Patent Publication Number: US-10779957-B2

Title: Expandable fusion device and method of installation thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation-in-part of U.S. application Ser. No. 15/189,188, filed on Jun. 22, 2016, which is a continuation-in-part of U.S. Ser. No. 15/014,189, filed Feb. 3, 2016, which is a continuation-in-part of U.S. patent Ser. No. 14/109,429 filed on Dec. 17, 2013, which is a divisional application of U.S. patent application Ser. No. 12/875,818 filed on Sep. 3, 2010, now U.S. Pat. No. 8,632,595, the entire disclosures of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     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. 
     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. 
     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. 
     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 
     In an exemplary embodiment, the present invention provides an expandable fusion device capable of being installed inside an intervertebral disc space to maintain normal disc spacing and restore spinal stability, thereby facilitating an intervertebral fusion. In one embodiment, the fusion device includes a central ramp, a first endplate, and a second endplate. The central ramp may be capable of moving in a first direction to push the first and second endplates outwardly and into an unexpanded configuration. The expandable fusion device may be capable of being placed into the disc space down an endoscopic tube and then expanded into an expanded configuration. 
     In an exemplary embodiment, an apparatus may be provided comprising: a first endplate for an intervertebral implant, wherein the first endplate may comprise a first plate portion having a first upper surface and a first lower surface, wherein the first endplate further comprises first front ramped portions extending away from the first lower surface and first rear ramped portions extending away from first lower surface. The apparatus may further comprise a second endplate for an intervertebral implant, wherein the second endplate may comprise a second plate portion having a second upper surface and a second lower surface, wherein the second endplate further comprises second front ramped portions extending away from the second lower surface and second rear ramped portions extending away from second lower surface. The apparatus may further comprise a body positioned between the first endplate and the second endplate, wherein the body may comprise rear endplate engaging ramps. The apparatus may further comprise a driving ramp positioned at a front end of the apparatus, wherein the driving ramp comprises front endplate engaging ramps. When the apparatus is in an unexpanded configuration, the rear endplate engaging ramps and the front endplate engaging ramps may have ramp angles with respect to a longitudinal axis of the apparatus that differ from ramp angles of the first rear ramped portions and first front ramped portions of the first endplate with respect to the longitudinal axis. The apparatus may be configured such that movement of the driving ramp in one direction causes the first and second endplates to move apart and a movement of the driving ramp in a second direction causes the first and second endplates to move towards one another. 
     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 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a side view of an embodiment of an expandable fusion device shown between adjacent vertebrae according to the present invention; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         FIG. 14  is a perspective view showing expansion of the expandable fusion device in accordance with one embodiment of the present invention; 
         FIG. 15  is a side schematic view of the expandable fusion device of  FIG. 1  having different endplates; 
         FIG. 16  is a partial side schematic view of the expandable fusion device of  FIG. 1  showing different modes of endplate expansion; 
         FIG. 17  is a side schematic view of the expandable fusion device of  FIG. 1  with artificial endplates shown between adjacent vertebrae; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         FIG. 43  is a side exploded view of the expandable fusion device of  FIG. 40  in accordance with one embodiment of the present invention; 
         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; 
         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; 
         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; 
         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; 
         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; 
         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; 
         FIG. 52  is an exploded view of the expandable fusion device of  FIG. 50  in accordance with one embodiment of the present invention; 
         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; 
         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; 
         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; 
         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; and 
         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. 
         FIG. 58  is an exploded view of an alternative embodiment of an expandable fusion device in accordance with one embodiment of the present invention. 
         FIG. 59  is a side view of the expandable fusion device of  FIG. 58  shown in partial cross-section in an unexpanded configuration in accordance with one embodiment of the present invention. 
         FIG. 60  is a side view of the expandable fusion device of  FIG. 58  shown in an unexpanded configuration in accordance with one embodiment of the present invention. 
         FIG. 61  is a perspective view of the expandable fusion device of  FIG. 58  shown in an unexpanded configuration in accordance with one embodiment of the present invention. 
         FIG. 62  is a side view of the expandable fusion device of  FIG. 58  shown in partial cross-section in a lordotic expanded configuration in accordance with one embodiment of the present invention. 
         FIG. 63  is a side view of the expandable fusion device of  FIG. 58  shown in a lordotic expanded configuration in accordance with one embodiment of the present invention. 
         FIG. 64  is a perspective view of the expandable fusion device of  FIG. 58  shown in a lordotic expanded configuration in accordance with one embodiment of the present invention. 
         FIG. 65  is a side view of the expandable fusion device of  FIG. 58  shown in partial cross-section in a fully expanded configuration in accordance with one embodiment of the present invention. 
         FIG. 66  is a side view of the expandable fusion device of  FIG. 58  shown in a fully expanded configuration in accordance with one embodiment of the present invention. 
         FIG. 67  is a perspective view of the expandable fusion device of  FIG. 58  shown in a fully expanded configuration in accordance with one embodiment of the present invention. 
         FIG. 68  is an exploded view of an expandable fusion device having a ratcheting mechanism in accordance with some embodiments. 
         FIGS. 69A-69C  are side views of the expandable fusion device of  FIG. 68  in the process of expansion in accordance with some embodiments. 
         FIGS. 70A-70C  are different views of the expandable fusion device of  FIG. 68  in a contracted state in accordance with some embodiments. 
         FIGS. 71A-71C  are different views of the expandable fusion device of  FIG. 68  in a tipped state without full expansion in accordance with some embodiments. 
         FIGS. 72A-72C  are different views of the expandable fusion device of  FIG. 68  in a fully expanded state in accordance with some embodiments. 
         FIG. 73  is an upper view of the expandable fusion device of  FIG. 68  in accordance with some embodiments. 
         FIG. 74  is an upper cross-sectional view of the expandable fusion device of  FIG. 68  in accordance with some embodiments. 
         FIG. 75  is a close up view of the ratcheting mechanism of the expandable fusion device of  FIG. 68  in accordance with some embodiments. 
         FIG. 76  is a close up view of the ratchet teeth of the expandable fusion device of  FIG. 68  in accordance with some embodiments. 
         FIG. 77  is a top perspective view of the expandable fusion device of  FIG. 68  in accordance with some embodiments. 
         FIGS. 78A-78G  are top perspective views of the expandable fusion device of  FIG. 68  transitioning from a locked configuration to a disengaged configuration in accordance with some embodiments. 
         FIG. 79  is an exploded view of an expandable fusion device having an expandable spacing mechanism in accordance with some embodiments. 
         FIG. 80  is a diagram showing a view of an exemplary “locked” configuration of the fusion device of  FIG. 79 . 
         FIG. 81  is a diagram showing a view of an exemplary “disengaged” configuration of the fusion device of  FIG. 79 . 
         FIGS. 82A-82C  are side views of the expandable fusion device of  FIG. 79  in the process of expansion in accordance with some embodiments. 
         FIGS. 83A-83C  are different views of the expandable fusion device of  FIG. 79  in a contracted state in accordance with one embodiment of the present invention. 
         FIGS. 84A-84B  are different views of the expandable fusion device of  FIG. 79  in a tipped state without full expansion in accordance with one embodiment. 
