Abstract:
An expandable spinal fusion device is provided. The expandable device comprises a first part slidingly coupled to a second part. An removable expandable member extends between the first part and the second part and is coupled to a rotating operator such that rotating the operator causes the first part and the second part to move away from each other and distract vertebral bodies. A spacer or clip is used to lock the first part in relation to the second part to allow bone growth the fuse the vertebral bodies.

Description:
RELATED APPLICATIONS AND CLAIM OF PRIORITY 
       [0001]    The present application is a continuation-in-part of U.S. patent application Ser. No. 11/456,038, titled EXPANDABLE SPINAL FUSION CAGE, which relates to U.S. Provisional Patent Application Ser. No. 60/456,590, filed Mar. 21, 2003, titled Expandable Spinal Fusion Device, which application is expired, the disclosure of which is incorporated herein by reference as if set out in full. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to spinal corrective surgery and, more particularly to an expandable spinal fusion cage to facilitate fusing a spinal segment into a solid bone mass. 
       BACKGROUND OF THE INVENTION 
       [0003]    The vertebrae of the human spine are arranged in a column with one vertebra on top of the next. Between each vertebra exists an intervertebral disc that transmits force between adjacent vertebrae and provides a cushion between the adjacent vertebrae. 
         [0004]    Sometimes, back pain is caused by degeneration or other deformity of the intervertebral disc (“diseased disc”). Conventionally, surgeons treat diseased discs by surgically removing the diseased disc and inserting an implant in the space vacated by the diseased disc, which implant may be bone or other biocompatible implants. The adjacent vertebrae are then immobilized relative to one another. Eventually, the adjacent vertebrae grow into one solid piece of bone. 
         [0005]    For example, a conventional method to fuse vertebrae together includes a bone graft and a plate to stabilize the device. The current process includes inserting a bone graft and fusing the adjacent vertebrae together. Traditionally, inserting a bone graft involves distracting the disc space and manually keeping the vertebral bodies separated. The bone graft or implant is located and, once the implant is placed, the surgeon releases the adjacent vertebrae allowing them to squeeze the implant and hold it in place. The segment would be immobilized to facilitate fusion. 
         [0006]    Immobilizing the superior and inferior vertebrae with a bone graft in the intervertebral disc space prompts fusion of the superior and inferior vertebrae into one solid bone. As can be appreciated, the superior and inferior vertebrae are distracted to allow sufficient space for the surgeon to implant and orient the implant. The larger the implant, the more difficult it is for the surgeon to place and orient the implant. Moreover, larger implants increase the risk of injury to the superior nerve root and the medially located thecal sack. Thus, it would be desirous to develop a compact fusion device that is expandable such that it can be inserted in a compact package allowing surgical site to be smaller, reducing the risk of injury. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides an expandable spinal fusion cage. The expandable spinal fusion cage includes a first part slidably connected to a second part. The first part includes a first vertebral body interface surface and a second surface opposite the first vertebral body interface surface. The second part includes a third vertebral body interface surface and a fourth surface opposite the third vertebral body interface surface. Dual walls coupled to the second surface extend from the second surface towards the fourth surface forming channels. Single walls coupled to the fourth surface extend from the fourth surface towards the second surface. The single walls are aligned the channels. A removable, expandable member extending from the second surface to the fourth surface, the removable, expandable member having a collapsed state and at least one expanded state. An operating arm having a proximate end coupled to the removable, expandable member and a distal end coupled to a rotating operator allows expansion of the removable, expandable member, which slidably moves the first part in relation to the second part. Spacers frictionally fit about the single walls. Such that rotating the rotating operator causes the operating arm to move the removable, expandable member from the collapsed state to the at least one expanded state and the at least one spacer locks the removable, expandable member in the at least one expanded state. 
         [0008]    The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention, and together with the description, serve to explain the principles thereof. Like items in the drawings are referred to using the same numerical reference. 
