Abstract:
A geared cam expandable spinal implant. Rotational motion of a rotating portion is translated into linear motion of a yoke, which moves geared cams at the distal end of the implant to mate with, and walk along, teeth of corresponding racks. The walking of the gear cam teeth along the rack teeth creates a regular rate of implant expansion, reduces initial excessive expansion force applied to the implant, and provides fine adjustment of the expansion rate and force. Spikes, pivotally mounted on the yoke, pivot outward as the implant expands, to a fully-deployed position into engagement with surfaces of adjacent vertebral bodies. The engagement between the deployed spikes and the vertebral bodies prevents inadvertent backout of the expanded implant.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a spinal implant, and a method for implanting the implant in a patient&#39;s disc space between two adjacent vertebral bodies. More particularly, the present invention relates to an expandable spinal implant including geared cams, configured to expand within the patient&#39;s disc space, from a collapsed position to an expanded position. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Expandable spinal implants are known. Existing expandable spinal implants use conventional “4-bar” and “crank slider” expansion mechanisms. Following insertion, while in the collapsed position, into a surgically-enhanced disc space, the existing expandable spinal implants are expanded. The existing expandable implants have been known at least to (1) apply an undesirable excessive initial expansion force to the disc space, (2) apply an irregular expansion force to the disc space, (3) occasionally inadvertently back out of the disc space, and (4) lack a reliable capability for fine adjustment. Existing expandable implants also lack different configurations at the distal tip of the implant, which often could be advantageous, e.g., to ensure engagement between the distal tip and the adjacent vertebral bodies. 
       SUMMARY OF THE INVENTION 
       [0003]    It is an object of the present invention to provide an expandable spinal implant which obviates one or more of the shortcomings of the related art. 
         [0004]    It is another object of the present invention to provide an expandable spinal implant for insertion into a patient&#39;s disc space between an upper vertebral body and a lower vertebral body. The implant has a proximal end and a distal end defining a mid-longitudinal axis therebetween, and is expandable between a collapsed position, a partially-expanded position, and a fully-expanded position. 
         [0005]    The implant includes an upper endplate. The upper endplate has a proximal end, a distal end, an outer surface, first and second side surfaces, and an inner surface. A portion of the inner surface includes an upper rack portion. The upper rack portion includes downwardly-projecting teeth intermediate the proximal end and the distal end of the upper endplate, and at least one distal-most downwardly-projecting tooth proximate the distal end of the upper endplate. The implant further includes a lower endplate. The lower endplate has a proximal end, a distal end, an outer surface, first and second side surfaces, and an inner surface. A portion of the inner surface includes a lower rack portion. The lower rack portion includes upwardly-projecting teeth intermediate the proximal end and the distal end of the lower endplate, and at least one distal-most upwardly-projecting tooth proximate the distal end of the lower endplate. The proximal end of the lower endplate is pivotally connected to the proximal end of the upper endplate. 
         [0006]    A chassis portion is mounted within the implant between the upper endplate and the lower endplate. The chassis portion has a proximal end and a distal end. The proximal end has an opening defined therein. 
         [0007]    A yoke is movably mounted within the chassis portion. The yoke has a proximal end and a distal end. The yoke is defined by first and second parallel spaced-apart walls extending from the proximal end to the distal end. A distal cross-piece, transverse to the longitudinal axis, connects the distal ends of the first and second walls of the yoke. 
         [0008]    A rotating portion is rotatably mounted within the chassis portion. The rotating portion has a proximal end and a distal end. The distal end is configured to contact the distal cross-piece of the yoke. The proximal end has an opening defined therein, configured to receive a distal end of an implant expansion tool. 
         [0009]    At least one first spur gear is rotatably mounted on a distal end of one of the first and second walls of the yoke. The at least one first spur gear has teeth configured to engage the downwardly-projecting teeth of the upper rack portion. At least one second spur gear is rotatably mounted on a distal end of one of the first and second walls of the yoke. The at least one second spur gear has teeth configured to engage the upwardly-projecting teeth of the lower rack portion. 
         [0010]    The rotating portion is configured to translate rotational motion thereof to linear motion of the yoke. The yoke translates the linear motion to rotation of the spur gears with respect to the yoke, causing the spur gears to walk along the upper rack gear teeth and lower rack gear teeth, respectively, toward the distal end of the implant, thereby moving the implant through the partially-expanded position. When the spur gear teeth abut against the distal-most teeth, respectively of the upper rack or the lower rack, the implant has reached the fully-expanded position. 
