Patent Publication Number: US-11648131-B2

Title: Expandable implant

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. application Ser. No. 15/959,716, filed on Apr. 23, 2018, which is a continuation of U.S. application Ser. No. 15/091,058, filed on Apr. 5, 2016, which is a continuation of U.S. application Ser. No. 13/587,205, filed on Aug. 16, 2012, which claims the benefit of the filing date of U.S. Provisional Patent Application No. 61/523,981 filed Aug. 16, 2011, the disclosures of which are hereby incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to expandable implants and tools for the insertion of such implants. More particularly, the invention pertains to an expandable spinal implant having opposed plates, which are expandable via wedge members and ramped surfaces included on the plates. An insertion instrument used for implantation of the implant, and methods of utilizing the same, are also disclosed. 
     BACKGROUND OF THE INVENTION 
     Common degenerative spinal diseases, such as chronic degeneration of an intervertebral disc of the spine, may result in substantial pain and discomfort for a patient. Frequently, diseases of this type need to be treated through surgical intervention, which may include replacing the affected disc(s) and potentially fusing the associated vertebrae through the use of an implant or other like device. In particular applications, adjacent vertebral bodies may be fused via an implant, through screw arrangements, and/or by using bone graft material to secure the vertebrae in a fixed state. Exemplary indications for such devices include, but are not limited to, spinal stenosis, degenerative disc disease with a loss of disc height, disc herniation, spondylolisthesis, retrolisthesis, and disogenic back pain. 
     In replacing a diseased intervertebral disc(s) and effecting fusion, it may also be necessary to ensure that proper spacing is maintained between the vertebral bodies. Stated differently, once the implant or other like device is situated between adjacent vertebrae, the implant or device should adequately recreate the spacing previously maintained via the excised intervertebral disc (e.g., in its natural condition). Various expandable implants have been designed for this purpose. As such, it is possible for a surgeon to adjust the height of particular intervertebral implants to intra-operatively tailor the implant height to match the natural spacing between vertebrae, or any desired implant height. This may reduce the number of different implants needed to accommodate the varying anatomical confines of different patients. 
     Certain components of expandable implants, however, such as plates forming a part thereof, may be subject to torsional forces and/or compressive forces upon distraction or implantation. In some cases, the expansion mechanism of the implant may serve to keep the plates in alignment with one another to counteract these forces. In addition, rods or support bars have been used to inhibit the effect of torsional forces acting on the plates. 
     Although several versions of expandable intervertebral implants are known, the need for an improved expandable implant, which is expandable in situ and provides structures for keeping plates of the expandable implant in alignment with one another remains. 
     BRIEF SUMMARY OF THE INVENTION 
     A first aspect of the invention provides an expandable intervertebral implant having top and bottom plates with inner and outer surfaces, the inner surfaces facing each other and each having a ramp surface and a recess disposed adjacent the ramp surface. An actuator is also situated between the inner surfaces of the top and bottom plates, and first and second expansion members are coupled to the actuator and located between the inner surfaces of the top and bottom plates. In some cases, the first and second expansion members each have at least one vertical projection extending outwardly therefrom. Rotation of the actuator in opposing directions may cause the first and second expansion members to move toward and away from one another along a longitudinal axis of the actuator, resulting in movement of the top and bottom plates toward and away from one another along a vertical axis perpendicular to the longitudinal axis. The at least one vertical projection of the first and second expansion members may also be received and guided at least partially within one of the recesses adjacent the ramp surfaces of the top or bottom plates while such plates move along the vertical axis. 
     In embodiments of the first aspect, the first and second expansion members may also each include at least one lateral projection received within a corresponding lateral slot situated adjacent the ramp surface of each of the top and bottom plates. The actuator may also include first and second threaded portions, the first and second threaded portions having oppositely facing threads configured to engage threads of the first and second expansion members, such that when the actuator is rotated, the first and second expansion members move along the longitudinal axis of the actuator in opposite directions. 
     In a second aspect of the invention, an expandable intervertebral implant is provided in which the implant comprises top and bottom plates having inner and outer surfaces, the inner surfaces facing each other and each having a ramp surface. An actuator may also be situated between the inner surfaces of the top and bottom plates, and first and second expansion members may be coupled to the actuator and located between the inner surfaces of the top and bottom plates, the first and second expansion members each having a horizontal portion with at least one projection extending outward therefrom. Rotation of the actuator in opposing directions may cause the horizontal portion of the first and second expansion members to translate along the ramp surfaces toward and away from one another along a longitudinal axis of the actuator, resulting in movement of the top and bottom plates toward and away from one another along a vertical axis perpendicular to the longitudinal axis, the projections of the horizontal portions being received within at least one lateral slot situated adjacent each ramp surface as the top and bottom plates move along the vertical axis. 
     In some embodiments of the second aspect, the inner surfaces of the top and bottom plates each include a recess adjacent the respective ramp surface, and the first and second expansion members each include a vertical portion adapted to translate within the recesses during movement of the top and bottom plates along the vertical axis. Other embodiments include the horizontal portion of the first and second expansion members having at least a first and second projection extending therefrom, the first projection being received within a lateral slot situated adjacent the ramp surface of the top plate, and the second projection being received within a lateral slot situated adjacent the ramp surface of the bottom plate. The lateral slots may also each include a terminal portion, and the first and second projections may be adapted to interact with the terminal portion to prevent movement of the first and second expansion members away from one another. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the subject matter of the present invention(s) and of the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which: 
         FIGS.  1 A-B  are perspective views of an expandable implant according to one embodiment of the present invention, with  FIG.  1 A  showing the implant in collapsed form, and  FIG.  1 B  showing the implant expanded. 
