Abstract:
A three column spinal fixation implant, including: an anterior cage configured to be disposed in an intervertebral space between adjacent vertebral bodies in a spine of a patient; an anterior plate coupled to the anterior cage; a pair of anterior screws coupled to the anterior cage and the anterior plate and extending posteriorly from the anterior cage and the anterior plate through a portion of one or more of the adjacent vertebral bodies and into or through posterior bony structures of the spine of the patient; a pair of anterior screws coupled to the anterior plate and extending posteriorly from the anterior plate through a portion of one or more of the adjacent vertebral bodies and into or through posterior bony structures of the spine of the patient; a plurality of posterior headbodies coupled to the anterior screws opposite the anterior cage and the anterior plate; and one or more connecting structures coupled to the plurality of posterior headbodies; wherein the three column spinal fixation implant provides structural stability to the spine of the patient across a first anterior column, a second middle column, and a third posterior column thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present patent application/patent claims the benefit of priority of co-pending U.S. Provisional Patent Application No. 62/160,754, filed on May 13, 2015, and entitled “THREE COLUMN FIXATED STAND-ALONE SPINAL IMPLANT,” U.S. Provisional Patent Application No. 62/166,635, filed on May 26, 2015, and entitled “TARGETING DEVICE AND METHOD FOR THREE COLUMN FIXATED STAND-ALONE SPINAL IMPLANT,” and U.S. Provisional Patent Application No. 62/185,751, filed on Jun. 29, 2015, and entitled “THREE COLUMN FIXATION HAVING SCREW COUPLING ABILITY,” the contents of all of which are incorporated in full by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to spinal fixation implants and associated surgical methods. More specifically, the present invention relates to three column spinal fixation implants and associated surgical methods operable for simultaneously anteriorly and posteriorly stabilizing a portion of the spine at a given level. 
       BACKGROUND OF THE INVENTION 
       [0003]    It is common in spinal surgery to perform a two incision operation, with implants placed from the front (i.e. anterior) portion of the vertebral column and supplemental fixation placed from the back (i.e. posterior) portion of the vertebral column. This effectively creates fixation in all three columns of the spine, and, hence, superior stabilization. The three columns of the spine—anterior  10 , middle  12 , and posterior  14 —are shown in  FIG. 1 . To create a stable, solid fusion, a surgeon typically needs to stabilize all three columns in order to prevent micro-motion from occurring, which can lead to non-union of the segment (i.e. pseudoarthrosis). 
         [0004]    To accomplish this, the surgeon frequently utilizes two different surgical approaches (anterior and posterior) and two separate spinal systems to achieve a stable construct. This is done using an Anterior Lumbar Interbody Fusion (ALIF) cage, with or without supplemental screws, via the anterior approach, and then using posterior pedicle screws or facet screws from the back of the patient. The surgeon performs an anterior discectomy and places the ALIF cage into the front disc space, and may secure it with screws into the vertebrae. Then the surgeon flips the patient over and places the screws from the back. This posterior approach is time consuming, technically challenging, and, for accuracy, sometimes it is robotically assisted to minimize the risk of nerve injury. 
         [0005]    Thus, truly unified three column spinal fixation implants and associated surgical methods operable for simultaneously anteriorly and posteriorly stabilizing a portion of the spine at a given level are still needed in the art. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    In various exemplary embodiments, the present invention allows a surgeon to insert one portion of an implant system with anterior screws from the front, and then connect posterior screws to the anterior screws from the back. This can be accomplished using one unified system and ‘coupling’ portions of the system together from the front and back, thereby creating a true 360 degrees of fixation. In general, it is novel to couple anterior and posterior implant systems to provide three column spinal fixation and stabilizing compression. The present invention provides enhanced operative simplicity and reduced operative time, with superior operative functionality. It is ideally suited for use in the lumbar spine, with the anterior aspect exposed at the operative level. Three column fixation is achieved when the anterior column across the vertebral body is fused and two posterior column fixation points (across the load bearing facet joints) are also fused, such that immobility and stability of the level is achieved, thereby eliminating instability and nerve irritation. 