         [0011]    One or more spikes are pivotally mounted in pockets within the implant. The linear motion of the yoke pushes distal ends of the spikes into contact with ramped surfaces defined in openings in the upper and lower endplates. Contact with the ramped surfaces causes the one or more spikes to pivot to fully-deployed positions, with distal edges of the one or more spikes engaging the upper and lower vertebral bodies. This engagement between the distal edges of the one or more spikes, and the upper and lower vertebral bodies prevents the implant, in the fully-expanded position, from inadvertently backing out of the disc space. 
         [0012]    First and second flaps are attached to the respective first and second side surfaces of the upper endplate and the lower endplate. The flaps can be made of porous, semi-porous, or solid materials, depending on the application. When the implant is in the collapsed position, the flaps can either be stretched tight between the respective side surfaces, or hang loosely between the respective side surfaces. When the implant is fully expanded, the flaps are stretched tight between the respective side surfaces, functioning as a barrier to prevent bone graft material from leaking out of the sides of the fully expanded implant. 
         [0013]    It is a further object of the present invention to provide a method of implanting the expandable spinal implant described above into a patient&#39;s disc space between an upper vertebral body and a lower vertebral body. The method includes inserting the implant into a surgically-prepared disc space, in the collapsed position, using an implant insertion tool, rotating the rotating portion, defining a rotational motion, translating the rotational motion of the rotating portion into a linear motion of the yoke toward the distal end of the implant, rotating the spur gears with respect to the yoke, thereby walking the spur gears along the projecting teeth of the respective upper and lower racks, and expanding the implant through the partially-expanded position to the fully-expanded position. The linear motion of the yoke also translates into pivotal motion of the one or more spikes mounted in the implant. The one or more spikes pivot from a collapsed position in the implant to a fully-deployed position with distal ends in engagement with upper and lower vertebral bodies adjacent the disc space. The fully-deployed spikes, in engagement with the upper and lower vertebral bodies, prevent the fully-expanded implant from backing out of the disc space. The insertion tool includes an outer hollow shaft, an inner hollow shaft configured to pass through the outer shaft, and an elongated driver configured to pass through the inner hollow shaft. The elongated driver has a blunt distal end configured to contact a portion of the implant. Application of a movement to the elongated driver is transferred to the implant, forcing the implant into the disc space. After removal of the elongated driver, bone growth material can be routed through the inner shaft and into the implant. The one or more fully-deployed spikes, in engagement with the upper and lower vertebral bodies, prevent the fully-expanded implant from inadvertently backing out of the disc space. 
         [0014]    These and other objects of the present invention will be apparent from review of the following specification and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a collapsed position; 
           [0016]      FIG. 2  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a partially expanded position; 
           [0017]      FIG. 3  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a partially expanded position; 
           [0018]      FIG. 4  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a fully expanded position; 
           [0019]      FIG. 5  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a fully expanded position; 
           [0020]      FIG. 6  is an exploded parts view of a geared cam expandable spinal implant in accordance with the invention; 
           [0021]      FIG. 7  is an upper perspective view of a lower endplate, chassis portion, yoke, rotating portion, and spur gears, of a geared cam expandable spinal implant in accordance with the invention; 
           [0022]      FIG. 8  is a cross-sectional side view of a geared cam expandable spinal implant in accordance with the invention, in a collapsed position; 
           [0023]      FIG. 9  is a cross-sectional side view of a geared cam expandable spinal implant in accordance with the invention, in a fully-expanded position; 
           [0024]      FIGS. 10-16  are side schematic views of a multi-stage expansion mechanism used in one preferred embodiment of a geared cam expandable spinal implant in accordance with the invention; 
           [0025]      FIG. 17  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a collapsed position; 
           [0026]      FIG. 18  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a fully open position; 
           [0027]      FIG. 19  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a partially expanded position; 
           [0028]      FIG. 20  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention, in a fully expanded position; 
