Abstract:
A cage device for performing spinal fusion surgery and related methods. In some embodiments, a housing defining one or more ports may be provided that may be configured to be selectively disposed in an intervertebral space between adjacent vertebrae. One or more extensible retention structures may also be provided that may be configured to be selectively advanced out of the housing through the one or more ports. The one or more extensible retention structures may comprise a cutting edge configured such that the cutting edge is positioned entirely within the housing prior to selective advancement of the one or more extensible retention structures out of the housing through the one or more ports. One or more actuation mechanisms configured for selectively advancing the one or more extensible retention structures out of the housing through the one or more ports may also be provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a continuation of patent application Ser. No. 12/371,008 filed Feb. 13, 2009 and titled “Anterior Lumbar Interbody Fusion Cage Device and Associated Method,” which application claims the benefit of priority of U.S. Provisional Patent Application No. 61/028,624 filed on Feb. 14, 2008 and titled “Anterior Lumbar Interbody Fusion Cage Device.” The contents of both of the foregoing applications are incorporated herein by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to devices and methods for performing spinal surgery. More specifically, the present invention relates to an anterior lumbar interbody fusion (ALIF) cage device and an associated method for performing fusion procedures of the lumbar spine. The fundamental concepts underlying this device and method may be extended to other surgical procedures as well, such as extreme lateral interbody fusion (XLIF) spinal procedures, cervical spinal procedures, and the like. 
       BACKGROUND OF THE INVENTION 
       [0003]    ALIF is a spinal fusion procedure that utilizes an anterior (i.e. frontal) approach through the abdominal region to fuse adjacent vertebrae of the lumbar spine. The intervertebral disc is removed using appropriate rasping and grasping tools and replaced with a cage device and/or bone graft after appropriate distraction and spacing tools are used to restore the normal height of the intervertebral space. ALIF is preferred when either one or multiple spinal levels are being fused and one or multiple intervertebral discs must be removed, and may be performed in conjunction with a posterior decompression (i.e. laminectomy) and/or the placement of stabilizing instrumentation (i.e. screws and rods, plates, etc.). Because during ALIF the spinal nerves and other neurologic structures do not have to be retracted, wide access to the intervertebral space(s) of interest is provided without unacceptable risk of neurologic injury. ALIF is used to treat a variety of painful spinal conditions, such as spondylolisthesis and degenerative disc disease, among others. 
         [0004]    Conventional ALIF cage devices typically include some sort of retention mechanism to hold them securely in the intervertebral space. Such retention mechanisms include biting and locking structures that engage the endplate(s) of the vertebral body or bodies of interest, screw assemblies that engage the vertebral body or bodies of interest, plate structures that engage the vertebral body or bodies of interest, etc. All of these retention mechanisms, however, suffer from the shortcomings that they are difficult to place, difficult to deploy, and/or tend to allow the associated cage device and/or bone graft to shift over time and thus fail to adequately maintain the normal height of the intervertebral space, for example. Thus, what is needed in the art is an improved ALIF cage device having an improved retention mechanism. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    In various exemplary embodiments, the present invention provides an improved ALIF cage device that has one or more extensible threaded retention pipe structures that are selectively deployed into one or more endplates of adjacent vertebrae once the ALIF cage device is disposed in an intervertebral space of interest. A bone graft is disposed within a housing and the extensible threaded retention pipe structure(s) of the ALIF cage device, as appropriate. Advantageously, the extensible threaded retention pipe structure(s) are selectively deployed into the endplate(s) of the adjacent vertebrae via the actuation of a simple keyed screw and gear mechanism or the like. Again, the fundamental concepts underlying the ALIF cage device of the present invention may be extended to other surgical procedures as well, such as XLIF spinal procedures, cervical spinal procedures, and the like. 