           [0010]      FIG. 1  is an axial view of an intervertebral disc space with implants constructed in accordance with an embodiment of the present invention; 
           [0011]      FIGS. 2A and 2B  are front partially exploded perspective view of an implant constructed in accordance with an embodiment of the present invention; 
           [0012]      FIG. 3  is a lateral view of the implant of  FIGS. 2A and 2B  in an intervertebral disc space in a collapsed or compact state; 
           [0013]      FIGS. 4A and 4B  show the implant of  FIGS. 2A and 2B  in an expanded state; 
           [0014]      FIG. 5  is a lateral view of the implant of  FIGS. 4A and 4B  in the intervertebral disc space in an expanded state; 
           [0015]      FIG. 6  is a front, perspective view of a spacer constructed in accordance with an embodiment of the present invention; 
           [0016]      FIG. 7  is a front, perspective view of the implant of  FIGS. 4A and 4B  with the spacer; and 
           [0017]      FIG. 8  is a lateral view of the implant of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The present invention will now be described with reference to the figures. Referring first to  FIG. 1 , an axial view of spinal segments  100   a  and  100   b  is shown. Spinal segment includes inferior vertebral body  102 , superior vertebral body (not specifically shown, but substantially identical to inferior vertebral body  102 ), and intervertebral disc space  104 . Intervertebral disc space  104  is typically occupied by an intervertebral disc comprising a disc annulus and disc nucleus. To fuse inferior vertebral body  102  and the superior vertebral body, the intervertebral disc may be fully or partially removed, but is shown as fully removed for convenience. Occupying intervertebral disc space  104  is at least one expandable spinal fusion device  106 . Depending on the surgical procedure, such as an anterior or posterior approach, and the discs to be fused, one or more devices  106  may be used by the surgeon. As shown in segment  100   a , a single device  106  is used. Spinal segment  100   b  uses two devices  106 . 
         [0019]    Referring now to  FIGS. 2A and 2B , an expandable fusion device  200  is shown in more detail. Device  200  includes a first part  202  and a second part  204 . First part  202  includes a first vertebral body interface surface  206 . First vertebral body interface surface  206  may include surface texturing  208 , such as the saw tooth projections shown or alternatively, striations, other shaped protrusions, or the like. First part  202  has a second surface  210  opposite first vertebral body interface surface  206 . Extending opposite optional surface texturing  208  from second surface  210  are a plurality of dual walls  212 . As shown, two sets of dual walls  212  form two channels  214 . Dual walls  212  and second surface  216  form a partially enclosed space  218 . Notice, while shown as solid walls for convenience, the various walls of the present device may have through openings or windows. 
         [0020]    Second part  204  comprises a third vertebral body interface surface  220 . Second vertebral body interface surface  220  may comprise optional surface texturing  208 . Second part  204  also comprises a fourth surface  222  opposite third vertebral body interface surface  220 . Extending from fourth surface  222  exist a plurality of single walls  224 . Single walls  224  are aligned to slidably engage channels  214 . Note, while two dual walls  212  forming two channels are shown on first part  202  and two single walls  224  to align with channels  214  are shown in second part  204 , dual walls  212  and single walls  224  may be alternatively arranged on second part and first part respectively. Alternatively, first part may have two dual walls  212  forming one channel  214  and one single wall  224  while second part may have two dual walls  212  forming one channel  214  and one single wall  224  such that the single walls align with the channels. Moreover, one of ordinary skill of the art would now recognize structure may not have two dual walls, but just one dual wall to provide the alignment or the second wall of dual walls  212  may be prongs, protrusions, ribs or the like. 
         [0021]    Residing in space  218  is a removable, expandable member  226 . Expandable member  226  operates in any conventional manner, similar to, for example, a car jack. Because the operation of expandable member is well known in the art, it will not be further explained herein. Extending from expandable member  226  is an operating arm  228 . Operating arm  228  is connected at a proximate end to expandable member  226  and at a distal end to a rotating operator  230 , which is shown as a dial, but could be other rotating devices. Rotating operator  230  has an indicating window  232  and indicia  234  in indicating window  232  to provide information to the surgeon as will be explained further below. As shown in  FIGS. 2A and 2B , device  200  is in the collapsed or compact state  236 . Correspondingly, indicia  234  indicates “0” or the like to show no expansion or full collapsed state. 
