Abstract:
The present invention relates generally to medical devices and methods for use in spinal surgery. In particular, the disclosed system relates to an intervertebral spinal implant assembly sized and dimensioned for the lumbar spine implantable via an anterior or anterolateral approach. The device includes an implant, bone screws, and instruments for delivering the implant and bone screws.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a non-provisional patent application claiming the benefit of priority from U.S. Provisional Patent Application Ser. No. 61/260,396, filed on Nov. 11, 2009, and U.S. Provisional Patent Application Ser. No. 61/367,862, filed on Jul. 26, 2010, the entire contents of which are hereby expressly incorporated by reference into this disclosure as if set forth in its entirety herein. 
     FIELD 
     The present invention relates generally to spinal surgery and, more particularly, to a device for spinal fusion comprising a spinal fusion implant of non-bone construction to be introduced into any variety of spinal target sites. 
     BACKGROUND 
     Currently there are nearly 500,000 spine lumbar and cervical fusion procedures are performed each year in the United States. One of the causes of back pain and disability results from the rupture or degeneration of one or more intervertebral discs in the spine. Surgical procedures are commonly performed to correct problems with displaced, damaged, or degenerated intervertebral discs due to trauma, disease, or aging. Generally, spinal fusion procedures involve removing some or the all of the diseased or damaged disc, and inserting one or more intervertebral implants into the resulting disc space. Anterior lumbar interbody fusion (ALIF) procedures provide unparalleled access to a desired spinal target site. The ALIF technique involves approaching the spine through the abdomen and exposing the front of the spine, as opposed to the side or the back. Approaching the spine this way generally allows for greater exposure and a more complete excision of the damaged disc. Introducing the intervertebral implant serves to restore the height between adjacent vertebrae (“disc height”), which reduces if not eliminates neural impingement commonly associated with a damaged or diseased disc. 
     SUMMARY 
     In a preferred aspect, the spinal fusion implant includes a body configured for implantation between a superior and inferior vertebra, having a top surface and a bottom surface, an anterior height and a posterior height, and a fusion aperture defined by an anterior wall, a posterior wall, and first and second lateral walls. In some implementations, the anterior height of the body is greater than the posterior height of the body, such that the top surface creates a posterior-to-anterior angle relative to the horizontal axis. The posterior-to-anterior angle may be between 5° and 15°. 
     The body may be constructed of radiolucent, non-bone material. At least one of the top surface and bottom surface may include anti-migration features. The body may also include at least one radiopaque marker. In some implementations, the body may include an engagement groove in the lateral walls dimensioned to receive a gripping element of an inserter. 
     The spinal fusion implant also includes a plurality of fastener apertures extending through the anterior wall at oblique angles relative to a horizontal axis. Each of the fastener apertures is dimensioned to receive a bone fastener for insertion into one of the superior or inferior vertebrae. The bone fasteners have a head, a shank and a collar disposed between the head and shank. The collar of the bone fastener may be at least partially threaded. 
     The fastener apertures have an anterior diameter that is greater than the posterior diameter. The fastener apertures further include an annular groove dimensioned to retain the head of the bone fastener therein. In some implementations, the fastener apertures may further comprise a visualization marker proximal to the annular groove. The fastener apertures may also include a ledge, wherein the ledge has a diameter that is smaller than the head of the bone fastener, such that the ledge is temporarily deformed while the head of the bone fastener is passing said ledge during insertion. 
     Implementations may include one or more of the following features. For example, fastener apertures extending through the anterior wall of the implant body may at angles between 35° and 55° relative to the horizontal axis. Preferably, the fastener apertures extend through the anterior wall of the body at a 45° angle relative to the horizontal axis. 
     The fastener apertures may also extend through the anterior wall at angles oblique to the longitudinal axis. In some implementations, the angles oblique to the longitudinal axis may be convergent. Preferably, the angles are between 5° and 15° relative to the longitudinal axis. More preferably, the fastener apertures extend through the anterior wall at a 12° angle relative to the longitudinal axis. 
