Abstract:
A method and system for performing bone fusion and/or securing one or more bones, such as adjacent vertebra, are disclosed.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to neurosurgical and orthopedic fixation systems. 
       BACKGROUND 
       [0002]    Spinal interbody fusion is a frequently performed procedure to treat various disorders such as degenerated disk disease, spondylolisthesis, trauma, infection, tumor and deformity. Usually, surgery involves placement of screws into the vertebral body through the vertebral pedicle and/or placement of an interbody cage with bone grafts into the disc space. Types of spinal fusion depend on the approach type such as posterior, transforaminal, lateral, etc. Although these approaches claim to be minimally invasive, they still require open incisions for cage and screw placement as well as compression and/or distraction of vertebral bodies. Improvements in the devices&#39; design enhance spinal fusion as well as minimize the invasiveness of the surgical implantation, which are desirable traits in clinical practice. 
       SUMMARY 
       [0003]    Presented are systems and methods for providing fusion and distraction between adjacent vertebral bodies. An aspect of the present disclosure is directed to an intervertebral cage including an upper bar and an opposing lower bar. The cage can further include a separator movable between the upper bar and the lower bar to cause movement of the upper bar towards and away from the lower bar. The cage can also include a pin having a first end extending into an opening provided in the upper bar and a second end extending into an opening provided in the second bar. 
         [0004]    Another aspect of the present disclosure is directed to an intervertebral cage including a first upper bar and opposing first lower bar. The cage can also include a first and second separator movable between the first upper bar and the first lower bar to cause movement of the first upper bar towards and away from the first lower bar. The cage can further include a second upper bar and opposing second lower bar and a third and fourth separator movable between the second upper bar and the second lower bar to cause movement of the second upper bar towards and away from the second lower bar. The cage can also include a threaded rod, where each of the bars include an arm extending from a side surface of each of the corresponding bars, the arms engaging the threaded rod. 
         [0005]    The details of one or more implementations of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0006]    The device is explained in even greater detail in the following exemplary drawings. The drawings are merely exemplary to illustrate the structure of preferred devices and certain features that may be used singularly or in combination with other features. The invention should not be limited to the implementations shown. 
           [0007]      FIG. 1  is a perspective view if an example intervertebral cage; 
           [0008]      FIG. 2A  is a perspective view of an example bar pair, 
           [0009]      FIG. 2B  is a front view of the example bar pair of  FIG. 2A  in an expanded configuration; 
           [0010]      FIG. 2C  is a front view of the bar pair of  FIG. 2A  in an unexpanded configuration; 
           [0011]      FIGS. 3A and 3B  are perspective views of an example bar; 
           [0012]      FIG. 3C  is an end view of an example bar; 
           [0013]      FIG. 3D  is a partial top perspective view of an example bar; 
           [0014]      FIG. 4A  is a perspective view of an example separator; 
           [0015]      FIG. 4B  is a side view of an example separator; 
           [0016]      FIGS. 4C and 4D  are perspective view of an example separator; 
           [0017]      FIG. 5A  is a perspective view of an example pin; 
           [0018]      FIG. 5B  is a front view of an example pin; 
           [0019]      FIGS. 5C and 5D  are perspective views of an example partial pin; 
           [0020]      FIG. 5E  is a front view of an example partial pin; 
           [0021]      FIGS. 5F and 5G  are perspective views of an example pin; 
           [0022]      FIG. 6A  is a perspective view of an example lower bar, separators, and pin; 
           [0023]      FIG. 6B  is a front view of an example lower bar, separators, and pin in an unexpanded configuration; 
           [0024]      FIG. 6C  is a front view of an example lower bar, separators, and pin in an expanded configuration; 
           [0025]      FIG. 7  is a perspective view of example upper and lower bar pair; 
           [0026]      FIGS. 8A and 8B  are top perspective views of opposing upper bars and threaded rod; 
           [0027]      FIG. 8C  is a perspective view of an example threaded rod and upper and lower bar pair; 
           [0028]      FIGS. 9A-9D  are perspective views of an example intervertebral cage; 
           [0029]      FIG. 10A  is a perspective view of example upper and lower bar pairs of an intervertebral cage; 
           [0030]      FIG. 10B  is a cross-section of the example cage of  FIG. 10A  in an unexpanded configuration; 
           [0031]      FIG. 10C  is a partial cross-section of the example cage of  FIG. 10A ; 
           [0032]      FIG. 10D  is a perspective view of an example cage of  FIG. 10A  in a horizontally expanded configuration; 
           [0033]      FIG. 10E  is a cross-section of the example cage of  FIG. 10A  in a vertically and horizontally expanded configuration; 