         [0006]    In one exemplary embodiment, the present invention provides a cage device for performing spinal fusion, including: a housing defining one or more ports that is selectively disposed in an intervertebral space between adjacent vertebrae; one or more extensible retention structures that are selectively advanced out of the housing through the one or more ports and into one or more endplates of the adjacent vertebrae; and one or more actuation mechanisms for selectively advancing the one or more extensible retention structures out of the housing through the one or more ports and into the one or more endplates of the adjacent vertebrae. The housing is sized and shaped to cover substantially all of the one or more endplates of the adjacent vertebrae. Optionally, the housing is at least partially manufactured from a radiolucent material. Preferably, the one or more extensible retention structures each consist of an annular structure having a substantially constant cross-sectional shape. The one or more extensible retention structures each include a cutting edge for engaging bony material of an associated endplate of an adjacent vertebrae. The one or more extensible retention structures each also include internal bone threading for engaging bony material of an associated endplate of an adjacent vertebrae. The one or more extensible retention structures each further include external machine threading for engaging corresponding internal machine threading of the housing and selectively advancing the one or more extensible retention structures out of the housing through the one or more ports and into the one or more endplates of the adjacent vertebrae. Preferably, the machine threading is allowed to escape the housing. The machine threading that is allowed to escape the housing serves to compress an associated endplate of an adjacent vertebrae against the housing. In one exemplary embodiment, the one or more actuation mechanisms consist of at least one worm gear/mandrel pair configured to engage the machine threading. Optionally, the one or more actuation mechanisms consist of at least one worm gear/mandrel pair configured to engage longitudinally oriented teeth manufactured into the machine threading. Preferably, the one or more extensible retention structures each include a retention structure configured to prevent that extensible retention structure from escaping the housing. Thus, the one or more extensible retention structures are selectively advanced out of the housing through the one or more ports and into the one or more endplates of the adjacent vertebrae with a rotational motion. Preferably, the one or more extensible retention structures are configured such that they may contain a bone graft. In one exemplary embodiment, the housing is selectively disposed in the intervertebral space between the adjacent vertebrae using an anterior surgical approach. 
         [0007]    In another exemplary embodiment, the present invention provides a method for performing spinal fusion using a cage device, including: providing a housing defining one or more ports that is selectively disposed in an intervertebral space between adjacent vertebrae; providing one or more extensible retention structures that are selectively advanced out of the housing through the one or more ports and into one or more endplates of the adjacent vertebrae; and providing one or more actuation mechanisms for selectively advancing the one or more extensible retention structures out of the housing through the one or more ports and into the one or more endplates of the adjacent vertebrae. The housing is sized and shaped to cover substantially all of the one or more endplates of the adjacent vertebrae. Optionally, the housing is at least partially manufactured from a radiolucent material. Preferably, the one or more extensible retention structures each consist of an annular structure having a substantially constant cross-sectional shape. The one or more extensible retention structures each include a cutting edge for engaging bony material of an associated endplate of an adjacent vertebrae. The one or more extensible retention structures each also include internal bone threading for engaging bony material of an associated endplate of an adjacent vertebrae. The one or more extensible retention structures each further include external machine threading for engaging corresponding internal machine threading of the housing and selectively advancing the one or more extensible retention structures out of the housing through the one or more ports and into the one or more endplates of the adjacent vertebrae. Preferably, the machine threading is allowed to escape the housing. The machine threading that is allowed to escape the housing serves to compress an associated endplate of an adjacent vertebrae against the housing. In one exemplary embodiment, the one or more actuation mechanisms consist of at least one worm gear/mandrel pair configured to engage the machine threading. Optionally, the one or more actuation mechanisms consist of at least one worm gear/mandrel pair configured to engage longitudinally oriented teeth manufactured into the machine threading. Preferably, the one or more extensible retention structures each include a retention structure configured to prevent that extensible retention structure from escaping the housing. Thus, the one or more extensible retention structures are selectively advanced out of the housing through the one or more ports and into the one or more endplates of the adjacent vertebrae with a rotational motion. Preferably, the one or more extensible retention structures are configured such that they may contain a bone graft. In one exemplary embodiment, the housing is selectively disposed in the intervertebral space between the adjacent vertebrae using an anterior surgical approach. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like device components/method steps, as appropriate, and in which: 
           [0009]      FIG. 1  is a top perspective view of one exemplary embodiment of the top half of the ALIF cage device of the present invention, highlighting the associated housing and extensible threaded retention pipe structure; 
           [0010]      FIG. 2  is a bottom perspective view of the top half of the ALIF cage device of  FIG. 1 , highlighting the associated housing, extensible threaded retention pipe structure, worm gear, and mandrel; 
           [0011]      FIG. 3  is a top perspective view of one exemplary embodiment of the housing of  FIGS. 1 and 2 ; 
           [0012]      FIG. 4  is a bottom perspective view of the housing of  FIG. 3 , highlighting the associated worm gear and mandrel; 
           [0013]      FIG. 5  is a top perspective view of one exemplary embodiment of the extensible threaded retention pipe structure of  FIGS. 1 and 2 ; 
           [0014]      FIG. 6  is a bottom perspective view of the extensible threaded retention pipe structure of  FIG. 5 ; and 
           [0015]      FIG. 7  is a bottom perspective view of one exemplary embodiment of the worm gear and mandrel of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring to  FIG. 1 , in one exemplary embodiment, the ALIF cage device  10  of the present invention includes a housing  12  and one or more extensible threaded retention pipe structures  14  that are selectively deployed into one or more endplates of adjacent vertebrae once the ALIF cage device  10  is disposed in an intervertebral space of interest. It should be noted that only the top half of the ALIF cage device  10  is illustrated herein (i.e. the top half of the housing  12  and the top extensible threaded retention pipe structure  14 ). The bottom half of the ALIF cage device  10  is substantially identical, including the bottom half of the housing  12  and the bottom extensible threaded retention pipe structure  14 , when used. The top and bottom halves of the ALIF cage device  10  (i.e. the top and bottom halves of the housing  12 ) are joined during the manufacturing process or prior to implantation to form an integrated whole. A bone graft is disposed within the housing  12  and the extensible threaded retention pipe structure(s)  14  of the ALIF cage device  10 , as appropriate. 
