Abstract:
An apparatus and method are provided that allow for the realignment and stabilization of adjacent vertebrae. An implant of this invention both repositions adjacent vertebrae and remains in situ to maintain a new position. The implant has an upper half and a lower half, which are interlocked such that they can slide horizontally with respect to each other. Movement of the implant halves and their respective positions are controlled by a reduction bar and reduction rod in combination with an internal locking block within the implant. The reduction rod, being connected to a lower half and placed adjacent to the upper half, is rotated to bring the implant halves into alignment. The internal locking block engages to permanently hold the alignment and maintain the new position. A release mechanism for the internal locking block allows for readjustment of the implant halves and realignment of the vertebrae.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional Application claiming priority benefit from U.S. patent application Ser. No. 12/459,221 filed Jun. 29, 2009, now U.S. Pat. No. 8,216,313, which is a Continuation-In-Part of U.S. patent application Ser. No. 11/821,717, now U.S. Pat. No. 7,744,649, filed on Jun. 25, 2007. 
    
    
     FIELD OF INVENTION 
     The present invention relates generally to the correction of spondylolisthesis and other spinal column injuries or deformities in the fields of neurosurgery and orthopedics. More specifically, the invention is used for the stabilization of repositioned vertebral bodies. 
     BACKGROUND OF THE INVENTION 
     Spondylolisthesis is a medical condition in which one vertebra slips forward in relation to an adjacent vertebra usually in the lumbar region of the spine. This condition can cause symptoms that include pain in the low back, thighs, and/or legs, muscle spasms, weakness, and/or tight hamstring muscles while in some cases only radiographic imaging reveals the condition. 
     To correct this condition and other similar conditions of vertebral dislocation, the only effective long-term curative treatment is reconstructive surgery and fusion of the affected vertebra to its adjacent neighbor. Vertebral fusion is generally accomplished by fixing apparatus to and between vertebrae. In addition to the stabilization and correction of spondylolisthesis, other spinal conditions may be: stabilization of fractures, correction of spinal deformities (e.g. scoliosis, kyphosis), stabilization and correction of degenerative spinal lesions and narrow spinal canal, reconstruction after tumor resection, and secondary spinal surgery. 
     The novel method and implant discussed herein allows for the correction of spondylolisthesis by movement of the vertebrae into better alignment while maintaining stabilization of the vertebrae in the new position in order for the spinal fusion to be completed by ossification. Specifically, the implant is used to move the vertebrae into a post-surgical position and keep the vertebrae in the post-surgical position during the ossification process. 
     Roggenbuck in U.S. Pat. No. 6,491,695 discloses the use of an apparatus and method for aligning vertebrae which involves creating a helical threaded surface in endcaps of the vertebrae and then threading a positioning device into position to align the vertebrae. Once the vertebrae are positioned, the positioning device is removed and an implant is inserted to maintain the vertebrae in position. 
     Ray in U.S. Pat. No. 6,582,431 discloses the use of an expandable non-threaded spinal fusion device which requires the vertebrae to be moved into correct position before the device can be inserted and implanted. 
     Betz in U.S. Pat. No. 6,533,791 discloses a device for stabilization of the lumbar spinal column which requires cutting helical thread marks into the vertebrae that are to be repositioned and then installing an implant to maintain the position. The repositioning device does not stay in the body after the surgery but instead an implant must be inserted to maintain the repositioning. 
     Therefore, there is a need in the art to combine an implant with a repositioning device in order to reduce the possible repositioning of the vertebrae. There is a further need in the art to provide for adjustment of the vertebrae after an implant has been installed. 
     SUMMARY OF INVENTION 
     Disclosed is an apparatus and method for aligning vertebrae due to slippage of the vertebrae relative to each other. To this end, a method and apparatus is disclosed for placing a novel implant between two vertebrae which will move the vertebrae into proper alignment and maintain that alignment until ossification can occur. The implant disclosed is left in situ once the vertebrae have been repositioned. The implant disclosed also provides support for the effected vertebrae superior to that of previous methods known in the prior art. The implant also allows for fine adjustments and post implantation adjustments of the vertebrae superior to that of the prior art. 
     The disclosed method includes approaching the vertebra anteriorly and removing a portion of vertebral disk between the misaligned vertebrae. Known interbody spacers are then inserted between the vertebrae until the proper restorative height is achieved. The spacers are removed and a distractor is placed between the vertebrae in order to guide the subsequent placement of the implant. A novel gate is inserted over a novel distractor to properly guide a novel saw mechanism to cut into the vertebrae at precise locations and allow for the insertion of a novel implant. Different gates are provided depending on the necessary restorative height to be achieved and amount of slip between the vertebrae. 
     The disclosed implant has two halves which include a dovetail groove system which locks the two halves together but allows them to slide with respect to each other along their longitudinal axis. The implant has radial anchors which extend from each half and which fit into slots in the vertebrae cut by the saw. The implant includes a drive bolt which engages the two halves and which, when turned, slides one half of the implant in relation to the other. The advancing halves of the implant carry the radial anchors with them that align the vertebrae. Depending on the amount of slip between the vertebrae and the necessary restorative height, different sized implants and associated tools may be used. 
     The implant is inserted through a distractor by use of an inserter. The halves of the implant are aligned so that the radial anchors correspond to slots made in the misaligned vertebrae. The implant is rotated into place by the inserter such that the radial anchors fit securely in the slots previously made by the saw in the vertebrae. The distractor is then removed. 
     In the case of anterior listhesis of the superior vertebra, the drive bolt of the implant is then rotated so that the upper half of the implant is advanced posteriorly. The superior vertebra is pulled posteriorly with respect to the inferior vertebra by the movement of the upper half of the implant with respect to the lower half. 
     In an alternative embodiment, the implant body is rectangular and contains a locking block, a spring and internal chambers to lock the aligned implant in place. 
     The position of the implant is locked into place by use of an articulating combination of a nut and a plate, thereby maintaining alignment of the vertebrae. The nut and plate can be removed, allowing for post-surgical adjustment of the implant. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosed inventions will be described with reference to the accompanying drawings, which show important sample embodiments of the invention and which are incorporated in the specification hereof by reference, wherein: 
         FIG. 1  is a side view of a section of human spine characterized by a spondylolisthesis condition. 
         FIG. 2  is an isometric view of a distractor of a preferred embodiment of the invention. 
         FIG. 3   a  is an isometric view of an impactor of a preferred embodiment of the invention. 
         FIG. 3   b  is an isometric view of an impactor in conjunction with a distractor of a preferred embodiment of the invention. 
         FIG. 4  is a side view of a section of a human spine with the distractor in place between vertebrae. 
         FIG. 5   a  is a partial isometric view of a gate of a preferred embodiment of the invention. 
         FIG. 5   b  is a plan view of a gate of a preferred embodiment of the invention. 
         FIG. 5   c  is an elevated view of a gate of a preferred embodiment of the invention. 
         FIG. 6  is an exploded isometric view of a saw of a preferred embodiment of the invention. 
         FIG. 7   a  is a partial plan view of the relational section of the saw of a preferred embodiment of the invention. 
         FIG. 7   b  is a partial isometric view of the spindle shaft of a preferred embodiment of the invention. 
         FIG. 7   c  is a partial side view of the spindle shaft of a preferred embodiment of the invention. 
         FIG. 8   a  is an end view of the saw with the saw blade in a lowered position of a preferred embodiment of the invention. 
         FIG. 8   b  is an end view of the saw with the saw blade in a raised position of a preferred embodiment of the invention. 
         FIG. 9  is a cut away side view of section of a human spine with the distractor, gate, and saw in place between the vertebrae. 
         FIG. 10  is an exploded isometric view of the implant of a preferred embodiment of the invention. 
         FIG. 11  is an isometric view of the implant of a preferred embodiment of the invention. 
         FIG. 12  is an isometric view of the implant in an extended position of a preferred embodiment of the invention. 
         FIG. 13   a  is an end view of the inserter of a preferred embodiment of the invention. 
         FIG. 13   b  is an isometric view of the inserter of a preferred embodiment of the invention. 
         FIG. 14  is a partial isometric view of the inserter and the implant of a preferred embodiment of the invention prior to attachment. 
         FIG. 15  is an isometric view of a guide block of a preferred embodiment of the invention. 
         FIG. 16  is a cut away side view of a section of a human spine and an implant during positioning by an inserter of a preferred embodiment of the invention. 
         FIG. 17  is a cut away side view of a section of a human spine and an implant in place prior to the alignment of the vertebrae. 