           [0029]      FIG. 21  is a side cross-sectional view of a geared cam expandable spinal implant in accordance with the invention, in a partially expanded position; 
           [0030]      FIG. 22  is a side cross-sectional view of a geared cam expandable spinal implant in accordance with the invention, in a fully expanded position; 
           [0031]      FIG. 23  is an upper perspective view of another embodiment of a geared cam expandable spinal implant in accordance with the invention, in a collapsed position; 
           [0032]      FIG. 24  is an upper perspective view of the embodiment of  FIG. 23 , in a fully expanded position; 
           [0033]      FIG. 25  is an exploded parts view of a geared cam expandable implant in accordance with the invention; 
           [0034]      FIG. 26  is a side cross-sectional view of a geared cam expandable spinal implant in accordance with the invention, in a collapsed position; 
           [0035]      FIG. 27  is a side cross-sectional view of a geared cam expandable spinal implant in accordance with the invention in a fully expanded position; 
           [0036]      FIGS. 28 and 29  are rear views of a geared cam expandable spinal implant in accordance with the invention; 
           [0037]      FIG. 30  is a side cross-sectional view of a geared cam expandable spinal implant in accordance with the invention in a collapsed position; 
           [0038]      FIG. 31  is a side cross-sectional view of a geared cam expandable spinal implant in accordance with the invention in a fully expanded position; 
           [0039]      FIGS. 32-34  are side schematic views of a spur gear and rack in a one-stage expansion mechanism; 
           [0040]      FIG. 35  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention in a collapsed position; 
           [0041]      FIG. 36  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention in a fully expanded position; 
           [0042]      FIG. 37  is an upper perspective view of a geared cam expandable spinal implant in accordance with the invention in a fully expanded position; 
           [0043]      FIG. 38  is an upper perspective cross-sectional view of an implant insertion tool in accordance with the invention connected to a geared cam expandable spinal implant in accordance with the invention; 
           [0044]      FIG. 39  is an upper perspective view of an implant insertion tool in accordance with the invention connected to a geared cam expandable spinal implant in accordance with the invention, depicting insertion of the implant into a disc space; 
           [0045]      FIG. 40  is an upper perspective cross-sectional view of an implant insertion tool in accordance with the invention connected to a geared cam expandable spinal implant in accordance with the invention; 
           [0046]      FIG. 41  is an upper perspective cross-sectional view of a geared cam expandable implant attached to an implant insertion tool in accordance with the invention; 
           [0047]      FIG. 42  is an upper perspective cross sectional view of a geared cam expandable implant in accordance with the invention being inserted into a disc space by an implant insertion tool in accordance with the invention; 
           [0048]      FIG. 43  is an upper perspective cross sectional view of a geared cam expandable implant in accordance with the invention being inserted into a disc space by an implant insertion tool in accordance with the invention; 
           [0049]      FIG. 44  is an upper perspective cross sectional view of a geared cam expandable implant inserted into the disc space, following removal of the implant insertion tool; 
           [0050]      FIG. 45  is an upper perspective view of a geared cam expandable implant in accordance with the invention being supported by a lower vertebral body; 
           [0051]      FIG. 46  is an upper perspective view depicting points of attachment between a geared cam expandable implant in accordance with the invention, and an implant insertion tool in accordance with the invention. 
           [0052]      FIG. 47  is a side cross-sectional view of a geared cam expandable spinal implant in accordance with the invention; 
           [0053]      FIG. 48  is a side cross-sectional view of a geared cam expandable spinal implant in accordance with the invention; 
           [0054]      FIG. 49  is a partial upper perspective view depicting a lower endplate, chassis, yoke, lower spur gear, and cylinder with circumferential ratchet teeth; 
           [0055]      FIG. 50  is a perspective view of a geared cam expandable implant in accordance with the invention, including deployable spikes, pivotally attached to the implant, in a fully-expanded position; 
           [0056]      FIG. 51  is a perspective view depicting a chassis portion, a yoke, a rotating portion, spur gears, and deployable spikes pivotally attached to the yoke, of a geared cam expandable implant in accordance with the invention; 
           [0057]      FIG. 52  is a side view of a geared cam expandable implant in accordance with the invention, including deployable spikes, pivotally attached to the implant, in a collapsed position; 
           [0058]      FIG. 53  is a side view of a geared cam expandable implant in accordance with the invention, including deployable spikes, pivotally attached to the implant in a partially expanded position; 