     In a preferred embodiment, the spinal fusion implant includes four fastener apertures. Two of the apertures may be dimensioned to receive bone fasteners for insertion into the inferior vertebra, and two of the apertures may be dimensioned to receive bone fasteners for insertion into the superior vertebra. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
         FIG. 1  is a perspective view of a spinal implant, according to one example embodiment; 
         FIG. 2  is a top view of the spinal implant of  FIG. 1 ; 
         FIG. 3  is a side view of the spinal implant of  FIG. 1 ; 
         FIG. 4  is a front view of the spinal implant of  FIG. 1 ; 
         FIG. 5  is a perspective view of a bone screw, according to one example embodiment, for use with the spinal implant of  FIG. 1 ; 
         FIG. 6  is a second perspective view of the bone screw of  FIG. 5 ; 
         FIG. 7  is a top view of the bone screw of  FIG. 5 ; 
         FIG. 8  is a perspective view of the spinal implant assembly including the spinal implant of  FIG. 1  and four of the bone screws of  FIG. 5 ; 
         FIG. 9  is a front view of the spinal implant assembly of  FIG. 8 ; 
         FIG. 10  is a side view of the spinal implant assembly of  FIG. 8 ; 
         FIG. 11  is a partial-cross section view of the spinal implant of  FIG. 8  showing the interaction between the spinal implant of  FIG. 1  and the bone screw of  FIG. 5 ; 
         FIG. 12  is an insertion instrument according to a first embodiment; 
         FIG. 13  is an exploded view of the insertion instrument of  FIG. 12 ; 
         FIG. 14  is an exploded view of the insertion head of the insertion instrument of  FIG. 12 ; 
         FIG. 15  is a perspective, detailed view of the lateral channels of the gripping instrument of  FIG. 12 ; 
         FIG. 16  is a perspective view of the insertion instrument of  FIG. 12  with the gripping arms in an open position; 
         FIG. 17  is a perspective view of the insertion instrument of  FIG. 12  with the gripping arms in an open position; 
         FIG. 18  is an insertion instrument according to a second embodiment; 
         FIG. 19  is an exploded view of the insertion head of the insertion instrument of  FIG. 18 ; 
         FIG. 20  is a side view of the insertion instrument of  FIG. 18 ; 
         FIG. 21  is a detailed, perspective view of the lateral channel of the gripping arm of  FIG. 18 ; 
         FIG. 22  is a cross-sectional side view showing the insertion mechanism of the insertion instrument of  FIG. 18 ; 
         FIG. 23  is an insertion instrument according to a third embodiment; 
         FIG. 24  is a side view of the insertion instrument of  FIG. 23 ; 
         FIG. 25  is a perspective view of the insertion instrument of  FIG. 23  in an open position; 
         FIG. 26  is a partial cross-sectional view of the insertion instrument of  FIG. 23 ; 
         FIG. 27  is a perspective view of the insertion instrument of  FIG. 23  in a closed position; 
         FIG. 28  is a side view of an insertion instrument according to a fourth embodiment; 
         FIG. 29  is a partial cross-section of the insertion instrument of  FIG. 28 ; 
         FIG. 30  is a perspective view of one embodiment of an inserter adapter for use with the insertion instrument of  FIG. 28 ; 
         FIG. 31  is an alternate perspective view of the inserter adapter of  FIG. 30 ; 
         FIG. 32  is a retractable angled awl according to a preferred embodiment; 
         FIG. 33  is a perspective view of the retractable angled awl of  FIG. 32  with the cover removed; 
         FIG. 34  is a cross-sectional view of the retractable angled awl of  FIG. 32 ; 
         FIG. 35  is an angled driver according to a first embodiment; 
         FIG. 36  is a perspective view of the angled driver of  FIG. 35   
         FIG. 37  is a perspective view of the angled driver of  FIG. 35  with a cover attached, according to a second embodiment; 
         FIG. 38  is an angled driver according to a third embodiment; 
         FIG. 39  is a perspective view of the angled driver of  FIG. 38 ; 
         FIG. 40  is a perspective view of the angled driver of  FIG. 38  with a cover attached, according to a fourth embodiment; 
         FIG. 41  is a perspective view of a guided straight driver according to a preferred embodiment; 
         FIG. 42  is an exploded perspective view of the guided straight driver of  FIG. 41 ; 
         FIG. 43  is a straight driver according to a first embodiment; 
         FIG. 44  is a straight driver according to a second embodiment; 
         FIG. 45  is a straight driver according to a third embodiment; and 
         FIG. 46  is a flow chart depicting the steps of implanting the spinal implant of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The spinal fusion implant disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
       FIGS. 1-11  illustrate a spinal fusion implant  110  according to a first broad aspect of the present invention. The spinal fusion implant  110  may be constructed of any suitable non-bone composition having suitable radiolucent characteristics, including but not limited to polymer compositions (e.g. poly-ether-ether-ketone (PEEK) and/or poly-ether-ketone-ketone (PEKK)) or any combination of PEEK and PEKK. The spinal fusion implant  110  includes a top surface  112 , a bottom surface  114 , two lateral sides  116 , an anterior side  118 , and a posterior side  120  (each defined relative to the regions of the target disc space when implanted). According to a preferred method of implantation the spinal fusion implant  110  may be implanted from an anterior approach such that anterior side  118  is the trailing side and posterior side  120  is the leading side during insertion. The anterior side  118  includes a pair of upper screw holes  122  and a pair of lower screw holes  124 , each for receiving a bone screw  126  therethrough. The screw holes are positioned such that there is a lateral upper screw hole  122 , a medial upper screw hole  122 , a lateral lower screw hole  124 , and a medial lower screw hole  124 . 
