Abstract:
A flexible keel is provided for use as a bone anchoring element for use with a range of orthopedic implants having portions configured for anchoring into boney tissue. The flexible keel includes two wings terminating proximally in a pair of outward flares, the wings further spaced from a bone contacting implant surface by a void. The flexibility of the keel wings increases the ease of revision or explantation procedures.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This claims priority to U.S. Patent Application Ser. No. 61/139,964 filed on Dec. 22, 2008, the disclosure of which is hereby incorporate by reference as if set forth in its entirety herein. 
     
    
     BACKGROUND 
       [0002]    Historically, complete removal of a disc from between adjacent vertebrae resulted in fusing the adjacent vertebrae together. This “spinal fusion” procedure, which is still in use today, is a widely accepted surgical treatment for symptomatic lumbar and cervical degenerative disc disease. More recently, disc arthoplasty may be utilized to insert an artificial intervertebral disc implant into the intervertebral space between adjacent vertebrae. Such a disc implant allows limited universal movement of the adjacent vertebrae with respect to each other. The aim of total disc replacement is to remove pain generation (caused by a degenerated disc), restore anatomy (disc height), and maintain mobility in the functional spinal unit so that the spine remains in an adapted sagittal balance. Sagittal balance is defined as the equilibrium of the trunk with the legs and pelvis to maintain harmonious sagittal curves and thus the damping effect of the spine. In contrast with fusion techniques, total disc replacement preserves mobility in the motion segment and attempts to mimic physiologic conditions. 
         [0003]    One such intervertebral implant includes an upper part mounted to an adjacent vertebra, a lower part mounted to another adjacent vertebra, and an insert located between these two parts. An example of such a total disc replacement intervertebral implant is shown in U.S. Pat. No. 6,936,071, titled “Intervertebral Implant”, the contents of which are incorporated herein by reference in their entirety. To provide an anchor to mount the upper and lower parts to the adjacent vertebrae, each part includes a vertically extending keel. While this and other known implants represent improvements in the art of artificial intervertebral implants, there exists a continuing need for improvements of these types of implants. Namely, it is desirable to provide bone-anchoring keels for use with orthopedic implants, such as total disc replacement implants, that are adapted for revision or explantation procedures. 
       SUMMARY 
       [0004]    In accordance with one aspect, an orthopedic implant is configured to be anchored into boney tissue. The implant includes an endplate configured to be inserted into the boney tissue along a longitudinal forward direction. The endplate presents a bone contacting surface, and a keel extending out from the bone contacting surface and configured to be disposed into a slot formed into the boney tissue. The keel includes a keel body and a wing extending rearward from the keel body, the wing including a flared portion that projects laterally outward with respect to a longitudinally rearward direction. The flared portion is spaced from the bone contacting surface by a void. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The foregoing summary, as well as the following detailed description of a preferred embodiment of the application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the flexible anchoring keel and related instruments of the present application, there is shown in the drawings a preferred embodiment. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
           [0006]      FIG. 1A  is a perspective view of a pair of vertebral bodies separated by an intervertebral space, wherein each of the vertebral bodies has keel slots formed therein; 
           [0007]      FIG. 1B  is a perspective view of the vertebral bodies illustrated in  FIG. 1 , and an intervertebral implant inserted into the intervertebral space between the two vertebral bodies; 
           [0008]      FIG. 2  is a perspective view of an intervertebral implant illustrated in  FIG. 1B , and constructed in accordance with one embodiment including first and second endplates; 
           [0009]      FIG. 3A  is a top plan view of the implant illustrated in  FIG. 2 ; 
           [0010]      FIG. 3B  is a bottom plan view of the implant illustrated in  FIG. 2 ; 
           [0011]      FIG. 4  is a front elevation view of the implant illustrated in  FIG. 2 ; 
           [0012]      FIG. 5  is a side elevation view of the implant illustrated in  FIG. 2 ; 
           [0013]      FIG. 6  is a cross-sectional view of the implant illustrated in  FIG. 4 , taken along line  6 - 6   
           [0014]      FIG. 7  is a cross-sectional view of the implant illustrated in  FIG. 5 , taken along line  7 - 7 ; 
           [0015]      FIG. 8  is a perspective view of a forked osteotome instrument, constructed in accordance with one embodiment; 
           [0016]      FIGS. 9A-B  are perspective views of the forked osteotome instrument illustrated in  FIG. 8  coupled to the first implant endplate illustrated in  FIG. 2 ; 
           [0017]      FIG. 10A  is a top plan view of an intervertebral implant including a pair of endplates constructed in accordance with an alternative embodiment, showing the coupling of an osteotome instrument constructed in accordance with an alternative embodiment to one of the endplates; 
           [0018]      FIG. 10B  is a top plan view of the intervertebral implant illustrated in  FIG. 10A , showing the osteotome instrument coupled to the endplate; 
           [0019]      FIG. 11A  is a perspective view of an intervertebral implant constructed in accordance with another alternative embodiment; 
           [0020]      FIG. 11B  is a top plan view the intervertebral implant illustrated in  FIG. 11A ; 
           [0021]      FIG. 12A  is a perspective view of an intervertebral implant constructed in accordance with yet another alternative embodiment; and 
           [0022]      FIG. 12B  is a top plan view the intervertebral implant illustrated in  FIG. 12A . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower” and “upper” designate directions in the drawings to which reference is made. The words “inwardly” or “distally” and “outwardly” or “proximally” refer to directions toward and away from, respectively, the geometric center of the implant assembly and related parts thereof. The words, “anterior”, “posterior”, “superior,” “inferior” and related words and/or phrases designate preferred positions and orientations in the human body to which reference is made and are not meant to be limiting. The terminology includes the above-listed words, derivatives thereof and words of similar import. 
