Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/793,481, titled “Expandable Fusion Device and Method of Installation Thereof,” filed on Mar. 11, 2013, which is a continuation-in-part of U.S. patent application Ser. No. 12/875,637, entitled “Expandable Fusion Device and Method of Installation Thereof,” filed on Sep. 3, 2010 (now U.S. Pat. No. 8,845,731), the entire disclosure of both of which are incorporated by reference herein in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the apparatus and method for promoting an intervertebral fusion, and more particularly relates to an expandable fusion device capable of being inserted between adjacent vertebrae to facilitate the fusion process. 
       BACKGROUND 
       [0003]    A common procedure for handling pain associated with intervertebral discs that have become degenerated due to various factors such as trauma or aging is the use of intervertebral fusion devices for fusing one or more adjacent vertebral bodies. Generally, to fuse the adjacent vertebral bodies, the intervertebral disc is first partially or fully removed. An intervertebral fusion device is then typically inserted between neighboring vertebrae to maintain normal disc spacing and restore spinal stability, thereby facilitating an intervertebral fusion. 
         [0004]    There are a number of known conventional fusion devices and methodologies in the art for accomplishing the intervertebral fusion. These include screw and rod arrangements, solid bone implants, and fusion devices which include a cage or other implant mechanism which, typically, is packed with bone and/or bone growth inducing substances. These devices are implanted between adjacent vertebral bodies in order to fuse the vertebral bodies together, alleviating the associated pain. 
         [0005]    However, there are drawbacks associated with the known conventional fusion devices and methodologies. For example, present methods for installing a conventional fusion device often require that the adjacent vertebral bodies be distracted to restore a diseased disc space to its normal or healthy height prior to implantation of the fusion device. In order to maintain this height once the fusion device is inserted, the fusion device is usually dimensioned larger in height than the initial distraction height. This difference in height can make it difficult for a surgeon to install the fusion device in the distracted intervertebral space. 
         [0006]    As such, there exists a need for a fusion device capable of being installed inside an intervertebral disc space at a minimum to no distraction height and for a fusion device that can maintain a normal distance between adjacent vertebral bodies when implanted. 
       SUMMARY 
       [0007]    In an exemplary embodiment, the present invention provides an intervertebral implant. The intervertebral implant may comprise an upper endplate comprising a first upper endplate portion and a second upper endplate portion. The intervertebral implant may comprise a lower endplate comprising a first lower endplate portion and a second lower endplate portion. The intervertebral implant may comprise a front sloped actuator configured to movingly engage a front end of the upper endplate and a front end of the lower endplate. The intervertebral implant may comprise a rear sloped actuator configured to movingly engage a rear end of the upper endplate and a rear end of the lower endplate. The intervertebral implant may be configured to transition from a collapsed configuration having a first height and a first width to an expanded configuration having a second height and a second width. 
         [0008]    In an exemplary embodiment, the present invention provides an intervertebral implant. The intervertebral implant may comprise an upper endplate. The upper endplate may comprise a first upper endplate portion comprising a front ramped surface and a rear ramped surface. The upper endplate may further comprise a second upper endplate portion comprising a front ramped surface and a rear ramped surface. The upper endplate may further comprise endplate pins connecting the first upper endplate portion and the second upper endplate portion. The intervertebral implant may further comprise a lower endplate. The lower endplate may comprise a first lower endplate portion comprising a front ramped surface and a rear ramped surface. The lower endplate may further comprise a second lower endplate portion comprising a front ramped surface and a rear ramped surface. The lower endplate may further comprise endplate pins connecting the first lower endplate portion and the second lower endplate portion. The intervertebral implant may further comprise a front sloped actuator configured to movingly engage the front ramped surface of the first upper endplate portion, the front ramped surface of the second upper endplate portion, the front ramped surface of the first lower endplate portion, and the front ramped surface of the second lower endplate portion. The intervertebral implant may further comprise a rear sloped actuator configured to movingly engage the rear ramped surface of the first upper endplate portion, the front ramped surface of the second upper endplate portion, the rear ramped surface of the first lower endplate portion, and the rear ramped surface of the second lower endplate portion. The intervertebral implant may be configured to transition from a collapsed configuration having a first height and a first width to an expanded configuration having a second height and a second width. 
         [0009]    In another embodiment, the present invention provides a method of installing an intervertebral implant, the method comprising: introducing the intervertebral implant into an intervertebral space; and contracting an actuator assembly to cause the intervertebral implant to transition from a collapsed configuration having a first height and a first width to an expanded configuration having a second height and a second width. 
         [0010]    In another embodiment, the present invention provides an intervertebral implant. The intervertebral implant may comprise an upper endplate comprising a first upper endplate portion and a second upper endplate portion. The intervertebral implant may further comprise a lower endplate comprising a first lower endplate portion and a second lower endplate portion. The intervertebral implant may further comprise an actuator assembly disposed between the upper endplate and the lower endplate, the actuator assembly being configured to movingly engage front ends of the upper endplate and the lower endplate and also movingly engage rear ends of the upper endplate and the lower endplate. The intervertebral implant may be configured to first transition from a collapsed configuration having a first width and a first height to a laterally expanded configuration having a second width and then transition to a vertically expanded configuration having a second height. 
         [0011]    In another embodiment, the present invention provides an intervertebral implant. The intervertebral implant may comprise an upper endplate comprising. The upper endplate may comprise a first upper endplate portion comprising a front ramped surface and a rear ramped surface. The upper endplate may further comprise a second upper endplate portion comprising a front ramped surface and a rear ramped surface. The upper endplate may further comprise endplate pins connecting the first upper endplate portion and the second upper endplate portion. The intervertebral implant may further comprise a lower endplate. The lower endplate may comprise a first lower endplate portion comprising a front ramped surface and a rear ramped surface. The lower endplate may further comprise a second lower endplate portion comprising a front ramped surface and a rear ramped surface. The lower endplate may further comprise endplate pins connecting the first lower endplate portion and the second lower endplate portion. The intervertebral implant may further comprise a front sloped actuator assembly disposed between the upper endplate and the lower endplate. The front sloped actuator assembly may comprise a pair of front height actuators, wherein the front height actuators each comprise opposing ramped surfaces in respective engagement with the upper endplate and the lower endplate. The front sloped actuator assembly may further comprise a front width actuator that is wedge shaped and disposed between the pair of front height actuators and in moving engagement with the pair of front height actuators, wherein the front width actuator is operable to force the pair of front height actuators laterally apart. The intervertebral implant may further comprise a rear sloped actuator assembly. The rear sloped actuator assembly may comprise a pair of rear height actuators, wherein the rear height actuators each comprise opposing ramped surfaces in respective engagement with the upper endplate and the lower endplate. The rear sloped actuator assembly may further comprise a front width actuator disposed between the pair of rear height actuators and in moving engagement with the pair of rear height actuators, wherein the front width actuator is operable to force the pair of front height actuators laterally apart. The intervertebral implant may be configured to first transition from a collapsed configuration having a first width and a first height to a laterally expanded configuration having a second width and then transition to a vertically expanded configuration having a second height. 
         [0012]    In another embodiment, the present invention provides a method of installing an intervertebral implant, the method comprising. The method may comprise introducing the intervertebral implant into an intervertebral space. The method may further comprise moving at least one of a front width actuator or a rear width actuator to cause the front width actuator and the rear width actuator to move closer to one another such that the intervertebral implant transitions from a laterally collapsed configuration having a first width to a laterally expanded configuration having a second width. The method may further comprise moving at least one of a front sloped actuator assembly or a rear sloped actuator assembly to cause the front sloped actuator assembly and the rear sloped actuator assembly to move closer to another such that the intervertebral implant transitions from a vertically collapsed configuration having a first height to a vertically expanded configuration having a second height. 
         [0013]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred or exemplary embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0015]      FIG. 1  is a side view of an embodiment of an expandable fusion device shown between adjacent vertebrae according to the present invention; 
           [0016]      FIG. 2  is a front perspective view of the expandable fusion device of  FIG. 1  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0017]      FIG. 3  is a front perspective view of the expandable fusion device of  FIG. 1  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0018]      FIG. 4  is a rear perspective view of the expandable fusion device of  FIG. 1  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0019]      FIG. 5  is a rear perspective view of the expandable fusion device of  FIG. 1  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0020]      FIG. 6  is a side view of the expandable fusion device of  FIG. 1  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0021]      FIG. 7  is a side view of the expandable fusion device of  FIG. 1  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0022]      FIG. 8  is a perspective view of the central ramp of the expandable fusion device of  FIG. 1  in accordance with one embodiment of the present invention; 
           [0023]      FIG. 9  is a perspective view of the driving ramp of the expandable fusion device of  FIG. 1  in accordance with one embodiment of the present invention; 
           [0024]      FIG. 10  is a perspective of an endplate of the expandable fusion device of  FIG. 1  in accordance with one embodiment of the present invention; 
           [0025]      FIG. 11  a perspective view showing placement of the first endplate of an embodiment of an expandable fusion device down an endoscopic tube and into the disc space in accordance with one embodiment of the present invention; 
           [0026]      FIG. 12  is a perspective view showing placement of the second endplate of the expandable fusion device down an endoscopic tube and into the disc space in accordance with one embodiment of the present invention; 
           [0027]      FIG. 13  is a perspective view showing placement of the central ramp of the expandable fusion device down an endoscopic tube and into the disc space in accordance with one embodiment of the present invention; 
           [0028]      FIG. 14  is a perspective view showing expansion of the expandable fusion device in accordance with one embodiment of the present invention; 
           [0029]      FIG. 15  is a side schematic view of the expandable fusion device of  FIG. 1  having different endplates; 
           [0030]      FIG. 16  is a partial side schematic view of the expandable fusion device of  FIG. 1  showing different modes of endplate expansion; 
           [0031]      FIG. 17  is a side schematic view of the expandable fusion device of  FIG. 1  with artificial endplates shown between adjacent vertebrae; 
           [0032]      FIG. 18  is a front perspective view of an alternative embodiment of an expandable fusion device shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0033]      FIG. 19  is a front perspective view of the expandable fusion device of  FIG. 18  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0034]      FIG. 20  is a rear perspective view of the expandable fusion device of  FIG. 18  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0035]      FIG. 21  is a rear perspective view of the expandable fusion device of  FIG. 18  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0036]      FIG. 22  is a side view of the expandable fusion device of  FIG. 18  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0037]      FIG. 23  is a side view of the expandable fusion device of  FIG. 18  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0038]      FIG. 24  is a perspective of an endplate of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0039]      FIG. 25  is a perspective view of the central ramp of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0040]      FIG. 26  is a side view of the central ramp of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0041]      FIG. 27  is a top view of the central ramp of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0042]      FIG. 28  a perspective view showing placement of the central ramp of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0043]      FIG. 29  is a perspective view showing placement of the first endplate of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0044]      FIG. 30  is a perspective view showing placement of the second endplate of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0045]      FIG. 31  is a perspective view showing placement of the actuation member of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0046]      FIG. 32  is a perspective view showing expansion of the expandable fusion device of  FIG. 18  in accordance with one embodiment of the present invention; 
           [0047]      FIG. 33  is a front perspective view of an alternative embodiment of an expandable fusion device shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0048]      FIG. 34  is a front perspective view of the expandable fusion device of  FIG. 33  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0049]      FIG. 35  is a rear perspective view of the expandable fusion device of  FIG. 33  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0050]      FIG. 36  is a rear perspective view of the expandable fusion device of  FIG. 33  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0051]      FIG. 37  is a side cross-sectional view of the expandable fusion device of  FIG. 33  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0052]      FIG. 38  is a side cross-sectional view of the expandable fusion device of  FIG. 33  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0053]      FIG. 39  is a perspective of an endplate of the expandable fusion device of  FIG. 33  in accordance with one embodiment of the present invention; 
           [0054]      FIG. 40  is a rear perspective view of an alternative embodiment of an expandable fusion device shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0055]      FIG. 41  is a rear perspective view of the expandable fusion device of  FIG. 40  shown in a partially expanded position in accordance with one embodiment of the present invention; 
           [0056]      FIG. 42  is a rear perspective view of the expandable fusion device of  FIG. 40  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0057]      FIG. 43  is a side exploded view of the expandable fusion device of  FIG. 40  in accordance with one embodiment of the present invention; 
           [0058]      FIG. 44  is a side cross-sectional view of the expandable fusion device of  FIG. 40  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0059]      FIG. 45  is a perspective view of an endplate of the expandable fusion device of  FIG. 40  in accordance with one embodiment of the present invention; 
           [0060]      FIG. 46  is a perspective view of the central ramp of the expandable fusion device of  FIG. 40  in accordance with one embodiment of the present invention; 
           [0061]      FIGS. 47-49  are perspective views of the driving ramp of the expandable fusion device of  FIG. 40  in accordance with one embodiment of the present invention; 
           [0062]      FIG. 50  is a rear perspective view of an alternative embodiment of an expandable fusion device shown in an expanded position in accordance with one embodiment of the present invention; 
           [0063]      FIG. 51  is a side cross-sectional view of the expandable fusion device of  FIG. 50  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0064]      FIG. 52  is an exploded view of the expandable fusion device of  FIG. 50  in accordance with one embodiment of the present invention; 
           [0065]      FIG. 53  is a top view of the expandable fusion device of  FIG. 50  shown in an unexpanded position in accordance with one embodiment of the present invention; 
           [0066]      FIG. 54  is a read end view of the expandable fusion device of  FIG. 50  shown in an expanded position in accordance with one embodiment of the present invention; 
           [0067]      FIG. 55  is a perspective view of an endplate of the expandable fusion device of  FIG. 50  in accordance with one embodiment of the present invention; 
           [0068]      FIG. 56  is a perspective of a central ramp of the expandable fusion device of  FIG. 50  in accordance with one embodiment of the present invention; 
           [0069]      FIG. 57  is a perspective view of a driving ramp of the expandable fusion device of  FIG. 50  in accordance with one embodiment of the present invention; 
           [0070]      FIG. 58  is a rear perspective view of an exploded expandable fusion device in accordance with one alternative embodiment; 
           [0071]      FIG. 59  is a front perspective view of an exploded expandable fusion device in accordance with one alternative embodiment; 
           [0072]      FIG. 60  is a top-down view of the expandable fusion device that lacks the top endplate, providing an interior view of the unexpanded expandable fusion device, in accordance with one embodiment of the present invention; 
           [0073]      FIG. 61  is a perspective view showing placement of the tool engagement service of the expandable fusion device of  FIG. 60  in accordance with one embodiment of the present invention; 
           [0074]      FIG. 62  is a top-down cross sectional view of an expandable fusion device shown in the unexpanded position in accordance with one embodiment of the present invention; 
           [0075]      FIG. 63  is a rear perspective view of the expandable fusion device in the expanded position in accordance with one alternative embodiment; 
           [0076]      FIG. 64( a )  is an angled side perspective view of the expandable fusion device in the unexpanded position in accordance with one alternative embodiment; 
           [0077]      FIG. 64( b )  is an angled side perspective view of the expandable fusion device in the expanded position in accordance with one alternative embodiment; 
           [0078]      FIG. 65  is a top-down perspective view of the expandable fusion device in the unexpanded position in accordance with one alternative embodiment; 
           [0079]      FIG. 66  is a rear perspective view of an exploded expandable fusion device in accordance with one alternative embodiment; 
           [0080]      FIG. 67  is side view of an exploded expandable fusion device in accordance with one embodiment of the present invention; 
           [0081]      FIG. 68  is a side cross-sectional view that lacks one front height actuator and one rear height actuator as well as one half of the upper and lower endplates, in order to show the interior of the expandable fusion device of  FIG. 66  in accordance with one embodiment of the present invention; 
           [0082]      FIG. 69  is a front perspective view of an expandable fusion device shown in the unexpanded position in accordance with one embodiment of the present invention; 
           [0083]      FIG. 70  is a side cross-sectional view of the expandable fusion device in the expanded position in accordance with one alternative embodiment; 
           [0084]      FIG. 71( a )  is top-down view of the expandable fusion device in the unexpanded position in accordance with one alternative embodiment; 
           [0085]      FIG. 71( b )  is top-down view of the expandable fusion device in the expanded position in accordance with one alternative embodiment; 
           [0086]      FIG. 72  is a view of the expandable fusion device with threaded instrument inserted and in the expanded position in accordance with one alternative embodiment; 
           [0087]      FIG. 73  is an angled perspective view of the expandable fusion device in the expanded position in accordance with one alternative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0088]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0089]    A spinal fusion is typically employed to eliminate pain caused by the motion of degenerated disk material. Upon successful fusion, a fusion device becomes permanently fixed within the intervertebral disc space. Looking at  FIG. 1 , an exemplary embodiment of an expandable fusion device  10  is shown between adjacent vertebral bodies  2  and  3 . The fusion device  10  engages the endplates  4  and  5  of the adjacent vertebral bodies  2  and  3  and, in the installed position, maintains normal intervertebral disc spacing and restores spinal stability, thereby facilitating an intervertebral fusion. The expandable fusion device  10  can be manufactured from a number of materials including titanium, stainless steel, titanium alloys, non-titanium metallic alloys, polymeric materials, plastics, plastic composites, PEEK, ceramic, and elastic materials. In an embodiment, the expandable fusion device  10  can be configured to be placed down an endoscopic tube and into the disc space between the adjacent vertebral bodies  2  and  3 . 
         [0090]    In an exemplary embodiment, bone graft or similar bone growth inducing material can be introduced around and within the fusion device  10  to further promote and facilitate the intervertebral fusion. The fusion device  10 , in one embodiment, is preferably packed with bone graft or similar bone growth inducing material to promote the growth of bone through and around the fusion device. Such bone graft may be packed between the endplates of the adjacent vertebral bodies prior to, subsequent to, or during implantation of the fusion device. 
         [0091]    With reference to  FIGS. 2-7 , an embodiment of the fusion device  10  is shown. In an exemplary embodiment, the fusion device  10  includes a first endplate  14 , a second endplate  16 , a central ramp  18 , and a driving ramp  260 . In an embodiment, the expandable fusion device  10  can be configured to be placed down an endoscopic tube and into the disc space between the adjacent vertebral bodies  2  and  3 . One or more components of the fusion device  10  may contain features, such as through bores, that facilitate placement down an endoscopic tube. In an embodiment, components of the fusion device  10  are placed down the endoscopic tube with assembly of the fusion device  10  in the disc space. 
         [0092]    Although the following discussion relates to the second endplate  16 , it should be understood that it also equally applies to the first endplate  14  as the second endplate  16  is substantially identical to the first endplate  14  in embodiments of the present invention. Turning now to  FIGS. 2-7 and 10 , in an exemplary embodiment, the second endplate  16  has a first end  39  and a second end  41 . In the illustrated embodiment, the second endplate  16  further comprise an upper surface  40  connecting the first end  39  and the second end  41 , and a lower surface  42  connecting the first end  39  and the second end  41 . In an embodiment, the second endplate  16  further comprises a through opening  44 , as seen on  FIG. 11 . The through opening  44 , in an exemplary embodiment, is sized to receive bone graft or similar bone growth inducing material and further allow the bone graft or similar bone growth inducing material to be packed in the central opening in the central ramp  18 . 
         [0093]    As best seen in  FIGS. 7 and 10 , the lower surface  42  includes at least one extension  46  extending along at least a portion of the lower surface  42 , in an embodiment. In an exemplary embodiment, the extension  46  can extend along a substantial portion of the lower surface  42 , including, along the center of the lower surface  42 . In the illustrated embodiment, the extension  46  includes a generally concave surface  47 . The concave surface  47  can form a through bore with the corresponding concave surface  47  (not illustrated) of the first endplate  14 , for example, when the device  10  is in an unexpanded configuration. In another exemplary embodiment, the extension  46  includes at least one ramped surface  48 . In another exemplary embodiment, there are two ramped surfaces  48 ,  50  with the first ramped surface  48  facing the first end  39  and the second ramped surface facing the second end  41 . In an embodiment, the first ramped surface  48  can be proximate the first end  39 , and the second ramped surface  50  can be proximate the second end  41 . It is contemplated that the slope of the ramped surfaces  48 ,  50  can be equal or can differ from each other. The effect of varying the slopes of the ramped surfaces  48 ,  50  is discussed below. 
         [0094]    In one embodiment, the extension  46  can include features for securing the endplate  16  when the expandable fusion device  10  is in an expanded position. In an embodiment, the extension  46  includes one or more protuberances  49  extending from the lateral sides  51  of the extension. In the illustrated embodiment, there are two protuberances  49  extending from each of the lateral sides  51  with each of the sides  53  having one of the protuberances  49  extending from a lower portion of either end. As will be discussed in more detail below, the protuberances  49  can be figured to engage the central ramp  18  preventing and/or restricting longitudinal movement of the endplate  16  when the device  10  is in an expanded position. 
         [0095]    As illustrated in  FIGS. 2-5 , in one embodiment, the upper surface  40  of the second endplate  16  is flat and generally planar to allow the upper surface  40  of the endplate  16  to engage with the adjacent vertebral body  2 . Alternatively, as shown in  FIG. 15 , the upper surface  40  can be curved convexly or concavely to allow for a greater or lesser degree of engagement with the adjacent vertebral body  2 . It is also contemplated that the upper surface  40  can be generally planar but includes a generally straight ramped surface or a curved ramped surface. The ramped surface allows for engagement with the adjacent vertebral body  2  in a lordotic fashion. While not illustrated, in an exemplary embodiment, the upper surface  40  includes texturing to aid in gripping the adjacent vertebral bodies. Although not limited to the following, the texturing can include teeth, ridges, friction increasing elements, keels, or gripping or purchasing projections. 
         [0096]    Referring now to  FIGS. 2-8 , in an exemplary embodiment, the central ramp  18  has a first end  20 , a second end  22 , a first side portion  24  connecting the first end  20  and the second end  22 , and a second side portion  26  (best seen on  FIG. 5 ) on the opposing side of the central ramp  12  connecting the first end  20  and the second end  22 . The first side portion  24  and the second side portion  26  may be curved, in an exemplary embodiment. The central ramp  18  further includes a lower end  28 , which is sized to receive at least a portion of the first endplate  14 , and an upper end  30 , which is sized to receive at least a portion of the second endplate  16 . 
         [0097]    The first end  20  of the central ramp  18 , in an exemplary embodiment, includes an opening  32 . The opening  32  can be configured to receive an endoscopic tube in accordance with one or more embodiments. The first end  20  of the central ramp  18 , in an exemplary embodiment, includes at least one angled surface  33 , but can include multiple angled surfaces. The angled surface  33  can serve to distract the adjacent vertebral bodies when the fusion device  10  is inserted into an intervertebral space. 
         [0098]    The second end  22  of the central ramp  18 , in an exemplary embodiment, includes an opening  36 . The opening  36  extends from the second end  22  of the central ramp  18  into a central guide  37  in the central ramp  18 . 
         [0099]    In an embodiment, the central ramp  18  further includes one or more ramped surfaces  33 . As best seen in  FIG. 8 , the one or more ramped surfaces  33  positioned between the first side portion  24  and the second side portion  26  and between the central guide  37  and the second end  22 . In an embodiment, the one or more ramped surfaces  33  face the second end  22  of the central ramp  18 . In one embodiment, the central ramp  18  includes two ramped surfaces  33  with one of the ramped surfaces  33  being sloped upwardly and the other of the ramped surfaces  33  being sloped downwardly. The ramped surfaces  33  of the central ramp can be configured and dimensioned to engage the ramped surface  48  in each of the first and second endplates  14 ,  16 . 
         [0100]    Although the following discussion relates to the second side portion  26  of the central ramp  18 , it should be understood that it also equally applies to the first side portion  24  in embodiments of the present invention. In the illustrated embodiment, the second side portion  26  includes an inner surface  27 . In an embodiment, the second side portion  26  further includes a lower guide  35 , a central guide  37 , and an upper guide  38 . In the illustrated embodiment, the lower guide  35 , central guide  37 , and the upper guide  38  extend out from the inner surface  27  from the second end  22  to the one or more ramped surfaces  31 . In the illustrated embodiment, the second end  22  of the central ramp  18  further includes one or more guides  38 . The guides  38  can serve to guide the translational movement of the first and second endplates  14 ,  16  with respect to the central ramp  18 . For example, protuberances  49  on the second endplate  16  may be sized to be received between the central guide  37  and the upper guide  38 . Protuberances  49  of the first endplate  16  may be sized to be received between the central guide  37  and the lower guide  35 . A first slot  29  may be formed proximate the middle of the upper guide  38 . A second slot  31  may be formed between end of the upper guide  38  and the one or more ramped surfaces  33 . The protuberances  49  may be sized to be received within the first slot  29  and/or the second slot  31  when the device  10  is in the expanded position. 
         [0101]    Referring now to  FIGS. 4-7 and 9 , the driving ramp  260  has a through bore  262 . In an embodiment, the driving ramp  260  is generally wedge-shaped. As illustrated, the driving ramp  260  may comprise a wide end  56 , a narrow end  58 , a first side portion  60  connecting the wide end  56  and the narrow end  58 , and a second side portion  62  connecting the wide end  56  and the narrow end  58 . The driving ramp  260  further may comprise ramped surfaces, including an upper ramped surface  64  and an opposing lower ramped surface  66 . The upper ramped surface  64  and the lower ramped surface  66  may be configured and dimensioned to engage the ramped surface  50  proximate the second end  41  in of the first and the second endplates  14 ,  16 . The first and second side portions  60 ,  62  may each include grooves  68  that extend, for example, in a direction parallel to the longitudinal axis of the through bore  262 . The grooves  68  may be sized to receive the central guide  37  on the interior surface  27  of each of the side portions  24 ,  26  of the central ramp  18 . In this manner, the grooves  68  together with the central guide  37  can surface to guide the translational movement of the driving ramp  260  in the central ramp  18 . 
         [0102]    A method of installing the expandable fusion device  10  of  FIG. 1  is now discussed in accordance with one embodiment of the present invention. Prior to insertion of the fusion device  10 , the intervertebral space is prepared. In one method of installation, a discectomy is performed where the intervertebral disc, in its entirety, is removed. Alternatively, only a portion of the intervertebral disc can be removed. The endplates of the adjacent vertebral bodies  2 ,  3  are then scraped to create an exposed end surface for facilitating bone growth across the intervertebral space. One or more endoscopic tubes can then be inserted into the disc space. The expandable fusion device  10  can then be introduced into the intervertebral space down an endoscopic tube and seated in an appropriate position in the intervertebral disc space. 
         [0103]    After the fusion device  10  has been inserted into the appropriate position in the intervertebral disc space, the fusion device  10  can then be expanded into the expanded position. To expand the fusion device  10 , the driving ramp  260  may move in a first direction with respect to the central ramp  18 . Translational movement of the driving ramp  260  through the central ramp  18  may be guided by the central guide  37  on each of the first and second side portions  24 ,  26  of the central ramp  18 . As the driving ramp  260  moves, the upper ramped surface  64  pushes against the ramped surface  50  proximate the second end  41  of the second endplate  16 , and the lower ramped surface  66  pushes against the ramped surface  50  proximate the second end  41  of the first endplate  14 . In addition, the ramped surfaces  33  in the central ramp  18  push against the ramped surface  48  proximate the first end  41  of the first and second endplates  14 ,  16 . In this manner, the first and second endplates  14 ,  16  are pushed outwardly into an expanded configuration. As discussed above, the central ramp  16  includes locking features for securing the endplates  14 ,  16 . 
         [0104]    It should also be noted that the expansion of the endplates  14 ,  16  can be varied based on the differences in the dimensions of the ramped surfaces  48 ,  50  and the angled surfaces  62 ,  64 . As best seen in  FIG. 16 , the endplates  14 ,  16  can be expanded in any of the following ways: straight rise expansion, straight rise expansion followed by a toggle into a lordotic expanded configuration, or a phase off straight rise into a lordotic expanded configuration. 
         [0105]    Turning back to  FIGS. 2-7 , in the event the fusion device  10  needs to be repositioned or revised after being installed and expanded, the fusion device  10  can be contracted back to the unexpanded configuration, repositioned, and expanded again once the desired positioning is achieved. To contract the fusion device  10 , the central ramp  18  is moved with respect to the central ramp  260  away from the central ramp  260 . As the central ramp  18  moves, the ramped surfaces  33  in the central ramp  18  ride along the ramped surfaces  48  of the first and second endplates  14 ,  16  with the endplates  14 ,  16  moving inwardly into the unexpanded position. 
         [0106]    With reference now to  FIG. 17 , fusion device  10  is shown with an exemplary embodiment of artificial endplates  100 . Artificial endplates  100  allows the introduction of lordosis even when the endplates  14  and  16  of the fusion device  10  are generally planar. In one embodiment, the artificial endplates  100  have an upper surface  102  and a lower surface  104 . The upper surfaces  102  of the artificial endplates  100  have at least one spike  106  to engage the adjacent vertebral bodies. The lower surfaces  104  have complementary texturing or engagement features on their surfaces to engage with the texturing or engagement features on the upper endplate  14  and the lower endplate  16  of the fusion device  10 . In an exemplary embodiment, the upper surface  102  of the artificial endplates  100  have a generally convex profile and the lower surfaces  104  have a generally parallel profile to achieve lordosis. In another exemplary embodiment, fusion device  10  can be used with only one artificial endplate  100  to introduce lordosis even when the endplates  14  and  16  of the fusion device  10  are generally planar. The artificial endplate  100  can either engage endplate  14  or engage endplate  16  and function in the same manner as described above with respect to two artificial endplates  100 . 
         [0107]    With reference to  FIGS. 11-14 , an embodiment for placing an expandable fusion device  10  into an intervertebral disc space is illustrated. The expandable fusion device  10  can be introduced into the intervertebral space down an endoscopic tube utilizing a tool  70  that is attached to endplate  16 , with the second endplate  16  being first placed down the tube with tool  70  and into the disc space, as seen in  FIG. 11 . After insertion of the second endplate  16 , the first endplate  14  can be placed down the same endoscopic tube with tool  72  and into the disc space, as shown on  FIG. 12 . Following the first endplate  14 , the central ramp  12  can be placed down the same endoscopic tube and into the disc space guided by tools  70  and  72 , as shown on  FIGS. 13 and 14 . 
         [0108]    Referring now to  FIGS. 18-23 , an alternative embodiment of the expandable fusion device  10  is shown. In an exemplary embodiment, the fusion device  10  includes a first endplate  14 , a second endplate  16 , a central ramp  18 , and an actuator assembly  200 . As will be discussed in more detail below, the actuator assembly  200  drives the central ramp  18  which forces apart the first and second endplates  14 ,  16  to place the expandable fusion device in an expanded position. One or more components of the fusion device  10  may contain features, such as through bores, that facilitate placement down an endoscopic tube. In an embodiment, components of the fusion device  10  are placed down the endoscopic tube with assembly of the fusion device  10  in the disc space. 
         [0109]    Although the following discussion relates to the second endplate  16 , it should be understood that it also equally applies to the first endplate  14  as the second endplate  16  is substantially identical to the first endplate  14  in embodiments of the present invention. With additional reference to  FIG. 24 , in an exemplary embodiment, the second endplate  16  has a first end  39  and a second end  41 . In the illustrated embodiment, the second endplate  16  further comprise an upper surface  40  connecting the first end  39  and the second end  41 , and a lower surface  42  connecting the first end  39  and the second end  41 . While not illustrated, in an embodiment, the second endplate  16  further comprises a through opening. The through opening, in an exemplary embodiment, is sized to receive bone graft or similar bone growth inducing material. 
         [0110]    In one embodiment, the upper surface  40  of the second endplate  16  is flat and generally planar to allow the upper surface  40  of the endplate  16  to engage with the adjacent vertebral body  2 . Alternatively, as shown in  FIG. 15 , the upper surface  40  can be curved convexly or concavely to allow for a greater or lesser degree of engagement with the adjacent vertebral body  2 . It is also contemplated that the upper surface  40  can be generally planar but includes a generally straight ramped surface or a curved ramped surface. The ramped surface allows for engagement with the adjacent vertebral body  2  in a lordotic fashion. While not illustrated, in an exemplary embodiment, the upper surface  40  includes texturing to aid in gripping the adjacent vertebral bodies. Although not limited to the following, the texturing can include teeth, ridges, friction increasing elements, keels, or gripping or purchasing projections. 
         [0111]    In one embodiment, the second endplate  16  further comprises a first side portion  202  connecting the first end  39  and the second end  41 , and a second side portion  204  connecting the first end  39  and the second end  41 . In the illustrated embodiment, the first and second side portions  202 ,  204  are extensions from the lower surface  42 . In an exemplary embodiment, the first and second side portions  202 ,  204  each include ramped surfaces  206 ,  208 . In the illustrated embodiment, the ramped surfaces  206 ,  208  extend from the first end  39  of the second endplate  16  to bottom surfaces  210 ,  212  of each of the side portions  202 ,  204 . In one embodiment, the ramped surfaces  206 ,  208  are forward facing in that the ramped surfaces  206 ,  208  face the first end  39  of the second endplate. As previously discussed, the slope of the ramped surfaces  206 ,  208  may be varied as desired for a particular application. 
         [0112]    In an embodiment, the first and second side portions  202 ,  204  each comprise at least one protuberance  214 . In an exemplary embodiment, the first and second side portions  202 ,  204  each comprise a first protuberance  214 , a second protuberance  216 , and a third protuberance  218 . In one embodiment, the protuberances  214 ,  216 ,  218  extend from the interior surface  220  of the first and second side portions  202 ,  204 . In an exemplary embodiment, the protuberances  214 ,  216 ,  218  extend at the lower side of the interior surface  220 . As best seen in  FIG. 24 , the first and the second protuberances  214 ,  216  form a first slot  222 , and the second and third protuberances  216 ,  218  form a second slot  224 . 
         [0113]    As best seen in  FIG. 24 , the lower surface  42  of the second endplate  16 , in an embodiment, includes a central extension  224  extending along at least a portion of the lower surface. In the illustrated embodiment, the central extension  224  extends between the first and second side portions  202  and  204 . In an exemplary embodiment, the central extension  224  can extend from the second end  41  of the endplate  16  to the central portion of the endplate. In one embodiment, the central extension  224  includes a generally concave surface  226  configured and dimensioned to form a through bore with the corresponding concave surface  226  (not illustrated) of the first endplate  14 . The central extension  224  can further include, in an exemplary embodiment, a ramped surface  228 . In the illustrated embodiment, the ramped surface  228  faces the first end  39  of the endplate  16 . The ramped surface  228  can be at one end of the central extension  224 . In an embodiment, the other end of the central extension  224  forms a stop  230 . In the illustrated embodiment, the stop  230  is recessed from the second end  41  of the second endplate  16 . 
         [0114]    Referring to  FIGS. 25-27 , in an exemplary embodiment, the central ramp  18  includes a body portion  232  having a first end  234  and a second end  236 . In an embodiment, the body portion  232  includes at least a first expansion portion  238 . In an exemplary embodiment, the body portion  232  includes a first expansion portion  238  and a second expansion portion  240  extending from opposing sides of the body portion with each of the first and second expansion portions  238 ,  240  having a generally triangular cross-section. In one embodiment, the expansion portions  238 ,  240  each have angled surfaces  242 ,  244  configured and dimensioned to engage the ramped surfaces  206 ,  208  of the first and second endplates  14 ,  16  and force apart the first and second endplates  14 ,  16 . In an embodiment, the engagement between the angled surfaces  242 ,  244  of the expansion portions  238 ,  240  with the ramped surfaces  206 ,  208  of the first and second endplates  14 ,  16  may be described as a dovetail connection. 
         [0115]    The second end  236  of the central ramp  18 , in an exemplary embodiment, includes opposing angled surfaces  246 . The angled surfaces  246  can be configured and dimensioned to engage the ramped surface  228  in the central extension  224  in each of the first and second endplates  14 ,  16 . In other words, one of the angled surfaces  246  can be upwardly facing and configured, in one embodiment, to engage the ramped surface  228  in the central extension  224  in the second endplate  16 . In an embodiment, the engagement between the angled surfaces  246  of the second end  236  of the central ramp  18  with the ramped surface  228  in the first and second endplates  14 ,  16  may be described as a dovetail connection. 
         [0116]    The second end  236 , in an exemplary embodiment, can further include an extension  252 . In the illustrated embodiment, the extension  252  is generally cylindrical in shape with a through bore  254  extending longitudinally therethrough. In one embodiment, the extension  252  can include a beveled end  256 . While not illustrated, at least a portion of the extension  252  can be threaded. 