     According to a preferred embodiment, the spinal fusion implant  110  includes at least one radiopaque marker  129 . In one embodiment, the implant  110  includes one or more pin elements  129  disposed within the posterior side  120  of the implant  110 . The pin element  129  may be manufactured from any of a variety of suitable radiopaque materials, including but not limited to a metal. The one or more pin elements  129  may each comprise a unitary element extending through the top surface  112  and bottom surface  114 . Alternatively, each pin element  129  may comprise a shorter element which only extends through a single surface. Alternatively, each pin element  129  may comprise a shorter element that does not extend beyond either surface. 
     The spinal fusion implant  110  of the present invention may be used to provide temporary or permanent fixation along an orthopedic target site. Once deposited in the intervertebral disc space, the spinal implant  110  effects spinal fusion over time as the natural healing process integrates and binds the implant  110  within the intervertebral space by allowing a bony bridge to form through the implant  110  and between the adjacent vertebral bodies. Top surface  112  and opposed bottom surface  114  are both adapted for contact with the upper and lower vertebra adjacent the disc space. Bone screws  126  may be introduced through the screw holes  122 ,  124  and into the adjacent vertebral bodies to fix the implant  10  in the desired position within the disc space. 
     The top and bottom surfaces  112 ,  114  preferably include anti-migration features situated along at least a portion of their area. Anti-migration features are designed to increase the friction between the spinal fusion implant  110  and the adjacent contacting surfaces of the vertebral bodies so as to further prohibit migration of the spinal fusion implant  110  after placement and during the propagation of natural bony fusion. Such anti-migration features may include ridges (or teeth)  128  provided along at least a portion of the top surface  112  and/or bottom surface  114 . 
     According to an additional embodiment (as depicted in  FIG. 3 ), the top and bottom surfaces  112 ,  114  may be angled between the anterior side  118  and posterior side  120 . In lumbar and cervical applications, the posterior side  10  will preferably be shorter in height than the anterior side  118  such that the implant  10  tapers down from anterior side  118  to posterior side  120 . For example, the posterior-to-anterior angle of the tapered top and bottom surfaces  112 ,  114  may range from 5° and 15° relative to a horizontal axis, and preferably 8° to 12°. In this manner, the implant  110  helps maintain the adjacent vertebral bodies in lordosis, which is the natural curvature found in the lumbar and cervical regions of the spine. The top and bottom surfaces  112 ,  114  may be configured in any number of suitable shapes to better match the natural contours of the vertebral end plates, such as, for example, concave, convex, or a combination of concave and convex. 
     As best viewed in  FIG. 2 , the implant  10  includes a central cavity  130  extending through the top and bottom surfaces  112 ,  114 . The generally D-shaped area of the cavity  130  is provided to maximize the size of the cavity  130  to allow the greatest area for bony through-growth, however cavity  130  may be provided in any number of other suitable shapes, including but not limited to generally circular, oblong, and rectangular. Additionally, multiple cavities may be provided and separated by one or more support walls. 
     Fusion may be facilitated or augmented by introducing or positioning various osteoinductive materials within cavity  130  and/or adjacent to the spinal fusion implant  110 . Such osteoinductive materials may be introduced before, during, or after insertion of the exemplary spinal fusion implant  110 , and may include (but are not necessarily limited to) autologous bone harvested from the patient receiving the spinal fusion implant  110 , bone allograft, bone xenograft, any number of non-bone implants (e.g. ceramic, metallic, polymer), bone morphogenic protein, and bio-resorbable compositions, including but not limited to, any of a variety of poly (D, L-lactice-co-glycolide) based polymers. 
