Abstract:
The present invention provides an expandable intervertebral implant, including: a superior member configured to engage a superior intervertebral body; an inferior member configured to engage an inferior intervertebral body; and an expansion mechanism disposed between the superior member and the inferior member configured to selectively adjust a separation of the superior member from the inferior member; wherein the expansion mechanism includes a proximal wedge structure and a distal wedge structure that are relatively translated between the superior member and the inferior member, wherein the proximal wedge structure and the distal wedge structure are each coupled to the superior member and the inferior member by a plurality of aligned and/or staggered (i.e. nested) track structures and rail structures.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    The present patent application/patent is a continuation-in-part (CIP) of co-pending U.S. patent application Ser. No. 12/974,511, filed on Dec. 21, 2010, and entitled “EXPANDABLE INTERVERTEBRAL IMPLANT AND ASSOCIATED SURGICAL METHOD,” which claims the benefit of priority of U.S. Provisional Patent Application No. 61/293,997, filed on Jan. 11, 2010, and entitled “EXPANDABLE INTERVERTEBRAL BODY STABILIZATION DEVICES AND ASSOCIATED SURGICAL METHODS” and U.S. Provisional Patent Application No. 61/296,932, filed on Jan. 21, 2010, and entitled “EXPANDABLE INTERVERTEBRAL BODY STABILIZATION DEVICES AND ASSOCIATED SURGICAL METHODS,” the contents of all of which are incorporated in full by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to minimally-invasive, surgically-implantable spinal devices and systems. More specifically, the present invention relates to an expandable intervertebral implant that is surgically implanted to, in-situ, distract, realign, and/or stabilize or fuse a portion of the spine of a patient in the treatment of injury, disease, and/or degenerative condition. Exemplary indications include, but are not limited to, spinal stenosis, degenerative disc disease with a loss of disc height, disc herniation, spondylolisthesis, retrolisthesis, and disogenic back pain. This expandable intervertebral implant may be surgically implanted via an open or, more preferably, a minimally-invasive surgical procedure. Advantageously, the expandable intervertebral implant has both a very small undeployed vertical cross-section and a very small undeployed horizontal footprint due to the use of superior and inferior members that nest against one another in a novel manner. 
       BACKGROUND OF THE INVENTION 
       [0003]    In various cases, it is desirable to restore the anatomic relationship between various vertebral elements, thereby re-establishing spinal stability, by means other than conventional monolithic and/or multi-piece interbody spacers. Typically, these devices require sizable working channels, soft tissue disruption, nerve root retraction, and significant bone resection, thereby increasing the resulting stress on other vertebral elements. Further, morbidities associated with these more-invasive procedures include, but are not limited to, greater blood loss, longer recovery, and increased risk of surgical site infection. 
         [0004]    In such cases, the use of an alternative intervertebral implant, especially one compatible with minimally-invasive surgical techniques, is desirable. An intervertebral implant that expands in-situ would allow implantation without the iatrogenic insult that is commonly associated with the implantation of conventional monolithic and/or multi-piece interbody spacers in a minimally-invasive manner. However, no such alternative devices or systems are currently available, at least not any that are adequate. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In various exemplary embodiments, the present invention provides an expandable intervertebral implant that is selectively disposed in the intervertebral space and deployed, thereby in-situ distracting, realigning, and/or stabilizing or fusing a portion of the spine of a patient in the treatment of injury, disease, and/or degenerative condition. The expandable intervertebral implant includes a superior member and an inferior member, each of which has a partially or substantially wedge or prismatic shape and a partially or substantially convex or other-shaped surface that is suitable for engaging the substantially concave surfaces of the associated bony superior and inferior intervertebral endplates. Optionally, the superior member and the inferior member are each thinner at the leading edge of the expandable intervertebral implant than they are at the trailing edge of the expandable intervertebral implant, such that insertion into the intervertebral space may be aided, although this is not a requirement and the expandable intervertebral implant may have a uniform thickness, when undeployed, from the leading edge to the trailing edge. For similar reasons, the leading edge of the both the superior member and the inferior member may have a knifed or rounded shape. Once disposed in the intervertebral space, the expandable intervertebral implant is actuated and deployed, with the superior member and the inferior member moving apart from one another, seating against the associated intervertebral endplates, and distracting, realigning, and/or stabilizing them to a desired degree. In order to ensure that the expandable intervertebral implant is held securely in the intervertebral space, the external surface of each of the superior member and the inferior member is provided with a plurality of ridges or other friction structures, providing purchase with the associated intervertebral endplates. 
         [0006]    When undeployed, the superior member and the inferior member are configured such that they nest against one another, thereby providing the undeployed expandable intervertebral implant with the smallest possible form factor for insertion through the skin and musculature of the patient and into the intervertebral space. In the exemplary embodiment provided, this is accomplished via the use of cut-away sections associated with the superior member and the inferior member, not unlike a tongue-in-groove joint assembly. The combined total height of the superior member and the inferior member when nested together in the undeployed state is less than the sum of the heights of the superior member and the inferior member individually. This is accomplished via a plurality of nesting ramp structures and/or other angled surfaces associated with the superior member and/or the inferior member that selectively cause distraction/separation of the superior member and the inferior member via interaction with a translating wedge structure. These various ramp structures are offset (i.e. staggered) in such a manner that the form factor of the expandable intervertebral implant is minimized when undeployed. 
