, for example opposing bones of a joint, result from movement of a patient into which an implant of the invention is implanted. As the first and second support components are attached to these bones, a corresponding motion is induced in the support components. In the natural body of the patient, these bones move in accordance with six degrees of motion. Each of these degrees of motion are enabled with an implanted implant of the invention, as follows, with reference to  FIG. 4 : 
     (1) translation in the direction indicated by line “X”, corresponding to the core sliding along an engaging surface; 
     (2) translation in the direction indicated by line “Y”, corresponding to axial compression of the core; 
     (3) translation in the direction indicated by line “Z”, corresponding to the core sliding along an engaging surface; 
     (4) rotation about an axis indicated by line “X”, corresponding to compression of one side of the core; 
     (5) rotation about an axis indicated by line “Y”, corresponding to the corerotating upon an engaging surface; and 
     (6) rotation about an axis indicated by line “Z”, corresponding to compression of one side of the core. 
     Alternatively stated, if an axis of the implant is defined as extending through an implant of the invention from a first adjacent bone to a second adjacent bone, the implant would enable relative motion of the first and second adjacent bones with respect to: 
     (a) opposite rotation about the axis; 
     (b) axially bending; 
     (c) axially compressing; and 
     (d) radial sliding with respect to the axis. 
     In an alternative embodiment, the core includes first and second segments separated by an inflection region that is substantially narrower than flanking segments, and thus bends to enable an angular displacement of the segments and their associated engaging surfaces. 
     In one embodiment of the invention, at least a portion of the support component has a core engaging surface configured as a curved smooth surface which slidably engages a mating region of the core. A curved slidable portion of the core engaging surface is recessed within a support component, and a mating slidable portion of an engaging surface projects from the core; alternatively, the core engaging surface may be projected, and an engaging surface of the core may be recessed. 
     Similarly, both sides of the core may be curved, each side mateable with a curved surface of a support component, for example, forming two convex surfaces. Mating surfaces on both sides of the core, for example, operate to foster a desired kinematic movement, and maintain a desired ligament tension throughout the expected range of motion. It should be understood, however, that in accordance with the invention, either surface may be either convex, concave, or flat, as the therapeutic needs of the patient dictate. In use, a configuration with a curved mating surface enables all six degrees of movement as described above, however, due to the mating curved slidable engaging surfaces, additional directional stability is provided. 
     In a further embodiment, the core is provided with a flat surface at a second engaging surface, which is matably connectable to a flat core engaging surface of a support component. One or more pins pass through pin bores or apertures provided in the core and support component, locking the two components together. In addition, a snap fit engagement between recessed and projecting portions of the core and a support component may be provided to further secure the core and support component together. 
     In yet another embodiment of the invention, the core engaging surface has a curved portion having a radius which is larger than a curved portion of a mating portion of the core. As such, the core may slide relative to the support component. The core may at the same time be rotated, and compressed evenly or laterally. 
     Mating surfaces of the core and a support component may include concave, convex, semi-spherical, or barrel shapes, whereby a resistance to sliding, spinning, rotating, rocking, or other relative movement may be uniform in all directions, or different in specific directions. 
     The invention provides a joint replacement implant, for example for replacement or stabilization of a cervical disc replacement, although other joints may be partially or completely replaced by the implant, for example one or more joints of the fingers, hand, wrist, elbow, shoulder, other areas of the spine, hip, knee, ankle, foot, or toes. 
     Implants of the invention are operative to restore the natural kinematic signature and natural joint properties, particularly for spinal discs, but for all joints which exhibit movement in all six degrees of motion, as detailed above. 
     All elements of implant may be made from a flexible material, although the core, in particular, flexes in order to accommodate an angular displacement of first and second support components. As the joint is flexed or extended, the flexible and or resilient material of the core may bulge or stretch to enable an angular displacement of opposing engaging surfaces. Additionally, or alternatively, an inflection region provides a relatively weaker region of the core, which is adapted through thickness and or shape to facilitate bending of the core. 