       FIG. 3  illustrates a lateral side  116  according to one example embodiment. Lateral sides  116  each include an engagement groove  132  opening in anterior side  118  and extending distally to a point short of posterior side  120 . At the distal-most portion of the engagement grooves  132 , the groove extends deeper into the lateral side wall  116  forming a gripping indent  134 . As described below, engagement grooves  132  are configured to mate with an array of insertion instruments. 
     As best appreciated in  FIGS. 1 and 4 , the upper screw holes  122  pass through the anterior side  118  at an angle such that when the bone screws  126  are inserted into the upper screw holes  122 , they extend from the implant  110  at an angle and penetrate into the vertebral body inferior to the implant  110 . By way of example only, the upper screw holes  122  may be angled such that the bone screws  126  penetrate into the vertebral body at an angle between 35 and 55 degrees, and preferably 45 degrees. Lower screw holes  124  also pass through the anterior side  118  at an angle, but in the opposite direction of the upper screw holes  122 . Thus, when the bone screw  126  is inserted into the lower screw holes  124 , it extends from the implant  110  at an angle and penetrates the vertebral body superior to the implant  110 . By way of example, the lower screw holes  124  may be angled such that the lower bone screws  126  penetrate into the vertebral body at an angle between 35 and 55 degrees, and preferably 45 degrees. The lateral screw holes  122 ,  124  may also be angled such that the distal end of the bone screws  126  converge towards each other. By way of example, the screw holes may be oriented such that the bone screws are angled medially between 5 and 15 degrees, and preferably 12 degrees. The medial bone screw holes  122 ,  124  may also be angled such that the distal end of the bone screws  126  converge towards each other. By way of example, the bone screw holes may be oriented such that the bone screws are angled medially between 5 and 15 degrees, and preferably 10 degrees. 
     With reference to  FIG. 4 , screw holes  122  and  124  are equipped with a ledge  136 . The ledge  136  acts as a stop for instruments including, but not limited to, the instruments described in  FIGS. 32-34  and  41 - 42 . Particularly, the ledge  136  may act as a stop for the retractable awl cover  298  and driver cover  314 . The covers  298 ,  314  initially fit within the screw holes  122 ,  124  but are restricted from further penetration at the ledge  136 . The retractable awl  280  and the guided straight driver  312  continue to travel and emerge from the cover  298  or  314  within the bone screw holes  122 ,  124 . 
     Past (distal to) the ledge  136 , the screw hole  122  or  124  tapers inward until the diameter is less than diameter of the bone screw rim  150 . The screw head  144  deforms the implant enough to travel past the point at which its diameter is larger than the hole to an annular groove  138  formed about an anterior surface within the screw hole  122  or  124 . The annular groove  138  cooperates with the screw  126  when fully inserted into the screw hole  122 ,  124  to prevent the bone screw  126  from backing out of the screw hole  122 ,  124 . Once the rim  150  enters the groove  138 , it is prevented from moving back out of the annular groove  138 . Beyond (distal to) the annular groove  138 , the hole  122  or  124  continues to taper inward. The degree of taper is such that the threaded neck  146  of the bone screw  126  will bite into the inner wall of the implant once the screw  126  advances enough for the rim  10  to enter the annular groove  138 . This provides tactile feedback to the user that the bone screw  126  is fully seated. 
     As illustrated in  FIG. 4 , the screw holes  122 ,  124  may also be provided with one or more visualization markers (e.g. arrows  140 ) in between the ledge  136  and the annular groove  138 . Arrows  140  provide a visual indication that the screw  126  has been properly positioned beyond the annular groove  138 . For example, the entire arrow is not visible (i.e. it is blocked from view of the user by the screw head  144  until the screw  126  is fully seated within the annular groove  138 ). 
     With reference to  FIGS. 5-7 , there is shown a bone screw  126  for use with the spinal fusion implant  110 . The bone screw  126  has a threaded shaft  142 , a head  144 , and a threaded neck  146  separating the threaded shaft  142  and the head  144 . The head  144  further comprises a tooling recess  148 , for example a hex recess, for engaging a driver (for example, driver  312  shown in  FIG. 41 ) and a rim  150 . The diameter of the rim  150  is slightly larger than the diameter of the interior of the screw hole  122  or  124  adjacent to the annular groove  138 . As the bone screw  126  is driven into the vertebra through screw hole  122  or  124 , the rim  150  slightly deforms the area above the annular groove  138  thereby allowing the bone screw  126  to pass into the annular groove  138 . The area above the annular groove  138  reforms, capturing the head  144  thereby preventing unwanted backout of the bone screw  126 . By way of example only, the diameter of the screw head  144  may be 6.985 mm while the diameter of the screw hole  122  or  124  may be 6.731 mm. As pictured in  FIG. 11 , when the bone screw  126  is fully seated, the visualization arrow  140  below the ledge  136  within the screw hole  122  or  124  will be fully visible. This indicates to the user that the bone screw  126  is fully captured in the annular groove  38 .  FIGS. 8-11  show perspective, anterior, lateral, and cross-sectional views of the spinal fusion implant  110  with the screws  126  fully positioned. 
