Abstract:
The described devices are bound spinal implants that may be surgically implanted into the spine to replace damaged or diseased discs using a posterior, lateral, or postero-lateral approach. The discs are prosthetic devices that approach or mimic the physiological motion and reaction of the natural disc.

Description:
[0001]    This application claims the benefit of provisional application Ser. No. 61/214,668 filed Apr. 27, 2009, which is fully incorporated herein. 
     
    
     FIELD 
       [0002]    The described devices are bound spinal implants that may be surgically implanted into the spine to replace damaged or diseased discs using a posterior, lateral, or postero-lateral approach. The discs are prosthetic devices that approach or mimic the physiological motion and reaction of the natural disc. 
       BACKGROUND 
       [0003]    The intervertebral disc is an anatomically and functionally complex joint. The intervertebral disc is composed of three component structures: (1) the nucleus pulposus; (2) the annulus fibrosus; and (3) the vertebral end plates. The biomedical composition and anatomical arrangements within these component structures are related to the biomechanical function of the disc. 
         [0004]    The spinal disc may be displaced or damaged due to trauma or a disease process. If displacement or damage occurs, the nucleus pulposus may herniate and protrude into the vertebral canal or intervertebral foramen. Such deformation is known as herniated or slipped disc. A herniated or slipped disc may press upon the spinal nerve that exits the vertebral canal through the partially obstructed foramen, causing pain or paralysis in the area of its distribution. 
         [0005]    To alleviate this condition, it may be necessary to remove the involved disc surgically and fuse the two adjacent vertebrae. In this procedure, a spacer is inserted in the place originally occupied by the disc and the spacer is secured between the neighboring vertebrae by the screws and plates or rods attached to the vertebrae. Despite the excellent short-term results of such a “spinal fusion” for traumatic and degenerative spinal disorders, long-term studies have shown that alteration of the biomechanical environment leads to degenerative changes particularly at adjacent mobile segments. The adjacent discs have increased motion and stress due to the increased stiffness of the fused segment. In the long term, this change in the mechanics of the motion of the spine causes these adjacent discs to degenerate. 
         [0006]    Artificial intervertebral replacement discs may be used as an alternative to spinal fusion. 
       SUMMARY 
       [0007]    Prosthetic intervertebral discs and methods for using such discs are described. The subject prosthetic discs include an upper end plate assembly, a lower end plate assembly, a compressible core member disposed between the two end plates, filamentary members connecting the upper and lower end plate assemblies, and an external sheath covering the filamentary member (or members). The disc may include fixation members for fixing the prosthetic disc in place against the adjoining vertebrae. The described prosthetic discs have shapes, sizes, and other features that are particularly suited for implantation using minimally invasive surgical procedures, particularly from a posterior approach. The described discs may be releasably bound with an elongate member, e.g., string, cable, wire, etc., to compress the disc for placement in the intervertebral space, and to allow remotely controlled expansion of the bound disc. 
         [0008]    The described bound prosthetic discs include top and bottom end plate assemblies separated by one or more compressible core members. We also refer to the top and bottom end plate assemblies as first and second end plate assemblies, particularly since the nature of this device is such that it operates the same way without regard to the orientation of the device. The two plate assemblies may be held together by at least one fiber wound around at least one region of the top end plate assembly and at least one region of the bottom end plate assembly. The described discs may include integrated or movable vertebral body fixation elements. When considering a lumbar disc replacement from the posterior access, the two plates are preferably elongated, having a length that is substantially greater than its width. Typically, the dimensions of the prosthetic discs range in height from 8 mm to 15 mm; the width ranges from 6 mm to 13 mm. The height of the prosthetic discs ranges from 9 mm to 11 mm. The widths of the disc may be 10 mm to 12 mm. The length of the prosthetic discs may range from 18 mm to 30 mm, perhaps 24 mm to 28 mm. Typical shapes include oblong, bullet-shaped, lozenge-shaped, rectangular, or the like. 
         [0009]    The described disc structures may be introduced into an intervertebral space in a compressed state. The prosthetic disc may be so compressed using an insertion tool including a severable banding member wrapped around the prosthetic disc. 
         [0010]    The described disc structures may include at least one fiber wound around at least one region of the upper end plate assembly and at least one region of the lower end plate assembly. The fibers are generally high tenacity fibers with a high modulus of elasticity. The elastic properties of the fibers, as well as factors such as the number of fibers used, the thickness of the fibers, the number of layers of fiber windings in the disc, the tension applied to each layer, and the crossing pattern of the fiber windings enable the prosthetic disc structure to mimic the functional characteristics and biomechanics of a normal-functioning, natural disc. 
         [0011]    A number of conventional surgical approaches may be used to place a pair of prosthetic discs. Those approaches include a modified posterior lumbar interbody fusion (PLIF) and a modified transforaminal lumbar interbody fusion (TLIF) procedures. We also describe apparatus and methods for implanting prosthetic intervertebral discs using minimally invasive surgical procedures. In one variation, the apparatus includes a pair of cannulae that are inserted posteriorly, side-by-side, to gain access to the spinal column at the disc space. A pair of prosthetic discs may then be implanted by way of the cannulae to be located between two vertebral bodies in the spinal column. 
         [0012]    Other and additional devices, apparatus, structures, and methods are described by reference to the drawings and detailed descriptions below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The Figures contained herein are not necessarily drawn to scale. Some components and features may be exaggerated for clarity. 
           [0014]      FIG. 1  shows a method for placement of prosthetic intervertebral discs using a posterior approach. 
           [0015]      FIG. 2A  is a perspective view of one variation of our prosthetic disc. 