         [0017]    Once the ALIF cage device  10  is disposed in the intervertebral space of interest, the extensible threaded retention pipe structure(s)  14  are selectively deployed into the endplate(s) of the adjacent vertebra(e) by deflecting outwards with respect to the housing  12 , optionally accompanied by a rotational motion. This deflection outwards is along the cranial/caudal axis of the spine. 
         [0018]    Referring to  FIG. 2 , in this exemplary embodiment, the extensible threaded retention pipe structure(s)  14  are each deployed into the endplate(s) of the adjacent vertebra(e) by a worm gear/mandrel pair  16 , 18 . The worm gear  16  is disposed along the anterior/posterior or lateral axis of the ALIF cage device  10 , while the mandrel  18  is disposed along the cranial/caudal axis of the ALIF cage device  10 . The worm gear  16  disposed along the anterior/posterior or lateral axis of the ALIF cage device  10  has a portion that protrudes or is accessible through a port (not specifically illustrated) manufactured into the associated half of the housing  12 . The mandrel  18  disposed along the cranial/caudal axis of the ALIF cage device  10  has portions that are seated in both the top and bottom halves of the housing  12 . Thus, the worm gear  16  rotates about the anterior/posterior or lateral axis of the ALIF cage device  10 , engages and rotates the mandrel  18 , which rotates about the cranial/caudal axis of the ALIF cage device  10  and engages drive threads  20  disposed concentrically about the outside diameter of the associated extensible threaded retention pipe structure  14 . Specifically, the mandrel  18  engages longitudinal teeth manufactured into the drive threads  20  disposed concentrically about the outside diameter of the associated extensible threaded retention pipe structure  14 . Thus, as the worm gear  16  is actuated by a surgeon and turns the mandrel  18 , the extensible threaded retention pipe structure  14  is “spun up” or “spun down” via the longitudinal teeth of these drive threads  20 , which engage a complimentary thread manufactured into the interior of the housing  12 , or, alternatively, a lip  24  ( FIGS. 3 and 4 ) manufactured into the interior/surface of the housing  12 . Preferably, each of the one or more extensible threaded retention pipe structures  14  is capable of extending a distance on the order of millimeters to centimeters from the housing  12  and into the endplate(s) of the adjacent vertebra(e). It will be readily apparent to those of ordinary skill in the art that different mechanisms could also be used to deploy the one or more extensible threaded retention pipe structures  14 , using gears and threads or not, employing rotational as well as extension motion or not, etc. For example, one set of worm gears/mandrels  16 ,  18  could be used to deploy both top and bottom extensible threaded retention pipe structures  14  simultaneously. Likewise, different actuation mechanisms and tools could be used for deployment. 