     As described in  FIGS. 12-31 , the present invention includes a plurality of inserters which provide the user with a suite of choices for implanting the implant  110 . According to a broad aspect of the present invention, the insertion instruments include a handle  178 , a thumbwheel housing  180 , an elongate tubular element  182 , an inserter shaft  184 , and a distal inserter head  186 , as illustrated in  FIGS. 12-13 . 
     The handle  178  is generally disposed at the proximal end of the insertion instrument  152 . The handle  178  may be further equipped with a universal connector  188  to allow the attachment of accessories for ease of handling of the insertion instrument  152  (e.g. a straight handle, or a T-handle, not shown). The handle  178  is fixed to the thumbwheel housing  180  allowing easy handling by the user. By way of example, the thumbwheel housing  180  holds a thumbwheel  190 , a set screw  192 , and at least one spacer  194 . Because the handle  178  is fixed, the user has easy access to the thumbwheel  190  and can stably turn the thumbwheel  190  relative to the thumbwheel housing  180 . Additionally, the relative orientation of the thumbwheel housing  180  to the handle  178  orients the user with respect to the distal insertion head  186 . The inserter shaft  184  is attached to the thumbwheel  190  and is freely rotatable with low friction due to the spacer  194 . The user may then employ the thumbwheel  190  to rotate the inserter shaft  184  thereby advancing it towards distal inserter head  186 . 
     The elongate tubular element  182  is generally cylindrical and of a length sufficient to allow the device to span from the surgical target site to a location sufficiently outside the patient&#39;s body so the handle  178  and thumbwheel housing  180  can be easily accessed by a clinician or a complimentary controlling device. The elongate tubular element  182  is dimensioned to receive a spring  196  and the proximal end of the inserter shaft  184  into the inner bore  198  of the elongate tubular element  182 . 
       FIGS. 12-17  detail an insertion instrument  152  according to a first embodiment of the present invention, preferably adapted for insertion from an anterior approach. The distal inserter head  186  is comprised of a fixed inserter base  202  extending generally perpendicularly from elongate tubular element  182 , an actuating member  204  extending generally perpendicularly from the inserter shaft  184  and two gripping arms  206 . 
     As best viewed in  FIGS. 14-15 , the inserter base  202  contains a central aperture  208 , two guide slots  210 , and two lateral channels  212 , and a central slot  214 . The central aperture  208  on the inserter base  202  is sized and dimensioned to allow slidable passage over the inserter shaft  184 . 
     Actuating member  204  contains two pin-receiving apertures  216 , two lateral channels  218 , and a central protrusion  220 . The pin-receiving apertures  216  are capable of receiving the pivot pins  224  centrally located on the gripping arms  206 . This provides a fixed point for the gripping arm to rotate in relation to the actuating member  204 . Each lateral channel  218  is sized and dimensioned such that the lateral aspect of each gripping arm  206  is seated within the lateral channel  218 . The central protrusion  220  is sized and dimensioned to be slideably received by central slot  214  on the inserter base  202 . As the central protrusion  220  of the actuating member  204  is being advanced by the inserter shaft  184 , it travels along the appropriate path within the central slot  214 . 
     The two gripping arms  206  each contain a laterally-disposed guide post  222 , a medially-disposed pivot pin  224 , and a terminal engagement hook  226 . Gripping arms  206  are seated within the inserter base  202  via the lateral channels  212  and seated within the actuating member  204  via the lateral channels  218 . Gripping arms  206  are attached to the actuating member  204  via the pivot pins  224  received within the pin-receiving apertures  216  on the actuating member  204 . The gripping arms  206  are pivotably disposed within the fixed inserter base  202  via the guide posts  222  positioned within the guide slots  210 . 
