Abstract:
Embodiments of the present disclosure relate to devices and methods for treating one or more damaged, diseased, or traumatized portions of the spine, including intervertebral discs, to reduce or eliminate associated back pain. In one or more embodiments, the present disclosure relates to an expandable interbody spacer. The expandable interbody spacer may comprise a first jointed arm comprising a plurality of links pivotally coupled end to end. The expandable interbody spacer further may comprise a second jointed arm comprising a plurality of links pivotally coupled end to end. The first jointed arm and the second jointed arm may be interconnected at a proximal end of the expandable interbody spacer. The first jointed arm and the second jointed arm may be interconnected at a distal end of the expandable interbody spacer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 13/837,209, filed Mar. 15, 2013, which is a continuation-in-part of U.S. patent application Ser. No. 13/483,852, filed May 20, 2012, now issued as U.S. Pat. No. 9,044,342, which are hereby incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure relates to embodiments of devices and methods for treating one or more damaged, diseased, or traumatized portions of the spine, including intervertebral discs, to reduce or eliminate associated back pain. In one or more embodiments, the present disclosure relates to an expandable interbody spacer. In addition, the present disclosure describes tools and methods for implanting the disclosed devices. 
       BACKGROUND OF THE INVENTION 
       [0003]    The vertebrate spine is the axis of the skeleton providing structural support for the other body parts. In humans, the normal spine has seven cervical, twelve thoracic and five lumbar segments. The lumbar spine sits upon the sacrum, which then attaches to the pelvis, and in turn is supported by the hip and leg bones. The bony vertebral bodies of the spine are separated by intervertebral discs, which act as joints but allow known degrees of flexion, extension, lateral bending, and axial rotation. 
         [0004]    The typical vertebra has a thick anterior bone mass called the vertebral body, with a neural (vertebral) arch that arises from the posterior surface of the vertebral body. The centra of adjacent vertebrae are supported by intervertebral discs. Each neural arch combines with the posterior surface of the vertebral body and encloses a vertebral foramen. The vertebral foramina of adjacent vertebrae are aligned to form a vertebral canal, through which the spinal sac, cord and nerve rootlets pass. The portion of the neural arch which extends posteriorly and acts to protect the spinal cord&#39;s posterior side is known as the lamina. Projecting from the posterior region of the neural arch is the spinous process. 
         [0005]    The intervertebral disc primarily serves as a mechanical cushion permitting controlled motion between vertebral segments of the axial skeleton. The normal disc is a unique, mixed structure, comprised of three component tissues: the nucleus pulpous (“nucleus”), the annulus fibrosus (“annulus”) and two vertebral end plates. The two vertebral end plates are composed of thin cartilage overlying a thin layer of hard, cortical bone which attaches to the spongy, richly vascular, cancellous bone of the vertebral body. The end plates thus act to attach adjacent vertebrae to the disc. 
         [0006]    The spinal disc and/or vertebral bodies may be displaced or damaged due to trauma, disease, degenerative defects, or wear over an extended period of time. One result of this displacement or damage to a spinal disc or vertebral body may be chronic back pain. A common procedure for treating damage or disease of the spinal disc or vertebral body may involve partial or complete removal of an intervertebral disc. An implant, which may be referred to as an interbody spacer, can be inserted into the cavity created where the intervertebral disc was removed to help maintain height of the spine and/or restore stability to the spine. An example of an interbody spacer that has been commonly used is a cage, which typically is packed with bone and/or bone-growth-inducing materials. However, there are drawbacks associated with conventional interbody spacers, such as cages and other designs. For instances, conventional interbody spacers may be too large and bulky for introduction into the disc space in a minimally invasive manner, such as may be utilized in a posterior approach. Further, these conventional interbody spacers may have inadequate surface area contact with the adjacent endplates if sized for introduction into the disc space in a minimally invasive manner. In addition, conventional interbody spacers designed for introduction into the disc space in a minimally invasive manner may lack sufficient space for packing of bone-growth-inducing material, thus potentially not promoting the desired graft between the adjacent endplates. 
         [0007]    Therefore, a need exists for an interbody spacer that can be introduced in a minimally manner that provides a desired amount of surface area contact with the adjacent endplates and has an increased space for packing of bone-growth-inducing material. 
       SUMMARY OF THE INVENTION 
       [0008]    Embodiments of the present disclosure relates to an expandable interbody spacer. The expandable interbody spacer may comprise a first jointed arm comprising a plurality of links pivotally coupled end to end. The expandable interbody spacer further may comprise a second jointed arm comprising a plurality of links pivotally coupled end to end. The first jointed arm and the second jointed arm may be interconnected at a proximal end of the expandable interbody spacer. The first jointed arm and the second jointed arm may be interconnected at a distal end of the expandable interbody spacer. The first jointed arm and the second jointed arm may each be configured to fold inward in opposite directions to place the expandable interbody spacer in an expanded position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Embodiments of the present disclosure will be more readily understood with reference to the embodiments thereof illustrated in the attached drawing figures, in which: 
           [0010]      FIG. 1  is a top view of an expandable interbody spacer shown in a collapsed position in accordance with embodiments of the present disclosure; 
           [0011]      FIG. 2  is a side view of the expandable interbody spacer of  FIG. 1  shown in a collapsed position; 
           [0012]      FIG. 3  is a proximal end view of the expandable interbody spacer of  FIG. 1  shown in a collapsed position; 
           [0013]      FIG. 4  is a distal end view of the expandable interbody spacer of  FIG. 1  shown in a collapsed position; 
           [0014]      FIG. 5  is an exploded view of the expandable interbody spacer of  FIG. 1 ; 
           [0015]      FIG. 6  is a top view of the expandable interbody spacer of  FIG. 1  shown in an expanded position; 
           [0016]      FIG. 7  is a right side view of the expandable interbody spacer of  FIG. 1  shown in an expanded position; 
           [0017]      FIG. 8  is a left side view of the expandable interbody spacer of  FIG. 1  shown in an expanded position; 
           [0018]      FIG. 9  is a proximal end view of the expandable interbody spacer of  FIG. 1  shown in an expanded position; 
           [0019]      FIG. 10  is a distal end view of the expandable interbody spacer of  FIG. 1  shown in an expanded position; 
           [0020]      FIG. 11  is a view showing disc space between adjacent vertebrae in accordance with embodiments of the present disclosure; 
           [0021]      FIG. 12  is a view of a tool for insertion of an expandable interbody spacer in accordance with embodiments of the present disclosure; 
           [0022]      FIG. 13  is a view showing the tool of  FIG. 12  introducing an expandable interbody spacer into a disc space in a collapsed position in accordance with embodiments of the present disclosure; 
           [0023]      FIG. 14  is a view showing the tool of  FIG. 12  expanding an expandable interbody spacer in a disc space in accordance with embodiments of the present disclosure; 
           [0024]      FIG. 15  is a view showing a funnel for introduction of bone-growth-inducing material into a disc space in accordance with embodiments of the present disclosure; 
           [0025]      FIG. 16  is an exploded view of another embodiment of an expandable interbody spacer; 
           [0026]      FIG. 17  is a top view of another embodiment of an expandable interbody spacer shown in a collapsed position; 
           [0027]      FIG. 18  is a top view of the expandable interbody spacer of  FIG. 17  shown in an expanded position; 
           [0028]      FIG. 19  is an exploded view of the expandable interbody spacer of  FIG. 17 ; 
           [0029]      FIG. 20  is an exploded view of a link of a jointed arm of the expandable interbody spacer of  FIG. 17 ; 
           [0030]      FIG. 21  is a top view of another embodiment of an expandable interbody spacer shown in a collapsed position; 
           [0031]      FIG. 22  is a top view of the expandable interbody spacer of  FIG. 21  shown in an expanded position; 
           [0032]      FIG. 23  is a view of the expandable interbody spacer of  FIG. 21  shown in a disc space in a collapsed position; 
           [0033]      FIG. 24  is a view of the expandable interbody spacer of  FIG. 21  shown in a disc space in an expanded position; 
           [0034]      FIG. 25  is a top view of a tool shown engaging the expandable interbody spacer of  FIG. 21  in accordance with embodiments of the present disclosure; 
           [0035]      FIG. 26  is a view showing the tool of  FIG. 24  expanding the expandable interbody spacer of  FIG. 24  in a disc space in accordance with embodiments of the present disclosure; 
           [0036]      FIG. 27A  is an isometric view of an exemplary expandable interbody spacer in an expanded position, in accordance with a further embodiment of the disclosure; 
           [0037]      FIG. 27B  is an isometric view of the expandable interbody spacer of  FIG. 27A  in the collapsed position; 
           [0038]      FIG. 28  is an exploded view of the expandable interbody spacer of  FIG. 27A . 
           [0039]      FIG. 29  depicts a cross-sectional view of the expandable interbody spacer of  FIG. 27A  in the collapsed position; 
           [0040]      FIG. 30  depicts an embodiment of an exemplary tool for implanting an embodiment of an exemplary expandable interbody spacer, in accordance with the principles of the present disclosure; 
           [0041]      FIG. 31  depicts a partially-exploded view of various components of the tool shown in  FIG. 30 ; 
           [0042]      FIG. 32A  depicts a cross-sectional view of a proximal portion of the tool of  FIG. 30 ; 
           [0043]      FIG. 32B  depicts a cross-sectional view of an actuator assembly; 
           [0044]      FIG. 32C  depicts an exploded view of the actuator assembly; 
           [0045]      FIGS. 33-43  depict various views of components of the exemplary tool of  FIG. 30  and their interaction with an exemplary interbody spacer; and 
           [0046]      FIG. 44  depicts a final implanted configuration of an exemplary embodiment of an expandable interbody spacer. 
