Abstract:
Two or more expandable fusion devices are capable of being installed inside an intervertebral disc space. The devices may be implanted at varying heights to maintain disc spacing and restore spinal stability, thereby facilitating an intervertebral fusion. In one embodiment, two implants are implanted into the intervertebral disc space and then expanded or contracted to different heights.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. Patent Application Ser. No. 13/273,994 filed on Oct. 14, 2011, which is a continuation application of U.S. Patent Application Ser. No. 12/579,833 filed on Oct. 15, 2009, now U.S. Pat. No. 8,062,375. The content and subject matter of these applications are hereby incorporated by reference in their entireties, including all text and figures, for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the apparatus and method for promoting an intervertebral fusion, and more particularly relates to an expandable fusion device capable of being inserted between adjacent vertebrae to facilitate the fusion process. 
       BACKGROUND OF THE INVENTION 
       [0003]    A common procedure for handling pain associated with intervertebral discs that have become degenerated due to various factors such as trauma or aging is the use of intervertebral fusion devices fur fusing one or more adjacent vertebral bodies. Generally, to fuse the adjacent vertebral bodies, the intervertebral disc is first partially or fully removed. An intervertebral fusion device is then typically inserted between neighboring vertebrae to maintain normal disc spacing and restore spinal stability, thereby facilitating an intervertebral fusion. 
         [0004]    There are a number of known conventional fusion devices and methodologies in the art for accomplishing the intervertebral fusion. These include screw and rod arrangements, solid bone implants, and fusion devices which include a cage or other implant mechanism which, typically, is packed with bone and/or bone growth inducing substances. These devices are implanted between adjacent vertebral bodies in order to fuse the vertebral bodies together, alleviating the associated pain. 
         [0005]    However, there are drawbacks associated with the known conventional fusion devices and methodologies. For example, present methods for installing a conventional fusion device often require that the adjacent vertebral bodies be distracted to restore a diseased disc space to its normal or healthy height prior to implantation of the fusion device. In order to maintain this height once the fusion device is inserted, the fusion device is usually dimensioned larger in height than the initial distraction height. This difference in height can make it difficult for a surgeon to install the fusion device in the distracted intervertebral space. 
         [0006]    As such, there exists a need for a fusion device capable of being installed inside an intervertebral disc space at a minimum to no distraction height and for a fusion device that can maintain a normal distance between adjacent vertebral bodies when implanted. 
       SUMMARY OF THE INVENTION 
       [0007]    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 body portion, a first endplate, and a second endplate. The first and second endplates are capable of being moved in a direction away from the body portion into an expanded configuration or capable of being moved towards the body portion into an unexpanded configuration. The expandable fusion device is capable of being deployed and installed in the unexpanded configuration or the expanded configuration. 
         [0008]    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 DRAWING 
         [0009]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a side view of an embodiment of an expandable fusion device shown between adjacent vertebrae according to the present invention; 
           [0011]      FIG. 2  is an exploded view of the expandable fusion device of  FIG. 1 ; 
           [0012]      FIG. 3  is a front perspective view of the expandable fusion device of  FIG. 1  shown in an unexpanded position 
           [0013]      FIG. 4  is a front perspective view of the expandable fusion device of  FIG. 1  shown in an expanded position; 
           [0014]      FIG. 5  is a rear perspective view of the expandable fusion device of  FIG. 1  shown in an unexpanded position; 
           [0015]      FIG. 6  is a rear perspective view of the expandable fusion device of FIG. I shown in an expanded position; 
           [0016]      FIG. 7  is a side view of the expandable fusion device of  FIG. 1  shown in an unexpanded position; 
           [0017]      FIG. 8  is a side view of the expandable fusion device of  FIG. 1  shown in an expanded position; 
           [0018]      FIG. 9  is a top view of the expandable fusion device of  FIG. 1 ; 
           [0019]      FIG. 10 . is a side partial cross-sectional view of the expandable fusion device of  FIG. 1  shown in an unexpanded position; 
           [0020]      FIG. 11  is a side partial cross-sectional view of the expandable fusion device of  FIG. 1  shown in an expanded position; 
           [0021]      FIG. 12  is a side schematic view of the expandable fusion device of  FIG. 1  having different endplates; 
           [0022]      FIG. 13  is a partial side schematic view of the expandable fusion device of  FIG. 1  showing different modes of endplate expansion; and 
           [0023]      FIG. 14  is a side schematic view of the expandable fusion device of  FIG. 1  with artificial endplates shown between adjacent vertebrae. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    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. 
         [0025]    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. 
         [0026]    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. 
         [0027]    With reference to  FIG. 2 , an exploded perspective view of one embodiment of the fusion device  10  is shown. In an exemplary embodiment, the fusion device  10  includes a body portion  12 , a first endplate  14 , a second endplate  16 , a translation member  18 , a plurality of pins  20 , an actuation member  22 , and a locking mechanism  24 . 