     As illustrated in  FIG. 16 , the initial position of the inserter shaft  184  is a fully advanced such that the actuating member  204  is at a distance distal to the inserter base  202  and the guide posts  222  are placed in a first, distal position within the guide slots  210 . The gripping arms  206  may be then be placed adjacent to the engagement grooves  132  of the spinal fusion implant  110 . The rotation of the thumbwheel  190  in the clockwise direction causes the inserter shaft  184  to retreat within the elongate tube member  182 , which will result in pulling the actuating member  204  closer towards the inserter base  202 . This movement will cause the gripping arms  206  to pivot about the pivot pins  224  of the gripping arms  206 . The gripping arms  206  are guided medially and proximally via the guide slots  210  on the inserter base  202  towards the second, proximal position. ( FIG. 17 ) When the inserter shaft  184  is fully retracted within the elongate tubular member  182  and the actuating member  204  has reached a final position with the inserter base  202 , the gripping hooks  226  are releaseably engaged to the engagement grooves  132  of the spinal fusion implant  110  such that the insertion instrument  152  is stabilized relative to the spinal fusion implant  110 . Once the implant  110  has been successfully inserted into the disc space, the thumbwheel  190  direction is reversed, thereby de-coupling the inserter  152  from the implant  110 . 
       FIGS. 18-22  detail an insertion instrument  154  according to a second embodiment of the present invention, preferably adapted for insertion from an antero-lateral approach. The distal insertion head  186  includes a fixed inserter body  228  and a moveable gripping arm  230 . 
     As best viewed in  FIG. 19 , the inserter base  228  extends generally obliquely from the elongate tubular member  182  includes a central aperture  232 , a lateral notch  234 , an guide slot  236  and a fixed gripping arm  238 . The central aperture  232  of the inserter base  228  is sized and dimensioned to be slidably received over the inserter shaft  184  at an offset (preferably 60 degrees offset). 
     The inserter shaft  184  contains a short pin channel  242  adjacent to a recess  240  at its distal end ( FIG. 19 ). The recess  240  is sized and dimensioned to snugly receive the movable gripping arm  230  such that when the short pin channel  242  of the inserter shaft  184  is aligned with the short pin channel  246  of the movable gripping arm  230 , a short pin  250  may be slidably received therethrough, providing a fixed point for the moveable gripping arm  230  to move in relation to the inserter shaft  184 . 
     The two gripping arms  238 ,  240  each contain a terminal gripping hook  248 . Moveable gripping arm  230  is seated within the inserter base  228  via the lateral notch  234 . The moveable gripping arm  230  contains a long pin channel  246  such that when the long pin channel  246  is aligned with the guide slot  236 , a long pin  252  may be slidably received therethrough, providing a fixed point for the moveable gripping arm  230  to move in relation to the inserter body  228 . 
     The initial position of the inserter shaft  184  is fully advanced in a distal direction such that the moveable gripping arm  230  is in the open position (at a maximum offset distance relative to the fixed gripping arm  238 ). In this open position, the long pin  252  linking the inserter body  228  to the moveable gripping arm  230  is in a first, proximal position. The gripping arms  238 ,  240  may then be placed adjacent to the engagement grooves  132  of the spinal fusion implant  110 . The rotation of the thumbwheel  190  in the clockwise direction causes the inserter shaft  184  to retreat within the elongate tube member  182  which will result in pulling the short pin  250  linkage between the inserter shaft  184  and the moveable gripping arm  230  proximally closer within the elongate tube member  812 . The moveable gripping arm  230  is guided medially via the guide slot  236  on the inserter base  228  towards a second, distal position. When the inserter shaft  184  is fully retracted within the elongate tubular member  182 , the terminal gripping hooks  248  are releaseably engaged to the engagement groove  132  of the spinal fusion implant  110  such that the insertion instrument  154  is stabilized relative to the spinal fusion implant  110 . Once the implant  110  has been successfully inserted into the disc space, the thumbwheel direction is reversed, thereby de-coupling the insertion instrument  154  from the implant  110 . 
       FIGS. 23-27  detail an insertion instrument  156  according to a third embodiment of the present invention, preferably adapted for insertion from an antero-medial approach. The distal insertion head  186  includes a top plate  254  and a bottom plate  256  cooperatively linked via a scissor jack  258 . Extending distally from the top plate  254  are two upper engagement plugs  260  sized and dimensioned for insertion within the lower screw holes  124  on the spinal fusion implant  110 . Extending distally from the bottom plate  256  are two lower engagement plugs  262  sized and dimensioned for insertion within the upper screw holes  122  on the spinal fusion implant  110 . 