       
    
    
       [0047]    Throughout the drawing figures, it should be understood that like numerals refer to like features and structures. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    The preferred embodiments of the disclosure will now be described with reference to the attached drawing figures. The following detailed description of the invention is not intended to be illustrative of all embodiments. In describing preferred embodiments of the present disclosure, specific terminology is employed for the sake of clarity. However, the embodiments described herein are not intended to be limited to the specific terminology so selected. It is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
         [0049]    As used herein, the term “proximal” may refer to a portion of a device or component thereof disposed closest to an operator or healthcare professional during an implantation procedure. Conversely, the term “distal” may refer to a portion of a device or component thereof disposed opposite the proximal portion and disposed farther from the operator or healthcare professional during an implantation procedure. As discussed below, the embodiments of expandable interbody spacers described herein may be implanted via any suitable approach known in the art. It is contemplated, however, that the disclosed embodiments may be implanted via an offset (e.g., 20-40 degree offset) posterior approach. Accordingly, solely for orientation purposes, a “proximal” portion of the device, when implanted, may be disposed posteriorly relative to a patient, if implanted via a posterior approach. 
         [0050]    Referring to  FIGS. 1-10 , an expandable interbody spacer  10  is shown in accordance with embodiments of the present disclosure. In the illustrated embodiment, the expandable interbody spacer  10  has a proximal end  20  and a distal end  30 . The expandable interbody spacer  10  may include a first jointed arm  40  and a second jointed arm  50  positioned on either side of longitudinal axis  15  of the spacer  10 . The first and second jointed arms  40 ,  50  may be interconnected at the proximal end  20 , for example, by a proximal connection member  60 . The first and second jointed arms  40 ,  50  may be interconnected at the distal end  30 , for example, by a distal connection member  70 . The first and second jointed arms  40 ,  50  of the expandable interbody spacer  10  may be made from a number of materials, including titanium, stainless steel, titanium alloys, non-titanium alloys, polymeric materials, plastic composites, polyether ether ketone (“PEEK”) plastic material, ceramic, elastic materials, and combinations thereof. While the expandable interbody spacer  10  may be used with a posterior, anterior, lateral, or combined approach to the surgical site, the spacer  10  may be particularly suited with a posterior approach. 
         [0051]    The first jointed arm  40  has a proximal end  80  and a distal end  90 . The proximal end  80  may be pivotally coupled to the proximal connection member  60 . The distal end  90  may be pivotally coupled to the distal connection member  70 . Any of a variety of different fasteners may be used to pivotally couple the proximal end  80  and the distal end  90  and the proximal connection member  60  and the distal connection member  70 , such as pins  100 , for example. In another embodiment (not illustrated), the connection may be a hinged connection. As illustrated, the first jointed arm  40  may comprise a plurality of links that are pivotally coupled to one another. In the illustrated embodiment, the first jointed arm  40  comprises first link  110 , second link  120 , and third link  130 . When the spacer  10  is in a collapsed position, the first link  110 , second link  120 , and third link may be generally axially aligned. As illustrated, the first link  110 , second link  120 , and third link  130  may be connected end to end. When the spacer  10  is in a collapsed position, the first link  110 , second link  120 , and third link  130  may be generally axially aligned. The first link  110  and the second link  120  may be pivotally coupled, and the second link  120  and the third link  130  may also be rotatably coupled. Any of a variety of different fasteners may be used to pivotally couple the links  110 ,  120 ,  130 , such as pins  100 , for example. In another embodiment (not illustrated), the coupling may be via a hinged connection. 
         [0052]    As best seen in  FIGS. 1 ,  5 - 7 ,  9 , and  10 , an upper surface  140  of the first jointed arm  40  may be defined by the links  110 ,  120 ,  130 . The upper surface  140  should allow for engagement of the first jointed arm  40  with one of the adjacent vertebral bodies. In some embodiments, the upper surface  140  may include texturing  150  to aid in gripping the adjacent vertebral bodies. Although not limited to the following, the texturing  150  can include teeth, ridges, friction-increasing elements, keels, or gripping or purchasing projections. 
         [0053]    As best seen in  FIGS. 7 ,  9 , and  10  a lower surface  160  of the first jointed arm  40  may be defined by the links  110 ,  120 ,  130 . The lower surface  160  should allow for engagement of the first jointed arm  40  with one of the adjacent vertebral bodies. In some embodiments, the lower surface  160  may include texturing  170  to aid in gripping the adjacent vertebral bodies. Although not limited to the following, the texturing  170  can include teeth, ridges, friction-increasing elements, keels, or gripping or purchasing projections. 
         [0054]    The second jointed arm  50  has a proximal end  180  and a distal end  190 . The proximal end  180  may be pivotally coupled to the distal connection member  70 . The distal end  190  may be pivotally coupled to the distal connection member  70 . Any of a variety of different fasteners may be used to pivotally couple the proximal end  180  and the distal end  190  and the proximal connection member  60  and the distal connection member  70 , such as pins  100 , for example. In another embodiment (not illustrated), the connection may be a hinged connection. As illustrated, the second jointed arm  50  may comprise a plurality of links that are pivotally coupled to one another. In the illustrated embodiment, the second jointed arm  50  comprises first link  200 , second link  210 , and third link  220 . When the spacer  10  is in a collapsed position, the first link  200 , second link  210 , and third link  220  may be generally axially aligned. As illustrated, the first link  200 , second link  210 , and third link  220  may be connected end to end. The first link  200  and the second link  210  may be pivotally coupled, and the second link  210  and the third link  220  may also be pivotally coupled. Any of a variety of different fasteners may be used to pivotally couple the links  200 ,  210 ,  220 , such as pins  100 , for example. In another embodiment (not illustrated), the coupling may be via a hinged connection. 
         [0055]    As best seen in  FIGS. 1 ,  2 ,  6 , and  8 - 10 , an upper surface  230  of the second jointed arm  50  may be defined by the links  200 ,  210 ,  220 . The upper surface  230  should allow for engagement of the second jointed arm  50  with one of the adjacent vertebral bodies. In some embodiments, the upper surface  230  may include texturing  240  to aid in gripping the adjacent vertebral bodies. Although not limited to the following, the texturing  240  can include teeth, ridges, friction-increasing elements, keels, or gripping or purchasing projections. 
         [0056]    As best seen in  FIGS. 8-10 , a lower surface  250  of the second jointed arm  50  may be defined by the links  200 ,  210 , and  220 . The lower surface  250  should allow for engagement of the second jointed arm  50  with one of the adjacent vertebral bodies. In some embodiments, the lower surface  250  may include texturing  260  to aid in gripping the adjacent vertebral bodies. Although not limited to the following, the texturing  260  can include teeth, ridges, friction-increasing elements, keels, or gripping or purchasing projections. 
         [0057]    With reference now to  FIGS. 3 ,  5 , and  9 , a bore  270  extends through proximal connection end  60 . The bore  270  may extend generally parallel to the longitudinal axis  12  (see  FIG. 1 ) of the spacer  10 . The first jointed arm  40  and the second jointed arm  50  may define a hollow interior portion (not shown) that extends axially through the spacer  10 . The bore  270  in the proximal connection end  60  may communicate with this hollow interior portion. As best shown on  FIG. 5 , the distal connection end  70  may include an opening  280 . As illustrated, the opening  280  may face inward and may not extend all the way through the distal connection  70 . In one embodiment, the opening  280  may be generally aligned with the bore  270  in the proximal connection end  60  such at a tool (e.g., tool  340  shown on  FIG. 12 ) inserted into the bore  270  may be received in the opening  280  for placement of the spacer  10  into a disc space and/or expansion of the spacer  10 . 
         [0058]      FIGS. 1-4  illustrate the expandable interbody spacer  10  in a collapsed position. In accordance with present embodiments, the expandable interbody spacer  10  may be laterally expanded to an expanded position.  FIGS. 6-10  illustrate the expandable interbody spacer  10  in an expanded position. In the expanded position, the first arm  40  and the second arm  50  have each been folded inward in opposite directions. For example, the proximal end  80  and the distal end  90  of the first arm  40  may be folded closer together. The links  110 ,  120 ,  130  should pivot with respect to one another when the first arm  40  is folded inward. The proximal end  80  should pivot at the proximal connection end  60 , and the distal end  90  should pivot at the distal connection end  70 . By way of further example, the proximal end  180  and the distal end  190  of the second arm  50  may also be folded together. The links  200 ,  210 ,  220  should pivot with respect to another when the second arm is folded inward. The proximal end  180  should pivot at proximal connection end  60 , and the distal end  190  should pivot at the distal connection end  70 . After placement in the expanded position, the expandable interbody spacer  10  can be secured in the expanded position to prevent collapse of the expandable interbody spacer  10  upon application of spacer. Any of a variety of different techniques may be used to secure the expandable interbody spacer  10 , including pins or other suitable locking mechanism, for example. 
         [0059]    As illustrated by  FIG. 6 , the first and second jointed arms  40 ,  50  define an interior cavity  290  when in an expanded position. The interior cavity  290  may be filled with a bone-growth-inducing material, such as bone material, bone-growth factors, or bone morphogenic proteins. As will be appreciated by those of ordinary skill in the art, the bone-growth-inducing material should induce the growth of bone material, thus promoting fusion of the adjacent vertebra. 
         [0060]    The expandable interbody spacer  10  may be sized to accommodate different applications, different procedures, implantation into different regions of the spine, or size of disc space. For example, the expandable interbody spacer  10  may have a width W 1  (as shown on  FIG. 1 ) prior to expansion of about 8 mm to about 22 mm and alternatively from about 10 mm to about 13 mm. By way of further example, the expandable interbody spacer  10  may be expanded to a width W 2  (as shown on  FIG. 6 ) in a range of about 26 mm to about 42 mm and alternatively from about 16 mm to about 32 mm. It should be understood that the width W 1  or W 2  whether prior to, or after, expansion generally refers to the width of the expandable interbody spacer  10  extending transverse to the longitudinal axis  12  of the spacer  10 . In general, the width W 2  of the expandable interbody spacer  10  after expansion should be greater than the width W 1  of the expandable interbody spacer  10  prior to expansion. 
