Patent Publication Number: US-9402739-B2

Title: Variable lordosis spacer and related methods of use

Description:
FIELD OF THE INVENTION 
     Various embodiments of the present disclosure relate generally to variable lordosis spacers and related systems and methods. More specifically, the present disclosure relates to devices, systems, and methods for correcting lordosis and/or other spinal abnormalities. 
     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. 
     Further, lordosis refers to a curvature of the spine, and in particular a curvature that is posteriorly concave. In certain patients, this curvature may, for example, be larger than desired. Traditional vertebral fusion procedures and devices do not adequately account for this curvature. As such, traditional devices do not properly align with adjacent vertebral bodies. To ensure proper fit of traditional devices, bone may be removed from the vertebral bodies, increasing procedure and healing time. 
     As such, there exists a need for a fusion device capable of being installed inside an intervertebral disc space at a minimum distraction height and for a fusion device that can maintain a normal distance between adjacent vertebral bodies when implanted. 
     SUMMARY OF THE DISCLOSURE 
     The present disclosure relates to embodiments of expandable fusion devices and related methods of use. 
     In one aspect, the present disclosure is directed to an expandable fusion device that may include a first endplate, and a second endplate. The expandable fusion device also may include a first ramp configured to mate with both the first and second endplates. The first ramp may be a wedge with an incline extending along a longitudinal axis of the expandable fusion device, and also may be a wedge having an incline extending along a lateral axis of the expandable fusion device. A second ramp may be configured to mate with both the first and second endplates. The first ramp may be a wedge having an incline extending along the longitudinal axis of the expandable fusion device, and also may be wedge having an incline extending along the lateral axis of the expandable fusion device. 
     Various examples of the present disclosure may include one or more of the following aspects: wherein the first and second endplates may each include at least one first mating feature configured to mate with at least one corresponding first mating feature disposed on the first ramp; wherein the at least one mating feature of the first and second endplates may be slidable with respect to the corresponding first mating feature disposed on the first ramp; wherein the first and second endplates may each include a second mating feature configured to mate with a corresponding second mating feature disposed on the first ramp; wherein the second mating feature and the corresponding second mating feature may each be C-shaped, V-shaped, or U-shaped; wherein the first and second endplates may each include a third mating feature configured to mate with a corresponding third mating feature disposed on the second ramp; wherein the third mating feature and the corresponding third mating feature may each be C-shaped, V-shaped, or U-shaped; wherein each of the first and second endplates may have an inner surface configured to mate with the first ramp, wherein the inner surface of each of the first and second endplates may be shaped as a concave curve, the concave curve being formed about a longitudinal axis of the expandable fusion device; wherein the expandable fusion device may be movable between a collapsed configuration and an expanded configuration; wherein the first ramp may be coupled to the second ramp by an actuating mechanism, and the expandable fusion device may be configured to transition from the collapsed configuration to the expanded configuration via actuation of the actuating mechanism to move the second ramp and the first ramp toward one another; wherein, in the expanded configuration, the expandable fusion device may be a wedge having an incline extending along the lateral axis of the expandable fusion device; and wherein the first and second endplates each may have an outer surface configured to contact a respective vertebral body, wherein each outer surface of the first and second endplates may have one or more of teeth, ridges, friction increasing elements, keels, or gripping or purchasing projections. 
     In another aspect, the present disclosure may be directed to an expandable fusion device. The expandable fusion device may include a first endplate and a second endplate, and both the first and second endplates may extend from a first side of the expandable fusion device to a second side of the expandable fusion device. The expandable fusion device also may include a first ramp and a second ramp. Both the first ramp and the second ramp may be configured to mate with both the first and second endplates, and both the first ramp and the second ramp may extend from the first side of the expandable fusion device to the second side of the expandable fusion device. At least one of the first and second sides of the expandable fusion device may pivotally expand about a pivot point. 
     Various examples of the present disclosure may include one or more of the following aspects: wherein both of the first and second sides of the expandable fusion device may pivotally expand about the same pivot point; wherein the same pivot point may be a point disposed outside of the expandable fusion device; wherein the pivot point may be disposed along the first side or between the first and second sides of the expandable fusion device; and wherein only the second side of the expandable fusion device may pivot about the pivot point. 
     In yet another aspect, the present disclosure may be directed to an expandable fusion device. The expandable fusion device may include a first endplate and a second endplate, and both the first and second endplates may extend from a first side of the expandable fusion device to a second side of the expandable fusion device. The expandable fusion device also may include a first ramp and a second ramp, and both the first ramp and the second ramp may be configured to mate with both the first and second endplates, and both the first ramp and the second ramp may extend from the first side of the expandable fusion device to the second side of the expandable fusion device. The first and second side of the expandable fusion device may form concentric arcs about a pivot point. 
     Various examples of the present disclosure may include one or more of the following aspects: wherein the expandable fusion device may be movable between a collapsed configuration and an expanded configuration, and both of the first and second sides of the expandable fusion device may have same angular rate of change when moving between the collapsed configuration and the expanded configuration; and wherein the first side of the expandable fusion device may be defined by a first radius, the second side of the expandable fusion device may be defined by a second radius, and the first radius may be smaller than the second radius. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various exemplary embodiments and together with the description, serve to explain the principles of the disclosed embodiments. 
         FIG. 1  is a side view of an embodiment of an expandable fusion device shown between adjacent lordotic vertebrae according to the present disclosure. 