         FIGS.  2 A-B  are cross-sectional views of the implant of  FIGS.  1 A- 1 B . 
         FIGS.  3 A-B  are exposed views of the top and bottom plates, respectively, of the implant of  FIGS.  1 A- 1 B , with the distraction mechanism shown alongside the relevant plate. 
         FIGS.  4 A-B  are perspective views of an instrument used for implantation, removal, and distraction of an expandable implant. 
         FIGS.  5 A-B  are perspective views of the instrument of  FIGS.  4 A-B , in which the instrument is being attached to the implant. 
         FIGS.  6 A-B  are perspective views of the instrument of  FIGS.  4 A-B , with the instrument configured for implantation of the implant. 
         FIGS.  7 A-B  depict the instrument of  FIGS.  4 A-B , in which the instrument is configured for distraction of the implant. 
         FIGS.  8 A-B  are perspective views of the instrument of  FIGS.  4 A-B , with the instrument configured to be removed from the implant. 
         FIG.  9    is an exploded view of another embodiment of an expandable implant according to the present invention. 
         FIGS.  10 A-B  are perspective views of the implant of  FIG.  9    in collapsed and expanded orientations, respectively. 
         FIGS.  11 A-B  are cross-sectional views of the implant of  FIGS.  10 A-B . 
         FIGS.  12 A-B  are exposed views of the bottom and top plates, respectively, of the implant of  FIG.  9   . 
         FIG.  13 A  is a perspective view of an alternate expandable implant according to one embodiment of the present invention, while  FIG.  13 B  is an exploded view of the distraction mechanism used with that implant. 
         FIG.  14    is a cross-sectional view of the implant of  FIG.  13 A . 
         FIG.  15    is an exposed view of one of the plates of the implant of  FIG.  13 A , the other plate being a mirror image thereof. 
     
    
    
     DETAILED DESCRIPTION 
     In describing the preferred embodiments of the invention(s) illustrated and to be described with respect to the drawings, specific terminology will be used for the sake of clarity. However, the invention(s) is not intended to be limited to any specific terms used herein, and it is to be understood that each specific term includes all technical equivalents, which operate in a similar manner to accomplish a similar purpose. For instance, while the terms “top” and “bottom” are used herein, such terms are utilized merely for convenience, and it is contemplated that the various implants disclosed may be situated in several orientations, such that these spatial terms may not apply (e.g., they may be reversed). 
     Referring to  FIGS.  1 A- 3 B , there is shown one embodiment of an expandable implant  10 , which in some cases may be used as an intervertebral implant, the expandable implant  10  having, generally: (1) top and bottom plates  20 ,  50  situated in opposition to one another; (2) a rod or axle  80  arranged between the top and bottom plates  20 ,  50 ; and (3) expansion members  100 ,  102  for contacting angled surfaces  22 ,  52  on top and bottom plates  20 ,  50 , respectively, and for expanding the implant  10  (e.g., in situ). In use, implant  10  may be inserted between adjacent vertebral bodies and expanded through use of an instrument, such as instrument  120  shown in  FIGS.  4 A-B , for example. This system provides a surgeon, nurse, or other skilled practitioner (hereinafter “the user”) with an improved expandable implant  10  for use in interventional procedures designed to combat various degenerative disorders, for example. 
     Referring to  FIGS.  1 A-B , top and bottom plates  20 ,  50  may include outer bone-contacting surfaces  24 ,  54  and inner surfaces  26 ,  56  opposed to the outer surfaces  24 ,  54 . In one embodiment, outer bone-contacting surfaces  24 ,  54  may include teeth, notches, serrations, keels, or other bone-penetrating features  28 ,  58  for engaging bone during use. An end of top and bottom plates  20 ,  50  may also be tapered  31 ,  61  for facilitating implantation of implant  10 , in one embodiment. Top plate  20  may also include, as shown in  FIG.  1 A , multiple elongate apertures  30  for facilitating bone in-growth or for receiving other biocompatible materials, for example. In some cases, top plate  20  may include four elongate apertures  30 , while bottom plate  50  may only include two, as reflected in  FIGS.  3 A-B , respectively. A separate set of apertures  34 ,  64  may also be formed in plates  20 ,  50  for receiving a post(s)  36  and nut(s)  38  construct, as shown in  FIGS.  2 A-B . In one embodiment, apertures  34  in top plate  20  may be generally thin in comparison to the elongate nature of apertures  64  in bottom plate  50 , thereby guiding and facilitating movement of posts  36  in apertures  64 . Each of plates  20 ,  50  may also include a projection  40 ,  70 , which in one embodiment may be dovetail-shaped. 