           [0034]      FIG. 11A  is a front view of example bar pair connected with a compliant mechanism; 
           [0035]      FIG. 11B  is a perspective view of the example bar pair connected with a compliant mechanism of  FIG. 11A ; 
           [0036]      FIG. 12  is a perspective view of an example bar pair connected with a compliant mechanism; 
           [0037]      FIG. 13  is a perspective view of an example bar pair connected with a compliant mechanism; 
           [0038]      FIG. 14  is a perspective view of an example bar pair connected with a compliant mechanism; 
           [0039]      FIG. 15  is a perspective view of an example intervertebral cage connected with compliant mechanisms; 
           [0040]      FIGS. 16A and 16B  are perspective views of an example intervertebral cage with overhanging supports and compliant mechanisms; 
           [0041]      FIG. 17A  is a top view of an example intervertebral cage with compliant mechanisms in a horizontally expanded configuration; 
           [0042]      FIGS. 17B and 17C  are perspective views of the example intervertebral cage with compliant mechanisms of  FIG. 17A ; 
           [0043]      FIGS. 18A-18C  are perspective views of an example intervertebral cage; 
           [0044]      FIG. 18D  is a perspective view of a lateral and a horizontal bar, central component, and actuating members; 
           [0045]      FIG. 18E  is a perspective view of a lateral and a horizontal bar and actuating members; 
           [0046]      FIG. 18F  is a perspective view of a central component and actuating members; 
           [0047]      FIG. 18G  is a perspective view of the actuating members; 
           [0048]      FIG. 18H  is an end view of the actuating members; 
           [0049]      FIG. 18I  is an end view of the example cage of  FIG. 18A  in horizontally expanded configuration; 
           [0050]      FIG. 18J  is a sectional view of the example cage of  FIG. 18A  in a horizontally expanded configuration; and 
           [0051]      FIG. 18K  is an end view of the example cage of  FIG. 18A  in a vertically and horizontally expanded configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0052]    Certain exemplary implementations of an expandable intervertebral cage used to facilitate fusion between two vertebral bodies will now be described with reference to the drawings. 
         [0053]    The cage  100  is designed for implantation and fusion between two vertebrae. The cage  100  can be implanted, for example between adjacent cervical, thoracic, lumbar, or sacral vertebrae. In non-expanded state, the cage  100  can be inserted through a small incision into the disc space or between two adjacent bones. Once expanded, the cage  100  can be used to provide distraction between the adjacent vertebrae or bones. As will be described in more detail below, the cage  100  can expand horizontally and/or vertically. For example, once positioned as desired by a medical professional, the cage  100  can be expanded in a horizontal direction; for example, in the horizontal plane of the intervertebral space in which the cage  100  is located. The cage  100  can also be expanded in a vertical direction to increase the vertical separation between the adjacent vertebrae. The horizontal expansion can be performed before the vertical expansion. A single actuator, or plurality of actuating devices, can be used to provide horizontal and vertical expansion. In one example, an actuator(s) can be used to first cause horizontal expansion followed by vertical expansion. In this way, a low height and width profile of the unexpanded cage  100  can be used for implantation and then with use of an actuator, the width and height profile can be expanded as desired. The space between the deployed components of the cage  100  can be accessed for placement of a bone filling material. 
         [0054]      FIG. 1  is a perspective view of an example intervertebral cage  100 . The cage  100  can include two pairs of upper and opposing lower longitudinal bars  120 , e.g., upper and lower bars  120   a   1 ,  120   b   1  and upper and lower bars  120   a   2 ,  120   b   2 . Each pair includes an upper bar  120   a  and a lower bar  120   b  and the pairs are spaced from one another across the vertical midline of the cage  100 . As will be described in more detail below, the lateral and vertical space between the bars  120  can be increased/decreased and the cage  100  is expanded/retracted (the cage  100  illustrated in  FIG. 1  is expanded in only the lateral direction). A separator  140  can be used to provide define a distance/separation between the upper and lower bar pairs  120   a,    120   b  and the height of the cage  100  in an expanded configuration. As will be described below, a threaded rod  170  and spacer  180  can be used to control/limit lateral and vertical expansion between adjacent bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . 
         [0055]      FIG. 2A  is a perspective view of an example bar pair including upper bar  120   a  and lower bar  120   b.    FIG. 2B  is a front view of the example bar pair  120   a,    120   b  of  FIG. 1  in an expanded configuration.  FIG. 2C  is a front view of the example bar pair  120   a,    120   b  of  FIG. 1  in an unexpanded configuration. As illustrated in  FIGS. 2B and 2C , and as will be described in more detail below, the separator  140  can be movable between the upper bar  120   a  and the lower bar  120   b  to cause movement of the bars towards and away from each other. 