         [0007]    In one exemplary embodiment, the present invention provides an expandable intervertebral implant, including: a superior member configured to engage a superior intervertebral body; an inferior member configured to engage an inferior intervertebral body; and an expansion mechanism disposed between the superior member and the inferior member configured to selectively adjust a separation of the superior member and the inferior member. The expansion mechanism includes a wedge structure that is translated between the superior member and the inferior member. The expansion mechanism also includes a screw that is coupled to the wedge structure and causes the wedge structure to translate when rotated. One or more of the superior member and the inferior member include a ramp structure on their opposed faces. Interaction of the wedge structure and the ramp structure of the one or more of the superior member and the inferior member as the wedge structure is translated causes adjustment of the separation of the superior member and the inferior member. The superior member is coupled to the inferior member through the wedge structure and the ramp structure of the one or more of the superior member and the inferior member. Optionally, the superior member is coupled to the inferior member via a track (i.e. channel) and rail system. The expansion mechanism disposed between the superior member and the inferior member may also be configured to selectively translate the superior member with respect to the inferior member. 
         [0008]    In another exemplary embodiment, the present invention provides an expandable intervertebral implant, including: a superior member configured to engage a superior intervertebral body; an inferior member configured to engage an inferior intervertebral body; and an expansion mechanism disposed between the superior member and the inferior member configured to selectively adjust a separation of the superior member and the inferior member, wherein the expansion mechanism includes a wedge structure that is translated between the superior member and the inferior member. The expansion mechanism also includes a screw that is coupled to the wedge structure and causes the wedge structure to translate when rotated. One or more of the superior member and the inferior member include a ramp structure on their opposed faces. Interaction of the wedge structure and the ramp structure of the one or more of the superior member and the inferior member as the wedge structure is translated causes adjustment of the separation of the superior member and the inferior member. The superior member is coupled to the inferior member through the wedge structure and the ramp structure of the one or more of the superior member and the inferior member. Optionally, the superior member is coupled to the inferior member via a track and rail system. The expansion mechanism disposed between the superior member and the inferior member may also be configured to selectively translate the superior member with respect to the inferior member. 
         [0009]    In a further exemplary embodiment, the present invention provides a spinal surgical method, including: providing an expandable intervertebral implant, including: a superior member configured to engage a superior intervertebral body; an inferior member configured to engage an inferior intervertebral body; and an expansion mechanism disposed between the superior member and the inferior member configured to selectively adjust a separation of the superior member and the inferior member; disposing the expandable intervertebral implant between the superior intervertebral body and the inferior intervertebral body; and selectively adjusting the separation of the superior member and the inferior member, thereby selectively adjusting a distraction of the superior intervertebral body from the inferior intervertebral body. The expansion mechanism includes a wedge structure that is translated between the superior member and the inferior member. The expansion mechanism also includes a screw that is coupled to the wedge structure and causes the wedge structure to translate when rotated. One or more of the superior member and the inferior member include a ramp structure on their opposed faces. Interaction of the wedge structure and the ramp structure of the one or more of the superior member and the inferior member as the wedge structure is translated causes adjustment of the separation of the superior member and the inferior member. The superior member is coupled to the inferior member through the wedge structure and the ramp structure of the one or more of the superior member and the inferior member. Optionally, the superior member is coupled to the inferior member via a track and rail system. The expansion mechanism disposed between the superior member and the inferior member may also be configured to selectively translate the superior member with respect to the inferior member. 
         [0010]    In a still further exemplary embodiment, the present invention provides an expandable intervertebral implant, including: a superior member configured to engage a superior intervertebral body; an inferior member configured to engage an inferior intervertebral body; and an expansion mechanism disposed between the superior member and the inferior member configured to selectively adjust a separation of the superior member from the inferior member; wherein the expansion mechanism includes a proximal wedge structure and a distal wedge structure that are relatively translated between the superior member and the inferior member, wherein the proximal wedge structure and the distal wedge structure are each coupled to the superior member and the inferior member by a plurality of track structures and rail structures. One or more track structures and rail structures associated with a top surface of the distal wedge structure are offset horizontally with respect to one or more track structures and rail structures associated with a bottom surface of the distal wedge structure. One or more track structures and rail structures associated with a top surface of the proximal wedge structure are aligned horizontally with respect to one or more track structures and rail structures associated with a bottom surface of the proximal wedge structure. The expansion mechanism also includes an actuation bolt that passes through the proximal wedge structure and is coupled to the distal wedge structure and causes the wedge structures to relatively translate when rotated. The superior member and the inferior member each include a plurality of ramp structures on their opposed faces. The superior member includes a ramp structure that engages the proximal wedge structure and a ramp structure that engages the distal wedge structure. The inferior member includes a ramp structure that engages the proximal wedge structure and a ramp structure that engages the distal wedge structure. The expandable intervertebral implant also includes a plurality of elongate arm structures protruding from the superior member and the inferior member and engaging a corresponding recess of the other component. 