     Inner surfaces  26 ,  56  of top and bottom plates  20 ,  50 , as shown, respectively, in  FIGS.  3 A- 3 B  may each include angled surfaces  22 ,  52  on either side of a center of the plate  20 ,  50 . In particular, referring to  FIG.  3 B , bottom plate  50  may include a raised center  72  having apertures  64 , and on either side of center  72  may be an angled surface(s)  52 . Such surfaces  52  may also be angled in a direction extending from respective ends of plate  50  to raised center  72 . Likewise, referring to  FIG.  3 A , top plate  20  may include a recessed center  42  having apertures  34 , and on either side of recessed center  42  may be an angled surface(s)  22 . Further, such surfaces  22  may be angled in a direction extending from respective ends of plate  20  to recessed center  42 . Thus, angled surfaces  22 ,  52  of plates  20 ,  50  may converge towards one another, in one embodiment, as shown in  FIGS.  3 A-B . 
     Angled surfaces  22 ,  52  of plates  20 ,  50  may also be bounded by adjacent side walls  44 ,  74  for guiding expansion members  100 ,  102 , as described in detail below. Further: (1) raised center portion  72  may include a cutout  78  for accommodating an hourglass-shaped structure  82 ; (2) one end of each plate  20 ,  50  may include a semi-cylindrical cutout  29 ,  59  for accommodating part of axle  80 ; and (3) dovetail-shaped projections  40 ,  70  may each include a semi-cylindrical opening  25 ,  55  for receiving another portion of axle  80 . Inner surfaces  26 ,  56  of plates  20 ,  50  may also include a channel  27 ,  57  for housing axle  80 . 
     Referring still to  FIGS.  3 A-B , axle  80  may be situated between plates  20 ,  50 , and may include an hourglass-shaped member  82 . First and second threaded sections  84 ,  86  may also be arranged on opposite sides of hourglass-shaped member  82 , such sections  84 ,  86  having opposed right and left-handed threading. In other words, as an example, threaded section  84  may be situated on one side of hourglass-shaped member  82  and include left-hand threads, while threaded section  86  may be positioned on an opposing side of hourglass-shaped member  82  and include right-hand threads. 
     Expansion members  100 ,  102  may also be situated on axle  80 , such members  100 ,  102  each including an internally-threaded bore (not shown) for receiving one of threaded sections  84 ,  86 . In some embodiments, expansion members  100 ,  102  may include top and bottom surfaces  108 ,  110  angled in opposition to angled surfaces  22 ,  52  and in opposition to one another. Stated differently, top surfaces  108  of expansion members  100 ,  102  may be angled to seat flush with angled surfaces  22  of top plate  20 , while bottom surfaces  110  of expansion members  100 ,  102  may be angled to seat flush with angled surfaces  52  of bottom plate  50 , as shown in detail in  FIGS.  2 A-B . As such, top and bottom surfaces  108 ,  110  of expansion members  100 ,  102  may form a wedge. 
     At one end of axle  80  there may also be an engagement nut  90 , while at an opposing end of axle  80  may be stop nut  94 . Engagement and/or stop nuts  90 ,  94  may either be separate components threaded onto axle  80 , or, in some embodiments, may be unitarily formed with axle  80 . Engagement nut  90  includes ridges or serrations  96  on an exterior surface thereof for attaching with a portion of instrument  120 , and stop nut  94  comprises a smooth and enlarged exterior surface for interacting with a portion of expansion members  100 ,  102 . In one embodiment, ridges  96  on engagement nut  90  may form a Torx structure. 
     To construct implant  10 , top and bottom plates  20 ,  50  may first be situated in opposition to one another with inner surfaces  26 ,  56  facing towards each other. Axle  80 , previously assembled to include expansion members  100 ,  102 , and engagement  90  and stop  94  nuts, may also be situated between plates  20 ,  50  and within channels  27 ,  57 . In this configuration, top surfaces  108  of expansion members  100 ,  102  may engage with angled surfaces  22  of top plate  20 , and bottom surfaces  110  of expansion members  100 ,  102  may engage with angled surfaces  52  of bottom plate  50 , as shown in  FIGS.  2 A-B . Further, engagement nut  90  may be surrounded by semi-cylindrical openings  25 ,  55  of dovetail-shaped projections  40 ,  70 , and stop nut  94  by semi-cylindrical openings  29 ,  59 . An end of posts  36 , which in some cases includes an enlarged head  32 , may also be accommodated within apertures  64  in bottom plate  50 , and a stop surface  65  within each aperture  64  may prevent passage of head  32  completely through the aperture  64  ( FIG.  2 B ). An opposing end of posts  36 , which in some instances includes threading, may also be situated within apertures  34  in top plate  20  and be engaged with nuts  38  housed in apertures  34 . As such, plates  20 ,  50  may be connected together via posts  36 , which may allow expansion of implant  10  through movement of heads  32  within apertures  64  in bottom plate  50 , as shown in detail in the progression between  FIGS.  2 A-B . 
     With plates  20 ,  50  connected together as described above, and in an unexpanded state ( FIGS.  1 A,  2 A ), raised center section  72  of bottom plate  50  may be accommodated within recessed center section  42  of top plate  20 , and a perimeter of inner surfaces  26 ,  56  may be in contact with one another. Further, hourglass-shaped member  82  of axle  80  may be situated within the cutout  78  in bottom plate  50 . What is more, protrusions  77  extending into cutout  78  may engage a portion of hourglass-shaped member  82  to stabilize axle  80  along a longitudinal axis of plates  20 ,  50  ( FIG.  3 B ). 