           [0059]      FIG. 54  is a side view of a geared cam expandable implant in accordance with the invention, including deployable spikes, pivotally attached to the implant, in a fully expanded position; 
           [0060]      FIG. 55  is a side view of a geared cam expandable implant in accordance with the invention, including deployable spikes, pivotally attached to the implant, and including apertures defined through internal parts, in a fully expanded position; 
           [0061]      FIG. 56  is a side view of a geared cam expandable implant in accordance with the invention, in a collapsed position, including deployable spikes, pivotally attached to the implant, and including lateral openings to allow flow of bone graft material out of sides of the implant, and further including a planar portion in the upper endplate to distribute load forces, in a fully expanded position; 
           [0062]      FIG. 57  is a front view of a geared cam expandable implant in accordance with the invention, including flaps attached to sides of the implant, in a closed position; 
           [0063]      FIG. 58  is an upper view of a geared cam expandable implant in accordance with the invention, including flaps attached to sides of the implant, in a closed position; 
           [0064]      FIG. 59  is a side view of a geared cam expandable implant in accordance with the invention, including flaps attached to sides of the implant, in a closed position; 
           [0065]      FIG. 60  is a side cross-sectional view of a geared cam expandable implant in accordance with the invention, in a collapsed position, with a bone graft insertion apparatus connected to a proximal end of the implant; 
           [0066]      FIG. 61  is a side cross-sectional view of a geared cam expandable implant in accordance with the invention, in a fully expanded position, with a bone graft insertion apparatus connected to a proximal end of the implant; and 
           [0067]      FIG. 62  is a side cross-sectional view of a geared cam expandable implant in accordance with the invention, in a fully expanded position, with a bone graft insertion apparatus connected to a proximal end of the implant, and a graft insertion tube filled with bone graft material provided within the bone graft insertion apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0068]    A geared cam expandable spinal implant  10  is configured to be inserted in a surgically-enhanced disc space between an upper vertebral body and an adjacent lower vertebral body. The implant  10  includes a proximal end  12  and a distal end  14 , defining a mid-longitudinal axis L-L therebetween. 
         [0069]    In one embodiment, the implant  10  includes an upper endplate  16 . As depicted in  FIGS. 6, 8, and 9 , the upper endplate  16  includes a proximal end  18 , a distal end  20 , side surfaces  22 , and an inner surface  24 . The inner surface  24  includes an upper rack portion  26 , which includes downwardly-projecting teeth  28 , and a distal-most downwardly-projecting tooth  29 . 
         [0070]    In one embodiment, the implant  10  includes a lower endplate  30 . The lower endplate  30  includes a proximal end  32 , a distal end  34 , side surfaces  36 , and an inner surface  38 . The inner surface  38  includes a lower rack portion  40 , which includes upwardly-projecting teeth  42 , and a distal-most upwardly-projecting tooth  43 . 
         [0071]    In one embodiment, the implant  10  includes a chassis portion  44  mounted within the implant between the upper endplate  16  and the lower endplate  30 . The chassis portion  44  includes a proximal end  46  and a distal end  48 . As depicted in  FIGS. 7-9, 21, 22, and 46 , the proximal end  46  of the chassis portion  44  is a wall perpendicular to the mid-longitudinal axis L-L, having an opening  50  defined through the wall, and one or more depressions  52  defined in the wall proximate the opening  50 . The chassis portion  44  further includes a first set of internal threads  54  defined in the opening  50  of the proximal end  46 . 
         [0072]    In one embodiment, as depicted in  FIGS. 1-7 , the chassis portion  44  includes an arcuate portion  56  intermediate the proximal end  46  and the distal end  48 . A second set of internal threads  58  is defined on an inner surface of the arcuate portion  56 . 
         [0073]    In one embodiment, a yoke  60  is movably mounted within the chassis portion  44 . The yoke  60  is defined by a first wall  62 , and a parallel second wall  64  spaced away from the first wall  62 . First wall  62  has a proximal end  66  and a distal end  68 . Second wall  64  has a proximal end  70  and a distal end  72 . As depicted in  FIGS. 6, 7, and 41-43 , distal ends  68  and  72  of first and second walls  62  and  64  can be connected by a distal end cross-piece  71 . As depicted in  FIG. 5 , the yoke  60  includes a slot  74  defined in at least one of first wall  62  and second wall  64 . Each slot  74  is configured to receive therein a pin  76  projecting from an inner side surface of the lower endplate  30 . Insertion of the pin  76  into the slot  74  assists in preventing separation of the implant  10 . 