         FIGS. 85A-85C  are different views of the expandable fusion device of  FIG. 79  in a fully expanded state according to one embodiment of the present invention. 
         FIG. 86  is a diagram showing an alternative view of the fusion device of  FIG. 79  in the locked position. 
         FIG. 87  is a diagram showing another alternative view of the fusion device of  FIG. 79  in the locked position. 
         FIG. 88  is a diagram showing the stem&#39;s position as the fusion device of  FIG. 79  is expanding. 
         FIG. 89  is a diagram showing the fusion device of  FIG. 79  in a locked position. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     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 . 
     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. 
     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. 
     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 . 
     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. 
     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. 
     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. 
     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 . 
     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. 
     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 . 
     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 . 
     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. 
     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 . 
     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. 
     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 . 
     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. 
     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. 
     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 . 
     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 . 
     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. 
     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. 
     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. 
     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. 
     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 . 
     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 . 
     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. 
     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. 
     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. 
     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 . 
     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 . 
     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 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 . 
     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 . 
     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 . 
     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. 
     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 turn below. 
     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 . 
     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 . 
     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 . 
     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. 
     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. 
     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 . 
     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 . 
     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. 
     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. 
     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 . 
     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. 
     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. 
     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. 
     With the fusion device  10  inserted into and seated in the appropriate position in the intervertebral disc space, the fusion device can then be 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 . 
     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 . 
     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 . 
     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. 
     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. 
     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. 
     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 . 
     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 . 
     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 . 
     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 . 
     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 . 
     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. 
     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 . 
     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 . 
     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. 
     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. 
     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. 
     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 . 
     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 ramped 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 . 
     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 . 
     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. 
     Referring now to  FIG. 58 , an alternative embodiment of the expandable fusion device  10  is shown in which the expandable fusion device  10  expands into a lordotic expanded configuration. In the illustrated embodiment, the expandable fusion device  10  includes a first endplate  14 , a second endplate  16 , an actuator assembly  200 , a driving ramp  300 , and a body  500 . As will be discussed in more detail below, the actuator assembly  200  functions, in an embodiment, to pull the driving ramp  300  and the body  500  together, which forces apart the first and second endplates  14 ,  16 . For example, the actuator assembly  200  may be rotated to pull the driving ramp  300  toward the body  500 . When this occurs, the expandable fusion device  10  first expands into a lordotic expanded configuration ( FIGS. 62-64 ) and then expands in height until it is fully expanded ( FIGS. 65-67 ). In embodiments, expandable fusion device  10  may have two stages of expansion, generally referred to as lordotic stage and parallel stage. In lordotic stage, the expandable fusion device  10  may expand at one end to achieve a lordotic angle. The expandable fusion device  10  may hen expand in parallel sage wherein the lordotic expansion may be maintained at both ends of the expandable fusion device  10  may expand at generally constant rates. In an embodiment, the expandable fusion device  10  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. 
     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 . 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 a plate portion  502  that may extend between first end  39  and the second end  41 . Plate portion  502  may comprise an upper surface  40  and a lower surface  42 . In an embodiment, the first endplate  14  may comprise a through opening  44 . The through opening  44 , in an exemplary embodiment, may be sized to receive bone graft or similar bone growth inducing material. 
     In one embodiment, the upper surface  40  of the plate portion  502  is flat and generally planar to allow the upper surface  40  of the plate portion  502  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. 
     In one embodiment, the first endplate  14  further comprises front side extensions  504  that extend from plate portion  502 . As illustrated, the front side extensions  504  may extend from either side of plate portion  502  proximate to second end  41  of first endplate  14 . The front side extensions  504  may extend opposite from the upper surface  40  of plate portion  502 . In one embodiment, the first endplate  14  may further comprise rear side extensions  506  that extend from plate portion  502 . As illustrated, the rear side extensions  506  may extend from either side of plate portion  502  proximate to first end  39  of first endplate  14 . The rear side extensions  506  may extend opposite from the upper surface  40  of plate portion  502 . As illustrated, the front side extensions  504  and the rear side extensions  506  may each include ramped portions. For example, the front side extension  504  may include front ramped portions  508  and the rear side extensions  506  may include rear ramped portions  510 . The front ramped portions  508  and the rear ramped portions  510  may be considered ramped as they may be at an oblique angle with respect to longitudinal axis  512  of expandable fusion device  10 . In an exemplary embodiment, the front ramped portions  508  may generally face the second end  41 , and the rear ramped portions  510  may generally face the first end  39 . 
     Embodiments of actuator assembly  200  will now be described in more detail with reference to  FIG. 58 . In the illustrated embodiment, the actuator assembly  200  is in the form of a drive screw. As illustrated, the actuator assembly  200  may include a head portion  324  and an extension  404 . 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  may have a larger diameter than the other components of the actuator assembly  200  to provide a contact surface with the body  500 . In the illustrated embodiment, ring  514  may ride in groove  516  on head portion  324 . In some embodiments, ring  514  may be a compressible ring, such as a c-ring as shown on  FIG. 58 , that is configured to retain head portion  324  in rear throughbore  536  of body  500 . In an embodiment, the extension  404  is a generally rod-like extension that may be threaded for engaging a corresponding opening  522  in driving ramp  300 . In another embodiment, the extension  404  may include ratchet teeth (not shown) for engaging opening  522  in driving ramp  300 . 
     Embodiments of driving ramp  300  will now be described in more detail with respect to  FIG. 58 . As illustrated, the driving ramp  300  may include a ramped body portion  518  and an extension  520 . In the illustrated embodiment, extension  520  may extend from ramped body portion  518  toward first end  39  of expandable fusion device  10 . Extension  520  may include an opening  522  that may engage extension  404  of actuator assembly  200 . In embodiments, extension  520  may threadingly engage the extension  404  of actuator assembly  200 . Rotation of driving ramp  300  may be limited so that when actuator assembly  200  may be rotated, driving ramp  300  may be pulled toward body  500 . Driving ramp  300  may be secured to actuator assembly  200  at a front end of expandable fusion device  10 . In embodiments, the front end of expandable fusion device  10  may be the front of the expandable fusion device  10  so that the driving ramp  300  may be considered the nose of the expandable fusion device  10 . In embodiments, the front end  524  of driving ramp  300  may be angled, rounded, or otherwise tapered so that the driving ramp may serve to distract the adjacent vertebral bodies when the expandable fusion device  10  is inserted into an intervertebral space. 
     As illustrated, driving ramp  300  may include front endplate engaging ramps  526 . Front endplate engaging ramps  526  may be at an oblique angle with respect to longitudinal axis  512  of the expandable fusion device  10 . As illustrated, a pair of front endplate engaging ramps  526  that engage second endplate  16  may be on one side of driving ramp while another pair of front endplate engaging ramps  526  that engage first endplate  14  may be on an opposite side of driving ramp  300 . In operation, front endplate engaging ramps  526  may engage front ramped portions  508  of the first and second endplates  14 ,  16 . The first and second endplates  14 ,  16  may ride up the front endplate engaging ramps  526  as the driving ramp  300  may be pulled towards the body  300  causing the first and second endplates  14 ,  16  to be pushed relatively apart such that a height of expandable fusion device  10  may be increased. 