         [0024]    Referring to  FIGS. 1A-2 , a pair of adjacent vertebral bodies  12 , including a superior vertebral body  12   a  and an inferior vertebral body  12   b , defines an intervertebral space  14  disposed therebetween. As illustrated, the intervertebral space  14  is illustrated after a discectomy, whereby the disc material has been removed to prepare the intervertebral space  14  to receive an implant, such as the intervertebral implant  10  illustrated in  FIG. 2 . Thus, the implant  10  is configured to be inserted into the intervertebral space  14 , and achieve improved stability between the vertebral bodies  12  (for fusion or non-fusion procedures). The intervertebral space  14  can be disposed anywhere along the spine, but is disposed in the cervical region of the spine in accordance with one embodiment. 
         [0025]    The implant  10  and various components of the implant are described herein extending horizontally along a longitudinal direction “L” and lateral direction “A”, and vertically along a transverse direction “T”. Unless otherwise specified herein, the terms “lateral,” “longitudinal,” and “transverse” are used to describe the orthogonal directional components of various components. 
         [0026]    It should be appreciated that while the longitudinal and lateral directions are illustrated as extending along a horizontal plane, and that the transverse direction is illustrated as extending along a vertical plane, the planes that encompass the various directions may differ during use. Accordingly, the directional terms “vertical” and “horizontal” are used to describe the implant  10  and its components as illustrated merely for the purposes of clarity and illustration. 
         [0027]    In the illustrated embodiment, the longitudinal direction L extends in an anterior-posterior direction, the lateral direction A extends in a medial-lateral direction, and the transverse direction T extends in a caudal-cranial direction. It should be appreciated, however, that the various directions defined by the implant  10  could alternatively be oriented at any desirable angle between 0° and 180° with respect to the medial-lateral and anterior-posterior directions and the transverse direction. 
         [0028]    Referring now to  FIGS. 1-7  generally, the implant  10  generally includes a first, or upper, endplate  20  and a second, or lower, endplate  22 . The endplates  20  and  22 , and components thereof, can be formed from a variety of biocompatible materials, such as cobalt chromium molybdenum (CoCrMo) with a porous plasma-sprayed titanium coating, titanium, stainless steel, ceramics, or polymers such as polyetheretherketone (PEEK). The endplates  20  and  22  define substantially planar outer transverse bone-contacting surfaces  24  and  26 , respectively, and respective flexible keels  28  and  30  extending transversely out from the surfaces  24  and  26 . In the illustrated embodiment, the keels  28  and  30  are perpendicular with respect to the surfaces  24  and  26 . The surfaces  24  and  26  can be smooth or textured to facilitate fusion with the associated vertebral body  12 . The implant  10  defines a longitudinally forward end  11  and a longitudinally rear end  13  with respect to the direction of insertion of the implant  10  into the intervertebral space  14 . Thus, the implant  10  is configured to be inserted into the intervertebral space  14  along the forward longitudinal direction that extends from the rear end  13  toward the front end  11 . Thus, the terms “forward” and “rearward” and derivatives thereof, as used herein with respect to the components of the implant  10 , are used reference to the forward and rear ends  11  and  13  of the implant  10 . 
         [0029]    In order to position implant  10  into the intervertebral disc space  14 , a cut is made in the inferior as well as in the superior vertebral bodies  12  to provide keel cuts or slots  18  that extend therein that conform generally to the size and shape of the keels  28  and  30 . The keel cuts or slots  18  can be provided using any method and apparatus as desired, such as a chisel or a drilling/milling system of the type disclosed in U.S. patent application Ser. No. 12/375,710, filed Jan. 30, 2009, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein. It should be appreciated that the slots  18  are formed in vertebral bodies  12   a - b , the slots can alternatively be disposed in boney tissue associated with any bone in the human body as desired, unless otherwise indicated. 
         [0030]    The implant  10  can further include a plastic insert, or inlay  116  connected to the lower endplate  22  and disposed between the lower endplate  22  and the upper endplate  20 . The implant  10  can define a width extending along the lateral direction A that can be between approximately 15-19 mm, a length extending along the longitudinal dimension L that can be approximately 12-16 mm, and a height extending between the outer surfaces  24  and  26  along the transverse direction T that can be approximately 5-9 mm. Thus, the implant  10  is suitable for implantation in an intervertebral space in the cervical region of the spine, which is characterized by the need for precision because of the relatively small dimensions of cervical intervertebral spaces. 
         [0031]    The dimensions described above with respect to the implant  10  in the illustrated embodiment are in contrast to the dimensions of the implant  10  if the implant were to be inserted into an intervertebral space in the a different spinal region, for instance the lumbar region. The implant  10  configured for implantation into the lumbar region can have a width between approximately 27 and 30 mm, a length of approximately 34-39 mm, and a height of approximately 10-14 mm. 
         [0032]    It is to be understood that the implant  10  can be constructed with any dimensions desirable for implantation of any intervertebral space along the spine, and is not limited to the cervical and lumbar regions unless otherwise indicated. Furthermore, while the implant  100  is configured as a total disc replacement device, implants constructed in accordance with the teachings described herein are readily configurable for use with a range of bone-anchored orthopedic prostheses, such as interbody spacers, hip and knee replacement implants, and the like. 
         [0033]    The first endplate  20  will now be described with particular reference to  FIGS. 2A-5 . It should be appreciated that the directions “transversely in” and “transversely out” and derivatives thereof are used with respect to the first endplate  20  to describe upward and lower directions, respectively, when the endplate  20  is provided as an upper endplate as illustrated. In particular, the upper endplate  20  defines the outer surface  24  that engages and supports the superior vertebral body  12   a . The outer surface  24  is bound by edges  32  that are slightly beveled all the way around with the largest portion of the bevel being at the forward end  11  of the implant  10 . The endplate  20  includes a peripheral side wall  34  that projects transversely in from the beveled edges  32 , and an inner transverse surface  36  positioned such that the side wall  34  extends between the outer surface  24  and the inner surface  36 . 
         [0034]    The keel  28  can be integrally connected to the outer surface  24  of the upper endplate  20 , and sized and configured to be inserted into the slot  18  formed in one of the vertebral bodies  12 , such as the superior vertebral body  12   a . In this regard, the keel  28  can be construed as an anchoring keel configured to be disposed in the slot  18 . The slot  18  can be pre-formed in the manner described above, or can be cut while inserting the keel  28  into the vertebral body. While the upper endplate  20  is illustrated as being associated with the superior vertebral body  12   a , and the lower endplate  22  is described as being associated with the inferior vertebral body  12   b , it should be appreciated that the endplate  20  can alternatively be attached to the inferior vertebral body  12   b , and the lower endplate  22  can alternatively be attached to the superior vertebral body  12   a , depending on the orientation of the implant  10 . 
         [0035]    The keel  28  defines a proximal end  38  disposed proximate to the forward end  11  of the implant  10 , and a distal end  40  disposed proximate to the rear end  13  of the implant  10 . The keel  28  includes a keel body  42  and a base  44 . The keel body  42  is spaced transversely out from the outer surface  24 . In particular, the keel body  42  extends transversely out from a base  44  that is integrally connected to, and extends transversely out from, the outer surface  24 . The keel body  42  defines a pair of opposing side walls  43  that extend transversely out from the base  44 , and can be co-planar with opposing side walls  45  of the base  44 . The base  44  further includes a distal engagement surface  47  that extends transversely out from the outer transverse surface  24 , and extends laterally between the distal, or rear, ends of the side walls  45 . 
         [0036]    The proximal end of the keel  28  includes a pair of v-shaped upper bevels  46   a - b  and a pair of v-shaped vertical beveled surfaces  48   a - b  extending transversely in from the upper bevels  46   a - b . The bevels  46   a  and  48   a  are spaced from each other by the bevels  46   b  and  48   b  by a substantially flat, laterally extending, front surface  50 . The bevels  46 ,  48 , and the front surface  50  define a front keel profile that is substantially “arrow” shaped. The “arrow” shape facilitates insertion of the keel  28  into the slot  18  formed in the corresponding vertebral body  12   a.    
         [0037]    A first aperture  52  extends transversely into the distal end of the keel body  42  and terminates at the base  44 . The aperture  52  is longitudinally elongated, and extends distally through the body  42 , such that the distal end of the body  42  is open. The aperture  52  defines a first wing  54  and a second wing  56  of the keel  28 . The first and second wings  54  and  56  extend rearward from the keel body  42 . The second wing  56  is laterally spaced from the first wing  54  via the aperture  52 . The wings  54  and  56  are laterally spaced from each other by the aperture  52 , which provides a void that separates the wings  54  and  56 . Each wing  54  and  56  can be flexible as illustrated and configured to move with respect to the outer transverse surface  24 . In accordance with the illustrated embodiment, each wing  54  and  56  terminates at its distal end at a first flexible flared distal region  58  and a second flexible flared distal region  60 , respectively. The flared regions  58  and  60  project laterally outward with respect to the side walls  43  in a distal, or rearward, direction along the flared regions  58  and  60 . 
         [0038]    A channel  62  extends longitudinally forward from the distal end of the keel  28  at a location transversely between the base  44  and the wings  54  and  56 . The channel  62  extends longitudinally into, but not longitudinally through, the keel  28  and terminates at a distance that is distal with respect to the longitudinal boundary of the aperture  52 . The channel  62  further extends laterally through the keel  28 . Accordingly, the wings  54  and  56 , including the flared regions  58  and  60 , are transversely spaced from the base  44  and the outer transverse surface  24  by channel  62 . The channel  62  thus defines a void that separates the wings  54  and  56  from the base  44  and the outer surface  24 . The wings  54  and  56  are thus spaced from the base  44 , or suspended above the base  44  when the first endplate  20  engages the superior vertebral body  12   a , but could be suspended below the base  44  if the first endplate  20  engages the inferior vertebral body  12   b.    
         [0039]    The keel  28  thus defines a pair of distally-facing surfaces  64  and  66 , respectively, extending transversely between the base  44  and the wings  54  and  56 . If desired, the engagement surfaces  64  and  66  can be curved along the transverse direction as illustrated. The keel  28  can further include a an instrument engagement feature in the form of a recess  68  protruding transversely into the base  44  at a location between the wings  54  and  56 , such that the recess  68  is accessible through the aperture  52 . 
         [0040]    The second endplate  22  will now be described with continuing reference to  FIGS. 2A-5 . It should be appreciated that the directions “transversely in” and “transversely out” and derivatives thereof are used with respect to the second endplate  22  to describe lower and upper directions, respectively, when the endplate  22  is provided as a lower endplate as illustrated. In particular, the lower endplate  22  defines the outer surface  26  that engages and supports the inferior vertebral body  12   b . It will be appreciated that the second endplate  22  is constructed substantially as described with respect to the first endplate  20 , such that the structural features extending transversely out from the outer transverse surface  26  of the second endplate  22  are aligned with like structural features that extend transversely out from outer the transverse surface  24  of the first endplate  20 . 
         [0041]    The outer surface  26  is bound by edges  70  that are slightly beveled all the way around with the largest portion of the bevel being at the forward end  11  of the implant  10 . The endplate  22  includes a peripheral side wall  72  that projects transversely in from the beveled edges  70 , and an inner transverse surface  74  positioned such that the side wall  72  extends between the outer surface  26  and the inner surface  74 . 
         [0042]    The keel  30  can be integrally connected to the outer surface  26  of the second endplate  22 , and sized and configured to be inserted into the slot  18  formed in one of the vertebral bodies  12 , such as the inferior vertebral body  12   b . The slot  18  can be pre-formed in the manner described above, or can be cut while inserting the keel  30  into the vertebral body. While the lower endplate  22  is illustrated as being associated with the inferior vertebral body  12   b , and the upper endplate  20  is described as being associated with the superior vertebral body  12   a , it should be appreciated that the endplate  22  can alternatively be attached to the superior vertebral body  12   a , and the upper endplate  20  can alternatively be attached to the inferior vertebral body  12   b , depending on the orientation of the implant  10 . 
         [0043]    The keel  30  defines a proximal end  76  disposed proximate to the forward end  11  of the implant  10 , and a distal end  78  disposed proximate to the rear end  13  of the implant  10 . The keel  30  includes a keel body  80  spaced transversely out from the outer surface  26 . In particular, the keel body  80  extends transversely out from a base  82  that is integrally connected to, and extends transversely out from, the outer surface  26 . The keel body  80  defines a pair of opposing side walls  81  that extend out from the base  82 , and can be co-planar with opposing side walls  83  of the base  82 . The base  82  further includes a distal engagement surface  85  that extends transversely out from the outer transverse surface  26 , and further extends laterally between the distal, or rear, ends of the side walls  83 . 