         FIG. 2  is a longitudinal side view of an embodiment of an expandable fusion device in a first configuration according to the present disclosure. 
         FIG. 3  is a lateral side view of the expandable fusion device of  FIG. 2 . 
         FIG. 4  is a cross-sectional view of the expandable fusion device of  FIG. 2  taken along line  4 - 4 . 
         FIG. 5  depicts the expandable fusion device of  FIG. 2  in a second configuration. 
         FIG. 6  is a lateral side view of the expandable fusion device of  FIG. 5 . 
         FIG. 7  is a cross-sectional view of the expandable fusion device of  FIG. 5  taken along line  7 - 7 . 
         FIG. 8  is a side view of the expandable fusion device of  FIG. 2  in the first configuration, showing a pivot point. 
         FIG. 9  is a side view of the expandable fusion device of  FIG. 2  in the second configuration, showing the pivot point of  FIG. 8 . 
         FIG. 10  is a perspective view of the expandable fusion device of  FIG. 2 . 
         FIG. 11  is an exploded view of the expandable fusion device of  FIG. 2 . 
         FIG. 12  is another exploded view of the expandable fusion device of  FIG. 2 . 
         FIG. 13  is a lateral side view of an endplate incorporated into the expandable fusion device of  FIG. 12 . 
         FIG. 14  is a top view of the endplate of  FIG. 13 . 
         FIG. 15  is a longitudinal side view of the endplate of  FIG. 13 . 
         FIG. 16  is a perspective view of a first ramp incorporated into the expandable fusion device of  FIG. 12 . 
         FIG. 17  is a lateral side view of the first ramp of  FIG. 16 . 
         FIG. 18  is a lateral side view of a second ramp incorporated into the expandable fusion device of  FIG. 12 . 
         FIG. 19  is a cross-sectional view of an expandable fusion device according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     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. Referring to  FIG. 1 , an expandable fusion device  10  is shown between adjacent vertebral bodies  2  and  3 . Expandable fusion device  10  may extend from a first side  22  (e.g., a posterior side) to a second side  24  (e.g., an anterior side). Expandable fusion device  10  may engage the endplates of adjacent vertebral bodies  2  and  3  and, in an installed position, maintain normal intervertebral disc spacing and restore spinal stability, thereby facilitating an intervertebral fusion. In some embodiments, expandable fusion device  10  may provide indirect decompression (e.g., by reducing the pressure of vertebral bodies  2  and  3  on adjacent nerves) while still providing lordosis correction. Expandable fusion device  10  may be formed from any suitable material or combination of materials, including, but not limited to, titanium, stainless steel, titanium alloys, non-titanium metallic alloys, polymeric materials, plastics, plastic composites, PEEK, ceramic, and elastic materials, among others. 
     In an embodiment, the expandable fusion device  10  may be configured and sized to be placed down an insertion tube and into the disc space between the adjacent vertebral bodies  2  and  3 . For example, expandable fusion device  10  may be configured for insertion through an insertion tube, such as, e.g., a cannula. It should be noted, however, that the insertion tube may alternatively have any suitable diameter. In one embodiment, expandable fusion device  10  may be inserted through a cannula having a diameter of about 8.5 mm. In some embodiments, the expandable fusion device  10  may have a width in a range of from about 8 mm to about 26 mm, and a length in a range from about 20 mm to about 65 mm, or may have other suitable dimensions. Expandable fusion device  10  may be inserted into a patient via a direct lateral procedure, although anterior, anterolateral, posterolateral or posterior procedures alternatively may be utilized. 
     Expandable fusion device  10  may be generally wedge shaped, and may have a height that increases from first side  22  toward second side  24 . In some embodiments, the expandable fusion device  10  may be expanded to a height that is equal to or greater than about 150% of its initial height. In one embodiment, the expandable fusion device  10  may be expanded to a height that is equal to or greater than about 200% of its initial height, or another suitable percentage of its initial height. 
     As shown in  FIG. 10 , expandable fusion device  10  may include one or more openings  26  to accommodate bone growth along the longitudinal length of the expandable fusion device  10 . In some embodiments, openings  26  may have the same dimensions, or may alternatively have different dimensions. In the embodiment shown, expandable fusion device  10  has two openings  26 , although other suitable numbers and dimensions of openings are also contemplated. Openings  26  may be sufficiently large to facilitate bone growth after installation of expandable fusion device  10  between vertebral bodies  2  and  3 . 
     In an exemplary embodiment, bone graft or similar bone growth inducing material may be introduced around and within the expandable fusion device  10  to further promote and facilitate the intervertebral fusion. The expandable fusion device  10 , in one embodiment, may be packed with bone graft (e.g., autograft or allograft) or similar bone growth inducing material to promote the growth of bone through and around the expandable fusion device  10 . The bone graft may be packed between the endplates of the adjacent vertebral bodies prior to, subsequent to, or during implantation of the fusion device. 
     In one embodiment, expandable fusion device  10  may be treated with a titanium and/or hydroxyapatite plasma spray coating to encourage bony on-growth, improving the strength and stability of the connection between the respective component and the underlying bone (e.g., a vertebral body). Any other suitable coating also may be provided on expandable fusion device  10 . Such coatings may include therapeutic agents, if desired. Expandable fusion device  10  also may include radiopaque markings to facilitate in vivo visualization. In some embodiments, portions of expandable fusion device  10  may be formed of a radiolucent material, while other portions of expandable fusion device  10  may be formed of radiopaque materials to facilitate imaging of the radiopaque portions of expandable fusion device  10 , such as, e.g., actuating mechanisms, endplates, ramps, or the like. 