         [0061]    In accordance with present embodiments, the expandable interbody spacer  10  may be used in the treatment of damage or disease of the vertebral column. In one embodiment, the expandable interbody spacer  10  may be inserted into a disc space between adjacent vertebrae in which the intervertebral disc has been partially or completely removed.  FIG. 11  illustrates a spinal segment  300  into which the expandable interbody spacer  10  (e.g.,  FIGS. 1-10 ) may be inserted. The spinal segment  300  includes adjacent vertebrae, identified by reference numbers  310  and  320 . Each of the adjacent vertebrae  310 ,  320  has a corresponding endplate  315 ,  325 . The disc space  330  is the space between the adjacent vertebrae  310 ,  320 .  FIG. 12  illustrates a tool  340  that may be used in the insertion of the expandable interbody spacer  10  into the disc space  330 . The tool  340  includes a shaft  350  having an elongated end portion  360  for coupling to the expandable interbody spacer  10 . The elongated end portion  360  has a distal tip  370 . 
         [0062]      FIGS. 13 and 14  illustrate introduction of an expandable interbody spacer  10  into the disc space  330  using tool  340 . For illustrative purposes, the upper vertebra  330  shown on  FIG. 11  has been removed from  FIGS. 13 and 14 . As illustrated, the spacer  10  may be secured to the tool  340 . For example, the elongated end portion  360  of the tool  340  may be disposed through the bore  270  (e.g., see  FIG. 5 ) in the proximal connection end  60  with the distal tip  370  (e.g., see  FIG. 12 ) of the end portion  360  secured in the opening  280  (e.g., see  FIG. 5 ) in the distal connection end  70 . As illustrated by  FIG. 13 , the tool  340  may introduce the spacer  10  into the disc space  330  through an access cannula  380 . After introduction into the disc space  330 , the spacer  10  may be laterally expanded. In accordance with present embodiments, the spacer  10  can be laterally expanded by folding the first arm  40  and the second arm  50  inward. By expanding laterally, the spacer  10  has an increased surface area contact with the endplate  325 . In addition, the spacer  10  may engage harder bone around the apophyseal ring. As previously mentioned, an interior cavity  290  should be formed in the spacer  10  when in the expanded position. The tool  340  may then be detached from the spacer  10  and removed from the cannula  380 . As illustrated by  FIG. 15 , a funnel  390  may then be placed on the cannula  380 . Bone-growth inducing material may then be placed into the interior cavity  290  through the cannula  380 . Because the spacer  10  has been laterally expanded, the interior cavity  290  should have a desirable amount of space for packing of the bone-growth-inducing material. 
         [0063]      FIG. 16  illustrates an expandable interbody spacer  10  in accordance with an alternative embodiment. In the illustrated embodiment, the expandable interbody spacer  10  comprises a first jointed arm  40  and a second jointed arm  50 . The first jointed arm  40  has a proximal end  80  and a distal end  90 . The first jointed arm  40  comprises a plurality of links  110 ,  120 ,  130  connected end to end, for example, by pins  100 . The first jointed arm  40  further may comprise washers  105  (e.g, PEEK washers) that may be disposed between the links  110 ,  120 ,  130  at their connections. The second jointed arm  50  has a proximal end  180  and a distal end  190 . The second jointed arm  50  comprises a plurality of links  200 ,  210 ,  220  connected end to end, for example, by pins  100 . The second jointed arm  50  further may comprise washers  105  (e.g, PEEK washers) that may be disposed between the links  200 ,  210 ,  220  at their connections. Washers  105  may also be disposed between the first arm  40  and the proximal connection member  60  and the distal connection member  70  at their respective connections. Washers  105  may also be disposed between the second arm  50  and the proximal connection member  60  and the distal connection member  70  at their respective connections. The washers  105  should have an interference fit to cause friction such that the spacer  10  may hold its shape in the entire range of the expanded implant. 
         [0064]    The proximal ends  80 ,  180  may be pivotally coupled, for example, by pin  100 , as shown on  FIG. 19 . The distal ends  90 ,  180  may also be pivotally coupled, for example, by pin  100 , as shown on  FIG. 19 . The first jointed arm  40  comprises first link  110  and third link  130 , the first link  110  and the third link  130  being pivotally coupled. In contrast to the first jointed arm  40  of  FIGS. 1-10 , there 
         [0065]    Referring now to  FIGS. 17-19 , an expandable interbody spacer  10  is illustrated in accordance with another embodiment of the present disclosure. In the illustrated embodiment, the expandable interbody spacer  10  comprises a first jointed arm  40  and a second jointed arm  50 . The first jointed arm  40  has a proximal end  80  and a distal end  90 . The second jointed arm  50  has a proximal end  180  and a distal end  190 . The proximal ends  80 ,  180  may be pivotally coupled, for example, by pin  100 , as shown on  FIG. 19 . The distal ends  90 ,  180  may also be pivotally coupled, for example, by pin  100 , as shown on  FIG. 19 . The first jointed arm  40  comprises first link  110  and third link  130 , the first link  110  and the third link  130  being pivotally coupled. In contrast to the first jointed arm  40  of  FIGS. 1-10 , there is no second link  120 . As shown by  FIG. 20 , the third link  130  may comprise a first link segment  400  and a second link segment  410 , which may be secured to one another by pins  420 , for example. First link segment  400  and second link segment  410  may also have a tongue-and-groove connection, for example a groove  430  in the first link segment  400  may receive a tongue  440  of the second link segment  410 . The second jointed arm comprises first link  200  and third link  220 , the first link  200  and the third link  220  being pivotally coupled. In contrast to the second joint arm  50  of  FIGS. 1-10 , there is no second link  210 . 
         [0066]    In accordance with present embodiments, lateral expansion of the expandable interbody spacer  10  of  FIGS. 17-19  may include folding the first arm  40  and the second arm  50  inward. For example, the proximal end  80  and the distal end  90  of the first arm  40  may be folded together, and the proximal end  180  and the distal end  190  of the second arm  50  may also be folded together. 
         [0067]    Referring now to  FIGS. 21 and 22 , an expandable interbody spacer  10  is illustrated in accordance with another embodiment of the present disclosure. In the illustrated embodiment, the expandable interbody spacer  10  has a proximal end  20  and a distal end  30 . The expandable interbody spacer  10  may include a first jointed arm  40  and a second jointed arm  50  positioned on either side of longitudinal axis  12  of the spacer  10 . As illustrated, the expandable interbody spacer  10  further may comprise an internal screw  450 . The internal screw  450  may comprise a head  460  and an elongated body  470 , which may extend generally parallel to the longitudinal axis  12  of the spacer  10 . In some embodiments, the internal screw  450  may extend from the proximal end  20  to the distal end  30  of the spacer  10 . In one embodiment, the elongated body  470  may be retractable. For example, the elongated body  470  may retract into the head  460 , as shown on  FIG. 22 . 
         [0068]    As illustrated by  FIGS. 23 and 24 , the spacer  10  may be introduced into the disc space  330 , wherein the spacer  10  can be laterally expanded. In accordance with present embodiments, the spacer  10  can be laterally expanded by folding the first arm  40  and the second arm  50  inward. In some embodiments, the elongated body  470  may be retracted into the head  460  to cause folding of the first arm  40  and the second arm  50  inward, as the first arm  40  and the second arm  50  are secured to the distal end  480  of the internal screw  450 . 
         [0069]      FIG. 25  shows attachment of a tool  490  to the expandable interbody spacer  10  of  FIGS. 22 and 23  in accordance with embodiments of the present disclosure. As illustrated, the tool  490  may have an attachment end  500 , which can be secured to the head  460  of the internal screw  450 . As shown by  FIG. 26 , the tool  40  can be used to introduce the spacer  10  into the disc space  330 , wherein the spacer  10  can be laterally expanded. 
         [0070]    Turning now to  FIG. 27A-29 , there are depicted multiple views of a further embodiment of an expandable interbody spacer  2700 , in accordance with an aspect of the present disclosure. The expandable interbody spacer  2700  may include one or more features of any of the other interbody spacers discussed herein. For example, although the spacer  2700  and its components may be made of titanium, any suitable biocompatible material known in the art may be used. 
         [0071]    With reference to  FIG. 27A , for example, spacer  2700  may include, among other things, a proximal portion  2702 . Proximal portion  2702  may include a substantially cylindrical portion  2703 . Cylindrical portion  2703  may include a complete cylindrical shape or a partial cylindrical shape. In addition, cylindrical portion  2703  may define a lumen  2704  therethrough. A surface of the lumen  2704  may include one or more geometric features, such as, for example, screw threads  2705 , as described in greater detail below. In one embodiment, lateral surfaces of cylindrical portion  2703  may include one or more geometric features  2706  to facilitate engagement by a tool  3000 , as discussed below in greater detail. The geometric features  2706  may include any suitable shape and/or configuration. In one embodiment, the geometric features  2706  may include elongate notches disposed in the side walls that define cylindrical portion  2703 . Further, the elongate notches may extend into the side walls in a direction that is substantially perpendicular. 
         [0072]    A plurality of cantilevered ledges  2707  may extend distally from a distal portion of cylindrical portion  2703 . Aside from being disposed in an opposing relation to one another, the cantilevered ledges  2707  may be substantially similar to one another. The ledges  2707  may include any suitable configuration, shape, and/or size known in the art. In one embodiment, the ledges  2707  may define a space  2708  therebetween for receiving a plurality of links (as described below) of spacer  2700 . External surfaces (e.g., inferior and superior surfaces) of ledges  2707  may include texturing  150  to aid in gripping adjacent vertebral bodies, as described herein. The external surfaces may also be configured to promote bone ingrowth. For example, in one embodiment, the external surfaces of ledges  2707  may include a porous configuration or may include a coating of, e.g., hydroxyapatite. External edges of ledges  2707  may include any suitable configuration for matingly coupling with corresponding portions of the plurality of links discussed below. In one embodiment, the external edges of ledges  2707  may be curved to facilitate the plurality of links pivoting relative to each of ledges  2707 . Further, each of ledges  2707  may include one or more openings  2707   a  for receiving a pivot pin  2709  therethrough, as described below in greater detail. 