         [0044]    The proximal end  76  of the keel  30  includes a pair of v-shaped upper bevels  84   a - b  and a pair of v-shaped vertical beveled surfaces  86   a - b  extending transversely in from the upper bevels  84   a - b . The bevels  84   a  and  86   a  are spaced by the bevels  84   b  and  86   b  by a substantially flat, laterally extending, front surface  88 . The bevels  84 ,  86 , and the front surface  88  define a front keel profile that is substantially “arrow” shaped. The “arrow” shape facilitates insertion of the keel  20  into the slot  18  formed in the corresponding vertebral body  12   b.    
         [0045]    A first aperture  90  extends transversely into the distal end  78  of the keel body  80  and terminates at the base  82 . The aperture  90  is longitudinally elongated, and extends distally through the body  80 , such that the distal end of the body  42  is open and defines a first wing  92  and a second wing  94  disposed at the distal end  78  of the keel  30 . The first and second wings  92  and  94  extend rearward from the keel body  80 . The wings  92  and  94  are laterally spaced from each other by the aperture  90 , which provides a void that separates the wings  92  and  94 . Each wing  92  and  94  can be flexible as illustrated and configured to move with respect to the outer transverse surface  26 . In accordance with the illustrated embodiment, each wing  92  and  94  terminates at its distal end at a first flexible flared region  96  and a second flexible flared region  98 , respectively. The flared regions  96  and  98  project laterally outward with respect to the side walls  81  in a distal, or rearward, direction along the flared regions  96  and  98 , respectively. 
         [0046]    A channel  100  extends longitudinally forward from the distal end of the keel  30  at a location transversely between the base  82  and the wings  92  and  94 . The channel  100  extends longitudinally into, but not longitudinally through, the keel  30  and terminates at a distance that is distal with respect to the longitudinal boundary of the aperture  90 . The channel  100  further extends laterally through the keel  30 . Accordingly, the wings  92  and  94 , including the flared regions  96  and  98 , are spaced from the base  82  and the outer transverse surface  26  by the channel  100 . The channel  100  thus defines a void that separates the wings  92  and  94  from the base  44  and the outer surface  24 . The wings  92  and  94  are thus suspended below the base  82  when the second endplate  22  engages the inferior vertebral body  12   b , but could be suspended above the base  82  if the second endplate  22  engages the superior vertebral body  12   a.    
         [0047]    The keel  30  thus defines a pair of distally-facing surfaces  102  and  104 , respectively, extending transversely between the base  82  and the wings  92  and  94 . If desired, the surfaces  102  and  104  can be curved along the transverse direction as illustrated. The keel  30  can further include an instrument engagement feature in the form of a recess  106  protruding transversely into the base  82  at a location between the wings  92  and  94 , such that the recess  106  is accessible through the aperture  90 . 
         [0048]    Referring now to  FIGS. 4-7 , the endplates  20  and  22  are mated at a joint  106  that is provided as an articulating joint configured to pivot each endplate  20  and  22  relative to the other endplate universally about 360°. The joint  106  can be constructed as described in U.S. patent application Ser. No. 11/669,273, the disclosure of which is hereby incorporated by reference as if set forth in its entirety herein, or in accordance with any suitable alternative embodiment. 
         [0049]    The endplates  20  and  22  thus each include respective mating joint members  108  and  110 , respectively. In particular, the lower endplate  22  includes a pair of C-shaped support members  112  that extend transversely inwardly from the inner surface  74 . The support members  112  present laterally inwardly facing receiving channels  114  that are configured to receive a plastic inlay  116 . The inlay  116  includes a base  118  having laterally outer ends  120  that are sized to fit inside the channels  114 . Thus, the inlay  116  can be inserted into the channels  114  in a direction from the rear end  13  of the endplate  22  toward the front end  11  of the endplate  22 . The endplate  22  can include a stop disposed at the front end  11  to prevent over-insertion of the inlay  116 . The inlay  116  can include a snap-in projection  122  that engages a snap-in recess  124  extending into the inner transverse surface  74  so that the inlay  116  can snap into place to prevent inadvertent removal. 
         [0050]    The inlay  116  further includes a dome-shape upper surface  126  centrally disposed on the base  118  and extending transversely in from the base  118 . The first endplate  20  includes a raised surface  128  extending transversely in from the inner surface  36 . The raised surface  128  defines a dome-shaped recess  130  projecting therein that is contoured and configured to receive and mate with the dome-shaped upper surface  126 . Thus, the endplates  20  and  22  are configured to pivot universally with respect to each other about a 360° range of motion. 
         [0051]    While the joint  106  has been described in accordance with one embodiment, it should be appreciated that the implant could include any alternatively constructed joint that enables relative motion between the endplates  20  and  22  in any direction, or that fixedly attaches the endplates  20  and  22 . In this regard, it should be appreciated that the first endplate  20  could carry the inlay  116 , and the second endplate  22  could carry a raised surface such as raised surface  128  that engages the inlay  116 . 
         [0052]    Referring now  FIG. 8 , a forked osteotome instrument  132  can be provided and configured to insert one or both of the endplates  20  and  22  into the intervertebral space  14  described above. Because the keels  28  and  30  are substantially identically constructed, the instrument  132  is described herein as engaging the keel  28  of the first endplate  20 , it being appreciated that the description applies to the engagement of the instrument with the second endplate  22 . In this regard, it should be further appreciated that a pair of instruments  132  can be provided to engage the upper and lower endplates  20  and  22 , or that a single instrument can be provided having a pair of transversely spaced arms  140  and  142  that are configured to engage the keels  28  and  30  of both endplates  20  and  22 , respectively. 
         [0053]    The instrument  132  includes a shaft  134  that is elongated along a longitudinal axis L, and defines a proximal end  136  that defines a handle  137 , and an opposing distal end  138 . The instrument further defines a first, or outer transverse, surface  119 , and a second, or inner transverse, surface  121  opposite the first surface  119 . The instrument  132  includes a first arm  140  and a second arm  142  that extend distally from the shaft  134 . The arms  140  and  142  are spaced laterally (or horizontally) by a gap  144 , such that the instrument defines a forked distal end  138 . Each arm  140  and  142  can define a distal edge  146  and  148 , respectively, that is beveled or flared longitudinally rearward in the transverse direction. In particular, the distal edges  146  and  148  are beveled in a transverse direction from the inner transverse surface  121  to the outer transverse surface  119  along the edges  146  and  148  from the distal end  138  toward the proximal end  136 . The beveled edges  146  and  148  can assist when inserting the implant  10  into the intervertebral space  14 . The instrument  132  defines longitudinally extending, and laterally opposing, inner guide surfaces  150  and  152  of the arms  140  and  142 , respectively, and an inner stop surface  154  that extends laterally between the arms  140  and  142 . 
         [0054]    In the illustrated embodiment, the distal edges  146  and  148  present laterally inner surfaces  147  and  149 , respectively, that are beveled or flared laterally outward with respect to the inner guide surfaces  150  and  152  along a longitudinal direction from the proximal end  136  toward the distal end  138 . Thus, the distal edges  146  and  148  define a lateral width therebetween that is greater than the lateral width disposed between the inner guide surfaces  150  and  152 . The width disposed between the arms  140  and  142  thus tapers outwardly, with respect to the longitudinal axis L, at the distal end  138  of the instrument  132 . The tapered width facilitates engagement of the instrument  132  with the endplate  20 . 
         [0055]    Referring now to  FIGS. 2 and 8 , the gap  144  has a lateral dimension substantially equal to, or slightly greater than, the lateral width that separates the opposing side walls  43  of the keel body  42 , and thus also has a lateral dimension substantially equal to, or slightly greater than, the lateral width that separates the opposing side walls  45  of the keel body  42 . Otherwise stated, the inner stop surface  154  has a lateral dimension substantially equal to, or slightly greater than, the lateral width that separates the opposing side walls  43  of the keel body  42 , and thus also has a lateral dimension substantially equal to, or slightly greater than, the lateral width that separates the opposing side walls  45  of the keel body  42   
         [0056]    At least a portion of the instrument  132  that engages the keel  28 , for instance a portion of the arms  140  and  142  and/or the shaft  134 , defines a height that can be substantially equal to the transverse height of the base  44 , or the engagement surface  47  (or the transverse distance between the outer transverse surface  24  of the endplate  20  and the outer transverse surface of the base  44  or engagement surface  47 ). Alternatively, the height can be greater than or less than the height of the base  44  or engagement surface  47 , such that the arms  140  and  142  are configured to engage the keel  28  during operation. 
         [0057]    In accordance with an alternative embodiment, the height of the portion of the instrument  132  that engages the keel can have a height that is substantially equal to, or slightly less than, the transverse distance between the base  44  and the wing  54  and  56 . Otherwise stated, the height of the portion of the instrument  132  that engages the keel  28  can be configured to fit within the channel  62 . Alternatively, if it is desired to prevent the instrument  132  from being inserted into the channel  62 , the inner stop surface  154  can have a height greater than that of the channel  62 . 