     With reference to  FIGS. 2-12 , an embodiment of the expandable fusion device  10  is shown. In an exemplary embodiment, the expandable fusion device  10  may include a first endplate  14 , a second endplate  16 , a first ramp  18 , and a second ramp  20 . Expandable fusion device  10  may be movable between a collapsed configuration shown in  FIGS. 2-4 and 8 , and an expanded configuration shown in  FIGS. 5-7 and 9 . The ability of expandable fusion device  10  to reciprocally move between the collapsed and expanded configurations may provide numerous benefits. For example, because expandable fusion device  10  can be inserted between the vertebral bodies  2  and  3  in a collapsed configuration that is smaller than the expanded configuration, the large impaction forces needed to install traditional fusion devices are not required to install expandable fusion device  10 . In one embodiment, expandable fusion device  10  may be in a lordotic state in the collapsed configuration, although other suitable configurations, such as, e.g., parallel or other starting angles, are also contemplated. 
     Expandable fusion device  10  may expand and collapse about a set pivot point P, shown in  FIGS. 8 and 9 . Expandable fusion device  10  may be constructed to alter the position of pivot point P. That is, first ramp  18 , second ramp  20 , and endplates  14 ,  16  may be constructed to exhibit a curvature (e.g., may have a radius of curvature) about pivot point P, as further described below. In the collapsed configuration shown in  FIGS. 2-4 and 8 , expandable fusion device  10  may maintain an angle α (shown only in  FIG. 8 ) with respect to pivot point P. In the expanded configuration shown in  FIGS. 5-7 and 9 , expandable fusion device  10  may maintain an angle β (shown only in  FIG. 9 ) with respect to pivot point P. The construction of expandable fusion device  10  also may select the rate of change between angles α and β in the transition of expandable fusion device  10  between the collapsed and expanded configurations. In some embodiments, expandable fusion device  10  may experience a linear increase in the lordotic angle during the transition from the collapsed configuration to the expanded configuration (i.e., through an expansion range). In some embodiments, expandable fusion device  10  may be constructed to set pivot point P closer to the expandable fusion device  10  (or even within the perimeter of expandable fusion device  10 ). As pivot point P moves toward expandable fusion device  10  (or further toward a midline  204  shown in  FIGS. 8 and 9 ), the rate of angle change per height change exhibited by expandable fusion device  10  may increase. Because second side  24  has a larger distance from Pivot point P than first side  22 , second side  24  may increase in height faster than first side  22  in the transition of expandable fusion device  10  from the collapsed configuration to the expanded configuration. Thus, expandable fusion device  10  may be constructed in various configurations to set different α and β angles (i.e., different ramp angles on the anterior and posterior sides of expandable fusion device  10 ). 
     The position of pivot point P may be dependent or independent upon the inclination of expandable fusion device  10  between first side  22  and second side  24 . That is, as the difference in height between first side  22  and second side  24  increases, pivot point P may be set closer to expandable fusion device  10 , or even within the perimeter of expandable fusion device  10 . Thus, as pivot point P is set closer to expandable fusion device  10  (or further toward midline  204 ), angles α and β may become larger. On the contrary, as the pivot point P is set further from expandable fusion device  10 , a smaller rate of angle change per height change, and smaller α and β angles will be present in expandable fusion device  10 . 
     In one embodiment, α may be about 10.4°, β may be about 22.5°, and a distance d between pivot point P and first side  22 , may be about 17 mm although other suitable values are also contemplated. 
     First and second sides  22 ,  24  or expandable fusion device  10  may thus be formed as arcs (e.g., concentric arcs) about pivot point P. In the collapsed configuration, first side  22  may be oriented at angle α with respect to pivot point P, and may have a radius r pc . In the collapsed configuration, second side  24  also may be oriented at angle α with respect to pivot point P, but may have a radius r ac  that is larger than radius r pc , as second side  24  may be oriented at a further distance from pivot point P than first side  22 . In the expanded configuration, first and second sides  22 ,  24  of expandable fusion device  10  may expand at a substantially similar angular rate, and may both become oriented at angle β with respect to pivot point P. In the expanded configuration, first side  22  may have a radius r pc  that is constant with radius r pc . 
     The curvatures of first ramp  18 , second ramp  20 , and endplates  14 ,  16 , may determine the location of pivot point P. As shown in  FIGS. 8 and 9 , the curvatures of first ramp  18 , second ramp  20 , and endplates  14 ,  16  may cause first and second sides  22 ,  24  of expandable fusion device  10  to be curved about pivot point P to form portions of the aforementioned concentric arcs. The curvature of first and second sides  22 ,  24 , may set the distance of pivot point P from first and second sides  22 ,  24 . That is, if expandable fusion device  10  is constructed so as to position pivot point P relatively farther from first and second sides  22 ,  24 , each of first and second sides  22 ,  24  may have shallower curvatures. On the contrary, if expandable fusion device  10  is constructed so as to position pivot point P relatively closer to first and second sides  22 ,  24  (or even between first and second sides  22 ,  24 ), each of first and second sides  22 ,  24  may have steeper curvature. 
     Referring to  FIGS. 11 and 12 , endplates  14 ,  16  may have a first end  30  and a second end  32 . In the illustrated embodiment, the endplates  14 ,  16  may include an outer surface  40  connecting the first end  30  and the second end  32 , and an inner surface  42  connecting the first end  30  and the second end  32 . Outer surface  40  and inner surface  42  may both be defined by first and second ends  30 ,  32 , and by a first side  44  and a second side  45 . First side  44  of endplates  14 ,  16  may be disposed at first side  22  of expandable fusion device  10 . Similarly, second side  45  of endplates  14 ,  16  may be disposed at second side  24  of expandable fusion device  10 . First and second sides  44 ,  45  may define a plurality of mating features configured to engage with one or more mating features of first ramp  18  and second ramp  20 . In one embodiment, both first and second sides  44 ,  45  may extend from inner surface  42 . Second side  45  may extend further from inner surface  42  than first side  44 . 
     First side  44  may include a mating feature  46  at first end  30 , at least one mating feature  47  at an intermediate portion, and a mating feature  48  at second end  32 . 
     Mating feature  46  may be substantially C-shaped, V-shaped, U-shaped, or otherwise suitably shaped. In the embodiment shown, mating feature  46  may form a slidable joint with a corresponding mating feature (e.g., one of mating features  77  or  146  described in further detail below). The slidable joint may be, e.g., a tabled splice joint, or another suitable joint. That is, mating feature  46  and its corresponding mating feature  77  or  146  may be similarly shaped to have a groove disposed between two shoulders. One shoulder of mating feature  46  may slide within the groove of the corresponding mating feature  77  or  146 , while one shoulder of the corresponding mating feature  77  or  146  may slide within the groove of mating feature  46 . In some embodiments, It should be understood that mating feature  46  and its corresponding mating feature  77  or  146  may be formed in any other suitable manner. For example, mating feature  46  and its corresponding mating feature  77  or  146  may form another splice joint, a tongue and groove joint, another suitable joint, or be related to each other in another suitable manner. In some embodiments, mating feature  46  and its corresponding mating feature  77  or  146  may be slidable and/or interlocking with one another. In some embodiments, mating feature  46  may be inclined along longitudinal axis  200  from first end  30  of endplates  14 ,  16  toward an intermediate portion of endplates  14 ,  16 . 
     In the embodiment shown by  FIGS. 11 and 12 , mating features  47  are shown as defining inwardly facing recesses or grooves. The recesses of mating features  47  may accept a protrusion or tongue of a corresponding mating feature (e.g., mating features  84  and  86  described in further detail below). Thus, mating features  47  and its corresponding mating features  84  or  86  may form a tongue and groove joint. That is, the tongue of the corresponding mating feature  84  or  86  may be slidable within the groove of mating feature  47 . It is also contemplated that mating feature  47  and its corresponding mating feature  84  or  86  may form another type of joint, such as, e.g., a splice joint, another suitable joint, or be related to each other in another suitable manner. In some embodiments, mating features  47  and their corresponding mating features  84  or  86  may be slidably interlocking with one another. In some embodiments, mating features  47  may be inclined along longitudinal axis  200  from a respective intermediate portion of endplates  14 ,  16  toward first end  30  of endplates  14 ,  16 . Thus, the inclinations of mating feature  46  and mating features  47  may generally oppose one another. Alternatively, mating features  47  may be inclined in any other suitable direction, such as, e.g., from a respective intermediate portion of endplates  14 ,  16  toward second end  32  of endplates  14 ,  16 . 
     Mating feature  48  and its corresponding mating feature (e.g., mating features  78  and  148  described in further detail below) may be substantially similar to mating feature  46  described above. In some embodiments, mating feature  48  may be inclined along longitudinal axis  200  from second end  32  of endplates  14 ,  16  toward an intermediate portion of endplates  14 ,  16 . Thus, the inclinations of mating features  46  and  48  may oppose one another, but the inclinations of mating features  47  and  48  may be generally aligned (e.g., substantially parallel). 
     Second side  45  may include a mating feature  49  at first end  30 , at least one mating feature  50  at an inner (or intermediate) portion, and a mating feature  51  at second end  32 . Mating feature  49  may be similar to mating feature  46  described above, except that mating feature  49  may have different (e.g., larger) dimensions than mating feature  46 . Similar to mating feature  46 , mating feature  49  may be inclined along longitudinal axis  200  from first end  30  of endplates  14 ,  16  toward an intermediate portion of endplates  14 ,  16 . 
     Mating features  50  may be similar to mating features  47 , except that mating features  50  may have different (e.g., larger) dimensions than mating features  47 . Similar to mating features  47 , mating features  50  may be inclined along longitudinal axis  200  from a respective intermediate portion of endplates  14 ,  16  toward first end  30  of endplates  14 ,  16 . Thus, the inclinations of mating feature  49  and mating features  50  may generally oppose one another. Alternatively, mating features  50  may be inclined in any other suitable direction, such as, e.g., from a respective intermediate portion of endplates  14 ,  16  toward second end  32  of endplates  14 ,  16 . 
     Mating feature  51  may be substantially similar to mating feature  46  described above. However, in some embodiments, mating feature  51  may have different (e.g., larger) dimensions than mating feature  46 . Similar to mating feature  46 , mating feature  51  may be inclined along a longitudinal axis  200  (referring to  FIG. 10 ) from second end  32  of endplates  14 ,  16  toward an intermediate portion of endplates  14 ,  16 . Thus, the inclinations of mating features  46  and  48  may oppose one another, but the inclinations of mating features  50  and  51  may be generally aligned (e.g., substantially parallel). 