         [0074]    In one embodiment, a rotating portion  78  is rotatably mounted within the chassis portion  44 . Rotating portion  78  includes a proximal end  80 , a distal end  82 , and an outer surface  84 , with outer threads  86  defined on the outer surface  84 . In one embodiment, as depicted in  FIGS. 6, 8, 9, 20-22, 25-27, 30, and 31 , the distal end  82  includes a T-shaped projection  88 . The invention, however, is not limited to having a T-shaped projection at the distal end  82  of the rotating portion  78 . In one embodiment, the proximal end  80  of the rotating portion includes an opening  89 , configured to receive therein a distal end of an implant expansion tool (not shown). The invention is not limited to any particular configuration for the opening  89 , as long as the rotating portion  78  can be rotated by the implant expansion tool. As depicted in  FIGS. 8 and 9 , the opening  89  has a polygonal shape to receive a polygonal-shaped distal end of the implant expansion tool. As another example, but not by way of limitation, the opening  89  could be threaded to receive a threaded distal end of the implant expansion tool. 
         [0075]    In one embodiment, as depicted in  FIG. 47-49 , the threaded rotating portion  78  has been replaced by a cylinder  164  with circumferential ratchet teeth  166 , and the mating threads  54  on the arcuate portion  56  have been replaced by integral pawls  168 . The ratchet teeth  166  are separated by grooves  170 . The pawls  168  are allowed to flex because they are integral with “live” springs  172  attached to the chassis portion  44 . In this embodiment, as the ribbed cylinder  164  is advanced, each pawl  168  advances to the next respective groove  170 . In this manner, the distal end of the cylinder  164  pushes on the yoke  60 , causing the spur gears  90  and  94  to walk toward the distal end  14  of the implant  10 , expanding the implant, while the pawls  168  are retained in the respective grooves  170  between the ratchet teeth  166 , thereby retaining the implant  10  in its current expanded position. 
         [0076]    In one embodiment, a pair of first spur gears  90  is rotatably mounted to the distal end  68  of the first wall  62  of the yoke  60 , and the distal end  72  of the second wall  64  of the yoke  60 , respectively. Each first spur gear  90  includes projecting first spur gear teeth  92 , configured to engage with the downwardly-projecting teeth  28  of the upper rack portion  26 . 
         [0077]    In one embodiment, as depicted in  FIGS. 5-7, 18, 24, 36, and 37 , a second spur gear  94  is rotatably mounted between the distal end  68  of the first wall  62  of the yoke  60 , and the distal end  72  of the second wall  64  of the yoke  60 , respectively. As depicted in  FIG. 6 , the spur gears  90  and  94  are rotatably attached to the yoke  60  with a pin  98 . The second spur gear  94  includes projecting second spur gear teeth  96 , configured to engage with the upwardly-projecting teeth  42  of the lower rack portion  40 . The invention is not limited to having two first spur gears  90  and one second spur gear  94 . For example, as depicted in  FIG. 20 , the invention can include two first spur gears  90  and two second spur gears  94 . It is also within the scope of the invention to have one first spur gear  90 , and two second spur gears  94 . 
         [0078]    In one embodiment, as depicted in  FIGS. 19 and 20 , a slot  160  is defined in the side surface  36  proximate the distal end  34  of the lower endplate  30 , and a pin  162  is defined projecting from a second spur gear  94 . Pin  162  is configured to engage with slot  160 , to help prevent the upper and lower endplates from separating. 
         [0079]    In one embodiment, the rotating portion  78  rotates within the chassis portion  44 , with the outer threads  86  of the rotating portion  78  engaging threaded portion  58  of the chassis portion  44 , until the distal end  82  of the rotating portion  78  contacts the distal cross-piece  71  of the yoke  60 . Rotation of the rotating portion  78  is translated into linear motion of the yoke  60  towards the distal end  14  of the implant  10 . Linear motion of the yoke  60  causes the first spur gears  90 , and the second spur gears  94  to rotate. The respective first spur gear teeth  92  and second spur gear teeth  96  “walk” towards the distal end  14  of the implant  10  in the respective downwardly-projecting teeth  28  of the upper rack portion  26 , and upwardly-projecting teeth  42  of the lower rack portion  40 . As the teeth “walk,” the upper endplate  16  is moved away from the lower endplate  30 , thereby moving the implant  10  into and through the partially-expanded position. When the respective spur gear teeth  92  and  96  reach the respective distal-most downwardly-projecting tooth  29 , or alternately the distal-most upwardly-projecting tooth  43 , they can “walk” no farther towards the distal end of the implant  10 , and the implant has reached the fully-expanded position. The amount of expansion in the fully-expanded position is related to the length of the spur gears. As depicted in  FIG. 6 , the spur gears have a length S 1 , but different spur gear lengths are possible, depending on the requirements of an individual patient. Different amounts of full expansion, related to spur gear length are depicted, for example, in  FIGS. 4, 5, 9, 20 , and  22 . 