         [0007]    In one exemplary embodiment, a three column spinal fixation implant, comprises: an anterior cage configured to be disposed in an intervertebral space between adjacent vertebral bodies in a spine of a patient; one or more anterior screws coupled to the anterior cage and extending posteriorly from the anterior cage through a portion of one or more of the adjacent vertebral bodies and into or through posterior bony structures of the spine of the patient; one or more posterior headbodies coupled to the one or more anterior screws opposite the anterior cage; and one or more connecting structures coupled to the one or more posterior headbodies; wherein the three column spinal fixation implant provides structural stability to the spine of the patient across a first anterior column, a second middle column, and a third posterior column thereof. The anterior cage comprises one or more friction surfaces configured to hold the anterior cage in the intervertebral space. The anterior cage defines one or more internal voids configured to contain a bone graft material. The anterior cage is manufactured from one or more of a surgically implantable polymeric material and a surgically implantable metallic material. Optionally, the one or more posterior headbodies are coupled to the one or more anterior screws via one or more posterior screws that threadingly engage the one or more anterior screws in a coaxial alignment. Alternatively, the one or more posterior headbodies are coupled to the one or more anterior screws via one or more compression fittings that compressively engage the one or more anterior screws in a coaxial alignment. Optionally, the implant also comprises an anterior plate coupled to the anterior cage. The one or more anterior screws are coupled to the anterior cage through the anterior plate. Optionally, the one or more anterior screws comprise a pair of anterior screws that are coupled to both the anterior cage and the anterior plate and a pair of anterior screws that are coupled only to the anterior plate. Optionally, the one or more connecting structures comprise one or more connecting rods that are coupled to adjacent posterior headbodies. Alternatively, the one or more connecting structures are coupled to adjacent posterior headbodies through a space between adjacent spinous processes of the spine of the patient, thereby distracting the adjacent spinous processes. Alternatively, the one or more connecting structures are coupled to adjacent posterior headbodies parallel to adjacent spinous processes of the spine of the patient, thereby distracting the adjacent spinous processes. Alternatively, the one or more connecting structures couple the one or more headbodies to one or more facets of the spine of the patient. 
         [0008]    In another exemplary embodiment, a three column spinal fixation implant, comprises: an anterior cage configured to be disposed in an intervertebral space between adjacent vertebral bodies in a spine of a patient; an anterior plate coupled to the anterior cage; a pair of anterior screws coupled to the anterior cage and the anterior plate and extending posteriorly from the anterior cage and the anterior plate through a portion of one or more of the adjacent vertebral bodies and into or through posterior bony structures of the spine of the patient; a pair of anterior screws coupled to the anterior plate and extending posteriorly from the anterior plate through a portion of one or more of the adjacent vertebral bodies and into or through posterior bony structures of the spine of the patient; a plurality of posterior headbodies coupled to the anterior screws opposite the anterior cage and the anterior plate; and one or more connecting structures coupled to the plurality of posterior headbodies; wherein the three column spinal fixation implant provides structural stability to the spine of the patient across a first anterior column, a second middle column, and a third posterior column thereof. 
         [0009]    In a further exemplary embodiment, a three column spinal fixation method, comprises: disposing an anterior cage in an intervertebral space between adjacent vertebral bodies in a spine of a patient; providing one or more anterior screws coupled to the anterior cage and extending posteriorly from the anterior cage through a portion of one or more of the adjacent vertebral bodies and into or through posterior bony structures of the spine of the patient; coupling one or more posterior headbodies to the one or more anterior screws opposite the anterior cage; and coupling one or more connecting structures to the one or more posterior headbodies; wherein the three column spinal fixation method provides structural stability to the spine of the patient across a first anterior column, a second middle column, and a third posterior column thereof. The anterior cage comprises one or more friction surfaces configured to hold the anterior cage in the intervertebral space. The anterior cage defines one or more internal voids configured to contain a bone graft material. The anterior cage is manufactured from one or more of a surgically implantable polymeric material and a surgically implantable metallic material. Optionally, the one or more posterior headbodies are coupled to the one or more anterior screws via one or more posterior screws that threadingly engage the one or more anterior screws in a coaxial alignment. Alternatively, the one or more posterior headbodies are coupled to the one or more anterior screws via one or more compression fittings that compressively engage the one or more anterior screws in a coaxial alignment. Optionally, the method also comprises providing an anterior plate coupled to the anterior