         [0056]      FIGS. 3A and 3B  are perspective views of an example upper bar  120   a  and/or lower bar  120   b.  The bar can include a top surface  124  and an opposing vertebral body contacting surface  125  for contacting the vertebral endplates of the adjacent vertebral bodies. The vertebral body contacting surface  125  can bend, deform or consist of specific surface area (either of irregular or regular shape) to accommodate the endplate of the adjacent vertebral body. The vertebral body contacting surface  125  can also consist of a sloping surface to intentionally induce uneven expansion. Likewise, the vertebral body contacting surface  125  of the upper and lower bars  120   a,    120   b  can include teeth or ridges for engaging the endplates of the adjacent vertebral bodies as shown, for example, in  FIG. 7 . The teeth can provide engagement and/or increased purchased between the cage  100  and the adjacent vertebral bodies. The teeth can have a pyramid shape (polygonal base and triangular faces that meet at a common point) or any other shape that can be used to provide increased friction, surface area contact and engagement between the bar  120  and the adjacent vertebral endplate. It is also contemplated that the vertebral body contacting surface  125  can include any type of biological or non-biological coating to enhance bone growth and attachment (fusion) with the cage  100 . 
         [0057]    As illustrated in  FIGS. 3A and 3B , the bar  120  can also include a contact surface  126  for contacting a corresponding surface  142  provided on the separator  140  such that movement of the separator  140  along the bar&#39;s contact surface  126  can increase and/or decrease the spacing between the upper and lower bars  120   a,    120   b.  Initially a lateral bar pair can be provided in the unexpanded configuration as illustrated in  FIG. 2C . In the unexpanded configuration the separator  140  is provided on the contact surface  126  proximate the end of the bar  120 . Movement of the separator  140  towards the midline of the bar  120  increases the spacing between the upper and lower bars  120   a,    120   b  and drives the cage  100  from an unexpanded to a vertically expanded configuration. 
         [0058]    As illustrated in  FIGS. 3A and 3B , the contact surface  126  can be inclined towards the midline of the bar  120  and configured to engage a corresponding inclined contact surface  142  of the separator  140 . As illustrated in  FIGS. 2B-2C and 3A-3C , contact surface  126  can include an inclined stepped surface. Likewise, the contact surface  142  of the separator  140  can include a corresponding inclined stepped surface. Because the upper and lower bars  120   a  and  120   b  are under compression when implanted, the flats of the stepped contact surface  126  prevent the separator  140  from backing out when under pressure. Likewise, the distance between adjacent flats can define the discrete expansion value for each step (e.g., 1 mm, 2 mm, 3 mm, 4 mm). It is contemplated that the contact surface  126  and/or the corresponding contact surface  142  can define a straight/flat surface, a curved surface (e.g., convex, concave, etc.) or any other regular or irregular shaped surface. While the distance between flats of a stepped design can define the expansion value of the separator  140 , an inclined design can have continuous expansion values ranging between, for example, 1 mm-4 mm. 
         [0059]    Though not illustrated, the upper and/or lower bars  120   a,    120   b  can include a single contact surface  126 . In another example, and as illustrated in  FIGS. 3A and 3B , the bar  120  can include two contact surfaces  126  provided at opposite ends of the bar  120 . The contact surfaces  126  can terminate at a stop surface  128  proximate the top surface  124  of the bar  120 . In another example (not shown), the contact surfaces  142  can terminate at a common edge or intersection point, e.g., the intersection point of two separator contact surfaces provided on the bar  120 . 
         [0060]    As provided in  FIGS. 3A-3C , the bar  120  can include a groove  130  included on an inside surface  131  of the bar  120 . The groove  130  can be inclined towards the midline of the bar  120  and configured to engage a corresponding projection  144  extending from a side surface  146  of the separator  140 , illustrated in  FIGS. 4A-4D . As illustrated in  FIGS. 3A-3C , the groove  130  can be stepped and be provided proximate the contact surface  126 . In another example (not shown), the groove  130  can be provided at any location on an inside surface  131  of the bar  120  separate from the location of the contact surface  126 . In a further example (not shown), bar  120  does not include a contact surface  126  and the groove  130  can be provided on an inside surface  131  of the bar  120 . 