         [0073]    With continued reference to  FIGS. 27A-29 , proximal portion  2702  may be rotatably coupled via a plurality of pivot pins  2709  to links  2710  and  2712 . Links  2710  and  2712  may be substantially similar to one another. Indeed, as depicted in, e.g.,  FIG. 27A , links  2710  and  2712  may be positioned as mirror images of each other. Thus, for the purposes of brevity, similar portions of links  2710  and  2712  will be described together. Proximal portions  2714  of links  2710  and  2712  may be received in space  2708 . The proximal portions  2714  of links  2710 ,  2712  may be appropriately configured and dimensioned to fit between ledges  2707 . In addition, each of proximal portions  2714  includes a through-hole  2716  for receiving a pivot pin  2709 . The through-hole  2716  may be disposed in a scalloped cut-out on proximal portions  2714  of each of links  2710 ,  2712 . 
         [0074]    Pivot pin  2709  may include any suitable fastener known in the art for movably coupling links  2710  and  2712  to proximal portion  2702 . In one embodiment, pivot pin  2709  may be inserted and retained within openings  2707   a  and through-holes  2716  via an interference or friction fit. 
         [0075]    In some embodiments, an interface between one or both of links  2710  and  2712  and proximal portion  2702  may be configured to retain one or both of links  2710  and  2712  in a predetermined position relative to proximal portion  2702 . For example, an edge of ledge  2707  may interact with a wall  2717  to frictionally retain in a predetermined position relative to proximal portion  2702 . In one embodiment, the wall  2717  may include a raised portion (not shown), such as, e.g., a rounded bump, or other suitable feature against which the edge of ledge  2707  may engage. 
         [0076]    Superior and inferior surfaces of links  2710  and  2712  may also include suitable texturing  150  as described above. In addition, the superior and inferior surfaces may be configured to promote bone ingrowth, as described above. Each link  2710  and  2712  also may define one more openings  2718  therethrough. The openings  2718  may include any suitable configuration known in the art. In one embodiment, openings  2718  may include a substantially rectangular configuration. In other embodiments, openings  2718  may include other shapes. In one embodiment, the openings  2718  may be disposed distally of wall  2717 . Openings  2718  may be configured as bone graft windows, allowing facilitating bone ingrowth into an interior of spacer  2700  through openings  2718  An edge of opening  2718  may be appropriately beveled, chamfered, and/or rounded, as is known in the art. Further, opening  2718  may be generally disposed in a central portion of each of links  2710  and  2712 . 
         [0077]    A distal end portion of links  2710 ,  2712  may be configured to be movably coupled to another link, as discussed herein. In one embodiment, the distal end portions of links  2710 ,  2712  may define a male hinge  2719  that includes a hole  2720  therethrough. The hole  2720  may be configured to receive a pivot pin  2709  for rotatable coupling the links  2710 ,  2712  to adjacent links described below. In one embodiment, a wall perpendicular to hinge  2719  may define one or more position retaining features  2721 . As will be described below, the position retaining features  2721  may be configured to interact with corresponding features on an adjacent link to frictionally retain links in a predetermined position. 
         [0078]    The ends of each of links  2710 ,  2712  that are opposite to the ends coupled to proximal portion  2702  may be movably coupled to links  2722  and  2724 . Each of links  2722  and  2724  may be substantially similar to one another. Thus, those of ordinary skill in the art will understand that either link  2722  or link  2724  may include features of the other link  2722  or link  2724 . A proximal end portion of each of links  2722  and  2724  may define a recess  2725  for receiving hinge  2719 . The recess  2725  may be disposed between a pair of proximally extending arms  2725   a  and  2725   b . Each of arms  2725   a ,  2725   b  may be substantially similar to one another and, thus, for the purposes of efficiency, only one arm  2725   a  will be discussed. 
         [0079]    Arm  2725   a  may include any suitable shape and/configuration known in the art. In one embodiment, an external surface of arm  2725   a  may be rounded to facilitate rotating relative to link  2712  or  2710 . A lateral surface of arm  2725   a  may include one or more position retaining features  2727  for engaging position retaining features  2721 . In use, as links  2724  and  2712  may rotate relative to one another, for example, position retaining features  2721  and  2727  may frictionally engage one another to retain links  2724  and  2712  in a desired position. Position retaining features  2727  may be similar to position retaining features  2721 . For example, in one embodiment, position retaining feature  2727  may be a bump that is raised relative to a remaining surface of arm  2725   a.    
         [0080]    Each link  2722  and  2724  may also include one or more openings  2718  disposed generally in a central portion of links  2722  and  2724 . As discussed above, openings  2718  may be configured to extend through each respective link  2722 ,  2724 , and may be configured to facilitate bone-ingrowth. One or more edges of openings  2718  may be beveled, rounded, and/or chamfered as known in the art. 
         [0081]    A distal end of each link  2722  and  2724  may include a plurality of extensions  2729 ,  2730 . Extensions  2729 ,  2730  may be configured to extend away from a central portion of the links  2722 ,  2724 , and may be configured to define a space  2732  therebetween. The space  2732  may be configured to receive a distal component of spacer  2700 . Each of extensions  2729 ,  2730  may include a through-hole  2734  therein. The through-hole  2734  may include any suitable configuration known in the art. The through-hole  2734  may be configured to receive a respective pivot pin  2709  for movably coupling links  2722 ,  2724  to the distal component discussed in greater detail below. 
         [0082]    Inward facing surfaces of one or both of extensions  2729 ,  2730  may be configured to interact or engage with corresponding surfaces of the extensions  2729 ,  2730  of an opposing link. For example, as shown in  FIG. 28 , the inward facing surfaces of extensions  2729 ,  2730  of one of links  2722 ,  2724  may include a plurality of teeth, recesses, protrusions, notches, or the like, that may be configured to engage corresponding geometry disposed on the inward facing surfaces of the extensions disposed on the other of links  2722 ,  2724 . In the preferred embodiment, the inward facing surfaces of extensions  2729 ,  2730  may include a plurality of gear teeth  2736 . The gear teeth  2736  of each extension  2729 ,  2730  may engage gear teeth  2736  of the opposing link to facilitate rotating one link relative to the other in a single plane. 
         [0083]    Each of links  2722  and  2724  may be movably coupled to a distal component  2740 . Distal component  2740  may include a substantially trapezoidal configuration. That is, distal component  2740  may taper in the distal direction from a larger width dimension to a smaller width dimension. With reference to  FIG. 28 , a proximal face of distal component  2740  may include an opening  2742  in communication with a hole  2744  through distal component  2740 . As shown in, e.g.,  FIG. 27A , hole  2744  extends completely through distal component  2740 . Hole  2744  may include any suitable configuration known in the art. In one embodiment, hole  2744  may include a substantially conical configuration as it tapers towards a smaller diameter in its distal portion. As will be discussed below, hole  2744  may include internal threads for engaging with an implantation tool. 
         [0084]    Superior and inferior surfaces of distal component  2740  may be configured to receive extensions  2729 ,  2730 . Accordingly, as best shown in  FIG. 28 , for example, these surfaces may include a stepped portion  2746  for receiving extensions  2729 ,  2730  of each link  2722 ,  2724 . Stepped portion  2746  may include a plurality of openings  2748  for receiving a pivot pin  2709  therein to rotatably couple the links  2722 ,  2724  to distal component  2740 . Those of ordinary skill in the art will understand that links  2722 ,  2724  may be coupled to distal component  2740  by any suitable means known in the art. Distal component  2740  may include a raised portion disposed distally of stepped portion  2746 . The raised portion  2750  may include any suitable configuration known in the art. In one embodiment, the raised portion  2750  may include a distally tapering configuration, as shown in  FIG. 27A . As also shown in  FIG. 27A , distal component  2740  may include a curved external configuration. 
         [0085]    With reference now to  FIGS. 28-29 , the spacer  2700  may be maintained in an expanded configuration (shown in  FIG. 27A ) by any suitable mechanism known in the art. As discussed above, the spacer  2700  may include certain position retaining features. To more permanently retain an expanded configuration of spacer  2700 , the spacer  2700  may include a locking feature  2760 . Those of ordinary skill in the art will understand that locking feature  2760  may include any suitable configuration known in the art. In one embodiment, locking feature  2760  may include a substantially cylindrical configuration. In addition, locking feature  2760  may define a lumen  2762  therethrough. In one embodiment, the walls of the lumen  2762  may include a plurality of geometric configurations  2762   a  to allow a tool (described in greater detail below) to engage and rotate locking feature  2760 . Further, locking feature  2760  may be configured and dimensioned to be received within lumen  2704  of proximal portion  2702 , as shown in  FIG. 29 . In one embodiment, an external surface of locking feature  2760  may include suitable geometric features for engaging lumen  2704 . In the embodiment where lumen  2704  includes threads  2705 , the external surface of locking feature  2760  may include corresponding threads  2764 . The threads  2705  in lumen  2704  and threads  2764  may cooperate to only allow locking feature  2760  to be advanced into lumen  2704  without being withdrawn, regardless of whether locking feature is rotated clockwise or counter-clockwise. For example, in one embodiment, threads  2705  may terminate short of the opening to lumen  2704 . In addition, or alternatively, one or more raised circumferential or partially circumferential protrusions  2705   a  may be formed just inside of the opening to lumen  2704 . In such embodiments, locking feature  2760  may be pre-disposed within lumen  2704  during a manufacturing or assembly process and before delivery to a user or healthcare professional. Thus, the user or healthcare professional is only able to rotate locking feature  2762  to advance it further into lumen  2704  and is unable to remove locking feature  2762  from  2704 . 