     Embodiments of body  500  will now be described in more detail with respect to  FIG. 58 . As illustrated, the body  500  may have a first body end  528  and a second body end  530 . Lateral sides  532  may connect the first body end  528  and the second body end  530 . In the illustrated embodiment, the body  500  may have a central opening  534  that may extend through the body  500  transverse to longitudinal axis  512  of expandable fusion device. As illustrated, first body end  528 , second body end  530 , and lateral sides  532  may define central opening  534 . Rear throughbore  536  may be formed through second body end  530 . Rear throughbore  536  may be centrally positioned and generally aligned with longitudinal axis  512  of expandable fusion device  10 . As previously described, head portion  324  of actuator assembly  200  may be retained in rear throughbore  536 , for example, using ring  514 . Washer  515  may also be retained on corresponding grooves of head portion  324 . Rear throughbore  506  may also be threaded, for example, to facilitate engagement with an insertion device. Second body end  530  may also include tool engaging features, such as side recesses  538 , which may facilitate use of a device for insertion of expandable fusion device  10  into a desired position in a patient. First body end  528  may include a corresponding front throughbore  540 . As illustrated, front throughbore  540  may be centrally positioned and generally aligned with longitudinal axis  512  of expandable fusion device. Extension  404  of actuator assembly  200  may extend through front throughbore  540  to engage driving ramp  300 . 
     As illustrated, second body end  530  may include rear endplate engaging ramps  542 . Rear endplate engaging ramps  542  may be at an oblique angle with respect to longitudinal axis  512  of the expandable fusion device  10 . In operation, rear endplate engaging ramps  542  may engage rear ramped portions  510  of the first and second endplates  14 ,  16 . As illustrated, a pair of rear endplate engaging ramps  542  that engage second endplate  16  may be on one side of second body end  530  while another pair of rear endplate engaging ramps  542  (not seen on  FIG. 58 ) that engage first endplate  14  may be on an opposite side of second body  530 . The first and second endplates  14 ,  16  may ride up the rear endplate engaging ramps  542  as the driving ramp  300  may be pulled towards the body  300  causing the first and second endplates  14 ,  16  to be pushed relatively apart such that a height of expandable fusion device  10  may be increased. 
     As previously described, the expandable fusion device  10  shown on  FIG. 58  may first expand lordotically and then expand in parallel until full expansion of the expandable fusion device  10  may be reached. To achieve this lordotic expansion, the front ramped portions  508  and rear ramped potions  510  of the first and second endplates  14 ,  16  may be at a different angle with respect to longitudinal axis  512  than the front endplate engaging ramps  526  of the driving ramp  300  and the rear endplate engaging ramps  542  of the body  500 . This difference in angles may be present when the expandable fusion device  10  is in the unexpanded configuration. As the driving ramp  300  may be pulled back towards the body  500 , the position of the first and second endplates  14 ,  16  and/or the driving ramp  300  and the body  500  with respect to body  500  may change so that the difference in angles may be reduced and potentially approach zero as the first and second endplates  14 ,  16  are pushed outward. As this angle is being reduced, the rear portion of the expandable fusion device may be expanding causing a lordotic angle. When this angle is reduced (or reaches approximately zero), the first and second endplates  14 ,  16  may then expand in parallel with the first end  39  and second end  41  expanding at approximately the same height until the expandable fusion device  10  may reach its full height. The lordotic angle may be maintained while the first and second endplates  14 ,  16  expand in parallel. 
       FIGS. 59 to 61  illustrate the expandable fusion device  10  in the unexpanded configuration in accordance with present embodiments. As seen on  FIG. 60 , the expandable fusion device  10  may have a lordotic angle θ LA  of approximately 0° when unexpanded. By way of example, the first and second endplates  14 ,  16  may be generally aligned with longitudinal axis  512  of expandable fusion device  10 . In accordance with present embodiments, lordotic expansion of expandable fusion device  10  may be achieved by use of different in ramp angles with respect to longitudinal axis  512 . As best seen on  FIG. 59 , rear endplate engaging ramps  542  of the body  500  may have an angle α body  and rear ramped portions  510  of first and second endplates  14 ,  16  may have an angle α rearendplate . The front endplate engaging ramps  526  of the driving ramp  300  may have an angle α driving  ramp and the front ramped portions  508  of the first and second endplates  14 ,  16  may have an angle α frontendplate . These angles may be selected, for example, to provide a desired rate of height increase during expansion of expandable fusion device  10 . By way of example, the angles may each individually by selected, for example, from about 5° to about 85° and alternatively from about 35° to about 65°. However, as described above, embodiments may provide differences in these angles, for example, to drive the lordotic expansion. As best seen on  FIG. 59 , the difference between the angles α rearendplate  and α body  may be provided by Δ rear , and the difference between the angles α frontendplate  and α driving ramped  may be provided by Δ front . Δ rear  and Δ front  may be the same or different. By way of example, Δ rear  and Δ front  may each range from 1° to about 20° and, alternatively, from about 2° to about 5°. 
       FIGS. 62 to 64  illustrate the expandable fusion device  10  in a lordotic expanded configuration in accordance present embodiments. The expandable fusion device  10  may be expanded to provide a lordotic angle θ LA  of up to about 15° and, more particularly, of about 4° to about 10°. Lordotic angles θ LA  of up to 12° may be desired in certain applications, such as cervical, but other lordotic angles θ LA  may be desired in alternative applications. 
     To expand the expandable fusion device  10 , driving ramp  300  may be moved in a first direction with respect to body  500 . By way of example, driving ramp  300  may be pulled towards body  500 . In some embodiments, actuator assembly  200  (best seen on  FIG. 58 ) may be rotated to pull driving ramp  300  towards body  500 . As driving ramp  300  may be pulled towards body  500 , the driving ramp  300  and body  500  may engage the first and second endplates  14 ,  16 . By way of example, the front ramped portions  508  of the first and second endplates  14 ,  16  may engage the front endplate engaging ramps  526  of the driving ramp  300  and the rear ramped portions  510  of the first and second endplates  14 ,  16  may engage the rear endplate engaging ramps  542  of the body  500 . However, because of the difference in ramp angles (shown as Δ rear  and Δ front  on  FIG. 59 ), the first and second endplates  14 ,  16  may not ride up the front endplate engaging ramps  526  and the rear endplate engaging ramps  542  to increase the height of the expandable fusion device. Instead, in some embodiments, the first and second endplates  14 ,  16  may pivot at the contact point between the first and second endplates  14 ,  16  and the body  500  causing expansion of the endplates  14 ,  16  at the opposite end. As seen in  FIGS. 62-64 , this pivoting may result in expansion of the first and second endplates  14 ,  16  into an expanded lordotic configuration. As will be appreciated, pivoting of the first and second endplates  14 ,  16  may cause the angles α rearendplate  and α frontendplate  with respect to longitudinal axis  512  to change, thus reducing the difference in ramp angles Δrear, Δfront. When the difference in ramp angles Δ rear , Δ front  approaches 0° (e.g., within 0.5°, 0.1°, or less), lordotic expansion may stop, and expandable fusion device  10  may be in its lordotic expanded configuration. 