         [0011]    In a still further exemplary embodiment, the present invention provides a surgical method including providing an expandable intervertebral implant, including: a superior member configured to engage a superior intervertebral body; an inferior member configured to engage an inferior intervertebral body; and an expansion mechanism disposed between the superior member and the inferior member configured to selectively adjust a separation of the superior member from the inferior member; wherein the expansion mechanism includes a proximal wedge structure and a distal wedge structure that are relatively translated between the superior member and the inferior member, wherein the proximal wedge structure and the distal wedge structure are each coupled to the superior member and the inferior member by a plurality of track structures and rail structures. One or more track structures and rail structures associated with a top surface of the distal wedge structure are offset (i.e. staggered) horizontally with respect to one or more track structures and rail structures associated with a bottom surface of the distal wedge structure. One or more track structures and rail structures associated with a top surface of the proximal wedge structure are aligned horizontally with respect to one or more track structures and rail structures associated with a bottom surface of the proximal wedge structure. Alternatively, one or more track structures and rail structures associated with a top surface of the proximal wedge structure are offset (i.e. staggered) horizontally with respect to one or more track structures and rail structures associated with a bottom surface of the proximal wedge structure. The expansion mechanism also includes an actuation bolt that passes through the proximal wedge structure and is coupled to the distal wedge structure and causes the wedge structures to relatively translate when rotated. The superior member and the inferior member each include a plurality of ramp structures on their opposed faces. The superior member includes a ramp structure that engages the proximal wedge structure and a ramp structure that engages the distal wedge structure. The inferior member includes a ramp structure that engages the proximal wedge structure and a ramp structure that engages the distal wedge structure. The expandable intervertebral implant also includes a plurality of elongate arm structures protruding from the superior member and the inferior member and engaging a corresponding recess of the other component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The expandable intervertebral implant of the present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like device components, as appropriate, and in which: 
           [0013]      FIG. 1  is a perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0014]      FIG. 2  is another perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0015]      FIG. 3  is a further perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0016]      FIG. 4  is a still further perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0017]      FIG. 5  is a planar end view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0018]      FIG. 6  is a still further perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0019]      FIG. 7  is another planar end view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0020]      FIG. 8  is a still further perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0021]      FIG. 9   a  is a partial perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0022]      FIG. 9   b  is another partial perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0023]      FIG. 10   a  is an exploded perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0024]      FIG. 10   b  is a partial exploded perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0025]      FIG. 10   c  is another partial exploded perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0026]      FIG. 10   d  is another exploded perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0027]      FIG. 10   e  is a further partial exploded perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0028]      FIG. 11  is a planar side view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0029]      FIG. 12  is another planar side view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0030]      FIG. 13  is a further planar side view of one exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0031]      FIG. 14  is a still further perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention, along with a partial perspective view of one exemplary embodiment of the implantation tool of the present invention; 
           [0032]      FIG. 15  is a still further perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention, along with another partial perspective view of one exemplary embodiment of the implantation tool of the present invention; 
           [0033]      FIG. 16  is a still further perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention, along with a perspective view of one exemplary embodiment of the implantation tool of the present invention; 
           [0034]      FIG. 17  is a still further perspective view of one exemplary embodiment of the expandable intervertebral implant of the present invention, along with another perspective view of one exemplary embodiment of the implantation tool of the present invention; 
           [0035]      FIGS. 18   a  and  18   b  are perspective views of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention in an unexpanded configuration; 
           [0036]      FIGS. 19   a  and  19   b  are perspective views of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention in a partially or wholly expanded configuration; 
           [0037]      FIG. 20  is a top/bottom planar view of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0038]      FIGS. 21   a  and  21   b  are side planar views of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention in both unexpanded and partially or wholly expanded configurations; 
           [0039]      FIGS. 22   a  and  22   b  are partial planar views of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention in both unexpanded and partially or wholly expanded configurations; 
           [0040]      FIGS. 23   a  and  23   b  are perspective views of the superior and inferior members of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0041]      FIGS. 24   a  and  24   b  are additional perspective views of the superior and inferior members of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0042]      FIG. 25  is an additional perspective view of the superior and inferior members of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0043]      FIG. 26  is a partial perspective view of the superior and inferior members of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention in an assembled configuration (see also  FIGS. 22   a  and  22   b  for partial planar views of the same); 
           [0044]      FIGS. 27   a  and  27   b  are end planar views of the superior member and the distal wedge structure of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention, respectively; 
           [0045]      FIGS. 28   a  and  28   b  are perspective views of the superior and inferior members of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention in an assembled configuration, both without and with the associated proximal and distal wedge structures in place, respectively; 
           [0046]      FIGS. 29   a  and  29   b  are perspective views of the distal wedge structure of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0047]      FIGS. 30   a  and  30   b  are side planar views of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention in both unexpanded and partially or wholly expanded configurations; 
           [0048]      FIGS. 31   a  and  31   b  are end planar views of the proximal wedge structure of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0049]      FIGS. 32   a  and  32   b  are perspective views of the proximal wedge structure of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0050]      FIGS. 33   a  and  33   b  are perspective views of the actuation bolt of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0051]      FIG. 34  is a perspective view of the proximal wedge structure, the distal wedge structure, and the actuation bolt of an alternative exemplary embodiment of the expandable intervertebral implant of the present invention in an assembled configuration; 
           [0052]      FIG. 35  is a perspective view of the implant inserter tool used to insert an alternative exemplary embodiment of the expandable intervertebral implant of the present invention; 
           [0053]      FIGS. 36   a  and  36   b  are perspective views of an end portion of the implant inserter tool used to insert an alternative exemplary embodiment of the expandable intervertebral implant of the present invention, both disengaged from and engaged with the expandable intervertebral implant, respectively; 
           [0054]      FIGS. 37   a  and  37   b  are perspective views of another end portion of the implant inserter tool used to insert an alternative exemplary embodiment of the expandable intervertebral implant of the present invention, both in unlocked and locked configurations, respectively; 