     In this orientation, rotation of axle  80  in one direction may cause corresponding outward movement of expansion members  100 ,  102  (e.g., towards the ends of axle  80 ), and rotation in another opposite direction may cause inward movement of expansion members  100 ,  102  (e.g., towards hourglass-shaped member  82 ). Such movement of expansion members  100 ,  102  may also interact with angled surface  22 ,  52  on plates  20 ,  50  to cause corresponding expansion or collapse of implant  10  (e.g., within an intervertebral disc space), as shown in  FIGS.  2 A-B . In particular, movement of expansion members  100 ,  102  generally towards the ends of axle  80  may cause such members  100 ,  102  to ride up angled surfaces  22 ,  52  on plates  20 ,  50  and thereby cause expansion of implant  10 . Further, with top and bottom surfaces  108 ,  110  of expansion members  100 ,  102  being angled in the manner discussed above, the movement of plates  20 ,  50  may be generally uniform. In other words, were respective planes drawn along outer bone-contacting surfaces  24 ,  54  of plates  20 ,  50 , upon expansion of implant  10 , such planes would remain in generally the same orientation with respect to one another (i.e., due to top and bottom surfaces  108 ,  110  of expansion members  100 ,  102  being set flush against angled surfaces  22 ,  52 ). It is also contemplated that, in one embodiment, the aforementioned planes (and thus outer bone-contacting surfaces  24 ,  54 ) may be arranged at lordotic angles to one another. This may appropriately accommodate lordosis of adjacent vertebral bodies, if present. Such lordotic angles may also be maintained upon expansion of implant  10 . 
     During the above-described expansion of implant  10 , axle  80  may rotate within channels  27 ,  57 , and particularly: (1) hourglass-shaped member  82  may rotate within cutout  78 ; (2) engagement nut  90  within semi-circular openings  25 ,  55 ; and (3) stop nut  94  within semi-circular openings  29 ,  59 . Further, as noted above, due to the reverse threading of threaded sections  84 ,  86 , upon rotation of axle  80 , expansion members  100 ,  102  may move towards or away from one another (i.e., in opposing directions). Such movement of expansion members  100 ,  102  may also be limited by engagement  90  and stop  94  nuts, and hourglass-shaped member  82 . In addition, during expansion of implant  10 , expansion members  100 ,  102  may be stabilized via side walls  44 ,  74  of inner surfaces  26 ,  76 , and posts  36  may limit and/or prevent over-expansion of implant  10 . Indeed, as expansion members  100 ,  102  move plates  20 ,  50  apart, the head  32  of posts  36  may slide within elongate apertures  64  in plate  50  until such a point as head  32  contacts stop surface  65 , as shown in  FIG.  2 B . Thus, posts  36  may act to prevent over distraction of implant  10 . Further, posts  36  may also operate to stabilize implant  10  upon expansion, since sections of posts  36  are engaged with both top and bottom plates  20 ,  50  during expansion. In other words, posts  36  may serve to provide torsional and/or compressive stability to plates  20 ,  50  in one embodiment. 
     As such, in use, implant  10  may be inserted into the intervertebral disc space of a patient, with outer bone-contacting surfaces  24 ,  54  engaging adjacent vertebrae, and such implant  10  may be expanded in the manner described above. Further details pertaining to this method of expansion, and the insertion of the implant  10  within an intervertebral space, are set forth in subsequent sections. 
     Referring to  FIGS.  4 A-B , there is shown an instrument  120  engageable with the aforementioned implant  10 , and usable to place implant  10  at the treatment site (e.g., within the intervertebral disc space). Instrument  120  may generally include: (1) a shaft  122  with a sleeve  128  overlying the shaft  122 ; (2) distal  124  and proximal  126  ends; (3) a socket  130  for engaging with engagement nut  90 ; and (4) a rotatable handle  132  connected to socket  130 , such that rotation of handle  132  may cause rotation of socket  130  and expansion of implant  10  (e.g., when instrument  120  is engaged with engagement nut  90 ). Distal end  124  of instrument  120  may also include fingers  134 ,  136  that are engageable with dovetail-shaped projections  40 ,  70 , and may be actuated via a knob  138  situated adjacent proximal end  126  of instrument  120 . Thus, instrument  120  may provide a useful tool for a user in the insertion and/or expansion of implant  10 , as detailed more fully below. 
     As shown in  FIG.  4 A , handle  132  of instrument  120  may be connected to a rod (not shown) extending generally within and along shaft  122  of instrument  120 . The rod may extend to distal end  124  of instrument  120  and may terminate in socket  130 , which in one embodiment may be configured to engage with engagement nut  90 . In some instances, socket  130  may be a Torx-type socket for engaging with an engagement nut  90  having Torx structure. A separate handle  142  may also be provided adjacent proximal end  126 , such handle  142  extending generally outward from instrument  120 . Instrument  120  may also include a grip  144 . Handle  142  and grip  144  may allow the user to effectively grasp instrument  120  during insertion of implant  10  into the intervertebral disc space. 
       FIG.  4 A  further depicts a knob  138  adjacent proximal end  126  that is rotatable about a longitudinal axis of shaft  122 . An interior of knob  138  may include internal threading for cooperating with an actuator (not shown) connected to sleeve  128 . The threading within knob  138  may be configured such that, upon rotation of knob  138  in one direction, the actuator and sleeve  128  may move longitudinally towards distal end  124 ; and, upon rotation of knob  138  in an opposing direction, the actuator and sleeve  128  may move longitudinally towards proximal end  126 . 