     The initial position of the position of the inserter shaft  184  is fully extended such that the inserter shaft  184  has placed the scissor jack  258  in a closed position with the top  254  and bottom  256  plates at their closest distance with respect to one another. The attachment plugs  260 ,  262  may then be inserted within their respective screw holes  122 ,  124 . The clockwise rotation of the thumbwheel  190  will cause the inserter shaft  184  to retreat within the elongate tubular element  182 . As this occurs, the scissor-jack  258  is actuated to simultaneously raise the top plate  254  and lower the bottom plate  262  such that they are reversibly secured within their respective screw hole  122 ,  124 . Specifically, the upper attachment plugs  260  coupled to the lower screw holes  124  on the implant  110  move upwards and the lower engagement plugs  262  coupled to the upper screw  222  holes on the implant  210  lower such that the engagement plugs  260  attached to the top plate  254  move away from the engagement plugs  260  that are attached to the bottom plate  256  thereby pinching the implant  110  for stable insertion. Once the implant  110  has been successfully inserted into the disc space, the thumbwheel  190  direction can be reversed, thereby de-coupling the inserter instrument  156  from the implant  110 . 
     According to a fourth embodiment, the distal inserter head  186  may be provided as an adaptor attachment  158  for other implant installation devices (as shown and described in  FIGS. 28-31 ). For example, the insertion instrument may be partially comprised of the implant installation device  276  shown and described in commonly-owned and co-pending U.S. patent application Ser. No. 12/378,685 filed Feb. 17, 2009. (Attachment A) The adaptor attachment  158  is comprised of an anterior side  264 , a posterior side  266 , and a top side  268 . The posterior aspect  266  of the insertion adaptor  158  is threadably connected via the threaded aperture  270  to the threaded member  276  of the insertion instrument  278 . The gripping arms  272  on the anterior side  264  of the adaptor attachment  258  may then be placed adjacent to the engagement grooves  132  of the spinal fusion implant  110  and may be frictionally fit within the engagement members  132 . Once the implant  110  has been successfully inserted into the disc space, light force may be used to de-couple the inserter adaptor  158  and insertion instrument  276  from the implant  110 . 
     The present invention further provides a plurality of awls for forming one or more pilot holes in the superior and inferior vertebral bodies to receive bone screws  126 . According to a broad aspect of one embodiment, a retractable, angled awl instrument  280  is comprised of a handle  178 , an elongate shaft  182 , a depth gauge region  282 , a transition region  284 , and a driver region  288 . ( FIGS. 32-34 ). 
     The handle  178  is generally disposed at the proximal end of the instrument  280 . The handle  178  may be further equipped with a universal connector  188  to allow the attachment of accessories for ease of handling of the instrument  280  (e.g. a straight handle, or a T-handle, not shown). The proximal end of the advancement shaft  288  is outfitted with depth markings  290  and a depth selector  292 . Once the appropriate depth has been selected, the awl tip  296  is limited to how far it will extend past the cover  298  into the bone. The elongate tubular element  182  is generally cylindrical and of a length sufficient to allow the device to span from the surgical target site to a location sufficiently outside the patient&#39;s body so the handle  178  can be easily accessed by a clinician or a complimentary controlling device. The elongate tubular element  182  is dimensioned to receive a spring  196  and the proximal end of the advancement shaft  288  into the inner bore of the elongate tubular element  182 . The driver region  286  is composed of an awl tip  296  and a distal cover  298 . Transition region  284  contains two linkages  294  for hingedly linking the advancement shaft  288  to the awl tip  296 . 
     In use, the desired depth of tapping is selected on the proximal portion of the instrument  280  by moving the depth selector  292  over the depth marker  290  representing the desired depth. Next, the distal end of the instrument  280  is placed within the screw hole  122 ,  124 . The diameter of the cover  298  bottoms out on the ledge  136  of the screw hole  122 ,  124  thereby acting as a guide. After the cover  298  bottoms out, the linkages  294  within the transition region  284  drives the awl tip  296  forward. Thus, the awl tip  296  may be used to form pilot holes in line with the axis of the screw hole  122 ,  124 . 
       FIGS. 35-45  further illustrate a plurality of drivers  300  for use with the present invention thereby providing the user with a host of options for securing the bone screws  126 . According to a broad aspect, the drivers may be comprised of an elongate shaft portion  302  coupled to a distal driving portion  304 . 