           [0016]      FIG. 2B  is a perspective view of the variation seen in  FIG. 2A . 
           [0017]      FIG. 2C  is a perspective, partially exploded view of the variation seen in  FIG. 2A . 
           [0018]      FIG. 2D  is a cross-sectional view of the variation seen in  FIG. 2A . 
           [0019]      FIGS. 2E and 2F  are side views of the variation seen in  FIG. 2A . 
           [0020]      FIG. 3A  is a top perspective view of an inner, end plate component. 
           [0021]      FIG. 3B  is a bottom perspective view of an inner, end plate component. 
           [0022]      FIG. 3C  is a top view of an inner, end plate component. 
           [0023]      FIG. 3D  is a side view of an inner, end plate component. 
           [0024]      FIG. 3E  is a bottom view of an inner, end plate component. 
           [0025]      FIG. 4A  is a bottom perspective view of an inner, end plate component. 
           [0026]      FIG. 4B  is a bottom view of an inner, end plate component. 
           [0027]      FIG. 5A  is a top perspective view of an upper, end plate component. 
           [0028]      FIG. 5B  is a bottom perspective view of an upper, end plate component. 
           [0029]      FIG. 5C  is a top view of an upper, end plate component. 
           [0030]      FIG. 5D  is a side view of an upper, end plate component. 
           [0031]      FIG. 5E  is a bottom view of an upper, end plate component. 
           [0032]      FIG. 6A  is a top perspective view of a sheath. 
           [0033]      FIG. 6B  is a bottom view of a sheath. 
           [0034]      FIG. 6C  is a side view of a sheath. 
           [0035]      FIG. 7  is a cross section of the assembly of upper and lower inner end plates, core member, and the filamentary members. 
           [0036]      FIGS. 8A and 8B  show perspective views of our disc with central anchoring members. 
           [0037]      FIG. 8C  shows a side view of our disc with central anchoring members. 
           [0038]      FIG. 8D  shows a perspective view of an isolated central anchoring member. 
           [0039]      FIGS. 9A and 9B  show perspective views of our disc with side anchoring members. 
           [0040]      FIG. 9C  shows a side view an isolated side anchoring member. 
           [0041]      FIG. 9D  shows a perspective view of an isolated side anchoring member. 
           [0042]      FIG. 10  illustrates the distal end of a deployment tool for our prosthetic discs. 
           [0043]      FIG. 11  schematically illustrates a method for expanding the described prosthetic discs using our deployment tool. 
           [0044]      FIG. 12A  shows a side-view of a deployment tool for our prosthetic discs. 
           [0045]      FIG. 12B  shows a perspective view of a deployment tool for our prosthetic discs. 
           [0046]      FIG. 12C  shows a perspective view of the distal end of a deployment tool for our prosthetic discs. 
           [0047]      FIG. 12D  shows a side view of the distal end of a deployment tool for our prosthetic discs. 
           [0048]      FIG. 13  schematically illustrates a method for implanting the described prosthetic discs. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]    Described below are prosthetic intervertebral discs, methods of using such discs, apparatus for implanting such discs, and methods for implanting such discs. It is to be understood that the prosthetic intervertebral discs, implantation apparatus, and methods are not limited to the particular embodiments described, as these may, of course, vary. It is also to be understood that the terminology used here is only for the purpose of describing particular embodiments, and is not intended to be limiting in any way. 
         [0050]    Insertion of the prosthetic discs may be approached using modified conventional procedures, such as a posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion (TLIF). In the modified PLIF procedure, the spine is approached via midline incision in the back. The erector spinae muscles are stripped bilaterally from the vertebral lamina at the required levels. A laminectomy is then performed to further allow visualization of the nerve roots. A partial facetectomy may also be performed to facilitate exposure. The nerve roots are retracted to one side and a discectomy is performed. Optionally, a chisel may then used to cut one or more grooves in the vertebral end plates to accept the fixation components on the prostheses. Appropriately-sized prostheses may then be inserted into the intervertebral space on either side of the vertebral canal. 
         [0051]    In a modified TLIF procedure, the approach is also posterior, but differs from the PLIF procedure in that an entire facet joint is removed and the access is only on one side of the vertebral body. After the facetectomy, the discectomy is performed. Again, a chisel may be used to create on or more grooves in the vertebral end plates to cooperatively accept the fixation components located on each prosthesis. The prosthetic discs may then be inserted into the intervertebral space. One prosthesis may be moved to the contralateral side of the access and then a second prosthesis then inserted on the access side. 
         [0052]    It should be apparent that we refer to these procedures as “modified” in that neither procedure is used to “fuse” the two adjacent vertebrae. 
         [0053]      FIG. 1  shows a top, cross section view of a spine ( 100 ), sectioned across an intervertebral disc ( 102 ). This Figure depicts a minimally invasive surgical procedure for implanting a pair of intervertebral discs in an intervertebral region formed by the removal of a natural disc. This minimally invasive surgical implantation method is performed using a posterior approach, rather than the conventional anterior lumbar disc replacement surgery or the modified PLIF and TLIF procedures described above. 
         [0054]    In  FIG. 1 , two cannulae ( 104 ) are inserted posteriorly, through the skin ( 107 ), to provide access to the spinal column. More particularly, a small incision is made and a pair of access windows created through the lamina ( 106 ) of one of the vertebrae ( 108 ) on each side of the vertebral canal ( 110 ) to access the natural vertebral disc. The spinal cord ( 112 ) and nerve roots are avoided or moved to provide access. Once access is obtained, the two cannulae ( 104 ) are inserted. The cannulae ( 104 ) may be used as access passageways in removing the natural disc with conventional surgical tools. Alternatively, the natural disc may be removed prior to insertion of the cannulae. The cannulae are also used to introduce the prosthetic intervertebral discs ( 114 ) to the intervertebral region. 