cage. The one or more anterior screws are coupled to the anterior cage through the anterior plate. Optionally, the one or more anterior screws comprise a pair of anterior screws that are coupled to both the anterior cage and the anterior plate and a pair of anterior screws that are coupled only to the anterior plate. Optionally, the one or more connecting structures comprise one or more connecting rods that are coupled to adjacent posterior headbodies. Alternatively, the one or more connecting structures are coupled to adjacent posterior headbodies through a space between adjacent spinous processes of the spine of the patient, thereby distracting the adjacent spinous processes. Alternatively, the one or more connecting structures are coupled to adjacent posterior headbodies parallel to adjacent spinous processes of the spine of the patient, thereby distracting the adjacent spinous processes. Alternatively, the one or more connecting structures couple the one or more headbodies to one or more facets of the spine of the patient. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    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, and in which: 
           [0011]      FIG. 1  is a perspective view of a portion of the spine, highlighting the three columns—the anterior column, the middle column, and the posterior column; 
           [0012]      FIG. 2  is a perspective view of one exemplary embodiment of the three column spinal fixation implant of the present invention in an installed configuration, highlighting the use of an optional anterior plate; 
           [0013]      FIG. 3  is a perspective view of one exemplary embodiment of the three column spinal fixation implant of the present invention in an assembled configuration, again highlighting the use of an optional anterior plate; 
           [0014]      FIG. 4  is a perspective view of one exemplary embodiment of the three column spinal fixation implant of the present invention in an exploded configuration, again highlighting the use of an optional anterior plate; 
           [0015]      FIG. 5  is a perspective view of one exemplary embodiment of the anterior cage of the three column spinal fixation implant of the present invention; 
           [0016]      FIG. 6  is a planar end view of one exemplary embodiment of the anterior cage of the three column spinal fixation implant of the present invention; 
           [0017]      FIG. 7  is a planar view of one exemplary embodiment of the optional anterior plate of the three column spinal fixation implant of the present invention; 
           [0018]      FIG. 8  is rear perspective view of one exemplary embodiment of the optional anterior plate of the three column spinal fixation implant of the present invention; 
           [0019]      FIG. 9  is a perspective view of one exemplary embodiment of the optional anterior plate of the three column spinal fixation implant of the present invention coupled to the anterior cage of the three column spinal fixation implant of the present invention; 
           [0020]      FIG. 10  is a planar and cross-sectional view of one exemplary embodiment of the anterior screw of the three column spinal fixation implant of the present invention; 
           [0021]      FIG. 11  is a planar and cross-sectional view of one exemplary embodiment of the posterior screw of the three column spinal fixation implant of the present invention; 
           [0022]      FIG. 12  is a planar and cross-sectional view of one exemplary embodiment of the anterior screw of the three column spinal fixation implant of the present invention coupled to the posterior screw of the three column spinal fixation implant of the present invention; 
           [0023]      FIG. 13  is an exploded perspective view of another exemplary embodiment of the anterior screw of the three column spinal fixation implant of the present invention, utilizing an integrated headbody; 
           [0024]      FIG. 14  is a partial perspective view of another exemplary embodiment of the anterior screw of the three column spinal fixation implant of the present invention, highlighting the spherical posterior head member; 
           [0025]      FIG. 15  is a cross-sectional side view of another exemplary embodiment of the anterior screw of the three column spinal fixation implant of the present invention, utilizing an integrated headbody; 
           [0026]      FIG. 16  is a planar view of one exemplary embodiment of an interspinous process distraction device that is coupled to laterally opposed pedicle screws of the three column spinal fixation implant of the present invention, providing slight flexion of the spine at the given level; 
           [0027]      FIG. 17  is a planar view of another exemplary embodiment of an interspinous process distraction device that is coupled to vertically opposed pedicle screws of the three column spinal fixation implant of the present invention, again providing slight flexion of the spine at the given level; 
           [0028]      FIG. 18  is a planar view of one exemplary embodiment of a facet attachment device that is coupled to a pedicle screw of the three column spinal fixation implant of the present invention; 
           [0029]      FIG. 19  is a schematic diagram illustrating one step in the placement of the anterior cage of the three column spinal fixation implant of the present invention; 
           [0030]      FIG. 20  is a schematic diagram illustrating another step in the placement of the anterior cage of the three column spinal fixation implant of the present invention; 
           [0031]      FIG. 21  is a schematic diagram illustrating a further step in the placement of the anterior cage of the three column spinal fixation implant of the present invention; 