         [0086]    With reference to  FIG. 29 , and as will be discussed in greater detail below, locking feature  2760  may be configured to be advanced into lumen  2704  and protrude out of cylindrical portion  2703  into space  2708 , which, as shown in  FIG. 29 , is occupied by proximal portions  2714  of links  2710  and  2712  when the spacer  2700  is in the collapsed configuration. When the spacer  2700  is in the expanded position, the proximal portions  2714  may be moved out of the space  2708 . Accordingly, locking feature  2760  may be rotated and consequently advanced further into lumen  2704  so that a distal portion of locking feature  2760  extends out of lumen  2708  and into the space  2704 . In this position, the locking feature  2762  may be configured to prevent links  2710  and  2712  from returning to their collapsed positions. 
         [0087]    The components of spacer  2700  may be fabricated from any suitable material known in the art, including, but not limited to those described above. In one embodiment, one or more components of spacer  2700  may be fabricated from titanium. Further, portions of spacer  2700  may include any suitable coating known in the art, including, but not limited to, coatings of suitable therapeutic, antiseptic, anesthetic, and/or antibiotic. In addition, as alluded to above, portions of spacer  2700  may be configured to promote bone ingrowth into the structure of spacer  2700 . 
         [0088]    Turning now to  FIGS. 30-31 , there is depicted an exemplary embodiment of a tool  3000  for effecting implantation, removal, and otherwise manipulation of the various embodiments of expandable interbody spacers described herein. Tool  3000  may include a plurality of components, each of which will be discussed in greater detail below. Those of ordinary skill in the art will recognize that any of the individual components discussed herein may be combined with other components or may be omitted altogether without departing from the principles of the present disclosure. 
         [0089]    Tool  3000  may include a handle assembly  3001 . Handle assembly may include an elongate structure  3002  configured to be held in the hand of an operator or healthcare professional. As such, the elongate structure  3002  may be appropriately configured and dimensioned as is known in the art. In some embodiments, elongate structure  3002  may include a plurality of geometric configurations or features  3004 , such as, e.g., bumps, grooves, indentations, ridges, knobs, cut-outs, etc. for gripping by an operator. In addition, elongate structure  3002  may include a constant cross-sectional dimension throughout its length, or elongate structure  3002  may include varying dimensions throughout its length. Further, elongate structure  3002  may include a substantially circular cross-sectional configuration. In some embodiments, however, elongate structure  3002  may include any suitable cross-sectional configuration, including, but not limited to, square, rectangular, triangular, etc. 
         [0090]    A generally cylindrical extension member  3006  may extend away from a superior surface  3005 . For the purposes of  FIGS. 30-31  only, the orientation depicted is presumed to be an orientation during operation. Thus, terms such as “superior,” “anterior,” “proximal,” “distal,” “inferior,” and “posterior” are used relative to this orientation. The extension member  3006  may serve to rotatably connect elongate structure  3002  to holder  3008 . 
         [0091]    Holder  3008  may include any suitable configuration known in the art. In one embodiment, holder  3008  may be configured, shaped, and sized to receive and frictionally engage a proximal portion of an inserter fork described in greater detail below. In one embodiment, for example, holder  3008  may include a substantially U-shaped configuration. The inserter fork may be received with the “U” portion  3008   a  of the holder  3008 . The U-shaped holder  3008  may include a base portion, and two superiorly extending arms  3009 . One or more of arms  3009  may be provided with one or more geometric features for frictionally engaging and retaining the inserter fork. For example, the geometric features may include dents, indents, recesses, apertures, protrusions, ribs, and the like. In one embodiment, an inner surface of an upper portion of each arm  3009  may include a rib  3010 . In some embodiments, the U-shaped holder  3008  may include a securing member for retaining (by, e.g., friction) the inserter fork within holder  3008 . In one embodiment, the securing member may be selectively actuatable. For example, the base portion of the holder  3008  may include a set screw (not shown) or other similar mechanism that may selectively engage a portion of the inserter fork to retain the inserter fork relative to the holder  3008 . The set screw may be configured to transition between a first configuration and a second configuration. In the first configuration, the set screw may be received substantially completely or completely within the base portion of holder  3008 . In the second configuration, the set screw may be advanced out of the base portion  3008  and into the “U” portion  3008   a . The set screw may be configured to transition between the first and second configurations by rotating elongate structure  3002  relative to holder  3008  in the directions shown by arrow A. For example, rotating elongate structure  3002  may rotate a head (not shown) of the set screw, thereby advancing the set screw out of the base portion of holder  3008 . 
         [0092]    With continued reference to  FIG. 31 , the inserter fork may include a generally elongate structure  3012 . In some embodiments, the elongate structure  3012  may define one or more lumens therein. For example, as shown in  FIG. 32A , the elongate structure  3012  may define a lumen  3014  therethrough. Elongate structure  3012  may include any suitable cross-sectional structure known in the art. For example, in some embodiments, the elongate structure  3012  may be a generally tubular structure. In other embodiments, elongate structure  3012  may include a substantially rectangular cross-sectional configuration. In a further embodiment, the cross-sectional configuration of elongate structure  3012  may vary along its length. For example, as shown in  FIG. 31 , a distal portion of elongate structure  3012  may include a substantially square or rectangular cross-sectional configuration and a proximal portion of elongate structure  3012  may include a substantially circular cross-sectional configuration. 
         [0093]    With reference to  FIGS. 31 and 33 , a distal portion of elongate structure  3012  may be configured in a fork-like configuration. More particularly, a distal portion of elongate structure  3012  may include a vertical slit  3016  defining two arms  3018  and  3020 . Although only two arms  3018 ,  3020  are shown, those of ordinary skill in the art will understand that a greater or lesser number of arms may be contemplate in accordance with the principles of the present disclosure. For example, the distal portion of elongate structure  3012  may include only a single arm. Alternatively, elongate structure  3012  may include two longitudinal slits disposed in perpendicular planes, thereby creating four arms (not shown). As a result of one or more of the configuration of the elongate structure  3012 , the configuration of slit  3016 , and the material properties of elongate structure  3012 , the arms  3018  and  3020  may exhibit resiliency or other spring-like characteristics. For examples, the arms  3018  and  3020  may be biased away from one another. In another embodiment, the arms  3018  and  3020  may be biased toward one another. 
         [0094]    The arms  3018  and  3020  may be substantially similar to one another. Accordingly, for the purposes of efficiency, only the features of arm  3020  will be described. Those of ordinary skill will understand that arm  3018  may include one or more features of arm  3020 . With specific reference to  FIG. 33 , a distal end  3022  of arm  3020  may be configured to releasably engage proximal portion  2702  of spacer  2700  via features  2706 . More particularly, the distal end  3022  of arm  3020  may include a projection  3024  configured and shaped to be received within feature  2706 . For example, as shown in  FIG. 33 , projections  3024  may be configured to extend towards each other. In some embodiments, feature  2706  may include a projection, and the distal end  3022  of arm  3020  may include a notch or other recess for releasably engaging the projection. Furthermore, a distal end portion of arm  3020  proximate to projections  3024  may include one or more geometric features configured for assisting in urging arm  3020  towards arm  3018  and vice versa. More particularly, an external surface of arm  3020  may include a rib  3026 , which may be engaged by sleeve  3030  to urge arm  3020  toward arm  3018 . The rib  3026  may include any suitable configuration known in the art. For example, in one embodiment, the rib may extend generally transverse to a longitudinal axis of the elongate structure  3012 . In some embodiments, a proximal portion of rib  3026  may be configured to transition smoothly to an external surface of the remainder of arm  3020 . That is, a proximal portion of rib  3026  may include a tapering or a generally ramp-like configuration. Further, although only one rib  3026  is depicted on arm  3020 , those of ordinary skill will understand that any suitable number of ribs  3026  may be provided. Furthermore, the rib  3026  may include a height dimension that correlates to an amount of travel needed to move arm  3020  toward arm  3018  (and vice versa) so as to effectively engage spacer  2700 . 
         [0095]    With renewed reference to FIGS.  31  and  32 A-B, a proximal end portion  3013  of elongate structure  3012  may be configured as follows. In one embodiment, the proximal end portion  3013  may include a horizontal slit  3028 , which may extend from the proximal end of elongate structure  3012  distally to a position just proximal of knob  3032  on elongate structure  3012 . The slit  3028  may define two arms  3028   a ,  3028   b , which may be configured to be either biased away or toward one another. A proximal end of each arm  3028   a ,  3028   b  may be configured to assist securing the inserter fork to an actuator assembly, which will be discussed in greater detail below. In an embodiment, the proximal end of at least one of arms  3028   a ,  3028   b  may include a raised flange  3027 . 
         [0096]    As alluded to above, elongate structure  3012  may include a knob  3032  disposed thereon. Knob  3032  may include any suitable configuration. In one embodiment, knob  3032  may be disposed distally of slit  3028 . An outer surface of knob  3032  may include suitable geometric features for securing knob  3032  within holder  3008 . For example, an outer surface of knob  3032  may include a plurality of knurls, indents, recesses, and/or projections thereon. In one embodiment, knob  3032  may include a plurality of channels  3031  disposed thereon. The channels  3031  may be configured to receive at least one of ribs  3010  to facilitate securing knob  3032  with holder  3008 . In some embodiments, elongate structure  3012  may include a mechanism for limiting longitudinal movement of elongate structure  3012  relative to holder  3008 . For example, elongate structure  3012  may include a radially extending flange  3033  configured to abut one of arms  3009  or the base portion of U-shaped holder  3008  so as to prevent elongate structure  3012  from moving proximally relative to handle  3001 . Furthermore, elongate structure  3012  may include a plurality of screw threads  3029  disposed on an external surface thereof. In one embodiment, the threads  3029  may be disposed proximally of slit  3016  but distally of flange  3033 . As shown in  FIG. 31 , threads  3029  may be disposed substantially closer to flange  3033  than slit  3016 . 