         [0080]    In one embodiment, as depicted in  FIGS. 32-34 , the spur gears  90  and  94  “walk” along the respective racks  26  and  40  in a one-stage expansion movement, with the respective spur simply rolling along the respective rack. 
         [0081]    In one embodiment, as depicted in  FIGS. 10-16 , the spur gears  90  and  94  “walk” along the respective racks  26  and  40  in a multi-stage expansion movement, including the respective spur initially rolling along the respective rack, as depicted in  FIGS. 10 and 11 , and subsequently pivoting in a ball and socket fashion, as depicted in  FIGS. 12 and 13 . As depicted in  FIGS. 14-16 , the circumferences of the pitch diameters translate along each other as the gear is advanced. This translation allows a higher angle of incidence at the starting point for the device as compared to a fixed-length link mechanism. The angle of incidence/mechanical advantage starts high and decreases as the gear is advanced, increasing as the gear advances further. The multi-stage expansion pattern allows a constant angle of attack of the gear with the rack. 
         [0082]    In one embodiment, as depicted in  FIGS. 1 and 2 , the upper endplate  16  includes projections  100 , configured to engage a surface of the endplate of the upper vertebral body (not shown). The upper endplate  16  further includes an opening  102  defined therein, configured to allow bone growth from bone growth material loaded in the implant  10  to pass through the opening  102  and fuse with the upper vertebral body. The upper endplate  16  further includes a smooth surface  104 , configured to distribute the vertebral body endplate loading. The smooth surfaces  104  can be configured along a majority of the length of the upper surface of the upper endplate  16 , as depicted in  FIGS. 1 and 2 , or for only a portion of the length of the upper surface, to contact only the softer cancellous-like bone off the upper vertebral body endplate. 
         [0083]    In one embodiment, as depicted in  FIGS. 8 and 9 , the lower endplate  30  includes projections  106  for engaging the endplate of the lower vertebral body (depicted in  FIG. 45 ), and an opening  108  configured to allow bone growth from the bone graft material in the implant  10  to pass through the opening  108  and fuse with the lower vertebral body. 
         [0084]    In one embodiment, the distal end  20  of the upper endplate  16 , and the distal end  34  of the lower endplate  30  define a tip  110 . The tip  110  can be beveled, as depicted in  FIG. 45 ; flat, as depicted in  FIGS. 23 and 24 ; or come to a central point, as depicted in  FIG. 26 . 
         [0085]    In one embodiment, the tip  110  can include bone-engaging projections  112 . In accordance with another embodiment, the tip  110  can have no projections. The bone-engaging projections  112  are configured to prevent implant migration as the implant  10  is expanding. The bone-engaging projections  112  may be perpendicular to the side surfaces  22  and  36 , but generally follow the shape of the tip  110 , or they could be parallel to the tip  110 . 
         [0086]    In one embodiment as depicted in  FIGS. 35 and 36 , an engaging pin  114  extends from at least one spur gear  90  or  94 , and is engaged in a slot  116  in a side of the upper endplate  16 . Engagement of the engaging pin  114  in slot  116  assists in preventing the endplates  16  and  30  from decoupling during expansion of the implant  10 . 
         [0087]    In one embodiment, as depicted in  FIGS. 35 and 36 , an upper gear  118  is defined at the proximal end  18  of the upper endplate  16 , in engagement with a lower gear  120  defined at the proximal end  32  of the lower endplate  30 . Engagement of the upper and lower proximal gears  118  and  120 , respectively, assists in preventing the endplates  16  and  30  from decoupling during expansion of the implant  10 . 