         [0055]    The described bound prosthetic discs are of a design and capability such that they may be employed at more than one level, i.e., disc location, in the spine. Specifically, several natural discs may be replaced with our discs. As will be described in greater detail below, each such level will be implanted with at least two of my discs. Kits, containing two of my discs for a single disc replacement or four of my discs for replacement of discs at two levels in the spine, perhaps with sterile packaging are contemplated. Such kits may also contain one or more cannulae having a central opening allowing passage and implantation of my discs. 
         [0056]    Once the natural disc has been removed and the cannulae ( 104 ) located in place, a pair of prosthetic discs ( 114 ) is implanted between adjacent vertebral bodies. The prosthetic discs have a shape and size suitable making them useful with (or adapted for) various minimally invasive procedures. The discs may have a shape such as the elongated one-piece prosthetic discs described below. 
         [0057]    A prosthetic disc ( 114 ) is guided through each of the cannula such that each of the prosthetic discs ( 114 ) is implanted between the two adjacent vertebral bodies. The two prosthetic discs ( 114 ) may be located side-by-side and spaced slightly apart, as viewed from above. Optionally, prior to implantation, grooves may be formed on the internal surfaces of one or both of the vertebral bodies in order to engage anchoring components or features located on or integral with the prosthetic discs ( 114 ). The grooves may be formed using a chisel tool adapted for use with the minimally invasive procedure, i.e., adapted to extend through a relatively small access space (such as the tunnel-like opening found in through the cannulae) and to chisel the noted grooves within the intervertebral space present after removal of the natural disc. 
         [0058]    These discs may be used as shown in  FIG. 1  or, optionally, they may be implanted with an additional prosthetic disc or discs, perhaps in the position shown for auxiliary disc ( 116 ). 
         [0059]    Additional prosthetic discs may also be implanted in order to obtain desired performance characteristics, and the implanted discs may be implanted in a variety of different relative orientations within the intervertebral space. In addition, the multiple prosthetic discs may each have different performance characteristics. For example, a prosthetic disc to be implanted in the central portion of the intervertebral space may be configured to be more resistant to compression than one or more prosthetic discs that are implanted nearer the outer edge of the intervertebral space. For instance, the stiffness of the outer discs (e.g.,  114 ) may each be configured such that those outer discs exhibit approximately 5% to 80% of the stiffness of the central disc ( 116 ), perhaps in the range of about 30% to 60% of the central disc ( 116 ) stiffness. Other performance characteristics may be varied as well. 
         [0060]    The lateral, or horizontal, surface area of each of the end plate assemblies—i.e., the area of the disc assembly surfaces that engage the vertebral bodies—is substantially larger than the cross-sectional surface area of the core member or members. The cross-sectional surface area of the core member or members may be from about 5% to about 90% of the cross-sectional area of a given end plate, perhaps from about 10% to about 60%, or from about 15% to about 50%. In this way, for a given compressible core having sufficient compression, flexion, extension, rotation, and other performance characteristics but having a relatively small cross-sectional size, the core member may be used to support end plates having a relatively larger cross-sectional size in order to help prevent subsidence into the vertebral body surfaces. In the variations described here, the compressible core and end plates also have a size that is appropriate for or adapted for implantation by way of posterior access or minimally invasive surgical procedures, such as those described above. 
         [0061]    Each of the described prosthetic discs depicted in the Figures has a greater length than width. The aspect ratio (length:width) of the discs may be about 1.5:1 to 5.0:1, perhaps about 2.0:1 to 4.0:1, or about 2.5:1 to 3.5:1. Exemplary shapes to provide these relative dimensions include rectangular, oval, bullet-shaped, lozenge-shaped, and others. These shapes facilitate implantation of the discs by the minimally invasive procedures described above. Of course, the shape of our discs is not limited to those listed just above, but may be any shape suitable for use as all or part of a complete intervertebral prosthetic disc. 
         [0062]    This description may describe a number of variations of prosthetic intervertebral discs. By “prosthetic intervertebral disc” is meant an artificial or manmade device that is so configured or shaped that it may be employed as a total or partial replacement of an intervertebral disc in the spine of a vertebrate organism, e.g., a mammal, such as a human. The described prosthetic intervertebral discs have dimensions that permit them, either alone or in combination with one or more other prosthetic discs, to substantially occupy the space between two adjacent vertebral bodies that is present when the naturally occurring disc between the two adjacent bodies is removed, i.e., a void disc space. By “substantially occupy” is meant that, in the aggregate, the discs occupy at least about 30% by surface area, perhaps at least about 80% by surface area or more. The subject discs may have a roughly bullet or lozenge shaped structure adapted to facilitate implantation by minimally invasive surgical procedures. 
         [0063]    The discs may include both an upper (or top) and lower (or bottom) end plate assembly, where the upper and lower end plate assemblies are separated from each other by a compressible element such as one or more core members, where the combination structure of the end plate assemblies and compressible element provides a prosthetic disc that functionally approaches or closely mimics a natural disc. The top and bottom end plate assemblies may be held together by at least one fiber attached to or wound around at least one portion of each of the top and bottom end plates. As such, the two end plate assemblies (or planar substrates) are held to each other by one or more fibers that are attached to or wrapped around at least one domain, portion, or area of the upper end plate assembly and lower end plate assembly such that the end plate assembliess are joined to each other. The prosthetic discs may include one or more sheaths surrounding the fibers connecting the upper and lower end plate assemblies. 