       FIGS. 65 to 67  illustrate expandable fusion device  10  in a fully expanded configuration, in accordance with present embodiments. In some embodiments, it may be desired to further expand the expandable fusion device  10  from the lordotic expanded configuration of  FIGS. 62-64 . By way of example, continued movement of driving ramp  300 , for example, translational movement towards body  500 , may cause further expansion of expandable fusion device  10 . This further expansion may be considered parallel expansion as both ends of the expandable fusion device  10  may expand at the same rate. Expansion may be continued, for example, until the expandable fusion device  10  has reached its fully expanded configuration or until a desired height of expandable fusion device  10  has been achieved. Expansion of expandable fusion device  10  may be limited by engagement of driving ramp  300  with body  500 . 
     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 , an 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  in the opposite direction may result in movement of the body  500  and the driving ramp  300  away from one another. As the body  500  and driving ramp  300  move away from one another, the endplates  14 ,  16  move inwardly into the unexpanded position. 
     Expanded heights of expandable fusion device  10  may typically range from 7 mm to 12 mm, but may be larger or smaller, including as small as 5 mm, and as large as 16 mm, although the size is dependent on the patient, and the joint into which the expandable fusion device  10  may be implanted. Expandable fusion device  10  may be implanted within any level of the spine, and may also be implanted in other joints of the body, including joints of the hand, wrist, elbow, shoulder, hip, knee, ankle, or foot. 
     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. 
     In some embodiments, an expandable fusion device can be provided whereby expansion is performed via a ratcheting mechanism. By providing a ratcheting mechanism, this advantageously provides for rapid, convenient, non-continuous expansion of the fusion device. 
       FIG. 68  is an exploded view of an expandable fusion device having a ratcheting mechanism in accordance with some embodiments. The expandable fusion device  600  comprises a first endplate  620 , a second endplate  630 , a body  610  positioned between the first endplate  620  and the second endplate  630 , a stem  660  and associated collar  670 , and a nose  680 . The stem  660  and associated collar  670  advantageously provide a non-continuous ratcheting mechanism to the expandable fusion device, whereby the expandable fusion device can alternatingly incrementally increase and then stop, until a desired expansion occurs. 
     The first endplate  620  comprises a lower endplate having a first end  622  and a second end  624 . The first end  622  comprises a pair of first end ramped portions  626   a ,  626   b . Each of these ramped portions  626   a ,  626   b  is configured to engage corresponding lower nose ramps  682   a ,  682   b  on the nose  680  to aid with expansion of the expandable fusion device. The second end  624  comprises a pair of second end ramped portions  628   a ,  628   b . Each of these ramped portions  628   a ,  628   b  is configured to engage corresponding rear lower ramps  616   a ,  616   b  on the body  610  to aid with expansion of the expandable fusion device. A first side portion  623  having a central ramp  627   a  and a second side portion  625  having a central ramp  627   b  are positioned between the first end  622  and the second end  624  of the first endplate  620 . Each of the central ramps  627   a ,  627   b  is configured to engage corresponding front lower ramps  615   a ,  615   b  (not visible) of the base  610  to aid with expansion of the expandable fusion device. The ramps of the first endplate  620  are formed along a perimeter that surrounds a central opening  629 . 
     The second endplate  630  comprises an upper endplate having a first end  632  and a second end  634 . The first end  632  comprises a pair of first end ramped portions  636   a ,  636   b . Each of these ramped portions  636   a ,  636   b  is configured to engage corresponding upper nose ramps  684   a ,  684   b  on the nose  680  to aid with expansion of the expandable fusion device. The second end  634  comprises a pair of second end ramped portions  638   a ,  638   b . Each of these ramped portions  638   a ,  638   b  is configured to engage corresponding rear upper ramps  618   a ,  618   b  on the body  610  to aid with expansion of the expandable fusion device. A first side portion  633  having a central ramp  637   a  and a second side portion  635  having a central ramp  637   b  are positioned between the first end  632  and the second end  634  of the second endplate  630 . Each of the central ramps  637   a ,  637   b  is configured to engage corresponding front upper ramps  617   a ,  617   b  of the base  610  to aid with expansion of the expandable fusion device. The ramps of the second endplate  630  are formed along a perimeter that surrounds a central opening  639 . 
     The body  610  comprises a front throughbore  612  and a rear throughbore  614 . The front throughbore  614  comprises an opening for receiving the collar  670 , and hence the stem  660 , therethrough. The rear throughbore  614  comprises an opening through which one or more tools (e.g., an expansion tool and a disengagement tool) can pass through, as shown in  FIGS. 78B and 78D . In some embodiments, the rear throughbore  614  is threaded to allow engagement by an insertion tool. In addition, the body  610  comprises one or more tool recesses  611  that can be engaged by an insertion tool to provide easy delivery of the implant into a surgical site. As shown in  FIG. 68  and discussed above, the body  610  comprises a number of angled surfaces or ramps that are configured to engage corresponding ramps on the first endplate  620  or second endplate  630 . As the ramps slide against one another, this causes expansion of the expandable fusion device. 
     The stem  660  and associated collar  670  form a ratcheting mechanism for causing expansion of the expandable fusion device. The stem  660  comprises a head  662  and a shaft  664 . The stem  660  (via its head  662 ) is receivable within the nose  680  of the implant, whereby it is capable of rotation. In some embodiments, rotation of the stem  660  causes the implant to be changed from a “locked” ratcheting configuration into a “disengaged” non-ratcheting configuration, as will be discussed further below. The head  662  of the stem  660  comprises one or more grooves or slots  668  for receiving one or more nose pins  690   a ,  690   b  that extend through the nose  680 . The shaft  664  of the stem  660  comprises an elongate body having an opening  663  for receiving an expansion tool  710  (shown in  FIG. 78C ) therethrough. The stem  660  further comprises ratchet teeth  665  that extend along a length of the shaft  664 . In addition, the stem  660  comprises one or more flat areas  667  that are positioned adjacent to the ratchet teeth  665 . In some embodiments, the stem  660  comprises a pair of flat areas  667  that are positioned 180 degrees apart from one another. In some embodiments, the stem  660  comprises a half ring portion  664  that is advantageously designed to hit against the body  610  at full expansion in order to prevent over expansion of the device. 
     The stem  660  is capable of two configurations. In a first “locked” configuration (shown in  FIG. 78D ), the ratchet teeth  665  of the stem  660  are engaged with corresponding ratchet recesses  675  of the collar  670 , thereby creating a ratcheting mechanism that provides for expansion of the implant  600 . In a second “disengaged” configuration (shown in  FIG. 78E ), the stem  660  is rotated such that the one or more flat areas  667  are positioned adjacent the ratchet recesses  675 , such that the ratcheting mechanism is not operable. In this second disengaged configuration, the stem  660  is capable of being pulled back, thereby causing contraction of the implant  600 . 