           [0032]      FIG. 22  is a schematic diagram illustrating a still further step in the placement of the anterior cage of the three column spinal fixation implant of the present invention; 
           [0033]      FIG. 23  is a schematic diagram illustrating a still further step in the placement of the anterior cage of the three column spinal fixation implant of the present invention; 
           [0034]      FIG. 24  is a schematic diagram illustrating a still further step in the placement of the anterior cage of the three column spinal fixation implant of the present invention; 
           [0035]      FIG. 25  is a perspective view of one exemplary embodiment of the anterior plate of the present invention including an additional screw hole for receiving a lag screw for segmental reduction, the lag screw disposed substantially parallel to one of the vertebral endplates of the spine of the patient (in this case the lower vertebral endplate opposite the other screws utilized); and 
           [0036]      FIG. 26  is another perspective view of one exemplary embodiment of the anterior plate of the present invention including an additional screw hole for receiving a lag screw for segmental reduction, the lag screw disposed substantially parallel to one of the vertebral endplates of the spine of the patient (in this case the lower vertebral endplate opposite the other screws utilized). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    Again, in various exemplary embodiments, the present invention allows a surgeon to insert one portion of an implant system with anterior screws from the front, and then connect posterior screws to the anterior screws from the back. This can be accomplished using one unified system and ‘coupling’ portions of the system together from the front and back, thereby creating a true 360 degrees of fixation. In general, it is novel to couple anterior and posterior implant systems to provide three column spinal fixation and stabilizing compression. The present invention provides enhanced operative simplicity and reduced operative time, with superior operative functionality. 
         [0038]    Referring now specifically to  FIGS. 2-4 , in one exemplary embodiment, the spinal implant  20  of the present invention includes an anterior cage  22  in the form of an interbody spacer that is disposed in the disc space of a desired segment. A plurality of anterior screws  24  are threaded through the anterior cage  22  into the adjacent vertebrae, thereby preventing the anterior cage  22  from moving and migrating in the disc space while maintaining a desired degree of distraction of the articulating surfaces and providing a void for bony ingrowth and fusion, for example. Accordingly, the anterior cage  22  may include a plurality of friction surfaces  38  ( FIGS. 3 and 4 ) on the lower and/or upper surfaces thereof, and may be made of a polymer material, such as polyetheretherketone (PEEK), titanium, or some other biocompatible material. In one exemplary embodiment, a pair of anterior screws  24  (for example) are threaded through the anterior cage  22  into the adjacent lower vertebra, while a pair of anterior screws  24  (for example) are threaded through the anterior cage  22  into the adjacent upper vertebra. These anterior screws  24  can be locked into place and prevented from backing out via an appropriate locking plate, locking mechanism, or locking screw disposed over the head(s) of the anterior screws  24 . In another exemplary embodiment, an anterior plate  26  is secured to the anterior cage  22  via a coupling bolt  28  and a pair of anterior screws  24  (for example) are threaded through the anterior cage  22 , either through or beneath the anterior plate  26 , into the adjacent lower vertebra. A pair of anterior screws  24  (for example) are then threaded through the anterior plate  26  into the adjacent upper vertebra. Again, these anterior screws  24  can be locked into place and prevented from backing out via an appropriate locking plate, locking mechanism, or locking screw, which may or may not consist of the anterior plate  26  and/or the coupling bolt  28 , disposed over the head(s) of the anterior screws  24 . Each of these components is described in greater detail herein below. It will be readily apparent to those of ordinary skill in the art that any number of anterior screws  24  can be used, in any configuration, and at any angle. Some or all of the anterior screws  24  can pass through the anterior cage  22  and/or anterior plate  26 , provided the anterior cage  22  is ultimately secured in the disc space and the anterior screws point towards the pedicles or facets of the vertebrae involved. The anterior screws  24  are long enough that they pass through the main vertebral body (i.e. anterior column  10  ( FIG. 1 )), middle column  12  ( FIG. 1 ), and go through the corresponding pedicle to the edge of the posterior column  14  ( FIG. 1 ) using a fluoroscopically guided targeting device, for example. On the posterior side, a coupling mechanism consisting of posterior screws  30 , connected articulating headbodies  32 , coupled rods  34 , and compressive set screws  36  ( FIG. 4 ) connect the pairs of screws  24  and  30  at the back of the patient. The posterior screws  30  may be coaxially aligned and engaged with the anterior screws  24 , or the articulating headbodies  32  can be connected directly to the anterior screws  24  via various mechanisms. This creates a strong unified implant construct that extends across all three vertebral columns with solid fixation and coronal compression. Again, each of these components is described in greater detail herein below. 