         [0088]    In one embodiment, an independent proximal expansion mechanism  122  is defined at the proximal end  12  of the implant  10 . As depicted in  FIGS. 28-31, 35, and 36 , the proximal expansion mechanism  122  includes a proximal-end polygonal-shaped toggle  124 , attached to the proximal end  80  of the rotating portion  78 . A pair of proximal-end pivot pins  126  projects from the proximal-end toggle  124 . In one embodiment, the toggle  124  can have one distraction position while in another embodiment, the toggle  124  can have progressive distraction positions. In one embodiment, the toggle  124  can be rotated, while in another embodiment, the toggle  124  can be translated. In the embodiment where the toggle  124  is rotated, the pivot pins  126  distract, using a cam-like action. In the embodiment where the toggle  124  is translated, the pivot pins  126  are distracted by sliding along proximal ramps  128 . 
         [0089]    In one embodiment, an insertion tool  130 , depicted in  FIGS. 38-44 and 46 , includes a proximal end  132 , and a distal end  134 . An outer hollow cylindrical shaft  136  extends between the proximal end  132  and the distal end  134 . An inner hollow cylindrical shaft  138  extends through the outer shaft  136 . The inner shaft  138  has a proximal end  140  and a distal end  142 . 
         [0090]    In one embodiment, as depicted in  FIG. 38 , a T-handle  158  is defined at the proximal end  140  of the inner shaft  138 . The T-handle  158  attaches to an elongated driver  143 , which extends through the inner shaft  138 . 
         [0091]    In one embodiment, as depicted in  FIGS. 42 and 43 , the elongated driver  143  has a blunt distal end  154 . 
         [0092]    In one embodiment, as depicted in  FIG. 39 , a tap cap  144  is defined at the proximal end  140  of the inner shaft  138 , attached to the driver  143 . 
         [0093]    In one embodiment, as depicted in  FIG. 40 , the tap cap  144  fits removably into a funnel  146  defined at the proximal end  140  of the inner shaft  138 . 
         [0094]    In one embodiment, a handle  148  is provided, gripping an outer surface of the outer shaft  136 . Handle  148  is configured to be held by a surgeon while using the insertion tool  130 . 
         [0095]    In one embodiment, as depicted in  FIG. 46 , the distal end  134  of the outer shaft  136  includes projecting fingers  150 , configured to fit into the depressions  52 , proximate the opening  50  in the proximal end  46  of the chassis portion  44 . 
         [0096]    In one embodiment, as depicted in  FIGS. 40 and 46 , the distal end  142  of the inner shaft  138  includes external threads  152 , configured to engage the first set of inner threads  54  in the opening  50  of the chassis portion  44 . 
         [0097]    In one embodiment, as depicted in  FIGS. 38, 39, and 42 , moving the elongated driver  143 , either by applying a force to the T-handle  158 , or by applying a force to the tap cap  144 , the elongated driver  143  is moved through the inner shaft  138 , through the opening  50  in the proximal end  46  of the chassis portion  44 , and through the chassis portion  44 , until the blunt proximal end opening  89  in the rotating portion  78 . Translation of the motion of the elongated driver  143  to the rotating portion  78  pushes the implant  10  into the disc space. Following removal of the elongated driver  143  from the implant  10  and the inner shaft  138 , as depicted in  FIG. 44 , bone growth material can be inserted through the inner shaft  138  and into the implant  10 . 
         [0098]    In one embodiment, as depicted in  FIGS. 50-54 , upper spikes  174  and lower spikes  176  are pivotally connected to the walls  62  and  64  of the yoke  60 . Each upper spike  174  includes a proximal end  177  pivotally connected to a wall of the yoke, and a distal end  178 . Each lower spike  176  includes a proximal end  180  pivotally connected to a wall of the yoke, and a distal end  182 . Each distal end  178  includes an upper arcuate distal end portion  184  and an upper edge  185 . Each distal end  182  includes a lower arcuate distal end portion  186  and a lower distal edge  188 . 
         [0099]    In one embodiment, as depicted in  FIG. 52 , upper pockets  190  are defined within the implant  10  to store the upper spikes  174  when the implant  10  is in the collapsed position. Likewise, lower pockets  192  are defined within the implant  10  to store the lower spikes  176  when the implant  10  is in the collapsed position. 