         [0061]      FIGS. 4A, 4C and 4D  provide perspective views of an example separator  140 .  FIG. 4B  is a side view of the example separator  140 . As illustrated, the separator  140  can include an inclined and/or stepped contact surface  142 . The projection  144  for engaging the groove  130  provided in the bar  120  can be located on the side of the separator  140  proximate the contact surface  142 . The separator  140  can include a single projection  144  or a plurality of projections  144 . The projections  144  can sized and shaped to slidably engage the groove  130 . For example, the projection  144  can define a round/hemispherical shape, or any other regular or irregular shape that permits movement between the projection  144  and the groove  130 . During use, engagement of the projection  144  and the groove  130  guides movement of the separator  140  with respect to the bar  120  from an unexpanded to expanded configuration, and vice versa. Engagement between the projection  144  and the groove  130  also helps to maintain contact and/or spacing between the contact surface  126  and the contact surface  142 .  FIGS. 5A and 5B  provide a perspective and front view of an example pin  150 . The pin  150  can include a main body  152  and a head  154 . The main body  152  can include an elongated shaft extending between two head portions  154  where the heads  154  have a width/diameter greater than a width/diameter of the main body  152 . The head  154  can be of a regular or an irregular shape and the pin  150  can consist of a symmetrical, as illustrated in  FIG. 5A , or asymmetrical shape (not illustrated). The pin  150  extends through/into and is movable within an opening  132  in the bars  120 . The pin  150  can be used to maintain alignment of the upper bar  120   a  and lower bar  120   b  during compression and distraction of the cage  100 , i.e., movement between the unexpanded and expanded configuration. For example, the pin  150  can maintain the upper bar  120   a  and the lower bar  120   b  in a parallel configuration. The upper bar  120   a  and/or lower bar  120   b  can include a recessed opening  134  as illustrated in  FIG. 3D  showing a partial top perspective view of the top surface  124  of an example bar  120 . The recessed opening  134  can have a width/diameter larger than the width/diameter of the main opening  132  and can be sized and configured to receive the head  154  of the pin  150 . The depth of the recessed opening  134  can define the limits of expansion of the cage  100 . That is, as the bottom of the heads  154  of the pin  150  impact/contact the bottom surface of the recessed opening  134  the cage  100  is prevented from further expansion. Accordingly, the distance between the heads  154  of the pin  150  can define the amount of expansion between the upper bar  120   a  and the lower bar  120   b.  Movement of the pin  150  within the openings  132  provided in the upper and lower bars  120   a,    120   b  also prevents the bars  120  from shearing, that is, the pin  150  prevents the bars  120  moving from left to right with respect to each other. The pin  150 , including the main body  152  and head(s)  154  can have unitary construction. In another example, illustrated in  FIGS. 5C-5G , the main body  152  and head(s)  154  can be constructed from separate pieces coupled during assembly of the cage  100 . For example, the main body  152  can be inserted through/into the main opening  132  of the upper and lower bars  120   a,    120   b  and the heads  154  can be coupled (permanently and/or removably coupled) to the opposing ends of the main body  152 . The main body  152  and head  154  can be coupled via press fit, snap fit, or any other form of mechanical fastening. 
         [0062]      FIGS. 6A-6C  show an example front view of an assembled lower bar  120   b,  separator  140  and pin  150 .  FIGS. 6A and 6B  illustrate the lower bar  120   b  and separators  140  in an unexpanded configuration and  FIG. 6C  illustrates the lower bars  120   b  and separators  140  in an expanded configuration. 
         [0063]    As outlined above, a threaded rod  170  can be used for controlling/limiting lateral and vertical expansion between adjacent bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 .  FIGS. 8A and 8B  illustrate a top perspective view of example threaded rod  170  opposing upper bars  120   a   1  and  120   b   1 .  FIG. 8C  is a perspective view of the example threaded rod  170  and upper and lower bar pair  120   a   2  and  120   b   2 . While the example cage  100  includes two upper and a lower bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 , it is contemplated that cage  100  can also include a single pair of upper and lower bars  120   a,    120   b  used in conjunction with a single actuator, or plurality of actuating devices, to provide horizontal and/or vertical expansion. For example,  FIG. 8C  illustrates an example of a cage  100  including a single pair of upper and lower bars  120   a,    120   b  used in conjunction with a threaded rod. 
         [0064]      FIGS. 8A and 8B  show a top view of upper bars  120   a   1  and  120   a   2  in an unexpanded ( FIG. 8A ) and horizontally expanded ( FIG. 8B ) configuration. The space between opposing upper bars  120   a   1 ,  120   a   2  can be widened when the cage is expanded in the horizontal/lateral direction. Likewise, the space between opposing lower bars  120   b   1  and  120   b   2  can be widened when the cage is expanded in the horizontal/lateral direction. As provided in  FIGS. 8A-8C , at least one of the bars  120  includes an arm  138  extending from a top surface  124  of the bar  120 . For example, as illustrated in  FIGS. 8A-8C , each bar  120  of the upper and lower bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  include an arm  138  extending from a top surface  124  of the bar  120 . The arm  138  extends in a direction towards the adjacent bar pair and engages the threaded rod  170 . The threaded rod  170  can include a channel(s)  172  for engaging the arms  138  such that the arms  138  are movable (in a perpendicular direction) with respect to the threaded rod  170 . For example, as the threaded rod  170  rotates, the arm  138  is maintained within the channel  172  and the shear movement between the opposing bars is limited. Shear movement of one bar pair (e.g.,  120   a   2 ,  120   b   2 ) with respect to the opposite side bar pair (e.g.,  120   a   1 ,  120   b   1 ) is controlled/limited by contact between the arm  138  and the side of the channel  172 . As illustrated in  FIGS. 8A-8C , the example threaded rod  170  can include two channels  172  (first channel  172   a  and second channel  172   b ). To prevent interference, the arms  138  extending from the upper bars  120   a   1 ,  120   a   2  engage opposite channels, e.g., the arm  138  extending from the first upper  120   a   1  bar can engage the first channel  172   a  and the arm extending from the second upper bar  120   a   2  can engage the second channel  172   b.  Likewise, the arms extending from the lower bars  120   b  can engage different channels, e.g., the arm extending from the first lower bar  120   b   1  can engage the second channel  172   b  and the arm extending from the second lower bar  120   b   2  can engage the first channel  172   a . The upper and lower bars  120   a,    120   b  can also include a recess  139  for receiving all or a portion of the arm  138  extending from the opposing upper/lower bar  120   a,    120   b.  For example, as illustrated in  FIGS. 8A and 8B , the first upper bar  120   a   1  can include a recess  139  for receiving a portion of the arm  138  extending from the second upper bar  120   a   2 . Likewise, the second upper bar  120   a   2  can include a recess  139  for receiving a portion of the arm  138  extending from the first upper bar  120   a   1 . The recess  139  allows the intervertebral cage  100  to have a smaller size when in an unexpanded configuration by allowing the arms  138  to overlap with each of the opposing bars  120 . In an example cage  100 , the recess  139  can define the limit of lateral movement between opposing bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  towards each other. The arms  138  and corresponding recesses  139  can be located at any point along the length of the bar  120 . As illustrated in  FIGS. 8A-8C , the arms  138  and recesses  139  are located proximate the pin  150  location. It is contemplated, however, that the arms  138  and recesses  139  can be located proximate the ends of the bars  120 . The arms  138  and recesses  139  can also be located at positions symmetrical or asymmetrical about the midline plane of the bars  120 . 
         [0065]    Expansion of the cage  100  will now be explained in reference to  FIGS. 9A-9D . As outlined above, and illustrated in annotated  FIG. 9A , the cage  100  can be expanded in both the lateral and vertical direction. Lateral and/or vertical expansion can be symmetrical or asymmetrical with respect to opposing bar pairs and/or opposite ends of the same bar pair.  FIGS. 9B-9D  are perspective views of the example intervertebral cage  100  in transition from an unexpanded configuration ( FIG. 9B ) to a lateral expanded configuration (FIG. C), to a fully expanded, lateral and vertical, configuration ( FIG. 9D ). Though not illustrated, asymmetrical expansion can be accomplished by including different height separators  140  between the opposing bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . For example, the first bar pair  120   a   1 ,  120   b   1  can include a separator  140  having a first height and the second bar pair  120   a   2 ,  120   b   2  can include a separator  140  having a second/different height. Likewise, asymmetrical expansion can be accomplished by including opposing bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  with different height. The example cage  100  includes a threaded rod  170  for controlling/limiting lateral movement between adjacent bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . Each of the bars upper and lower bars  120   a,    120   b  include an arm  138  for engaging all or a portion of the corresponding recess/channel  139  in the respective opposing bar pair. For example, as illustrated in  FIGS. 9A-9D , the first upper bar  120   a   1  can include a recess  139  for receiving the arm  138  extending from the second upper bar  120   a   2 . Likewise, the second upper bar  120   a   2  can include a recess  139  for receiving the arm  138  extending from the first upper bar  120   a   1 . Similar arm  138 /recess  139  configurations can be included on the first and second lower bar  120   b   1  and  120   b   2 . Shear movement between the bar pairs  120   a   1 ,  120   a   2  and  120   b   1 ,  120   b   2  can be controlled/limited by contact between the arms  138  and the side walls of the recesses  139 . In the example cage  100 , the recess  139  can extend through the entire width of the bars  120 . Each of the bars  120  can also include a projection  137  extending from the side surface  136  of the bar  120  in a direction towards the opposing upper/lower bar  120   a,    120   b.  The projection  137  can allow the bar pairs  120   a   1 ,  120   a   2  and  120   b   1 ,  120   b   2  to be in contact once the intervertebral cage  100  is as it maximum horizontal expansion The projection  137  can also contact the threaded rod  170  and/or spacer  180  during lateral expansion. The projection  137  can be used to maintain connection between both sets of bars  120  after the cage  100  is fully laterally expanded, as illustrated in  FIGS. 9C and 9D . 
         [0066]    As outlined above, the bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  are spaced from one another across the vertical midline of the cage  100 . The space between the bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  can be widened when the cage  100  is expanded in the horizontal/lateral and vertical direction. To cause movement of each bar pair  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  in the lateral and vertical direction the cage  100  includes at least one spacer  180  having a threaded opening  182  for engaging the threaded rod  170 . The spacer  180  is coupled to the separator  140  via connectors  184  and pins  186 , allowing the spacer  180  to pivot relative to each connector  184  and allowing the connectors  184  to pivot relative to the separator  140 . 
         [0067]    The spacer  180  is moveable along the threaded rod into and between the space between the bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . To cause expansion, the threaded rod  170  engages the threads provided in the threaded opening  182  of the spacer  180  to move the spacer  180  into the space between the bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . The spacers  180 , for example, may be drawn to each other along the threaded rod  170  by having different direction threads within their respective openings  182 . As the spacers  180  advance towards each other, the connectors  184  pivot relative to the spacers  180  and to the separators  140 . This movement urges the bars  120  horizontally away from the midline plane of the cage  100  as provided in  FIG. 9C , illustrating the cage  100  in a horizontally expanded configuration. Once horizontal expansion is complete, vertical expansion of the cage  100  is accomplished by further engagement between the threaded rod  170  engages the threads provided in the threaded opening  182  of the spacer  180 . For example, the connectors  184  can pivot approximately 90° with respect to the spacers  180 , further rotation of the threaded rod  170  results in vertical expansion of the cage  100 /bars  120 . As the spacer  180  advances on the threaded rod  170 , the separator  140  is advanced along the contact surface  126  of the bar  120 .  FIG. 9D  illustrates an example cage  100  after both horizontal and vertical expansion. 
         [0068]      FIG. 10A  is a perspective view of another example upper and lower bar pair  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  of an intervertebral cage  100 . The cage  100  components illustrated in  FIGS. 10A-10E  includes similar components and function as that described in reference to  FIGS. 9A-9D . As provided in  FIG. 10A , cage  100  can include two openings  132  for pins  150  on the bars  120 .  FIGS. 10B-10D  are cross-section views of the example cage  100 .  FIG. 10B  provides the cage  100  in an unexpanded configuration.  FIG. 10D  provides the cage in a fully horizontal expanded configuration.  FIG. 10E  shows a perspective view of the cage  100  in a horizontally and vertically expanded configuration. 
         [0069]    Cage  100  can include spacers  180 . The spacers  180  can have varying external structure to facilitate insertion/implantation and/or fusion. For example, the spacer  180  can include a sloped leading surface  185  to facilitate insertion into the vertebral disc space and facilitate vertical expansion of the disc space. The sloped surface  185  can begin proximate the distal end of the spacer  180 . Likewise, the spacer  180  located at the trailing end can include a sloped/curved surface  187  starting at position recessed from the leading edge for receiving bone filling material. The curved or sloped surface  187  can receive bone filling material. The curved/sloped surface  187  can also be used to guide bone filling material into the cage  100  when fully expanded. 
         [0070]    The spacers  180  can also include a support portion  188  for providing support to the arms  138  extending from the upper and lower bars  120   a,    120   b.  The support portion  188  can include a lower surface, an incline (that may mirror the incline of the separators  140 ) and an upper surface. The lower surface provides support to the arms  138  when the cage  100  is in an horizontally expanded configuration ( FIG. 10D ) and the upper surface provides support to the arms  138  when the cage  100  is in a fully (horizontally and vertically) expanded configuration ( FIG. 10E ). 
         [0071]    As described above, a separator  140  can be used to define a distance/separation between the upper and lower bar pairs  120   a,    120   b  and the height of the cage  100 . In another example, illustrated in  FIGS. 11-15 , a compliant mechanism  160  can be used to control expansion and contraction of the upper and lower bars  120   a,    120   b.  The compliant mechanism  160  can be used in conjunction with or exclusive from the separator  140  and/or pin  150 . As the upper and lower bars  120   a,    120   b  are compressed, the compliant member  160  acts as a spring providing a resistive force. In an example cage  100 , the compliant mechanism  160  can be in equilibrium in the fully compressed state and accordingly provides resistive force during distraction of the compliant member  160 /upper and lower bars  120   a,    120   b.  The compliant member  160  can provide a constant resistive force in response to the distraction of the upper and lower bars  120   a,    120   b.  In another example, the compliant member  160  can provide an irregular or phase resistive force in response to the distraction of the upper and lower bars  120   a,    120   b.    FIGS. 11A and 11B  show a front and perspective view of an example an upper and lower bar pair  120   a,    120   b  including a round/circular-shaped compliant member  160 . The round complaint member  160  can be formed integral to the upper and lower bars  120   a,    120   b.  Distraction of the upper and lower bars  120   a ,  120   b  causes the compliant member  160  to deform within the opening provided in the bars  120 . Distraction can be limited by the clearance provided between the compliant member  160  and the upper and lower bars  120   a,    120   b,  that is, the distraction can be limited by contact of the compliant member  160  with the surface of the bar opening  162 . Distraction can also be limited by modifying the stiffness of the compliant member  160 .  FIGS. 12 and 13  provide perspective views of an upper and lower bar pair  120   a,    120   b  including additional examples of compliant members  160 . In  FIG. 12 , the compliant member  160  includes two u-shaped or saddle shaped compliant members  160 . In  FIG. 13 , the compliant member  160  includes a loop-shaped structure. In another example, illustrated in the perspective view of  FIG. 14 , the compliant member  160  can be coupled to the side surface  136  of the upper and lower bars  120   a,    120   b.  For example, the compliant member  160  can include an arched structure coupled to the side of the bars and providing resistance against distraction of the upper and lower bars  120   a,    120   b.    