         [0039]    Procedurally, the surgeon utilizes an anterior approach through the retroperitoneal space of the patient and removes the disc in the regular fashion. He or she then sizes the space for the optimal cage fit with a fluoroscopically guided targeting method, as is described in greater detail herein below. He or she then places the new cage  22  into the disc space attached to the targeting device, for example. This new cage  22  includes a drill guide or the like that connects to the face of the new cage  22  that allows the surgeon to accurately drill the holes into the vertebrae. Alternatively, the anterior plate  26  acts as the drill guide. Using the targeting device, a hole is drilled through the vertebra and into the pedicle at each level. Guide wires may be used initially to help with the trajectory and image guidance. The anterior screws  24  are then placed through the new cage  22  and screwed into the posterior pedicles. The anterior screws  24  are then locked to the front face of the new cage. The wound is closed and the patient is flipped over and an incision at the affected levels is performed at the back. With the pedicle markers in place, exposure and posterior fixation is through a smaller, less invasive approach that is safer and more efficient. The pedicles are exposed and a reamer type of instrument is used to remove bony material around the end of the anterior screws  24 . Once the ends of the anterior screws  24  have been cleared, a posterior screw  30  and headbody  32  is coupled to the end of each anterior screw  24 , for example. A rod  34  or other coupling device is coupled to pairs of anterior screws  24 /posterior screws  30  and locked into position using set screws  36 , for example. If desired, a compressor may be used to create additional compression on the implant  20  and adjust the lordosis of the patient. Bone graft material may be placed inside the anterior cage  22  and around the posterior elements. 
         [0040]    Since there are relatively large variations in the human anatomy, it may not be possible to get the required angle of the screw projection into the pedicles. The incoming screw angle going into the pedicle may be too steep and could cause a screw to break through the edge of the pedicle, causing nerve damage. By having a metal marker or the like on the posterior aspect of the anterior cage  22  and using the targeting device described in greater detail herein below, the anterior cage  22  is placed at such safe depth that allows optimal alignment with the pedicle inlet. Again, if needed in order to get a shallower angle, the anterior plate  26  may be added to the anterior cage  22 . The screw holes are offset on the anterior plate  26 , allowing the surgeon to target the pedicles and drive the anterior screw  24  from the front of the anterior cage  22  all the way through the pedicle, without breaching the pedicle side wall. 
         [0041]    Referring now specifically to  FIGS. 5 and 6 , in one exemplary embodiment, the anterior cage  22  consists of a prismatic interbody spacer that is disposed in the disc space of a desired segment. The anterior cage  22  may be made of a polymer material, such as PEEK, titanium, or some other biocompatible material and may include one or more metallic portions for visualization and imaging. The anterior cage  22  may be sized to accommodate a variety of anatomies and provide multiple degrees of vertebral distraction. The anterior cage  22  may include a plurality of friction surfaces  38  ( FIG. 5 ) on the lower and/or upper surfaces configured to prevent the anterior cage  22  from moving and migrating in the disc space while maintaining the desired degree of distraction of the articulating surfaces. Preferably, the body  40  of the anterior cage  22  defines one or more voids  42  for receiving bone graft material for promoting bony ingrowth and fusion. The face  44  and body  40  of the anterior cage  22  include one or more apertures  46  for receiving the anterior screws  24  ( FIGS. 2-4 ). These apertures  46  may be disposed at various downwards/upwards angles to properly orient and direct the anterior screws  24  towards the pedicles at the posterior of the spine. The body  40  may also include appropriate cutaways  48  for this purpose. In the exemplary embodiment illustrated, only downwards oriented anterior screws  24  are disposed through the anterior cage  22  (with upwards oriented anterior screws  24  disposed only through the coupled anterior plate  26  ( FIGS. 2-4 )). The face  44  and body  40  of the anterior cage  22  further include an aperture  50  for receiving the coupling screw  28  ( FIGS. 2-4 ) associated with the anterior plate  26 . Again, this coupling screw  28  and/or the anterior plate  26  may be used as a locking mechanism to hold any of the anterior screws  24  in place and prevent them from backing out. Finally, the face  44  of the anterior cage  22  may include a groove or recess  52  configured to receive a corresponding protruding structure  54  ( FIG. 8 ) on the back surface of the anterior plate  26 , thereby ensuring proper alignment of the anterior plate  26  with the anterior cage  22  (see  FIG. 9 ). It should further be noted that the body  40  of the anterior cage  22  may have a wedge shape or tapered leading edge to aide in the insertion of the anterior cage  22  into the disc space. 
         [0042]    Referring now specifically to  FIGS. 7-9 , in one exemplary embodiment, the anterior plate  26  consists of a substantially planar structure having curved surfaces that conform to the bony anatomy of the anterior column  10  ( FIG. 1 ) of the lumbar spine, for example. The anterior plate  26  includes one or more apertures  56  for receiving the anterior screws  24  ( FIGS. 2-4 ). These apertures  56  may be disposed at various downwards/upwards angles to properly orient and direct the anterior screws  24  towards the pedicles at the posterior of the spine and may substantially coincide with any number of apertures  46  ( FIGS. 5 and 6 ) of the anterior cage  22  ( FIG. 9 ). Again, in the exemplary embodiment illustrated, only downwards oriented anterior screws  24  are disposed through the anterior cage  22  (with upwards oriented anterior screws  24  disposed only through the coupled anterior plate  26 ). The anterior plate  26  further includes an aperture  58  for receiving the coupling screw  28  ( FIGS. 2-4 ) associated with the anterior cage  22 . Again, this coupling screw  28  and/or the anterior plate  26  may be used as a locking mechanism to hold any of the anterior screws  24  in place and prevent them from backing out. Finally, the back surface of the anterior plate  26  may include a protruding structure  54  ( FIG. 8 ) configured to engage the groove or recess  52  ( FIGS. 5 and 6 ) of the face  44  ( FIGS. 5 and 6 ) of the anterior cage  22 , thereby ensuring proper alignment of the anterior plate  26  with the anterior cage  22  (see  FIG. 9 ). 
         [0043]    Referring now specifically to  FIGS. 10-12 , in one exemplary embodiment, the anterior screw  24  ( FIGS. 10 and 12 ) includes a head portion  60 , a threaded shaft portion  62 , a threaded posterior engagement portion  64 , and a threaded tip portion  66 . The head portion  60  includes a recess  68  for receiving a driver or the like and is optionally externally threaded, such that the head portion  60  lockingly engages the corresponding aperture  56  ( FIGS. 7-9 ) of the anterior plate  26  ( FIGS. 7-9 ), for example. The threaded shaft portion  62  engages the corresponding aperture  46  ( FIGS. 5 and 6 ) of the anterior cage  22  ( FIGS. 5 and 6 ), for example, as well as the corresponding bony vertebral structure. The threaded tip portion  66  passes through the corresponding bony vertebral structure and protrudes from the posterior anatomy. The anterior screw  24  includes a narrowed and/or weakened portion  70  just below the threaded tip portion  66 , such that, in this exemplary embodiment, the threaded tip portion  66  can be removed from the anterior screw  24 , leaving the threaded posterior engagement portion  64  exposed for subsequent coaxial engagement by a corresponding internally threaded chamber  72  of the threaded shaft  74  of the pedicle screw  30  ( FIGS. 11 and 12 ). The pedicle screw  30  also includes a head portion  76  including a recess  78  for receiving a driver or the like.  FIG. 12  shows the coaxially assembled anterior screw  24  and posterior screw  30 . It should be noted that the pitch of the thread of the pedicle screw  30  preferably matches the pitch of the thread of the end portion of the anterior screw  24  (which may be quad-lead, for example), such that the pedicle screw  30  may be smoothly driven into the posterior bony structure and onto the end portion of the anterior screw  24 . 