         [0028]    With additional reference to  FIGS. 3-8 , in an exemplary embodiment, the body portion  12  has a first end  26 , a second end  28 , a first side portion  30  connecting the first end  26  and the second end  28 , and a second side portion  32  connecting the first end  26  and the second end  28 . The body portion  12  further includes an upper end  34 , which is sized to receive at least a portion of the first endplate  14 , and a lower end  36 , which is sized to receive at least a portion of the second endplate  16 . 
         [0029]    The first end  26  of the fusion device  10 , in an exemplary embodiment, includes at least one angled surface  38 , but can include multiple angled surfaces. The angled surface can serve to distract the adjacent vertebral bodies when the fusion device  10  is inserted into an intervertebral space. In another preferred embodiment, it is contemplated that there are at least two opposing angled surfaces forming a generally wedge shaped to distract the adjacent vertebral bodies when the fusion device  10  is inserted into an intervertebral space. 
         [0030]    The second end  28  of the body portion  12 , in an exemplary embodiment, includes an opening  40  which may include threading. In another exemplary embodiment, the opening  40  may include ratchet teeth instead of threading. The opening  40  extends from the second end  28  of the body portion  12  into a central opening  42  in the body portion  12 . In one embodiment, the central opening  42  is sized to receive the translation member  18  and the opening  40  is sized to threadingly receive the actuation member  22 . In another exemplary embodiment, the opening  40  is sized to receive the actuation member  22  in a ratcheting fashion. In yet another exemplary embodiment, first side portion  30  and second side portion  32  each include a recess  44  located towards the second end  28  of the body portion  12 . The recess  44  is configured and dimensioned to receive an insertion instrument (not shown) that assists in the insertion of the fusion device  10  into an intervertebral space. 
         [0031]    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 . Turning now to  FIGS. 2-11 , in an exemplary embodiment, the first endplate  14  has an upper surface  46 , a lower surface  48 , and a through opening  49 . The through opening  49 , 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  42  in the body portion  12 . 
         [0032]    In one embodiment, the lower surface  48  includes at least one extension  50  extending along at least a portion of the lower surface  48 . As best seen in  FIGS. 2 and 4 , in an exemplary embodiment, the extension  50  can extend along a substantial portion of the lower surface  48 , including, along each side of the endplate  14  and along the front end of the endplate  14 . In another exemplary embodiment, the extension  50  includes at least one slot  52 , but can include any number of slots  52 , including two sets of slots  52  opposing each other, as best seen in  FIG. 2 . The slots  52  are configured and dimensioned to receive pins  20  and are oriented in an oblique fashion. In another embodiment, the slots  52  may be oriented in a generally vertical orientation. 
         [0033]    In an exemplary embodiment, the extension  50  is sized to be received within the central opening  42  of the body portion  12 . As best seen in  FIGS. 11-12 , the lower surface  48  of the first endplate  14  further includes, in an exemplary embodiment, at least one ramped surface  54 . In another exemplary embodiment, there are two spaced ramped surfaces  54 ,  56 . It is contemplated that the slope of the ramped surfaces  54 ,  56  can be equal or can differ from each other. The effect of varying the slopes of the ramped surfaces  54 ,  56  is discussed below. 
         [0034]    Referring now to  FIGS. 2-9 , in one embodiment, the upper surface  46  of the first endplate  14  is flat and generally planar to allow the upper surface  46  of the endplate  14  to engage with the adjacent vertebral body  2 . Alternatively, as shown in  FIG. 12 , the upper surface  46  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  46  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. Turning back to  FIGS. 2-9 , in an exemplary embodiment, the upper surface  46  includes texturing  58  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. 
         [0035]    With reference to FIGS.  2  and  10 - 11 , in an exemplary embodiment, the translation member  18  is sized to be received within the central opening  42  of the body portion  12  and includes at least a first expansion portion  60 . In another embodiment, the translation member  18  includes a first expansion portion  60  and a second expansion portion  62 , the expansion portions  60 ,  62  being connected together via a bridge portion  68 . It is also contemplated that there may be more than two expansion portions where each of the expansion portions is connected by a bridge portion. The expansion portions  60 ,  62  each have angled surfaces  64 ,  66  configured and dimensioned to engage the ramp surfaces  54 ,  56  of the first and second endplates  14 ,  16 . In an exemplary embodiment, the translation member  18  also includes recesses  70 ,  72 , the recesses  70 ,  72  are sized to receive and retain pins  20 . In one embodiment, the expansion portion  60  includes an opening  74 , which is sized to receive a portion of the actuation member  22 , and the expansion portion  62  includes a nose  76 , which is received within an opening  78  in the first end  26  to stabilize the translation member  18  in the central opening  42  of the body member  12 . 