         [0058]    Referring now to  FIGS. 9A-B , the instrument  132  engages the keel  28  of the endplate  20  in order to facilitate insertion of the endplate  20  into the intervertebral space  14 . In particular, the instrument  132  is oriented such that the second surface  121  is positioned to rest against the outer transverse surface  24  of the endplate  20 . The instrument  132  is positioned such that the gap  144  separating the arms  140  and  142  is aligned with the engagement surface  47  of the base  44 . The instrument  132  can be oriented such that the inner transverse surface  121  is generally aligned with the engagement surface  47 . 
         [0059]    The instrument  132  can then be translated with respect to the endplate  20  in the longitudinally forward direction indicated by arrow F, such that the gap  144  receives the base  44  therein. The beveled surfaces  147  and  149  can correct any slight misalignments between the gap  144  and the base  44  during insertion. Thus, as the instrument  132  engages the endplate  20 , the inner surfaces  150  and  152  of the arms  140  and  142  ride along the side walls  45  of the base  44  until the base  44  is captured between the arms  140  and  142 . The instrument  132  is translated longitudinally forward to a fully mated position with the keel  28 , whereby the stop surface  154  abuts the engagement surface  47 . Continued forward motion of the instrument  132  then translates the endplate  20  into the intervertebral space  14 . Thus, the engagement surface  47  is configured to abut the stop surface  154  and receive a longitudinally forward biasing force from the stop surface  154  that biases the endplate in the longitudinally forward direction. 
         [0060]    When the instrument  132  and the endplate  20  are fully mated, the beveled edges  146  and  148  flare transversely out from the outer transverse surface  24 , and thus assist when inserting the endplate  20  into the intervertebral space  14 . In one embodiment, the beveled edges  146  and  148  are disposed behind the beveled front edge  32  of the endplate  20  such that the bevel  32  first engages the intervertebral space, followed by the beveled edges  146  and  148 . The bevels  32 ,  146 , and  148 , thus cooperate to facilitate insertion of the endplate  10  into the intervertebral space  14 . 
         [0061]    The wings  54  and  56 , including the first and second flared regions  58  and  60 , are inserted into the slot  18  formed in the vertebral body  12   a , such that the flared regions  58  and  60  of the wings  54  and  56 , respectively, engage the vertebral wall that defines the slot  18 . Because the aperture  52  separates the flared regions  58  and  60 , the flared regions  58  and  60  are flexible, and capable of flexing toward each other relative to the remainder of the endplate  20 . Thus, the flared regions  58  and  60  are capable of moving with respect to the bone contacting outer transverse surface  24  and the base  44 . Because the flared regions  58  and  60  are transversely spaced from the surface  24  and the base  44 , the transverse inner edge of the flared regions  58  and  60  are flexible with respect to the surface  24  and the base  44 . The inclusion of the flexible keel  28  may reduce the insertion force necessary to implant a device featuring the keel  28  when compared to an implant featuring a conventional, nonflexible keel. Because the flared regions  58  and  60  of the wings  54  and  56  are spaced transversely out from the base  44 , interference between the insertion instrument  132  and the flared regions  58  is avoided as the endplate  20  is inserted into the intervertebral space  14 . 
         [0062]    It should be appreciated that a keel similar to the flexible keels  28  and  30  described above can alternatively be configured for use with interbody spacers or other orthopedic implants designed to be anchored to boney tissue. The alternate implants may then be revised and/or explanted using a similar method to those described above for the implant having the endplate  10  with the flexible keel  28 . Thus, the implant  10  can be considered as an orthopedic implant. 
         [0063]    Referring to  FIGS. 10A-B , the endplate  20  can be constructed in accordance with an alternative embodiment so as to facilitate easy removal of the endplate  20  from the intervertebral space  14 . In particular, the keel  28  includes a pair of engagement walls  160  and  162  that extend laterally inward from respective laterally inner surfaces  57  and  59  of the wings  54  and  56 . The engagement walls  160  and  162  present rear engagement surfaces  164  and  166 , respectively, that are angled longitudinally rearward from the inner surfaces  57  and  59  along a laterally inward direction along the surfaces  164  and  166 . 