     According to one embodiment, the drivers may include an elongate shaft portion  302  hingedly coupled to a distal driving portion  304  via a universal joint  306  that engages the screw  126  at a variety of angles (for example, the drivers shown in  FIGS. 35-40 ). According to a second embodiment, the driver  300  may be further provided with a self-retaining hex  308  such that the screw head  144  may be friction fit on the driver  300  during screw delivery (for example, the drivers  300  shown in  FIGS. 38-40 ). According to a third embodiment, the driver  300  may be provided with a sleeve  310  to prevent wrapping of tissue during use (for example, the drivers  300  shown in  FIGS. 37 and 40 ). Use of the sleeve  310  also allows for the driver  300  to engage the screw  126  at a fixed angle of preferably 60 degrees and further allows for more torque to be applied, should patient anatomy or surgeon preference so require. 
     As shown in  FIGS. 41-42 , a guided straight driver  312  may also be provided. According to a broad aspect of the present invention, the guided straight driver includes a handle  178 , a thumbwheel housing  180 , an elongate tubular element  182 , an inserter shaft  184 , a distal driving portion  304 , and a distal sheath  314 . 
     The handle  178  is generally disposed at the proximal end of the guided straight driver  312 . The handle  178  may be further equipped with a universal connector  188  to allow the attachment of accessories for ease of handling of the insertion instrument  312  (e.g. a straight handle, or a T-handle, not shown). The handle  178  is fixed to the thumbwheel housing  180  allowing easy handling by the user. By way of example, the thumbwheel housing  180  holds a thumbwheel  190 , a set screw  192 , and at least one spacer  194 . Because the handle  178  is fixed, the user has easy access to the thumbwheel  190  and can stably turn the thumbwheel  190  relative to the thumbwheel housing  180 . Additionally, the relative orientation of the thumbwheel housing  180  to the handle  178  orients the user with respect to the distal insertion head  186 . The inserter shaft  184  is attached to the thumbwheel  190  and is freely rotatable with low friction due to the spacer  194 . The user may then employ the thumbwheel  190  to rotate the inserter shaft  184  thereby advancing it towards distal end of the sheath  314 . 
     The elongate tubular element  182  is generally cylindrical and of a length sufficient to allow the device to span from the surgical target site to a location sufficiently outside the patient&#39;s body so the handle  178  and thumbwheel housing  180  can be easily accessed by a clinician or a complimentary controlling device. The elongate tubular element  182  is dimensioned to receive a spring  196  and the proximal end of the inserter shaft  184  into the inner bore of the elongate tubular element  182 . 
     The distal end of the guided straight driver  312  is placed within the screwhole  122 ,  124 , the diameter of the sheath  314  bottoms out on the ledge  136  of the screw hole  122 ,  124  thereby acting as a guide. The initial position of the inserter shaft  184  is fully retracted such that the screw  126  is at a distance proximal to the distal end of the sheath  298 . The rotation of the thumbwheel  190  in the clockwise direction causes the inserter shaft  84  to advance within the sheath  314  and drives the screw  126  into the bone. 
     As shown in  FIGS. 43-45 , a straight driver  316  may be provided. Further, the driving portion of the straight driver may be outfitted with a self-retaining hex  318  ( FIG. 44 ) or with a ball end  320  to engage the screw  126  at a variety of angles up to 10 degrees ( FIG. 45 ). 
     As highlighted in the flowchart in  FIG. 46 , a standard anterior approach to the spine is performed per surgeon preference at step  322 . At step  324 , an annulotomy template is placed onto the disc space and a centering pin is placed, penetrating the annulus at the midline. The centering pin may have a length of between 10 and 25 mm, preferably 20 mm. Anterior-posterior fluoroscopy may be used to verify midline placement of the centering pin. Additionally, lateral fluoroscopy may be used to check depth. At step  326 , a surgical knife is used to cut the annulus, using the lateral edges of the annulotomy template as a guide. Additionally, if the spinal fusion implant is to be further used as a partial vertebral body replacement, the necessary resections may also be made to the vertebral body or bodies. At step  328 , a desired trial may be implanted into the annulotomy cut and gently impacted into the disc space such that it is subflush, preferably approximately 2 mm from the anterior lip of the vertebral body. At step  330 , the implant corresponding to the appropriate trial side should be selected and attached to the proper size implant inserter (as described above), and filled with an appropriate graft material. The implant is gently impacted into the disc space. Lateral fluoroscopy may be used to confirm proper implant placement. At step  332 , the pilot hole is prepared. By way of example only, retractable awl  280  may be used. At step  334 , the screw is placed. Steps  332  and  334  may be repeated for each additional screw.