     Implant may be fabricated using any biocompatible and materials known to one skilled in the art, having sufficient strength, flexibility, resiliency, and durability for the patient, and for the term during which the device is to be implanted. 
     In accordance with the invention, a single implant may be used, to provide stabilization for a weakened joint or joint portion. Alternatively, two, three, or more implants may be used, at a single joint level, or in multiple joints. Moreover, implants of the invention may be combined with other stabilizing means. 
     Any surface or component of the invention may be coated with or impregnated with therapeutic agents, including bone growth, healing, antimicrobial, or drug materials, which may be released at a therapeutic rate, using methods known to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
         FIG. 1  depicts a perspective view of an implant in accordance with the invention; 
         FIG. 2  illustrates a cross section of the implant of  FIG. 1 , taken centrally through bane engaging projections of the implant; 
         FIG. 3  illustrates the implant of  FIG. 1 , positioned between two adjacent bones in a body; 
         FIG. 4  illustrates the implant of  FIG. 1 , with lines indicating degrees of motion of the implant; 
         FIG. 5  depicts a perspective exploded view of another embodiment of an implant of the invention; 
         FIG. 6  illustrates a cross section of the implant of  FIG. 5 , taken centrally through bone engaging projections of the implant: 
         FIG. 7  depicts a perspective exploded view of a further embodiment of an implant of the invention; and, 
         FIG. 8  illustrates a cross section of the implant of  FIG. 7 , taken centrally through hone engaging projections of the implant; 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the description which follows, any reference to direction or orientation is intended primarily and solely for purposes of illustration and is not intended in any way as a limitation to the scope of the present invention. Also, the particular embodiments described herein are not to be considered as limiting of the present invention. 
     Referring now to the figures, in which like reference numerals refer to like elements,  FIGS. 1 and 2  illustrate an implant  100  in accordance with the invention, including a flexible core  200 , a fast support component  300 , operative to contact a first engaging surface  204  of core  200 , and a second support component  400 , operative to contact an opposing second engaging, surface  208  of core  200 . 
     With reference to  FIG. 3 , implant  100  is operative, when positioned between adjacent bones of a joint, such as for example vertebrae  10 ,  12 , to stabilize a joint formed by adjacent vertebrae. Implant  100  further enables natural kinematic movement of the joint while limiting movement beyond a therapeutic range of motion. In one embodiment, this range of motion reflects the complete natural kinematic signature for the patient. 
     Referring again to  FIGS. 1 and 2 , flexible core  200  includes a first engaging surface  204  disposed upon a first segment  202 , and a second engaging surface  208 , disposed upon a second segment  206 . In the embodiment shown in  FIGS. 1 and 2 , flexible core  200  is provided with an inflection region  210  of greater flexibility, which enables a displacement or changed orientation of engaging surface  204  with respect to engaging surfaces  208 . In particular, first segment  202  tapers at one end to form inflection region  210 , which may deform or buckle to enable a relative angular displacement of engaging surfaces  204 ,  208 . 
     In addition, core  200  may compress to reduce a distance between portions of first and second engaging surfaces  204 ,  208 . Compression may include an expansion of material outwards relative to an interior  214  of core  200 , resulting in an increase in a diameter of core  200 , or material of core  200  may collapse into an interior of core  200 , thereby partially or completely maintaining an exterior dimension of core  200 . Alternatively, spaces within the material of core  200  may be reduced in size, for example spaces formed by a cellular or porous matrix of the material of core  200  may compress, whereby expansion of an exterior dimension of core  200  may be maintained or limited. 
     First support component  300  includes an engagement plate  302  having a core engaging surface  304 , and a bone engaging surface  306 . A keel or other projection  308  extends from bone engaging surface  306 , and is operative to engage a bony surface, for example, an interior portion of vertebra  10  or  12 . Projection  308  includes bone ingrowth spaces  310 , operative to provide an area for bone ingrowth, to further secure plate  302  into engagement with the bone to which plate  302  is attached. 
     Second support component  400  includes an engagement plate  402  having a core engaging surface  404 , and a bone engaging surface  406 . A keel, extension, or projection  408  extends from bone engaging surface  406 , and is operative to engage a bony surface, for example, an interior portion of vertebra  10  or  12 . Projection  408  includes bone ingrowth spaces  410 , operative to provide an area for bone ingrowth, to further secure plate  402  into engagement with the bone to which plate  402  is attached. 
     Bone ingrowth spaces  310 ,  410  may each advantageously be formed at an angle with respect to a direction of projection  308 ,  408  insertion, thereby potentially reducing an incidence of separation of implant  100  from the bone, after bone ingrowth has taken place. 
     Core engaging surfaces  304 ,  404  of first and second support component  300 ,  400  are advantageously formed with a lubricious material relative to a surface material of engaging surface  204 ,  208  of core  200 , if sliding or rotating relative to core  200  is intended. 
       FIG. 2  additionally illustrates a tether, or lanyard  218 , operative to limit a maximum displacement of core  200  and one or both of first and second support components  300 ,  400 . Lanyard  218  is affixed to two of either core  200  and one of support components  300 ,  400 , or both support components  300 ,  400 . Lanyard  218  is formed of a flexible material which does not prevent movement within an intended range of motion of implant  100 , as described herein, and may advantageously be formed of a resilient material, to avoid an abrupt relative cessation of movement, at a limit of travel, of elements to which it is affixed. 
     In the embodiment of  FIGS. 1-4 , inflection region  210  is most flexible at a point proximate engaging surface  204 . A hollow interior  212  may be included, operative to provide a space into which material forming region  210  may deflect during displacement of engaging surface  204  relative to engaging surface  208 . A tether  218  may be provided, operative to limit a maximum extent of motion of first and second support components  300 ,  400 . In this embodiment, core engaging surface  404  is provided with a smooth surface, upon which a second engaging surface of flexible core  200  may slide. Core engaging surface  404  is illustrated as substantially planar in  FIG. 4 , although a projection and recess, as described for  FIGS. 1 and 2 , may alternatively be provided. A lip or raised portion extending from core engaging surface  404 , not shown, may further, or in alternative to lanyard  218 , operate to limit an extent of movement of engaging surface  208  upon core engaging surface  404 . 
     With reference to  FIGS. 3 and 4 , relative motion of bones  10  and  12  result from movement of a patient into which implant  100  is implanted. As first and second support components  300 ,  400  are attached to bones  10 ,  12 , respectively, a corresponding motion is induced in components  300 ,  400 . It should be understood that, in accordance with the invention, component  400  may be connected to bone  10 , and component  300  may be connected to bone  12 ; that is, either component  300  or  400  may be positioned superiorly with respect to the other. 
     In the natural body of the patient, bones  10  and  12  move in accordance with six degrees of motion. Each of these degrees of motion is enabled with an implanted implant  100 , as diagrammed in  FIG. 4 . Specifically: 
     (1) translation in the direction indicated by line “X”, corresponding to core  200  sliding along engaging surface  404 ; 
     (2) translation in the direction indicated by line “Y”, corresponding to axial compression of core  200 ; 
     (3) translation in the direction indicated by line “Z”, corresponding to core  200  sliding along engaging surface  404 ; 
     (4) rotation about an axis indicated by line “X”, corresponding to compression of one side of core  200 ; 
     (5) rotation about an axis indicated by line “Y”, corresponding to core  200  rotating upon engaging surface  404 ; and 
     (6) rotation about an axis indicated by line “Z”, corresponding to compression of one side of core  200 . 