         FIG. 18  is an isometric view of a nut of a preferred embodiment of the invention. 
         FIG. 19   a  is an isometric view of a plate of a preferred embodiment of the invention. 
         FIG. 19   b  is a cut away side of a plate of a preferred embodiment of the invention. 
         FIG. 20  is a cut away side view of a section of a human spine with an implant in a retracted position and a nut and a bolt in place. 
         FIG. 21  is a cut away side view of a saw in an alternate saw embodiment. 
         FIG. 22   a  is a cut away side view of the end of saw in an alternate embodiment of the invention. 
         FIG. 22   b  is an end view of the end of an alternate saw embodiment. 
         FIG. 23   a  is a top view of the top of the chuck of an alternate saw embodiment. 
         FIG. 23   b  is a partial cut away side view of the chuck of an alternate saw embodiment. 
         FIG. 24   a  is a side view of an implant in another embodiment of the invention. 
         FIG. 24   b  is an end view of an implant in another embodiment of the invention. 
         FIG. 25  is an isometric view of an impactor in conjunction with a distractor of another embodiment of the invention. 
         FIG. 26  is an exploded isometric view of the implant of another preferred embodiment of the invention. 
         FIG. 27  is a cut away view of the implant of another preferred embodiment of the invention. 
         FIG. 28   a  is an isometric view of a reduction bar of a preferred embodiment of the invention. 
         FIG. 28   b  is an elevated view of a reduction rod of a preferred embodiment of the invention. 
         FIG. 28   c  is an elevated view of a thrumbscrew of a preferred embodiment of the invention. 
         FIG. 28   d  is an isometric view of a reduction wheel of a preferred embodiment of the invention. 
         FIG. 29   a  is an elevated view of a spacer of a preferred embodiment of the invention. 
         FIG. 29   b  is an elevated view of a spacer of a preferred embodiment of the invention. 
         FIG. 30  is an isometric view of a bolt of a preferred embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is an illustration of a lumbar spine in a patient who has contracted spondylolisthesis. The vertebrae  10  are separated by vertebral disk  50 . As a result of advanced spondylolisthesis, superior vertebra  20  slips forward in relation to the next inferior vertebra  40  and causes distended disk  70 . To repair slippage of the vertebrae, superior vertebra  20  and inferior vertebra  40  are realigned and fused together. To accomplish this, a portion of distended disk  70  is removed and replaced with an implant which maintains realignment and supports the spine until ossification occurs whereby superior vertebra  20  and inferior vertebra  40  are permanently fused. 
     In order to assure proper alignment, a magnetic resonance image (“MRI”) or plain lateral radiographs are used to observe the supine position to measure the severity of the spondylolisthesis condition prior to surgery. The restorative height of the interbody space after partial removal of distended disk  70  and the necessary amount of re-alignment can be estimated by review of the MRI or plain lateral radiographs. The implant size can be determined by the estimates. 
     The present invention uses the anterior surgical approach to the lumbar spine in order to reach the vertebrae that will receive the implant. The anterior surgical approach to the lumbar spine is understood in the art and is not discussed in detail here. 
     Referring still to  FIG. 1 , once the lumbar spine is exposed to the surgeon, superior vertebra  20 , inferior vertebra  40 , and distended disk  70  are located and identified. A standard marking pin known in the art is inserted into distended disk  70  at the putative midline and left in place. 
     The implant should be optimally placed at the midline in the sagittal plane. Lateral radiographs or x-rays are utilized to confirm the appropriate surgical level and anterior-posterior x-ray imaging demonstrates the midline relative to the marking pin. Once confirmed, the midline of distended disk  70  is marked on distended disk  70  by use of generally accepted marking means. The marking pin is then removed. 
     Portion of distended disk  70  is removed. Boundaries of generous rectangular annulatomy are created in distended disk  70  by use of scalpel. The size of the annulatomy will depend upon the size of the implant and allows additional space on either side of implant to allow interbody arthodesis on both sides of implant after implant is deployed. The width of annulatomy will be in the range of between about 2 cm and about 5 cm. Portion of distended disk  70  within the boundary of annulatomy is removed by use of rongeurs and curettes. 
     Vertebral endplate preparation is performed in standard fashion as known in the art while maintaining cortical endplate integrity centrally. Anterior osteophytes may also be removed from the ventral aspect of the vertebral bodies during this stage of the surgery. 
     In order to gain the appropriate restorative height between superior vertebra  20  and inferior vertebra  40 , sequentially larger interbody spreaders are impacted into the rectangular annulatomy in distended disk  70  until optimal height restoration is achieved. Interbody spreaders are known in the art. When optimal height restoration is achieved, interbody spreaders are removed and appropriate height distractor  110  is inserted. 
       FIG. 2  illustrates one embodiment of distractor  110 . Distractor  110  is made of titanium, stainless steel, or other commercially available material which is easily sterilized. Rigid plastics can be used such as polyvinyl chloride (PVC) in disposable embodiments. Distractor  110  is rectangular in cross-section and includes hollow distractor channel  115 . Distractor channel  115  is rectangular in cross-section and runs the length of distractor  110 . The dimensions of distractor  110  vary depending on the optimal height restoration to be achieved, but height of distractor  110  should generally range between about 0.5 cm and about 1.5 cm and the width of distractor  110  should range between about 2 cm and about 5 cm. The length of distractor  110  is between about 30 cm and about 60 cm. The thickness of walls of distractor  110  should range between about 1 mm and about 5 mm depending on the material of construction to achieve a rigid structure. The dimensions of distractor channel  115  should range between about 0.4 cm and about 1.4 cm high, about 1.9 cm and about 4.9 cm wide. 
     Posterior end of distractor  110  contains distractor arm  117  and distractor arm  118 . Distractor arm  117  extends longitudinally from side  80  of distractor  110 . Distractor arm  117  includes distractor point guide  246  having angled surfaces  253  and  254 . Opposing angled surfaces  253  and  254  is distractor stop  119 . Distractor arm  118  extends longitudinally from the side  81  of distractor  110  and includes distractor point guide  256  having rounded surfaces  258  and  255 . Opposing rounded surfaces  258  and  255  is distractor stop  122 . The height of distractor arm  117  and distractor arm  118  are approximately the same as the height of distractor  110 . The width of distractor arm  117  and distractor arm  118  are between about 0.5 mm and about 1 mm. The width of the distractor arms should provide rigidity with respect to the body of the distractor. Distractor arm  118  and distractor arm  117  form implant hollow  130 . End gap  120  is formed at the forward end of implant hollow  130 . The preferred design of end gap  120  is between about 1.7 cm and about 4.7 cm. Distractor stop  122  and distractor stop  119  are between about 0.5 mm and about 2 mm in length. 
     Torque handle  235  is rigidly mounted to distractor body  99 . Torque handle  235  is generally in the range of about 2 cm to about 5 cm in length with a diameter in the range of about 0.5 cm to about 2 cm. The preferred location of torque handle  235  is approximately between ¼ to ½ from the anterior end  111  of distractor  110 . A set of distractor graticules  135  are etched at 1 mm intervals on the side of distractor  110  along the outside of distractor arm  118  and distractor arm  117 . 
     In the preferred embodiment, the cross-sectional height and width of distractor  110  may vary. In its preferred use, a set of variable height distractors is provided so that the distractor height which matches the vertical distance between the vertebrae may be used during surgery. The preferred set of heights preferably varies in one millimeter increments between about 5 mm and about 2 cm. 
       FIG. 3   a  illustrates the preferred embodiment of impactor  140 . Impactor  140  includes impactor handle  170  which is cylindrical with a diameter in the range of about 0.3 cm and about 2 cm. The length of impactor handle  170  ranges between about 5 cm and about 25 cm. In one embodiment, impactor handle  170  is etched with impactor centerline  165  across its diameter. Impactor centerline  165  is parallel to the long cross-sectional axis of impactor body  160 . 
     Impactor body  160  is formed integrally with impactor handle  170 . Impactor body  160  is rectangular in cross-section and sized to fit within distractor channel  115  without excessive play. In the preferred embodiment, the impactor body is sized to allow for approximately 0.3 mm play between the exterior of the impactor body and the distractor channel. 
     Angled section  141  extends from impactor handle  170  to impactor body  160  at an angle between about 25 and about 65 degrees. Angled section  141  serves to center the impactor handle with respect to the impactor body and distribute impact loads from the impactor handle to the impactor body as will be further described. The preferred length of impactor body  160  should range between about 30 cm and about 45 cm. The posterior end of impactor body  160  includes impactor seat  150  integrally formed with impactor body  160 . Impactor seat  150  is sized and shaped to fit within end gap  120  shown in  FIG. 2 . Impactor seat  150  has rounded surface  155 . On either side of impactor seat  150  are stop surface  152  and stop surface  153 . Impactor  140  is preferably made from titanium, stainless steel, or other materials which are readily sterilized or from a rigid plastic such as PVC which may be disposed of after use. 
     Other cross-sectional shapes of the impactor and distractor are also acceptable, such as elliptical, as long as the impactor fits inside the distractor channel such that it can move longitudinally in distractor channel  115  without rotation and without significant “play” or angular displacement. 
     In use, impactor  140  is placed inside distractor channel  115 , such that impactor seat  150  fits into end gap  120  as shown in  FIG. 3   b . Impactor centerline  165  is aligned with the anatomical midline marked previously. Distractor  110  and impactor  140  are aligned with the anatomical midline and inserted into the rectangular annulatomy in distended disk  70 . A mallet is used to tap impactor  140  and distractor  110  into the midline sagittal plane under fluoroscopic guidance until posterior edge of distractor  110  reaches the dorsal epiphyseal ring on the ventrally superior vertebra  20 . Impactor  140  is then withdrawn from distractor channel  115  and distractor  110  is left in situ. 
     In the preferred embodiment, impactor  140  is also provided in a set of variable sizes to match the set of variable sizes of distractor  110 , as previously described. 
       FIG. 4  shows distractor  110  in situ between superior vertebra  20  and inferior vertebra  40 . Distractor  110  is between superior vertebra  20  and inferior vertebra  40 . Once in position, distractor graticules  135  are used to gauge the amount of slip existing between superior vertebra  20  and inferior vertebra  40 . 
       FIGS. 5   a ,  5   b  and  5   c  illustrate an embodiment of gate  180 . Gate  180  has a gate body  223  bordered by side wall  271 , bottom side  269 , side wall  284  and top side  268 . The gate body also includes saw end  249  and distractor end  251 . In the preferred embodiment, gate  180  has a length of between about 5 cm and about 10 cm, a width of between about 2.2 cm and 5.8 cm and a height of between about 0.7 cm and about 2.9 cm. 
     Gate  180  is provided with saw guide  220  and saw guide  230 . Saw guides  220  and  230  are a pair of slots which are situated approximately the center of top side  268  to the center of side wall  284 , encompassing approximately ¼ of the perimeter of gate body  223 . The pair of saw guides are in parallel planes. Saw guide  220  and saw guide  230  terminate in handle guide  257 . Handle guide  257  forms a slot generally in the center of side wall  284 . Handle guide  257  is provided with handle stop  252 . The width of saw guides  220  and  230  and handle guide  257  in the preferred embodiment is between about 0.5 cm and 1.5 cm. 
     Gate body  223  is also provided with saw guide  200  and saw guide  210 . Saw guides  200  and  210  are a matched pair of slots which are situated approximately the center of bottom side  269  to the center of side wall  271 , encompassing approximately ¼ of the perimeter of gate body  223 . The pair of saw guides are in parallel planes. Saw guide  200  and saw guide  210  terminate in handle guide  240 . Handle guide  240  forms a slot generally in the center of side wall  271 . Handle guide  240  is provided with handle stop  242 . The width of saw guide  200 , saw guide  210  and handle guide  240  in preferred embodiment is between about 0.5 cm and about 1.5 cm. 
     Saw guide  220 , saw guide  230  and handle guide  257  are ductedly connected. Saw guide  220  and saw guide  230  are on centers of between about 0.5 cm to 3.5 cm in the preferred embodiment. Further, saw guide  220  is approximately 0.9 cm from saw end  249 . 
     Saw guide  210 , saw guide  200  and handle guide  240  are ductedly connected. Saw guide  210  and saw guide  200  are on centers of between about 0.5 cm to 3.5 cm in the preferred embodiment. Further, saw guide  210  is approximately 1.9 cm from saw end  249 . 
     Gate body  223  is further provided with interior channel  195  which is longitudinally centered within gate body  223 . Interior channel  195  includes saw entrance  247 . Saw entrance  247  in the preferred embodiment has dimensions slightly larger than guide body  310  which will be described in more detail with respect to  FIG. 6 . The diameter of saw entrance  247  is maintained by interior channel  195  from saw entrance  247  until gate lip  185 . At gate lip  185 , interior channel  195  increases in height and width to accommodate the exterior of distractor  110 . The dimensions of interior channel  195  remain constant from gate lip  185  to distractor end  251  terminating in distractor entrance  248 . 
     In one embodiment, gate  180  can also include raised indicator arrow  245  or other visual aid or tactile indicator to indicate which end of gate  180  is to be inserted over distractor  110 . 
     In the preferred embodiment, many gates are provided in a kit during surgery. The gates each have saw guides that are spaced apart at different lengths with respect to the top and the bottom of each gate. The different spacings correspond to different distances that the vertebrae have slipped. In one preferred embodiment, in the less severe cases, saw guides  230  and  220  will be offset from saw guides  200  and  210  by about 1 mm. The offset between saw guides  230  and  220  and saw guides  200  and  210  will increase by 2 mm increments. In more severe cases, the amount of slip will be more pronounced and the offset can be approximately 20 mm. Position of saw guides  200  and  210  on gate  180  will stay constant. The gates also vary in height to match the variable height of the distractor. 
     Referring now to  FIGS. 6 and 7   a , an embodiment of saw  250  can be seen. Saw  250  includes saw handle  260  to conical section  262 . Conical section  262  is connected to handle post  265 . Handle post  265  integrally supports saw guide post  270 . Saw guide post  270  is perpendicular to the longitudinal axis of saw  250 . Handle post  265  includes abutment surface  272  narrows to the diameter of spindle shaft  273 . Abutment surface  272  connects spindle shaft  273  with blade seating shoulder  275 . Blade seating shoulder  275  is flat surface  276  and semicircular section  277 . Blade seating shoulder  275  is connected to bolt  295 . Bolt  295  has threaded section  296  which is directly adjacent to flat surface  276  and semicircular section  277 . Bolt  295  has a threaded section  296  and a flat surface  297 . 
     Saw  250  includes guide body  310 . Guide body  310  includes a rectangular section  311  and an angular section  312 . Rectangular section  311  in the preferred embodiment is sized to fit within saw entrance  247  as shown in  FIG. 5   b  and distractor channel  115  shown in  FIG. 2 . The rectangular section tolerance must be such that rectangular section  311  slides longitudinally with respect to distractor channel  115  and interior channel  195  without significant angular play about the longitudinal axis. In the preferred embodiment, these tolerances are approximately 0.3 mm. Angular section  312  connects to flat surface  313 . Guide body  310  also includes spindle hole  301  which traverses the longitudinal axis of guide body  310  and is sized to fit around spindle shaft  273 . Spindle hole  301  is sized to allow rotation with respect to spindle shaft  273 . 
     Rectangular section  311  includes spacer  300 , saw alignment stop  281  and saw alignment stop  279 . As can be seen best in  FIG. 7   a  and  FIG. 6 , saw alignment stop  281  includes a horizontal surface  282 . Saw alignment stop  279  includes vertical surface  283 . 
     When assembled, saw  250  provides for 90 degrees rotation of saw handle  260  with respect to guide body  310 . Thrust bearing  302  rests adjacent abutment surface  272 . Guide body  310  rests on spindle shaft  273  via spindle hole  301 . Flat surface  313  is adjacent angular section  312  and thrust bearing  302  providing a bearing surface between abutment surface  272  and flat surface  313 . Thrust bearing  278  resides around semicircular section  277  of blade seating shoulder  275  adjacent vertical end  315  of rectangular section  311 . Locking hole  285  of saw blade  280  is adjacent flat surface  276  and semicircular section  277  of blade seating shoulder  275 . Locking hole  285  includes flat surface  316  which when brought into contact with flat surface  276 , prevents rotation of saw blade  280  with respect to blade seating shoulder  275 , consequently, with respect to saw handle  260 . Lock nut  290  is threaded onto threaded section  296  of bolt  295 . Flat surface  276 , flat surface  316  and saw alignment stop  281  are parallel with the axis of saw guide post  270 . 
     Saw  250  and all its components are made from titanium, stainless steel, or other material which is used with surgical tools and equipment. In the preferred embodiment, rectangular section  311  of saw  250  is provided in several sizes in a set of several sizes to match the sizes of the distractor  110 , as previously described. Alternatively, a set of several saws  250  is provided, each having a rectangular section  311  whose cross-section is sized to match the distractor channel  115  of the set of distractors  110 . In addition, a set of blades may be provided each having different dimensions to achieve different lumbar dimensions. 
       FIGS. 8   a  and  8   b  are end views of saw  250 .  FIG. 8   a  illustrates saw blade  280  in lowered position. In lowered position, saw blade  280  is flush with guide body  310 .  FIG. 8   b  illustrates saw blade  280  in raised position. In raised position, saw blade  280  is perpendicular to guide body  310 . 
     In the preferred embodiment, saw blade  280  is between 0.9 cm and 4.9 cm long with a width of between 1 mm and 5 mm. Saw blade  280  has a flat bottom and two curved ends  303  and  305 . Saw blade  280  includes a locking hole  285  of approximate diameter and shape as bolt  295 . Curved end  305  includes saw teeth  304  having a height of about 0.5 mm and about 1.5 mm. Saw blade  280  also includes notches  317  and  318 . As shown in  FIG. 8   b , saw blade  280  in its raised position rests adjacent vertical surface  283  which prevents it from rotating counterclockwise. In lowered position, as shown in  FIG. 8   a , notch  318  rests adjacent horizontal surface  282  and prevents rotation of the saw blade clockwise. 
     Referring now to  FIG. 9 , in use, gate  180  is placed over the anterior end of distractor  110  and advanced until anterior end  111  rests against gate lip  185 . Saw  250  is placed in lowered position. Rectangular section  311  is placed in interior channel  195  and advanced through distractor channel  115  until spacer  300  reaches distractor stop  122  or saw guide post  270  reaches handle stop  242 . 
     In use, the saw is used to make two sets of receiving notches in the upper and lower vertebrae that correspond to the positions of the saw guides. More particularly, saw  250  is retracted until saw guide post  270  is directly adjacent saw guide  230 . Saw handle  260  is rotated clockwise 90 degrees such that saw guide post  270  advances through saw guide  230  on gate  180 . Rotation of saw handle  260  will rotate saw blade  280  causing it to cut into superior vertebra  20  thereby forming a slot  900 . Distractor torque handle  235  is grasped to apply counter torque and prevent rotation of the saw from displacing distractor  110  angularly with respect to the effected vertebrae. Saw handle  260  is then rotated counterclockwise positioning saw guide post  270  in handle guide  257 . Saw  250  is then extracted such that saw guide post  270  is adjacent saw guide  220 . Saw handle  260  is then rotated clockwise 90 degrees such that saw guide post  270  advances into saw guide  220 . Rotation of saw handle  260  rotates saw blade  280  thereby cutting into superior vertebra  20  and forming slot  902 . Saw guide post  270  is then rotated counter-clockwise so that saw guide post  270  resides in handle guide  257 . 
     Saw blade  280  is placed in its lowered position. Saw  250  is then removed from distractor channel  115  through interior channel  195 . Saw  250  is then rotated 180 degrees about its axis and rectangular section  311  replaced is in interior channel  195  of gate  180 . Saw  250  is further reinserted into distractor channel  115 . 
     Saw guide post  270  is adjacent saw guide  210 . The saw handle is rotated clockwise 90 degrees such that saw guide post  270  enters saw guide  210 . Rotation of saw handle  260  consequently rotates saw blade  280  exposing saw teeth  304  to inferior vertebra  40  thereby cutting into inferior vertebrae  40  thereby forming slot  903 . Distractor torque handle  235  is used to apply counter torque and prevent the saw rotation from displacing distractor  110 . Saw handle  260  is then rotated clockwise such that saw guide post  270  advances through the saw guide and into handle guide  240 . Saw  250  is then extracted such that saw guide post  270  advances through handle guide  240  until it is adjacent saw guide  200 . Saw handle  260  is then rotated 90 degrees such that saw guide post  270  advances into saw guide  200 . The rotation of saw handle  260  rotates saw blade  280  causing a second cut into inferior vertebra  40  thereby forming slot  904 . 
     Saw  250  is removed through distractor channel  115  and interior channel  195 . Gate  180  is then removed from the anterior end of distractor  110 . 
     Slots  900 ,  902 ,  903  and  904  in superior vertebra  20  and inferior vertebra  40  are substantially consistent with the spacing on gate  180  between saw guides  200 ,  210 ,  220 , and  230 , respectively. 
     The novel implant is then prepared to be inserted. 
     Referring to  FIGS. 10 ,  11  and  12 , implant  320  is described. Implant  320  is comprised of two semi-cylindrical halves, upper half  340  and lower half  330 . Upper half  340  includes parallel radially exposed and planar radial anchors  264  and  261 . The radial anchors are integrally formed with upper half  340 . Radial anchor  264  further includes curved surface  266 . Radial anchor  261  includes curved surface  263 . 
     Lower half  330  includes two parallel planar radial anchors  370  and  371 . Radial anchors  370  and  371  are integrally formed with lower half  330 . Radial anchor  370  includes curved surface  372 . Radial anchor  371  includes curved surface  373 . 
     Upper half  340  includes upper threaded collar  345 . Lower half  330  includes lower threaded collar  355 . The exterior of the upper half includes index marks  360 . Index marks  360  correspond with index marks  361  on lower half  330 . 
     Upper half  340  includes upper channel  380  which is threaded. Lower half  330  includes lower channel  390 . Lower channel  390  is not threaded. Upper half  340  is joined to lower half  330  with a mating interconnection between dovetail guide  386  and dovetail guide  385  found on upper half  340  and dovetail slot  396  and dovetail slot  395 , respectively, located on lower half  330 . 
     Lower half  330  includes set screw stop  400  integrally formed with lower half  330  and residing within lower channel  390 . Set screw stop  400  is solid plug which fills lower channel  390  beyond end of set screw  350 . 
     Lower half  330  includes set screw step  392 . Set screw step  392  extends into upper channel  380  and in upper half  340  and lower channel  390  in lower half  330 . Set screw step  392  decreases diameter of upper channel  380  and lower channel  390  by approximately 2 mm. 
     As can best be seen in  FIG. 12 , when assembled, upper half  340  and lower half  330  of implant  320  are engaged in a sliding relationship provided by the dovetail guides  385  and  386  residing in dovetail slots  395  and  396 . As can be seen in  FIG. 11 , when assembled, upper half  340  and lower half  330  form implant body  346 . Radial anchor  264  is aligned with radial anchor  370 . Radial anchor  261  is aligned with radial anchor  371 . Furthermore, upper threaded collar  345  and lower threaded collar  355  are aligned and form a cylindrical threaded attachment collar  356 . 
     In use, set screw  350  can be rotated either counter-clockwise or clockwise within lower channel  390  and upper channel  380 . The set screw is retained in position by set screw stop  400  and set screw step  392 . As set screw  350  is rotated, threads  351  engage the threads on upper channel  380  and slide upper half  340  with respect to lower half  330 . As upper half  340  and lower half  330  are displaced, radial anchors  264  and  261  are displaced with respect to radial anchors  370  and  371  along the longitudinal axis of implant  320 . 
     Implant  320  in the preferred embodiment is made from titanium, stainless steel, alloys such as titanium allow, or other materials which are easily sterilizable. Implant  320  or parts thereof, may also be made from composite materials such as synthetic bone. Some composites or synthetic bone products include demineralized bone matrix, collagen, ceramics, cements, and polymers, such as silicone and some acrylics and include products such as Vitoss, Cortoss, Rhakoss, Pro Osteon, and Gu-Bang. 
     In the preferred embodiment, implant body  346  is between about 0.5 cm to about 2.5 cm in diameter and between about 2.0 cm and about 4.5 cm in length. In the preferred embodiment, cylindrical threaded attachment collar  356  is between about 0.4 to about 2.4 cm in diameter and between about 0.5 and 2.0 cm in length. In the preferred embodiment, radial anchors  264 ,  261 ,  370  and  371  have a height (as measured from the center plane of the implant) of between about 0.5 cm and about 3.5 cm with an aspect ratio of ½ to 1½ between radial anchors  264 ,  261 ,  370 , and  371  and diameter of implant body  346 . 
     In the preferred embodiment, upper half  340  includes exactly two radial anchors and lower half  330  includes exactly two radial anchors. However, in other embodiments, the upper half and lower half of the implant may include more or less than two radial anchors. Furthermore, the upper half and lower half of implant  320  do not necessarily need to include the same number of radial anchors. In embodiments which include different numbers of radial anchors, it will be understood by those skilled in the art that the same number of saw guides must be included on gate  180  in order to correspond with the number and orientation of the radial anchors. 
       FIGS. 13   a  and  13   b  illustrate inserter  430 . Inserter  430  includes upper half  440  and lower half  450 . Upper half  440  includes upper hexagonal section  441  and upper cylindrical section  442 . Within upper cylindrical section  442  resides upper dovetail guide  454 . Adjacent upper dovetail guide  454  is implant channel  446 . Implant channel  446  includes locking thread  445 . 
     Lower half  450  includes lower hexagonal section  451  and lower cylindrical section  453 . Lower cylindrical section  453  includes lower dovetail channel  452 . Upper dovetail guide  454  fits within lower dovetail channel  452  and allows for sliding movement between upper half  440  and lower half  450 . As can best be seen in  FIG. 13   b , when upper half  440  and lower half  450  are assembled, inserter  430  assumes an outer circular perimeter. In the preferred embodiment, this outer circular perimeter is sized to fit within distractor channel  115 , shown in  FIG. 2 , with sufficient clearance to allow for rotation of inserter  430 . Further, in the preferred embodiment, the hexagonal shape of upper half  440  and lower half  450  and inserter  430  is sized to allow for rotation with a tool such as a spanner wrench. In the preferred embodiment, the length of inserter  430  is sufficient to span the length of distractor body  99 . 
     Locking thread  445  is sized to mate with upper threaded collar  345  on implant  320  as shown in  FIGS. 10 ,  11  and  12 . 
     Referring to  FIG. 15 , guide block  460  will be described. Guide block  460  includes guide block bottom  465  and guide block top  475 . Guide block  460  also includes guide hole  470  which is centrally located within the guide block and spans its length. Guide block bottom  465  is sized to fit within distractor channel  115 . Guide block top  475  is sized so that it will not fit within distractor channel  115  but rather abut anterior end  111  of distractor body  99  (as shown in  FIG. 2 ). 
     In use, inserter  430  is used to place the implant in position between the affected vertebra and rotated into position. More particularly then to implant the implant, the amount of offset calculated according to the radiograph is reduced to a number of millimeters. The implant is adjusted using upper adjustment index marks  360  and lower adjustment index marks  361  to an offset position using set screw  350 . The amount of offset can be observed by observing the offset between index marks  360  and  361 . In an alternate embodiment, the offset can be derived by calculating the number of rotations of the set screw and multiplying by the pitch of the threads. In an alternate embodiment, the pitch of the threads is set to a convenient number so that a single rotation of the set screw results in a predetermined movement of the upper and lower halves, such as 1 mm for example. An example of an offset position is shown in  FIG. 12 . 
     In use, inserter  430  is assembled and its cylindrical section is guided into and through guide hole  470  until guide block top  475  reaches the hexagonal section of the inserter. 
     Implant  320  is then connected to inserter  430  as shown in  FIG. 14 . Locking thread  445  of inserter  430  is engaged with upper threaded collar  345  of implant  320 . Inserter lower half  450  is advanced towards implant  320  whereby dovetail guides  386  and  385  of implant  320  are engaged by lower dovetail channel  452  on inserter  430  thereby securing implant  320  to inserter  430 . 
     Referring now to  FIG. 16 , the process of inserting implant  320  into the affected vertebra will be described. As previously described, distractor  110  is in position between superior vertebra  20  and inferior vertebra  40 . Implant  320 , while attached to inserter  430  is oriented and placed within distractor channel  115 . Implant  320  is placed in distractor channel  115  with radial anchors  264  and  261 ,  370  and  371  positioned so that clockwise rotation of the implant will result in radial anchor  264  and  261  encountering superior vertebra  20  and radial anchor  370  and  371  encounter inferior vertebra  40 . Using the hexagonal section of inserter  430 , implant  320  is advanced within distractor channel  115  a sufficient distance to allow guide block bottom  465  to be inserted into distractor channel  115 . Guide block bottom  465  is advanced within distractor channel  115  until guide block top abuts anterior end  111  of distractor body  99 . 
     Implant  320  is then advanced within distractor channel  115  until the hexagonal section of inserter  430  abuts guide block top  475 . 
     The dimensions of guide block top  475  and cylindrical section of inserter  430  are such that when the hexagonal section of the inserter abuts guide block top  475 , implant  320  is in proper position in relation to slots  900 ,  902 ,  903  and  904  such that radial anchor  264  is adjacent slot  900 , radial anchor  261  is adjacent slot  902 , radial anchor  370  is adjacent slot  904  and radial anchor  371  is adjacent slot  903 . 
     Inserter  430  is then rotated 90 degrees clockwise such that the radial anchors are rotated into position in the slots in their respective vertebrae. 
     Once in position, implant  320  is released from inserter  430 . 
     The diameter of inserter guide hole  470  should provide sufficient clearance for rotation and transition of cylindrical portion of inserter  430  without excessive play. In the preferred embodiment, the diameter of guide hole  470  should not exceed the diameter of the cylindrical section of inserter  430  by more than 0.1 mm. 
     To release implant  320  from inserter  430 , inserter lower half  450  is retracted anteriorly past superior locking thread  445  and disengages from lower dovetail channel on lower cylindrical section  453  of the inserter. Inserter  430  is rotated 180 degrees such that upper threaded collar  345  is disengaged from locking thread  445  on implant channel  446  on the inserter. Inserter  430  and guide block  460  are then removed from distractor  110 . 
     Distractor  110  is then removed from between superior vertebra  20  and inferior vertebra  40  by pulling anteriorly. 
       FIG. 17  illustrates the positioning of implant  320  between superior vertebra  20  and inferior vertebra  40  after distractor  110  has been removed. Upper half  340  is adjacent superior vertebra  20 , radial anchor  264  is located in slot  900 , radial anchor  261  is located in slot  902 . Lower half  330  is adjacent inferior vertebra  40  and radial anchor  370  is located in slot  904 . Radial anchor  371  is located in slot  903 . 
     In order to align superior vertebra  20  and inferior vertebra  40 , upper half  340  and lower half  330  are aligned. A spanner is inserted into spanner slot  405  of implant  320 . Set screw  350  is rotated to move lower implant half  330  anteriorly and upper implant half  340  posteriorly. In one embodiment, for each complete 360 degrees turn of the set screw will move lower half  330  1 mm with respect to upper when alignment of the implant halves is complete, the threads in upper threaded collar  345  and in lower threaded collar  355  will align. Ideally, alignment of the implant halves will align the vertebrae. 
     After alignment of the vertebrae, an interbody arthrodesis is performed on each side of implant  320  and between remaining distended disk  70 . The technique for interbody arthrodesis is surgeon&#39;s choice from those known techniques. 
       FIGS. 19   a  and  19   b  illustrates one embodiment of plate  540 . Plate  540  is selected based on shape and size of individual patient&#39;s vertebrae. In one embodiment, the height of plate  540  is between 2.5 cm and 7 cm and the width of plate  540  is between 1.5 cm and 5 cm. Depth of plate  540  is between 0.2 cm and 1.5 cm. Plate  540  is slightly concave to approximate the curvature of inferior vertebra  40  and superior vertebra  20 . 
     Plate  540  includes plate nut hole  560  in its approximate center. The diameter of plate nut hole  560  on the anterior side of plate  540  is between 0.65 cm and 3.4 cm while the diameter of plate nut hole  560  on the posterior side of plate  540  is between 0.45 cm and 2.5 cm. 
     Plate  540  also includes four holes  550 . Each hole  550  should have diameter between about 1 mm and about 9 mm. But these diameters can vary. The plate is secured to the vertebra by stainless steel screws as known in the art. 
     Preferably, plate  540  should be made of titanium or stainless steel. 
       FIG. 18  illustrates one embodiment of nut  500 . Nut  500  has nut head  520  which is elliptical. Diameter of nut head  520  is between 0.65 cm and 3.4 cm preferably. Nut head  520  contains spanner holes  535 . Nut body  510  has diameter of between 0.5 cm and 2.5 cm. The diameter of nut body  510  should be approximately the same as diameter of implant body  346 . The length of nut body  510  is between 0.2 cm and 6 cm. Nut  500  should be construction of titanium or stainless steel. Other rigid materials can be used. Nut body  510  includes threaded hole  526 . Threaded hole  526  is threaded to match the threads of upper threaded collar  345  and lower threaded collar  355  on implant  320 . 
     In use, to help secure implant  320  in position, nut  500  and plate  540  are used, as illustrated in  FIG. 20 . Nut body  510  is placed through plate nut hole  560 . Nut thread  525  of threaded hole  526  is then aligned with and threaded onto upper threaded collar  345  and lower threaded collar  355 . Nut  500  prevents implant upper half  340  and implant lower half  330  from moving horizontally against each other. 
     Plate  540  is then properly aligned with the shape of superior vertebra  20  and inferior vertebra  40 . Corticocancellous screws  570  are placed into each of the plate screw holes  550  and screwed into the respective vertebrae by traditional techniques within the field. The difference in diameters between plate nut hole  560  from front to back allows articulation of the bolt with respect to the plate. Once plate  540  is attached to superior vertebrae  20  and inferior vertebrae  40  with screws  570 , and is secured via nut  500  to implant  320  the device acts as a monolithic structure preventing rotational, lateral or anterior/posterior movement of vertebral bodies  20  and  40  with respect to each other, allowing ossification of said vertebral bodies. 
     Surgery is completed by standard anterior approach surgery techniques and implant is in place. 
     In the event that adjustments need to be made to implant  320 , screws  570 , nut  500  and plate  540  can be removed and set screw  350  adjusted with any appropriate spanner head wrench. Nut  500 , plate  540  and screws  570  are then replaced. 
       FIGS. 21 ,  22   a  and  22   b  illustrate another preferred embodiment of the saw.  FIG. 21  shows saw  802  with mill bit  750 . Saw  802  includes handle  817  and conical section  814 . Interior of handle  817  includes motor  860 . Motor  860  is attached to mounting frame  808 . Motor  860  is connected to transmission shaft  700 . Switch  840  is integrated into handle  817  and is connected to motor  860  through wire  850 . Switch  840  activates and deactivates motor  860 . Motor  860  is connected to power source such as a rechargeable lithium ion battery or another renewable power supply as known in the art. 
     Motor  860  rotates transmission shaft  700  between 15,000 to 20,000 rpm. In another preferred embodiment, motor  860  has variable speeds and speed of motor  860  is modulated through use of switch  840 . 
     Conical section  814  is connected to handle post  811 . Handle post  811  integrally supports saw guide post  812 . Saw guide post  812  is perpendicular to the longitudinal axis of saw  802 . Handle post  811  is rigidly attached to spindle shaft  800 . Shoulder  822  is positioned between handle post  811  and guide body  795 . Guide body  795  is free to rotate with respect to handle post  811  and spindle shaft  800 . 
     Transmission hole  815  extends through handle  817 , conical section  814 , handle post  811  and spindle shaft  800 . 
     Transmission shaft  700  extends through transmission hole  815 . Transmission shaft  700  is kept in position within transmission hole  815  by bushings  880 . Transmission shaft  700  extends beyond spindle shaft  800  and into transmission housing  725 . 
     Guide body  795  has spindle hole  810  which transverses the longitudinal axis of guide body  795 . Spindle shaft  800  fits within spindle hole  810 . Spindle hole  810  allows rotation of spindle shaft  800  about the longitudinal axis of guide body  795 . Transmission shaft  700  extends through washer  670  and nut  680  into transmission housing  725 . 
       FIG. 22   a  illustrates the mechanics inside transmission housing  725 . Bearings  710  and  712  maintain position of transmission shaft  700  within transmission housing  725  while allowing it to rotate. Transmission shaft  700  terminates in bevel gear  735 . Thrust bushing  709  is affixed between bevel gear  735  and bearing  712  and constrains the axial movement of transmission shaft  700 . Bevel gear  735  meshes with bevel gear  610  creating 90 degree transmission. Other transmission schemes, such as a flexible cable, will suffice in other embodiments. 
     Bevel gear  610  is rigidly integrally connected to bearing shaft  620 . Bearing shaft  620  is rigidly integrally connected to frustroconical section  637  which is rigidly integrally connected to jaws  650  of chuck  660 . Mill bit  750  is inserted into jaws  650 . The position of chuck  660  with respect to transmission housing  725  is maintained by bearings  740  and  730  and thrust bushing  708 . Mill bit  750  is parallel to saw guide post  812 . 
       FIGS. 23   a  and  23   b  are further illustrations of chuck  660 . Bevel gear  610  is integrally connected to bearing shaft  620 . Bearing shaft  620  is integrally connected to jaws  650 . Jaws  650  are approximately cylindrical in shape with mill bit hole  882  removed which is same shape as end of mill bit  750 . Jaws  650  have set screw hole  640 . Set screw hole  640  is threaded to mate with set screw  630 . 
     In one embodiment, mill bit hole  882  has flat surface  642  and semicircular surface  641 . Set screw hole  640  is centered along the latitudinal axis of flat surface  642 . 
     Referring to  FIGS. 22   a  and  22   b , mounting plate  720  is attached to transmission housing  725  through use of screws  722 . Mounting plate  720  has set screw hole  770 . Set screw hole  770  allows access to set screw  630  for locking mill bit  750  into chuck  660 . Mounting plate  720  has bit stop  836  and mounting bracket  835 . 
     Referring now to  FIG. 22   b , guide body  795  includes horizontal stop  780  and vertical stop  790 . Horizontal stop  780  extends from top  782  of guide body  795  and has horizontal surface  787 . Vertical stop  790  is aligned with bottom  783  of guide body  795 . Vertical stop  790  and horizontal stop  780  cooperate with bit stop  836  to limit the rotation of the transmission housing and the mill bit to 90 degrees between a vertical position and a horizontal position. 
     When handle  817  is turned counter-clockwise with respect to the longitudinal axis of guide body  795 , bit stop  836  is rotated counterclockwise until bit stop  836  abuts saw guide vertical stop  790 . Mill bit  750  will be substantially perpendicular to guide body  795  when bit stop  836  abuts guide vertical stop  790 . When handle  817  is rotated clockwise with respect to the longitudinal axis of guide body  795 , bit stop  836  will rotate clockwise until bit stop  836  abuts horizontal stop  780 . When bit stop  836  abuts horizontal stop  780 , mill bit  750  will be substantially parallel to guide body  795 . 
     In use, mill bit  750  is inserted into mill bit hole  882 . Set screw  630  is advanced through set screw hole  770 , into set screw hole  640  until abuts mill bit  750 . Saw  802  is then inserted into a distractor as described in previous embodiment. Switch  840  activates motor  860  by connecting it to a power source, which rotates transmission shaft  700  and bevel gear  735 . Rotation of bevel gear  735  rotates bevel gear  610  and chuck  660 , which causes mill bit  750  to rotate. Handle  817  is manually rotated counterclockwise around the longitudinal axis of guide body  795  which rotates mill bit  750  in relation to the longitudinal axis of guide body  795  and exposing mill bit  750  to vertebrae in order to cut a slot in the vertebra. After a slot has been cut, handle  817  is manually rotated clockwise around the longitudinal axis of guide body  795  until mill bit  750  is substantially parallel to latitudinal axis of guide body  795 . Switch  840  then deactivates motor  860 . The procedure is repeated for cutting additional slots in vertebra as previously described with manual saw embodiment. 
     Mill bit  750  has a diameter of between approximately 1 mm and 5 mm and a length of between 0.6 cm and 3.9 cm and corresponds to the size of the radial anchors of the implant being inserted between vertebra. Multiple size mill bits are included and the appropriate size is inserted to correspond to size needed for the particular implant. 
     In some spondylolisthesis conditions, the relocation of vertebra may either be minor or unnecessary, however the natural tilt and location between two adjacent vertebrae needs to be maintained and stabilized. For this type of condition, another embodiment of an implant and instrumentation are used which includes a tapering to match the tilt of the vertebrae. 
       FIGS. 24   a  and  24   b  are illustrative of an additional preferred embodiment of a tapered implant. Implant  845  has an implant body  853  that is tapered creating a frustroconical shape. Implant body  853  has implant body front end  870  and back end  861 . The cross-section of front end  870  is circular. The cross-section of back end  861  is circular. Degree of tapering  875  is the degree by which the tapering occurs along implant body  853  and ranges between approximately 2 and 10 degrees. 
     Implant body  853  has two halves, upper half  862  and lower half  864 . Upper half  862  and lower half  864  meet at implant seam  855 . 
     Implant body  853  has radial anchors  876  and  877  on upper half  862  and radial anchors  878  and  879  on lower half  864 . Radial anchors  876 ,  877 ,  878 , and  879  are substantially perpendicular to implant seam  855 . Radial anchors  878  and  876  have less surface area than radial anchors  877  and  879 , and are reduced in area to conform to a modified distractor as shown in  FIG. 25 . Other features of implant  845  are similar to those previously described in other embodiment. 