           [0055]      FIGS. 38   a  and  38   b  are partial perspective views of another end portion of the implant inserter tool used to insert an alternative exemplary embodiment of the expandable intervertebral implant of the present invention, both in unlocked and locked configurations, respectively; 
           [0056]      FIG. 39  is a perspective view of another end portion of the implant inserter tool used to insert an alternative exemplary embodiment of the expandable intervertebral implant of the present invention, highlighting the engagement of the associated handle assembly; 
           [0057]      FIG. 40  is a perspective view of the implant inserter tool used to insert an alternative exemplary embodiment of the expandable intervertebral implant of the present invention, highlighting the engagement of the associated handle assembly; 
           [0058]      FIGS. 41   a  and  41   b  are perspective views of another alternative exemplary embodiment of the expandable intervertebral implant of the present invention in an unexpanded configuration; 
           [0059]      FIG. 42  is a perspective view of the implant inserter tool used to insert an alternative exemplary embodiment of the expandable intervertebral implant of the present invention, highlighting the engagement of the associated handle assembly and actuation handle assembly; 
           [0060]      FIG. 43  is an exploded perspective view of another end portion of the implant inserter tool used to insert alternative exemplary embodiments of the expandable intervertebral implant of the present invention; and 
           [0061]      FIGS. 44   a  and  44   b  are perspective views of the implant inserter tool used to insert alternative exemplary embodiments of the expandable intervertebral implant of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0062]    Referring to  FIG. 1 , in one exemplary embodiment, the present invention provides an expandable intervertebral implant  10  that is selectively disposed in the intervertebral space and deployed, thereby in-situ distracting, realigning, and/or stabilizing or fusing a portion of the spine of a patient in the treatment of injury, disease, and/or degenerative condition. The expandable intervertebral implant  10  includes a superior member  12  and an inferior member  14 , each of which has a partially or substantially wedge or prismatic shape and a partially or substantially convex or other-shaped surface that is suitable for engaging the substantially concave surfaces of the associated bony superior and inferior intervertebral endplates. Optionally, the superior member  12  and the inferior member  14  are each thinner at the leading edge of the expandable intervertebral implant  10  than they are at the trailing edge of the expandable intervertebral implant  10 , such that insertion into the intervertebral space may be aided, although this is not a requirement and the expandable intervertebral implant  10  may have a uniform thickness, when undeployed, from the leading edge to the trailing edge. For similar reasons, the leading edge of the both the superior member  12  and the inferior member  14  may have a knifed or rounded shape. Once disposed in the intervertebral space, the expandable intervertebral implant  10  is actuated and deployed, with the superior member  12  and the inferior member  14  moving apart from one another, seating against the associated intervertebral endplates, and distracting, realigning, and/or stabilizing them to a desired degree. The mechanisms by which this happens are described in greater detail herein below. This operation is analogous to placing a jack under a car, positioning it appropriately, snugging it in the space beneath the car, and then jacking it up. In order to ensure that the expandable intervertebral implant  10  is held securely in the intervertebral space, the external surface of each of the superior member  12  and the inferior member  14  is provided with a plurality of ridges  16  or other friction structures, providing purchase with the associated intervertebral endplates. The overall dimensions of the expandable intervertebral implant  10  are on the order of several millimeters to tens of millimeters, such that a set of implants containing a series of incremental implant sizes can provide a height expansion range of 7-18 mm or more than 3-5 mm each, for example. Other suitable dimensions may, of course, be utilized. 
         [0063]    When undeployed, the superior member  12  and the inferior member  14  are configured such that they nest against one another, thereby providing the undeployed expandable intervertebral implant  10  with the smallest possible form factor (i.e. smallest possible undeployed vertical cross-section and smallest/shortest possible undeployed horizontal footprint) for insertion through the skin and musculature of the patient and into the intervertebral space. In the exemplary embodiment illustrated in  FIG. 1 , this is accomplished via the use of cut-away sections  18  and  20  associated with the superior member  12  and the inferior member  14 . 
         [0064]    By way of overview, the superior member  12  and the inferior member  14  are actuated via the rotation of a screw  22  disposed through a housing  24  located at the trailing edge of the expandable intervertebral implant  10 . This screw  22  is disposed along the central axis of the expandable intervertebral implant  10 , between the superior member  12  and the inferior member  14 . The screw  22  engages an internally-threaded wedge structure  26  disposed between the superior member  12  and the inferior member  14 , selectively translating the wedge structure  26  along the central axis of the expandable intervertebral implant  10  with rotation. This translation causes the wedge structure  26  to interact with an associated wedge shape or structure of the superior member  12  and/or inferior member  14 , thereby forcing the superior member  12  and the inferior member  14  apart/together with translation of the wedge structure  26 . Preferably, the superior member  12  and the inferior member  14  each include a track structure  28  and  30 , thereby securely coupling the superior member  12  to the inferior member  14  through the wedge structure  26 . The interaction of the wedge structure  26  with the wedge shape or structure of the superior member  12  and/or inferior member  14  during translation preferably causes the superior member  12  and the inferior member  14  to move apart/together while maintaining a substantially parallel relationship. Alternatively, the superior member  12  and the inferior member  14  may move apart with a predetermined lordotic angle. The superior member  12  and the inferior member  14  may move apart in a substantially-continuous fashion, or they may move apart in 0.5-mm or smaller increments, for example. In addition, the interaction of the wedge structure  26 , the superior member  12 , and the inferior member  14  may be designed such that as the superior member  12  and the inferior member  14  move apart, they also translate with respect to one another. This is helpful in, for example, ensuring that the plurality of ridges  16  or other friction structures are securely seated in the bony material. 
         [0065]    Another view of the expandable intervertebral implant  10  is provided in  FIGS. 2 and 3 . As is evident from  FIGS. 2 and 3 , the superior member  12  and the inferior member  14  may each include one or more holes  32  or fenestrations to promote bony in-growth and fusion, as appropriate. Preferably, the superior member  12  and the inferior member  14  each include a groove  34  and  36  in which the screw  22  is disposed. This nesting of the screw  22  within the superior member  12  and the inferior member  14  provides the expandable intervertebral implant  10  with the smallest possible form factor when undeployed, allowing the superior member  12  and the inferior member  14  to collapse together, without interference from the screw  22 . The wedge structure  26  has a corresponding bore portion  38  ( FIG. 3 ), through which the screw  22  passes and which sits within the grooves  34  and  36  of the superior member  12  and the inferior member  14 , respectively. This configuration permits the wedge structure  26  to translate smoothly along the central axis of the expandable intervertebral implant  10  with rotation of the screw  22 , distracting the superior member  12  and the inferior member  14 , which holding the entire assembly in secure alignment. Along these same lines, the cut-away sections  18  and  20  of the superior member  12  and the inferior member  14 , respectively, may form abutting surfaces  40  perpendicular to the central axis of the expandable intervertebral implant  10  that aide in holding the superior member  12  and the inferior member  14  in alignment, despite their degree of deployment, by resisting rotation of the superior member  12  and the inferior member  14  with respect to one another. Thus, the expandable intervertebral implant  10  will expand upon deployment, as opposed to “clamshelling.” Also along these same lines, the track structures  28  and  30  of the superior member  12  and the inferior member  14  are “dove-tailed” on one or both sides and engage corresponding channels  42  and  44  manufactured into the superior and inferior surfaces of the wedge structure  26 , again thereby securely coupling the superior member  12  to the inferior member  14  through the wedge structure  26 . 
         [0066]    Referring to  FIG. 4 , the screw  22  preferably includes a keyed recess  46  for receiving a driver, such as a hexalobular driver, by which the screw  22  is rotated to translate the wedge structure  26 . The housing  24  includes a plurality of recesses  48  or the like for receiving a holding/placement tool. As is described in greater detail herein below, the driver and holding/placement tool may be incorporated into one assembly, such that the expandable intervertebral implant  10  may be grasped, positioned, expanded, and released in a series of simple steps, by a single surgeon, using a single tool. As is also illustrated in  FIG. 4 , the housing  24  may include a cylindrical recess  50  that is configured to substantially contain the head of the screw  22 , again reducing the overall footprint of the expandable intervertebral implant  10 . 
         [0067]      FIG. 5  illustrates the cross-sectional footprint of the expandable intervertebral implant  10  along its central axis, demonstrating how the superior member  12  and the inferior member  14  nest with one another about the screw  22  during implantation.  FIG. 6  illustrates the expandable intervertebral implant  10  in an only partially-deployed state, while  FIG. 7  illustrates the cross-sectional footprint of the expandable intervertebral implant  10  along its central axis, demonstrating how the superior member  12  and the inferior member  14  expand away from one another about the screw  22  and wedge structure  26  during actuation and deployment. As is illustrated clearly in  FIGS. 5 and 7 , the screw  22  may be cannulated, and a have a bore  52  passing through it along the central axis of the expandable intervertebral implant  10 . This cannulation aides in the placement of the expandable intervertebral implant  10  over a guide-wire or the like. 
         [0068]    Referring to  FIG. 8 , it may be seen that the track structures  28  and  30  of the superior member  12  and the inferior member  14 , respectively, are offset (i.e. staggered) from one another relative to the central axis of the expandable intervertebral implant  10  such that they sit side-by-side when the expandable intervertebral implant  10  is un-depolyed, thereby making the assembly as compact as possible. This also allows the track structures  28  and  30  of the superior member  12  and the inferior member  14  to be longer (versus vertically aligned tracks  28  and  30 ), thereby permitting the wedge structure  26  of a fully contracted (i.e. fully unexpanded) implant  10  to be disposed within the horizontal footprint of the superior member  12  and the inferior member  14  while maintaining minimum wedge translation (i.e. travel) length requirements to effect the required distraction of the implant  10 . Again, this makes the assembly as compact as possible, with the smallest possible undeployed vertical cross-section and the smallest/shortest possible undeployed horizontal footprint. Accordingly, the channels  42  and  44  manufactured into the superior and inferior surfaces of the wedge structure  26 , respectively, are also offset from one another relative to the central axis of the expandable intervertebral implant  10 .  FIG. 8  also illustrates the interaction of the slopes of the wedge structure  26  and, in this exemplary embodiment, the superior member  12 . Again, the interaction of the wedge structure  26  with the wedge shape or structure of the superior member  12  and/or inferior member  14  during translation preferably causes the superior member  12  and the inferior member  14  to move apart/together while maintaining a substantially parallel relationship. 
         [0069]    Referring to  FIGS. 9   a  and  9   b , the screw  22  includes a head portion  54  that selectively sits within the cylindrical recess  50  of the housing  24  and a threaded portion  56  that passes through the housing  24  to engage the wedge structure  26 . When properly positioned, the head portion  54  of the screw  22  sits flush with the exterior surface of the expandable intervertebral implant  10  and does not protrude. Preferably, the back side of the head portion  54  of the screw  22  includes a plurality of teeth  58  or the like that frictionally engage the screw  22  with a corresponding plurality of teeth  60  or the like manufactured into the exposed floor of the cylindrical recess  50  of the housing  24 . This ratcheting or spiral jaw clutch mechanism aides in preventing unwanted rotation of the screw  22  and corresponding translation of the wedge structure  26 . This may also aide in allowing the screw  22  to be rotated in a ratcheting or step-wise manner, with specific detent points. It should be noted that a lock-washer or the like could also be used for this purpose, and that a non-screw-based translation assembly could be used to translate and secure the wedge structure  26 , as will be readily apparent to those of ordinary skill in the art. Each of the plurality of holding/placement tool recesses  48  includes a lip structure  62  that is selectively engaged by a corresponding hook structure of the tool. 
         [0070]    Referring to  FIGS. 10   a - 10   e,  the superior member  12  and the inferior member include opposing flanges  64  and  66  that fit within the corresponding cut-away sections  68  and  18  of the inferior member  14  and the superior member  12 , respectively, when the superior member  12  and the inferior member  14  are nested against one another and/or separated by a predetermined distance. These opposing flanges  64  and  66  aide in providing stability to the expandable intervertebral implant  10  by preventing the superior member  12  and the inferior member  14  from sliding with respect to one another and the central axis of the expandable intervertebral implant  10 . These figures illustrate that the superior member  12  and the inferior member  14  are coupled to one another, but allowed to expand away from/contract towards one another, via a pair of “dove-tailed” inserts  70  or the like disposed on either side of the expandable intervertebral implant  10  that engage both a channel  72  manufactured into the housing  24  and a channel  74  manufactured into the superior member  12  and the inferior member  14 . It will be readily apparent to those of ordinary skill in the art that other suitable coupling mechanisms may also be used. In the exemplary embodiment illustrated, only the portion of the inserts  70  engaging the superior member  12  and the inferior member  14  is “dove-tailed,” while the portion engaging the housing  24  is not. 
         [0071]      FIGS. 11-13  illustrate the “opening” of the expandable intervertebral implant  10  via rotation of the screw  22  and translation of the wedge structure  26  towards the housing  24 . The constant, substantially-parallel relationship of the superior member  12  and the inferior member  14  should be noted as the wedge structure  26  move along the “rails” of the superior member  12  and the inferior member  14 . 
         [0072]    Referring to  FIGS. 14 and 15 , in one exemplary embodiment, the combination placement/deployment tool  76  of the present invention includes a pair of elongate arms  78  that each have a hook structure  80  on the end that is configured to selectively and releasably engage the corresponding recess  48  of the housing  24 . The combination placement/deployment tool  76  also includes a driver  82  disposed between the pair of elongate arms  78  that is configured to selectively and releasably engage the keyed recess  46  of the screw  22 . When rotated, the driver  82  rotates the screw  22 , thereby translating the wedge structure  26  (not illustrated) and expanding/contracting the superior member  12  and the inferior member  14  of the expandable intervertebral implant  10 . 
         [0073]    Referring to  FIGS. 16 and 17 , the combination placement/deployment tool  76  further includes a handle  84  for grasping and a socket  86  for attaching a rotating or driver handle  88 , such as a ratcheting handle. It will be readily apparent to those of ordinary skill in the art that the expandable intervertebral implant of the present invention may be placed via an open surgical procedure, or via any suitable minimally-invasive portal-type of system. 
         [0074]    Referring to  FIGS. 18   a ,  18   b ,  19   a , and  19   b , in an alternative exemplary embodiment, the present invention provides an expandable intervertebral implant  110  that is selectively disposed in the intervertebral space and deployed, thereby in-situ distracting, realigning, and/or stabilizing or fusing a portion of the spine of a patient in the treatment of injury, disease, and/or degenerative condition.  FIGS. 18   a  and  18   b  illustrate the expandable intervertebral implant  110  in an unexpanded, or unactuated, configuration, while  FIGS. 19   a  and  19   b  illustrate the expandable intervertebral implant  110  in a partially or wholly expanded, or partially or wholly actuated, configuration. The expandable intervertebral implant  110  again includes a superior member  112  and an inferior member  114 , each of which has a proximal ramp portion  113  and  115 , respectively, and a distal ramp portion  117  and  119 , respectively, and a partially or substantially convex or flat opposing surface  121  and  123 , respectively, that is suitable for engaging the substantially concave or flat opposing surfaces of the associated bony superior and inferior intervertebral endplates, once properly prepared. Optionally, the superior member  112  and the inferior member  114  are each thinner at the proximal and distal ends of the expandable intervertebral implant  110  than they are in the central portion of the expandable intervertebral implant  110 , such that insertion into the intervertebral space may be aided, although this is not a requirement and the expandable intervertebral implant  110  may have a uniform thickness, when undeployed and/or deployed, from the proximal end to the distal end through the central portion. For similar reasons, the proximal and distal ends of the both the superior member  112  and the inferior member  114  may have a narrowed or rounded shape in any dimension or direction. Once disposed in the intervertebral space, the expandable intervertebral implant  110  is actuated and deployed, with the superior member  112  and the inferior member  114  moving apart from one another, while remaining in a substantially parallel and translationally constant configuration, seating against the associated intervertebral endplates, and distracting, realigning, and/or stabilizing them to a desired degree. The mechanisms by which this happens are described in greater detail herein below. This operation is analogous to placing a jack under a car, positioning it appropriately, snugging it in the space beneath the car, and then jacking it up. In order to ensure that the expandable intervertebral implant  110  is held securely in the intervertebral space, the external surface of each of the superior member  112  and the inferior member  114  is provided with a plurality of ridges  116  or other friction structures, providing purchase with the associated intervertebral endplates. The overall dimensions of the expandable intervertebral implant  10  are on the order of several millimeters to tens of millimeters, such that a set of implants containing a series of incremental implant sizes can provide a height expansion range of 7-18 mm or more than 3-5 mm each, for example. Other suitable dimensions may, of course, be utilized. 
         [0075]    When undeployed, the superior member  112  and the inferior member  114  are configured such that they nest against and interlock with one another, thereby providing the undeployed expandable intervertebral implant  110  with the smallest possible form factor (i.e. the smallest possible undeployed vertical cross-section and the smallest/shortest possible undeployed horizontal footprint) for insertion through the skin and musculature of the patient and into the intervertebral space. Again, the mechanisms by which this happens are described in greater detail herein below. 
         [0076]    By way of overview, the superior member  112  and the inferior member  114  are actuated via the rotation of an actuation bolt  122  disposed through an internally-bored proximal wedge structure  125  that securely, and in a sliding manner, engages the proximal ramp portions  113  and  115  of the superior member  112  and the inferior member  114 , respectively, at the proximal end of the expandable intervertebral implant  110 . This actuation bolt  122  is disposed along and through the central axis of the expandable intervertebral implant  110 , between the superior member  112  and the inferior member  114 . At the distal end of the expandable intervertebral implant, the actuation bolt  122  engages an internally-threaded distal wedge structure  126  that securely, and in a sliding manner, engages the distal ramp portions  117  and  119  of the superior member  112  and the inferior member  114 , respectively. The proximal and distal wedge structures  125  and  126  are thereby translated along the central axis of the expandable intervertebral implant  110  with rotation of the actuation bolt  122 , at least with respect to one another. This translation causes the proximal and distal wedge structures  125  and  126  to interact with the proximal and distal ramp portions  113 ,  115 ,  117 , and  119  of the superior member  112  and the inferior member  114 , thereby forcing the superior member  112  and the inferior member  114  apart/together with translation of the proximal and distal wedge structures  125  and  126 . Preferably, the superior member  112  and the inferior member  114  each include a nested track structure (described in greater detail herein below), thereby securely coupling the superior member  112  to the inferior member  114  through the proximal and distal wedge structures  125  and  126 . This also allows the track structures of the superior member  112  and the inferior member  114  to be longer (versus vertically aligned tracks), thereby permitting the wedge structures  125  and  126  of a fully contracted (i.e. fully unexpanded) implant  110  to be disposed within the horizontal footprint of the superior member  112  and the inferior member  114  while maintaining minimum wedge translation (i.e. travel) length requirements to effect the required distraction of the implant  110 . Again, this makes the assembly as compact as possible, with the smallest possible undeployed vertical cross-section and the smallest/shortest possible undeployed horizontal footprint. The interaction of the proximal and distal wedge structures  125  and  126  with the proximal and distal ramp portions  113 ,  115 ,  117 , and  119  of the superior member  112  and the inferior member  114  during translation preferably causes the superior member  112  and the inferior member  114  to move apart/together while maintaining a substantially parallel, translationally constant relationship. Alternatively, the superior member  112  and the inferior member  114  may move apart with a predetermined lordotic angle. The superior member  112  and the inferior member  114  may move apart in a substantially continuous fashion, or they may move apart in 0.5-mm or smaller increments, for example. In addition, the interaction of the proximal and distal wedge structures  125  and  126  with the proximal and distal ramp portions  113 ,  115 ,  117 , and  119  of the superior member  112  and the inferior member  114  may be designed such that as the superior member  112  and the inferior member  114  move apart, they also translate with respect to one another. This is helpful in, for example, ensuring that the plurality of ridges  116  or other friction structures are securely seated in the bony material. 
         [0077]    Another view of the expandable intervertebral implant  110  is provided in  FIG. 20 . As is evident from  FIG. 20 , the superior member  112  and the inferior member  114  (not shown here) may each include one or more holes  132  or fenestrations to promote bony in-growth and fusion, as appropriate. For example, the expandable intervertebral implant  110  may include a  40  mm 2  or larger axial graft chamber opening or the like for the placement of a fusion material. 
         [0078]    Referring to  FIGS. 21   a  and  21   b , preferably, the proximal and distal wedge structures  125  and  126  are disposed within the footprint(s) of the superior member  112  and the inferior member  114  in both the fully unexpanded and fully expanded states—meaning that the expandable intervertebral implant  110  has a known and constant or predictable size, which is a great advantage to an implanting surgeon. The superior member  112  and the inferior member  114  each (or collectively) define an internal space in which the actuation bolt  122  is disposed. This nesting of the actuation bolt  122  within the superior member  112  and the inferior member  114  provides the expandable intervertebral implant  110  with the smallest possible form factor when undeployed, allowing the superior member  112  and the inferior member  114  to collapse together, without interference from the actuation bolt  122 . The proximal wedge structure  125  has a corresponding bore portion through which the actuation bolt  122  passes, while the distal wedge structure  126  has a corresponding threaded hole portion through which the actuation bolt  122  passes. This configuration permits the proximal and distal wedge structures  125  and  126  to translate smoothly along the central axis of the expandable intervertebral implant  110  with rotation of the actuation bolt  122 , distracting the superior member  112  and the inferior member  114 . One or more stabilization members  131  protruding from either or both of the superior member  112  and/or the inferior member  114  and engaging a corresponding stabilization recess  133  manufactured in the side of the other member  112  or  114  securely hold the superior member  112  and the inferior member  114  in a fixed translational alignment and prevent undesirable slipping between the two in any direction, as well as undesirable rotation or tilting. Thus, the expandable intervertebral implant  110  will predictably expand upon deployment, as opposed to “clamshelling,” for example. 
         [0079]    Referring to  FIGS. 22   a ,  22   b ,  23   a ,  23   b ,  24   a ,  24   b ,  25 , and  26 , in the exemplary embodiment illustrated, the superior member  112  and the inferior member  114  are essentially mirror images of one another, such that manufacturing, inventory, and assembly costs are minimized, although this is not strictly required. Furthermore, in this exemplary embodiment, the superior member  112  and the inferior member  114  are the same part, designed to nest with itself when rotated  180  degrees, such that manufacturing efficiencies are increased and production and inventory costs are minimized. As described above, one or more stabilization members  131  protruding from either or both of the superior member  112  and/or the inferior member  114  and engaging a corresponding stabilization recess  133  manufactured in the side of the other member  112  or  114  securely hold the superior member  112  and the inferior member  114  in a fixed translational alignment and prevent undesirable slipping between the two in any direction, as well as undesirable rotation or tilting. Each of the stabilization members  131  includes a horizontal shelf structure  135  manufactured into the interior portion thereof This horizontal shelf structure  135  is configured to mate with a corresponding horizontal shelf structure  137  manufactured into an exterior portion of each of the stabilization recesses  133 . Together these shelf structures  135  and  137  impart significant stability when the superior member  112  and the inferior member  114  are mated, and provide a stopping point for collapse of the superior member  112  and the inferior member  114  together vertically. Each of the proximal ramp portions  113  and  115  and the distal ramp portions  117  and  119  of the superior member  112  and the inferior member  114 , respectively, includes one or more raised parallel rail structures  128  that run from the central portion of the expandable intervertebral implant  110  to the respective end portion of the expandable intervertebral implant  110 . These raised parallel rail structures  128  are positioned and configured to engage corresponding recessed parallel slot structures  130  of the proximal and distal wedge structures  125  and  126  (see  FIGS. 27   a ,  27   b ,  28   a ,  28   b ,  29   a ,  29   b ,  32   a , and  32   b ). Preferably, each of the rail structures  128  and/or slot structures  130  includes a lip structure and/or is “dove-tailed” on one or both sides, such that the rail structures  128  and slot structures  130  are allowed to translate with respect to one another, but are prevented from disengaging one another all together. The rail structures  128  and slot structures  130  are staggered or offset such that the proximal ramp portions  113  and  115  and the distal ramp portions  117  and  119  of the superior member  112  and the inferior member  114  and the proximal and distal wedge structures  125  and  126  are “nested” when assembled, such that the form factor (i.e. both the vertical cross-section and the horizontal footprint) of the expandable intervertebral implant  110  is minimized when undeployed (i.e. unexpanded). This allows the track structures of the superior member  112  and the inferior member  114  to be longer (versus vertically aligned tracks), thereby permitting the wedge structures  125  and  126  of a fully contracted (i.e. fully unexpanded) implant  110  to be disposed within the horizontal footprint of the superior member  112  and the inferior member  114  while maintaining minimum wedge translation (i.e. travel) length requirements to effect the required distraction of the implant  110 . Again, this makes the assembly as compact as possible, with the smallest possible undeployed vertical cross-section and the smallest/shortest possible undeployed horizontal footprint. Again, this also allows the proximal and distal wedge structures  125  and  126  to be disposed within the footprint(s) of the superior member  112  and the inferior member  114  in the fully unexpanded state—meaning that the expandable intervertebral implant  110  has a known and constant or predictable size, which is a great advantage to an implanting surgeon. Further, this configuration preserves the integrity and continuity of the leading (i.e. distal) edge of the superior member  112  and the inferior member  114 , and allows the proximal ramp portions  113  and  115  and the distal ramp portions  117  and  119  to be made longer, without the rail structures  128  interfering with one another, thereby increasing bony surface purchase area. 
