Patent Publication Number: US-7722621-B2

Title: Laparoscopic spinal stabilization surgical method

Description:
This application is a divisional of U.S. patent application Ser. No. 10/627,589, filed Jul. 25, 2003, now U.S. Pat. No. 7,135,026, which is a continuation of U.S. patent application Ser. No. 09/369,614, filed Aug. 6, 1999, now U.S. Pat. No. 6,599,320, which is a continuation of U.S. patent application Ser. No. 08/902,746, filed Jul. 29, 1997, now abandoned, which is a divisional of U.S. patent application Ser. No. 08/752,818, filed Nov. 21, 1996, now U.S. Pat. No. 5,947,971, which is a continuation of U.S. patent application Ser. No. 08/482,025, filed Jun. 7, 1995, now U.S. Pat. No. 5,720,748, which is a divisional of U.S. patent application Ser. No. 08/299,807, filed Sep. 1, 1994, now U.S. Pat. No. 5,489,307, which is a continuation of U.S. patent application Ser. No. 08/015,863, filed Feb. 10, 1993, now abandoned, the disclosures of which are hereby incorporated herein by reference in their entirety. 

   I. BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention pertains to a spinal stabilization surgical procedure. More particularly, this invention pertains to a method for implanting a fusion spinal implant between two vertebrae. 
   2. Description of the Prior Art 
   Chronic back problems cause pain and disability for a large segment of the population. In many cases, the chronic back problems are attributed to relative movement between vertebrae in the spine. 
   Orthopaedic surgery includes procedures to stabilize vertebrae. Common stabilization techniques include fusing the vertebrae together. 
   Fusion techniques include removing disc material which separates the vertebrae and impacting bone into the disc area. The impacted bone fuses with the bone material of the vertebrae to thereby fuse the two vertebrae together. 
   As in any surgical technique, it is desirable in back surgery to provide a procedure which permits rapid post-operative recovery. To this end and to increase the probability of a successful fusion, spinal implants have been developed. An example of such a spinal implant is shown in commonly assigned and co-pending U.S. patent application Ser. No. 07/702,351 filed May 15, 1991 (claiming priority to Jul. 6, 1989). That patent application teaches a threaded spinal implant which includes a hollow cylinder into which bone chips or bone slurry may be placed. The cylinder has holes extending radially therethrough. The bone material grows through the holes to fuse with the bone material of the vertebrae. 
   A threaded spinal implant is also shown in U.S. Pat. No. 5,015,247, dated May 14, 1991. In addition to teaching a threaded spinal implant, U.S. Pat. No. 5,015,247 shows a method of implantation including certain tools to form a bore into which the implant is threaded. 
   A threaded fusion cage and a method of inserting such a cage is also shown in U.S. Pat. No. 4,961,740 to Ray et al. dated Oct. 9, 1990 as well as U.S. Pat. No. 5,026,373 to Ray et al. dated Jun. 25, 1991. The latter patent teaches preparing a bore for the implant by drilling over a pilot rod. In addition to the above, spinal implants are shown in U.S. Pat. No. 4,875,915 to Brantigan dated Nov. 7, 1989, German Patent 3505567A1 dated Jun. 5, 1986 to Vich, U.S. Pat. No. 4,834,757 to Brantigan dated May 30, 1989 and U.S. Pat. No. 4,507,269 to Bagby dated Feb. 27, 1985. The latter is not a threaded implant but uses a cage or basket which is impacted into a bore formed between bone to be fused. 
   When performing back surgery (such as placing implants in a spine) it is desirable that the surgical procedure be performed as quickly and as accurately as possible. Accordingly it is an object of the present invention to provide a surgical procedure for placing an implant in a spine in a procedure which can be done quickly and accurately. 
   In addition to the foregoing, it is known to be desirable to place two implants between opposing vertebrae (although a single implant procedure may be advisable in some circumstances). In a two implant procedure, bores are formed on opposite sides of the vertebrae to receive each of the implants. I have found that in such a procedure, the forming of the bores can cause misalignment of the vertebrae which is undesirable. Also, prior art techniques (e.g., drilling over a guide rod) can result in a bore which does not cut equally into both vertebrae. Accordingly, it is a further object of the present invention to provide a surgical implant procedure which assures accurate alignment of the vertebrae throughout the procedure. 
   Furthermore, it is an object of the present invention to provide a surgical procedure that can be performed posteriorly, anteriorly or as a laparoscopic procedure. 
   II. SUMMARY OF THE INVENTION 
   A surgical method for implanting at least two spinal fusion implants into a disc space of a disc material which separates two vertebrae is disclosed. The surgical method includes the steps of distracting one side of the disc space with a spacer and forming an implant receiving bore in an opposite of the disc space. After implanting the implant into the opposite side, the spacer is removed and a bore receiving implant is formed to receive a second implant. 