     Alternatively stated, if an axis of the implant is defined as extending through an implant of the invention from a first adjacent bone to a second adjacent bone, the implant would enable relative motion of the first and second adjacent bones with respect to: 
     (a) opposite rotation about the axis; 
     (b) axially bending; 
     (c) axially compressing; and 
     (d) radial sliding with respect to the axis. 
     In an alternative embodiment, shown in  FIGS. 5 and 6 , core  200 A includes first and second segments  202 A,  206 A, separated by an inflection region  210 A that is substantially narrower than flanking segments  202 A,  206 A, and thus bends to enable an angular displacement of segments  202 A,  206 A, and accordingly enables an angular relative displacement of engaging surfaces  204 A,  208 A. 
       FIG. 6  illustrates a cross-section of the implant  100  of  FIG. 5 , taken through projections  308  and  408 . At least a portion of core engaging surface  404 A is configured as a curved smooth surface upon which a mating region of curved smooth surface of second engaging surface  208 A of flexible core  200 A may slide. In the illustration, a curved slidable portion of core engaging surface  404 A is recessed within second support component  400 A, and a mating slidable portion of engaging surface  208 A projects from core  200 A; however, it should be understood that engaging surface  404 A may be projected, and engaging surface  208 A may be recessed. 
     Similarly, a portion of first engaging surface  204 A is a curved smooth surface upon which a mating curved smooth surface of core engaging surface  306 A may slide. In the embodiment shown in  FIGS. 5-6 , core  200 A forms two convex surfaces  204 A,  208 A, to foster a desired kinematic movement, and to maintain a desired ligament tension throughout the expected range of motion, and to promote a natural resting position of the bones. It should be understood, however, that in accordance with the invention, either surface  204 A or  208 A may be either convex or concave, as the therapeutic needs of the patient dictate. Alternatively, either surface may be flat, as illustrated in  FIGS. 1-4 , discussed above, or  FIGS. 7-8 , discussed below. 
     In one embodiment, a projection  312  extends from first engaging surface  306 A into core aperture or hollow interior  212 A, and is operative to limit an extent of movement of first support component  300  with respect to core  200 . A similar configuration could be provided for slidably mating engaging surfaces  404 A and  208 A. 
     Embodiments of the invention may be provided with one or more apertures  316 ,  416  through which fasteners may be installed, to further secure implant  100  within a patient. For example, a bone screw may be passed through aperture  316  in first support component  300  and into bone  10 , and another bone screw may be passed through aperture  416  in second support component  400 , and into bone  12 . A bone growth agent may alternatively or additionally be provided within aperture  316  or  416 , or upon bone engaging surface  306  and or  406 , to promote bone growth thereinto. Bone growth surfaces may be provided with openings or texture into which tissue may grow and adhere. 
     In use, the embodiment of  FIGS. 5-6  enables all six degrees of movement as described above, however, due to the mating curved slidable engaging surfaces  208 A and  404 A, additional directional stability is provided, whereby sliding is inhibited to an extent in the absence of flexion or extension of the joint. This inhibition arises from a natural gravitational resting state of the mating curved engaging surfaces  208 A and  404 A. 
     Referring now to the embodiment illustrated in  FIGS. 7-8 , in which core  200 B is provided with a flat surface at second engaging surface  208 B, matably connectable to flat core engaging surface  404 B of second support component  400 . In this embodiment, core  200 B is configured to affix core  200 B with respect to rotation upon second engaging surface  404 B, by one or more pins  414 , which pass through one or more pin bores or apertures  216 ,  416 , provided in core  200 B and second support component  400 B, respectively. While pins are illustrated, it should be understood that other fastener configuration are possible, including screws, adhesive, set screws, interference fit, press fit, or other methods as would be understood by one skilled in the art. Pins  414  may be threaded or press fit into apertures  216  or  416 , or secured using adhesive, and may be secured to either or both of core  200 B or second support component  400 B. 