         [0022]    Referring now to  FIG. 3 , spinal segment  100   a  is shown in a lateral view. Device  200  is implanted in intervertebral disc space  302  initially in the collapsed state  236  with operating arm  228  extending from the disc space  302  to terminate in a position where rotating operator  230  is accessible by a surgeon. 
         [0023]    Referring now to  FIGS. 4A and 4B , device  200  is shown in an expanded state  400 . To obtain expanded state  400 , rotating operator  230  is rotated, for example in a clockwise direction as shown by arrow  402 . Device  200  may be expandable to a plurality of positions over a spectrum, a contiguous spectrum or a step function spectrum. As device  200  expands to various positions, indicia  234  will indicate the corresponding expansion state in indicating window  232 . For example, indicia  234  indicates a position “ 5 ” in  FIGS. 4A and 4B . Position  5  would correspond to a desired distraction by the surgeon. As rotating operator  230  is rotated, single walls  224  slidably move in channels  214  as shown by arrows  410  such that channels  214  and single walls  224  provide a traveling guide. As single walls  224  moves in channels  214 , gaps  404  form between a bottom edge  606  of dual walls  212  and fourth surface  222 . 
         [0024]    Referring to  FIG. 5 , device  200  in an expanded state  400  is shown in intervertebral disc space  302 . Device  200  provides distraction between superior and inferior vertebral discs. 
         [0025]    Referring to  FIG. 6 , a spacer  600  is shown. Spacer  600  has a plurality of spacer walls  602  separated by a distance  604 , which generally corresponds to a thickness t of single wall  224 . Spacer walls  602  have a width w of sufficient size such that a bottom edge  606  of dual walls  212  can rest a leading edge  608  of spacer walls  602 . Spacer walls extend all or part of the length of single wall  224 . A spacer wall connector  610  traverses one end of spacer  600  connecting the spacer walls  602 . Spacer  600  forms a frictional fitting with single wall  224 . Spacer walls  602  may be parallel as shown, converge, or diverge to facilitate use as a matter of design choice. Single wall  224  and spacer walls  602  may have texturing  612  to facilitate the frictional fitting between spacer  600  and single wall  224 . Spacer  600  is sized to fit into gap  404 , which corresponds to the expansion state selected by the surgeon. Thus, expansion state corresponding to indicia “ 1 ” would have a corresponding spacer  600  as would expansion corresponding to indicia “ 2 ”, “ 3 ”, “ 4 ”, or the like. Thus, spacer  600  has indicia  610  corresponding to indicia  234 . Implanting spacer  600  locks device  200  in the expansion selected by the surgeon. In this case, as shown in  FIGS. 4A and 4B , spacer  600  corresponding to expansion state  5  as shown by indicia  234  is selected. Referring to  FIG. 7 , device  200  with spacer  600  is shown. 
         [0026]    Once spacers  600  are placed, the surgeon may operate rotating operator  230  back to the collapsed stated, position “ 0 ” (or some other less collapsed position if the full collapsed position is not desired). Once in the collapsed position, expandable member  226  may be removed from space  218 . Space  218  may be packed with material  700 , such as bone chips or the like, to facilitate bone growth between superior and inferior vertebral discs. Moreover, as shown in phantom in  FIG. 7 , dual walls  212  and single walls  224  may have channels  702 , such as, divots, in growth channels, or the like, to further facilitate bone growth and fusion. Alternatively to removing expandable member, material  700  may be packed about expandable member  226  and operating arm  228  may be detachable and removable from expandable member  226 . 
         [0027]    First part and second part may be constructed from, for example, a number of biocompatible materials, such as, for example, milled bone, PEEK material, titanium, resorbable material, shaped memory alloys, or the like. First part and second part need not be constructed from the same material. 
         [0028]    While the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention.