Abstract:
Featured are a methods, systems, apparatus, and devices for fixing adjacent bone segments, segments of a bony structure and adjacent vertebrate of a spine utilizing an implant member as well as device kits related thereto. The methods, apparatuses and devices utilize an apparatus to forming a channel or aperture in or within the bone or bony structure segments or adjacent vertebra. In more particular embodiments such apparatuses and methods including forming an arcuate channel or aperture and which channel can receive therein a curved rod or implant member, which also preferably is arcuate, and avoids the associated problems with prior cage or straight rod and screw systems.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application Serial No. 60/133,356 filed May 10, 1999, which is incorporated herein by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention generally relates to methods, systems and apparatuses for bony fixation and more particularly to methods, systems and apparatuses adapted for fixing the bones of the spine.  
           [0004]    2. Background of the Invention.  
           [0005]    Fixation or fusion of vertebral columns with bone or material, rods or plates is a common, long practiced surgical method for treating a variety of conditions. Many of the existing procedures involve the use of components that protrude outwardly, which may contact and damage a body part, such as the aorta, the vena cava, the sympathetic nerves, the lungs; the esophagus, the intestine and the ureter. Also, many constructions involve components that may loosen and cause undesirable problems, often necessitating further surgical intervention. Additionally, limiting the success of these procedures are the bio-mechanical features of the spine itself, whose structure must simultaneously provide support to regions of the body, protect the vertebral nervous system and permit motion in multiple planes.  
           [0006]    As indicated above, spinal surgery for spine fusion generally involves using implants and instrumentation to provide support to the affected area of the spine while allowing the bones thereof to fuse. The technology initially evolved using bond chips around and on top of an area of the Spine that had been roughened to, simulate a fracture in its consistency. The area, having encountered the bone chips, would then proceed to heal like a fracture, incorporating the bone chips. However, surgical procedures dealing with the spine present notable challenges. For example, bioengineers have been required to identify the various elements of the complex motions that the spine performs, and the components of the complex forces it bears. This complexity has made it difficult to achieve adequate stability and effective healing in surgical procedures directed to the spine.  
           [0007]    One surgical technique provided by Cloward, involves cutting a dowel type hole with a saw across or through the moveable intervertebral disc and replacing it with a bone graft that was harvested from the hip bone. This procedure limits motion and mobility and results in a fusion of the adjacent vertebral bodies. However, as a result of the complex motions of the spine, it is often difficult to secure the dowel from displacing. Further, it has become apparent over time, however, that this particular technique does not always yield a secure fusion.  
           [0008]    Other techniques have been developed that involve the placement of various hardware elements, including rods and hooks, rods and screws and plates and screws. The dowel technique also has advanced over the past five years or so, with dowels being fabricated from cadaver bone or, metals such as titanium or stainless steel. These techniques, whether using hardware, dowels or some combination thereof, have a common goal to enhance stability by diminishing movement, thereby resulting in or enhancing the potential of a fusion of adjacent vertebral bones. For example, in one of these other techniques, the disc is removed and adjacent vertebrae are positioned in a stable position by placing a plate against and traversing them, which plate is secured or anchored to each by means of screws.  
           [0009]    In another procedure, cages in the form of two parallel circular or rectangular devices are made out of a material such as titanium or stainless steel and these devices are fenestrated. Bone is packed in the center of the devices that will heal to adjacent bone through each fenestration. In this procedure, the disc space is distracted so all ligamentous structures are taut and the bones are held in their normal maximal position of distraction. Because the cages are implanted in spongy bone, they are more likely to collapse the surrounding bone, thus resulting in loss of distraction and subsequently cage dislodgment.  
           [0010]    U.S. Pat. No. 5,591,235 reports a certain spinal fixation device and technique for stabilizing vertebrae. In this technique, a hollow screw is inserted into a hole, preferably a hole saw recess, in each adjoining vertebrae. A channel is cut into the vertebrae, which is lined up with corresponding axial slots in the screw. A rod is inserted into the channel and so as to pass through the axial slots in the screw. The rod is secured to each of the screws by means of a locking cap. The rod also is arranged so as to provide a bridge between the hollow screws in the adjoining vertebrae. Certain disadvantages have been surmised using such a device and technique. For example, it has become apparent that the trough in the vertebral bodies destabilizes some of the cortex of the vertebrae body wall, which is the strongest component.  
           [0011]    Thus, it would be desirable to provide a new apparatus, system and methods for spinal fixation that enhances healing of the bone while providing structural support to the spine. It would be particularly desirable to provide such an apparatus, system and method that would involve the use of open surgical, or minimally invasive surgical techniques as well as a technique in which the implant burrows in the bone spine, traverses across the disk space, and ends in an adjacent or neighboring vertebrae or vertebras, providing limited or no protrusions. It also would be desirable to provide such an apparatus, system and method where the implant is retained within the bone without requiring contour-varying external vertebral wall fixation as compared to conventional devices, as such a device would avoid many of the problems associated with conventional devices such as blood vessel injury, erosion into organs, as well as placement near nerves.  
         SUMMARY OF THE INVENTION  
         [0012]    I have now found new methods and apparatus for fixing adjacent vertebrate of a spine. The methods and apparatus of the invention utilize a new implant member, which preferably is arcuate, and avoids the associated problems with prior cage or straight rod and screw systems. It is within the scope of the present invention for the implant member to have any geometric shape or configuration consistent with the intended use including a straight member.  
           [0013]    Preferred methods of the invention for stabilizing adjacent vertebrae of the spine, include the steps of providing a positioning apparatus including two guide sleeves, each guide sleeve having a long axis and locating the two guide sleeves with respect to the adjacent vertebrae such that a vertex formed by the long axis of each guide sleeve is located in the intervertebral space for the adjacent vertebrae. The method further includes forming an aperture in each of the adjacent vertebrae using the guide sleeves and inserting an implant into the apertures formed in each of the adjacent vertebrae so that the implant extends between the adjacent vertebrae and through the intervertebral space.  
           [0014]    Preferably, the aperture formed in the vertebrae is arcuate and the implant being inserted also is arcuate. The arcuate aperture in each vertebrate can be suitably formed by drilling or other ablation. More particularly, an initial aperture can be drilled in each of the adjacent vertebrae to create intersecting apertures with convergent paths within the intervertebral space; and the initial aperture then enlarged to receive the implant. That enlarging of the initial aperture can be suitably performed by a variety of procedures, e.g. by using a drill bit, a reamer, an awl, impaction drill, shape memory coring device, or, curved coring device, or the like.  
           [0015]    The step of forming an aperture also can further include inserting a guide member, after drilling of the initial aperture, into one of the guide sleeves, down through the initial aperture in one adjacent vertebrae, through the intervertebral space and into the initial aperture in the other adjacent vertebrae; and advancing an aperture enlarging device over the guide member so as to enlarge the initial aperture. In this case, the aperture enlarging device is suitably a curved reamer or a curved drill bit, and the curved reamer or the curved drill bit is advanced over the guide member so as to form an arcuate aperture in each of the adjacent vertebrae. It also should be appreciated that multiple vertebral holes can be created using the same methods as disclosed herein. In that manner, multiple arcuate implants can be placed, e.g. if greater mechanical stability is considered desirable.  
           [0016]    The positioning apparatus can further include a cross member and an intervertebral spacer, preferably where the guide sleeves are pivotally mounted to the cross member and the intervertebral spacer is spaced from the cross member and interconnected thereto at about a mid point between the pivot points for the guide sleeves. In this case, the stabilizing method can further include locating the intervertebral spacer in the intervertebral space between the adjacent vertebrae; and maintaining alignment of the guide sleeves with respect to the adjacent vertebrae so that a consistent angle is maintained between the guide sleeve and the vertebrae during at least a portion of said forming of the aperture. The intervertebral spacer also can be configured so as to provide, protection to the spine during the drilling when disposed in the intervertebral space.  
           [0017]    In an alternative embodiment, the positioning system being provided includes a cutter bracket system and a curved drilling sub-system affixed thereto. The cutter bracket system includes a pivot arm whose pivot point is disposed between the adjacent vertebrae opposite the intervertebral space. More particularly, the pivot point is at about the midpoint between the adjacent vertebrae. The curved drilling sub-system is affixed to the pivot arm such that as the pivot arm rotates about the pivot point the curved drill sub-system follows an established cutting path. In a more specific embodiment, the drilling sub-system is affixed proximal or at the distal end of the pivot arm. The positioning apparatus according to the alternative embodiment can further include a mechanism that temporarily secures the cutter bracket system to the adjacent vertebra to be fused and which positions and maintains the pivot point at the desired location. Also, the curved drill subsystem can include a curved cannula, a flexible member running through the curved cannula and a cutting burr secured to an end of the flexible member.  
           [0018]    As, to the step of forming an aperture using a positioning system according to the alternative embodiment, this step includes rotating the pivot arm in one direction about the pivot point so the curved drilling sub-system forms an aperture in one of the adjacent vertebrae and rotating the pivot arm in another direction about the pivot point so as to form an aperture in the other of the adjacent vertebrae. Ina more specific embodiment, the step of forming further includes remounting the curved drilling sub-system to the pivot arm before rotating the pivot arm in the another direction so a cutting element of the curved drilling subsystem is aligned for the direction of movement.  
           [0019]    As to inserting the implant, the method step includes successively drawing a portion of the implant through the arcuate aperture in one adjacent vertebrae, through the intervertebral space and into the arcuate aperture of the other adjacent vertebrae. In a specific embodiment, the step of inserting includes securing one end of a guide wire to an end of the implant; passing, a free end of the guide wire through the arcuate aperture in one of the adjacent vertebrae through the intravertebral space and through the arcuate aperture in the other adjacent vertebrae, and pulling on the guide wire free end to thereby successively draw the portion of the implant.  
           [0020]    In another embodiment, the step of inserting includes inserting a beginning end of the implant into an entrance opening of one of the adjacent vertebrae; applying a force to the portion of the implant extending from the entrance opening so as to drive the implant beginning end though the arcuate aperture in the aperture of said one of the adjacent vertebrae, through the intervertebral space and into the arcuate aperture in the other of the adjacent vertebrae.  
           [0021]    The implant being inserted into the final aperture is made from one or more of a metal (e.g., titanium or stainless steel), bone, morphogenic protein (including a combination of bone and bone morphogenic protein), carbon fiber composite, nitinol or biodegradable materials such as polyactic acid or polyglycolic acids and copolymers and other derivatives thereof, or collagen and collagen coated metal or bone. The implant also may comprise an in situ-formed plug where the aperture acts as a mold for an epoxy or other polymer-based system. Also, the implant can be solid or hollow and arranged with or without ingrowth fenestrations and screw holes for post-insertion securement. The implant also can be configured so the implant includes a first and a second section, where a distal end of each, of the first and second sections is configured so as to be capable of being secured together. For such an implant, the method further includes the steps of inserting the first section into the aperture in one of the adjacent vertebrae so that the distal end therefore is disposed in the intervertebral space; inserting the implant second section into the aperture in one of the adjacent vertebrae so that the distal end therefore is disposed in the intervertebral space; and securing the distal ends of the first and second sections together. The implant sections being inserted can be arcuate with a radius substantially the same as the arcuate aperture or substantially straight. In particular embodiments, the distal ends of the implant sections are secured to each other by e.g. a nut, bolt, pin, expansion or press-fit device, or interlocking member on the end of each section. Other stabilization methods also can be employed. For instance, a plate can be applied to the vertebrae surface with attachments at each end of the tunnel traversed by an implant in accordance with the invention.  
           [0022]    Another method of the present invention for stabilizing adjacent, vertebrae of the spine includes the step of forming a common channel in and between the adjacent vertebrae and inserting a biscuit implant in the common channel so as to bridge between the adjacent vertebrae. In more specific embodiments, the step of forming includes simultaneously cutting a slot, preferably an arcuate slot, in each of the adjacent vertebrae so as to form the common channel and providing a device configured so as to be capable of simultaneously cutting the slot in each, of the adjacent vertebrae. Also for said step of inserting, the biscuit implant can be further configured so as to include a spacer element that is received in the intervertebral space between the adjacent vertebrae when the biscuit is disposed in the common channel.  
           [0023]    In another alternative aspect of the invention, a diskectomy can be performed and a stabilizing wedge (inner) implant inserted between the vertebrae. The wedge (inner tool) establishes lordosis, provides a construction reference, and carries on it the stabilizing wedge implant. Retracted stop-cut blades on the inner tool are then engaged, cutting into the vertebrae in the vertical plane. A hole saw cane be used to create a circular cut in the vertebrae to facilitate insertion of the outer implant. Once the cut is complete, the bone harvested in the tubular cutter can be manipulated into the implant. A circular (outer) implant is then inserted over the inner tool. The outer tool then references the position of the inner tool and guides the implant into place. After the two implants nest together along a key and groove, the outer tool is re moved. A fenestrated circular member then replaces the outer cutting tool and the inner tool is rotated about 90 degrees and then removed. Working together, the two rotated implants capture the vertebral body sections, which are now rotated about 90 degrees and through their many holes, provide blood exchange with the adjacent bone to accomplish fusion.  
           [0024]    Also featured is a system and apparatus embodying the described methods or techniques for internal fixation of the spine.  