         [0036]    In an exemplary embodiment, the actuation member  22  has a first end  80 , a second end  82  and threading  84  extending along at least a portion thereof from the first end  80  to the second end  82 . The threading  84  threadingly engages the threading extending along a portion of opening  40  in the body portion  12 . In another exemplary embodiment, the actuation member  22  includes ratchet teeth instead of threading. The ratchet teeth engage corresponding ratchet teeth in the opening  40  in the body portion  12 . The first end  80  includes a recess  86  dimensioned to receive an instrument (not shown) that is capable of advancing the actuation member  22  with respect to the body portion  12  of the fusion device  10 . The second end  82  of the actuation member  22  includes an extension  88  that is received within the opening  74  of the expansion portion  60 . In one embodiment, the extension  88  may include a plurality of slits and a lip portion. The plurality of slits allows the extension portion  88  to flex inwardly reducing its diameter when received in the opening  74 . Once the lip portion of the extension portion  88  is advanced beyond the end of the opening  74 , the extension portion  88  will return back to its original diameter and the lip portion will engage the expansion portion  60 . It is further contemplated that a pin member  90  can be included to prevent the extension portion from flexing inwardly thereby preventing the actuation member  22  from disengaging from the translation member  18 . 
         [0037]    In an exemplary embodiment, the fusion device  10  can further include a locking mechanism  24 . The mechanism  24  is designed to resist rotation of the actuation member  22  rather than prevent rotation of the actuation member  22 . In an exemplary embodiment, either deformable threading can be included on actuation member  22  or a disruption of the threading may be included where a deformable material is included in the threading disruption. It is contemplated that the deformable member or deformable threading can be made from a deformable or elastic, biocompatible material such as nitinol or PEEK. 
         [0038]    Turning now to  FIGS. 1-8  and  10 - 11 , a method of installing the expandable fusion device  10  is now discussed. Prior to insertion of the fusion device  10 , the intervertebral space is prepared. In one method of installation, a diskectomy 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 invertebral space. The expandable fusion device  10  is then introduced into the intervertebral space, with the first end  26  being inserted first into the disc space followed by the second end  28 . In an exemplary method, the fusion device  10  is in the unexpanded position when introduced into the intervertebral space. The wedged shaped first end  26  will assist in distracting the adjacent vertebral bodies  2 ,  3  if necessary. This allows for the option of having little to no distraction of the intervertebral space prior to the insertion of the fusion device  10 . In another exemplary method, the intervertebral space may be distracted prior to insertion of the fusion device  10 . The distraction provide 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. 
         [0039]    With the fusion device  10  inserted into and seated in the appropriate position in the intervertebral disc space, the fusion device can then expanded into the expanded position, as best seen in  FIGS. 1 ,  4 ,  6 ,  8 , and  11 . To expand the fusion device  10 , an instrument is engaged with recess  86  in the actuation member  22 . The instrument is used to rotate actuation member  22 . As discussed above, actuation member  22  is threadingly engaged body portion  12  and is engaged with translation member  18 ; thus, as the actuation member  22  is rotated in a first direction, the actuation member  22  and the translation member  18  move with respect to the body portion  12  toward the first end  26  of the body portion  12 . In another exemplary embodiment, the actuation member  22  is moved in a linear direction with the ratchet teeth engaging as means for controlling the movement of the actuation member  22  and the translation member  18 . As the translation member  18  moves, the ramped surface  64 ,  66  of the expansion portions  60 ,  62  push against the ramped surfaces  54 ,  56  of the endplates  14 ,  16  pushing endplates  14 ,  16  outwardly into the expanded position. This can best be seen in  FIGS. 10 and 11 . 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 actuation member  22 . As discussed above, the fusion device  10  includes a locking mechanism  24  which assists in retaining the endplates  14 ,  16  at the desired height. 
         [0040]    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  54 ,  56 ,  64 ,  66 . As best seen in  FIG. 13 , 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. 
         [0041]    Turning back to  FIGS. 1-8  and  10 - 11 , in the event the fusion device  10  needs to be repositioned or revised after being installed and expanded, the fusion device  10  can be contracted back to the unexpanded configuration, repositioned, and expanded again once the desired positioning is achieved. To contract the fusion device  10 , the instrument is engaged with recess  86  in the actuation member  22 . The instrument is used to rotate actuation member  22 . As discussed above, actuation member  22  is threadingly engaged body portion  12  and is engaged with translation member  18 ; thus, as the actuation member  22  is rotated in a second direction, opposite the first direction, the actuation member  22  and translation member  18  move with respect to the body portion  12  toward the second end  28  of the body portion  11  As the translation member  18  moves, the pins  20 , a portion of which are located within the slots  52 , ride along the slots  52  pulling the endplates  14 ,  16  inwardly into the unexpanded position. 
         [0042]    With reference now to  FIG. 14 , 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 . 
         [0043]    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 e fusion device  10  may vary from unexpanded to fully expanded. 
         [0044]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.