         [0080]      FIGS. 29   a  and  29   b  further illustrate the distal wedge structure  126  of this alternative embodiment of the expandable intervertebral implant  110  of the present invention, highlighting the configuration of the slot structures  130  and threaded bore  139 . 
         [0081]    Referring to  FIGS. 30   a  and  30   b , the superior member  112  includes one or more downward projecting portions  140  on one side thereof (in the exemplary embodiment illustrated). The inferior member  114  includes one or more corresponding recesses  142  on one side thereof (in the exemplary embodiment illustrated). When the expandable intervertebral implant  110  is in its collapsed state, these features act as a locking mechanism, increasing implant shear strength and overall stability during delivery and positioning in the intervertebral space, which may require the use of a slap hammer or other similar striking instrument. Similar locking tabs  144  and notches  146  may also be used for this purpose in a variety of configurations. 
         [0082]    Referring to  FIGS. 31   a  and  31   b , the proximal wedge structure  125  includes a recessed radial spline  148  (or spiral jaw clutch mechanism) disposed around the central bore  150 , such that the expandable intervertebral implant  110  may be expanded in a “ratcheted” manner (i.e. incrementally) and securely hold a given degree of expansion. This “ratcheted” expansion may be reversed for repositioning and redeployment. The recessed nature of the radial spline  148  again reduces the overall footprint of the expandable intervertebral implant  110 , accepting and “hiding” the head portion of the actuation bolt  122 . Further, the sides of the proximal wedge structure  125  include grooves  152  and recessed pockets  154  that are configured to receive various grasping and deployment tools, as described in greater detail herein below. 
         [0083]    Referring to  FIGS. 33   a  and  33   b , the actuation bolt  122  includes a complimentary radial spline  156  on the back side of the head portion, a smooth shaft portion  158  for passing through the proximal wedge structure  125 , and a threaded portion  160  for engaging the distal wedge structure  126 . This assembly is illustrated in  FIG. 34 . The head portion of the actuation bolt  122  also includes a keyed recess  162  for receiving a driver, such as a hexalobular driver, by which the actuation bolt  122  is rotated to translate the proximal and/or distal wedge structure(s)  125  and  126 . As is described in greater detail herein below, the driver and holding/placement tool may be incorporated into one assembly, such that the expandable intervertebral implant  110  may be grasped, positioned, expanded, and released in a series of simple steps, by a single surgeon, using a single tool. 
         [0084]    Referring to  FIGS. 35 ,  36   a ,  36   b ,  37   a ,  37   b ,  38   a ,  38   b ,  39 ,  40 ,  42 ,  43 ,  44   a , and  44   b , in an alternative exemplary embodiment, the combination placement/deployment tool  200  of the present invention includes a pair of movable elongate arms  202  that each have an interior retention structure  204  that is configured to selectively and releasably engage the corresponding recessed pocket  154  of the expandable intervertebral implant  110  in an anti-rotational manner. The combination placement/deployment tool  200  also includes a driver disposed between the pair of elongate arms  202  that is configured to selectively and releasably engage the keyed recess  162  of the actuation bolt  122 . When rotated, the driver rotates the actuation bolt  122 , thereby translating the wedge structures  125  and  126  and expanding/contracting the superior member  112  and the inferior member  114  of the expandable intervertebral implant  110 . The elongate arms  202  are engaged/released via the actuation of a lever mechanism  212  disposed at the opposite end of an elongate shaft  210 . The combination placement/deployment tool  200  further includes a handle  214  (e.g. an MIS side handle) for grasping and a socket  216  (e.g. a torque limiting handle) for rotating the driver. It will be readily apparent to those of ordinary skill in the art that the expandable intervertebral implant  110  of the present invention may be placed via an open surgical procedure, or via any suitable minimally-invasive portal-type of system. 
         [0085]    As an alternative,  FIGS. 41   a  and  41   b  illustrate a lordotic version of the expandable intervertebral implant  310  of the present invention—which is “thicker” at one end than at the other end, similar to embodiments described above. This is advantageous for TLIF and ALIF procedures. Side slope versions may also be produced for DLIF procedures, for example. 
         [0086]    Although the expandable intervertebral implant of the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples fall within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.