         [0064]    A removal instrument  170  includes a shaft  172  and a pair of laterally spaced arms  174  and  176 , respectively, each having a respective distal engagement surface  178  and  180 . Each engagement surface  178  and  180  is angled longitudinally rearward along a laterally inward direction along the surfaces  178  and  180 . Thus, the engagement surfaces  178  and  180  are configured to align and mate with the engagement surfaces  164  and  166 . The arms  174  and  176  are rigid at least with respect to lateral movement, such that forward motion of the removal instrument  170  relative to the endplate  20  along the direction of Arrow F causes the engagement surfaces  170  and  180  to engage the engagement surfaces  164  and  166 . Continue forward movement causes the surfaces  164  and  166  to ride laterally inward along the engagement surfaces  170  and  180 . As the surfaces  164  and  166  ride along the engagement surfaces  170  and  180 , the engagement surfaces  170  and  180  impart a laterally inward biasing force against the engagement surfaces  170  and  180 , and thus against the corresponding flared regions  58  and  60  of the wings  54  and  56  that causes the flared regions  58  and  60  to flex or retract laterally inward toward each other along the direction of Arrow I. Thus, the engagement surfaces  164  and  166  are disposed between the flared regions  58  and  60 , and are configured to receive a force from an instrument that biases the flared regions  58  and  60  toward each other. 
         [0065]    Thus, the flared regions  58  and  60  are configured to retract from a first outer position illustrated in  FIG. 10A , whereby the regions  58  and  60  are configured to abut, and engage, the surfaces of the vertebral body  12   a  that define the slot  18 , to a second inner position illustrated in  FIG. 10B , whereby the flared regions  58  and  60  are flexed laterally inward away from, and thus disengaged from, the surfaces of the vertebral body  12   a  that define the slot  18 . Accordingly, the flared regions  58  and  60  can be disengaged from the vertebral surfaces to facilitate revision and/or explantation of the endplate  20 . 
         [0066]    It should be appreciated that the second endplate  22  can be constructed substantially as described above with respect to the endplate  20 . Accordingly, the second endplate can include engagement walls as described with respect to the engagement walls  160  and  162  extending from the laterally inner surfaces of the wings  92  and  94  in the manner described above. 
         [0067]    It should be appreciated that the keels  28  and  30  have been described in accordance with certain embodiments, and that the keels  28  and  30  can be constructed in accordance with any alternative embodiment, such that at least one or both of the keels  28  and  30  includes a flexible and/or flared wing. For instance, referring to  FIGS. 11A  and B, the keel  28  is illustrated in accordance with an alternative embodiment, it being appreciated that the keel  30  can be similarly constructed. The keel  28  is constructed substantially as described above, however one of the wings (wing  54  as illustrated) extends longitudinally out from the keel body  42 , and thus defines a laterally outer surface  55  that is coplanar with the outer surface  43  of the keel body  42  along its entire longitudinal length. Thus, the distal region  58  is not outwardly flared in the lateral direction, and in fact does not extend in a direction having a lateral component, but rather extends longitudinally rearward toward the distal end  13 . The opposing wing  56  can include the flared region  60  in the manner described above. 
         [0068]    Referring now to  FIGS. 12A-B , in accordance with another alternative embodiment, at least one or both of the keels  28  and  30  is devoid of one of the distal regions of the wings, and is further devoid of an entire one of the wings. For instance, as illustrated, the keel  28  is constructed substantially as described above, however the keel  28  is devoid of one of the wings (wing  54  as illustrated). The keel body  42  can further be devoid of the entire lateral portion of the keel body  42  that would extend transversely out from the base  44  at a location on the same lateral side as the missing wing  54  with respect to a longitudinal axis L 1  that extends centrally through the endplate  20 . The opposing wing  56  can include the flared region  60  in the manner described above. 
         [0069]    It should be appreciated that the keels  28  and  30  constructed in accordance with any of the embodiments described herein defines a maximum lateral width defines as the lateral distance between opposing laterally outermost surfaces. For instance, as illustrated in  FIG. 2 , the maximum lateral width of the keel  28  extends laterally between the laterally outer surfaces of the flared regions  58  and  60  at the distal edges of the flared regions  58  and  60 . As illustrated in  FIGS. 11A-B , the maximum width is illustrated as extending between the laterally outer surface of the flared region  60  at the distal edge of the flared region  60  and the laterally outer surface  55  of the wing  54 . As illustrated in  FIGS. 12A-B , the maximum width is illustrated as extending between the laterally outer surface of the flared region  60  at the distal end of the flared region  60  and the laterally outer surface  43  of the keel body  42 . The maximum width of the keels  28  and  30  in each of the above-described embodiments can be the same as, greater than, or less than, the maximum widths in any of the other embodiments. Accordingly, the keels  28  and  30  can fit into the same sized slot  28 , or differently sized slots as desired. 
         [0070]    The embodiments described in connection with the illustrated embodiments have been presented by way of illustration, and the present invention is therefore not intended to be limited to the disclosed embodiments. Furthermore, the structure and features of each the embodiments described above can be applied to the other embodiments described herein, unless otherwise indicated. Accordingly, those skilled in the art will realize that the invention is intended to encompass all modifications and alternative arrangements included within the spirit and scope of the invention, for instance as set forth by the appended claims.