     Mating features  46 - 51  may be configured to mate with a corresponding mating feature on one of first and second ramps  18  and  20  in a slidable and/or interlocking relationship. 
     Outer surface  40  and/or inner surface  42  may be curved about one or more axes. For example, outer surface  40  and/or inner surface  42  may be curved about longitudinal axis  200 . Thus, in one embodiment, outer surface  40  may be convex, while inner surface  42  may be concave about the longitudinal axis  200 . In some embodiments, material can be added to or removed from outer surface  40  to modify the interaction between outer surface  40  and vertebral bodies  2  and  3 . For example, material can be added to give outer surface  40  a generally flat configuration while maintaining the concavity of inner surface  42 . 
     The respective mating features of endplates  14 ,  16  may be curved in order to impart a curvature to first and second sides  22 ,  24  of assembled expandable fusion device  10  as set forth above. As best seen in  FIG. 13 , first and second sides  44  and  45  may be curved (e.g., may have a radius of curvature) about pivot point P, and thus mating features  46 - 51  that are disposed in one of first and second sides  44 ,  45  may be similarly curved with respect to pivot point P. 
     In some embodiments, the outer surface  40  of endplates  14 ,  16  may be flat and generally planar to allow the outer surface  40  engage with an adjacent vertebral body. Alternatively, the outer surface  40  may be curved convexly or concavely to allow for a greater or lesser degree of engagement with the adjacent vertebral body. It is also contemplated that the outer surface  40  may be generally planar but include a generally straight ramped surface or a curved ramped surface. The ramped surface may allow for engagement with the adjacent vertebral body in a further lordotic fashion. In one embodiment, the outer surface  40  may include texturing to aid in gripping the adjacent vertebral bodies. Although not limited to the following, the texturing may include teeth, ridges, friction increasing elements, keels, or gripping or purchasing projections. 
     Referring now to  FIGS. 11, 12, and 16 , the first ramp  18  may have a first end  70 , a second end  72 , a first side portion  74  connecting the first end  70  and the second end  72 , and a second side portion  76  on the opposing side of the first ramp  18  connecting the first end  70  and the second end  72 . The first ramp  18  may further include a third end (e.g., an upper end)  28 , which is sized to receive at least a portion of the first endplate  14 , and an fourth end (e.g., a lower end)  29 , which is sized to receive at least a portion of the second endplate  16 . 
     The first end  70  of the first ramp  18 , in an exemplary embodiment, may include four mating features  77 ,  78 ,  80 , and  82  (mating feature  82  shown only in  FIG. 16 ). Each of mating features  77 ,  78 ,  80 ,  82  may be shaped to mate with a respective mating feature disposed on one of endplates  14 ,  16 . Mating feature  77  may be configured to mate with, and may be similarly shaped as mating feature  46  of endplate  14 . Mating feature  78  may be configured to mate with, and may be similarly shaped as mating feature  48  of endplate  16 . Mating feature  80  may be configured to mate with, and may be similarly shaped as mating feature  49  of endplate  14 . Mating feature  82  may be configured to mate with, and may be similarly shaped as mating feature  51  of endplate  16 . Each of mating features  77 ,  78 ,  80 , and  82  may have substantially similar inclinations (with respect to an assembled expandable fusion device  10 ) their respective and corresponding mating features set forth above. In one embodiment, each of mating features  77 ,  78 ,  80 , and  82  are inclined from an intermediate portion of first ramp  18  toward first end  70  of first ramp  18 , although other suitable configurations are also contemplated. In one embodiment, mating features  77  and  78  extend from third end  28 , while mating features  78  and  82  extend from fourth end  29 . 
     First side portion  74  may include mating features  84  and  86  that are configured to mate with various mating features of endplates  14 ,  16 . 
     Mating features  84  may be protrusions extending from an intermediate portion of first side portion  74  toward first end  70 . In one embodiment, mating features  84  may have a surface that is inclined from the intermediate portion of first side portion  74  toward first end  70 . The inclined surface of mating features  84  also may extend laterally outward from first side portion  74 . Mating features  84  also may extend from third end  28  of first ramp  18 . The inclined surface of mating features  84  may extend toward a generally flattened surface that is substantially parallel to longitudinal axis  200  of expandable fusion device  10 . In one embodiment, first ramp  18  may include at least two mating features  84  that are staggered along first side portion  74 , although other suitable numbers of mating features  84  may alternatively be utilized. In the embodiment shown, mating features  84  are substantially similar to one another, although it is contemplated that mating features  84  may be different than one another. Mating features  84  may be configured to mate with mating features  47  of endplate  14 . In the embodiment shown in  FIGS. 11 and 12 , mating features  47  and  84  may form a slidable and interlocking (e.g., a tongue and groove) joint that allows expandable fusion device  10  to move between the collapsed and expanded configurations. However, it is contemplated that mating features  47  and  84  may be modified to other suitable configurations that allow expandable fusion device  10  to move between the collapsed and expanded configurations. For example, in one alternative embodiment, mating features  47  may be formed as protrusions, while mating features  84  are formed as recesses. In another alternative embodiment, each of mating features  47  and  84  may be formed as grooves disposed between two shoulders such that mating features  47  and  84  form a splice joint (e.g., similar to the tabled splice joints described above). 
     Mating features  86  may be protrusions extending from an intermediate portion of first side portion  74  toward first end  70 . In one embodiment, mating features  86  may have a surface that is inclined from the intermediate portion of first side portion  74  toward first end  70 . The inclined surface of mating features  86  also may extend laterally outward from first side portion  74 . Unlike mating features  84 , mating features  86  may extend from fourth end  29  of first ramp  18 . Thus, mating features  84  and  86  may extend in generally opposite vertical directions from first side portion  74 . The inclined surface of mating features  86  may extend toward a generally flattened surface that is substantially parallel to longitudinal axis  200  of expandable fusion device  10 . In one embodiment, first ramp  18  may include at least two mating features  86  that are staggered along first side portion  74 , although other suitable numbers of mating features  86  may alternatively be utilized. In some embodiments, each of mating features  84  and  86  may be staggered from one another, although other suitable configurations are also contemplated. In the embodiment shown, mating features  86  are substantially similar to one another, although it is contemplated that mating features  86  may be different than one another. Mating features  86  may be configured to mate with mating features  47  of endplate  16 . In the embodiment shown in  FIGS. 11 and 12 , mating features  47  and  86  may form a slidable and interlocking (e.g., a tongue and groove) joint that allows expandable fusion device  10  to move between the collapsed and expanded configurations. However, it is contemplated that mating features  47  and  86  may be modified to other suitable configurations that allow expandable fusion device  10  to move between the collapsed and expanded configurations (e.g., in a substantially similar manner as described above with reference to mating features  47  and  84 ). 
     Second side portion  76  may include mating features  88  and  90  that are configured to mate with various mating features of endplates  14 ,  16 . 
     Mating features  88  may be protrusions extending from an intermediate portion of second side portion  76  toward first end  70 . In one embodiment, mating features  88  may have a surface that is inclined from the intermediate portion of second side portion  76  toward first end  70 . The inclined surface of mating features  88  also may extend laterally outward from second side portion  76 . Mating features  88  also may extend from third end  28  of first ramp  18 . The inclined surface of mating features  88  may extend toward a generally flattened surface that is substantially parallel to longitudinal axis  200  of expandable fusion device  10 . In one embodiment, first ramp  18  may include at least two mating features  88  that are staggered along second side portion  76 , although other suitable numbers of mating features  88  may alternatively be utilized. In the embodiment shown, mating features  88  are substantially similar to one another, although it is contemplated that mating features  88  may be different than one another. Mating features  88  may be configured to mate with mating features  50  of endplate  14 . In the embodiment shown in  FIGS. 11 and 12 , mating features  50  and  88  may form a slidable and interlocking (e.g., a tongue and groove) joint that allows expandable fusion device  10  to move between the collapsed and expanded configurations. However, it is contemplated that mating features  50  and  88  may be modified to other suitable configurations that allow expandable fusion device  10  to move between the collapsed and expanded configurations (e.g., in a substantially similar manner as described above with reference to mating features  47  and  84 ). 
     Mating features  90  may be protrusions extending from an intermediate portion of second side portion  76  toward first end  70 . In one embodiment, mating features  90  may have a surface that is inclined from the intermediate portion of second side portion  76  toward first end  70 . The inclined surface of mating features  90  also may extend laterally outward from second side portion  76 . Unlike mating features  88 , mating features  90  may extend from fourth end  29  of first ramp  18 . Thus, mating features  88  and  90  may extend in generally opposite vertical directions from second side portion  76 . The inclined surface of mating features  90  may extend toward a generally flattened surface that is substantially parallel to longitudinal axis  200  of expandable fusion device  10 . In one embodiment, first ramp  18  may include at least two mating features  90  that are staggered along second side portion  76 , although other suitable numbers of mating features  90  may alternatively be utilized. In some embodiments, each of mating features  88  and  90  may be staggered from one another, although other suitable configurations are also contemplated. In the embodiment shown, mating features  90  are substantially similar to one another, although it is contemplated that mating features  90  may be different than one another. Mating features  90  may be configured to mate with mating features  50  of endplate  16 . In the embodiment shown in  FIGS. 11 and 12 , mating features  50  and  90  may form a slidable and interlocking (e.g., a tongue and groove) joint that allows expandable fusion device  10  to move between the collapsed and expanded configurations. However, it is contemplated that mating features  50  and  90  may be modified to other suitable configurations that allow expandable fusion device  10  to move between the collapsed and expanded configurations (e.g., in a substantially similar manner as described above with reference to mating features  47  and  84 ). 
     The respective mating features of first ramp  18  may be curved in order to impart the curvature to first and second sides  22 ,  24  of assembled expandable fusion device  10  as set forth above. That is, the mating features of first ramp  18  may have a radius of curvature about pivot point P. Further, as the mating features of first ramp  18  may be complimentary to corresponding mating features along endplates  14 ,  16 , the mating features of endplates  14 ,  16  also may have a radius of curvature about pivot point P. Referring to  FIG. 17 , mating features  77 ,  78 ,  80 ,  82 ,  84 ,  86 ,  88 , and  90  may each have a radius of curvature about pivot point P. Thus, all or a portion of first ramp  18  may be bent about pivot point P. The geometry of first ramp  18  (e.g., any of the aforementioned radii of curvature) may be approximated with simpler features for manufacturing ease. 
     As shown in  FIG. 11 , first ramp  18  may include both a bore  418  and a bore  515 . In some embodiments, the bore  418  may be threaded and configured to receive a threaded member  302  of an actuating mechanism  300 . The central longitudinal axis of the bore  418  may be off-center from the central longitudinal axis of the first ramp  18  in order to accommodate the bore  515 . 
     The adjacent bore  515  may serve as an access port to allow graft material to be delivered through the first ramp  18 , either prior to insertion or even in situ, if desired. The bore  418  may align with a bore  366  in second ramp  20  and bore  515  may align with an additional bore  512  in the second ramp  20 , as discussed below. 
     Second ramp  20  may be disposed adjacent to first ramp  18  in expandable fusion device  10 . Second ramp  20  may include four mating features  146 ,  148 ,  149 , and  151 . Each of mating features  146 ,  148 ,  149 , and  151  may be substantially similar to mating feature  46  described above, and may be configured to mate with a respective mating feature disposed on one of endplates  14 ,  16 . Mating feature  146  may be configured to mate with mating feature  46  of endplate  16 . Mating feature  148  may be configured to mate with mating feature  48  of endplate  14 . Mating feature  149  may be configured to mate with mating feature  49  of endplate  16 . Mating feature  151  may be configured to mate with mating feature  51  of endplate  14 . 
     The respective mating features of second ramp  20  may be curved in order to impart the curvature to first and second sides  22 ,  24  of assembled expandable fusion device  10  as set forth above. Further, as the mating features of second ramp  20  may have a radius of curvature about pivot point P, the mating features of endplates  14 ,  16  also may have a radius of curvature about pivot point P. Mating features  146 ,  148 ,  149 , and  151  may be all curved about pivot point P. Thus, all or a portion of second ramp  20  may be bent about pivot point P. The geometry of second ramp  20  (e.g., any of the aforementioned radii of curvature) may be approximated with simpler features for manufacturing ease. 
     In one alternative embodiment, expandable fusion device  10  may be formed so as to locate pivot point P within lateral width of the expandable fusion device  10  along first side  22  of expandable fusion device  10 . In this alternative embodiment, all mating features (e.g., tracks, protrusions, grooves, shoulders, and the like) disposed along first side  22  of expandable fusion device  10  (e.g., along endplates  14 ,  16 , and first and second ramps  18  and  20 ) may be replaced by linkage or pivoting mechanisms. When pivot point P is located within lateral width of the expandable fusion device  10  along first side  22  of expandable fusion device  10 , only second side  24  may pivot about pivot point P during expansion and collapse of expandable fusion device  10 . 
     As described above, the second ramp  20  may include a bore  366  adjacent bore  512 . The bore  366  may be configured to receive an actuating mechanism  300  therethrough, and may be aligned with the bore  418  in the first ramp  18 . Accordingly, the bore  366  may have a central longitudinal axis that is off-set from the central longitudinal axis of the second ramp  20  to accommodate the adjacent bore  512 . The bore  512  of the second ramp  20  may be aligned with the bore  515  of the first ramp  18  to allow graft material to be inserted into the implant, either prior to or even after insertion of the implant. 
     First and second ramps  18  and  20  may each be a wedge having an incline extending in at least two planes. That is, each of first and second ramps  18  and  20  may be a wedge having an incline extending along a plane defined by longitudinal axis  200  (i.e., may be inclined along the longitudinal axis  200 ), while also being a wedge having an incline extending along a plane defined a lateral axis  202  (i.e., may be inclined along the lateral axis  202 ). The inclination of first and second ramps  18  and  20  (and their associated mating features) along the longitudinal axis  200  of expandable fusion device  10  may allow for the expansion/compression of endplates  14  and  16  as first and second ramps  18  and  20  translate with respect to one another along the longitudinal axis  200 . The inclination of first and second ramps  18  and  20  along the lateral axis  202  of expandable fusion device  10  may accommodate the uneven lengths of first and second sides  44 ,  45  of endplates  14 ,  16 . 
     A method of installing the expandable fusion device  10  of  FIG. 1  is now discussed in accordance with one embodiment of the present disclosure. Prior to insertion of the expandable fusion device  10 , the intervertebral space may be prepared. In one method of installation, a discectomy may be performed where the intervertebral disc, in its entirety, may be removed. Alternatively, only a portion of the intervertebral disc can be removed. The endplates of the adjacent vertebral bodies  2 ,  3  may be then scraped to create an exposed end surface for facilitating bone growth across the intervertebral space. One or more introduction sheaths then can be inserted into the disc space. The expandable fusion device  10  can then be introduced into the intervertebral space down an insertion sheath and seated in an appropriate position in the intervertebral disc space. 
     After the expandable fusion device  10  has been inserted into the appropriate position in the intervertebral disc space, the expandable fusion device  10  can then be transitioned from the collapsed configuration to the expanded configuration. To expand the expandable fusion device  10 , the second ramp  20  may be moved toward the first ramp  18 . As the first and second ramps  18  and  20  move toward one another, the respective mating features of first and second ramps  18  and  20  may push against corresponding mating features disposed on endplates  14  and  16  to move expandable fusion device  10  into the expanded configuration. In some embodiments, one or more of endplates  14 ,  16 , and first and second ramps  18 ,  20  may include locking features for securing expandable fusion device  10  in the expanded configuration. 