     A viewing window  148  may also be provided with instrument  120 , as shown in close-up in  FIG.  4 B , for indicating to a user of instrument  120  the particular mode in which instrument  120  is situated (e.g., “implant” mode, “distract” mode, or “remove” mode). An indicator  150  may be housed within viewing window  148 , and a series of markings  152  may also be situated adjacent the window  148 . Further, in one embodiment, wording or other information may be provided proximate viewing window  148  and markings  152  to inform a user of the mode in which instrument  120  is placed. 
     Referring to  FIGS.  5 A-B , distal end  124  of shaft  122  of instrument  120  may be provided with resilient fingers  134 ,  136  running along opposing sides of shaft  122 , and positioned within channels (not shown) in shaft  122 . Each finger  134 ,  136  may include an end having generally angled surfaces  154  for engaging with projections  40 ,  70  on implant  10 . In one embodiment, fingers  134 ,  136  may be shaped to conform to the dovetail shape of projections  40 ,  70 . 
     In use, referring still to  FIGS.  5 A-B , distal end  124  of instrument  120  may be positioned adjacent dovetail-shaped projections  40 ,  70  of implant  10  so that socket  130  of instrument  120  may be attached to engagement nut  90 . Specifically, as shown in the progression between  FIGS.  5 A-B , resilient fingers  134 ,  136  may be inserted over projections  40 ,  70  with sleeve  128  in its retracted position. Such position of sleeve  128  may, in one embodiment, correspond to the “remove” mode shown in  FIG.  8 A . Upon insertion of fingers  134 ,  136  over projections  40 ,  70 , fingers  134 ,  136  may translate outwards to accommodate the shape of projections  40 ,  70 . After full insertion of fingers  134 ,  136  over projections, angled surfaces  154  may seat within or accommodate the shape of projections  40 ,  70 . Stated differently, since fingers  134 ,  136  may be biased to remain within the channels in shaft  122 , after insertion of fingers  134 ,  136  over projections  40 ,  70 , fingers  134 ,  136  may return to their normal un-translated state and conform to the shape of projections  40 ,  70 . Such is shown in detail in  FIG.  5 B . 
     With socket  130  connected to engagement nut  90  and fingers  134 ,  136  situated about projections  40 ,  70 , sleeve  128  of instrument  120  may then be translated longitudinally via knob  138  until such a point as sleeve  128  contacts implant  10 , as shown in  FIGS.  6 A-B . This position of sleeve  128  may correspond to the “implant” mode of instrument  120 , which may be indicated by the movement of indicator  150  within viewing window  148 . In particular, movement of sleeve  128  may cause movement of indicator  150  within window  148 , such that indicator  150  becomes aligned with a marking  152  corresponding to the “implant” mode of instrument  120 , as shown in  FIG.  6 A . Further, as sleeve  128  moves longitudinally in the manner described above, fingers  134 ,  136  may be compressed against projections  40 ,  70 , thereby securing instrument  120  to implant  10 . Implant  10  may then be inserted into the intervertebral disc space via instrument  120 , such that outer bone-contacting surfaces  24 ,  54  engage upper and lower vertebral bodies. The approach for implantation of implant  10 , in some cases, may be a posterior or posterior-lateral approach, although other approaches are contemplated. In some embodiments, the vertebral bodies may also be prepared (e.g., through the use of cutting instruments) according to traditional spinal procedures prior to implantation of implant  10 . It is also contemplated that, during insertion of implant  10 , tapered ends  31 ,  61  of plates  20 ,  50  may provide easier insertion of implant  10  into the intervertebral space via insertion instrument  120 . In addition, the lordotic angle between plates  20 ,  50  may, in one embodiment, accommodate lordosis of the adjacent vertebrae, if present. 
     To distract implant  10  once inserted, instrument  120  may be placed in “distract” mode. Referring to  FIGS.  7 A-B , this involves rotating knob  138  in one direction to move the actuator and sleeve  128  toward proximal end  126  of instrument  120 . As sleeve  128  moves toward proximal end  126 , indicator  150  may also move within viewing window  148  so as to line up with the particular marking  152  corresponding to “distract” mode. Thus, a user may be informed when instrument  120  is placed in “distract” mode via rotation of knob  138 . With sleeve retracted a sufficient distance towards proximal end  126 , some pressure may be relieved from between fingers  134 ,  136  and projections  40 ,  70 , thereby allowing plates  20 ,  50  to move apart from one another without fingers  134 ,  136  inhibiting such movement. Stated differently, sleeve  128  may be retracted towards proximal end  126 , such that fingers  134 ,  136  may still retain projections  40 ,  70  and implant  10 , but that pressure therebetween is somewhat relieved so as to allow distraction of implant  10 . To achieve such distraction, the user may simply rotate handle  132  ( FIG.  4 A ) causing socket  130  to rotate within engagement nut  90 . This rotation of engagement nut  90 , as described previously, may cause expansion members  100 ,  102  to interact with ramped surfaces  22 ,  52  of plates  20 ,  50  and force plates  20 ,  50  apart. Distraction of plates  20 ,  50  in this manner may also cause distraction of adjacent vertebral bodies. It is thusly possible for implant  10  to accommodate varying degrees of intervertebral spacing, as required during different surgeries or with different patients. Implant  10 , in its expanded state as discussed above, is shown in detail in  FIG.  7 B . 