         [0097]    Elongate structure  3012  may be configured to be received within a lumen  3030   a  of sleeve  3030 . Sleeve  3030  may include any suitable configuration known in the art. For example, sleeve  3030  generally may include a configuration corresponding to an outer periphery of elongate structure  3012 . More particularly, sleeve  3030  may include a distal portion having a substantially rectangular cross-sectional configuration, and a proximal portion having a substantially circular cross-sectional configuration. The lumen  3030   a  within sleeve  3030  may be similarly configured. That is, lumen  3030   a  may include a configuration that corresponds to an outer periphery of elongate structure  3012 . That is, lumen  3030   a  may include a distal portion having a substantially rectangular cross-sectional configuration, and a proximal portion having a substantially circular cross-sectional configuration. A proximal portion of lumen  3030   a  may include a width dimension larger than a similar width dimension at a distal portion of lumen  3030   a . In addition, a distal end of lumen  3030   a  may be configured to urge arms  3018  and  3020  towards one another so that they may engage spacer  2700 , as discussed herein. Further, in one embodiment, sleeve  3030  may be a substantially elongate hollow member having a neck portion  3034  and a proximal lip  3036  at a proximal end thereof. Instead of lip  3036 , those of ordinary skill in the art will understand that any suitable geometric configuration may be used within the principles of the present disclosure. 
         [0098]    Prior to being received over elongate structure  3012 , a proximal portion of sleeve  3030  may be operably coupled to an inserter knob  3038 . Inserter knob  3038  may be any suitable knob known in the art and may include any suitable configuration. In one embodiment, knob  3038  may include a generally cylindrical configuration. However, any suitable configuration may be used in accordance with the principles of the present disclosure. Knob  3038  may include at least one lumen  3040 . Lumen  3040  may extend completely through knob  3038  or partially therethrough. A distal portion of an inner surface of lumen  3040  may include at least one geometric feature  3042  for interacting with lip  3036  so as to retain inserter knob  3038  on sleeve  3030 . In one embodiment, geometric feature  3042  may include a circumferential channel configured to receive lip  3036  therein. With reference now to  FIG. 32A , lumen  3040  may include a plurality of screw threads  3044  for cooperating with threads  3029  on elongate structure  3012 . Although the depicted embodiment illustrates that screw threads  3044  are disposed at a proximal portion of lumen  3040 , threads  3044  may be disposed along any portion of lumen  3040 . For example, in one embodiment, threads  3044  may extend from a midpoint of lumen  3040  to a proximal end thereof. 
         [0099]    With reference now to  FIGS. 31-32C , actuator assembly  3050  will be described. Actuator assembly  3050  may include a plurality of components operably coupled together and operable to facilitate expanding spacer  2700 , as discussed below in greater detail. Although the plurality of components are described individually, those of ordinary skill in the art will appreciate that any of the described components may be combined with one or more of the other components and/or eliminated altogether without departing from the principles of the present disclosure. 
         [0100]    Actuator assembly  3050  may include a central portion  3052 , which may include a proximal head  3054  and an elongate tubular member  3056  extending therefrom. Central portion  3052  may define a lumen  3058 . Lumen  3058  may extend completely through central portion  3052 . Lumen  3058  may include any suitable configuration known in the art. For example, as shown, lumen  3058  may include a substantially circular cross-sectional configuration. In one embodiment, proximal end  3054  may include a channel  3060  for receiving a locking tab  3062  therein, which will be discussed in greater detail below. Channel  3060  may include any suitable configuration, and may be dimensioned and shaped to correspond to locking tab  3062 . Further, channel  3060  may be configured to cut through lumen  3058 , as shown in  FIG. 32B . In addition, a portion of lumen  3058  may include a plurality of screw threads  3064 . The screw threads  3064  may be disposed along any portion of lumen  3058 . For example, in the depicted embodiment, screw threads  3064  may be disposed along only a proximal portion of lumen  3058 . Screw threads  3064  may be disposed in lumen  3058  on either side of channel  3060 . The screw threads  3064  may extend until a proximalmost end of lumen  3058 . 
         [0101]    Externally, proximal head  3054  may include any suitable configuration. In the depicted embodiment, for example, proximal head  3054  may include a substantially planar proximal end face  3066 . The end face  3066  may include an opening  3067  in communication with lumen  3058 . In addition, end face  3066  may include a second opening  3068  for receiving a retention pin  3069  therein. Opening  3068  include a diameter that is smaller than opening  3067 . As will be discussed below, retention pin  3067  may be disposed in opening  3068  for retaining tab  3062  in channel  3060 . Proximal head  3054  may include a generally circular cross-sectional configuration. In one embodiment, however, proximal head  3054  may include substantially planar superior  3070  and inferior (not shown) surfaces. As depicted in  FIG. 32C , planar superior surface  3070  may include an opening  3071  in communication with channel  3060  for receiving tab  3062  therein. With continued reference to  FIGS. 32B-32C , central portion  3052  may include any suitable external configuration known in the art. In one embodiment, central portion  3052  may include a substantially uniform external configuration. In the depicted embodiment, central portion  3052  may include a step  3072 . Step  3072  may be located at any portion along a length of central portion  3052 . In one embodiment, step  3072  may be located at a midpoint of central portion  3052 . Step  3052  may include any suitable configuration. For example, step  3052  may be the interface between a relatively smaller diameter distal portion  3052   a  of central portion  3052  and a relatively larger diameter proximal portion  3052   b  of central portion  3052 . As shown in, e.g.,  FIG. 32C , step  3072  may include a ramped surface in some embodiments. Further, a portion of proximal portion  3052   b  may be configured to receive sleeve member  3076  thereon. Accordingly, proximal portion  3052   b  may include one or more suitable geometric configurations, such as, e.g., screw threads  3074 , for coopering with corresponding screw threads  3077  within sleeve member  3076 , as described in greater detail below. Screw threads  3074  may extend along any portion of proximal portion  3052   b . For example, screw threads  3074  may extend along a substantial entirety of proximal portion  3052   b  or only for a portion thereof. 
         [0102]    Distal portion  3052  may be configured, sized, and dimensioned to be received within a lumen defined by arms  3028   a  and  3028   b . In one embodiment, distal portion  3052  may include a diameter (or if not tubular, a width dimension) that is larger than a diameter (or width dimension) of the lumen defined by arms  3028   a ,  3028   b , so as to spread apart arms  3028   a ,  3028   b  when distal portion  3052  is received therebetween. In this manner, distal portion  3052  may be frictionally retained by the inherent resilient properties of arms  3028   a ,  3028   b  acting on distal portion  3052 . To facilitate with orientation and guiding distal portion  3052  into the lumen defined by arms  3028   a ,  3028   b , distal portion  3052  may include one or more projections  3075 , which may be configured to be slidably received within slit  3028 . 
         [0103]    As noted above, opening  3071  and channel  3060  may be configured to receive therein a locking tab  3062  for receiving a tool within lumen  3058  of actuator  3050 . Tab  3062  may include any suitable configuration known in the art. In one embodiment, tab  3062  may be resiliently biased in a direction out of channel  3060  by one or more springs or spring like members  3063 . Further, tab  3062  may be retained in channel  3060  by retention pin  3069 , described above. Tab  3062  may further define a passageway  3062   a  therethrough. Passageway  3062   a  may include any configuration known in the art. As discussed below, passageway  3062   a  may be configured (e.g., may include one more projections) to engage channel  3206  of threaded shaft  3200  for retaining threaded shaft within actuator assembly  3050 . 
         [0104]    Sleeve  3076  may include a generally cylindrical member defining a lumen  3078  therethrough. Sleeve  3076  may include any suitable configuration known in the art. In one embodiment, sleeve  3076  may include a generally circular cross-sectional configuration. However, sleeve  3076  may include any suitable cross-sectional configuration. Further, a distal end of sleeve  3076  may include a generally tapered configuration. Lumen  3078  may include a generally circular cross-sectional configuration, and may be configured to receive proximal portion  3052   b  therein. Indeed, as alluded to above, lumen  3078  may include a plurality of threads  3077  configured to mate with threads  3074  to retain sleeve  3076  on central portion  3052 . Threads  3077  may extend along any suitable portion of lumen  3078 . In one embodiment, for example, threads may extend an entirety of lumen  3078 . In another embodiment, threads  3077  may extend along only a portion of lumen  3078 . 
         [0105]    An overall maximum diameter of sleeve  3076  may be less than a diameter or width of proximal head  3054 . In addition, sleeve  3076  may include a step  3079  that defines an interface between a relatively larger diameter distal portion  3076   b  of sleeve  3076  and relatively smaller diameter proximal portion  3076   a  of sleeve  3076 . Step  3079  may be disposed at any suitable location along sleeve  3076 . Further, sleeve  3076  may include one or more longitudinal grooves  3080  extending distally from a proximal end thereof. The grooves  3080  may be configured to receive rods  3081  therein, which may be configured to prevent sleeve  3076  from rotating within housing  3090  of actuator  3050 , as described below in greater detail. 
         [0106]    A washer  3082  may be configured to be frictionally retained on proximal portion  3076   a , as shown in  FIG. 32B . Washer  3082  may include a generally cylindrical structure that defines a lumen  3084  therethrough. In addition, washer  3082  may define a proximal ledge  3085  configured to abut a distal face of proximal head  3054 . Washer  3082  may also include a plurality of external threads  3086  for securing housing  3090  thereon. 
         [0107]    Housing  3090  may include a generally cylindrical structure defining a lumen  3092  therethrough. Lumen  3092  may include any suitable configuration known in the art. For example, lumen  3092  may include a generally circular cross-sectional configuration. However, any suitable cross-sectional configuration may used within the principles of the present disclosure. In embodiments where lumen  3092  includes a circular cross-sectional configuration, lumen  3092  may include a generally constant diameter throughout its length or a diameter that varies over the length of lumen  3092 . For example, a proximal portion of lumen  3092  may include a counter bore and therefore may include a larger diameter than a remainder of lumen  3092 . A proximal portion of lumen  3092  may also include screw threads  3093  for threadingly engaging threads  3086  of washer  3082  to retain housing  3090  thereon. Threads  3093  may extend along any suitable portion of lumen  3092 . Walls of lumen  3092  may include one or more grooves  3094 , which may correspond to grooves  3080  and be configured to receive rods  3081 . Rods  3081 , grooves  3904 , and grooves  3080  cooperate to prevent sleeve  3076  from rotating within housing  3090 . Further, housing  3090  may be made of any suitable biocompatible material known in the art, including, for example, PEEK. 
         [0108]    Externally, housing  3090  may include any suitable configuration known in the art. In the depicted embodiment, housing  3090  may include a raised proximal portion  3095 . Proximal portion  3095  may include any suitable configuration. In one embodiment, proximal portion  3095  may include a hexagonal configuration (e.g., a hexagonal cross-sectional configuration) for being engaged by an appropriately configured tool. Similarly, proximal portion  3095  may include one or more geometric features  3096  configured to assist with retaining a tool (discussed below) on proximal portion  3095 . The geometric features  3096  may include a plurality of indentations, bumps, recesses, channels, etc. Housing  3090  may further include a raised distal portion  3097 . Raised distal portion  3097  may define a channel  3098  through housing  3090 . Channel  3098  may include any suitable configuration. For example, in one embodiment, channel  3098  may extend in a direction that is substantially perpendicular to a longitudinal axis of lumen  3092 . Channel  3098  may be configured to receive catch  3100  slidably therein. Further, raised distal portion  3097  may include one or more openings  3099  for receiving fasteners  3099   a  therein. In embodiments where fasteners  3099  include threaded fasteners such as, e.g., screws, openings  3099  may include corresponding threads. 
         [0109]    Catch  3100  may include any suitable configuration, and may be dimensioned and shaped to be received within channel  3098 . Catch  3100  may be made of any suitable material known in the art, including, e.g., PEEK. In one embodiment, catch  3100  may include a substantially rectangular configuration. As shown in  FIG. 31C , lateral surfaces  3102  of catch  3100  may be radiused or curved so that an outer profile of catch  3100  may correspond to raised distal portion  3097  when catch  3100  is received within channel  3098 . Further, superior  3104  and/or inferior surfaces of catch  3100  may include one or more openings corresponding to openings  3099 . As shown in  FIG. 32C , opening  3104  may include any suitable configuration. For example, opening  3104  may include a substantially elongate configuration, whereby fastener  3099   a  may be slidably disposed in opening  3104 . Consequently, catch  3100  may be configured to slide back and forth relative to channel  3098  without becoming disengaged when fasteners  3099  are disposed in openings  3104 . Moreover, catch  3100  may define a passageway  3106  therethrough for receiving flange  3027  (at the proximal end of the inserter fork shown in  FIG. 31 ) and/or distal portion  3052   a  therethrough. Passageway  3106  may include any suitable configuration known in the art. In one embodiment, a wall of passageway  3106  may define a circumferential channel  3108  (shown in  FIG. 32B ) configured to engage flange  3027 . The circumferential channel  3108  may be disposed completely around passageway  3106  or only partially around passageway  3106 . 
         [0110]    With reference now to  FIGS. 34-44  a method of operating tool  3000  and its various components to implant an exemplary embodiment of spacer  2700  will be described. As shown in  FIG. 34 , sleeve  3030  may be advanced distally to squeeze arms  3018 ,  3020  towards one another so that projections  3024  may engage features  2706  to secure spacer  2700  to tool  3000 . Sleeve  3030  may be moved distally by rotating knob  3038  relative to elongate structure  3012 . As a result of the coupling via threads  3044  and  3029 , rotating knob  3038  relative to elongate structure  3012  may result in knob  3038  and sleeve  3030  moving longitudinally relative to elongate structure  3012 . 
         [0111]    Once the spacer  2700  is secured to tool  3000 , the spacer  2700  may be ready for implantation within a patient. As discussed above, spacer  2700  may be delivered to the interbody disc space within a patient via any suitable procedure known in the art. For example, in one embodiment, the spacer is delivered via an anterior approach. In another embodiment, the spacer may be delivered via a posterior approach. Further, the approach angle may be any suitable angle known in the art. For example, the spacer  2700  may be delivered by tool  3000  inserted via a posterior approach at an angle of 20-40 degrees offset from a center line of a patient. 
         [0112]    Once spacer  2700  is secured to the distal end of the inserter fork, a threaded shaft  3200  may be inserted into a proximal end of actuator assembly  3050  and all the way through the distal end of sleeve  3030  into lumen  2705  of proximal portion  2702  and threaded into lumen  2744  of distal component  2740  of spacer  2700 . With reference to  FIG. 35 , threaded shaft  3200  may include any suitable configuration. In one embodiment, threaded shaft  3200  may include an elongate member  3202 . Elongate member  3202  may include any suitable configuration. In embodiment, elongate member  3202  may include a generally cylindrical configuration. For example, elongate member  3202  may include a generally circular cross-sectional configuration. Further, elongate member  3202  may be configured to gradually taper toward its distal end. That is, a proximal portion of elongate member  3202  may include a diameter that is relative larger than a distal portion of elongate member  3202 . 
         [0113]    In one embodiment, a distal portion, e.g., a distal end, of elongate member  3202  may be configured to engage distal component  2740  of spacer  2700 . For example, a distal portion of elongate member  3202  may include one or more geometric configurations configured to cooperate with geometric configurations disposed within lumen  2744  of distal component  2740 . In embodiments where lumen  2744  may include threads, for example, a distal portion of elongate member  3202  may also include threads  3208 . 
         [0114]    A proximal end of elongate member  3202  may include an actuating member  3204 . Actuating member  3204  may include any suitable configuration known in the art. In one embodiment, actuating member  3204  may be removably coupled to a proximal portion of elongate member  3202 . In another embodiment, actuating member  3204  may be integrally formed with elongate member  3202 . Actuating member  3204  may include a knob or a handle in some embodiments. Accordingly, actuating member  3204  may include one or more geometric configurations  3210  to facilitate gripping by an operator. Geometric configurations  3210  may include ridges, channels, protrusions, projections, dents, bumps, recesses, surface texturing, etc. Further, elongate member  3202  may include a channel  3206 . Channel  3206  may be disposed at any suitable position along elongate member  3202 . In one embodiment, channel  3206  may be disposed closer to a proximal end of elongate member  3202  than a distal end. Channel  3206  may be defined by a portion of elongate member  3202  including a relatively smaller diameter than immediately adjacent portions of elongate member  3202 . Channel  3206  may be positioned at a location on elongate member  3202  suitable for being engaged by passageway  3062   a  (shown in  FIG. 32C ). Further, actuating member  3204  may include one or more markings  3212  (shown in  FIG. 38A ) for indicating a degree of expansion of spacer  2700 , as described further below. The markings  3212  may include any suitable markings known in the art and may include numerical values corresponding to a percentage of expansion of spacer  2700 . 
         [0115]    Turning now to  FIG. 36 , tool  3000  may be secured to spacer  2700  and threaded shaft  3200  may be received within tool  3000 . Tool  3000  may be then inserted into a patient to effect implantation of spacer  2700  within the patient. In some embodiments, however, tool  3000  and spacer  2700  may be already positioned within a patient when threaded shaft  3200  is inserted into tool  3000  and secured to spacer  2700 . 
         [0116]    Turning now to  FIG. 37 , an expanding hex cap  3700  may be positioned over a proximal end of tool  3000  and actuating member  3204 . In one embodiment, hex cap  3700  may include a generally cylindrical member defining a lumen  3702  therein. Lumen  3702  may extend completely through hex cap  3700  or may be blind, such that hex cap  3700  includes a closed proximal end. A distal end portion  3704  of hex cap  3700  may be configured to be received over and engage proximal portion  3095 . Accordingly, distal end portion  3704  may include a configuration that corresponds to proximal portion  3095 . For example, distal end portion  3704  may be shaped as a hexagonal tool. Further, an inner surface of lumen  3702  in distal portion  3704  may include one or more geometric features  3706  configured to engage geometric features  3096  on proximal portion  3095 . In one embodiment, geometric features  3706  may include a plurality of bumps while geometric features  3096  may include a plurality of recesses, or vice versa. In addition, as depicted in  FIG. 37 , distal end portion  3704  may include a diameter relatively larger than a proximal portion  3708  of hex cap  3700   
         [0117]    Further, a proximal portion  3708  of hex cap  3700  may include a plurality of windows or openings  3710  disposed radially thereabout. The openings  3710  may include any suitable configuration known in the art and may facilitate visualizing the markings  3212  disposed on actuating member  3204 . Proximal portion  3708  may include any suitable number of openings desired. 
         [0118]    In operation, and while spacer  2700  is appropriately positioned (e.g., by moving hex cap  3700  in the direction of arrow  3712 ) within a patient, hex cap  3700  may be positioned over a proximal end of tool  3000  so that distal end portion  3704  may engage proximal portion  3095  of actuator assembly and actuating member  3204  may be visible to an operator through openings  3710 . Next, the operator may rotate hex cap  3700  to expand spacer  2700  until the desired amount of expansion if achieved. Rotating hex cap  3700  causes proximal portion  3095  (and, consequently, housing  3090 ) to be rotated via its engagement with distal end portion  3704 . As a result of the various components and their connections of actuator assembly  3050  described above, when housing  3090  is rotating, sleeve  3076  is also rotated because it is fixed relative to housing  3090  via rods  3081 . Consequently, sleeve  3076  and housing  3090  are translated longitudinally relative to central portion  3052 . Further, because a proximal end flange  3027  is secured to housing  3090  via catch  3100 , the entire inserter fork also translates longitudinally relative to central portion  3052  when hex cap  3700  is rotated. And, since threaded shaft  3200  is secured to central portion  3052  via catch  3206  and tab  3062 , the distal threads  3208  threaded into distal component of spacer  2700  may move relative to proximal portion  2702  of spacer  2700  as the inserter fork is moved when hex cap  3700  is rotated. Such relative movement between the distal end of the inserter fork and the threaded shaft  3200  causes proximal portion  2702  to move towards distal component  2740 , thereby effecting expansion of spacer  2700  as the various components of spacer are rotated from the positions depicted in  FIG. 27B  to the positions depicted in  FIG. 27A  or any suitable, desired intermediate position. As alluded to above, a degree of travel of, e.g., housing  3090  relative to actuating member  3054  may correspond to a degree of expansion of spacer  2700 . Accordingly, actuating member  3054  may include a plurality of markings to assist an operator in determining a degree of expansion of spacer  2700 . 
         [0119]    After desired expansion of spacer  2700  is achieved and spacer  2700  is appropriated positioned within the patient, hex cap  3700  may be removed. Subsequently, tab  3062  may be actuated (e.g., depressed) so that it may temporarily be disengaged from channel  3206  and threaded shaft  3200  may be also removed from tool  3000 . In the meantime, position retaining features  2721  and  2727  may interfere with one another to frictionally retain an expanded configuration of spacer  2700 . Subsequently, a locking instrument  3900  may be inserted into lumen  3058  and advanced through tool  3000  until it engages within locking feature  2760 . 
         [0120]    Locking instrument  3900  (see  FIG. 39 ) may include a generally elongate member  3902  having a distal portion  3904  including one or more geometric configurations  3906  configured to engage with geometric configurations  2762   a  in such a manner that when locking instrument  3900  is rotated, locking feature  2760  will be rotated. As its proximal end, locking instrument may include a suitable actuating member, such as, e.g., a handle or knob  3908 . Handle or knob  3908  may be secured to elongate member  3902  by any suitable means known in the art. In one embodiment, handle or knob  3908  may be removably coupled to elongate member  3902 . In other embodiments, handle or knob  3908  may be integrally formed with elongate member  3902 . In some embodiments, locking instrument  3900  may be a torque limiting tool. That is, locking instrument  3900  may be configured to prevent application of torque above a predetermined limit. For example, once a predetermined limit of applied torque is exceeded, handle or knob  3908  may rotate freely relative to elongate member  3902 . Handle or knob  3908  may include any suitable configuration known in the art to facilitate gripping and operation by a user. In one embodiment, handle or knob  3908  may include one or more geometric features  3909  (e.g., detents, recesses, protrusions, etc.) configured to allow manipulation by a user. 
         [0121]    In operation, distal portion  3904  may be inserted into lumen  2762  so as to engage geometric configurations  2762   a , as shown in  FIG. 40 . Next, handle or knob  3908  may be rotated to advance locking feature  2760  into space  2708  to prevent links  2710  from returning to their collapsed position, thereby locking spacer  2700  in the expanded configuration. 
         [0122]    Next, locking instrument  3900  may be removed from tool  3000  and a funnel tube  4100  (see  FIG. 41 ) having a funnel  4200  removably coupled thereto may be inserted into tool  3000  via lumen  3058 . Funnel tube  4100  may include any suitable configuration known in the art. In one embodiment, funnel tube  4100  may include an elongate member  4102  defining a lumen  4104  therethrough. Elongate member  4102  may include any suitable configuration. For example, elongate member  4102  may include a generally circular cross-sectional configuration. In some embodiments, however, other cross-sectional configurations, such as, e.g., rectangular, may be used. Similarly, lumen  4104  may include a substantially circular cross-sectional configuration, but any suitable configuration may be employed within the principles of the present disclosure. Elongate member  4102  may have a length sufficient to extend from outside a proximalmost end of tool  3000  to beyond a distal end of locking feature  2760 , so as to deliver material into a center of spacer  2700  when it is in the expanded configuration, as discussed below in greater detail. 
         [0123]    A proximal end portion  4106  of elongate member  4102  may be configured to be removably secured within lumen  3058 . More particularly, proximal end portion  4106  may include threads  4108  configured to engage threads  3064  in proximal head  3054  so as to retain funnel tube  4100  therein. Funnel tube  4100  may further include a knob  4110  disposed proximally of threads  4108 . In some embodiments, knob  4110  may include a diameter that is relatively larger than a diameter of a remainder of funnel tube  4100 . In addition, knob  4110  may define a lumen (not shown) therethrough. In some embodiments, the lumen of knob  4110  may include a diameter that is relatively larger than a diameter of the lumen  4104  through a remainder of funnel tube  4100 . Knob  4110  may also include a plurality of geometric configurations  4112  located on an external surface thereof. The geometric configurations  4112  may include any suitable configuration known in the art. In one embodiment, the geometric configurations may include a plurality of raised ridges, bumps, notches, recesses, detents, etc. 
         [0124]    Funnel  4200  may be any suitable funnel known in the art. For example, funnel  4200  may include a conical portion  4202  having a tapering cavity therein. The conical portion  4202  may be secured to or integrally formed with a neck portion  4204  having a lumen defined therethrough. The lumen in neck portion  4204  may be in communication with conical portion  4202 . Neck portion  4204  may be removably secured to proximal end portion  4106  by any suitable means known in the art. In one example, neck portion  4204  may include threads configured to matingly engage corresponding threads  4113  (shown in  FIG. 43 ) disposed on proximal end portion  4106 . In one embodiment, a portion of proximal end portion may be received within neck portion  4204 . In another embodiment, a portion of neck portion  4204  may be received within proximal end portion  4106 . 
         [0125]    In use, funnel tube  4100  may be advanced into lumen  3058  and secured therein by engaging threads  4108  with threads  3064 , such that a distal opening of lumen  4104  is disposed through locking feature  2760  within spacer  2700 , as shown in  FIG. 42 . Next, the space within spacer  2700  may be filled with morcellated bone (e.g., autograft) or any other suitable material into the center of spacer  2700  when it is in the expanded position. Subsequently, funnel  4200  may be decoupled from funnel tube  4100  by, e.g., unscrewing it. Next, a bone funnel pusher  4300  may be inserted through funnel tube  4100  to push or advance any morcellated bone graft or other material remaining in funnel tube  4100  out of funnel tube  4100  and into a center of spacer  2700 . 
         [0126]    As shown in  FIG. 43 , bone funnel pusher  4300  may include a generally elongate member  4302  having a proximal end  4304  and a distal end  4306 . Pusher  4300  may include any suitable configuration known in the art. Elongate member  4302  may include any suitable configuration known in the art. For example, elongate member  4302  may include a generally circular cross-sectional configuration. However, elongate member  4302  may include any suitable configuration known in the art. In one embodiment, pusher  4300  may be sized to be advanced through tool  3000  to spacer  2700 . At its proximal end  4304 , pusher  4300  may include a handle  4305 . Handle  4305  may include any suitable configuration. For example, handle  4305  may include a generally tubular structure. Handle  4305  may include a diameter that is relatively larger than a diameter of elongate member  4302 . At its distal end  4306 , elongate member may include a pushing member  4307 . Pushing member  4307  may include any suitable configuration. For example, pushing member  4307  may be substantially tubular. In one embodiment, pushing member  4307  may include a diameter that is relatively larger than a diameter of elongate member  4302 , but relatively smaller than a diameter of handle  4305 . 
         [0127]    In use, the bone funnel pusher  4300  may be used to fill spacer  2700  with, e.g., finely milled autogenous bone graft material to tightly pack spacer  2700 . Once the graft material is tightly packed within spacer  2700 , the inserter knob  3038  may be rotated to withdraw sleeve  3030  to disengage the inserter fork from spacer  2700 . Prior to final disengagement, however, a user may choose to verify a final positioning of the spacer  2700  via radiographic visualization, such as, e.g., fluoroscopy, X-ray, or any other suitable imaging technique, as shown in  FIG. 44 . 
         [0128]    If necessary, the spacer  2700  may be removed or otherwise manipulated by first inserting a removal tool (not shown) through a distal end of lumen  2744  in distal component  2740 . The removal tool may engage locking feature  2760  and advance it completely back into cylindrical portion  2703  of proximal portion  2702 , thereby removing the impediment to links  2710  and  2712  returning to their collapsed position. Next, projections  3024  of arms  3018 ,  3020  may engage features  2706  as described above. Threaded shaft  3200  may then be inserted through tool  3000  to engage threads  3208  within distal component  2740 . Subsequently, hex cap  3700  may be provided over a proximal end of tool  3000  for rotation so as to collapse  2700  for removal from within the patient. 
         [0129]    As described above, the devices, tools, and methods described herein may be used to provide an interbody spacer for positioning between adjacent vertebral bodies. Prior to performing the above-described steps, those of ordinary skill in the art will understand that a patient&#39;s native intervertebral disc may be first removed via a conventional discectomy, for example. Alternatively, scrapers may be used for disc distractions and to loosen the disc space without damaging vertebral endplates. In one embodiment, an operator may begin distraction with a relatively small scraper and proceed with increasingly larger scrapers. Next, the disc space may be prepared for receiving, for example, spacer  2700  as known in the art. Subsequently, measurements may be made of a height and width of the interbody disc space to ensure a spacer of correct dimensions is selected for implantation. The measurements may be made by any suitable means known in the art. For example, a user may conduct one or more adjustable footprint trials. In particular, one or more trials may be inserted into the prepared disc space in a collapsed configuration and expanded. The trial may be observed under suitable imaging means, such as, e.g., fluoroscopy, to identify appropriate sizing suitable for the prepared disc space. 
         [0130]    While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations can be made thereto by those skilled in the art without departing from the scope of the invention as set forth in the claims.