         [0072]      FIGS. 15, 16A and 16B  are perspective views of an intervertebral cage  100 . The cage  100  includes two upper and lower bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 , and a compliant member  160 . The compliant member  160  can include ligaments/legs  164  extending from a center member  166  and coupled to a side surface  136  of the upper and lower bars  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . The ligaments  164  can provide a resistive force in both the vertical and lateral directions by providing tension between upper and lower bars pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  and the center member. The center member  166  connects the ligaments  164  and can receive a (threaded) bar which can inhibit rotation of the upper and lower bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  with respect to the center member  166 , thereby limiting shearing (lateral movement) between the upper and lower bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . As illustrated in  FIGS. 16A and 16B , the upper and lower bars  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  can include an arm  122  extending from the top surface  124  of each of the bars  120 . The arm  122  can be used to provide stability to the coupled upper and lower bar pair  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . The arms  122  can be used maintain the bar pairs in a parallel configuration. For example, the arms  122  can include a bottom projection/lip  123  that engages the center member  166  of the compliant mechanism  160 . This engagement can be used to maintain a parallel relationship between the bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  and further limit rotational movement of the cage  100 . The arms  122  can be constructed from a rigid, semi-rigid or compliant material. In one example, the arms  120  can bend or deform to accommodate the endplate of the adjacent vertebral body. 
         [0073]      FIGS. 17A-17C  provide another example intervertebral cage  100  including a threaded rod  170  and a compliant member  160  for controlling/limiting lateral movement between adjacent bar pairs. The example cage  100  can include two upper and lower bar pairs (each pair including an upper bar and a lower bar)  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 , a threaded rod  170  extending between the bar pairs along the midline of the cage  100 , spacers  180  operatively coupled to the threaded rod  170  and the bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  via connectors  184 . The example cage  100  can also include two compliant members  160  having ligaments/legs  164  extending from a center member  166  and coupled to a side surface  136  of the upper and lower bars  120   a,    120   b.  The ligaments  164  can provide a resistive force in both the vertical and lateral directions by providing tension between upper and lower bars pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  and the center members  166 . The center member  166  connects the ligaments  164  and can receive a partial or fully threaded bar  182  which can inhibit rotation of the upper and lower bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  with respect to the center members  166  and each other, thereby limiting shearing (lateral movement) between the upper and lower bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2 . The bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  are spaced from one another across the vertical midline of the cage  100 . The space between the bar pairs  120   a   1 ,  120   b   1  and  120   a   2 ,  120   b   2  can be widened when the cage  100  is expanded in the horizontal and vertical direction by rotation of the threaded shaft  170  and engagement of the spacers  180  and separators  140 , as outlined above. 
         [0074]      FIGS. 18A-18K  provide another example cage  200 . Similar to cage  100  described above, cage  200  is designed for implantation and fusion between adjacent vertebrae. It is contemplated that cage  100  and cage  200  may include like components. Where possible, corresponding element numbers are used to describe like components. 
         [0075]    As will be described in more detail below, cage  200  can expand horizontally and/or vertically. For example, once positioned the cage  200  can be expanded in a horizontal direction in the plane of the intervertebral space in which the cage  200  is located. The cage  200  can also be expanded in a vertical direction to increase the vertical separation between the adjacent vertebrae. A single actuator, or plurality of actuating devices, can be used to provide horizontal and vertical expansion. 
         [0076]    The cage  200  can include a pair of front and back lateral bars  210   a,    210   b  and a pair of upper and lower horizontal bars  220   a,    220   b.  The lateral and horizontal bars surround a central component  240 . The cage  200  can include a plurality of actuating members, for example, threaded rod  270  and screws  275 . The threaded rod  270  and screws  275  can be used to drive the expandable surfaces (lateral and horizontal bars  210 ,  220 ) of the cage  200 . 
         [0077]    As will be described in more detail below, the lateral and vertical space between the lateral and horizontal bars  210 ,  220  can be increased/decreased as the cage  200  is expanded/retracted.  FIG. 18A  is a perspective view of the cage  200  in an unexpanded configuration.  FIG. 18B  is a perspective view of the cage  200  in a horizontally expanded configuration.  FIG. 18C  is a perspective view of the cage  200  in a fully expanded (horizontal and vertical) configuration. 
         [0078]      FIGS. 18D-18G  provide perspective views of various cage  200  components. As illustrated, the threaded rod  270  can extend through a bore provided in the central component  240 . The bore can include a threaded or non-threaded interior surface. The screws  275  can extend through bores and/or channels provided in the central component  240 . For example, as illustrated in  FIG. 18D , vertical screws  275   a  can extend through bores extending between the top and bottom surface of the central component  240 . Likewise, horizontal screws  275   b  can extend through horizontal channels/openings extending between the front and back side surfaces of the central component  240 . The central component  240  can have braces extending from the horizontal/lateral surface to maintain the distance between the screws  275  and the central component  240 . As provided in  FIG. 18E, 18G and 18H , screws  275  can movably engage the threaded rod  270  in an orthogonal arrangement. For example, screws  275  and threaded rod  270  can form a worm drive. In an example cage  200 , the threads of the threaded rod  270  engage corresponding gears and/or threads of the screws  275 . Each of the vertical screws  275   a  and horizontal screws  275   b  can engage and rotate with the threaded rod  270 . 