         [0117]    Referring still to  FIGS. 25-27 , the central ramp  18  can further include features for securing the first and second endplates  14 ,  16  when the expandable fusion device  10  is in an expanded position. In an embodiment, the body portion  232  of the central ramp  18  includes one or more protuberances  248 ,  250  extending from opposing sides of the body portion  232 . As illustrated, the protuberances  248 ,  250 , in one embodiment, can be spaced along the body portion  232 . In an exemplary embodiment, the protuberances  248 ,  250  can be configured and dimensioned for insertion into the corresponding slots  222 ,  224  in the first and second endplates  14 ,  16  when the device  10  is in an expanded position, as best seen in  FIGS. 19 and 21 . The protuberances  248 ,  250  can engage the endplates  14 ,  16  preventing and/or restricting movement of the endplates  14 ,  16  with respect to the central ramp  18  after expansion of the device  10 . 
         [0118]    With reference to  FIGS. 20-23 , in an exemplary embodiment, the actuator assembly  200  has a flanged end  253  configured and dimensioned to engage the stop  232  in the central extension  224  of the first and the second endplates  14 ,  16 . In an embodiment, the actuator assembly  200  further includes an extension  254  that extends from the flanged end  253 . In a further embodiment, the actuator assembly  200  includes a threaded hole  256  that extends through the actuator assembly  200 . It should be understood that, while the threaded hole  256  in the actuator assembly  200  is referred to as threaded, the threaded hole  256  may only be partially threaded in accordance with one embodiment. In an exemplary embodiment, the threaded hole  256  is configured and dimensioned to threadingly receive the extension  252  of the central ramp  18 . 
         [0119]    With additional reference to  FIGS. 28-32 , a method of installing the expandable fusion device  10  of  FIGS. 18-27  is now discussed in accordance with one embodiment of the present invention. Prior to insertion of the fusion device, the disc space may be prepared as described above and then one or more endoscopic tubes may then be inserted into the disc space. The expandable fusion device  10  can then be inserted into and seated in the appropriate position in the intervertebral disc space, as best seen in  FIGS. 28-32 . The expandable fusion device  10  can be introduced into the intervertebral space down an endoscopic tube (not illustrated), with the central ramp  18  being first placed down the tube and into the disc space, as seen in  FIG. 28 . After insertion of the central ramp, the first endplate  14  can be placed down an endoscopic tube, as shown on  FIG. 29 , followed by insertion of the second endplate  16 , as shown on  FIG. 30 . After the second endplate  16 , the actuator assembly  200  can then be inserted to complete assembly of the device  10 , as best seen in  FIG. 31 . 
         [0120]    After the fusion device  10  has been inserted into and assembled in the appropriate position in the intervertebral disc space, the fusion device  10  can then be expanded into the expanded position. To expand the fusion device  10 , the actuator assembly  200  can be rotated. As discussed above, the actuator assembly  200  is in threaded engagement with the extension  250  of the central ramp  18 . Thus, as the actuator assembly  200  is rotated in a first direction, the central ramp  18  moves toward the flanged end  253  of the actuator assembly  200 . In another exemplary embodiment, the actuator assembly  200  can be moved in a linear direction with the ratchet teeth as means for controlling the movement of the central ramp  18 . As the central ramp  18  moves, the angled surfaces  242 ,  244  in the expansion portions  238 ,  240  of the central ramp  18  push against the ramped surfaces  206 ,  208  in the first and second side portions  202 ,  204  of the first and second endplates  14 ,  16 . In addition, the angled surfaces  246  in the second end  236  of the central ramp  18  also push against the ramped surfaces  228  in the central extension  224  of each of the endplates  14 ,  16 . This is best seen in  FIGS. 22-23 . 
         [0121]    Since the expansion of the fusion device  10  is actuated by a rotational input, the expansion of the fusion device  10  is infinite. In other words, the endplates  14 ,  16  can be expanded to an infinite number of heights dependent on the rotational advancement of the actuator assembly  200 . As discussed above, the central ramp  16  includes locking features for securing the endplates  14 ,  16 . 
         [0122]    In the event the fusion device  10  needs to be repositioned or revised after being installed and expanded, the fusion device  10  can be contracted back to the unexpanded configuration, repositioned, and expanded again once the desired positioning is achieved. To contract the fusion device  10 , the actuator assembly  200  can be rotated in a second direction. As discussed above, actuator assembly  200  is in threaded engagement with the extension  250  of the central ramp  18 ; thus, as the actuator assembly  200  is rotated in a second direction, opposite the first direction, the central ramp  18  moves with respect to the actuator assembly  200  and the first and second endplates  14 ,  16  away from the flanged end  253 . As the central ramp  18  moves, the first and second endplates are pulled inwardly into the unexpanded position. 
         [0123]    Referring now to  FIGS. 33-38 , an alternative embodiment of the expandable fusion device  10  is shown. In the illustrated embodiment, the fusion device includes a first endplate  14 , a second endplate  16 , a central ramp  18 , and an actuator assembly  200 . The fusion device  10  of  FIGS. 33-38  and its individual components are similar to the device  10  illustrated on  FIGS. 18- 23  with several modifications. The modifications to the device  10  will be described in tum below. 
         [0124]    Although the following discussion relates to the second endplate  16 , it should be understood that it also equally applies to the first endplate  14  as the second endplate  16  is substantially identical to the first endplate  14  in embodiments of the present invention. With additional reference to  FIG. 39 , in an exemplary embodiment, the lower surface  42  of the second endplate  16  has been modified. In one embodiment, the central extension  224  extending from the lower surface  42  has been modified to include a second ramped surface  258  rather than a stop. In an exemplary embodiment, the second ramped surface  258  faces the second end  41  of the second endplate  16 . In contrast, ramped surface  228  on the central extension  228  faces the first end  39  of the second endplate. The concave surface  228  connects the ramped surface  228  and the second ramped surface  258 . 
         [0125]    With reference to  FIGS. 35-38 , in an exemplary embodiment, the actuator assembly  200  has been modified to further include a driving ramp  260 . In the illustrated embodiment, the driving ramp  260  has a through bore  262  through which the extension  254  extends. In an embodiment, the driving ramp  260  is generally wedge-shaped. As illustrated, the driving ramp  260  may comprise a blunt end  264  in engagement with the flanged end  253 . In an exemplary embodiment, the driving ramp  260  further comprises angled surfaces  266  configured and dimensioned to engage the second ramped surface  258  of each of the endplates  14 ,  16  and force apart the first and second endplates  14 ,  16 . 
         [0126]    Referring now to  FIGS. 40-44 , an alternative embodiment of the expandable fusion device  10  is shown. In the illustrated embodiment, the fusion device  10  includes a first endplate  14 , a second endplate  16 , a central ramp  18 , an actuator assembly  200 , and a driving ramp  300 . As will be discussed in more detail below, the actuator assembly  200  functions, in an embodiment, to pull the central ramp  18  and the driving ramp  300  together, which forces apart the first and second endplates  14 ,  16 . In an embodiment, the expandable fusion device 
         [0127]    Although the following discussion relates to the first endplate  14 , it should be understood that it also equally applies to the second endplate  16  as the second endplate  16  is substantially identical to the first endplate  14  in embodiments of the present invention. With reference to  FIGS. 40-45 , in an exemplary embodiment, the first endplate  14  has a first end  39  and a second end  41 . In the illustrated embodiment, the first endplate  14  further comprises an upper surface  40  connecting the first end  39  and the second end  41 , and a lower surface  42  connecting the first end  39  and the second end  41 . While not illustrated, in an embodiment, the first endplate  14  may comprise further comprises a through opening. The through opening, in an exemplary embodiment, is sized to receive bone graft or similar bone growth inducing material. 
         [0128]    In one embodiment, the upper surface  40  of the first endplate  14  is flat and generally planar to allow the upper surface  40  of the endplate  14  to engage with the adjacent vertebral body  2 . Alternatively, as shown in  FIG. 15 , the upper surface  40  can be curved convexly or concavely to allow for a greater or lesser degree of engagement with the adjacent vertebral body  2 . It is also contemplated that the upper surface  40  can be generally planar but includes a generally straight ramped surface or a curved ramped surface. The ramped surface allows for engagement with the adjacent vertebral body  2  in a lordotic fashion. While not illustrated, in an exemplary embodiment, the upper surface  40  includes texturing to aid in gripping the adjacent vertebral bodies. Although not limited to the following, the texturing can include teeth, ridges, friction increasing elements, keels, or gripping or purchasing projections. 
         [0129]    In one embodiment, the first endplate  14  further comprises a first side portion  202  connecting the first end  39  and the second end  41 , and a second side portion  204  connecting the first end  39  and the second end  41 . In the illustrated embodiment, the first and second side portions  202 ,  204  are extensions from the lower surface  42 . In an embodiment, the first and second side portions each have an interior surface  302  and an exterior surface  304 . In an exemplary embodiment, the first and second side portions  202 ,  204  each include one or more ramped portions. In the illustrated embodiment, the first and second side portions  202 ,  204  include first ramped portions  306 ,  308  at the first end  39  of the endplate  14  and second ramped portions  310 ,  312  at the second end  41  of the endplate. The first and second side portions  202 ,  204  each can include a bridge portion  314  connecting the first ramped portions  306 ,  308  and the second ramped portions  310 ,  312 . In an embodiment, the first ramped portions  306 ,  308  abut the exterior surface  304  of the respective side portions  202 ,  204 , and the second ramped portions  310 ,  312  abut the interior surface  302  of the respective side portions  202 ,  204 . As illustrated, the first ramped portions  306 ,  308  may include tongue portions  316 ,  318  with the tongue portions  316 ,  318  extending in an oblique direction with respect to the upper surface  40  of the endplate  14 . As further illustrated, the second ramped portions  310 ,  312  may include tongue portions  320 ,  322  that extend in an oblique direction with respect to the upper surface  40  of the endplate  14 . 
         [0130]    As best seen in  FIG. 45 , the lower surface  42  of the second endplate  16 , in an embodiment, includes a central extension  224  extending along at least a portion of the lower surface. In the illustrated embodiment, the central extension  224  extends between the first and second side portions  202  and  204 . In an exemplary embodiment, the central extension  224  can extend generally between the first ramped portions  306 ,  308  and the second ramped portions  310 ,  312 . In one embodiment, the central extension  224  includes a generally concave surface  226  configured and dimensioned to form a through bore with the corresponding concave surface  226  (not illustrated) of the second endplate  16 . 
         [0131]    With reference to  FIGS. 43 and 44 , the actuator assembly  200  includes a head portion  324 , a rod receiving extension  326 , and a connecting portion  328  that connecting portions that connects the head portion  324  and the rod receiving extension  326 . As illustrated, the head portion  324  may include one or more instrument gripping features  330  that can allow it to be turned by a suitable instrument. In addition, the head portion  324  has a larger diameter than the other components of the actuator assembly  200  to provide a contact surface with the driving ramp  300 . In the illustrated embodiment, the head portion  324  includes a rim  332  that provides a surface for contacting the driving ramp  300 . As can be seen in  FIG. 44 , in an exemplary embodiment, the rod receiving extension  326  includes an opening sized and dimensioned to receive the extension  336  of the central ramp  18 . In an embodiment, the rod receiving extension  326  includes threading for threadingly engaging the extension  336 . In another embodiment, the rod receiving extension  326  includes ratchet teeth for engaging the extension  336 . In the illustrated embodiment, the head portion  324  and the rod receiving extension  326  are connected by connecting portion  328  which can be generally cylindrical in shape. 
         [0132]    With reference to  FIGS. 43, 44, and 46 , the central ramp  18  includes expansion portion  334  and extension  336 . As best seen in  FIG. 46 , the expansion portion  334  may include an upper portion  338  and side portions  340 ,  342  that extend down from the upper portion  338 . In an embodiment, each of the side portions  340 ,  342  include dual, overlapping ramped portions. For example, side portions  340 ,  342  each include a first ramped portion  344  that overlaps a second ramped portion  346 . In the illustrated embodiment, the first ramped portion  344  faces the extension  336  while the second ramped portion  344  faces away from the extension  336 . In one embodiment, angled grooves  348 ,  350  are formed in each of the first and second ramped portions  344 ,  346 . In another embodiment, the angled grooves  348 ,  350  are sized to receive the corresponding tongues  316 ,  318 ,  320 ,  322  in the first and second endplates with angled grooves  348  receiving tongues  320 ,  322  in the second endplate  16  and angled grooves  350  receiving tongues  316 ,  318  in the first endplate  14 . Although the device  10  is described with tongues  316 ,  318 ,  320 ,  322  on the endplates  14 ,  16  and angled grooves  348 ,  350  on the central ramp  18 , it should be understood that that device  10  can also be configured with grooves on the endplates  14 ,  16  and tongues on the central ramp  18 , in accordance with one embodiment of the present invention. 
         [0133]    In an exemplary embodiment, the extension  336  is sized to be received within the rod receiving extension  326  of the actuator assembly  200 . In one embodiment, the extension  336  has threading with the extension  336  being threadingly received within the rod receiving extension  326 . In another embodiment, the extension  336  has ratchet teeth with the extension  336  being ratcheted into the rod receiving extension  336 . In an embodiment, the extension  336  include nose  352  at the end of the extension  336 . 
         [0134]    With reference to  FIGS. 47-49 , in an exemplary embodiment, the driving ramp  300  includes an upper portion  354  having an upper surface  356  and an oblique surface  358 . In an embodiment, the driving ramp  300  further includes side portions  360 ,  362  that extend from the upper portion  354  connecting the upper portion  354  with the lower portion  364  of the driving ramp  300 . As best seen in  FIGS. 48-49 , the driving ramp  300  further includes a bore  366 , in an exemplary embodiment, sized to receive the connection portion  328  of the actuator assembly  200 . In one embodiment, the driving ramp  300  moves along the connection portion  328  when the actuator assembly  200  is pushing the driving ramp  300 . In an exemplary embodiment, the driving ramp  300  further includes contact surface  368  that engages the rim  332  of the head portion  324  of the actuator assembly  200 . In the illustrated embodiment, the contact surface  368  has a generally annular shape. 
         [0135]    In an exemplary embodiment, the side portions  360 ,  362  of the driving ramp  300  each include overlapping ramped portions. For example, the side portions  360 ,  362  each include first ramped portions  370  that overlap second ramped portions  372 . In the illustrated embodiment, the first ramped portions  370  face central ramp  18  while the second ramped portions  372  face the opposite direction. In one embodiment, angled grooves  374 ,  376  are formed in each of the first and second ramped portions  370 ,  372 .  FIG. 48  is a perspective view of the driving ramp  300  that shows the top ends of the angled grooves  374  in ramped portions  370 .  FIG. 49  is a perspective view of the driving ramp  300  that shows the top ends of the angled grooves  376  in ramped portions  372 . In an exemplary embodiment, the angled grooves  374 ,  376  are sized to receive corresponding tongues  316 ,  318 ,  320 ,  322  in the first and second endplates  14 ,  16  with angled grooves  370  receiving tongues  316 ,  318  in the second endplate  16  and angled grooves  372  receiving tongues  320 ,  322  in the first endplate  14 . Although the device  10  is described with tongues  316 ,  318 ,  320 ,  322  in the first and second endplates  14 ,  16  and angled grooves  370 ,  372 ,  374 ,  376  on the driving ramp  300 , it should be understood that that device  10  can also be configured with grooves on the second endplate  16  and tongues on the driving ramp  300 , in accordance with one embodiment of the present invention. 
         [0136]    Turning now to  FIGS. 40-42 , a method of installing the expandable fusion device  10  of  FIGS. 40-49  is now discussed in accordance with one embodiment of the present invention. Prior to insertion of the fusion device, the disc space may be prepared as described above. The expandable fusion device  10  can then be inserted into and seated in the appropriate position in the intervertebral disc space. The expandable fusion device  10  is then introduced into the intervertebral space, with the end having the expansion portion  334  of the central ramp  18  being inserted. In an exemplary method, the fusion device  10  is in the unexpanded position when introduced into the intervertebral space. In an exemplary method, the intervertebral space may be distracted prior to insertion of the fusion device  10 . The distraction provides some benefits by providing greater access to the surgical site making removal of the intervertebral disc easier and making scraping of the endplates of the vertebral bodies  2 ,  3  easier. 
         [0137]    With the fusion device  10  inserted into and seated in the appropriate position in the intervertebral disc space, the fusion device can then expanded into the expanded position, as best seen in  FIG. 42 . To expand the fusion device  10 , an instrument is engaged with the head portion  324  of the actuator assembly  200 . The instrument is used to rotate actuator assembly  200 . As discussed above, actuator assembly  200  is threadingly engaged with the extension  336  of the central ramp  18 ; thus, as the actuator assembly  200  is rotated in a first direction, the central ramp  18  is pulled toward the actuator assembly  200 . In an exemplary embodiment, the actuator assembly  200  is moved in a linear direction with the ratchet teeth engaging as means for controlling the movement of the actuator assembly  200  and the central ramp  18 . As the central ramp  18  is pulled towards the actuator assembly  200 , the first ramped portions  344  of the central ramp  18  push against the second ramped portions  310 ,  312  of the second endplate  16  and the second ramped portions  346  of the central ramp  18  push against first ramped portions  306 ,  308  of the first endplate  14 . In this manner, the central ramp  18  acts to push the endplates  14 ,  16  outwardly into the expanded position. This can best be seen in  FIGS. 40-42 . As the endplates  14 ,  16  move outwardly the tongues  316 ,  318 ,  320 ,  322  in the endplates  14 ,  16  ride in the angled grooves  348 ,  350  with the tongues  320 ,  322  in the second endplate  16  riding in angled grooves  348  and the tongues  316 ,  318  in the first endplate  14  riding in angled grooves  350 . 
         [0138]    As discussed above, the actuator assembly  200  also engages driving ramp  300 ; thus, as the actuator assembly  200  is rotated in a first direction, the actuator assembly  200  pushes the driving ramp  300  towards the central ramp  18  in a linear direction. As the driving ramp  300  is pushed towards the central ramp  18 , the first ramped portions  370  of the driving ramp  300  push against the first ramped portions  306 ,  308  of the second endplate  16  and the second ramped portions  372  of the driving ramp  300  push against the second ramped portions  310 ,  312  of the first endplate  14 . In this manner, the driving ramp  300  also acts to push the endplates  14 ,  16  outwardly into the expanded position. This can best be seen in  FIGS. 40-42 . As the endplates  14 ,  16  move outwardly the tongues  316 ,  318 ,  320 ,  322  in the endplates  14 ,  16  ride in the angled grooves  370 ,  372  with the tongues  316 ,  318  in the second endplate  16  riding in angled grooves  370  and the tongues  320 ,  322  in the first endplate  14  riding in angled grooves  372 . 
         [0139]    Since the expansion of the fusion device  10  is actuated by a rotational input, the expansion of the fusion device  10  is infinite. In other words, the endplates  14 ,  16  can be expanded to an infinite number of heights dependent on the rotational advancement of the actuator assembly  200 . 
         [0140]    Referring now to  FIGS. 50-54 , an alternative embodiment of the expandable fusion device  10  is shown. In the illustrated embodiment, the fusion device  10  includes a first endplate  14 , a second endplate  16 , a central ramp  18 , an actuator assembly  200 , and a driving ramp  300 . As will be discussed in more detail below, the actuator assembly  200  functions, in an embodiment, to pull the central ramp  18  and the driving ramp  300  together, which forces apart the first and second endplates  14 ,  16 . In an embodiment, the expandable fusion device may contain features, such as a through bore, that facilitate placement down an endoscopic tube. In an embodiment, the assembled fusion device  10  may be placed down the endoscopic tube and then expanded. 
         [0141]    Although the following discussion relates to the first endplate  14 , it should be understood that it also equally applies to the second endplate  16  as the second endplate  16  is substantially identical to the first endplate  14  in embodiments of the present invention. It should be understood that, in an embodiment, the first endplate  14  is configured to interlock with the second endplate  16 . With additional reference to  FIG. 55 , in an exemplary embodiment, the first endplate  14  has a first end  39  and a second end  41 . As illustrated, the first end  39  may be wider than the second end  41 . In the illustrated embodiment, the first endplate  14  further comprises an upper surface  40  connecting the first end  39  and the second end  41 , and a lower surface  42  connecting the first end  39  and the second end  41 . As best seen in  FIG. 54 , the lower surface  42  can be curved concavely such that the first and second endplates  14 ,  16  form a through bore when the device  10  is in a closed position. In an embodiment, the first endplate  14  may comprise a through opening  44 . The through opening  44 , in an exemplary embodiment, is sized to receive bone graft or similar bone growth inducing material. 
         [0142]    In one embodiment, the upper surface  40  of the first endplate  14  is flat and generally planar to allow the upper surface  40  of the endplate  14  to engage with the adjacent vertebral body  2 . Alternatively, as shown in  FIG. 15 , the upper surface  40  can be curved convexly or concavely to allow for a greater or lesser degree of engagement with the adjacent vertebral body  2 . It is also contemplated that the upper surface  40  can be generally planar but includes a generally straight ramped surface or a curved ramped surface. The ramped surface allows for engagement with the adjacent vertebral body  2  in a lordotic fashion. As illustrated, in an exemplary embodiment, the upper surface  40  includes texturing to aid in gripping the adjacent vertebral bodies. For example, the upper surface  40  may further comprise texturing  400  to engage the adjacent vertebral bodies. Although not limited to the following, the texturing can include teeth, ridges, friction increasing elements, keels, or gripping or purchasing projections. 
         [0143]    In one embodiment, the first endplate  14  further comprises a first side portion  202  connecting the first end  39  and the second end  41 , and a second side portion  204  connecting the first end  39  and the second end  41 . In the illustrated embodiment, the first and second side portions  202 ,  204  are extensions from the lower surface  42 . In an embodiment, the first and second side portions  202 ,  204  each include an interior surface  302  and an exterior surface  304 . In an embodiment, the first end  39  of the first endplate  14  is generally designed and configured to fit over the second end  41  of the second endplate  16  when the device  10  is in a closed position. As illustrated, the first and second side portions  202 ,  204  each may include first ramped portions  306 ,  308 , second ramped portions  310 ,  312 , and/or central ramped portion  402 . 
         [0144]    In an embodiment, the first ramped portions  306 ,  308  are proximate the first end  39  of the endplate  14 . In accordance with embodiment of the present invention, the first ramped portions  306 ,  308  of the first endplate  14  are generally designed and configured to fit over the second ramped portions  310 ,  312  of the second endplate  16  when the device  10  is in a closed position. In an exemplary embodiment, the first ramped portions  306 ,  308  generally face the first end  39  and can extend in an oblique direction with respect to the upper surface  40 , for example. As illustrated, the first ramped portions  306 ,  308  may include tongue portions  316 ,  318  extending in an oblique direction with respect to the upper surface  40  of the endplate  14 . 
         [0145]    In an embodiment, the second ramped portions  310 ,  312  are proximate the second end  41  of the endplate  14 . In an exemplary embodiment, the second ramped portions  310 ,  312  can extend in an oblique direction with respect to the upper surface  40  and generally face the second end  41 . The first and second side portions  202 ,  204 , in an embodiment, each can include a bridge portion  314  connecting the first ramped portions  306 ,  308  and the second ramped portions  310 ,  312 . As further illustrated, the second ramped portions  310 ,  312  may include tongue portions  320 ,  322  that extend in an oblique direction with respect to the upper surface  40  of the endplate  14 . 
         [0146]    In an embodiment, the endplate  14  further may include a central ramped portion  402  proximate the bridge portion  314 . In the illustrated embodiment, the endplate  14  includes a central ramped portion  402  proximate the bridge portion  314  of the second side portion  204 . In an exemplary embodiment, the central ramped portion  402  can extend in an oblique direction with respect to the upper surface  40  and face the first end  39  of the endplate  14 . As illustrated, the first ramped portions  306 ,  308  may include tongue portions  316 ,  318  with the tongue portions  316 ,  318  extending in an oblique direction with respect to the upper surface  40  of the endplate  14 . 
         [0147]    With reference to  FIGS. 50-52 and 54 , in an embodiment, the actuator assembly  200  includes a head portion  324 , an extension  404 , and a through bore  406  that extends longitudinally through the actuator assembly  200 . As illustrated, the head portion  324  may include one or more instrument gripping features  330  that can allow it to be turned by a suitable instrument. In addition, the head portion  324  has a larger diameter than the other components of the actuator assembly  200  to provide a contact surface with the driving ramp  300 . In the illustrated embodiment, the head portion  324  includes a rim  332  that provides a surface for contacting the driving ramp  300 . In an embodiment, the extension  404  is a generally rod-like extension. In another embodiment, the extension  404  includes ratchet teeth for engaging the extension  336 . 
         [0148]    With reference to  FIGS. 51, 52, and 56 , the central ramp  18  has a first end  408  and a second end  410 . In an embodiment, the central ramp  18  includes a first expansion portion  412 , a second expansion portion  414 , a rod-receiving extension  416 , and a through bore  418  that extends longitudinally through the central ramp  18 . In an exemplary embodiment, first expansion portion  412  can be proximate the first end  408  of the central ramp  18 . As best seen in  FIG. 56 , the first expansion portion  412  may include side portions  420 ,  422 . In an embodiment, each of the side portions  420 ,  422  includes dual, overlapping ramped portions that extend in oblique directions with respect to the through bore  418 . For example, side portions  420 ,  422  each include a first ramped portion  424  that overlaps a second ramped portion  426 . In the illustrated embodiment, the first ramped portion  424  faces the rod-receiving extension  416  while the second ramped portion  426  faces the opposite direction. In one embodiment, angled grooves  428 ,  430  are formed in each of the first and second ramped portions  424 ,  426 . In an exemplary embodiment, the angled grooves  428 ,  430  are sized to receive the corresponding tongues  316 ,  318 ,  320 ,  322  in the first and second endplates  14 ,  16  with angled grooves  428  receiving tongues  320 ,  322  in the second endplate  16  and angled grooves  430  receiving tongues  316 ,  318  in the first endplate  14 . Although the device  10  is described with tongues  316 ,  318 ,  320 ,  322  on the endplates  14 ,  16  and angled grooves  428 ,  430  on the central ramp  18 , it should be understood that that device  10  can also be configured with grooves on the endplates  14 ,  16  and tongues on the central ramp  18 , in accordance with one embodiment of the present invention. 
         [0149]    In an embodiment, the second expansion portion  414  is located on the rod-receiving extension  416  between the first end  408  and the second end  410  of the central ramp  18 . In an exemplary embodiment, the second expansion portion  414  includes central ramped portions  432 . In one embodiment, the second expansion portion  414  includes two central ramped portions  432  on opposite sides of the rod-receiving extension  416 . In an exemplary embodiment, the central ramped portions  424  extend in an oblique direction with respect to the through bore  418  and face the second end  410  of the central ramp  18 . 
         [0150]    The rod-receiving extension  416  extends from the first expansion portion  412  and has an opening  434  at the second end of the central ramp  18 . In an embodiment, the rod-receiving extension  416  is sized and configured to receive the extension  404  of the actuator assembly  200 . In an embodiment, the rod-receiving extension  416  has threading with the rod-receiving extension  416  threadingly receiving extension  404  of the actuator assembly  200 . In another embodiment, the rod-receiving extension  416  has ratchet teeth with the extension  404  being ratcheted into the rod-receiving extension  416 . 
         [0151]    With reference to  FIGS. 50-52 and 57 , in an exemplary embodiment, the driving ramp  300  includes an upper portion  354  having an upper surface  356  and an oblique surface  358 . In an embodiment, the driving ramp  300  further includes a bore  366 , in an exemplary embodiment, sized to receive the extension  404  of the actuator assembly  200 . In the illustrated, embodiment, the upper portion  354  has a hole  436  that extends through the upper surface  356  to the bore  366 . Set screw  438  may be inserted through the hole  436  to secure the driving ramp  300  to the actuator assembly  200 . In one embodiment, the driving ramp  300  further includes contact surface  368  that engages the rim  332  of the head portion  324  of the actuator assembly  200 . In the illustrated embodiment, the contact surface  368  has a generally annular shape. 
         [0152]    In an embodiment, the driving ramp  300  further includes side portions  360 ,  362  that extend from the upper portion  354  connecting the upper portion  354  with the lower portion  364  of the driving ramp  300 . In an exemplary embodiment, the side portions  360 ,  362  of the driving ramp  300  each include a ramped portion  438 . In the illustrated embodiment, the ramped portion  438  faces central ramp  300 . In an embodiment, the ramped portion  438  is configured and dimensioned to engage the ramped portions  306 ,  308  at the first end  39  of the second endplate  16 . In one embodiment, angled grooves  440  are formed in the ramped portions  316 ,  318 . In an exemplary embodiment, the angled grooves  440  are sized to receive the corresponding tongues  316 ,  318  in the second endplate  16 . Although the device  10  is described with tongues  316 ,  318  on the second endplate  16  and angled grooves  440  on the driving ramp  300 , it should be understood that that device  10  can also be configured with grooves on the second endplate  16  and tongues on the driving ramp  300 , in accordance with one embodiment of the present invention. 
         [0153]    A method of installing the expandable fusion device  10  of  FIGS. 50-57  is now discussed in accordance with one embodiment of the present invention. Prior to insertion of the fusion device, the disc space may be prepared as described above. The expandable fusion device  10  can then be inserted into and seated in the appropriate position in the intervertebral disc space. In an embodiment, the device  10  is assembled prior to insertion. The expandable fusion device  10  can be introduced into the intervertebral space, with the end having the first end  408  of the central ramp  18  being inserted. In an exemplary method, the fusion device  10  is in the unexpanded position when introduced into the intervertebral space. In an exemplary method, the intervertebral space may be distracted prior to insertion of the fusion device  10 . The distraction provides some benefits by providing greater access to the surgical site making removal of the intervertebral disc easier and making scraping of the endplates of the vertebral bodies  2 ,  3  easier. 
         [0154]    With the fusion device  10  inserted into and seated in the appropriate position in the intervertebral disc space, the fusion device can then expand into the expanded position. To expand the fusion device  10 , an instrument is engaged with the head portion  324  of the actuator assembly  200 . The instrument is used to rotate actuator assembly  200 . As discussed above, actuator assembly  200  is threadingly engaged with the rod receiving extension  416  of the central ramp  18 ; thus, as the actuator assembly  200  is rotated in a first direction, the central ramp  18  is pulled toward the actuator assembly  200 . In an exemplary embodiment, the actuator assembly  200  is moved in a linear direction with the ratchet teeth engaging as means for controlling the movement of the actuator assembly  200  and the central ramp  18 . 
         [0155]    As the central ramp space  18  is pulled towards the actuator assembly  200 , the central ramp  18  acts to push endplates  14 ,  16  outwardly into the expanded position. By way of example, the first ramped portions  424 , second ramped portions  426 , and central ramped portions  432  push against the corresponding ramped portions in the first and second endplates  14 ,  16 . The first ramped portions  424  in the first expansion portion  412  of the central ramp  18  push against the second ramped portions  310 ,  312  of the second endplate  16  with the corresponding tongues  320 ,  322  in the second ramped portions  310 ,  312  of the second endplate  16  riding in angled grooves  428  in the first rampep portions  424  in the first expansion portion  412 . The second ramped portions  426  in the first expansion portion  412  push against the first ramped portions  316 ,  318  of the first endplate  14  with the corresponding tongues  316 ,  318  in first ramped portions  316 ,  318  of the first endplate  14  riding in angled grooves  430  in the second ramped portions  426  in the first expansion portion  412 . The central ramped portions  432  in the second expansion portion  414  push against the central ramped portion  402  in the first and second endplates  14 ,  16 . 
         [0156]    As discussed above, the actuator assembly  200  also engages driving ramp  300 ; thus, as the actuator assembly  200  is rotated in a first direction, the actuator assembly  200  pushes the driving ramp  300  towards the central ramp  18  in a linear direction. As the driving ramp  300  is pushed towards the central ramp  18 , the driving ramp  300  also acts to push the endplates  14 ,  16  outwardly into the expanded position. By way of example, the ramped portions  438  of the driving ramp  300  push against ramped portions  306 ,  308  at the first end  39  of the second endplate  16 . As the endplates  14 ,  16  move outwardly, the tongues  316 ,  318  in the ramped portions  306 ,  308  of the second endplate  16  ride in the angled grooves  440  in the ramped portions  438  of the driving ramp  300 . 
         [0157]    It should also be noted that the expansion of the endplates  14 ,  16  can be varied based on the differences in the dimensions of the various ramped portions in the central ramp  18 , the driving ramp  300 , and the first and second endplates  14 ,  16 . As best seen in  FIG. 16 , the endplates  14 ,  16  can be expanded in any of the following ways: straight rise expansion, straight rise expansion followed by a toggle into a lordotic expanded configuration, or a phase off straight rise into a lordotic expanded configuration. 
         [0158]    In the event the fusion device  10  needs to be repositioned or revised after being installed and expanded, the fusion device  10  can be contracted back to the unexpanded configuration, repositioned, and expanded again once the desired positioning is achieved. To contract the fusion device  10 , the instrument can be used to rotate the actuator assembly  200  in a second direction that is opposite the first direction. Rotation of the actuator assembly  200  results in movement of the central ramp  18  and the driving ramp  300  away from one another. As the central ramp  18  and the driving ramp  300  move, the endplates  14 ,  16  move inwardly into the unexpanded position. 
         [0159]    Although the preceding discussion only discussed having a single fusion device  10  in the intervertebral space, it is contemplated that more than one fusion device  10  can be inserted in the intervertebral space. It is further contemplated that each fusion device  10  does not have to be finally installed in the fully expanded state. Rather, depending on the location of the fusion device  10  in the intervertebral disc space, the height of the fusion device  10  may vary from unexpanded to fully expanded. It should be noted that, as well as the height being varied from an unexpanded state to an expanded state, the fusion  10  may be positioned permanently anywhere between the expanded state and the unexpanded state. 
         [0160]    Referring now to  FIGS. 58-65 , an alternative embodiment of the expandable fusion device  10  is shown. In the illustrated embodiment, the fusion device  10  includes an upper endplate  480 , a lower endplate  485 , and actuator assembly  445 . The actuator assembly  445  comprises a front sloped height actuator  450 , a rear sloped height actuator  455 , and a linear actuator  460 . In an embodiment the linear actuator  460  functions to pull the front sloped actuator  450  and the rear sloped actuator  455  together, which forces apart the upper endplate  480  and lower endplate  485 . 
         [0161]    With reference to  FIGS. 58-59 , in an exemplary embodiment of fusion device  10 , the actuator assembly  445  comprises a front sloped actuator  450 , a rear sloped actuator  455 , and a linear actuator  460 . As illustrated, the linear actuator  460  may comprise a head portion  465  and an extension  466 . In an embodiment, the extension  466  is a generally rod-like extension that comprises surface threads  470 . It should be understood that, while the surface threads  470  of the linear actuator  460  are referred to as threaded, the surface threads  470  may only be partially threaded in accordance with one embodiment. The linear actuator  460  of the actuator assembly  445  may extend through an opening  456  in the rear sloped actuator  455  where the surface threads  470  of the linear actuator  460  engage the complimentary threads  500  of the extension  475  of the front sloped actuator  450 . Thus, as the linear actuator  460  is rotated in a first direction, the actuator assembly  445  pulls the front sloped actuator  450  towards the rear sloped actuator  455  and consequently also towards the head portion  465  of the linear actuator  460  in a linear direction. As the front sloped actuator  450  is pulled towards the rear sloped actuator  455 , the sloped surfaces  454 ,  459  respectively, of the front sloped actuator  450  and the rear sloped  455  actuator push the upper  480  and lower  485  endplates outwardly into the expanded position. 
         [0162]    With reference to  FIGS. 58-59 and 63 , in an exemplary embodiment, the upper and lower endplates  480 ,  485  may comprise two portions, such as two opposing mirrored halves. Both the upper endplate  480  and lower endplate  485  may comprise a front end  481  and a rear end  482 . The front and rear ends  481 ,  482  of each portion of each endplate may be substantially similar to the front and rear ends  481 ,  482  of every other portion of every other endplate. It should be understood that that references to the front and rear ends  481 ,  482  of each endplate are with respect to the front and rear of the expandable fusion device  10 , which is with respect to the direction of placement into an intervertebral disc space with the front of the expandable fusion device  10  placed into the space first, followed by the rear of the expandable fusion device  10 . Each portion of the upper and lower endplates  480 ,  485  further may comprise front ramped surface  483  and rear ramped surface  484 , as a component of the front and rear ends  481 ,  482  of each portion of the upper and lower endplate  480 ,  485 . The front ramped surface  483  may be located on the front end  481  of each half of the upper and lower endplates  480 ,  485 . The rear ramped surface  484  may be located on the rear end  482  of each half of the upper and lower endplates  485 . With additional reference to  FIGS. 60 and 61 , in the illustrated embodiment, the front and rear ends  481 ,  482  of each portion of upper and lower endplates  480 ,  485  contains a slot  490  that engages the corresponding elevated and angled tongues  495  of the front sloped actuator  450  and the rear sloped actuator  455 . The elevated and angled tongues  495  may be substantially identical in design and function for both the front sloped actuator  450  and the rear sloped actuator  455 . Because the elevated and angled tongues  495  are angled at a slant that directs away from the center of the expandable fusion device, as the front sloped actuator  450  is pulled towards the rear sloped actuator  455  by rotation of the linear actuator  460 , the ramped sections  454 ,  459  of the front and rear sloped actuators  450 ,  455 , in conjunction with the elevated and angled tongues  495  of the front and rear sloped actuators  450 ,  455  pushes both portions of the upper and lower endplates  480 ,  485  outward simultaneously in both horizontal and vertical directions. 
         [0163]    With reference to  FIGS. 58-62 , front sloped actuator  450  may comprise a front end  451  and a rear end  453 . The front end  451  may comprise opposing sloped surfaces  452 . In some embodiments, the front end  451  of the front sloped actuator  450  is the section of the expandable fusion device  10  that is first inserted into an intervertebral disc space. The front sloped actuator  450  may also comprise a rear end  453  connected to extension  475  from the front slope actuator  450 . The rear end  453  of the front sloped actuator  450  also may comprise opposing sloped surfaces  454 . The opposing sloped surfaces  454  of the rear end  453  of the front sloped actuator  450  may be sloped towards the rear sloped actuator  455 . The opposing sloped surfaces  454  of the rear end  453  of the front sloped actuator  450  also comprises the elevated and angled tongues  495  that engage the slots  490  of the halves of the upper and lower endplates  480 ,  485 , as described in the preceding paragraph. The front sloped actuator  450  also comprises a threaded screw opening  463 . As illustrated, the extension  475  from the front sloped actuator  450  may comprise extending threaded prongs  476   a,    476   b.  The extension  475  is generally located in the center of the actuator assembly  445 , and with respect to the front end  451  of the front sloped actuator  450 , the extension  475  extends longitudinally towards the rear sloped actuator  455  and the linear actuator  460 . The extension  475  may be sized and configured to receive the extension  466  of the linear actuator  460 . The extension  475  may comprise threads  500  that engage with the threads  470  of the extension  466  of the linear actuator  460 . Turning the linear actuator  460 , rotates the threads  470  of the linear actuator  460 , which are threadingly engaged to the threads  500  of the extension  475  of the front sloped actuator  450 , and consequently can push or pull the extension  475  and therefore the front sloped actuator  450  towards or away from the rear sloped actuator  455  and the linear actuator  460 , dependent upon which direction the linear actuator  460  is rotated. 
         [0164]    With continued reference to  FIGS. 58-62 , rear sloped actuator  455  may comprise an opening  456 . The opening  456  may be disposed in the center of the rear sloped actuator  455  and may run longitudinally throughout the entirety of the rear sloped actuator  455 . The opening  456  may be sized to receive the extension of the  475  of the front sloped actuator  450  with the extension  466  of the linear actuator  460  disposed therein. The rear sloped actuator  455  also contains a front side  458  which faces the extension  475  of the front sloped actuator  450 . The front side  458  of the rear sloped actuator  455  has opposing sloped surfaces  459 , that are sloped towards the extension  475  and consequently the front sloped actuator  450 . The front side  458  of the rear sloped actuator  455  also comprises the elevated and angled tongues  495  that engage the slots  490  of the halves of the upper  480  and lower  485  endplates, as described above. As best seen in  FIGS. 61 and 63 , in an exemplary embodiment, the rear sloped actuator  455  comprises tool engagement surfaces  510 . Tool engagement surface  510  is a surface for engagement of a placement and positioning tool (not shown) which allows for insertion and adjustment of the fusion device  10  into an intervertebral space as best shown in  FIG. 1 . Tool engagement surfaces  510  may be located horizontally on opposing sides of sloped rear actuator  455 . 
         [0165]    As discussed above, the linear actuator  460  may comprise a head portion  465  and an extension  466 . Surface threads  470  may be disposed on the extension  466  of the linear actuator  460 . Surface threads  470  are complimentary to and engage the threads  500  of the extension  475  of the front sloped actuator  450 . In another embodiment, the extension  466  includes ratchet teeth for engaging the front sloped actuator  450 . Linear actuator  460  also comprises opening  468  in the head portion  465  of linear actuator  460 . In the illustrated embodiment, the opening  468  includes one or more instrument gripping features  472  that can allow it to be turned by a suitable instrument. Linear actuator  460  may disposed in the opening  456  of the rear sloped actuator  455  with the extension  466  running through the opening  456 . The head portion  465  may be of a diameter that is too large to pass through the opening  456  and thus allows the linear actuator  460  to reach an endpoint where it, or from another perspective the front sloped actuator  450 , cannot be drawn closer through rotation of the linear actuator  460 . 
         [0166]    As best seen in  FIGS. 60-62 , in an exemplary embodiment, the front sloped actuator  450  comprises an extension  475  further comprising threads  500  that engage the surface threads  470  of the linear actuator  460 . Thus, as the linear actuator  460  is rotated in a first direction by a threaded instrument (not shown), the front sloped actuator  450  moves toward the flanged end  465  of the linear actuator  460 . In the event the fusion device  10  needs to be repositioned or revised after being installed and expanded, the fusion device  10  can be contracted back to the unexpanded configuration, repositioned, and expanded again once the desired positioning is achieved. To contract the fusion device  10 , the thread locking screw  460  can be rotated in a second direction. As discussed above, actuator assembly  445  is in threaded engagement with the extension  475  of the front sloped actuator  450 ; thus, as linear actuator  460  is rotated in a second direction, opposite the first direction, the front sloped actuator  450  moves with respect to the actuator assembly  445  and the upper and lower endplates  480 ,  485  away from the flanged end  465 . 
         [0167]    With reference to  FIGS. 58-59, and 63 , in an exemplary embodiment the upper and lower endplates  480 ,  485  may further comprise endplate pins  515 . As illustrated, the upper and lower endplates  480 ,  485  may each comprise two endplate pins  515 . Endplate pins  515  may rest in slots disposed in each portion of the upper and lower endplates  480 ,  485 . In the illustrated embodiment, the endplate pins  515  connect the portions of the upper endplate  480  and the portions of the lower endplate  485 . Endplate pins  515  can provide for even and simultaneous movement of endplate portions. With specific reference to  FIGS. 64( a ) and 64( b ) , endplate pins  515  can be seen in both the unexpanded fusion device configuration as shown in  FIG. 64( a )  and the expanded fusion device configuration as shown in  FIG. 64( b ) . 
         [0168]    In an exemplary embodiment,  FIG. 65  depicts bone graft hole  520 , which is shown disposed in upper endplate  480 . Bone graft hole  520  in conjunction with threaded hole  470  of the linear actuator  460  provides space for bone grafts that may be used in the intervertebral fusion procedure. 
         [0169]    A method of installing the expandable fusion device  10  of  FIGS. 58-65  is now discussed in accordance with one embodiment of the present invention. Prior to insertion of the fusion device  10 , the disc space may be prepared as described above. The expandable fusion device  10  can then be inserted into and seated in the appropriate position in the intervertebral disc space. In an embodiment, the device  10  is assembled prior to insertion. The expandable fusion device  10  can be introduced into the intervertebral space, with the end having the first end of the front sloped actuator  450  being inserted. In an exemplary method, the fusion device  10  is in the unexpanded position when introduced into the intervertebral space. In an exemplary method, the intervertebral space may be distracted prior to insertion of the fusion device  10 . The distraction provides some benefits by providing greater access to the surgical site making removal of the intervertebral disc easier and making scraping of the endplates of the vertebral bodies  2 ,  3  easier as depicted in  FIG. 1 . 
         [0170]    With the fusion device  10  inserted into and seated in the appropriate position in the intervertebral disc space, the fusion device  10  can then expand into the expanded position. To expand fusion device  10 , an instrument may be engaged with the instrument gripping features  472  the linear actuator  460 . The threaded instrument may rotate the linear actuator  460  in the first direction, drawing the front sloped actuator  450  and the rear sloped actuator  455  together and contracting the actuator assembly  455 . In an exemplary embodiment the front sloped actuator  450  and the linear actuator  460  may be drawn together in a linear fashion with the threads  500  of the extension  475  of the front sloped actuator  450  engaging the surface threads  470  of the linear actuator  460  as a means for controlling the movement of the contraction of the actuator assembly  445  and consequently the expansion of the upper and lower endplates  480 ,  485 , which expand horizontally and vertically with contraction of the actuator assembly  445 . 
         [0171]    It should also be noted that the expansion of the upper and lower endplates  480 ,  485  may be varied based on the differences in the dimensions of the sloped surfaces  454  and  459  and the direction of the angle in the elevated and angled tongues  495 . As best seen in  FIG. 16 , the upper and lower endplates  480  and  485  can be expanded in any of the following ways: straight rise expansion, straight rise expansion followed by a toggle into a lordotic expanded configuration, or a phase off straight rise into a lordotic expanded configuration. 
         [0172]    Although the preceding discussion only discussed having a single fusion device  10  in the intervertebral space, it is contemplated that more than one fusion device  10  can be inserted in the intervertebral space. It is further contemplated that each fusion device  10  does not have to be finally installed in the fully expanded state. Rather, depending on the location of the fusion device  10  in the intervertebral disc space, the height of the fusion device  10  may vary from unexpanded to fully expanded. It should be noted that, as well as the height being varied from an unexpanded state to an expanded state, the fusion  10  may be positioned permanently anywhere between the expanded state and the unexpanded state. 
         [0173]    Referring now to  FIGS. 66-73 , an alternative embodiment of the expandable fusion device  10  is shown. In the illustrated embodiment, the fusion device  10  includes an upper endplate  570 , a lower endplate  580 , and a collective actuator assembly  520 . The collective actuator assembly  520  comprises a front sloped actuator assembly  530 , a rear sloped actuator assembly  540 , and threaded locking screws  550 . In an embodiment a threaded instrument  560  functions to pull the front sloped actuator assembly  530  and the rear sloped actuator assembly  540  together, which forces apart the upper endplate  570  and lower endplate  580 . 
         [0174]    With reference to  FIGS. 66-68 and 71 , in an exemplary embodiment of fusion device  10 , the collective actuator assembly  520  comprises a front sloped actuator assembly  530 , a rear sloped actuator assembly  540 , and threaded locking screws  550 . The threaded locking screws  550  have flanged ends  551  and surface threads  552  that extend at least partially through the collective actuator assembly  520 . It should be understood that, while the surface threads  552  of the threaded locking screws  550  are referred to as threaded, the surface threads  552  may only be partially threaded in accordance with one embodiment. The threaded locking screws  550  of the collective actuator assembly  520  may rest in an opening  541  in the rear width actuator  542  of the rear sloped actuator assembly  540  where the surface threads  552  of the threaded locking screws  550  engage threaded screw openings  595  of the front height actuator  532  of the front sloped actuator assembly  530 . The threaded instrument  560  ( FIG. 72 ) may extend through an instrument opening  561  in the rear width actuator  542  of the rear sloped actuator assembly  540 . As the threaded instrument  560  is rotated in a first direction, the collective actuator assembly  520  pulls the front sloped actuator assembly  530  towards the rear sloped actuator assembly  540  and consequently also towards the flanged ends  551  of the threaded locking screws  550  in a linear direction. As the front sloped actuator assembly  530  is pulled towards the rear sloped actuator assembly  540 , the front width actuator  536  and the rear width actuator  542  are pulled together. As they are pulled together, the front and rear width actuators  536 ,  542  drive apart the portions of the upper endplate  570  and the portions of the lower endplate  575 . More particularly, the front and rear width actuators  536   542  engage the front height actuators  532  and the rear height actuators  546  to force them horizontally outward, which in tum engage the upper and lower endplates  570 ,  575  to force them horizontally outward. The front stop pins  533  may have one end disposed in the retaining bores  534  of the front height actuator  532  and opposite ends disposed in the front stop pint track  535  of the front width actuator  536 . The front stop pins  533  may slide in the front stop pin track  535  of the front width actuator  536  until they reach the end of the front stop pin track  535  and movement of the front width actuator  536  is stopped, thus restricting lateral expansion of the device  10 , as best seen on FIG.  68 . Simultaneously, the rear stop pins  543  disposed in the retaining bores  544  of the rear width actuator  542 , slide in the rear stop pin tracks  545  of the rear height actuators  546  until they reach the end of the rear stop pin tracks  545  and movement of the rear width actuator  542  is stopped, as best seen on  FIGS. 68 and 71 . When the front width actuator  536  is stopped, the front sloped actuator assembly  530  may be pulled towards the rear sloped actuator assembly  540 , by simultaneously turning threaded locking screws  550 . As threaded locking screws  550  are rotated simultaneously in a first direction, the sloped surfaces  537 ,  547  respectively, of the front height actuators  532  and the rear height actuator  546  push the upper  570  and lower  580  endplates vertically outward into the expanded position. 
         [0175]    With reference to  FIGS. 66-68 , in an exemplary embodiment, the upper and lower endplates  570 ,  580  may split into two portions, such as being bifurcated into two opposing mirrored halves. The portions of the upper endplate  570  maybe substantially identical to the portions of the lower endplate  580  in embodiments of the present invention. Both the upper and lower endplates  570 ,  580  may comprise front and rear ends  571 ,  572 . The front and rear ends  571 ,  572  of each portion of each endplate may be substantially similar to the front and rear ends  571 ,  572  of every other portion of every other endplate. It should be understood that that references to the front and rear ends  571 ,  572  of each endplate are with respect to the front and rear of the expandable fusion device  10 , which is with respect to the direction of placement into an intervertebral disc space with the front of the expandable fusion device  10  placed into the space first, followed by the rear of the expandable fusion device  10 . Each portion of the upper and lower endplates  570 ,  580  further comprises front and rear ramped surface portions  573 ,  574 , as a component of the front and rear ends  571 ,  572  of each portion of the upper and lower endplate  570 ,  580  respectively. The front ramp surface  573  is located on the front end  571  of each portion of the upper and lower endplates  570 ,  580 . The rear ramp surface  574  is located on the rear end  572  of each portion of the upper and lower endplates  570 ,  580 . The front and rear ends  571 ,  572  of each half of upper endplate  570  contains a slot  575  that engages the corresponding elevated tongues  590  of the front height actuator  532  and the rear height actuator  546  of the front sloped actuator assembly  530  and the rear sloped actuator assembly  540  respectively. The elevated tongues  590  may be substantially identical in design and function for both the front height actuator  532  and the rear height actuator  546 . 
         [0176]    As best seen in  FIGS. 66-67 and 69 , the front sloped actuator assembly  530  may comprise a front width actuator  536 . As illustrated, the front width actuator  536  may be wedge-shaped. The front width actuator  536  may further comprise a sloped front end  538 . The sloped front end  538  may be the section of the expandable fusion device  10  that is first inserted into an intervertebral disc space. The front width actuator  536  may further comprise a front stop pin track  535  that is complimentary to the front stop pins  533 . The front width actuator  536  may also comprise a threaded instrument opening  539 . The threaded instrument opening  539  also comprises threads that engage the threaded instrument  560 . The front sloped actuator assembly  530  may also comprise a pair of front height actuators  532 . The front height actuators  532  may be mirrored analogues that have substantially the same function. The front width actuator  536  may be disposed between the pair of front height actuators  532 . The front height actuators  532  comprise a sloped surface  537  and elevated tongues  590  that vertically expand the upper  570  and lower  580  endplates. The front height actuators  532  additionally comprise a threaded screw opening  595 . The threaded screw opening  595  engages the threaded locking screws  550 . When threaded locking screws  550  are turned in a first direction, upper  570  and lower  580  endplates are expanded vertically, due to the contraction of the front sloped actuator assembly  530  and the rear sloped actuator assembly  540 . Front height actuators  532  may additionally comprise retaining bores  534 , wherein the front stop pins  533  are disposed. 
         [0177]    Rear sloped actuator assembly  540  may comprise a rear width actuator  542 . As illustrated, the rear width actuator  542  may be generally wedge-shaped. The rear width actuator  542  may further comprise an instrument opening  561  wherein the threaded instrument  560  may be inserted to operate the expandable fusion device  10 . The rear width actuator  542  may additionally comprise openings  541 . Threaded locking screws  550  may be inserted into openings  541  of the rear width actuator  542  and run through the collective actuator assembly  520  to connect to the threaded screw openings  595  in the front height actuators  532 . Rear width actuator  542  may additionally comprise retaining bores  544  which house the rear stop pins  543 . The rear stop pins  543  are fixed in the retaining bores  544  and do not move relative to and apart from the retaining bores  544 . The rear stop pins  543  and retaining bores  544  may be present in pairs, located on the top and bottom of the rear width actuator  542 . Rear stop pins  543  connect the rear width actuator  542  to the rear height actuators  546 . Rear height actuators  546  comprise rear stop pin tracks  545  in which the rear stop pins  543  may be disposed. When the threaded instrument  560  is turned in a first direction to contract the collective actuator assembly  520  and draw the front sloped actuator assembly  530  and the rear sloped actuator  540 , the rear stop pins  543  slide in the rear stop pin tracks  545  to expand the upper and lower endplates  570 ,  580  horizontally, until the rear stop pins  543  contact the end of the rear stop pin tracks  545 . The rear sloped actuator assembly  540  may also comprise a pair of rear height actuators  546 . The rear height actuators  546  may be mirrored analogues that have substantially the same function. The rear width actuator  542  may be disposed between the pair of rear height actuators  546 . Rear height actuators  546  may comprise a sloped surface  547  and elevated tongues  590  that vertically expand the upper  570  and lower  580  endplates. Sloped surface  547  is sloped towards the front sloped actuator assembly  530 . Elevated tongues  590  engage the corresponding slots  575  of the upper  570  and lower  580  endplates. 
         [0178]    As discussed above, the threaded locking screws  550  of the collective actuator assembly  520 , may each comprise a flanged end  551  and surface threads  552 . Surface threads  551  are disposed on the front end  553  of the threaded locking screws. The front end  553  of the threaded locking screws  550  are longitudinally opposite the flanged ends  551  of the threaded locking screws  550 . Surface threads  551  are complimentary to and engage the threads of the threaded screw openings  595  of the front height actuators  532  of the front sloped actuator assembly  530 . Threaded locking screws  550  also comprise an instrument opening  554  in the flanged ends  551  of the threaded locking screws  550 . In an exemplary embodiment, the instrument opening  554  is configured and dimensioned to receive a locking screw instrument (not shown). Threaded locking screws  550  are disposed in the threaded screw openings  541  of the rear width actuator  542  with the front end  553  running through the threaded screw openings  541 . The flanged ends  551  may be of a diameter that is too large to pass through the threaded screw openings  541  and thus allows the threaded locking screws  550  to reach an endpoint where it, or from another perspective the front sloped actuator assembly  530 , cannot be drawn closer through rotation of the threaded locking screws  550 . 
         [0179]    As best seen in  FIG. 68 , as the threaded locking screws  550  are rotated in a first direction by a locking screw instrument (not shown), the front height actuators  532  are pulled towards the flanged ends  551  of the threaded locking screws  550 . In the event the fusion device  10  needs to be repositioned or revised after being installed and expanded, the upper  570  and lower  580  endplates of fusion device  10  can be contracted back to the unexpanded configuration, repositioned, and expanded again once the desired positioning is achieved. To contract the endplates  570 , 580  of fusion device  10 , the threaded instrument  560  and the threaded locking screws  550  can be rotated in a second direction. As discussed above, rear sloped actuator assembly  540  is in threaded engagement with the front sloped actuator assembly  530 ; thus, as the threaded instrument  560  is rotated in a second direction, opposite the first direction, the front sloped actuator assembly  530  is pushed away from the rear sloped actuator assembly  540  and the upper  570  and lower  580  endplates are pulled inward horizontally, this may continue until the front stop pins  533  and the rear stop pins  543  reach the end of their collective stop pin tracks  535  and  545  respectively. When the upper  570  and lower  80  endplates have been contracted to their initial unexpanded horizontal positions, the threaded locking screws  550  can be turned in a second direction opposite the first direction. Rotating the threaded locking screws  550  in a second direction will continue to push the front sloped actuator assembly  530  away from the rear sloped actuator assembly  540 . This can continue, until the endplates  570 , 580  are fully contracted into the default unexpanded configuration. 
         [0180]    With reference to  FIGS. 66-68 , in an exemplary embodiment the upper and lower endplates  570 ,  580  each comprise endplate pins  600 . As illustrated, the upper and lower endplates  570 ,  580  each comprise two endplate pins  600 . Endplate pins  600  rest in slots disposed in each half of the upper and lower endplates  605 ,  610 . Endplate pins  600  connect the halves of the upper endplate  470  and the halves of the lower endplate  580 . Endplate pins  600  provide for even and simultaneous movement of endplate halves. 
         [0181]    In an exemplary embodiment,  FIGS. 71( a )-71( c )  depict bone graft hole  615  in the upper and lower endplates  570 ,  580 . Bone graft hole  615  in conjunction with the threaded instrument opening  561  provides space for bone grafts that may be used in the intervertebral fusion procedure. 
         [0182]    A method of installing the expandable fusion device  10  of  FIGS. 66-72  is now discussed in accordance with one embodiment of the present invention. Prior to insertion of the fusion device, the disc space may be prepared as described above. The expandable fusion device  10  can then be inserted into and seated in the appropriate position in the intervertebral disc space. In an embodiment, the device  10  is assembled prior to insertion. The expandable fusion device  10  can be introduced into the intervertebral space, with the end having the first end of the front sloped actuator  450  being inserted. In an exemplary method, the fusion device  10  is in the unexpanded position when introduced into the intervertebral space. In an exemplary method, the intervertebral space may be distracted prior to insertion of the fusion device  10 . The distraction provides some benefits by providing greater access to the surgical site making removal of the intervertebral disc easier and making scraping of the endplates of the vertebral bodies  2 ,  3  easier as depicted in  FIG. 1 . 
         [0183]    With the fusion device  10  inserted into and seated in the appropriate position in the intervertebral disc space, the fusion device  10  can then expand into the expanded position. To expand fusion device  10 , a threaded instrument is inserted into the threaded instrument opening  561  and the threaded instrument opening  539  of the rear sloped actuator assembly  540  and the front sloped actuator assembly  530  respectively. The threaded instrument is rotated in the first direction, drawing the front sloped actuator assembly  530  and the rear sloped actuator  540  together and contracting the collective actuator assembly  520 . In an exemplary embodiment the front sloped actuator assembly  530  and the rear sloped actuator assembly  540  are drawn together in a linear fashion with the threads of the threaded instrument opening  539  of the front sloped actuator assembly  530  engaging the surface threads  561  of the threaded instrument  560  as a means for controlling the movement of the contraction of the collective actuator assembly  520  and consequently the horizontal expansion of the upper  570  and lower  580  endplates, which expand horizontally with contraction of the collective actuator assembly  520 . When horizontal expansion of endplates  570  and  580  has reached its maximum, threaded locking screws  550  may be rotated in a first direction simultaneously to further draw the front actuator assembly  530  towards the rear actuator assembly  540 . This contraction of the collective actuator assembly  520  expands the upper  570  and lower  580  endplates until they reach their maximum vertical expansion. 
         [0184]    It should also be noted that the expansion of the upper  570  and lower  580  endplates may be varied based on the differences in the dimensions of the sloped surfaces  537  and  547 . As best seen in  FIG. 16 , the upper  570  and lower  580  endplates may be expanded in any of the following ways: straight rise expansion, straight rise expansion followed by a toggle into a lordotic expanded configuration, or a phase off straight rise into a lordotic expanded configuration. 
         [0185]    Although the preceding discussion only discussed having a single fusion device  10  in the intervertebral space, it is contemplated that more than one fusion device  10  can be inserted in the intervertebral space. It is further contemplated that each fusion device  10  does not have to be finally installed in the fully expanded state. Rather, depending on the location of the fusion device  10  in the intervertebral disc space, the height of the fusion device  10  may vary from unexpanded to fully expanded. It should be noted that, as well as the height being varied from an unexpanded state to an expanded state, the fusion  10  may be positioned permanently anywhere between the expanded state and the unexpanded state. 
         [0186]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. Although individual embodiments are discussed, the invention covers all combinations of all those embodiments.

Technology Category: a