         [0100]    In one embodiment, as depicted in  FIGS. 50, 52 and 53 , an upper opening  194  is defined in the upper endplate  16  proximate the upper pocket  190 . A lower opening  196  is defined in the lower endplate  30  proximate the lower pocket  192 . The upper opening  194  includes an upper ramped surface  198  at a distal end thereof, and the lower opening  196  includes a lower ramped surface  200  at a distal end thereof. When the yoke  60  begins to move in the distal direction, and the implant  10  begins to expand, the upper spikes  174  and the lower spikes  176  are simultaneously pushed by the yoke  60  in the distal direction. Upper arcuate distal end portions  184  of the upper spikes  174  are pushed into contact with the upper ramped surface  198  of the upper opening  194  in the upper endplate  16 , and lower arcuate distal end portions  186  of the lower spikes  176  are pushed into contact with the lower ramped surface  200  of the lower opening  196  of the lower endplate  30 . The distal force applied by the yoke  60 , pushing the upper arcuate distal end portions  184  of the upper spikes  174  into contact with the upper ramped surface  198  defined in the distal end of the upper opening  194  defines a torque T (upper). Torque T (upper) forces the upper spikes  174  to pivot clockwise, through the upper opening  194 . Likewise, the distal force applied by the yoke  60 , pushing the arcuate distal end portions  186  of the lower spikes  176  into contact with the lower ramped surface  200  of the lower opening  196  defines a torque T (lower). Torque T (lower) forces the lower spikes  176  to pivot counter-clockwise, through the lower opening  196  in the lower endplate  30 . As the implant  10  continues to expand, the upper spikes  174  continue to pivot until they reach an orientation along an axis which is transverse to the mid-longitudinal axis L-L of the implant  10 , with the upper edges  185  engaging the upper vertebral body. Likewise, the lower spikes  176  continue to pivot until they reach an orientation along an axis transverse to the mid-longitudinal axis L-L of the implant  10 , with the lower edges  188  engaging the lower vertebral body. 
         [0101]    In one embodiment, as depicted in  FIG. 55 , apertures can be defined in internal parts of the implant, for example co-axial apertures  202  and transverse apertures  204  defined in the rotating portion  78 . The apertures  202  and  204  are configured to permit flow of bone graft material therethrough as it is injected from the proximal end  46  of the chassis  44 . 
         [0102]    In one embodiment, as depicted in  FIG. 55 , as the yoke  60  moves in the distal direction, deploying the upper and lower spikes  174  and  176 , a co-axial aperture  206  is opened in the chassis  44  behind the proximal ends  177  and  180  of the spikes  174  and  176 , respectively. Co-axial aperture  206  also is configured to allow a flow of bone growth material therethrough. 
         [0103]    In one embodiment, as depicted in  FIG. 57 , flaps  208  are attached to the right and left sides of the implant  10  (only one side shown), with upper and lower edges thereof connected between the upper endplate  16  and the lower endplate  30 . The flaps  208  can be made of a porous material, a semi-porous material, or a solid material. When the implant  10  is expanded, as depicted in  FIG. 57 , the flaps  208  are deployed, stretched tightly between the upper endplate  16  and the lower endplate  30 . 
         [0104]    In one embodiment, as depicted in  FIGS. 60-62 , an implant  10  includes a bone graft inserter  210 , attachable to attachment clamps  212  provided at the proximal end  46  of the chassis portion  44 . The bone graft inserter includes an outer tube  214  defining a lumen  216  therethrough, and a handle  218 . The attachment clamps  212  are positioned to firmly grip a distal end of the outer tube  214 . 
         [0105]    In one embodiment, as depicted in  FIGS. 60-62 , a graft tube  220  is provided within the lumen  216 . Bone graft material in the graft tube  220  is in position to flow into the chassis portion  44  of the implant  10  via the connection between the attachment clamps  212  and the outer tube  214 . As further depicted in  FIGS. 60-62 , the bone graft material inserted into the chassis portion  44  of the implant  10  can flow out of the implant  10  via multiple small apertures (not shown) in the upper and lower endplates  16  and  30 , respectively, and via the open distal end of the expanded implant  10 . 
         [0106]    In one embodiment, as depicted in  FIGS. 58 and 59 , a rigid plunger  222  is provided in the lumen  216 . The plunger  222  includes a head portion  224  at a distal end thereof. The head portion  224  has a diameter approximately equal to a diameter of the lumen  216 . When the plunger  222  slides within the lumen  216  in the distal direction, the head portion  224  pushes bone graft material in the distal direction and into the proximal end  46  of the chassis portion  44 . 
         [0107]    Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.