     Referring now to  FIGS.  8 A-B , with implant  10  inserted into the intervertebral disc space, instrument  120  may be placed in “remove” mode, which again may be indicated by movement of indicator  150  within viewing window  148 . In particular, knob  138  may be rotated in one direction causing movement of sleeve  128  towards proximal end  126  of instrument  120  and corresponding movement of indicator  150 . Further, during movement of sleeve  128  towards proximal end  126 , fingers  134 ,  136  may be fully released and allowed to resiliently deform outwards as instrument  120  is removed from about projections  40 ,  70 . Instrument  120  may then be removed from the surgical site and implant  10  left to affect fusion of the adjacent vertebral bodies. To achieve improved fusion, it is also contemplated that bone-chips, synthetic graft material, or other biocompatible material may be inserted within the intervertebral disc space prior to or during the implantation of implant  10 , and such material may adhere to the apertures in plates  20 ,  50  (e.g., apertures  30 ) provided for in-growth. 
     An alternate embodiment implant  210  is shown in  FIG.  9   . Due to the similarity between the structures of implants  10 ,  210 , like numerals will refer to like elements and, predominantly, only the structural differences between implants  10 ,  210  will be highlighted. Thus, apart from the below-mentioned distinguishing features, it is contemplated that implants  10 ,  210  may have the same structure and may operate in the same manner (e.g., as set forth above) to accomplish the same purpose. 
     Referring to  FIG.  9   , implant  210  may include top and bottom plates  220 ,  250 , such plates including, inter alia: (1) outer bone-contacting surfaces  224 ,  254  and opposed inner surfaces  226 ,  256 ; (2) projections  240 ,  270 , which in one embodiment may be dovetail-shaped; (3) apertures  234 ,  264  for receiving posts  236  and nuts  238 ; (4) recessed and raised center portions  242 ,  272 ; and (5) angled surfaces  222 ,  252  for engaging with expansion members  300 ,  302 . Other similar features to implant  10  are also present in implant  210 ; and, although not discussed in detail herein, such features are indicated by like reference numerals in the figures. 
     Several differentiating features of implant  210  will now be described, such features providing improvements in the operation of expandable implant  210 . Referring to  FIG.  9   , implant  210  may include an axle  280  disposed between top and bottom plates  220 ,  250 , with axle  280  including a center member  282  that is slightly different in shape than hourglass-shaped member  80  of implant  10 . Even so, center member  282  of axle  280  may include opposed discs  400  for engaging with cutouts  402  formed in bottom plate  250 , and a center portion having a reduced diameter for seating within cutout  278 , as shown in detail in  FIG.  12 A . With center member  282  situated in bottom plate  250  as described, axle  280  may be longitudinally stabilized with respect to plate  250  (e.g., through the interaction of opposed discs  400  and cutouts  402 ), as is the case with axle  80  of implant  10 . 
     Implant  210  may also include expansion members  300 ,  302  having top and bottom surfaces  308 ,  310  that are angled in the manner described with reference to expansion members  100 ,  102 , as shown in  FIGS.  11 A-B , but expansion members  300 ,  302  may also have vertically-extensive projections  312 ,  314  extending outward therefrom. Expansion members  300 ,  302  may also include a set (or one or more) of pins  316  extending from the sides of members  300 ,  302 . Vertically-extensive projections  312 ,  314  of expansion members  300 ,  302  may be received in elongate apertures  230  formed in top and bottom plates  220 ,  250 , such apertures  230  being configured to allow translation of vertically-extensive projections  312 ,  314  during expansion of implant  210 . Pins  316  of expansion members  300 ,  302  may ride along slots  318  formed within side walls  244 ,  274  situated adjacent angled surfaces  222 ,  252  for guiding expansion members  300 ,  302  during expansion of implant  210 , as shown in detail in  FIGS.  9  and  12 A -B. 
     In use, implant  210  may be implanted and/or expanded in much the same manner as implant  10 . Particularly, it is contemplated that insertion instrument  120  may be modified only slightly to properly operate with and engage implant  210 , and to distract such implant  210  after implantation. For example, while it is contemplated that engagement nut  290  of implant  210  may include Torx structure, it is shown in the figures as a hexagonal nut  290  ( FIGS.  9 ,  11 A -B). Thus, socket  130  of instrument  120  may be modified to accommodate this structure, and to engage with engagement nut  290  in the manner described in relation to implant  10 . To be exact, such modified socket  130  may be inserted over engagement nut  290 , and rotated via handle  132  so as to expand implant  210 . It is also contemplated that instrument  120  may be placed into the various modes (e.g., “implant” mode, “distract” mode, and/or “remove” mode) upon engaging, distracting, and/or separating from implant  210 , as discussed previously. Significantly, however, during expansion of implant  210  through the use of instrument  120 , several structures of implant  210  may operate differently to provide a more stabilized and improved distraction procedure. 
     In one embodiment, referring now to  FIGS.  9  and  12 A -B, during expansion of implant  210  via the interaction between socket  130  and engagement nut  290 , expansion members  300 ,  302  may engage with angled surfaces  222 ,  252 ; but, during separation of expansion members  300 ,  302  via the reverse threading of threaded sections  284 ,  286 , pins  316  extending from expansion members  300 ,  302  may ride along slots  318  formed in respective side walls  244 ,  274  of top and bottom plates  220 ,  250 . The engagement between pins  316  and slots  318  may act to stabilize the movement of expansion members  300 ,  302 , and may also serve to limit the expansion of implant  210 . Indeed, slots  318  may terminate at one section of side walls  244 ,  274 , and pins  316  may abut this section upon full expansion of implant  210  to prohibit further movement of expansion members  300 ,  302  (e.g., away from one another). In one embodiment, pins  316  may be situated on diagonally opposite sides of each respective expansion member  300 ,  302 , although it is contemplated that additional pins  316  may be used (e.g., on all four (4) corners of expansion members  300 ,  302 ). The engagement between pins  516  and slots  518  may also, at least partially, serve to keep plates  220 ,  250  in registration with one another during distraction. 
     An additional stabilization and/or expansion-limiting feature may be included with implant  210  in the form of elongate apertures  230 . In particular, referring to  FIGS.  10 A- 11 B , during expansion of implant  210  via the use of instrument  120 , vertically-extensive projections  312 ,  314  of expansion members  300 ,  302  may interact with elongate apertures  230  in top and bottom plates  220 ,  250  to stabilize such members  300 ,  302  and plates  220 ,  250 . As shown in the progression between  FIGS.  10 A- 10 B and  11 A- 11 B , vertically-extensive projections  312 ,  314  may be arranged within elongate apertures  230  of plates  220 ,  250 ; and, upon expansion of implant  210 , vertically-extensive projections  312 ,  314  may translate within apertures  230 , such that plates  220 ,  250  and expansion members  300 ,  302  are stabilized during distraction. Upon reaching an end of apertures  230 , expansion members  300 ,  302  may also be limited from further outward movement. Apertures  230  may also, like apertures  30  of implant  10 , operate to receive bone graft or other osteoinductive material to facilitate fusion of adjacent vertebral bodies upon implantation of implant  210 . Although not discussed in detail herein, the remainder of steps pertaining to the implantation and/or expansion of implant  210 , and its interaction with instrument  120 , is again substantially identical to that discussed above with respect to implant  10 . 
     Another embodiment of an expandable implant, implant  410 , is shown in  FIGS.  13 A- 15   . Here, like numerals will refer to like elements, with the structural differences between implants  10 ,  210 ,  410  being discussed. Thus, as with above, apart from the distinguishing features detailed in subsequent sections, it is contemplated that implants  10 ,  210 ,  410  may have the same structure and operate in the same manner to accomplish the same purpose. Here, it is worthwhile to note that, while  FIG.  15    only depicts top plate  420 , bottom plate  450  is a mirror image thereof, and thus,  FIG.  15    is an accurate representation of both plates  420 ,  450  (e.g., with like reference numerals referring to like elements). 
     Referring to  FIGS.  13 A and  15   , implant  410  may include top and bottom plates  420 ,  450  with angled inner surfaces  422 ,  452  for engaging with expansion members  500 ,  502 , much like implants  10 ,  210 . Further, expansion members  500 ,  502  of implant  410  may also include vertically-extensive projections  512 ,  514  for engaging with elongate apertures  430  in plates  420 ,  450 , such that upon expansion of implant  410 , vertically-extensive projections  512 ,  514  may translate within apertures  430 . Other similar features to implants  10 ,  210  are also included with implant  410 , such as: (1) outer bone-contacting surfaces  424 ,  454  with teeth or serrations  428 ,  458 ; (2) tapered ends  431 ,  461  of plates  420 ,  450 ; (3) dovetail-shaped projections  440 ,  470 ; (4) slots  518  in side walls  444 ,  474  of plates  420 ,  450 ; and (5) expansion members  500 ,  502  including pins  516  for engaging with slots  518 . Yet, other features, such as the distraction mechanism of implant  410 , may operate differently than found with implants  10 ,  210 . 
     Referring to  FIG.  13 B , the distraction mechanism of implant  410  may include a rod or axle  480 , a capture mechanism  530 , and a containment ring  532 . Axle  480 , like axles  80 ,  280 , may be threaded in one embodiment, and may include separate sections  484 ,  486  with left-handed and right-handed threads. An engagement nut  490  structure may also be disposed on one end of axle  480 , and a center of axle may include a radially-extending flange  534  and a press-fit region  536 . 
     Capture mechanism  530  may include a set of apertures  538 ,  540  for receiving a portion of axle  480 , and a slot  542  for receiving containment ring  532 . Slot  542  may be dimensioned to allow free movement of containment ring  532  and axle  480  once situated therein. In one embodiment, aperture  538  of capture mechanism  530  may have a diameter that is larger than aperture  540  so as to allow flange  534  to be received in aperture  538 . Further, each aperture  538 ,  540  may be smaller in diameter than an outer diameter of containment ring  532 . In a particular embodiment, containment ring  532  includes an inner diameter such that, upon insertion of press-fit region  536  into containment ring  532 , a dimensional interference is established therebetween. 
     Apart from the differences between distraction mechanisms amongst implants  10 ,  210 ,  410 , implant  410  may also include plates  420 ,  450  with apertures  550  for receiving a portion of capture mechanism  530 , as shown in  FIG.  14   . Inner surfaces  426 ,  456  of plates  420 ,  450  may also include structure (e.g. a housing  560 ) for stabilizing capture mechanism  530  (and thus axle  480 ) in a longitudinal direction, as shown in  FIG.  15   . In one embodiment, plates  420 ,  450  also include openings  520  through which pins  516  may be inserted. Similarly, expansion members  500 ,  502  may include openings  522  for receiving pins  516 . 