   
     III. BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevation view of an implant for use with the method of the present invention; 
       FIG. 2  is the view of the implant of  FIG. 1  with the implant rotated 90° about its axis; 
       FIG. 3  is a view taken along line  3 - 3  of  FIG. 1 ; 
       FIG. 4  is a view taken along lines  4 - 4  of  FIG. 3 ; 
       FIG. 5  is a view taken along lines  5 - 5  of  FIG. 2 ; 
       FIG. 6  is a view taken along lines  6 - 6  of  FIG. 3 ; 
       FIG. 7  is a cross-sectional side view of an end cap for use with the implant of  FIG. 1 ; 
       FIG. 8  is a plan view of the implant of  FIG. 7 ; 
       FIG. 9  is a top plan view of an alignment guide assembly; 
       FIG. 10  is an end plan view of the guide assembly of  FIG. 9 ; 
       FIG. 11  is a side elevation view of a drill tube guide removal handle; 
       FIG. 12  is a side elevation view of a drill tube guide; 
       FIG. 13  is a side elevation view of a drill tube planar according to the present invention; 
       FIG. 13A  is a cross-sectional side view of the planar of  FIG. 13 ; 
       FIG. 14  is a view taken along line  14 - 14  of  FIG. 13 ; 
       FIG. 15  is a side elevation view of a starter vertebral reamer according to the present invention; 
       FIG. 16  is a proximal end view of the reamer of  FIG. 15 ; 
       FIG. 17  is an enlarged side elevation view of a reamer head of the starter reamer of  FIG. 15 ; 
       FIG. 18  is a distal end elevation view of the reamer head of  FIG. 17 ; 
       FIG. 19  is a side elevation view of an end cap inserter according to the present invention; 
       FIG. 20  is a distal end view of the inserter of  FIG. 19 ; 
       FIG. 21  is a side elevation view of a starter alignment guide handle; 
       FIG. 22  is a side elevation view of a drill tube inserter cap; 
       FIG. 23  is a view taken along lines  23 - 23  of  FIG. 22 ; 
       FIG. 24  is a distal end view of the inserter cap of  FIG. 22 ; 
       FIG. 25  is a side elevation view of a distraction plug inserter; 
       FIG. 26  is a side elevation view of a slap hammer; 
       FIG. 27  is a distal end elevation view of the slap hammer of  FIG. 26 ; 
       FIG. 28  is a side elevation view of a distraction plug for use with the present invention; 
       FIG. 29  is a side sectional view of a drill tube sleeve according to the present invention; 
       FIG. 29A  is a side elevation view of a sheath for use with the present invention; 
       FIG. 29B  is a distal end elevation view of the sheath of  FIG. 29A ; 
       FIG. 30  is a distal end elevation view of the drill tube sleeve of  FIG. 29 ; 
       FIG. 31  is a side elevation view of a drill tube for use with the present invention; 
       FIG. 32  is a view taken along line  32 - 32  of  FIG. 31 ; 
       FIG. 33  is an enlarged side elevation view of a distal end of the drill tube of  FIG. 31 ; 
       FIG. 34  is a side elevation view of a final vertebral reamer; 
       FIG. 35  is an elevation view of a proximal end of the final reamer of  FIG. 34 ; 
       FIG. 36  is an enlarged view of a reamer head of the reamer of  FIG. 34 ; 
       FIG. 37  is an end elevation view of a distal end of the reamer head of  FIG. 36 ; 
       FIG. 38  is a side elevation view of a vertebral reamer guide pin; 
       FIG. 39  is a plan end view of the guide pin of  FIG. 38 ; 
       FIG. 40  is a side elevation view of a starter tap; 
       FIG. 41  is a view taken along line  41 - 41  of  FIG. 40 ; 
       FIG. 42  is an enlarged sectional view of thread cutting teeth of the tool of  FIG. 40 ; 
       FIG. 43  is a side elevation view of an implant driver for use with the present invention; 
       FIG. 44  is an end view of a hub on a distal end of the tool if  FIG. 43 ; 
       FIG. 45  is a view taken along line  45 - 45  of  FIG. 43 ; 
       FIG. 45A  is a side elevation view of a shaft of the tool of  FIG. 43  showing an attached collet; 
       FIG. 45B  is a cross sectional view of  FIG. 45A  taken along lines  45 B- 45 B; 
       FIG. 46  is a side elevation exploded view of a vertebral reamer hand driver; 
       FIG. 47  is an end elevation view of the tool of  FIG. 46 ; 
       FIG. 48  is a side elevation view of two vertebrae separated by a disk; 
       FIG. 48A  is a view taken along lines  48 A- 48 A of  FIG. 48 ; 
       FIGS. 49 and 49A  are views similar to  FIGS. 48 ,  48 A showing insertion of a starter alignment guide assembly; 
       FIGS. 50 and 50A  are views similar to  FIGS. 48 and 48A  showing placement of a distraction plug by use of an inserter; 
       FIGS. 51 and 51A  are views showing the distraction plug in place; 
       FIGS. 52 ,  52 A are views similar to the preceding views showing placement of a vertebral reamer guide pin, 
       FIGS. 53 ,  53 A are views similar to the foregoing views showing placement and use of a drill tube planar; 
       FIGS. 54 ,  54 A are views similar to the foregoing views showing placement of a drill tube; 
       FIGS. 55 ,  55 A are views similar to the foregoing showing placement of a drill tube sleeve; 
       FIGS. 56 ,  56 A are views similar to the foregoing showing preboring of an implant bore; 
       FIGS. 57 ,  57 A are views similar to the foregoing views showing a partially formed bore following the preboring of  FIGS. 56 ,  56 A; 
       FIGS. 58 ,  58 A are views similar to the foregoing views showing final boring of an implant bore; 
       FIGS. 59 ,  59 A are views similar to the foregoing showing formation of a completed bore after removal of the final boring tool of  FIGS. 58 ,  58 A; 
       FIGS. 60 ,  60 A are views similar to the foregoing showing tapping of the bore formed in  FIGS. 59 ,  59 A; 
       FIGS. 61 ,  61 A are views similar to the foregoing showing the tapped bore; 
       FIGS. 62 ,  62 A are views similar to the foregoing showing placement of an implant within a threaded bore; 
       FIGS. 63 ,  63 A are views showing completed placement of an implant within the bore; 
       FIG. 64  is a view showing placement of a drill tube using an end cap inserter; and 
       FIG. 64A  is a view showing use of a sheath on a drill tube. 
   

   IV. DESCRIPTION OF THE PREFERRED EMBODIMENT 
   1. Generally 
   Referring now to the several drawing figures in which identical elements are numbered identically throughout, a description of the preferred embodiment will now be provided. For purposes of illustrating a preferred embodiment, a description of the surgical procedure will be given with respect to an implant  10  such as that shown and described in commonly assigned and co-pending U.S. patent application Ser. No. 07/702,351. It will be appreciated that the present surgical procedure can apply to a wide variety of implants including threaded implants such as those shown in the aforementioned U.S. Pat. Nos. 5,015,247 and 4,961,740 as well as non-threaded implants such as shown in U.S. Pat. No. 4,507,269 or other implants. The term “implant” as used herein may also include bone implants (e.g., autograft, allograft or artificial bone). 
   The implant  10  ( FIGS. 1-6 ) is a hollow cylinder  12  having male threads  14  exposed on the exterior cylindrical surface of cylinder  12 . The cylinder includes a forward interior chamber  16  and a rear interior chamber  17  separated by a reinforcing rib  19 , a bone slurry or bone chips may be compacted into chambers  16 , 17  as will be described. 
   A first plurality of holes  18  extend radially through the cylinder wall and communicate with the chambers  16 , 17 . A second (and enlarged) plurality of holes  21  are disposed on diametrically opposed sides of the implant  10 . 
   A rear end  22  of the implant has a slot  24  which communicates with the chamber  17 . The slot  24  allows the bone slurry or bone chips to be impacted into the implant  10 . A slot  25  is defined by rib  19 . The slot  25  is sized to receive the distal end of a tool (as will be more fully described) to place the implant within a bore formed between opposing vertebrae. 
   An endcap  26  ( FIGS. 7 ,  8 ) is provided to snap fit onto the rear end  12  by means of snap tabs  27 . In a preferred embodiment, the endcap  26  is polyethylene or some other radiolucent material to permit post-operative x-ray inspection and determine the adequacy of the fusion after the implant surgery has been performed. 
   2. Tools 
   A. Generally 
   In a preferred embodiment the technique of the present invention will be performed with a prescribed kit of tools. For the purpose of illustrating the preferred embodiment, the tools of the kit will now be described. It will be appreciated that the method of the surgery can be practiced using a wide variety of tools of different size and shapes. 
   Each of the tools of a kit necessary to perform the surgery as described in this application will be separately described. The use of the tools will become apparent with the description of the method of the invention in Section IV.3 of this application. Unless otherwise specified, all tools are formed of stainless steel. 
   Since vertebrae size and disc space size vary from patient-to-patient (and since such sizes vary along the length of the spine of any given patient), several sizes of implants  10  are anticipated. Presently, implants  10  having minor outside diameters (D m ) of 3 mm, 5 mm, 7 mm, 9 mm, 11 mm, 13 mm, 15 mm, 17 mm, 19 mm and 21 mm with lengths (L) of 10 mm, 12 mm, 14 mm, 16 mm, 16 mm, 20 mm, 24 mm, 28 mm, 28 mm and 30 mm, respectively, are anticipated to accommodate various spine locations and sizes. The major outside diameters (D M ) of the implants  10  are 2.5 mm larger than the minor outside diameters D m . 
   Several of the tools to be described (e.g., reaming tool  126 ) are sized for particular sizes of implants. Namely, the reaming tool  121  must form a bore sized to receive the implant. Since ten sizes of implants are anticipated, ten sizes of boring tools  126  are anticipated as will become apparent to one of ordinary skill in the art. 
   B. Starter Alignment Guide Handle 
   The kit of the present invention includes a starter alignment guide handle  28  (see  FIG. 21 ). The handle includes a distal end  30  having an impact flange  31  and an axially extending threaded stud  32 . A proximal end  34  of the handle is knurled to permit a surgeon to firmly grip the handle  28 . 
   C. Starter Alignment Guide Assembly 
   The starter alignment guide assembly  36  ( FIGS. 9 and 10 ) includes a main body  40  having a threaded bore  42  sized to receive the threaded end  32  of handle  28 . Extending from the body  40  are parallel pins  44 ,  46 . The pins are spaced apart by a distance D 1  as will be more fully described. The pins  44 ,  46  have stop surface  45 ,  47 . 
   As mentioned, since human anatomy varies significantly from one patient to another (and since the sizing of vertebrae varies depending on the location within the spine), it is anticipated that the kit will require various sizes of tools. With respect to starter alignment guide assembly  36 , it is anticipated that at least ten tools will be provided having pin spacings D 1  selected to identify a desired spacing of two implants each of diameters of 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21 mm, respectively. However, such a kit will only require one guide handle  28  which can be inserted and attached to each of the starter alignment guide assemblies  36 . 
   The main body  40  is nylon to be X-ray transparent. Also, the body  40  has curved edges  49  with a radius of curvature to match a radius of a corresponding drill tube  92 . For example, for placing two 13 mm (D m ) implants  10 , a drill tube  92  with an inside diameter of 16.0 mm (for a D M  of 15.5) is required (the 0.5 mm difference providing clearance). The edges  49  match the contour of the drill tube  92  and are spaced apart equal to a spacing of the drill tube when operating on either the right or left side. As a result, the back surface  43  of main body  40  may be placed against the spine to outline an area which must be cleared for the procedure. This aids the surgeon in determining the proper laminectomy size or required amount of vessel retraction. 
   D. Distraction Plug Inserter 
   A distraction plug inserter  48  ( FIG. 25 ) is provided and includes a shaft  50  and a handle end  51  which is knurled to provide a secure grip. A distal end  53  has a threaded shaft  52  extending axially therefrom. End  51  has a larger diameter than shaft  50  to provide a surface  49  against which slap hammer  192  ( FIG. 26 ) may strike as will become apparent. 
   E. Distraction Plug 
   A distraction plug  54  ( FIG. 28 ) is provided having a generally cylindrical body  56  with a tapered forward end  58 . The rear end has a reduced diameter portion  55  terminating at a flange  57  having a diameter the same as the body  56 . A threaded bore  62  is formed through the rear end to receive the threaded shaft  52  of the distraction plug inserter  48 . The body  56  is knurled to prevent undesired axial movement of the plug  54  after it is inserted. 
   As will be more fully described, the distraction plug  54  is used to initially distract opposing vertebrae. The amount of desired distraction will vary from patient to patient and from spine location to spine location. Accordingly, it is anticipated that distraction plugs having diameters D 2  ranging from 3 to 14 mm (by one millimeter increments) shall be included within the kit. Each of the distraction plugs fits on the inserter  48  such that only one inserter  48  is required for the kit. 
   F. Vertical Reamer Guide Pin 
   A vertebral reamer guide pin  64  ( FIGS. 38 and 39 ) is provided including a generally cylindrical body  66  having a tapered forward end  68  and a reduced diameter threaded rear end  70 . The tapered forward end  68  has three flats  69  that grind away disc material when the pin  64  is secured to a starter reamer  112  ( FIG. 15 ) as will be described. 
   As with the distraction plug  54 , a wide variety of sizes of guide pins  64  are anticipated to be required in the kit having diameters D 3  ranging from 3 through 14 mm (increasing by one millimeter increments). For reasons that will become apparent, it is desired that all of the guide pins  64  have a threaded stud  70  of identical size. 
   G. Drill Tube Guide 
   A drill tube guide  72  ( FIG. 12 ) is provided including a cylindrical shaft  74  and a distal end  76 . The distal end  76  has a predetermined maximum outside diameter D 4 . Provided on the axial face  78  of distal end is a bore  80  which is threaded and sized to receive stud  70  of the guide pin  64 . A proximal end  82  (of diameter D 4 ) of the drill tube guide has a threaded bore  81  for purposes that will be described. End  82  terminates at a flat axial face  83 . 
   In application, various sizes of implants  10  will be required depending on the anatomical sizing of the vertebrae to be fused. It is anticipated that implants  10  of ten different major outside diameters D M  will be required to accommodate a wide variety of applications. Accordingly, the kit of the present invention will include ten drill tube guides having outside diameters D 4  to finally prepare bores to receive the three sizes of implants as will be described. The outside diameters D 4  are equal to D M  for each matching pair of implant  10  and drill tube guide  72 . 
   H. Drill Tube Planar 
   In some applications, it may be desirable to plane a surface of a vertebrae. For example, tissue may covet the surface of the vertebrae to be bored. The various tools of the present invention should abut vertebrae bone to insure that an implant  10  is inserted to a proper depth. A drill tube planar  84  removes the tissue and provides a flat surface on the vertebrae bone against which to place tools. 
   The drill tube planar  84  ( FIGS. 13 and 14 ) includes a hollow tube  86  having an inside diameter D 5 . The distal end  88  of the drill tube planar  84  includes a toothed rasp surface  85  to rasp away bone material as the distal end  88  is placed against bone and the planar  84  is rotated about its axis. The proximal end  90  of the planar  84  includes a knurled handle to permit a surgeon to securely grasp the planar during the planing operation. 
   As will be more fully described, in the anticipated method of the present invention, the planar  84  will slip over the drill tube guide  72  with the diameter D 4  selected in close tolerance to D 5  (i.e., D 5  is 0.5 mm larger than D 4 ). As a result, ten planars  84  are required to fit on the ten sizes of drill tube guides  72 . 
   The planar  84  includes an internal stop  87  positioned to oppose surface  83  of guide  72  when the planar  84  is placed over guide  72 . A clean out hole  89  is provided to clean out planar  84 . 
   I. Drill Tube 
   A drill tube  92  ( FIGS. 31 ,  32 , and  33 ) is provided in the form of a hollow cylindrical tube  94 . The distal end  96  of the tube  94  is provided axially projecting teeth  98 . The proximal end  99  of the tube  94  is flared outwardly for purposes that will become apparent. As will be apparent, ten sizes of tube  92  are required with inside diameters D 6  to slip in close tolerance over ten sizes of drill tube guide  72  (i.e., D 6  is 0.5 mm larger than D 4 ). 
   The teeth  98  each have a length, T L , of preferably 3 mm. The valleys  97  are flat to provide stop surfaces to hit bone as teeth  98  are forced into vertebrae. This helps prevent the drill tube  92  from being forced too far into bone. 
   J. Drill Tube Inserter Cap 
   As will be more fully described, the drill tube  92  is secured to vertebrae by forcing the teeth  98  into the vertebrae bone material. This is done by impacting the proximal end  99  of the drill tube  92 . An inserter cap  100  ( FIGS. 22 ,  23  and  24 ) is provided in the form of a solid cylinder having an axial bore  102  with an inside diameter D 9  terminating at a flat annular face  101 . Diameter D 9  is slightly larger than outside diameter D 4  of drill tube guide  72  ( FIG. 12 ) so that cap  100  can slip over end  82  of guide  72  with a stop surface  103  opposing end  83  and with surface  101  opposing flared end  99  of drill tube  92 . The cap  100  has an opposite flat end  104  against which a surgeon may impact. This impacts the drill tube  92  to force the teeth  98  into the bone of a vertebrae. 
   K. Drill Tube Sleeve 
   A drill tube sleeve  105  ( FIGS. 29 and 30 ) is provided in the form of a hollow tube having a flat distal end and an outwardly flared proximal end  110 . Ten sizes of sleeves  105  are required in the kit having outside diameters D 7  sized to slip within, in close tolerance, the ten sizes of drill tubes  92 . The inside diameter D 10  is selected to be slightly greater (e.g., 0.5 mm larger) than the minor outside diameter D M  of the implants  10 . 
   L. Starter Vertebral Reamer 
   To start a bore between opposing vertebrae, a starter vertebral reamer  112  is provided ( FIGS. 15 through 18 ). The starter reamer  112  has a shaft  114 . A reamer head  116  is secured to the distal end of the shaft  114 . An axial face of the reamer  116  has a threaded bore  118  sized to receive the threaded shaft  70  of the vertebral reamer guide pin  64 . A proximal end  120  has an outwardly flared hub  122  to act as a positive stop against flare  110  of the drill tube sleeve  106  as will be more fully described. A shaft  124  extends from the distal end. The reamer  116  includes cutting blades  117  that provide both end cutting and side cutting into bone as the starter reamer  112  is rotated about its axis. 
   To accommodate ten sizes of implants, ten sizes of vertebral reamers  112  are included in the kit. The reamers  112  have outside diameters D 11  equal to the minor outside diameters D m  of the implants  10 . 
   M. Final Vertebral Reamer 
   A final vertebral reamer  126  ( FIGS. 34 through 37 ), is provided for completing a bore started by the starter vertebral reamer  112 . The final reamer  126  includes a shaft  128 . A distal end of the shaft is provided with a reamer end  130  having side and end cutting blades  131 . A proximal end of the shaft is provided with an outwardly flared hub  132 . Extending from hub  132  is an axial shaft  134 . For reasons given with respect to starter reamer  112 , ten sizes of final reamers  126  are required with the kit. The outside diameter D 12  of final reamer  126  equals the minor outside diameter D m  of implants  10 . 
   N. Vertebral Reamer Hand Driver 
   To operate reamers  112  and  126 , a hand driver  136  ( FIGS. 46 and 47 ) is provided. The hand driver includes an axial bore  138  to receive either of shafts  124  or  134 . The hand driver  136  also includes a manually engageable handle  140  to be actuated by a surgeon performing the surgery of the present invention. 
   The handle has an enlarged barrel portion  137  with radial grooves  139 . With one hand, a surgeon puts axial pressure on handle  140  and with the other hand the surgeon rotates barrel  137  with fingers in grooves  139 . Thus, the surgeon can securely turn a reamer secured to the drive  136 . 
   Radial bores  141 , 143  extend through barrel  137  to receive set screws to fix a shaft  124  or  134  received within bore  138 . 
   O. Bone Tap 
   In the event a threaded implant is utilized (as is the case in the preferred embodiment of the present invention), the bores for the implant are partially prethreaded. To prethread, a bone tap  142  ( FIGS. 40 through 42 ) is provided, having a shaft  144 . At the distal end of the shaft  144  is a tapping head  146  having tapping threads  148 . Near the proximal end of the shaft  144  is an enlarged diameter portion  156  having an outwardly flared flange  158 . A handle  160  is secured to the enlarged portion  156 . The shaft  144  is also enlarged at portion  162  adjacent tapping head  146 . The enlarged portion  156  is sized with diameter D 8  to be received, in close tolerance, within the drill tube  92  such that the tube  92  will guide the tap  142  as will be more fully described. 
   Since ten sizes of implants  10  are intended to be utilized, ten sizes of bone taps  142  are required. Diameter D 8  is equal to the major outside diameter D M  of implant  10 . The head  146  has a minor outside diameter D 13  (i.e., the diameter without threads  148 ) equal to the minor outside diameter D m  of the implants  10 . 
   P. Implant Driver 
   To place implant  10 , an implant driver  164  ( FIGS. 43 through 45 ) is provided. The driver  164  includes a shaft  166  having a reduced diameter distal portion  166   a . A distal end of the shaft  166  is provided with a hub  168  sized to be received within slot  24  of the implant  10  to urge the implant  10  to rotate as the implant driver  164  is rotated. The implant driver  164  includes a stepped enlarged portion  170  including a first diameter portion  172 , a second diameter portion  174  and a third diameter portion  176  to accommodate the different diameters of drill tubes  92 . A handle  178  is secured to the shaft  164 . Grooves  180 ,  180   a  are formed on the shafts  166 ,  166   a  and extend along their axial lengths. The grooves  180  provide a means for a surgeon to sight the alignment of the implant. 
     FIGS. 45A and 45B  show the implant driver  164  with a collet  171 . The collet  171  has a cylindrical, knurled body  173  slidably carried on shaft  166   a . A pin  175  extending from body  173  into groove  180   a  permits collet  171  to slide on shaft  166  but not rotate. Four prongs  177  extend axially from body  173  toward hub  168 . 
   In use, shaft  166  is passed through end opening  24  of implant  10 . Hub  168  is receiving within slot  25 . The prongs  177  are forced by a surgeon pushing on body  171  for the prongs  177  to be urged between opposing surfaces of the implant  10  and shaft  166   a  to thereby securely capture the implant  10  on driver  164 . As a result, the implant  10  cannot inadvertently fall off. (For ease of illustration, the Figures showing the method of the invention,  FIGS. 48-63A , do not show use of collet  171 ). 
   Q. Endcap Inserter 
   Once an implant is placed between two vertebrae an endcap must be secured to the implant according to the preferred embodiment. To this end, an endcap inserter  180  ( FIGS. 19 and 20 ) is provided. The inserter  180  includes a shaft  182 . At the distal end of the shaft, a head  184  is provided having a cupped surface  186  to receive and temporarily hold an endcap  26  before it is secured in place. An enlarged portion  180  of the shaft is sized to be received, in close tolerance, within drill tube  92  to be guided by the tube  92 . Since ten sizes of drill tubes are required for ten sizes of implants, ten sizes of endcap inserters are also required. The inserter  180  has an outside diameter D 14  just smaller than (e.g., 0.5 mm smaller) than the inside diameter D 6  of the drill tube  92 . A knurled handle  190  is provided on the proximal end of the shaft  182 . 
   R. Slap Hammer 
   To remove the distraction plug  54  or drill tube guide  72 , a slap hammer  192  ( FIGS. 26 and 27 ) is provided. The slap hammer is a cylindrical body having a knurled surface to permit a surgeon to securely grip the body. The hammer has an axial slot  196 . The hammer is placed on the shafts  202 ,  50  of handle  200  or inserter  48 , respectively, with the tool shaft received within slot  196 . By pulling back on hammer  192  and impacting it against a stop surface (e.g., surface  49  of tool  48 ), a tool can be removed. 
   S. Drill Tube Guide Removal Handle 
   A handle  200  ( FIG. 11 ) is provided to remove the drill tube guide  72 . The handle  200  includes a shaft  202 . At the distal end, a threaded stub  204  is provided sized to be threadably received within the threaded bore  84  of the drill tube guide  72 . A proximal end of the handle  200  is provided with an enlarged diameter knurled handle  206  to permit a surgeon to securely grasp the handle  200  and to stop the travel of slap hammer  192 . 
   T. Drill Tube Sheath 
   As will become apparent, drill tube  92  or planar  84  are passed through a patient&#39;s body to an implant site. To avoid risk of teeth  85  or  98  damaging vessels, nerves or organs, a drill tube sheath  300  is provided ( FIGS. 29A ,  29 B). The sheath  300  is a hollow tube with inside diameter D 15  slightly smaller than the outside diameter of drill tubes  92  or planars  84  (accordingly ten sizes of sheath  300  are required). The sheath  300  has an axial slit  301  extending its entire length. The sheath  300  has a blunt distal end  302  and a flared proximal end  304 . 
   The sheath is slipped onto the drill tube  92  or planar  84  with end  302  extending beyond the teeth  85  or  98  (see  FIG. 64A  illustrating use of sheath  300  with drill tube  92 ). As the planar  84  or drill tube  92  are passed to an implant site the blunt end  302  covers the teeth and prevents the unwanted cutting of vessels, nerves or organs. When pressed against vertebrae, the end  302  abuts the vertebrae. With continued advancement of the tube  92  or planar  84  toward the vertebrae, the sheath  300  slides on the planar  84  or tube  92  until teeth  85 , 98  abut the vertebrae. 
   In the method of the invention, sheath  300  remains in place whenever planar  84  or drill tube  92  are used. However, for ease of illustration, sheath  300  is not shown in  FIGS. 46-63A . 
   3. Posterior Technique 
   A. Surgical Approach 
   The present invention will first be described with reference to use in a posterior approach. In a posterior approach, a surgeon seeks access to the spine through the back of the patient. An alternative approach is an anterior approach where the surgeon seeks access to the spine through the abdomen of a patient. The anterior approach can be done through open surgery or through laparoscopic surgery. 
   While a posterior approach will be described in detail, it will be appreciated that the present invention can be used in an anterior approach for both laparoscopic or non-laparoscopic procedures. 
   Once a surgeon has identified two vertebrae which are to be fused together, the surgeon identifies an implant of desired size and the surgeon determines the desired amount of distraction to be required between the vertebrae before placement of the implant. In selecting the implant size, the surgeon should ensure that the device will remain within the lateral borders of the intervertebral disc while also penetrating at least 3 mm into the vertebral bodies cephalad and caudal to the disc. 
   In the posterior technique, a patient is placed on the operating table in either a prone or kneeling-sitting position. At the discretion of the surgeon, the spine is flexed slightly. Anesthesia is administered. 
   Exposure of the intervertebral disc is obtained through any suitable technique well-known in the art. The facet of the vertebrae is removed in as limited amount as possible to permit insertion of the instruments and the implants. Preferably, bone dissected from the lamina, facets and spinous process are preserved for later use as bone graft. 
   Referring to  FIG. 48 , two vertebrae  210 ,  212  are separated by a disc  214 . The disc  214  is shown in plan view in  FIG. 48A . As shown in the figures, no procedure has yet been performed on the disc such that the disc  214  is in a relaxed, undistracted state. 
   B. Identifying Desired Implant Locations 
   After having selected the implant size, the surgeon selects the starter alignment guide assembly  36  and secures the handle  28  to the assembly  36  by threading shaft  32  into bore  42 . The prongs  44 ,  46  of the guide  36  are placed on either side of the cauda equina such that they are at mid-disc height and equidistant from the mid-sagittal plane. The guide is pressed ventrally to make two points  44   a ,  46   a  on the disc for implant insertion as shown in  FIGS. 49 ,  49 A. The two points  44   a ,  46   a  mark right and left side desired implant location points. For the purposes of this discussion, right and left will mean with respect to the view of the back of the spine as viewed by the surgeon performing the surgery through the posterior approach. 
   After the starter alignment guide  36  is urged into position as shown in  FIG. 49 ,  49 A, the handle  28  is unscrewed and removed from the guide  36 . Lateral a anterior-posterior x-rays or C-arm fluoroscopy are taken the alignment guide  36  to verify its orientation within the disc space. If the alignment guide  36  is determined to be correctly positioned, it is removed from the disc space by reattaching handle  28  and pulling the guide  36  out. A limited discectomy is performed through the two openings  44   a ,  46   a  in the disc to permit insertion of a distraction plug  54 . 
   C. Left Side Distraction 
   Once the left and right side desired implant locations are identified by placement of the starter alignment guide  36 , and after the guide  36  is removed, the surgeon selects a side (i.e., left or right) in which to initiate the distraction procedure. Beginning with the left side for purposes of example, the distraction plug inserter  48  is secured to a distraction plug  54  by threading end  52  into bore  62 . The distraction plug  54  is forced into the disc space at the indent  46   a  made at the left side of the vertebrae by the prong  46  (see  FIGS. 50 and 50A ). The size of distraction plug  54  is selected to distract the annulus fibrosus without causing damage to the surrounding vertebral bone, annular fibers or spinal nerves. Accordingly, it is recommended the surgeon initially insert a relatively small plug  54  (for example, 8 mm) followed by successively larger plugs until the annulus is distracted to the surgeon&#39;s satisfaction. Once the correct maximum size distraction plug  54  has been chosen, it is left in place and the handle  48  removed as shown in  FIGS. 51 and 51A . The disc  214  has now been stretched so that a parallel distraction of the opposing end plates  210 ′, 212 ′ of the vertebrae  210 , 212  has occurred on both the left and right sides. The distraction plug  54  is fully inserted such that it is either flush or slightly recessed within the disc space. 
   In performing the procedures of the present method, the surgeon takes care to retract the cauda equina and nerve roots from the area being prepared for the drill tube  92  as will be described. To this end, the distraction plug  54  is placed recessed. As a result, the cauda can be moved over into the region of the distractor plug  54  without the distractor plug  54  damaging the cauda equina. 
   D. Right Side Alignment 
   Once the distraction plug  54  is inserted as shown in  FIGS. 51 ,  51 A, the surgeon proceeds to the right side location  44   a . The vertebral reamer guide pin  64  is secured to the drill tube guide  72  by threading the shaft  70  within the bore  80 . The guide pin  64  selected is preferably the same diameter as the final distraction plug  54  left in place within the disc space on the left side. As a result, upon insertion of the guide pin  64  as shown in  FIGS. 52 ,  52 A, the guide pin  64  abuts the opposing end plates  210 ′, 212 ′ of the vertebrae  210 , 212  as does plug  54 . The axis of pin  64  is equidistant from the end plates  210 ′, 212 ′. 
   E. Planing Vertebral Surface 
   The surface of the vertebrae  210 ,  212  against which tools are to be placed should be smooth with the surface of the two vertebrae  210 ,  212  aligned. Frequently, this condition will not naturally exist. Therefore, the vertebrae  210 ,  212  must be pre-planed to a flat surface. 
   If planing is deemed necessary by the surgeon, the drill tube planar  84  is passed over the drill tube guide  72  with the rasp end  88  abutting the disc material  214  and vertebrae  210 ,  212  or tissue (not shown) on the vertebrae as shown in  FIG. 53 ,  53 A. The interior diameter of the planar  84  is selected to have a close tolerance with the exterior diameter of the drill tube guide  72 . As a result, the planar  84  can rotate on the drill tube guide  72  and move axially relative thereto but cannot move laterally relative to the tube guide  72 . The surgeon rotates the planar  84  to rasp a planed flat surface on the vertebrae. The rasping will provide a smooth surface for placing of the drill tube as will be described. For purposes of illustration, the rasp end  88  is shown deeply received with the vertebrae after rasping. 
   The drill tube guide  72  prevents planar  84  from excessive axially movement. Namely, when planar  84  is fully advanced, surface  87  abuts surface  83  signalling completion of the rasping operation. 
   F. Fixing Right side Alignment 
   After the surface of the vertebrae has been planed smooth, the planar  84  is removed and the appropriately sized drill tube  92  is passed over the drill tube guide  72  (see  FIGS. 54 ,  54 A). The teeth  98  of the drill tube  92  are secured to the posterior vertebral bodies using the drill tube inserter cap  100  to pound the teeth  98  into the vertebral bodies  210 ,  212 . The drill tube guide  72  and the vertebral reamer guide plug  64  are then removed from the drill tube  92  leaving the drill tube  92  in place and with the teeth  98  thereby retaining the vertebral bodies in the distracted state. To remove the guide  72 , handle  18  is attached to guide  72  by threading stud  204  into bore  84 . The surgeon uses the slap hammer  192  to remove the guide and handle assembly. 
     FIG. 64  illustrates use of the cap  100  to advance teeth  98  into the vertebrae  210 , 212 . As shown, the drill tube guide  72  is longer than drill tube  92 . With teeth  98  aligned with end  78 , end  83  protrudes beyond flange  99 . The cap  100  is positioned as shown in  FIG. 22A . The cap is sized for the distance, X, between surfaces  83 , 103  to be about 3 mm when teeth  98  are flush with end  78 . Pounding on surface  104 , teeth  98  are driven in 3 mm until surface  103  stops against surface  83 . The flats  97  of the teeth  98  prevent further advancement of the drill tube  92  into the bone. 
   The drill tube  92  has an inside diameter approximate to the outside diameter of the drill tube guide  72 . Accordingly, the drill tube guide  72  accurately places the drill tube  92  in proper alignment. In this alignment, the tube  92  has its axis equidistant from the end plates  210 ′, 212 ′ of vertebrae  210 , 212 . Since all insertion tools and tubes of the kit have lengths sized off of the drill tube guide  72 , the guide  72  insures that a final desired depth of implant penetration is attained. 
   G. Placement of Drill Tube Sleeve 
   With the drill tube guide  72  and the vertebral reamer guide plug  64  removed from the drill tube  92 , a drill tube sleeve  106  is placed in the drill tube with the top end  110  abutting the top end  99  of the drill tube  98 . As shown in  FIGS. 55 ,  55 A, when the sleeve is fully inserted, its flared end  110  abuts the flared end of the drill tube. 
   H. Pre-Boring of Implant Bore 
   The vertebral reamer guide pin  64  is then threaded on to the starter vertebral reamer  112 . The guide pin  64  used is the same pin  64  previously used on the drill tube guide  72 . The cavity  65  ( FIG. 55 ) left after removal of the pin  64  (described in step G, above) receives the pin  64 /reamer  112  assembly to guide the reamer  112  such that the reamer  112  cuts equal amounts of bone from both vertebrae  210 , 212 . 
   The starter vertebral reamer  112  is inserted into the drill tube sleeve  106  and then a bore is partially reamed until a shoulder  122  on the reamer  112  abuts the drill tube sleeve  106  as shown in  FIGS. 56 ,  56 A. The hand driver  136  ( FIG. 46 ) is used to turn reamer  112 . However, for ease of illustration, the driver  136  is not shown in  FIGS. 56 ,  56 A. The reamer  112  and the drill tube sleeve  106  are then removed from the drill tube  92  (see  FIGS. 57 ,  57 A) exposing a pre-drilled bore  200  with a diameter equal to the minor outside diameter D m  of implant  10 . 
   I. Final Reaming 
   The preparation of the implant bore is then completed by inserting the final vertebral reamer  126  into the drill tube  92  ( FIGS. 58 ,  58 A). The reamer  126  is rotated with driver  136  (not shown in  FIG. 46 ) until the shoulder  132  on the reamer  126  meets the flared end of the drill tube  92  to thereby provide a positive stop. 
   Since bore  200  is pre-drilled, a drill sleeve  106  is not required for final drilling since the bore  200  initially guides final reamer  126 . This provides greater clearance and ease of operation of final reamer  126 . The final reamer  126  is removed leaving a fully drilled implant receiving bore  220  with a diameter equal to the minor outside diameter D m  of implant  10  (see  FIGS. 59 and 59A ). 
   In the foregoing, the reader will note that the lengths of the various drill tubes, drill tube sleeves and reamers are selected such that the flared ends provide accurate depth of reaming between the vertebral bodies. Also, the reader will note that both vertebrae  210 ,  212  are equally drilled. Additionally, the reader will not the pre-boring of step H, above, ensures the final bore  220  is cut parallel to end plates  210 ′, 212 ′ and equally cut into both vertebrae  210 , 212 . 
   J. Bone Tap 
   In the event a threaded implant is used (as is the case in the preferred embodiment), a bone tap  142  is passed through the drill tube  92  and rotated to partially pre-tap the bore  210 . The tap is introduced until the stop  158  on the handle abuts the top of the drill tube  92  as shown in  FIGS. 60 ,  60 A. 
   The tap is then removed to expose a partially tapped, fully bored implant bore  300  with the drill tube  92  remaining in place (see  FIGS. 61 and 61A ). 
   K. Placing Implant 
   The front chamber  16  of the implant  10  is packed with bone graft. The graft may be autograft obtained previously from the iliac crest or some other graft material (e.g., allograft or artificial bone). The implant  10  is attached to the implant driver  164  by placing the hub  188  within the slot  24  and securing the implant with collet  171  (not shown in  FIGS. 62 ,  62 A). The implant  10  is then passed into the drill tube  92  ( FIGS. 62 ,  62 A). The implant  10  is threaded into the bore  300  with implant driver  168  by the surgeon rotating the driver  168  and advancing it into the tube  92  until the driver stop  176  contacts the top of the drill tube  92 . 
   It is desirable that the large holes  211  of the implant are oriented in a superior-inferior direction (i.e., the large holes are facing the vertebrae). This orientation is guaranteed by orienting the slots  180  in the implant driver  168  to be vertical. 
   After the implant  10  is fully in place (recessed into bore  300 ), the implant driver  168  and the drill tube  92  are removed from the right-side hole (see  FIGS. 63 and 63A ). Simply pulling on driver  164  releases the implant  10  from the collet  171 . 
   At this point in the procedure, it is recommended that the surgeon obtain a lateral radiograph or C-arm fluoroscopy to verify the positioning of the implant  10  within the intervertebral space. If proper positioning has been obtained, the back chamber  17  of the implant  10  is packed with bone graft. Alternative to the above, the drill tube  92  may be left in place with the graft inserted to chamber  17  through tube  92 . If removed, tube  92  is re-positioned after chamber  17  is filled. The polyethylene endcap  26  is attached to the end of the implant  10  with the endcap inserter  180  by passing the endcap through the drill tube  92 . 
   At this stage in the procedure, the right side implant is fully inserted. 
   The reader will note in placing the implant  10 , the movement of driver  164  is limited by stop  176 . If a smaller implant  10  is used (and hence a smaller diameter drill tube  92 ), the movement is stopped by surface  174  or  176  (see  FIG. 43 ). 
   L. Left Implant and Closure 
   The surgeon returns to the left side and removes the distraction plug  54  by threading the handle  48  into the distraction plug  54  and pulling it out using slap hammer  192 . If, for any reason, the threaded stud  52  on handle  48  were to break, the reduced diameter portion  55  of plug  54  permits a surgeon to pull on flange  57  to remove plug  54 . 
   The left side is now prepared for receiving an implant in a manner identical to that described above for the right disc space with the procedures identified in  FIGS. 52 through 63A . 
   After the right and left implant are fully inserted, it is recommended that a lateral radiograph be taken of the implants. Assuming proper positioning, bone graft is impacted between and surrounding the implants to better facilitate fusion. The wound is closed. 
   4. Other Surgical Procedures 
   The foregoing procedure illustrates the method of the present invention with respect to a posterior approach. However, the identical procedure can be used with an anterior approach. Also, those skilled in the art will note that the present procedure is readily adaptable to a laparoscopic approach. Through placement of a cannula (not shown) in a laparoscopic approach, all the procedures can be performed through the cannula with the various tubes and sleeves described above passed through the cannula and accurately placed. 
   All of the foregoing tools of the kit of the invention can be passed through a cannula except for alignment guide assembly  36 . Instead of using assembly  36  in a laparoscopic approach, the implant sites can be marked through any other suitable technique or a collapsible alignment guide assembly can be provided to pass through a cannula. 
   In addition to the above, the method and tools of the invention can be used with a single implant (either a threaded implant  10 , a non-threaded implant or a bone or any other implant). In this method, the plug  54  is inserted at a desired site. The plug  54  is then removed and the pin  64  inserted into the same site using the guide  72 . All procedures described above are then used to form an implant receiving bore. 
   From the foregoing detailed description of the present invention, it has been shown how the objects of the invention have been obtained in the preferred manner. However, modifications and equivalents of the disclosed concepts such as those which would occur to one of ordinary skill in the art, are intended to be included within the scope of the present invention.