         [0044]    Referring now specifically to  FIGS. 13-15 , in another exemplary embodiment, the anterior screw  24  ( FIGS. 13 and 15 ) includes a head portion  60 , a threaded shaft portion  62 , a posterior engagement portion  82 , and, optionally, a threaded tip portion (not illustrated). The head portion  60  includes a recess  68  for receiving a driver or the like and is optionally externally threaded, such that the head portion  60  lockingly engages the corresponding aperture  56  ( FIGS. 7-9 ) of the anterior plate  26  ( FIGS. 7-9 ), for example. The threaded shaft portion  62  engages the corresponding aperture  46  ( FIGS. 5 and 6 ) of the anterior cage  22  ( FIGS. 5 and 6 ), for example, as well as the corresponding bony vertebral structure. The threaded tip portion, when used, passes through the corresponding bony vertebral structure and protrudes from the posterior anatomy. Optionally, the anterior screw  24  includes a narrowed and/or weakened portion (not illustrated) just below the threaded tip portion, such that, in this exemplary embodiment, the threaded tip portion can be removed from the anterior screw  24 , leaving the posterior engagement portion  82  exposed for subsequent coaxial engagement by a corresponding headbody assembly  80 . The headbody assembly  80  includes a headbody  84  including an aperture  90 . A spherical structure  86  including a plurality of deflection petals  92  (including one or more concentric internal recesses  93 ) is disposed partially through the aperture  90 , where the plurality of deflection petals  92  engage one or more concentric external rings  94  disposed about the posterior engagement portion  82  of the anterior screw  24 . In general, the deflection petals  92  are segmented and have a degree of flexibility such that they may be deflected outwards to accommodate the one or more concentric external rings  94  disposed about the posterior engagement portion  82  of the anterior screw  24  and then compress inwards about the one or more concentric external rings  94  disposed about the posterior engagement portion  82  of the anterior screw  24 . A saddle structure  88  also including a plurality of deflection petals  96  is disposed concentrically within the headbody  84  adjacent to and partially about the spherical structure  86 . Again, in general, the deflection petals  96  are segmented and have a degree of flexibility such that they may be deflected outwards to accommodate the spherical structure  86 . The saddle structure  88  also includes a recess for receiving the rod construct. When the rod construct is biased into the headbody  84  by the set screw construct, the saddle structure  88  is biased into and compresses the spherical structure  86 , which is based into and compresses the posterior engagement structure  82  of the anterior screw  24 . This locks the polyaxial headbody  84  to the anterior screw  24 , thereby forming a rigid posterior construct. Preferably, the tip of the posterior engagement structure  82  of the anterior screw  24  can be “clipped” as desired by the surgeon, such that a predetermined degree of protrusion is provided. If the screw is exposed and extending out of the pedicle too far, then one can slide down a cylindrical screw cutter in which a pair of holes intersect to cut/shear the screw between the grooves. 
         [0045]      FIG. 16  is a planar view of one exemplary embodiment of an interspinous process distraction device  100  that is coupled to laterally opposed pedicle screws of the three column spinal fixation implant of the present invention, providing slight flexion of the spine at the given level. The interspinous process distraction device  100  includes a horizontal spanning member  101  that extends from pedicle screw to pedicle screw between adjacent spinous processes and a pair of opposed pedicle screw engaging members  103  that are optionally disposed at an angle to the horizontal spanning member  101 . 
         [0046]      FIG. 17  is a planar view of another exemplary embodiment of an interspinous process distraction device  102  that is coupled to vertically opposed pedicle screws of the three column spinal fixation implant of the present invention, again providing slight flexion of the spine at the given level. The interspinous process distraction device  102  includes a curved spanning member  105  and an integrally formed pair of opposed pedicle screw engaging members. 
         [0047]      FIG. 18  is a planar view of one exemplary embodiment of a facet attachment device  104  that is coupled to a pedicle screw of the three column spinal fixation implant of the present invention. This facet attachment device  104  takes the form of a clip structure  107  that both engages the facet and is secured to the pedicle screw via a suitable appendage  109  extending from the clip structure  107 . 