     In use, the distraction mechanism of implant  410  may be situated between plates  420 ,  450  such that axle  480  is inserted into capture mechanism  530  and through containment ring  532 , as shown in  FIG.  14   . In particular, containment ring  532  may be disposed within slot  542  in capture mechanism  530 , and axle  480  may be inserted through apertures  538 ,  540 . To be exact, axle  480  may be inserted through containment ring  532  until such a point as press-fit region  536  is situated within containment ring  532  and flange  534  is housed within aperture  538  and abuts containment ring  532 . In this orientation, press-fit region  536  may interact with containment ring  532  to establish a dimensional interference between such structures, such that axle  480  may be securely retained within capture mechanism  530 . To be exact, the interaction between flange  534  and containment ring  532  may prevent movement of axle  480  in one direction, and the cooperation between press-fit region  536 , containment ring  532 , and slot  542  may prevent movement of axle  480  in another opposing direction. With axle situated in capture mechanism  530  in the manner described above, capture mechanism  530  may then be inserted into apertures  550  in plates  420 ,  450 . 
     Capture mechanism  530 , axle  480 , and expansion members  500 ,  502  may be situated between plates  420 ,  450 , with the inner surfaces  426 ,  456  of plates  420 ,  450  facing one another, as discussed above, and pins  516  may be inserted through openings  520  in plates  420 ,  450  and into openings  522  in expansion members  500 ,  502 . Indeed, pins  516  may be press-fit into openings  522  in expansion members  500 ,  502 , such that pins  516  are firmly retained in expansion members  500 ,  502 . Pins  516  are also designed to ride within slots  518  to limit movement of expansion members  500 ,  502 , and such pins  516  may also serve to keep plates  420 ,  450  firmly connected together. In other words, as at least one pin  516  on each expansion member  500 ,  502  engages with a slot  518  in top plate  420 , and at least one pin  516  with a slot  518  in bottom plate  450 , such plates  420 ,  450  may be securely retained together via the interaction between pins  516  and slots  518 . A terminal portion of slots  518  may also serve to prevent over-expansion of implant  410 , as discussed above with respect to implant  210 . 
     Implant  410  may also interact with instrument  120  in the same manner as implants  10 ,  210  (e.g., for purposes of implantation and/or distraction). For instance, rotation of handle  132  with respect to engagement nut  490  in one direction may cause expansion members  500 ,  502  to move outwardly, and pins  516  to engage with slots  518 . Such movement of expansion members  500 ,  502  may also cause outward movement or distraction of plates  420 ,  450 , as with implants  10 ,  210 ; and additional rotation of handle  132  may cause pins  516  of expansion members  500 ,  502  to engage with a terminal portion of slots  518  to prevent further outward movement of expansion members  500 ,  502 . 
     What is more, during the aforementioned movement of expansion members  500 ,  502 , vertically-extensive projections  512 ,  514  may translate within apertures  430  in plates  420 ,  450 , and apertures  550  in plates  420 ,  450  may interact with capture mechanism  530 . Stated differently, as expansion members  500 ,  502  engage with angled surfaces  422 ,  522  to distract implant  410  (e.g., via use of instrument  120 ), apertures  550  in plates  420 ,  450  may slide along portions of capture mechanism  530 , vertically-extensive projections  512 ,  514  may translate within apertures  430 , and pins  516  may ride within slots  518 . Such movement of expansion members  500 ,  502  may therefore serve to stabilize implant  410  during distraction. For instance, the interaction between vertically-extensive projections  512 ,  514  and apertures  430 , and apertures  550  and capture mechanism  530 , may provide torsional and/or compressive stability to implant  410  during distraction, and pins  516  may act as distraction-limiting features. Thus, as with implants  10 ,  210 , implant  410  may provide an expandable implant with improved features for maintaining stability and/or controlling distraction during replacement of an intervertebral disc. 
     In the devices shown in the figures, particular structures are shown as being adapted for use in the implantation, distraction, and/or removal of an expandable implant according to the present invention(s). The invention(s) also contemplates the use of any alternative structures for such purposes, including structures having different lengths, shapes, and/or configurations. For example, as alluded to above, although certain structures are used for socket  130  and engagement nut  90 ,  290 ,  490  (e.g., Torx or hexagonal), it is contemplated that a variety of different socket/nut combinations may be used, such as square, triangular, etc. 
     In addition, while angled surfaces  22 ,  52 ,  222 ,  252 ,  422 ,  452  are shown in the figures as being predominantly flat, it is also contemplated that surfaces  22 ,  52 ,  222 ,  252 ,  422 ,  452  may be curved in one embodiment so as to facilitate expansion of implants  10 ,  210 ,  410 . Top and bottom surfaces  108 ,  110 ,  308 ,  310 ,  508 ,  510  of expansion members  100 ,  102 ,  300 ,  302 ,  500 ,  502  may likewise be shaped to accommodate the curvature of angled surfaces  22 ,  52 ,  222 ,  252 ,  422 ,  452 , as previously discussed with respect to implants  10 ,  210 ,  410 . 
     Although the invention(s) herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention(s). It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention(s) as defined by the appended claims. 
     It will also be appreciated that the various dependent claims and the features set forth therein can be combined in different ways than presented in the initial claims. It will also be appreciated that the features described in connection with individual embodiments may be shared with others of the described embodiments.