     In the event the expandable fusion device  10  needs to be repositioned or revised after being installed and expanded, the expandable fusion device  10  can be contracted back to the collapsed configuration, repositioned, and expanded again once the desired positioning is achieved. To contract the expandable fusion device  10 , the first ramp  18  is moved away from the second ramp  20  via the actuating mechanism  300 . 
     Actuating mechanism  300  may include any suitable actuating mechanism configured to translate first and second ramps  18  and  20  toward and away from each other along the longitudinal axis  200 . Referring to  FIGS. 4 and 7 , actuating mechanism  300  may include a threaded member  302  (e.g., a screw) that, when rotated in a first direction, directs first and second ramps  18  and  20  toward each other, moving expandable fusion device  10  from the collapsed configuration to the expanded configuration. When threaded member  202  is rotated in a second direction that is opposite to the first direction, first and second ramps  18  and  20  may be moved away from each other, causing expandable fusion device  10  to move back toward the collapsed configuration. In one embodiment, threaded member  302  may be partially disposed through bore  515  of first ramp  18 , and may further extend through bore  515  as expandable fusion device  10  is moved from the collapsed configuration to the expanded configuration. In this embodiment, threaded member  302  may push second ramp  20  toward first ramp  18 , and may move coextensively with second ramp  20  during the transition of expandable fusion device  10  from the collapsed configuration to the expanded configuration, and from the expanded configuration to the collapsed configuration. 
     In an alternative embodiment shown in  FIG. 19 , threaded member  302  may be at least partially disposed within bore  515  in the collapsed configuration. However, to transition from the collapsed configuration to the expanded configuration, threaded member  302  may be actuated through second ramp  20 . Unlike the embodiment shown in  FIGS. 4 and 7 , in the embodiment of  FIG. 19 , threaded member  302  may pull first ramp  18  toward second ramp  20 , and may move coextensively with first ramp  18  during the transition of expandable fusion device  10  from the collapsed configuration to the expanded configuration, and from the expanded configuration to the collapsed configuration. Any other suitable actuating mechanism may utilized, such as, e.g., sliders, pushers, ratchets, or the like. 
     In some embodiments, threaded member  302  may be rotated directly to actuate the actuating mechanism  300 . In some embodiments, an inserter (not shown) may be configured to thread into or be otherwise coupled to threaded member  302 . In such embodiments, the inserter may be actuated by suitable mechanisms (e.g., tools, ratchets, or the like) to rotate threaded member  302  and adjust the relative position of the first and second ramps  18  and  20 . 
     In some embodiments, only one of bores  366  and  418  may be threaded, such that expandable fusion device  10  may be actuated by linear movement of actuating mechanism  300 . For example, in one embodiment, bore  366  may be threaded while bore  418  may not be threaded. In such an embodiment, threaded member  302  may be threaded into bore  366 , and may be slidable through bore  418 . After threaded member  302  is threaded through bore  366 , threaded member  302  can be selectively pushed through bore  418  to move expandable fusion device  10  from the collapsed configuration to the expanded configuration (e.g., by moving first ramp  18  and second ramp  20  closer to one another). Additionally, threaded member  302  may be pulled in the opposite direction to move expandable fusion device  10  from the collapsed configuration to the expanded configuration (e.g., by moving first ramp  18  and second ramp  20  away from one another). In this embodiment, second ramp  20  may be pushed toward first ramp  18  to move expandable fusion device  10  from the collapsed configuration to the expanded configuration. 
     In an alternative embodiment, bore  418  may be threaded and bore  366  may not be threaded. In such an embodiment, threaded member  302  may be disposed through bore  366  and threaded into bore  418  (e.g., referring to  FIG. 19 ). Threaded member  302  may be pulled linearly to move expandable fusion device  10  from the collapsed configuration to the expanded configuration (e.g., by moving first ramp  18  and second ramp  20  closer to one another). Additionally, threaded member  302  may be pushed to move expandable fusion device  10  from the expanded configuration back to the collapsed configuration (e.g., by moving first ramp  18  and second ramp  20  away from one another). In this embodiment, first ramp  18  may be pulled toward second ramp  20  to move expandable fusion device  10  from the collapsed configuration to the expanded configuration. 
     In one embodiment, a locking member (e.g., a screw not shown) may be disposed separately of expandable fusion device  10  during the transition between the collapsed and expanded configurations. Once the final position is achieved (e.g., the expanded configuration of expandable fusion device  10 ), the locking member may be advanced to lock expandable fusion device  10  into a desired configuration. In some embodiments, the locking member may be integral with expandable fusion device  10 , or may be alternatively introduced after expansion. In some embodiments, the locking member may be captured within the expandable fusion device  10  so that it is not lost. In some embodiments, peening the tip of the locking member may prevent the locking member from becoming lost. 
     Once expandable fusion device  10  has been moved to the expanded configuration and locked via the locking member, bores  366  and  418 , previously used to expand the expandable fusion device  10  via actuating mechanism  300  may be utilized to pack graft or other bone growth inducing substances into expandable fusion device  10 . That is, bores  366  and  418  may be utilized to pack graft into the expandable fusion device  10  to fill any potential gaps that formed during expansion of expandable fusion device  10 . 
     Any aspect set forth in any embodiment may be used with any other embodiment set forth herein. Every device and apparatus set forth herein may be used in a suitable medical procedure, such as, e.g., a vertebral disc replacement procedure, and may be advanced through any suitable body lumen and body cavity. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed systems and processes without departing from the scope of the disclosure. Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only. The following disclosure identifies some other exemplary embodiments.