       FIG. 25  is illustrative of other preferred embodiments for a distractor and impactor to be used with tapered implant  845 .  FIG. 25  illustrates impactor  950  within distractor  940 . 
     Distractor  940  has distractor arm  895  and distractor arm  892 . Distractor arm  895  extends longitudinally from side  955  of distractor  940 . Distractor arm  892  extends longitudinally from side  945  of distractor  940 . Distractor arm  895  has taper arm  890  which tapers both the top and bottom between an approximate 2 and 10 degree angle along the longitudinal axis of distractor arm  895 . Taper arm  897  on distractor arm  892  tapers the height from both the top and the bottom between an approximate 2 and 10 degree angle. Taper arm  897  includes distractor stop  910  and taper arm  890  has distractor stop  906 . The remaining features of distractor  940  are consistent with previously disclosed embodiment of distractor. 
     Impactor  950  has impactor head  911 . The posterior end of impactor head  911  has tapered end  898 . Tapered end  898  has between approximately 2 and 10 degrees of taper along the longitudinal axis of impactor head  911 . Tapered end  898  ends in impactor seat  920  and on either side of impactor seat  920  are stop surfaces  930  and  931 . The tapering of tapered end  898  corresponds to the tapering of taper arm  890  and taper arm  897  such that stop surfaces  930  and  931 , when fully inserted, touch distractor stop  906  and distractor stop  910  and do not extend beyond edges of distractor arms  892  or  895 . The remaining features of impactor  950  are consistent with previously disclosed embodiment of impactor. 
     As disclosed with prior embodiments, with the tapered implant system, the implant, distractor, impactor, and other parts necessary to complete the disclosed surgery have a variety of heights depending on the patient and the condition to be resolved. 
       FIGS. 26A-C  and  27  are illustrative of an additional preferred embodiment of an implant with a different locking mechanism. 
     Implant  1000  has an upper half  1010  and a lower half  1020 . Upper half  1010  has a generally rectangular shape and includes integrally formed and parallel planar radial anchors  1040  and  1045 . Radial anchor  1045  includes curved surface  1047 . Radial anchor  1040  includes curved surface  1042 . In other embodiments, the upper half and lower half of the implant may include different numbers of radial anchors. Furthermore, the upper half and lower half of implant  1000  do not necessarily need to include the same number of radial anchors. In embodiments which include different numbers of radial anchors, it will be understood by those skilled in the art that the same number of saw guides must be included on the gate in order to correspond with the number and orientation of the radial anchors. 
     Upper half  1010  includes upper channel  1050  which extends along its longitudinal axis. Upper channel  1050  is bounded by side wall  1013 , side wall  1023 , and top wall  1033 . Side wall  1013  and side wall  1023  are substantially perpendicular to top wall  1033 . 
     Side wall  1023  includes connection guide  1100  which is substantially perpendicular to side wall  1023  and substantially parallel to top wall  1033 . 
     Side wall  1013  includes connection guide  1091  which is substantially perpendicular to side wall  1013  and substantially parallel to top wall  1033 . Gap  1052  exists between connection guide  1100  and connection guide  1091  and traverses the longitudinal axis of upper half  1010 . 
     Side wall  1023  includes thumbscrew hole  1065  located on front end  1083 . Thumbscrew hole  1065  includes with threads  1070 . 
     As shown in  FIG. 27 , top wall  1033  includes locking recess  2300 . Locking recess  2300  forms a recess in top wall  1033  adjacent to upper channel  1050 . Locking recess  2300  is generally centered along the longitudinal axis of upper half  1010 . 
     In the preferred embodiment, upper half  1010  includes a single thumbscrew hole, however, in alternative embodiments upper half  1010  could contain up to four thumbscrew holes located at the corners of upper half  1010 . The additional holes accommodate additional thumbscrews to aid in assembly of the implant as will be further described later. 
     Lower half  1020  includes platform  1135 . Platform  1135  includes two parallel planar radial anchors  1030  and  1035 . Radial anchors  1030  and  1035  are integrally formed with platform  1135 . Radial anchor  1030  includes curved surface  1031 . Radial anchor  1035  includes curved surface  1036 . 
     Platform  1135  includes positioning block  1150 . Platform  1135  has front end  1079 . Positioning block  1150  is located adjacent front end  1079 . 
     Positioning block  1150  includes connecting grooves  1155  and  1160  adjacent platform  1135 . Connecting grooves  1155  and  1160  align with and engage connection guides  1091  and  1100 . 
     Positioning block  1150  includes locking arms  1090  and  1095 . Locking arms  1090  and  1095  are adjacent locking hollow  1085 . Locking hollow  1085  is bounded by sidewalls  1086  and  1087 . 
     Locking arm  1095  includes extension  1097 , adjacent to and substantially perpendicular to sidewall  1086 . Locking arm  1090  includes extension  1092 , adjacent to and substantially perpendicular to sidewall  1087 . 
     Spring  1060  is positioned within locking hollow  1085  between sidewalls  1086  and  1087  adjacent surface bottom  1165 . Spring  1060  is shorter than the distance between sidewalls  1086  and  1087  to allow for deflection. Spring  1060  is nonmetallic so as to be MRI compatible. In another preferred embodiment, the spring can be a coil spring fixed to surface bottom  1165 . 
     Locking arm  1095  includes holes  1075  and  1080 . Holes  1075  and  1080  intersect locking hollow  1085  on sidewall  1086 . 
     Locking arm  1095  includes bolt hole  1140 . Bolt hole  1140  extends through locking arm  1095  but does not extend into locking hollow  1085 . Bolt hole  1140  includes threads  1145 . 
     Locking block  1055  fits within locking hollow  1085 . Locking block  1055  includes upper section  1110  and lower section  1105 . Lower section  1105  includes positioning stop  1115  and positioning stop  1130 . Lower section  1105  is capable of vertical movement within locking hollow  1085 . Positioning stops  1115  and  1130  interfere with extensions  1097  and  1092  and impede the vertical movement of locking block  1055  at its upper limit. 
     Lower section  1105  also includes incline section  1125 . Incline section  1125  is adjacent upper section  1110  has an incline of between about 10° and about 75°. 
     Upper section  1110  is integrally formed with lower section  1105  and is approximately centered along the longitudinal axis of lower section  1105 . Upper section  1110  fits within locking recess  2300  without significant longitudinal play. 
     In order to assemble implant  1000 , locking block  1055  is positioned adjacent spring  1060  inside locking hollow  1085 . Locking block  1055  is depressed until upper section  1110  is aligned horizontally with locking arms  1090  and  1095 . Upper half  1010  is connected with lower half  1020  by sliding connection guides  1091  and  1100  into connecting grooves  1155  and  1160 . When assembled, upper half  1010  and lower half  1020  form cavity  1141 . 
       FIGS. 28A-D , are illustrative of a preferred embodiment of implements to aid installation of implant  1000  and include reduction rod  2000 , reduction bar  2100 , thumbscrew  2050  and reduction wheel  2070 . 
     Reduction bar  2100  includes a substantially rectangular cross-section which corresponds to the outside cross-section of implant  1000  when assembled. Reduction bar  2100  includes sides  2115  and  2120 , top  2125 , bottom  2130 , front end  2145  and back end  2150 . Torque handle  2110  has circular cross-section and extends at a generally perpendicularly angle from side  2115 . Torque handle  2110  is integrally formed with reduction bar  2100 . 
     Reduction bar  2100  includes channels  2135  and  2140  which traverse the longitudinal span of reduction bar  2100 . Channels  2135  and  2140  have substantially circular cross-sections. The axis of channel  2135  is generally centered on the longitudinal axis of the reduction bar. The axis of channel  2140  is offset from the axis of channel  2135 . 
     Back end  2150  includes implant spacer  2155 . Implant spacer  2155  forms a raised stanchion. The implant spacer is designed to rest within cavity  1141  shown in  FIG. 27 . 
     Reduction rod  2000  includes a cylindrical section  2010  and hexagonal section  2040 . Hexagonal section  2040  is integrally formed with cylindrical section  2010 . In one preferred embodiment, hexagonal section  2040  includes etching  2033  at predetermined intervals the etchings are substantially perpendicular to the logistical axis of the reduction rod. Cylindrical section  2010  includes back end  2025  and front end  2030 . Back end  2025  includes threads  2020 . Front end  2030  includes threads  2035 . Cylindrical section  2010  is sized to fit within channel  2135 . 