     While pins  414  may be utilized to prevent rotation as well as to maintain core  200 B in a position upon engagement surface  404 B, an axial position of core  200 B against engagement surface  404 B may alternatively or additionally be maintained by a snap fit engagement between recessed portion  220  and projected portion  420  of core  200 B and core engaging surface  404 B, respectively. Alternatively, core  200 B may be provided with a projecting portion, and core engaging surface  404 B may be provided with a mating recess. 
     In any of the embodiments of the invention, should it be desired to maintain a position of either or both core engagement surfaces  304 ,  304 A,  304 B and  404 ,  404 A,  404 B relative to core  200 ,  200 A,  200 B, pins, a snap fit, or other fasteners may be used, as described above. 
     With further reference to  FIG. 8 , it can be seen that core engaging surface  304 B has a curved portion having a radius which is larger than a curved portion of first engaging surface  204 B. As such, core engaging surface  304 B and first engaging surface  204 B may readily slide, to a limited extent, relative to each other, as influenced by the difference between their respective curvatures. Core  200 B may also be rotated, and compressed evenly or laterally, as detailed elsewhere herein with respect to other embodiments of the invention. 
     It should be understood that superior and inferior positions of components, as illustrated, are for the convenience of the reader in understanding the invention, and that implant  100  may be implanted in a reverse orientation than is shown, as benefits the patient. 
     In use, the embodiment of  FIGS. 7-8  enables all six degrees of movement as described above, however, due to the mating curved slidable engaging surfaces  204 B and  304 B, additional directional stability is provided, whereby sliding is inhibited to an extent in the absence of flexion or extension of the joint. This inhibition arises from a natural gravitational resting state of the mating curved engaging surfaces  204 B and  304 B. Rotation, or spinning, of bone  10  with respect to bone  12 , is translated only through an interface between first engaging surface  204 B and core engaging surface  304 B, as second engaging surface  208 B is affixed with respect to core engaging surface  404 B. Similarly, sliding is carried out solely through this interface, for the same reasons. Surfaces  208 B and  404 B may alternatively slide with respect to each other, as detailed herein with respect to other embodiments. 
     Mating surfaces  204 ,  204 A,  204 B and  304 ,  304 A,  304 B; or  208 ,  208 A,  208 B and  404 ,  404 A,  404 B, may, for example, be concave, convex, semi-spherical, elliptical, complex, or barrel shaped, whereby a resistance to sliding, spinning, rotating, rocking, or other relative movement may be uniform in all directions, or different in specific directions. 
       FIG. 8  further illustrates insertion tool channels, bores, openings, or apertures  218 ,  418 , in first and second support components  300 B,  400 B. As implant  100  is inserted between joint surfaces maintained in spaced relation by ligaments, it may be necessary to mechanically compress implant  100  prior to insertion within the joint. A tool, not shown, such as is known in the art, may be provided with tines which engage tool apertures  218 ,  418 , whereupon first and second support components  300 B,  400 B may be moved together, or apart, as determined by the practitioner, during implantation. Further, implant  100  may be implanted through an anterior, anterolateral, or lateral approach, and accordingly, tool apertures  218 ,  418  provide a means for mechanically grasping and manipulating implant  100  during implantation. 
     The invention provides a joint replacement implant, for example for replacement or stabilization of a cervical disc replacement, although other joints may be partially or completely replaced by implant  100 , for example one or more joints of the fingers, hand, wrist, elbow, shoulder, other areas of the spine, hip, knee, ankle, foot, or toes. 
     Implant  100  is operative to restore the natural kinematic signature and natural joint properties, particularly for spinal discs, but for all joints which exhibit movement in all six degrees of motion, as detailed above. 
     All elements of implant  100  may be made from a flexible material, although core  200 , in particular, flexes in order to accommodate an angular displacement of first and second support components  300 ,  400 . As the joint is flexed or extended, the flexible and or resilient material of core  200  may bulge or stretch to enable an angular displacement of first and second engaging surfaces  204 ,  208 . Additionally, or alternatively, inflection region  210  provides a relatively weaker region of core  200  which is adapted through thickness and or shape to facilitate bending of core  200 . 