         [0019]    Referring to  FIG. 3 , in one exemplary embodiment, each half of the housing  12  is sized and shaped such that, collectively, the housing  12  fits comfortably within the intervertebral space into which it is inserted. In the exemplary embodiment illustrated, the housing  12  is substantially oval or “kidney”-shaped, mimicking the shape of the vertebral endplates adjacent to which it is disposed. It is desirable that the ALIF cage device  10  ( FIGS. 1 and 2 ) cover as much of the vertebral endplates as possible. Each half of the housing includes a port  22  through which the associated extensible threaded retention pipe structure  14  ( FIGS. 1 ,  2 ,  5 , and  6 ) is deployed. As described above, this port  22  may include a thread (not specifically illustrated) manufactured into its interior, or, alternatively, a lip  24  manufactured into its interior, for engaging the longitudinal teeth of the drive threads  20  ( FIGS. 1 ,  2 ,  5 , and  6 ) of the associated extensible threaded retention pipe structure  14 . Preferably, each half of the housing  12  is manufactured from a metal or another biocompatible material, and some or all components of the housing  12  may be manufactured from a radiolucent material that is transparent to X-ray, CT, and MRI imaging modalities, such that anatomical structures may be visualized without interference. As alluded to above, a one-piece housing may be substituted for the two-piece housing illustrated and described without departing from the spirit and scope of the present invention. 
         [0020]    Referring to  FIG. 4 , in this exemplary embodiment, each half of the housing  12  includes a substantially hollow interior portion  26 , to conserve weight, defining channels or access spaces for the worm gears/mandrels  16 , 18  and other structures/devices disposed within the housing  12 . 
         [0021]    Referring to  FIGS. 5 and 6 , in one exemplary embodiment, each extensible threaded retention pipe structure  14  is an annular structure with a substantially circular cross-sectional shape. However, any suitable cross-sectional shape, being constant or variable along the longitudinal axis of the extensible threaded retention pipe structure  14 , may be used. Likewise, each extensible threaded retention pipe structure  14  may be a substantially solid structure. Each extensible threaded retention pipe structure  14  is manufactured from a metal or another biocompatible material. Preferably, each extensible threaded retention pipe structure  14  includes a cutting edge  28  along the surface or edge that engages the associated vertebral endplate, such that the extensible threaded retention pipe structure  14  securely seats itself in this bony structure upon deployment. The extensible threaded retention pipe structure  14  also includes threads  30 ,  32  disposed concentrically about its outside and/or inside diameter(s) for this purpose. The outer threads  30  cover about one-half the length of the extensible threaded retention pipe structure  14  and are preferably machine threads, while the inner threads  32  cover substantially the entire length of the extensible threaded retention pipe structure  14  and are preferably bone threads. Finally, each extensible threaded retention pipe structure  14  includes a retention thread or lip  34  configured to engage the lip  24  ( FIGS. 3 and 4 ) manufactured into the interior/surface of the housing  12  ( FIGS. 1-4 ), such that the extensible threaded retention pipe structure  14  cannot be expelled from the housing  12  when “spun up” or “spun down.” Preferably, the machine threads  30  stop at least a full tum before the retention thread or lip  34 , such that they may “escape” the housing. These machine threads  30  are wider than the retention thread or lip  34 . The machine threads  30  may or may not be integral with the drive threads  20  ( FIGS. 1 ,  2 ,  5 , and  6 ) described above. The pitch of the drive threads  20 /machine threads  30  determine the rate at which the extensible threaded retention pipe structure  14  advances out of the housing  12 . Once the machine threads  30  are clear of the housing  12 , they serve to compress the vertebral endplate(s) against the housing  12 . 
         [0022]    Again, a bone graft is disposed within the housing  12  and the extensible threaded retention pipe structure(s)  14  of the ALIF cage device  10  ( FIGS. 1 and 2 ), as appropriate. Optionally, the bone graft is accessible through an anterior window (not specifically illustrated) of the ALIF cage device  10  when positioned and seated. This anterior window may be capped at will. 
         [0023]      FIG. 7  is an isolation view of the worm gears/mandrels  16 , 18  of the exemplary embodiment provided above. Each of these worm gears/mandrels  16 ,  18  is manufactured from a metal or another biocompatible material. Again, it will be readily apparent to those of ordinary skill in the art that different mechanisms could also be used to deploy the one or more extensible threaded retention pipe structures  14  ( FIGS. 1 ,  2 ,  5 , and  6 ), using gears and threads or not, employing rotational as well as extension motion or not, etc. For example, one set of worm gears/mandrels  16 ,  18  could be used to deploy both top and bottom extensible threaded retention pipe structures  14  simultaneously. Likewise, different actuation mechanisms and tools could be used for deployment. 
         [0024]    Although the present invention is illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.