     The stem  660  is insertable through the collar  670 , whereby it is placed in either the “locked” ratcheting configuration or the “disengaged” non-ratcheting configuration. In some embodiments, the collar  670  comprises a C-shaped ring having inner ratchet recesses  675  formed along an inner wall. In some embodiments, the collar  670  is housed within the front throughbore  616  of the body  610 . In some embodiments, the collar  670  comprises a compressible C-ring type body that is capable of compression within the front throughbore  616 . In some embodiments, the collar  670  is not rotatable, and can be keyed into place to prevent rotation. Advantageously, the collar  670  can comprise a tab  679  that prevents rotation of the collar  670  within the body  610 . With the stem  660  attached to the collar  670 , a ratcheting mechanism is formed whereby an expansion tool  710  (shown in  FIG. 78C ) can extend through the collar  670  and into the stem  660  via the shaft opening  663 . The expansion tool  710  is capable of pulling or ratcheting the stem  660  in a direction towards the second ends of the first endplate  620  and second endplate  630 . As the stem  660  is operably connected to the nose  680 , the nose  680  is also drawn, thereby causing ramps of the first endplate  620  and second endplate  630  to slide up corresponding ramps of the body  610  and nose  680 . 
     The nose  680  comprises a throughhole  685  through which the head  662  of the stem  660  can extend therethrough. A pair of nose pins  682   a ,  682   b  can then extend through the nose  680  and into the head  662 , thereby retaining the stem  660  in the nose  680 . As noted above, the nose  680  comprises one or more upper nose ramps  684   a ,  684   b , which are configured to mate and engage corresponding ramps on the second endplate  630 . In addition, the nose  680  comprises one or more lower nose ramps  682   a ,  682   b , which are configured to mate and engage corresponding ramps on the first endplate  620 . 
       FIGS. 69A-69C  are side views of the expandable fusion device of  FIG. 68  in the process of expansion in accordance with some embodiments. In some embodiments, the expandable fusion device  600  is advantageously capable of expansion, and in particular, lordotic expansion. In some embodiments, the device  600  can begin in a contracted state, as shown in  FIG. 69A . Afterwards, by pulling the nose  680  via a ratcheting mechanism, the device  600  can expand and tip into lordosis, as shown in  FIG. 69B . Once the device  600  has achieved maximum lordosis, the device  600  can continue to expand in height in a parallel fashion, whereby both the anterior and posterior aspects expand at the same rate, until the implant  600  reaches a maximum expansion, as shown in  FIG. 69C . In other words, once the device  600  reaches a particular lordotic angle (as shown in  FIG. 69B ), the device  600  will maintain the lordotic angle throughout the expansion range until maximum expansion has been achieved, as shown in  FIG. 69C . More details on the expansion of the device  600  are provided with respect to  FIGS. 70A-72C . 
       FIGS. 70A-70C  are different views of the expandable fusion device of  FIG. 68  in a contracted state in accordance with some embodiments. From the contracted state, the device  600  is capable of first expanding and tipping into lordosis, and then expanding in a parallel fashion. The angle tipping is driven by a difference in ramp angle x that is seen between the first end ramped portions  636   a ,  636   b  of the second endplate  630  and the upper nose ramps  684   a ,  684   b  of the nose  680 . Similarly, the same difference in ramp angle x is also seen between the second end ramped portions  638   a ,  638   b  of the second endplate  630  and the rear upper ramps  618   a ,  618   b  of the body  610 . In other words, at the contracted height, the difference in angle x between the different ramps causes a gap  702  between the ramps, with a first end gap  702   a  formed closer to the first end of the second endplate  630  and a second end gap  702   b  formed closer to the second end of the second endplate  630 . The degree of the gap  702  will determine what lordosis the device will tip into upon expansion. For example, if the degree of the gap  702  is 4 degrees (e.g., x=4), the second endplate  630  will tip into 4 degrees of lordosis. As the same mechanism is provided for the first endplate  620 , the first endplate  620  will also tip into 4 degrees of lordosis, thereby providing an overall lordosis of 8 degrees once both endplates  620 ,  630  have been tipped. In some embodiments, the endplates  620 ,  630  themselves can have built-in lordosis. For example, if the built in lordosis of both endplates  620 ,  630  was 7 degrees inclusive, then the overall lordosis following expansion wherein x=4 is 15 degrees of lordosis. While the present embodiment shows an angle x difference of 4 degrees, the angle can be less or more, thereby resulting in less or more lordosis. 
       FIGS. 71A-71C  are different views of the expandable fusion device of  FIG. 68  in a tipped state without full expansion in accordance with some embodiments. To tip the expandable fusion device  600  into lordosis, the nose  680  is initially ratcheted or pulled back towards the body  610 , thereby causing the gaps x to close and the corresponding ramps to mate. The amount of lordosis will be pre-determined based on the initial ramp gap x. In the present embodiment, the expandable fusion device  600  has been tipped into a lordotic angle of 4 degrees for the second endplate  630  and 4 degrees for the first endplate  620 , thereby resulting in a total of 8 degrees of lordosis (as shown in  FIG. 71B ). One skilled in the art can appreciate that the total degree of lordosis can be less than or greater than 8 degrees, and that 8 degrees in just a representative example. 
       FIGS. 72A-72C  are different views of the expandable fusion device of  FIG. 68  in a fully expanded state in accordance with some embodiments. As the nose  680  is pulled back further the corresponding ramps of the device  600  are fully mated, the implant then begins to expand in overall height in a parallel fashion. In other words, the anterior and posterior aspects of the device  600  expand at the same rate. As this happens, the device maintains the same lordosis allowing the lordotic angle to be seen throughout the expansion range. For example, the degree of lordosis of the device  600  in the fully expanded state (as shown in  FIG. 72B ) is the same as the degree of lordosis of the device  600  after the endplates have been tipped (as shown in  FIG. 71B ). However, due to further parallel expansion, the height of the device  600  in the fully expanded state (as shown in  FIG. 72B ) is greater than the height of the device  600  after the endplates have been tipped (as shown in  FIG. 71B ). 
     The expandable fusion device  600  can advantageously be expanded via a ratcheting mechanism. More details regarding the ratcheting mechanism—in particular, the stem  660  and the collar  670 —will be provided with respect to  FIGS. 73-76 . 
       FIG. 73  is an upper view of the expandable fusion device of  FIG. 68  in accordance with some embodiments. From this view, one can see how collar  670  is housed in the body  610 , and how the stem  660  is received in the collar  670 . The stem  660  is further received in the nose  680 , such that as the stem is pulled back, the nose  680  can also be pulled back thereby causing ratcheted expansion of the device  600 . 
       FIG. 74  is an upper cross-sectional view of the expandable fusion device of  FIG. 68  in accordance with some embodiments. In this view, one can see how the stem  660  having ratchet teeth  665  is engaged with the collar  670  to create an expandable ratcheting mechanism. In some embodiments, the stem  660  comprises the “male” ratcheting feature, while the collar  670  comprises the “female” ratcheting feature. 
       FIG. 75  is a close up view of the ratcheting mechanism of the expandable fusion device of  FIG. 68  in accordance with some embodiments. This view shows the male ratchet of the stem  660  and the female ratchet of the collar  670  in more detail. As the stem  660  is pulled back, the collar  670  springs open like a C-ring and allows the ratchet teeth  665  of the stem  660  to advance to the next slot or recess  675  formed in the collar  670 . The stem  660  advantageously moves in increments through the collar  670 . These non-continuous increments drive height increases. In some embodiments, the height increases can increase in increments greater than 0.2 mm and 0.8 mm. In some embodiments, the height increases are in increments of approximately 0.5 mm. 
       FIG. 76  is a close up view of the ratchet teeth of the expandable fusion device of  FIG. 68  in accordance with some embodiments. Each of the ratchet teeth  665  comprises an inclusive angle  668   a  and a back angle  668   b . In some embodiments, the ratchet teeth  665  comprise an inclusive angle  668   a  of between 30 and 60 degrees, and in particular about 45 degrees. In some embodiments, the back angle  668   b  comprises between 2 and 8 degrees, and in particular about 5 degrees. Under load, the ratchet connection is pulled in the direction of disengagement. Advantageously, the purpose of the back angle  668   b  is to keep the stem  660  more engaged, especially in the back area when the device  600  is under load by pulling the collar  670  closer to the ratchet teeth  665  when pulled in the direction of disengagement. 
       FIG. 77  is a top perspective view of the expandable fusion device of  FIG. 68  in accordance with some embodiments. In this configuration, the fusion device  600  is capable of ratcheted expansion. In addition to providing ratcheted expansion, the device is also capable of collapse and contraction. To accommodate contraction, the device  600  advantageously provides ratchet teeth  665  on only a portion of the stem  660 , whereby the ratchet teeth  665  are separated by one or more flat areas  667 . In the particular embodiment, the device  600  includes two sets of ratchet teeth  665  each of which is adjacent two sets of flat areas  667 . These features allow a device to be converted between a “locked” configuration whereby ratcheting is enabled and a “disengaged” configuration whereby ratcheting is disabled. These features are discussed below with respect to  FIGS. 78A-78G . 
       FIGS. 78A-78G  are top perspective views of the expandable fusion device of  FIG. 68  transitioning from a locked configuration to a disengaged configuration in accordance with some embodiments.  FIG. 78A  shows an expandable fusion device in a “locked” configuration whereby the device is capable of ratcheted expansion. As shown in  FIG. 78A , the ratchet teeth  665  of the stem  660  are aligned and engaged with the ratchet recesses  675  of the collar  670 , thereby enabling ratcheted expansion. 
       FIG. 78B  shows the expandable fusion device with an expansion tool inserted therein. The expansion tool  710  is capable of engaging the stem  660  in the “locked” configuration, whereby the stem  660  (and hence the nose  680 ) is capable of being pulled back. As the stem  660  and nose  680  are drawn back, this causes incremental ratcheting expansion of the device  600  based on the design of the ratchet teeth. 
       FIG. 78C  shows the expandable fusion device when fully expanded. As shown in the figure, the stem  660  has been pulled further into the body  610 , thereby causing greater height expansion of the device. The fusion device  600  has a relatively higher height in  FIG. 78C  than in  FIG. 78B . Advantageously, the fusion device  600  can also be contracted by a surgeon if desired. 
       FIG. 78D  shows the expandable fusion device prior to contraction with the device still in a “locked” ratcheting configuration. To contract the device  600 , a disengagement tool  720  (separate from the expansion tool  710 ) is provided. The disengagement tool  720  comprises a shaft having a distal nub  730 . The disengagement tool  720  is advantageously designed to rotate the stem  660 , such that the device is changed from a “locked” ratchetable configuration to a “disengaged” unratchetable configuration, as discussed above. To rotate the stem  660 , the distal nub  730  of the disengagement tool  720  mates with a correspondingly shaped recess  669  in the stem  660 . With the disengagement tool  720  engaged with the stem  660 , the stem  660  can be rotated (e.g., 90 degrees), thereby converting the device into a disengaged configuration, as shown in  FIG. 78E . 
       FIG. 78E  shows the expandable fusion device in a “disengaged” non-ratchetable configuration. The stem  660  has been rotated such that its pair of flat areas  667  align and face the collar  670 . As such, the ratchet teeth  665  of the stem are no longer engaged with ratchet slots of the collar  670 , thereby allowing the stem  660  to be pushed forward to contract the device. 
       FIG. 78F  shows the expandable fusion device in a “disengaged” configuration whereby the device has been fully contracted. At this stage, the device  600  is the same height as it was prior to expansion. The device  600  is fully capable of expansion again. A surgeon simply needs to rotate the stem  660  in an opposite direction 90 degrees, such that the device is brought back into a “locked” ratcheting configuration. 
       FIG. 78G  shows the expandable fusion device whereby the device is brought back to a “locked” ratcheting configuration. By rotating the disengagement tool  720  in a reverse direction 90 degrees, this rotates the stem  660  whereby the ratchet teeth  665  are once again engaged with ratchet slots of the collar  670 . The fusion device  600  can once again be expanded via a ratcheting mechanism if desired. Advantageously, the expandable fusion devices described above are each capable of being inserted through a minimal incision, as the devices can maintain a minimal profile prior to expansion. 
     In posterior interbody fusion procedures, surgeons are required to consider a number of anatomical aspects when implanting a device. For example, surgeons must often consider the surrounding nerve roots and avoid disrupting them, or they may need to consider the size of the intervertebral disc being replaced. In many cases, a collapsed disc space is involved that requires surgical intervention to restore height. When the posterior margin of any disc is smaller than the anterior margin and when the disc is collapsed, the posterior margin is even smaller, making it very difficult to insert a device. The reduced posterior margin restricts the surgeon because they need the device to be small enough to be able to be fully implanted while at the same time being large enough to fill the anterior space and restore disc height. The expandable fusion device described in more detail below with respect to  FIGS. 79-89  provides the advantage of allowing the surgeon the insert the device at a collapsed height past the posterior margin while not disrupting the surrounding nerve roots. The device can subsequently be expanded in the anterior space to restore the disc height and provide an endplate to endplate fit. 
       FIG. 79  is an exploded view of an expandable fusion device having an expandable spacing mechanism in accordance with some embodiments. The expandable fusion device  722  comprises a first endplate  724 , a second endplate  726 , a body  728  positioned between the first endplate  724  and the second endplate  726 , a stem  730 , a middle (mid) ramp piece  732 , and two ramp pins  734 . The stem  730  and associated mid ramp piece  732  advantageously provide an expandable spacing mechanism to the expandable fusion device. The expandable fusion device can be expanded or contracted to achieve a desired expansion. 
     Although the following discussion relates to the first endplate  724 , it should be understood that it also equally applies to the second endplate  726 , as the second endplate  726  is substantially identical to the first endplate  724  in various embodiments of the present invention. It should be understood that, in one embodiment, the first endplate  724  is configured and dimensioned to interlock with the second endplate  726 . The first endplate  724  comprises a lower endplate having a first end  736  and a second end  738 . The first end  736  comprises a pair of first end ramped portions  740   a ,  740   b . Each of these ramped portions  740   a ,  740   b  is configured and dimensioned to engage corresponding lower ramps  742   a ,  742   b  of the front end  744  of the body  728  to aid with expansion of the expandable fusion device. 
     The second end  738  of the first endplate  724  comprises a pair of second end ramped portions  746   a ,  746   b . Each of these ramped portions  746   a ,  746   b  is configured and dimensioned to engage corresponding lower ramps  748   a ,  748   b  on the back end  750  of body  728  to aid with expansion of the expandable fusion device. The first endplate  724  also includes a third pair of mid ramps  752   a ,  752   b  that are positioned between the first end ramped portions  740   a ,  740   b  and second end ramped portions  746   a ,  746   b . It may be desirable for the mid ramps  752   a ,  752   b  to be configured and dimensioned to be positioned near the first end ramped portions  746   a ,  746   b , as shown in  FIG. 79 . Each of the mid ramps  752   a ,  752   b  is configured and dimensioned to engage corresponding lower ramps  754   a ,  754   b  ( 754   b  not visible) of the mid ramp piece  732  to aid with expansion of the expandable fusion device  722 . The mid ramp piece  732  may also include upper ramps  755   a ,  755   b  ( 755   b  not visible) that are configured and dimensioned to engage with corresponding mid ramps of the second endplate  726 . The ramps of the first endplate  724  are formed along a perimeter that surrounds a central opening  756 . 
     In one embodiment, the body  728  comprises a front throughbore  758  and rear throughbore  760 . The front throughbore  758  comprises an opening for receiving the stem  730  therethrough. The front throughbore  758  may include recesses, as described in more detail below. The rear throughbore  760  comprises an opening through which one or more tools (e.g., an expansion tool and a disengagement tool) can pass through, as discussed with respect to  FIGS. 78B and 78D  above. In some embodiments, the rear throughbore  760  is threaded to allow engagement by an insertion tool. As shown in  FIG. 79  and discussed above, the body  728  comprises at least one angled surface or ramps that are configured and dimensioned to engage corresponding ramps on the first endplate  724 , second endplate  726 , or mid ramp piece  732 . Sliding the ramps against one another causes the expansion of the expandable fusion device. 
     The mid ramp piece  732  may include at least one angled surface or ramp that is configured and dimensioned to engage corresponding ramps on the first endplate  724 , second endplate  726 , and/or the body  728 , as discussed above. The mid ramp piece  732  also includes a throughbore  762  that comprises an opening for receiving the stem  730  therethrough. In some embodiments the throughbore  762  may be threaded to allow it to be fixed to the mid ramp piece  732 . It is desirable for the stem  730  to be operable to rotate within the throughbore  762 . The mid ramp piece  732  may also include at least two openings  732  (one not visible) that are configured and dimensioned to receive a portion of each of the two ramp pins  734 . When the ramp pins  734  are inserted into the openings  732 , a portion of them extends outside the openings  764  of the mid ramp piece  732 . When the mid ramp piece  732  is inserted into the body  728 , the portion of the ramp pins  734  that extends outside of the openings  764  engages with slots  766  in the body  728 . The slots  766  may be configured and dimensioned on one or more interior surfaces of the body  728 . When engaged, the ramp pins  734  and slots  766  allow the mid ramp piece  732  to slide horizontally, or translate, within the body  728 . In one embodiment, the slots  766  may be configured and dimensioned in the body  728  so that they keep the mid ramp piece  732  on a centerline of the interior of the body  728 , as shown in  FIG. 79 . In an alternate embodiment, the ramp pins  734  may comprise protrusions that are configured and dimensioned as part of the mid ramp piece  732  to engage with the slots  766 . 
     According to one embodiment, the stem  730  and the mid ramp piece  732  form a mechanism for causing expansion of the expandable fusion device. The stem  730  comprises an elongate shaft that may include two portions. In one embodiment, the two portions of the shaft may have different diameters, although in other embodiments the shaft may have the same diameter throughout. In one embodiment, the first portion  768  of the shaft may be configured and dimensioned to be received in the throughbore  762  of the mid ramp piece  732 . In embodiments where the throughbore  762  is threaded, the first portion  768  has corresponding threads that allow it to matingly engage with the mid ramp piece  732 . As discussed above, it may be desirable for the first portion  768  to be operable to rotate a predetermined amount within the throughbore  762 . 
     A second portion  770  of the stem  730  includes grooves, e.g., teeth  772  configured and dimensioned along a portion of the length of the shaft, as shown in  FIG. 79 . One advantage of including grooves  772  is that, in some embodiments, rotation of the stem  730  causes the expandable fusion device to be changed from a “locked” configuration into a “disengaged” configuration, as will be discussed further below. At least part of the stem  730  comprises an elongate body that includes an opening  774  for receiving a tool, such as an expansion tool or the like, therethrough. In addition, the second portion  770  of the stem  730  comprises one or more flat areas  776  that are positioned adjacent to the teeth  772 . In some embodiments, the second portion  770  comprises a pair of flat areas  776  that are positioned about 180 degrees apart from one another. 
     According to one embodiment, the stem  730  is capable of two configurations. In a first “locked” configuration shown in  FIG. 80 , the teeth  772  of the stem  730  are engaged with corresponding recesses  778  of the front throughbore  758  of the body  728 , as circled in  FIG. 80 . In a second “disengaged” configuration, shown in  FIG. 81 , the stem  730  is rotated such that the one or more flat areas  776  are positioned adjacent the recesses  778  of the front throughbore  758 , such that movement of the stem  730  within the throughbore  758  is possible. In this second disengaged configuration, the stem  730  may move back and forth within the throughbore  758 , causing expansion or contraction of the expandable fusion device, as described in more detail below. 
       FIGS. 82A-82C  are side views of the expandable fusion device  722  of  FIG. 79  in the process of expansion in accordance with some embodiments. In one embodiment, the expandable fusion device  722  is advantageously operable to expand and, in particular, lordotically expand. According to one embodiment, the device  722  may begin in a contracted state, as shown in  FIG. 82A . When the stem  730  is rotated to the released position, the mid ramp piece  732  may be pushed towards the front end of the first endplate  724  and second endplate  726 , as shown in  FIG. 82B . When the expandable fusion device  722  expands, the endplates  724 ,  726  first tip into lordosis, as shown in  FIG. 82B . Once the fusion device  722  has achieved maximum lordosis, the device  722  can continue to expand in height in a parallel fashion, whereby both the anterior and posterior aspects expand at the same rate until the fusion device  722  reaches a maximum expansion, as shown in  FIG. 82C . In other words, once the device  722  reaches a particular lordotic angle (as shown in  FIG. 82B ), the device  722  will maintain the lordotic angle throughout the expansion range until maximum expansion has been achieved, as shown in  FIG. 82C . More details on the expansion of the device  722  are provided below. 
       FIGS. 83A-83C  are different views of the expandable fusion device of  FIG. 79  in a contracted state in accordance with one embodiment of the present invention. From the contracted state, the device  722  is operable to first expand and tip into lordosis, and then expand in a parallel fashion. In one embodiment, the angle tipping is generated by a difference in ramp angle x that is seen between the first end ramps  740   a ,  740   b  and the lower ramps  742   a ,  742   b  as well as between the mid ramps  752   a ,  752   b  and the lower ramps  754   a ,  754   b  of the mid ramp piece  732 . Similarly, the same difference in ramp angle x is seen between the corresponding ramped portions of the second endplate  726  and the body  728  and the mid ramp of the second endplate  726  and the mid ramp piece  732 . In other words, at the contracted height, the difference in angle x between the different ramps causes a first gap  780  between the body  728  and the first and second endplates  724 ,  726 , and a second gap  782  between the mid ramp piece  732  and the mid ramps  752   a ,  752   b  of the first and second endplates  724 ,  726 . 
     The degree of the gaps  780 ,  782  determines what lordosis the device will tip into upon expansion. For example, if the degree of the gaps  780 ,  782  is 4 degrees (e.g., x=4), the first endplate  724  will tip into 4 degrees of lordosis. As the same mechanism is provided for the second endplate  726 , the second endplate  726  will also tip into 4 degrees of lordosis, thereby providing an overall lordosis of 8 degrees once both endplates  724 ,  726  have been tipped if the endplates  724 ,  726  do not have any built-in lordosis, as shown in  FIG. 83B . In some embodiments, the endplates  724 ,  726  themselves can have built-in lordosis. For example, if the built-in lordosis of both endplates  724 ,  726  was 7 degrees inclusive, then the overall lordosis following expansion wherein x=4 is 15 degrees of lordosis. While the present embodiment shows an angle x difference of 4 degrees, the angle can be less or more, thereby resulting in less or more lordosis. 
       FIGS. 84A-84B  are different views of the expandable fusion device of  FIG. 79  in a tipped state without full expansion in accordance with one embodiment. To tip the expandable fusion device  722  into lordosis, the mid ramp piece  732  may be pushed forwards towards the front end  744  of the body  728 . In this manner, the first gap  780  and second gap  782  will close, thereby causing the gaps x to close to zero degrees and the corresponding ramps to mate, as shown in  FIG. 84A . The amount of lordosis will be predetermined based on the first gap  780  and the second gap  782 . For example, if the ramp angle difference is 4 degrees for each endplate  724 ,  726  in one embodiment, the total lordosis is 8 degrees once the endplates are tipped, as shown in  FIG. 84B . One skilled in the art can appreciate that the total degree of lordosis can be less than or greater than 8 degrees, and that 8 degrees in just a representative example. 
     Another way to describe the lordotic and parallel expansion of the expandable fusion device of  FIG. 79  is with respect to the movement of the mid ramp piece  732 . In other words, the mid ramp piece  732 , and therefore the stem  730 , may begin in a fully contracted state, with no lordosis or parallel expansion (assuming zero lordosis of the endplates  724 ,  726 ). When the mid ramp piece  732  is pushed towards the front end  744  of the body  728  by a first predetermined amount from the fully contracted state, it will engage the ramps and cause the first gap  780  and second gap  782  to close, as shown in  FIG. 84A . As the mid ramp piece  732 , and therefore the stem  730  continue to move towards the front end  744  of the body  728  by a second predetermined amount, each endplate  724 ,  726  will continue to expand away from one another in parallel, as described further with respect to  FIGS. 85A-85C , until fully expanded. 
     In one embodiment, for instance, the first predetermined amount may be 3 mm while the second predetermined amount may be an additional 3 mm, for a total of 6 mm. In this example, the first predetermined amount may also be represented as a range between 0.5 mm and 3 mm, for instance, and the second predetermined amount may be represented as a range between 3.5 mm and 6 mm, assuming that the increments of the teeth are 0.5 mm increments, as described below. In other words, lordotic movement of each endplate  724 ,  726 , will occur as the mid ramp piece  732 , and therefore the stem  730 , is moved up to 3 mm and the first gap  780  and second pag  782  are closed. After 3 mm, the first gap  780  and second gap  782  are closed, resulting in parallel movement of each endplate  724 ,  726 . Similarly, if the mid ramp piece  732 , and therefore the stem  730  is then moved away from the front throughbore  758  near the front end  744  of the body  728 , the endplates  724 ,  726  will move towards one another in parallel between 6 mm and 3 mm. When the mid ramp piece  732 , and therefore the stem  730  is moved away from the front throughbore  758  near the front end  744  of the body  728  between 3 mm and 0 mm (the fully contracted state), the endplates  724 ,  726  will reduce their lordosis until there is zero lordosis, as shown in  FIG. 83B . 
       FIGS. 85A-85C  are different views of the expandable fusion device of  FIG. 79  in a fully expanded state according to one embodiment of the present invention. As the mid ramp piece  732  is pushed further towards the front end  744  of the body  728  and the corresponding ramps are fully mated, the fusion device  722  will begin to expand in overall height in a parallel fashion. In other words, the anterior and posterior aspects of the device  722  may expand at the same rate. As this happens, the device maintains the same lordosis, allowing the lordotic angle to be maintained throughout the expansion range. For example, the degree of lordosis of the device  722  in the fully expanded state, as shown in  FIG. 85B , is the same as the degree of lordosis of the device  722  after the endplates have been tipped, shown in  FIG. 84B . However, due to further parallel expansion, the height of the device  722  in the fully expanded state (as shown in  FIG. 85B ) is greater than the height of the device  722  after the endplates have been tipped (as shown in  FIG. 84B ). 
       FIGS. 86-87  show alternative views of the fusion device  722  in the locked position. In one embodiment, the expandable fusion device  722  comprises a disengaged and a locked position, as described above with respect to  FIG. 80 . According to this embodiment, the fusion device  722  is operable to expand or collapse in the disengaged position and is not capable of movement when in the locked position. The device  722  may start in the locked position when the stem  730  engages with the body  728 , as shown in the top down view in  FIG. 86  and the cross-sectional view through the middle of the device  722  in  FIG. 87 . The locked connection is circled in  FIG. 87  for illustrative purposes. 
     When the user is ready to expand the fusion device  722 , the stem  730  is turned, for example, clockwise by 90 degrees, putting the device  722  in the disengaged position with no teeth  772  engaged, as shown in  FIG. 81 . Once in the released position, the user may drive the device  722  up (expanded) and down (contracted) as desired.  FIG. 88  shows the stem&#39;s  730  position as the device is expanding (as compared with the stem&#39;s  730  position in  FIG. 81 ). The stem  730  advantageously moves continuously through the front throughbore  758 , in one embodiment, when in the disengaged position. The teeth  772  of the stem  730  (circled in  FIG. 80 ) may be configured and dimensioned to drive the overall height requirements of the fusion device  722 . For instance, the teeth  722  may be configured and dimensioned with 0.5 mm height increments. In this embodiment, the tooth  722  profile may be substantially similar to a M3.5×0.45 thread profile, except that the cuts are not helical like threads but spherical like grooves. The 0.45 mm “pitch” may comprise the increment that drives the overall height expansion discussed above. These non-continuous increments drive height increases. In some embodiments, the height increases can increase in increments between about 0.2 mm and about 0.8 mm. In other embodiments, the height increases are in increments of approximately 0.5 mm. 
     When the user is satisfied with the magnitude of expansion of the fusion device  722 , the stem  730  may be turned, for example, counterclockwise by 90 degrees such that the teeth  772  of the stem  730  engage with the recesses  778  in the front throughbore  758  of the body  728 , locking the implant as shown in  FIG. 89 . Any expansion tool known to those skilled in the art may be used to engage with the stem  730 , such as the tool described with respect to  FIGS. 78B and 78C . Advantageously, the expandable fusion devices described above are each capable of being inserted through a minimal incision, as the devices can maintain a minimal profile prior to expansion. 
     The disclosure 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 various embodiments are described separately herein for the purposes of facilitating their descriptions, those skilled in the art will understand that various aspects of each embodiment may be combined with other embodiments as desired.