     Implant  100  may be fabricated using any biocompatible materials known to one skilled in the art, having sufficient strength, flexibility, resiliency, and durability for the patient, and for the term during which the device is to be implanted. Examples include but are not limited to metal, such as, for example titanium and chromium alloys; polymers, including for example, PEEK or high molecular weight polyethylene (HMWPE); and ceramics. 
     Portions or all of the implant may be radiopaque or radiolucent, or materials having such properties may be added or incorporated into the implant to improve imaging of the device during and after implantation. 
     Opposing mating surfaces which rotate, spin, or slide, including core engaging surfaces  304 ,  304 A,  304 B,  404 ,  404 A,  404 B, and first and second engaging surfaces  204 ,  204 A,  204 B and  208 ,  208 A,  208 B, may be made of the same or different materials, which combination produces a therapeutic fluidity of motion, or desired drag. Surfaces of implant  100  may be plasma sprayed, for example by titanium plasma spray, and may be bead blasted or electropolished. 
     More particularly, the support components may be manufactured from cobalt-chrome-molybdenum alloy, Co—Cr—Mo, as specified in ASTM F1537 (and ISO 5832-12). The smooth surfaces may be plasma sprayed with commercially pure titanium, as specified in ASTM F1580, F1978, F1147 and C-633 (and ISO 5832-2). The core may be manufactured from ultra-high molecular weight polyethylene, UHMWPE, as specified in ASTM F648 (and ISO 5834-2). 
     Core  200 ,  200 A,  200 B, may alternatively, in one embodiment, be fabricated using polycarbonate urethane (PCU), or a thermoplastic polycarbonate urethane (TPU) such as Bionate, a registered trademark of DSM IP Assets B.V. Corporation, of Heerlen Netherlands, for a thermoplastic elastomer formed as the reaction product of a hydroxyl terminated polycarbonate, an aromatic diisocyanate, and a low molecular weight glycol used as a chain extender. Other polymeric materials with suitable flexibility, durability, and biocompatibility may also be used, as understood by one skilled in the art. 
     In accordance with the invention, implants of various sizes may be provided to best fit the anatomy of the patient. Support components and a core of matching or divergent sizes may be assembled during the implantation procedure by a medical practitioner as best meets the therapeutic needs of the patient, the assembly inserted within the body using an insertion tool. Implants of the invention may also be provided with an overall angular geometry, for example angular mating dispositions of support components and core, to provide for a natural lordosis, or a corrective lordosis, for example of from 0° to 6° for a cervical application, although much different values may be advantageous for other joints. Implant heights, for use in the cervical vertebrae for example, may typically range from 7 mm to 12 mm, although the size is dependent on the patient, and the joint into which an implant of the invention is to be implanted. 
     In accordance with the invention, a single implant  100  may be used, to provide stabilization for a weakened joint or joint portion. Alternatively, two, three, or more implants  100  may be used, at a single joint level, or in multiple joints. Moreover, implants  100  may be combined with other stabilizing means. 
     Additionally, implant  100  may be fabricated using material that biodegrades in the body during a therapeutically advantageous time interval. Further, implant  100  is advantageously provided with smooth and or rounded exterior surfaces, which reduce a potential for deleterious mechanical effects on neighboring tissues. 
     Any surface or component of the invention may be coated with or impregnated with therapeutic agents, including bone growth, healing, antimicrobial, or drug materials, which may be released at a therapeutic rate, using methods known to those skilled in the art. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention. 
     All references cited herein are expressly incorporated by reference in their entirety. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. There are many different features to the present invention and it is contemplated that these features may be used together or separately. Thus, the invention should not be limited to any particular combination of features or to a particular application of the invention. Further, it should be understood that variations and modifications within the spirit and scope of the invention might occur to those skilled in the art to which the invention pertains. 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.