     Thumbscrew  2050  has cylindrical section  2023  and knurled thumbscrew head  2065 . Cylindrical section  2023  is sized to fit within channel  2140 . Cylindrical section  2023  includes threads  2060 . Thumbscrew head  2065  is integrally formed with cylindrical section  2023 . Thumbscrew head  2065  is substantially cylindrical in shape and has a diameter greater than cylindrical section  2023 . 
     Reduction wheel  2070  includes integrally formed cylindrical section  2090  and conical section  2095 . Conical section  2095  is coaxial with cylindrical section  2090 . Coaxial channel  2075  extends through cylindrical section  2090  and conical section  2095 . Channel  2075  is circular and includes threads  2080 . Threads  2080  mate with threads  2035  of reduction rod  2000 . 
     In alternate embodiments of upper half  1010 , more than one thumbscrew hole is provided, and reduction bar  2100  includes a corresponding number of channels to accommodate the thumbscrew holes. Additional thumbscrews  2050  are provided, corresponding to the number of thumbscrew holes. 
     In practice, the vertebrae are prepared and slots are cut as previously discussed. Distractor  110  (as shown in  FIG. 2 ) remains between the vertebrae. 
     Implant  1000  is prepared by sliding upper half  1010  over lower half  1020  until a predetermined spacing between the radial anchors is achieved. The predetermined spacing is based on the distance that the vertebrae must be moved to correct their alignment. 
     Guide block  460 , as shown in  FIG. 15 , is guided onto reduction bar  2100  such that guide block  460  is between torque handle  2110  and back end  2150 . The diameter of guide hole  470  should provide sufficient clearance for rotation and transition of reduction bar  2100  without excessive play. 
     Reduction bar  2100  is placed adjacent to implant  1000  such that implant spacer  2155  is properly aligned with implant  1000 . 
     Thumbscrew  2050  is inserted into channel  2140 . Channel  2140  is aligned with thumbscrew hole  1065  on upper half  1010 . Threads  2060  are advanced into threads  1070  until upper half  1010  is adjacent to back end  2150 , thus securing upper half  1010  to reduction bar  2100 . 
     Reduction rod  2000  is then inserted into channel  2135 , which is aligned with bolt hole  1140 , until threads  2020  meet bolt hole  1140 . Threads  2020  are advanced into threads  1145  until lower half  1020  is secured to reduction rod  2000 . 
     Reduction wheel  2070  is connected to reduction rod  2000 . Conical section  2095  slides over hexagonal section  2040  until it engages front end  2030 . Threads  2080  are engaged with threads  2035 . Reduction wheel  2070  is rotated until the desired marking becomes visible at the top of reduction wheel  2070  corresponding to the amount of adjustment needed between the vertebrae, or until conical section  2095  abuts reduction bar  2100 . 
     In another preferred embodiment, upper half  1010  is aligned with reduction bar  2100  and attached to reduction rod by thumbscrew  2050 . Lower half  1020  is then connected to upper half  1010  by engaging connection guides  1100  and  1091  with connecting grooves  1160  and  1155  until the appropriate spacing exists between the radial anchors. Reduction rod  2000  is then placed through channel  2135  and threaded into bolt hole  1140 . Reduction wheel  2070  is connected to front end  2030  of reduction rod  2000 . Reduction wheel  2070  is then rotated to complete and secure the proper positioning of upper half  1010  in relation to lower half  1020 . 
     In another preferred embodiment, reduction wheel  2070  can be connected to reduction rod  2000  prior to reduction rod  2000  being inserted into channel  2135 . 
     Implant  1000  is placed within distractor channel  115  and advanced within distractor channel  115  until guide block bottom  465  is inserted into distractor channel  115 . Guide block bottom  465  is advanced within distractor channel  115  until guide block top  475  abuts anterior end  111  of distractor body  99  and implant  1000  is placed between the vertebrae where radial anchors  1045 ,  1040 ,  1030 , and  1035  align with the cut slots. Implant  1000  is rotated by use of the reduction bar  2100  so that radial anchors  1045 ,  1040 ,  1030 , and  1035  enter their respective slots in the vertebrae. Reduction bar  2100  is sized so as to allow rotation within distractor channel  115 . 
     To adjust the vertebrae into proper position, reduction bar  2100  is held in position by use of torque handle  2110 . Reduction wheel  2070  is rotated such that reduction rod  2000  is moved anteriorly and lower half  1020  is aligned with upper half  1010 . In one embodiment, for each complete 360 degrees turn of reduction wheel  2070 , lower half  1020  will move 1 mm with respect to upper half  1010 . When upper half  1010  and lower half  1020  are aligned, spring  1060  pushes locking block  1055  vertically into locking recess  2300  thus locking the upper half  1010  and lower half  1020  in place. In the preferred embodiment, when implant  1000  is aligned, back end  2030  of reduction rod  2000  will be horizontally aligned with the surface of cylindrical section  2090 . 
     When implant  1000  is aligned and locked in place, reduction wheel  2070  is unthreaded from reduction rod  2000 . Reduction rod  2000  is unthreaded from bolt hole  1140 . Thumbscrew  2050  is unthreaded from thumbscrew hole  1065  and reduction bar  2100  is removed from implant  1000  leaving implant  1000  in place. Guide block  460  and distractor  110  are then removed. 
     In the event that implant  1000  needs to be adjusted, upper half  1010  and lower half  1020  can be unlocked. Referring again to  FIG. 27 , pin  2303  is inserted through holes  1075  and/or  1080 . Pin  2303  engages the incline section and forces locking block  1055  downward into locking hollow  1085  thus allowing upper half  1010  to move in relation to lower half  1020 . 
     After alignment of the vertebrae, an interbody arthodesis is performed on each side of implant  1000  and between remaining distended disk as discussed with prior embodiments. 
       FIGS. 19   a  and  19   b  illustrate one embodiment of plate  540  which can be used with the different embodiments of implants, including implant  1000 , and has previously been discussed. 
       FIGS. 29   a  and  29   b  illustrate one embodiment of spacer  2320 . Spacer  2320  has front  2335  and back  2330 . Back  2330  has a similar shape as locking arm  1095 . Front  2335  has a curvature which corresponds to curvature of back of plate  540  (shown in  FIG. 19   a ). Spacer  2320  has hole  2325  which has diameter similar to bolt hole  1140  on implant  1000 . Hole  2325  extends through the longitudinal axis of spacer  2320 . 
       FIG. 30  illustrates one embodiment of bolt  2400 . Bolt  2400  includes elliptical bolt head  2410 . Diameter of bolt head  2410  is between about 0.65 cm and 3.4 cm preferably. Bolt head  2410  contains spanner holes  2405 . The diameter of bolt body  2415  should be approximately the same as diameter of bolt hole  1140 . Bolt body  2415  has threads  2420  which engage bolt hole  1140  in implant  1000 . The length of bolt body  2415  should be between 0.2 cm and 8 cm. The dimensions are suggested, but not critical. 
     In use, plate  540 , spacer  2320 , and bolt  2400  are used to secure implant  1000  in position. Bolt body  2415  is placed through plate nut hole  560 . Spacer  2320  is engaged with bolt body  2415 . Front  2335  of spacer  2320  is adjacent plate  540 . Threads  2420  are threaded into bolt hole  1140 . Back  2330  is aligned with and adjacent to positioning locking arm  1095 . Plate  540  is then properly aligned and secured to the vertebrae as discussed with prior embodiments. 
     Reduction bar  2100 , reduction rod  2000 , thumbscrew  2050 , and reduction wheel  2070  are preferably made from titanium, stainless steel, or other materials which are readily sterilized or from a rigid plastic such as PVC which may be disposed of after use. 
     Implant  1000 , spacer  2320 , and bolt  2400  in the preferred embodiment are made from titanium, stainless steel, alloys such as titanium allow, or other materials which are easily sterilizable. Implant  1000  or parts thereof, may also be made from composite materials such as synthetic bone. Some composites or synthetic bone products include demineralized bone matrix, collagen, ceramics, cements, and polymers, such as silicone and some acrylics and include products such as Vitoss, Cortoss, Rhakoss, Pro Osteon, and Gu-Bang. 
     As with other embodiments, different size implants, reduction bars, reduction rods, thumbscrews, reduction wheels, plates, spacers, and bolts are included to best fit the patient&#39;s individual vertebrae and needed alignment. Further, different length spacers can also be included to account for the difference lengths between the outside of the vertebrae and the implant. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.