         [0048]    Referring now specifically to  FIGS. 19-24 , in various exemplary embodiments, the surgical procedure of the present invention begins with the removal of the anterior disc and the insertion of a pre-machined trial implant that closely matches the required disc height, after measurement of the depth of the disc space (see  FIG. 19 ). Ultimately, the cage is then inserted and a drill guide is coupled to the cage (see  FIG. 22 ), with holes for the fixation screws drilled into the vertebral body endplates. The disc is removed in a typical fashion, using rongeurs, pituitaries, curettes, and similar instrumentation, well known to those of ordinary skill in the art. Once the disc is removed, a series of (optionally interlocking multi-piece) paddle distractors are used (see  FIGS. 20 and 21 ). The paddle distractors are placed in the disc space with the flat sides adjacent to the vertebral endplates, for example, and are then rotated ninety degrees. This rotation widens the disc space and distracts the vertebral bodies apart. Alternatively, the height at the front and rear of the disc space is measured using separate interlocking paddle pieces. 
         [0049]    Once the disc has been cleared out and the posterior longitudinal ligament has been removed, spanners are optionally inserted on either side of the disc space, acting as guide structures for subsequent insertions (see  FIG. 24 ). These spanners each have a groove running along their lengths from front to back. Various gage blocks of different heights are designed to slide down the spanner grooves. The surgeon selects a certain gage block and slides it down the guides to the posterior portion of the vertebrae and then takes a lateral x-ray to determine if the gage block has created the required height. If enough distraction is not created, the surgeon chooses a taller gage block, etc. Once the posterior portion of the disc space has been properly measured, the anterior portion of the disc space can be gaged and measured in a similar fashion. Once the disc space height requirements have been determined, an appropriately sized drill guide targeting jig can be inserted. The targeting jig is also slid down onto the guides located on the staples. Using x-rays, fluoroscopy, image guidance, or the like, the angulation of the drill holes is determined. Using x-ray markers, an image of the pedicle and the anterior drill is taken. The x-ray should be positioned such that the x-ray pin lines up precisely with the posterior pedicle. The x-ray pin can be rotated in the jig so that the exact trajectory can be determined. Multiple x-rays may need to be taken. Once the drill guide is correctly positioned, it is locked into position (see  FIG. 22 ). This can be done by either screwing the drilling guide to the cage or by some other method. Optionally, a pin is inserted into the drill guide and advanced through the vertebral body and pushed through the posterior pedicle. The pin is left in place temporarily. The same procedure is performed for the remaining drill guides. Once all the pins have been inserted, an anterior-posterior and lateral x-rays can be taken to confirm placement. The pins and jig are then removed, with the staples left in place. The appropriate sized implant is chosen from the initial measurements. The implant is placed on an inserter and placed into the disc space by aligning the two keels on the implant with the grooves on the staples. Once the implant has been inserted to the correct depth based on limits on the staple grooves, the inserter instrument is removed. The screws are then placed through the holes created by the guide pins and/or drilling. Once all of the screws are inserted, they are locked in position and the patient wound is closed. The patient is then flipped 180 degrees face down and exposure is made at the affected levels that were worked anteriorly. The spinous processes are exposed, a tensiometer is applied, and a decision is made to posteriorly apply an interspinous tension band or include tulips on the pedicle screws. If a decision is made to apply tulips to the pedicle screws, the pedicles are exposed and the existing screws are found. If necessary, a reamer may be used to remove bone. The heads are connected to the screws and locked in position. The rods or other connectors are connected to the superior and inferior heads. The affected level may be compressed using a compressor to get the correct spinal alignment. X-rays are taken to confirm the final alignment. If the tensiometer indicates sufficient stiffness, then the pedicles screws can be broken off percutaneously, if necessary, and the site closed. 
         [0050]      FIG. 25  is a perspective view of one exemplary embodiment of the anterior plate  26  of the present invention including an additional screw hole  150  for receiving a lag screw  152  ( FIG. 26 ) for segmental reduction, the lag screw  152  disposed substantially parallel to one of the vertebral endplates of the spine of the patient (in this case the lower vertebral endplate opposite the other screws utilized). 
         [0051]      FIG. 26  is another perspective view of one exemplary embodiment of the anterior plate  26  of the present invention including the additional screw hole  150  for receiving the lag screw  152  for segmental reduction, the lag screw  152  disposed substantially parallel to one of the vertebral endplates of the spine of the patient (in this case the lower vertebral endplate opposite the other screws utilized). 
         [0052]    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 non-limiting claims.