         [0064]      FIG. 2A  shows a perspective view of one variation of our prosthetic intervertebral disc ( 200 ). This variation comprises an upper end plate assembly ( 202 ) and a lower end plate assembly ( 204 ) separated by a compressible core (not seen in this view) and a sheath ( 206 ) covering the filamentary member (not seen in this view) connecting the upper end plate assembly ( 202 ) and the lower end plate assembly ( 204 ). Also seen in this view is a groove ( 208 ) extending axially along the upper surface ( 210 ) of upper end plate assembly ( 202 ) that may be used as a determinate passageway for a severable banding member forming a portion of an insertion tool (discussed in more detail below) for inserting the prosthetic disc into an intervertebral space. The groove ( 208 ) may be matched in the lower surface of the lower end plate assembly ( 204 ). 
         [0065]    Also as will be discussed below, the groove ( 208 ) and the matching groove in the lower end plate assembly ( 204 ) may also be used to receive and secure a fixation member such as a keel. 
         [0066]    The upper surface ( 210 ) of upper end plate assembly ( 202 ) and the corresponding lower surface of the lower end plate assembly ( 204 ) are configured to contact bone surfaces on the adjacent vertebrae in the intervertebral space. 
         [0067]      FIG. 2B  is another perspective view of the variation ( 20 ) shown in  FIG. 2A  but with the sheath ( 206 ) and the filamentary members removed to better illustrate the structure of the prosthetic disc ( 202 ). Upper end plate assembly ( 202 ) is made up of an outer end plate member ( 214 ) and an inner end plate member ( 216 ). The outer end plate member ( 214 ) may be welded to the inner end plate member ( 216 ), for instance, at the site where the posts ( 218 ,  220 ) extend upwardly from the inner end plate member ( 216 ) into the outer end plate member ( 214 ). 
         [0068]    The inner end plate member ( 216 ) in this variation ( 200 ) includes a number of openings or apertures ( 222 ), perhaps slots, through which is threaded the filamentary member (omitted from this view) connecting the upper inner end plate member ( 216 ) of the upper end plate assembly ( 202 ) and the lower inner end plate member ( 224 ) of the lower end plate assembly ( 204 ). The lower end plate assembly ( 204 ) is made up of an outer end plate member ( 226 ) and an inner end plate member ( 224 ). They may also be attached together in the same manner as is the upper end plate assembly. The placement and function of the filamentary member will be explained below. 
         [0069]    The core member ( 228 ) may be seen residing between the lower inner end plate member ( 224 ) and the upper inner end plate member ( 216 ). 
         [0070]      FIG. 2C  shows a partially exploded, perspective view of the device ( 200 )—again without the filament or sheath—but showing the modified olive shape of the core ( 228 ). The core resides in recesses within the lower inner end plate member ( 224 ) and the upper inner end plate member ( 216 ). The surfaces of those recesses form bearing surfaces for support of the core ( 228 ). This view also shows the posts ( 218 ,  220 ) extending up from the upper inner end plate member ( 216 ) that may be used for welding to the upper outer end plate member ( 216 ) to form the upper end plate assembly ( 202 ). 
         [0071]      FIG. 2D  shows a perspective, cutaway view of the device (without the filamentary member) ( 200 ). This view shows the modified olive-like shape of the core ( 229 ) and its residence in the conforming. This view also shows the conformance of the recesses within the lower inner end plate member ( 224 ) and the upper inner end plate member ( 216 ) with the exterior surface of the core ( 228 ). 
         [0072]    The core member ( 228 ) provides support to and maintains the relative spacing between the upper and lower end plate assemblies. The core member may comprise one or more relatively compliant materials. In particular, the compressible core member in this variation and the others discussed herein, may comprise a thermoplastic elastomer (TPE) such as a polycarbonate-urethane TPE having, e.g., a Shore value of 50 D to 60 D, e.g. 55 D. An example of such a material is the commercially available TPE, BIONATE. Shore hardness is often used to specify flexibility or flexural modulus for elastomers. 
         [0073]    We have had success with core members comprising TPE that are compression molded at a moderate temperature from an extruded plug of the material. For instance, with the polycarbonate-urethane TPE mentioned above, a selected amount of the polymer is introduced into a closed mold upon which a substantial pressure may be applied, while heat is applied. The TPE amount is selected to produce a compression member having a specific height. The pressure is applied for 8-15 hours at a temperature of 70°-90° C., typically about 12 hours at 80° C. 
         [0074]    Compliant polyurethane elastomers are discussed generally in, M. Szycher, J. Biomater. Appl. “Biostability of polyurethane elastomers: a critical review”, 3(2):297 402 (1988); A. Coury, et al., “Factors and interactions affecting the performance of polyurethane elastomers in medical devices”, J. Biomater. Appl. 3(2):130 179 (1988); and Pavlova M, et al., “Biocompatible and biodegradable polyurethane polymers”, Biomaterials 14(13):1024 1029 (1993). Examples of suitable polyurethane elastomers include aliphatic polyurethanes, segmented polyurethanes, hydrophilic polyurethanes, polyether-urethane, polycarbonate-urethane, and silicone-polyether-urethane. 
         [0075]    Other suitable elastomers include various polysiloxanes (or silicones), copolymers of silicone and polyurethane, polyolefins, thermoplastic elastomers (TPE&#39;s) such as atactic polypropylene, block copolymers of styrene and butadiene (e.g., SBS rubbers), polyisobutylene, and polyisoprene, neoprene, polynitriles, artificial rubbers such as produced from copolymers produced of 1-hexene and 5-methyl-1,4-hexadiene, polybutylene terephthalate (PBT), polybutylene glycol (polytetramethylene oxide or PMTO), polyesters (e.g., Hytrel®), their mixtures or the like. 
         [0076]    One variant of the construction for the core member comprises a nucleus formed of a hydrogel and an elastomer reinforced fiber annulus. 
         [0077]    For example, the nucleus, the central portion of the core member, may comprise a hydrogel material. Hydrogels are water-swellable or water-swollen polymeric materials typically having structures defined either by a crosslinked or an interpenetrating network of hydrophilic homopolymers or copolymers. In the case of physical crosslinking, the linkages may take the form of entanglements, crystallites, or hydrogen-bonded structures to provide structure and physical integrity to the polymeric network. 
         [0078]    Suitable hydrogels may be formulated from a variety of hydrophilic polymers and copolymers including polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyethylene oxide, polyacrylamide, polyurethane, polyethylene oxide-based polyurethane, and polyhydroxyethyl methacrylate, and copolymers and mixtures of the foregoing. 
         [0079]    Silicone-base hydrogels are also suitable. Silicone hydrogels may be prepared by polymerizing a mixture of monomers including at least one silicone-containing monomer and or oligomer and at least one hydrophilic co-monomer such as N-vinyl pyrrolidone (NVP), N-vinylacetamide, N-vinyl-N-methyl acetamide, N-vinyl-N-ethyl acetamide, N-vinylformamide, N-vinyl-N-ethyl formamide, N-vinylformamide, 2-hydroxyethyl-vinyl carbonate, and 2-hydroxyethyl-vinyl carbamate (beta-alanine). 
         [0080]    Returning to  FIG. 2D , in this variation, the sheath ( 206 ) is secured within the prosthetic disc ( 200 ) by placing it between the respective inner and outer end plate members ( 214 ,  216  and  224 ,  226 ). A small lip ( 230 ) may be formed on the sheath ( 206 ) to further secure the sheath ( 206 ) in place during assembly of the prosthetic disc ( 200 ), e.g., during fixation of the inner disc members to the outer disc members by, perhaps, welding the two together, and later after implantation. 
         [0081]      FIGS. 2E and 2F  show variations of the prosthetic disc discussed above.  FIG. 2E  shows a prosthetic disc ( 250 ) that is configured to provide a lordotic angle after implantation. In this variation, the inner disc components ( 252 ) are tapered to provide the desired angle, be that angle be lordotic or kyphotic. The outer disc components ( 254 ) may, in the alternative, be tapered to reach such a result. Both inner ( 252 ) and outer ( 254 ) disc components may be tapered to provide lordotic or kyphotic angles. 
         [0082]      FIG. 2F  shows a variation ( 256 ) having parallel end plate outer surfaces ( 258 ), i.e., providing neither a lordotic nor a kyphotic angle. 
         [0083]      FIGS. 3A-3E  show various views of an inner end plate component ( 260 ). Although it is not necessary, the upper and lower inner end plate components as shown in  FIG. 2A  and following, may be identical. 
         [0084]      FIG. 3A  provides a perspective, top view of an inner end plate ( 260 ). The Figure shows the dual posts ( 262 ,  264 ) that extend upwardly from the upper surface ( 266 ) of that inner end plate member ( 260 ) for joining to the cooperative outer end plate. Also seen is a spacer post ( 268 ) for providing crush strength to the prosthetic disc. The inner disc component ( 260 ) contains a plurality of openings ( 270 ) for passage of the filamentary member discussed below. In this variation, a pair of lengthy notches ( 272 ) are positioned along the side of the inner end plate component to allow flow of sterilizing gas into the space between the inner and outer end plate components. A region ( 276 ) for contact with the adjacent outer end plate is provided at each end. 
         [0085]      FIG. 3B  shows a bottom perspective view of the inner end plate ( 260 ). The openings ( 270 ) for the filamentary member may be seen. Central on this side of the inner end plate ( 260 ) is the generally rounded recess ( 274 ) that conforms in shape to the exterior of the modified olive-shaped core member. The surface of the recess ( 274 ) provides a bearing surface for that core member after the device is assembled. 
         [0086]      FIG. 3C  is a top view of the inner end plate ( 260 ) with openings ( 270 ) for the filamentary member, region ( 276 ) for contact with the adjacent outer end plate, dual posts ( 262 ,  264 ), and spacer post ( 268 ). 
         [0087]      FIG. 3D  is a side view of the inner end plate ( 260 ) showing dual posts ( 262 ,  264 ) and spacer post ( 268 ). Note that, in this variation, post ( 262 ) is a different height than is post ( 264 ). In this way, the inner end plate ( 260 ) may be used to provide the lordotic or kyphotic angle of the resulting implant. 
         [0088]      FIG. 3E  shows a bottom view of the inner end plate ( 260 ) with openings ( 270 ) for the filamentary member and the generally rounded recess ( 274 ). 
         [0089]      FIG. 4A  shows a bottom perspective view and  FIG. 4B  shows a bottom view of a variation of inner end plate ( 280 ) similar in most respects to the variation shown in  FIGS. 3A-3F  excepting inclusion of a groove ( 282 ) for attachment of an alternative sheath to that shown, for instance, in  FIG. 2D . 
         [0090]      FIGS. 5A-5E  are, respectively, a top perspective view, a bottom perspective view, a top view, a side view, and a bottom view of an outer end plate component ( 300 ) having a surface ( 302 ) that contacts bone of adjacent vertebrae in the intervertebral space after implantation of the device ( 300 ), openings or passageways ( 304 ,  306 ) for insertion of the dual posts ( 262 ,  264  in  FIG. 3A ), groove ( 308 ) for banding member and (optionally) for a fixation member such as a keel, a recess ( 310 ) for accepting the inner end plate component, and openings ( 312 ) for use with an insertion tool. 
         [0091]    The end plate assemblies may be considered generally planar substrates having a length of from about 7 mm to about 45 mm, such as from about 13 mm to about 44 mm, a width of from about 11 mm to about 28 mm, such as from about 12 mm to about 25 mm, and a thickness of from about 0.5 mm to about 5 mm, such as from about 1 mm to about 3 mm. They may be fabricated or formed from a physiologically acceptable material that provides for the requisite mechanical properties, primarily structural rigidity and durability. Representative materials from which the end plates may be fabricated are known to those of skill in the art and include: metals such as titanium, titanium alloys, stainless steel, cobalt/chromium, etc.; plastics such as polyethylene with ultra high molar mass (molecular weight) (UHMW-PE), polyether ether ketone (PEEK), etc.; ceramics; graphite; etc. 
         [0092]    Further, each of the described variations may additionally include a porous covering or layer (e.g., sprayed Ti metal) allowing boney ingrowth and may include some osteogenic materials. 
         [0093]    As noted above, the upper and lower inner end plates each contain a plurality of apertures through which the fibers may be passed through or wound, as shown. The actual number of apertures contained on an end plate is variable. Increasing the number of apertures allows an increase in the circumferential density of the fibers holding the end plates together. The number of apertures may range from about 3 to 100, perhaps in the range of 10 to 30. In addition, the shape of the apertures may be selected so as to provide a variable width along the length of the aperture. For example, the width of the apertures may taper from a wider inner end to a narrow outer end, or vice versa. 
         [0094]    The apertures provided in the various end plates discussed here, may be of a number of shapes. Such aperture shapes include slots with constant width, slots with varying width, openings that are substantially round, oval, square, rectangular, etc. Elongated apertures may be radially situated, circumferentially situated, spirally located, or combinations of these shapes. More than one shape may be utilized in a single end plate. 
         [0095]      FIGS. 6A-6C  show, respectively, a perspective view, an end view, and a side view of a sheath ( 330 ) having flutes or accordion pleats ( 332 ), flat regions ( 334 ) for placement between the inner and outer end plate components (see,  FIG. 2D ), and a small lip ( 336 ) for placement of the sheath ( 330 ) between the inner and outer end plate components (see, ( 230 ) in  FIG. 2D ). 
         [0096]    The sheath ( 330 ) may be made of an appropriate polymer, such as polyurethane, silicone, polyethylene, polypropylene or the materials discussed above, and may be fabricated by injection molding, two-part component mixing, or RIM. The sheath ( 330 ) may be oblong with straight sidewalls or with one or more bellows formed in the sidewalls. A function of the sheath ( 330 ) is to act as a barrier that keeps the disc materials (e.g., fiber strands) within the body of the disc, and that keeps potential, natural in-growth outside the disc. 
         [0097]      FIG. 7  is a cross-section of a partially assembled device ( 350 ) having an upper, inner end plate member ( 352 ), a lower, inner end plate member ( 354 ), a core member ( 356 ), and a filamentary member ( 358 ) wound through the openings ( 360 ) in the upper, inner end plate member ( 352 ) and the lower, inner end plate member ( 354 ). 
         [0098]    The filamentary member (or member) ( 538 ) comprise fibers wound between and connecting the upper and lower end plates. These fibers may extend through a plurality of openings or apertures ( 360 ) found on portions of each of the upper and lower inner end plate components. Thus, a fiber extends between the pair of end plate assemblies, and extends up through an aperture ( 360 ) in the upper inner end plate member and back down through an adjacent aperture in that end plate member. The fibers need not be tightly wound, thereby allowing a degree of axial rotation, bending, flexion, and extension by and between the end plate assemblies. The amount of axial rotation generally is in the range from about 0° to about 15°, perhaps from about 2° to 10°. The amount of bending generally has a range from about 0° to about 18°, perhaps from about 2° to 15°. The amount of flexion and extension generally has a range from about 0° to about 25°, perhaps from about 3° to 15°. The fibers may be more or less tightly wound to vary the resultant values of these rotational values. The core member may be provided in an uncompressed or in a compressed state. 
         [0000]    Additionally, the fibers may be wound multiple times within the same aperture, thereby increasing the radial density of the fibers. In each case, this improves the wear resistance and increases the torsional and flexural stiffness of the prosthetic disc, thereby further approximating natural disc stiffness. In addition, the fibers may be passed through or wound on each aperture, or only on selected apertures, as needed. The fibers may be wound in a uni-directional manner, where the fibers are wound in the same direction, e.g., clockwise, which closely mimics natural annular fibers found in a natural disc, or the fibers may be wound bi-directionally. Other winding patterns, both single and multi-directional, may also be used. Choice of the number of slots or openings, typically an odd number, and choice of an appropriate number of “skipped” slots during weaving results in an appropriate layer. 
         [0099]    One purpose of the fibers is to hold the upper and lower end plate assemblies together and to limit the range-of-motion to mimic or at least to approach the range-of-motion of a natural disc. The fibers may comprise high tenacity fibers having a high modulus of elasticity, for example, at least about 100 MPa, perhaps at least about 500 MPa. By high tenacity fibers is meant fibers able to withstand a longitudinal stress of at least 50 MPa, and perhaps at least 250 MPa, without tearing. The fibers are generally elongate fibers having a diameter that ranges from about 100 μm to about 1000 μm, and preferably about 200 μm to about 400 μm. The fibrous components may be single strands or, more typically, multi-strand assemblages. Optionally, the fibers may be injection molded or otherwise coated with an elastomer to encapsulate the fibers, thereby providing protection from tissue ingrowth and improving torsional and flexural stiffness. The fibers may be coated with one or more other materials to improve fiber stiffness and wear. Additionally, the core may be injected with a wetting agent such as saline to wet the fibers and facilitate the mimicking of the viscoelastic properties of a natural disc. The fibers may comprise a single or multiple component fibers. 
         [0100]    The fibers may be fabricated from any suitable material. Examples of suitable materials include polyesters (e.g., Dacron® or the Nylons), polyolefins such as polyethylene, polypropylene, low-density and high density polyethylenes, linear low-density polyethylene, polybutene, and mixtures and alloys of these polymers. HDPE and UHMWPE are especially suitable. Also suitable are various polyaramids, poly-paraphenylene terephthalamide (e.g., Kevlar®), carbon or glass fibers, various stainless steels and superelastic alloys (such as nitinol), polyethylene terephthalate (PET), acrylic polymers, methacrylic polymers, polyurethanes, polyureas, other polyolefins (such as polypropylene and other blends and olefinic copolymers), halogenated polyolefins, polysaccharides, vinylic polymers, polyphosphazene, polysiloxanes, liquid crystal polymers such as those available under the tradename VECTRA, polyfluorocarbons such as polytetrafluoroethylene and e-PTFE, and the like. 
         [0101]    The fibers may be terminated on an end plate in a variety of ways. For instance, the fiber may be terminated by tying a knot in the fiber on the superior or inferior surface of an end plate. Alternatively, the fibers may be terminated on an end plate by slipping the terminal end of the fiber into an aperture on an edge of an end plate, similar to the manner in which thread is retained on a thread spool. The aperture may hold the fiber with a crimp of the aperture structure itself, or by an additional retainer such as a ferrule crimp. As a further alternative, tab-like crimps may be machined into or welded onto the end plate structure to secure the terminal end of the fiber. The fiber may then be closed within the crimp to secure it. As a still further alternative, a polymer may be used to secure the fiber to the end plate by welding, including adhesives or thermal bonding. That terminating polymer may be of the same material as the fiber (e.g., UHMWPE, PE, PET, or the other materials listed above). Still further, the fiber may be retained on the end plates by crimping a cross-member to the fiber creating a T-joint, or by crimping a ball to the fiber to create a ball joint. 
         [0102]    The prosthetic disc may include anchoring or fixation surfaces, features, or components typically associated with the outer surfaces of the upper and lower end plates, i.e., those surfaces in contact with and eventually adherent to the respective opposed bony surfaces of the upper and lower vertebral bodies, for securing those end plates to the vertebral bodies. For example, the anchoring feature may be one or more “keels,” a fin-like extension often having a substantially triangular cross-section and having a sequence of exterior barbs or serrations. This anchoring component is intended to cooperatively engage a mating groove that is formed on the surface of the vertebral body and to thereby secure the end plate to its respective vertebral body. The serrations enhance the ability of the anchoring feature to engage the vertebral body. 
         [0103]    Other anchoring features, e.g., spikes, nubs, knurled surfaces, etc., may be included if so desired. 
         [0104]      FIG. 8A  is a perspective view of a variation of the device ( 400 ) showing a centrally located, slidable anchoring member ( 402 ). This anchoring member ( 402 ) is received within the axial groove ( 404  or  208  in  FIG. 2A ). In this variation, the anchoring member ( 402 ) is a keel having multiple barbs ( 406 ) configured to slide or move within the groove ( 404 ).  FIG. 8B  shows anchoring member ( 402 ) sliding in groove ( 404 ). Note that the groove ( 404 ) is triangular in cross-section in this variation and provides an open passageway beneath the anchoring member ( 402 ). The triangular shape is not required in that other cross-sectional shapes are acceptable for providing the passageway. The passageway is configured to allow passage of the banding member for collapsing the implant ( 400 ) during the placement operation. 
         [0105]      FIGS. 8C and 8D  show, respectively, a side view of the implant ( 400 ) with the anchoring member ( 402 ) in place and a perspective view of the slidable anchoring member ( 402  with the integral barbs ( 404 ). 
         [0106]      FIG. 9A  shows a variation of our device ( 410 ) having side grooves ( 412 ) in one end plate assembly ( 414 ) for receiving slidable side-mounted anchoring members ( 416 ). In this variation of the implant ( 410 ), the other end plate assembly ( 418 ) includes only a central, axial groove, the other end plate assembly ( 418 ) may instead include side grooves for including side-mounted anchoring members ( 416 ). 
         [0107]      FIG. 9B  shows another perspective view of the device ( 410 ) having side grooves ( 412 ) in one end plate assembly ( 414 ), side-mounted anchoring members ( 416 ), and the other end plate assembly ( 418 ) with a central, axial groove. 
         [0108]      FIGS. 9C and 9D  show, respectively, a side-view and a perspective view of a side mounted anchoring member. as may be placed in the implant ( 410 ) as seen in  FIGS. 9A and 9B . 
         [0109]      FIG. 10  provides a schematic representation of the distal tip of an installation tool ( 454 ) suitable for implanting our prosthetic disc ( 450 ) into a spine. In this variation, a banding member ( 452 ) is situated in the axial groove (see, e.g., ( 208 ) in  FIG. 2A ) and pulled taut by a pull-rod ( 456 ) to collapse the prosthetic disc ( 450 ) to a low profile for placement in an intravertebral space in a spine. A surrounding, hollow shaft ( 458 ) provides a reactive force countering that provided by pull-rod ( 456 ). After the prosthetic disc is suitably placed in the spine, the banding member ( 452 ) may be severed or untied or the like to allow the prosthetic disc ( 450 ) to expand into position in the spine. The axial groove allows removal of the banding member ( 452 ) after completion of the installation step. A feature for cutting the banding member ( 452 ) by, e.g., twisting the pull-rod ( 456 ), may be used to remove the banding member ( 452 ). 
         [0110]    The utility of the tool variation with its binding element described here is multiple. First, the profile (or height) of the disc is minimized enhancing the ability of the user to easily and accurately place the prosthetic disc in a prepared intervertebral space. Some commercial prosthetic discs are not at all compressible, a factor that limits those discs&#39; suitability for many situations. Our discs&#39; lower profile is better able to pass through small access points into the intervertebral space. This allows the physician to utilize accesses, e.g., through spinal ligaments, that are smaller. The narrow form factor of the described discs combined with the binding element allows, in some variations, the physician to introduce the prosthetic disc “vertically” through a narrower ligament opening and then to rotate it into placement position. The user&#39;s ability to situate the bound prosthetic disc in the intervertebral space with a simple placement tool and then to release the binding element by a simple twist to finally place the disc in its final implantation site is significant. The ease of “tool use” is a very positive attribute. The form of the binding element may be tailored for specific situations. The binding element may be attached in such a way that only one end or the other end or both ends of the prosthetic disc is compressed. The binding element may be attached to provide differential compression, e.g., wherein one end of the disc is compressed more than is the other. 
         [0111]    The binding element or member ( 452 ) may be made from a wide variety of materials. Suitable materials include synthetic polymers, natural polymers (e.g., silk), metals, alloys (including superelastic alloys such as nitinol), coated materials (e.g., lubricious polymers on “strength” polymers, lubricious polymers on metals or alloys, etc.), and the like. The form of the binding element may be a monofilament, thread, or multifilament, cable, ribbon, etc. 
         [0112]      FIG. 11  schematically depicts deployment of the prosthetic disc ( 450 ) using a deployment tool ( 460 ) as discussed in regard to  FIG. 10 . In step (a), the deployment tool ( 490 ) has been prepared with a collapsed prosthetic disc ( 450 ) mounted on the distal end ( 454 ). The central pull-rod ( 456 ) includes a threaded proximal end ( 464 ) engaged by a release nut ( 462 ). 
         [0113]    In step (b), the release nut ( 462 ) is turned allowing the pull rod ( 456 ) to advance distally and the prosthetic disc ( 450 ) to expand into position. 
         [0114]    In step (c), the release nut ( 462 ) and the pull rod ( 456 ) are twisted together to sever the banding member ( 452 ). The cutting surface is not shown in these drawings but its function and placement are easily understood. The banding member ( 452 ) is then removed from the implant ( 452 ) and is then withdrawn from the body along with the placement tool ( 460 ). 
         [0115]      FIG. 12A  shows a variation of the placement tool ( 470 ) having a prosthetic disc ( 472 ) attached. The tool handle ( 474 ) and release nut ( 476 ) may also be seen. 
         [0116]      FIG. 12B  shows another variation of the placement tool ( 480 ) having a prosthetic disc ( 472 ) distally placed. The banding member has been omitted from the Figure although the axial groove ( 484 ) into which it is to be placed may be seen. The release nut ( 482 ) and pull-rod ( 486 ) may also be seen. 
         [0117]      FIGS. 12C and 12D  show, respectively, a perspective view and a side-view of the distal end ( 490 ) of the prosthetic device with the collapsed prosthetic device ( 472 ) installed. 
         [0118]    Finally,  FIG. 13 , step (a), shows the placement of a compressed disc ( 500 ) into the intervertebral space ( 502 ) between an upper vertebra ( 504 ) and the adjacent lower vertebra ( 506 ) using a posterior approach. No placement tool is shown, for ease of explanation. The compressed disc ( 500 ) has been passed through a cannula ( 510 ) to the implantation site with a binding element ( 512 ) in place. 
         [0119]      FIG. 13 , step (b), shows the disc ( 500 ) after removal of the binding element ( 512 ) and expansion of the disc ( 500 ). The cannula ( 510 ) and the binding element ( 512 ) are shown being removed. 
         [0120]    Where a range of values is provided, it is understood that each intervening value within the range, to the tenth of the unit of the lower limit (unless the context clearly dictates otherwise), between the upper and lower limit of that range and any other stated or intervening value in that stated range is described. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges is also described, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also described. 
         [0121]    Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the medical devices art. Although methods and materials similar or equivalent to those described here may also be used in the practice or testing of the described devices and methods, the preferred methods and materials are described in this document. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. 
         [0122]    It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. 
         [0123]    As will be apparent to those of skill in the art upon reading this disclosure, each of the individual variations described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of this disclosure. For example, and without limitation, several of the variations described here include descriptions of anchoring features, protective capsules, fiber windings, and protective covers covering exposed fibers for integrated end plates. It is expressly contemplated that these features may be incorporated (or not) into those variations in which they are not shown or described. 
         [0124]    All patents, patent applications, and other publications mentioned herein are hereby incorporated herein by reference in their entireties. The patents, applications, and publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that contents of those patents, applications, and publications are “prior” as that term is used in the Patent Law. 
         [0125]    The preceding merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles otherwise described here and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the described principles of my devices and methods. Moreover, all statements herein reciting principles, aspects, and variation as well as specific examples thereof, are intended to encompass both structural and functional equivalents. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.