         [0079]    As illustrated in  FIGS. 18A-18E , the screws  275  extend through the central component  240  and engage the lateral and horizontal bars  210 ,  220 . For example, the vertical screws  275   a  engage the top and bottom horizontal bars  220   a,    220   b.  Likewise, the horizontal screws  275   b  engage the front and back lateral bars  210   a,    210   b.  The screws  275  can engage the lateral and horizontal bars  210 ,  220  via a threaded connection provided in the corresponding lateral or horizontal bar  210 ,  220 . Rotation of the screws  275  can result in translation of the corresponding lateral or horizontal bar  210 ,  220 . Screws  275  can include a head/lip for limiting motion between corresponding lateral or horizontal bar  210 ,  220 . As provided in  FIGS. 18A and 18B , the bores provided in the lateral and horizontal bars  210 ,  220  can include a counter bore/recess sized to accommodate the head/lip of the screw  275 . 
         [0080]    The cage  200  can be expanded horizontally and/or vertically. As outlined above, it is contemplated that the cage  200  is expanded horizontally, followed by vertical expansion.  FIGS. 18B and 18I  illustrate cage  200  in horizontally expanded configuration. To ensure that horizontal expansion occurs before vertical expansion, the top and bottom horizontal bars  220   a,    220   b  do not contact the threaded portions of the vertical screws  275   a.  Accordingly, vertical expansion of the cage  200  will not occur until contact between the vertical screws  275   a  and the top and bottom horizontal bars  220   a,    220   b.    FIG. 18J  illustrates the cage  200  in an almost complete horizontally expanded configuration. As provided in  FIG. 18J , the inside surface of the lateral bars  210  can include a lip/protrusion  212  for engaging a corresponding beveled edge  222  included on an inside surface of the horizontal bars  220 . Engagement between the lip  212  and edge  222  can cause articulation between the lateral bars  210  and horizontal bars  220 . That is, engagement between the lip  212  and edge  222  directs the upper and lower horizontal bars  220   a ,  220   b  vertically, thereby causing the upper and lower horizontal bars  220   a,    220   b  to engage the vertical screws  275   a.    
         [0081]    Once the horizontal expansion of the front and back lateral bars  201   a,    210   b  is complete, the vertical screws  275   a  engage the upper and lower horizontal bars  220   a,    220   b.  Additional rotation of the threaded rod  270  results in vertical expansion/separation of the upper and lower horizontal bars  220   a,    220   b.  To inhibit excess lateral expansion, while vertical expansion is occurring, the ends of horizontal screws  275   b  do not include threads. Accordingly, only vertical expansion occurs at the end phase of the cage  200  expansion.  FIG. 18K  illustrates the cage  200  in a vertically and horizontally expanded configuration. 
         [0082]    The cage  200  can include surface features, treatment and/or recesses to encourage fusion between the cage  200  and the adjacent vertebral bodies. As illustrated in  FIGS. 18A-18C , the lateral bars  210  and/or horizontal bars  220  can include rectangular openings  224  to receive bone filing material/biologics. The openings  224  can also permit the worm/gears associated with the screws  275  to rotate without impacting or otherwise damaging the lateral and/or horizontal bars  210 ,  220 . 
         [0083]    One or more components of the cage  100 / 200  may be made from any biocompatible material known including, for example, metals such as titanium, titanium alloys, stainless steel and cobalt chromium. Other materials include, for example, composites, polymers, ceramics, bone (allograft) and any other materials suitable for the cage  100 / 200 . In one example, the cage  100 / 200  can be constructed from a radiopaque material including, for example, stainless steel such as 17-4PH stainless steel. Likewise, one or more components of the cage  100 / 200  can be constructed from a radiolucent material to enhance visibility of the assembly during radiographic imaging. Example radiolucent materials can include “life science” grade PEEK (Ketron 450G PEEK). Life science grade PEEK can improve wear and abrasion characteristics as well as provide high yield strength. 
         [0084]    While the foregoing description and drawings represent the an example implementation of the present invention, it will be understood that various additions, modifications, combinations and/or substitutions may be made therein without departing from the spirit and scope of the present invention as defined in the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other specific forms, structures, arrangements, proportions, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. One skilled in the art will appreciate that the invention may be used with many modifications of structure, arrangement, proportions, materials, and components and otherwise, used in the practice of the invention, which are particularly adapted to specific environments and operative requirements without departing from the principles of the present invention. In addition, features described herein may be used singularly or in combination with other features. The presently disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims and not limited to the foregoing description. 
         [0085]    It will be appreciated by those skilled in the art that changes could be made to the example implementations described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular examples disclosed, but it is intended to cover modifications within the spirit and scope of the present invention, as defined by the following claims.