           [0025]    Other aspects and embodiments of the invention are discussed below.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0026]    [0026]FIG. 1A is a schematic view of a positioning jig according to the present invention;  
         [0027]    [0027]FIG. 1B is a front view of the intervertebral spacing member of FIG. 1A;  
         [0028]    [0028]FIG. 2A is a schematic view of the positioning jig of FIG. 1A disposed about two vertebral bodies;  
         [0029]    [0029]FIG. 2B is a schematic view of an alternative positioning jig according to the present invention disposed about two vertebral bodies;  
         [0030]    FIGS.  3 A-E are schematic views that illustrate the various steps of the process to form a hole in each vertebral body for implanting a fixating member therein;  
         [0031]    [0031]FIGS. 4A and 4B are schematic views that illustrate alternate ways of making a hole in each vertebral body;  
         [0032]    [0032]FIG. 4C is a plan view of a Romano device for making a curved hole. Shown is one of the two opposed curved cutter guides and a flexible cable having a cutting bit attached to one end;  
         [0033]    [0033]FIG. 5A is a schematic view of one device for implanting the fixating member;  
         [0034]    [0034]FIG. 5B is a schematic view of alternate device for implanting the fixating member;  
         [0035]    [0035]FIG. 6A is a schematic view of the vertebral bodies illustrating the implantation of the fixating member in the holes;  
         [0036]    [0036]FIG. 6B is a schematic view of the vertebral bodies to illustrate securing of the fixating member;  
         [0037]    FIGS.  7 A-C are schematic views of the implantation of a fixating member made from nitinol;  
         [0038]    FIGS.  8 A-B are exemplary cross sectional views of a guide sleeve including a mechanical guide to guide the nitinol fixating member during insertion;  
         [0039]    [0039]FIG. 9 is a schematic view of the vertebral bodies with a fixating member according to a second aspect of the present invention;  
         [0040]    [0040]FIG. 10 is a schematic view of the vertebral bodies with a fixating member according to a third aspect of the present invention;  
         [0041]    [0041]FIG. 11A is a schematic view of a cutter bracket system according to the present invention;  
         [0042]    [0042]FIG. 11B is a schematic view of a curved drill used with the cutter bracket system of FIG. 11A;  
         [0043]    [0043]FIG. 12A is a perspective view of a common channel cutting device according to the present invention;  
         [0044]    [0044]FIG. 12B is a perspective view of a portion of the channel cutting device of FIG. 12A with the cutting implement extended;  
         [0045]    [0045]FIG. 12C is a schematic view of the channel cutting device of FIG. 12A disposed on two vertebral bodies;  
         [0046]    [0046]FIG. 12D is a schematic view of the two vertebral bodies to illustrate the implantation of the biscuit implant in the cut common channel;  
         [0047]    [0047]FIG. 12E is another view: of the two vertebral bodies to illustrate the implantation of the biscuit implant including a spacing element in the cut common channel  
         [0048]    [0048]FIG. 12F is a perspective view of the biscuit implant of FIG. 12D;  
         [0049]    [0049]FIG. 12G is a side view of the biscuit implant with spacing element of FIG. 12E;  
         [0050]    FIGS.  12 H-K are perspective views of various exemplary biscuit implants according to the present invention;  
         [0051]    FIGS.  13 A- 13 F illustrate an alternative implant system of the invention; where FIG. 13A is an isometric view of an inner implant, FIG. 13B is an isometric view of an outer implant, FIG. 13C is a lateral view showing a preferred positioning of the implant system, FIG. 13D is an anterior view of the outer implant within which the inner implant is secured, FIG. 13F is an anterior view of the outer and inner implant after rotation, and FIG. 13F is a perspective view of an embodiment of the implant system;  
         [0052]    [0052]FIG. 14A is a schematic view of an inner tool positioned within the intervertebral disk space;  
         [0053]    [0053]FIG. 14B is an isomeric view of the inner tool;  
         [0054]    [0054]FIG. 14C is a cross-sectional view of the inner tool, with retracted and extended stop-cut blades;  
         [0055]    [0055]FIG. 15 is a schematic view of the inner and outer tool system positioned in relation to the vertebral bodies; and  
         [0056]    [0056]FIG. 16 is a schematic view showing bone-to-bone with no gap application. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0057]    Referring now to the various figures of the drawing wherein like reference characters refer to like parts, there is shown in FIGS.  1 - 2  various schematic views of a  10  drill guide or positioning jig  100  that positions or aligns the drill bits before making the holes in each of the vertebral bodies  2 . The positioning jig  100  includes two guide sleeves  102 , a cross member  104  and an intervertebral spacing member  110 . Each guide sleeve  102  preferably is a hollow tubular member having a lumen or passage therein for receiving and guiding the means for forming at least the initial aperture in the adjacent vertebrae such as a drill bit  150  (FIG. 3B). As indicated elsewhere herein, the aperture may be formed using other techniques such as the ablation of bone by an energy source, e.g., high-pressure water, high-pressure air, ultrasound, or a laser. As such, it shall be understood that the internal sizing and configuration of the guide sleeves is established to accommodate the particular mechanism used for forming the aperture.  
         [0058]    The guide sleeves  102  are mounted to the cross member  104  in such a way that they are each pivotal about the cross member and so each can be secured or locked in a particular angular position with respect to the cross member. Although a single mounting/pivot point  106  is illustrated, it is within the scope of the present invention for the cross member  104  and each guide sleeve  102  to be configured with a plurality or more of such pivot/mounting points. In an exemplary embodiment, the cross member  104  and guide sleeves  102  are constructed from stainless steel; and each guide, sleeve is pivotally secured to the cross member by screws.  
         [0059]    The distal end  108  of each guide sleeve  102  is configured for mechanically engaging a surface, edge, comer or other surface artifact or feature of the vertebral body.  2 . In an exemplary embodiment and as more clearly illustrated in FIG. 3A, the guide sleeve distal end  108  is configured or arranged with a cutout that is designed to accept the corner of the vertebral body  2 . Additionally, the cutout area and thus the distal end  108  also are configured with a plurality or more of teeth  107 . The teeth  107  are configured and arranged so the teeth bite into the bony surface of the vertebral body when the comer of the vertebral body  2  is received within the cutout area of the guide sleeve distal end  108 . Each guide sleeve is suitable about 20 cm in length, although suitable and preferred guide sleeve length s can vary-depending on the method of access.  
         [0060]    The intervertebral spacing member  110  includes an intervertebral spacer  112  and an interconnecting member,  114  that mechanically interconnects the cross member  104  and the intervertebral spacer  112 . The interconnecting member  114  is secured to or, retained by the cross member  104  so as to be maintained in fixed relation with respect to the pivots  106  for both guide sleeves  102 . In an exemplary embodiment, the interconnecting member  114  is located at about the midpoint of the cross member  104  between the pivots  106 . The interconnecting member  114  also is secured to the cross member  104  so the intervertebral spacer  112  is positioned between the distal ends  108  of the guide sleeves  102 . More particularly, the interconnecting member  114  is positioned so the intervertebral spacer  112  is received within the distended disc space between the adjacent vertebral bodies  2 .  
         [0061]    In an exemplary embodiment, the interconnecting member  114  is in the form of a rod and the cross member  104  is configured with a through aperture  109  in which the rod is received. This configuration provides a mechanism by which the interconnecting member  114  is put into and maintained in fixed relation with respect to the pivot points  106 . It is within the scope of the present invention for the cross member  104  to have any geometric shape, as well as being hollow or solid in construction, that is otherwise consistent for the intended use of the positioning jig  100 .  
         [0062]    The interconnecting member  114  also can be configured so as to prevent rotational motion of the interconnecting member with respect to the through aperture  109 . For example, the rod and through aperture  109  may be configured so as to include a flat side in a portion of the circumference for the through aperture and the rod. Alternatively, the through aperture and rod maybe arranged; with a key and notch arrangement to prevent rotation.  
         [0063]    When the guide sleeves  102  are secured to the cross member  104  and each guide sleeve distal end  108  mechanically engages the surface of the, vertebral body  2 , the guide sleeves are arranged so they maintain a consistent angle with respect to the vertebral body. Additionally, and in combination with the intervertebral spacer  112 , this arrangement provides a three-point reference that ensures appropriate angles, and alignment are maintained. Additionally, such a configuration establishes a condition whereby the positioning jig  100  locks down on the motion segment of the spine to be stabilized.  
         [0064]    The use of the positioning jig  100  in the method of the present invention can be understood from the following discussion with reference to FIGS.  1 - 6 . It shall be understood that as preparation for spinal fixation/stabilization the medical personnel (e.g., surgeon) obtains access to the motion segment or structures to be stabilized or fused using any of a number medical/surgical procedures known to those skilled in the art. In this regard, this would involve such actions as preparing the disc space and performing retraction of vessels, muscles and nerves.  
         [0065]    In this regard, it should be recognized that the method and positioning jig  100  of the present invention are particularly advantageous when performing a minimally invasive surgical procedure. The minimally invasive procedure can be performed through three holes, each about 1 inch across, in the abdomen and allows for the procedure to be executed without visualizing the vertebrae. Thus, and in contrast to a number of prior procedures, methods of the invention are not limited to an anterior presentation. Such methods of the invention also can be performed through a posterior, posteriolateral or pedicular approach.  
         [0066]    In addition, when using a nitinol implant, the positioning jig  100  allows the implant to be properly positioned for and during insertion thereof. After gaining access, the surgeon also could scrape out the material from the failed disc or use this disc or its space as a reference point.  
         [0067]    As preparation, the surgical personnel also select an intervertebral spacing member  110  that is appropriately sized so it can accommodate the distended disc space. The intervertebral spacer  112  portion of the intervertebral spacing member  110  is inserted into the intervertebral space  4  between the adjacent vertebrae. In this way, the approximate center or mind point of, and the staring point on, the adjacent vertebrae to be fused or stabilized is thereby established, or defined.  
         [0068]    The intervertebral spacer allows the surgeon to maintain extremely accurate disk spacing. The intervertebral spacer also protects the spinal cord from accidental drilling or boring. If desired, the spacer can be made of bone and can be made with or without a through hole. The spacer design is suitably based on a construction that facilitates the selected technique for creating an arcuate aperture. An intervertebral spacer that is comprised of bone offers the advantage of being able to remain implanted following the procedure.  
         [0069]    Other materials also can be suitably employed to form an intervertebral spacer. The placement of an implant provides a central axis through which a compressible, functional intervertebral disk member can be reliably secured. The artificial disk member suitably can be made from a variety of compressible materials, including e.g. silicon, elastomeric polymers, polyurethanes and copolymers thereof, hydrogels, collagen or bioabsorbables.  
         [0070]    Next, the positioning jig  100  is locked down on top of the motion segment to be immobilized, as more clearly shown in FIG. 2. In this regard, the surgical personnel slide the interconnecting member  114  of the intervertebral spacing member  110  into an aperture  109  provided in the cross member  104 . In this way, the aperture  109  in the cross member  104  positions the intervertebral spacing member  110  between the distal and proximal ends of the drilling guides  102 . Although illustrated as being located in the mid-point, the intervertebral spacing member can be centrally located or offset to either side to enable drilling of holes in the vertebrae laterally against the spine.  
         [0071]    Preferably, the aperture  109  in the cross member  104  is configured so as to prevent the cross member  104  or intervertebral spacing member  110  from rotating with respect to each other. For example, a portion of the aperture  109  and a portion of the interconnecting member  114  is flattened so as to predefine a given orientation. Alternatively, the aperture  109  is configured with a notch or keyway and the interconnecting member  114  is configured with a key or protrusion that is received in the keyway.  
         [0072]    As provided above, the distal end  108  of each guide sleeve  102  is preferably configured so each distal end mechanically engages the surface of the vertebrae  2 . In the illustrated embodiment, the distal end  108  is arranged with a cutout area that is designed to accept the corner of the vertebrae  2  as more clearly illustrated in FIG. 3. As also shown in FIG. 3, the cutout area is provided with a plurality of teeth  107  that bite into the bony surface of the vertebrae  2 . It is within the scope of the present invention for the guide sleeve distal end  108  to be disposed at other positions on the surface of the vertebrae  2  such as that illustrated in FIG. 6A.  
         [0073]    After locating the positioning jig  100  with respect to the motion segment to be fused, the surgical personnel secure the guide sleeves  102  at each of the pivots  106 . This advantageously ensures that the appropriate angles and, alignment of the guide sleeves  102  with respect to the vertebrae  2  are maintained as well as locking the positioning jig  100  down on the motion segment to be fused.  
         [0074]    As noted above, an initial through hole is formed in each vertebrae  2  by any of a number of methods, e.g. by a drill, by ablation of the material comprising the vertebrae using an energy source such as RF, ultrasonic waves, cryogenics and water jets or by any other as known to those skilled in the art and which can be adapted for use with the positioning jig  100  of the present invention. For purposes of describing the present invention however the following discussion is simplified to describing the terms of drilling the initial aperture or initial through hole  6  in the vertebrae  2 . This, however, shall not be inferred as being a limitation on the method according to the present invention to only drilling.  
         [0075]    A fixed or flexible drill bit  150  is inserted into and down each drill guide  102  so the ends thereof contact the surface of the vertebrae  2 . The surgical personnel operate the drill bits in accordance with accepted techniques so as to create an initial through hole  6  in each of the vertebrae. Preferably, and as shown in FIG. 3B, the through holes  6  being created are intersecting with convergent paths within the intervertebral space  4 . In other words, the projection of the long axis for each of these through holes  6  intersects so the vertex created by intersection of the long axes is located within the intervertebral space  4 .  
         [0076]    The initial through hole  6  initially formed in each vertebrae  2  has a diameter much less than that of the implant  160  that is to be used to stabilize or fuse the motion segment. After forming the initial through hole  6 , the surgical personnel insert a guide wire  170 , such as a 0.093 inch nitinol guide wire, into and down one guide sleeve  102  and through the through hole in one vertebrae  2 . The surgical personnel continue to push the guide wire  170  across the intervertebral space  4  and into the through hole  6  in the other vertebrae as more clearly illustrated in FIGS.  3 C-D. In a particular, embodiment the guide wire  170  is configured with a slightly curved tip. The guide wire  170  is generally in a curved configuration when disposed in the through hole  6  of the vertebrae  2 .  
         [0077]    A flexible/curved drill bit  152  is then passed through one of the guide sleeves  102  and over the, guide wire  170  so as to form a curved through aperture  6   a  in each of the vertebrae as shown in FIG. 3E. The curved or arcuate through aperture  6   a  is formed with a cross-section that complements the cross-sectional shape of the implant  160 . Preferably, the arcuate through aperture is sized to be slightly smaller than that of the implant  160  so there is a friction; snug or interference fit between the implant  160  and the arcuate through aperture  6   a.    
         [0078]    In this way, when the implant  160  is inserted into the arcuate through aperture  6   a , it will remain therein without further need of screws or other artifacts or devices for securing the ends of the implant to each vertebrae  2 . It is within the scope of the present invention, however, for screws or other devices be provided as an additional measure or protection for securing the implant  160  within the vertebrae  2 .  
         [0079]    Alternatively, the curved or arcuate through aperture  6   a  is formed using any of a number of other techniques as described below. In one case, and as shown in FIG. 4A, the arcuate through aperture  6   a  is formed in the vertebrae  2  by using a flexible reamer  200 . The flexible reamer is run or passed over the guide wire  170  to ream or core out the arcuate through aperture  6   a . The cancellous bone of the vertebrae  2  is relatively soft so that it is possible to use a reamer to core the hole aperture. Similarly, and as shown in FIG. 4B, a curved awl or a progressively larger guide wire  170   a  can be used to punch a curved hole in the vertebrae. FIG. 4C shows a Romano device suitable for drilling a curved bore such as that disclosed in U.S. Pat. No. 5,700,265 the teachings of which are incorporated herein by reference. A swing arm  830  and curved guide arm  834  navigate the drill bit  840  through a defined radius of curvature.  
         [0080]    In addition to the mechanical devices for drilling, punching or reaming out the arcuate through aperture  6   a , the discharge end of an energy source, such as RF, ultrasonic, cryogenics laser and water, can be located within the guide sleeve  102  and passed over the guide wire so as to form the arcuate through aperture. For example, the nozzle(s) of a high pressure water source can be arranged so the discharging or ice crystal water impinges on the bony material of the vertebrae  2  and the material is thereby ablated away to form the arcuate through aperture  6   a . Similarly, laser light, RF waves or ultrasonic waves can be focused on the bony material within the vertebrae  2  to form the arcuate through aperture  6   a.    
         [0081]    The foregoing describes the formation of the arcuate through aperture  6   a  that receives the implant  160  by passing a mechanism from the entrance to the exit of the initially formed through hole  6 . It is within the scope of the present invention, for a guide to be located within the intervertebral space  4  so the curved through aperture is formed by drilling from the intervertebral space out, rather from the outside in.  
         [0082]    There is shown in FIG. 2B a schematic view of an alternative positioning jig  100   a  that is disposed about two vertebral bodies. This alternative positioning jig  100   a  is similar to the positioning jig  100  of FIG. 2A except for the guide sleeves. As such reference shall be made to the foregoing discussion regarding FIGS.  1 - 2 A for further details as to the common features for these two positioning jigs  100 , 100   a . In thee illustrated embodiments, a guide wire  170  is being inserted into one of the guide sleeves  102   a  and  4  is configured so that the proximal end of the guide wire  170  is arranged so as to include an impact fitting to protect the guide wire about the proximal end.  
         [0083]    In the alternative embodiment, the guide sleeves  102   a  are tubular members that are configured so that at least a portion  103  of each guide sleeve is arcuate. In the illustrated embodiment, the arcuate portion  103  of the guide sleeve  102   a  is proximal the vertebral body such that one end of the arcuate portion comprises the distal end  108  of the guide sleeve that is in contact with the vertebral body  2 . It is contemplated, however, that the guide sleeve can be configured so as to be substantially arcuate between the vertebral body  2  and the cross member  104 .  
         [0084]    The arcuate shape provides a convenient mechanism that can simplify the above-described process for making an arcuate through hole  6   a  in the vertebral body  2 . The arcuate shape also provides a mechanism to orient the tool, device or apparatus being inserted into the guide sleeves  102   a , for example the drill or high energy source for forming the initial through hole, so use of the tool etc. is more convenient to the surgical personnel performing the procedure.  
         [0085]    After the arcuate through aperture  6   a  is formed, then the implant  160  is inserted therein so it is disposed within the through aperture  6   a  in one vertebrae  2 , passes or extends across the intervertebral space  4  and disposed within the through aperture  6   a  of the other vertebrae. The implant  160  is made from any one ore more suitable materials such as e.g. a metal such as titanium or stainless steel, bone, bone with bone morphogenic protein, carbon fiber composite, nitinol. The implant being inserted into the final aperture is made from one or more of a metal (e.g., titanium or stainless steel), bone, morphogenic protein (including a combination of bone and bone morphogenic protein), carbon fiber composite, nitinol or biodegradable materials such as polyactic acid or polyglycolic acids and copolymers and other derivatives thereof, or collagen and collagen coated metal or bone. The implant also may comprise an in situ-formed plug where the aperture acts as a mold for an epoxy or other polymer based system. The implant, preferably is curved so it generally conforms; to the radius of the arcuate through apertures  6   a  in each vertebrae  2 , however, other geometric shapes are contemplated that are consistent with the intended use including straight members.  
         [0086]    The implant  160  suitably can be provided with a circular or oval shape. The diameter or width of the implant can vary over a relatively broad range and may depend on the size of the vertebrae and desired implant stiffness. More specifically, in preferred embodiments, the implant may suitably range in diameter or width from about 5 mm or as small as is mechanically sufficient, to sizes approaching that of large intramedullar rods, or about, 22 mm. Preferably the implant should have a diameter or width from about 7 to 12 mm, more preferably about 9 mm. The implant also preferably should have an appropriate radius of curvature such that both vertebrae are engaged while staying well clear of the spinal cord. That radius preferably is about 1.5 inches, as referenced from the arcuate implant&#39;s inner radius.  
         [0087]    The implant  160 , is suitably a solid or hollow (e.g., tubular) member. The implant can be suitably configured so as to have fenestrations  166  (FIG. 6A) that allow biologic elements of bone to traverse through it or across it, thereby enhancing potential for stability and for cross-segmental healing. In particular, the implant  160  can have cutting fenestrations similar to a cheese grater, allowing fragments of bone to be pared off as the implant  160  is being inserted into the through apertures in either vertebrae. A fenestrated implant  160  that is hollow can be filled with bone chips or synthetic or engineered bone healing materials, allowing for bone ingrowth, and a cheese grater type of implant with cutting fenestrations can add freshly pared fragments of bone to the packed bone chips or other materials to enhance bony ingrowth. Additionally, the fenestrations,  166  can be surface dimples, sharpened edges, cutting indentations or other alterations in the exterior surface of the implant  160 : to enhance or further ensure the secure fitting of the implant into the arcuate through aperture  6   a  as well as for facilitating bone growth.  
         [0088]    The particular technique for inserting the implant  170  into the through aperture  6   a  of a vertebrae  2  for fixing of the movable segment is dependent upon the material used to make the implant. For an implant  160  made from titanium, and as shown in FIG. 5A, a threaded end  162  (e.g., a female threaded end) is provided at one end of the titanium implant  160  for threaded engagement with the threaded counterpart (e.g., male counterpart) at one end  172 , the distal end of the guide wire  170 . This can be accomplished for example by removing at least one of the guide sleeves  102  from the entrance opening of one through aperture  6   a  so the threaded end  172  of the guide wire is exposed. The implant threaded end  162  is then screwed onto the guide wire threaded end  172  and the so tethered end  162  of the implant  160  is positioned at the entrance opening of the through aperture  6   a  and pulled into place by pulling on, for example, the proximal end  174  of the guide wire  170 .  
         [0089]    Preferably, the distal end  108  of one guide sleeve  102  remains engaged at the entrance opening for the other through aperture  6   a , so as to serve as a bearing surface or brace for the guide wire  170  as it is being pulled out of this entrance opening. This is done to keep the guide wire  170  from cutting through the cantellous bone when the guide wire is under tension because of the pulling action. Alternatively, a tubular member with a rounded surface may be advanced over the guide wire and through the remaining guide sleeve  102 , to ensure that the guide wire pulls from the appropriate angle. This technique is suitable for use with metallic and other rigid material type of implants.  
         [0090]    Alternatively, and as shown in FIG. 5B, a pushing mechanism is, useable for inserting or tamping the implant  160  into the arcuate through apertures  6   a . In the illustrated embodiment, an arcuate pushing mechanism  300  is configured so as to rotate about an axis of rotation that corresponds generally to the center of the circle subscribed by the arcuate through apertures  6   a . The arcuate pushing mechanism applies a force to the distal end of the implant  160  so as to drive the proximal end of the implant through the arcuate through aperture  6   a  in one vertebrae, across the intervertebral space  4  and into the arcuate through aperture  6   a  of the other vertebrae  2 .  
         [0091]    In the illustrated embodiment; the positioning jig  100  is removed except for the intervertebral spacing member  110  or bone intervertebral spacer where the intervertebral spacer  114  remains disposed in the intervertebral space  4 . The arcuate pushing mechanism  300  is attached to the end of the interconnecting member  112  by means of a jig or other member or device so the pushing mechanism can rotate about the end of the interconnecting member. In this way, the arcuate arm  302  of the pushing mechanism  300  can be advanced by having one of the surgical personnel rotating it about its axis of rotation. Alternatively, or in addition to the surgical personnel can strike one end  304  of the arm  302  with a mallet or other weighted object so as to drive the implant  160  into the through aperture  6   a . For example, striking may be required near the end of the insertion process when there is maximum friction being developed on the inserted implant. The arm  302  also may be configured with a curved support sleeve  306  in which the implant is received.  
         [0092]    Although the implant  160  and through apertures  6   a  are sized so that there is preferably at least a snug fit therebetween, as an extra measure of protection, the implant  160  may be further secured in place at its ends by means of screws  400  as shown in FIG. 6B. Alternatively, the implant  160  may be secured in place by a plate, screw, staple or a combination thereof. Additionally, the implant can be arranged so as to include a biting or expansion element(s) that can be driven out in a lateral direction so as to engage the bony structure of the vertebrae  2 .  
         [0093]    As provided above, and as shown in FIGS.  7 A-B, the implant  160   a  can be made from nitinol. A nitinol implant  160   a  is advantageous in that a curved nitinol implant can be straightened as shown in FIG. 7B prior to insertion into the arcuate through apertures  6   a . The straightened nitinol implant  160   a  can be advanced down one of the guide sleeves  102  in any of a number of ways, for example, by pushing or pulling, so it can be driven into the arcuate through apertures  6   a . The nitinol implant  160   a  also can be inserted into the arcuate through apertures  6   a  in any of the other fashions described above in connection with FIGS.  5 A-B.  
         [0094]    Additionally, d sharp edge of the nitinol implant can be used like a reamer or awl to thereby enlarge the initial through hole  6  as the implant is being inserted or driven into the initial though aperture. This avoids the intermediate step of drilling or otherwise forming the arcuate through aperture  6   a  before, insertion of the implant.  
         [0095]    [0095]FIG. 7C depicts an illustrative device  400  for inserting a nitinol implant  160   a , which device includes a guide tube  402  and a pusher  404 . The distal end  408  of the guide tube  402 , similar to the positioning jig guide sleeve distal end  108  is preferably configured so as to be capable of releasably mating with a surface, or portion thereof, of the vertebrae  2  where the entrance of the arcuate through aperture  6   a  is located. In the illustrated embodiment, the guide tube distal end  408  is configured with a cut out so as to receive a corner of the vertebrae  2  therein.  
         [0096]    The distal end  408  is disposed on the vertebrae so that the lumen therein is aligned with the arcuate through aperture  6   a . The straightened nitinol implant  160   a  is inserted into the guide tube  402  along with the pusher  404  such that the distal end of the pusher is in contact with the proximal end of the nitinol implant. The pusher distal end  408  mates with the implant proximal end so as to maintain the orientation and direction of the nitinol implant  160   a  within the guide tube  402  so that it curves in the proper direction when it exits the guide tube. Alternatively, and as shown in FIGS.  8 A-B, the orientation of the nitinol implant  160   a  within the guide tube  402  is maintained with a flat side or with a key and notch type of arrangement.  
         [0097]    The pusher  404  includes a stop  406  to limit the travel of the pusher within the guide tube  402 . This in turn limits the amount of travel by the nitinol implant  160   a  so as to assure that the implant remains buried within the vertebrae and not exposed above the surface thereof.  
         [0098]    The placement of the implant according to the systems and methods of the present invention is advantageous in that the inserted implant resides completely within the vertebrae and, thus, within the spine, with no protrusion as compared with prior art devices. The implant and its placement provide a configuration which allows for some compression and cantilever force, but deters rotation and sheer. Additionally, in the present device, the moment arm is more centrally located within the spine as compared to prior devices. This central location also provides better stability in the face of torsion as compared to prior art devices.  
         [0099]    In general, the placement of an arcuate implant within the arcuate through apertures as described herein is particularly advantageous because the implant is buried to avoid contact with neurovascular structures. The placement provides load sharing and thus provides a better healing bio-mechanical environment and also provides a more advantageous fixation to avoid mechanically sub-optimal stresses. Also important, this method allows securement and avoids displacement of a spinal fusion or disk replacement device without modification or damage to the vertebrae&#39;s load bearing surface. Rather, one or two holes placed in or around the center of a vertebrae can be sufficient. The method and positioning jig  100  of the present invention also are advantageous in that the jig can be adapted for use in minimally invasive procedures. Additionally, the capability to position implants in accordance with the methods described herein enables avoiding blood vessel injury, erosion into organs and damage to adjacent nerves. This provides a significant advantage over presently existing technologies for disorders of the spine including fractures, arthritis, deformity, infections, tumor and mechanical spinal disorders.  
         [0100]    Although the foregoing method describes extending a single implant between adjacent vertebrae this description should not be construed as being a limitation as one or more implants can be positioned across each motion segment as described herein.  
         [0101]    In addition, the above described method can be further adapted so as to be used to secure an intravertebral prosthetic device  500  (i.e., artificial disc) such as that shown in FIG. 6A. According to this aspect of the invention, the implant is made partly or wholly from a flexible material such as silicon, elastomeric, polymers, polyurethanes and copolymers thereof, hydrogels, collagen, bioabsorbables, compositions, or a metallic spring or coil, so as to allow continual mobility betweent the vertebral bodies. One or more arcuate implants are provided which pass through a partial or complete hold in the prosthesis. This effectively prevents the prosthesis from becoming dislodged as well as maintaining its location and orientation within the disc space.  
         [0102]    [0102]FIG. 9 shows a method for inserting an implant  600  according to a second aspect of the present invention. A final through aperture  604  is formed in each of the vertebrae in accordance with above described techniques such as by drilling. Except that the through aperture  604  that receives the implant can be straight as shown in FIG. 9 or can be arcuate as shown in any of FIGS.  3 - 6 . As such, reference should be made to the foregoing discussion for further details regarding the formation of the final through aperture  604 .  
         [0103]    In the method according to the second aspect, the implant is in two sections  602   a,b . The proximal ends  608  of the two sections  602   a,b  are particularly configured so they can be mated to each other and interlocked to each other by means of an interference fit, a nut and bolt, a screw or a pin  606 . Thus, to fix the moveable segment, one section  602   a  is inserted into the through aperture  604  in one vertebrae  2  and the second section  602   b  is inserted into the through aperture  604  of the other vertebrae. The two sections  602   a,b  are inserted into their respective through apertures until the proximal ends  608  thereof are mated to each other. The pin  606  or other securing mechanism is then used to interlock the proxima ends and thus form a rigid implant. Although the sections are illustrated as being straight, it is within the scope of the present invention for the sections to arcuate so as to form an interlocking rod when assembled.  
         [0104]    [0104]FIG. 10 shows a method for inserting an implant  600  according to a third aspect of the present invention. According to this method, the apertures  702  in each vertebrae.  2  are formed so they extend from the vertebral space  4  outwards, penetrating into the cancellous bone. In this aspect, the apertures  704  formed in the vertebrae need not be through apertures. The implant  600  is like that described above for the second aspect of the present invention except that it is inverted from that shown in FIG. 9.  
         [0105]    There is respectively shown in FIGS. 11A,B a cutter bracket system  1100  and a curved bit or drill system  1120 , the curved drill system being for use with such a cutter bracket system. The cutter bracket system  1100  and curved drill system  1120  comprises another embodiment of the present invention for forming arcuate apertures  6   a  (FIG. 6A) in each of the adjacent vertebral bodies  2 . Referring now to FIG. 11A, the cutter bracket system includes temporary vertebral screws  1102 , pivot brackets  1104  and a pivot arm  1106 . In the illustrated embodiment, there is two temporary vertebral screws,  1102  that are each secured to the adjacent vertebral body  2  that is to be fused, however, this shall, not be construed as a limitation on the number of intervertebral screws. Extending from the temporary vertebral screws  1102  are the pivot brackets  1104 , which locate the pivot point  1108  with respect to the adjacent vertebral bodies  2  and maintain the pivot point in this orientation. The pivot arm  1106  is rotatably mounted to the pivot brackets  1104  using any of a number of mechanisms or techniques known in the art so that the pivot arm pivots or rotates about the pivot point  1108 . In an exemplary embodiment, the temporary vertebral screws  1102 , the pivot brackets  1104  and the pivot arm  1106  are e made from stainless steel although other materials are contemplated.  
         [0106]    The drill system illustrated in FIG. 11B includes a curved cannula  1122 , a flexible cable  1124 , a cutting head or burr  1126  and a motor  1130 . The flexible cable  1124  is rotatably disposed with the curved cannula  1122 . One end of the flexible cable  1124  is attached to the cutting burr  1112  and the other end of the flexible cable  1124  is attached to the motor  1130 , whereby the motor drives the cutting burr so it to rotates in the desired manner. In the illustrated embodiment, the motor  1130  also is mounted to an end of the curved cannula  1122 . In an exemplary embodiment, the curved cannula  1122  is made from stainless steel and the flexible cable  1124  is a flexible, teflon coated stainless steel cable, the cutting burr  1126  is made from stainless steel, although it is within the scope of the present invention for other materials to be used.  
         [0107]    The motor  1130  includes any of a number of devices known in the art that develop or provide a rotary output which can be used to rotate the flexible cable  1124 , such devices include, but are not limited to electric or pneumatic drills, DC/AC electric motors, or, pneumatic air driven rotary motors. It also is within the scope of the present invention for the drill system  1120  to further include a coupling member, as is known in the art, that operably and rotatably interconnects the flexible cable  1124  and the motor  1130  such that the motor is located remote from the curved cannula  1122 . In this way, any of a number of rotary devices such as a drill, that are readily available, can be adapted for use in the drill system  1120  of the present invention and interconnected to the flexible cable  1124  by means of the coupling member.  
         [0108]    The drill system  1120  is mounted or attached to the pivot arm  1106 , distal from the pivot point  1108 , by means of a connector  1128  on the curved cannula  1122 . The connector  1128  and the corresponding feature on the pivot arm  1106  comprises any of a number of mechanisms or devices known in the art (e.g., clamp type mechanism) by which the curved cannula can be removably secured to the pivot arm so there is essentially no relative movement therebetween. In a particular embodiment, the curved cannula  1122  is secured proximal to or at the distal end of the pivot arm. In this way when the drill system  1120  is secured to the cutter bracket pivot arm  1106  and the cutter bracket pivot arm  1106  is rotated about the pivot point  1108 , the pivot arm guides the curved drill system, in particular the cutting burr  1126  on a well-defined circular path.  
         [0109]    In use, the cutter bracket system  1110  is temporarily secured to the adjacent vertebral bodies  2  to be fused by the temporary vertebral screws  1102 . In particular the cutter bracket system  1110  is secured to the vertebral bodies  2  so that the pivot point  1108  is positioned so as to be spaced from a surface of the vertebral bodies and so as to be between the adjacent vertebral bodies, more particularly, at about the midpoint of the intervertebral space  4 . After securing the cutter bracket system to the vertebral bodies the curved drill system  1120  is mounted to the pivot arm as described above.  
         [0110]    The pivot arm  1106  is then rotated in one direction, for example a clockwise direction, about the pivot point  1108 . As the pivot arm  1106  is rotated thereabout, the cutting burr  1126  is operated so the drill system  1120  drills an arcuate hole in the vertebral body  2  on one side of the pivot point. The curved drill is then remounted so the cutting burr  1126  is on the other side of the pivot point  1108  and the pivot arm is rotated in a counter clockwise direction so the, drill system  1120  drills an arcuate hole in the vertebral body  2  on the other side of the pivot point  1108 . In an exemplary embodiment, the arcuate hole is completely formed when the pivot arm  1106  bottoms out or contacts the vertebrae being drilled. After forming the arcuate holes, the curved drill system  1120  is dismounted from the pivot arm  1106  and the cutter bracket system  110  is disconnected from the adjacent vertebral bodies  2 . In this way, two matched arcuate holes are formed in the adjacent vertebral bodies  2  that are sized and configured to receive an arcuate, implant being inserted therein Reference shall be made to the foregoing discussion for further details regarding such an arcuate implant or fixation member.  
         [0111]    Although the foregoing describes the formation of the arcuate holes or apertures  6   a  in the adjacent vertebral bodies  2  using a curved drill system  1120  mounted to the pivot arm  1106 , this shall not be construed as a limitation. As discussed hereinabove is within the scope of the present invention for other devices, mechanism or techniques, such as the above-described ablation energy sources, to be adapted for use with a rotating pivot arm  1106  to form the, through holes/apertures. As such these other devices, mechanisms or techniques are contemplated for use with the above described cutter bracket system.  
         [0112]    In accordance to another method of the present invention, a slot is cut in each of the adjacent vertebral bodies and a biscuit implant is inserted into the slots so as to also bridge across the intervertebral space  4 . Preferably the slots are simultaneously cut in the vertebral bodies so a common channel is formed therein. In an example embodiment, and with reference to FIGS. 12A,B there is provided a cutting device  1200  having a cutting implement, for example a circular blade  1206  that is rotated by a motor (not shown). The cutting device  1200  also is configured so the blade  1206  is moveable between a first position, where the blade is disposed within the device housing  1202  (FIG. 12A), and a second position where a portion of the blade extends outwardly a predetermined distance from an exterior side  1204  of the housing (FIG. 12B). Preferably, the exterior side  1204  from which the blade  1206  extends is configurable so that in one position the exterior side is substantially parallel to a tangent at the midpoint of the blade and further includes indicia  1208  representative of the mid-point of the blade.  
         [0113]    In use, and as shown in FIG. 12C the cutting, device  1200  is positioned so the device housing exterior side  1204  abuts or is adjacent to the vertebral bodies  2  and so the indicia  1208  representative of the blade midpoint is pointing towards the intervertebral space  4 , preferably about a midpoint between the adjacent vertebral bodies. The rotating circular blade  1206  is then moved from the first to the second position so as to simultaneously cut an arcuate slot in each of the adjacent vertebral bodies  2 . After cutting the slot, the circular blade  1206  is returned to the first position with the device housing  1202  and the cutting device  1200  is removed from the vertebral bodies.  
         [0114]    As shown in FIG. 12D, after the arcuate slot  1209  is cut in the adjacent vertebral bodies  2 , a biscuit implant  1210  such as that shown in FIG. 12F, is inserted into the arcuate slot in each of the adjacent vertebral bodies and so as to bridge therebetween. The biscuit implant  120   a  is secured in the arcuate slot  1209  using any of the methods described herein for the other implants of the present invention thereby fusing and stabilizing the adjacent vertebral bodies. Alternatively, a biscuit implant  1210   b  such as that shown in FIG. 12G, is configured so as to include a spacer element  1212 . Thus, when the biscuit, implant  1210   b  is inserted into the arcuate slots  1209  the spacer element  1209  thereof is received and disposed in the intervertebral space as shown in FIG. 12E.  
         [0115]    In addition to the exemplary biscuits implants  1210   a,b  illustrated in FIGS.  12 F-G it is with within the scope of the present invention for the biscuit implant whether it is configured with or without a spacer element  1212 , to be formed in any of a number of geometric shapes that are otherwise consistent with the intended use. This includes the biscuit implants  1210   c - f  shown in FIGS.  12 H-K. Reference shall be made to the foregoing discussion regarding the other implants or fixation members of the present invention as to the materials and other features (e.g., fenestartions) which apply equally for a biscuit implant according to the present invention.  
         [0116]    There is shown in FIGS.  13 A- 13 F, an implant-system according to these systems and methods. FIG. 13A shows an embodiment of the inner implant  800  adapted for inspection within the outer implant  810  shown in FIG. 13B. The inner implant  890  in FIG. 13A is shown as a substantially hollow device equipped with a fenestrated wall  802 . The inner implant  800 , bears on a lateral surface  814  a key slat  804  adapted to secure and orient the inner implant  800  within the outer implant  810  shown in FIG. 13B. Specifically, the key slat  804  in the illustrated embodiment can slide into a key groove  808  situated on the inner aspect  818  of the outer implant  810 . In the embodiment shown in FIG. 5B, the outer implant is equipped with a trough and trough slit and a fenestrated wall  812  as shown in FIG. 13D. It is understood that the devices shown in these figures can be fabricated from a plurality of materials including both absorbable and non-absorbable biocompatible materials. Materials may include metallics, ceramics, plastics, polymers, biological materials and materials produced by biotechnology. A variety of suitable materials will be readily envisioned by those of ordinary skill in the art for use in the system and methods of the present invention.  
         [0117]    [0117]FIG. 13C shows a lateral view of two vertebral bodies  820  and  822  showing the general position of the implant system  824 . In more detail, the edge of the outer implant  828  is shown imbedded and buried in the vertebral bodies  820  and  822 . The edge of the inner implant  830  is shown positioned within the intervertebral disc space  834 . A set of bone cuts  832  and  836  are made at the buried end of the implant, system  824 . FIG. 13D shows an anterior view of the outer implant  838  positioned with the inner implant  840  secured within it according to the systems and methods of the present invention. FIG. 13E shows an anterior view of the inner implant  844  secured within the outer implant  842  according to the systems and methods of the present invention. In FIG. 13E, however, the entire implant system  845  is shown in the rotated 90 degrees relative to the angle at which the implant system  848  is inserted into the vertebral bodies and disc space (not shown). The inner implant  844  in this view assumes a vertical position within the implant system  848 , and the outer implant is rotated 90 degrees to effect this repositioning.  
         [0118]    [0118]FIG. 13F shows in more detail a perspective view of an embodiment of the implant system  850  according to the present invention. The inner implant  854  is shown positioned within the outer implant  858 , the entire implant system  850  being turned vertically. As a consequence of this repositioning two bone sections  860  contained between the inner implant  854  and the outer implant  858  are turned to a vertical position. These bone sections  860  thus provide structural stability to the system  850  and to a spine unit (not shown). The vertical repositioning places cortical bone in a more supportive position.  
         [0119]    In the illustrated embodiment, the outer implant  858  is shown with a fenestrated wall  852  for facilitating bony ingrowth. These fenestrations are larger at the upper and lower confines of the repositioned bone graft sites to enhance fusion. Also in the illustrated embodiment, the inner implant  854  is shown with a hollow interior section  862  available for containing a solid displacing shim and bone chips, bone matrices, growth factors, or other agents for encouraging or facilitating bony ingrowth and, enhancing stable positioning of the verticalized cortical bone sections. Other substances useful to the healing process can be provided within this interior section  862 . For example, antibiotics can be placed in this interior section  862  in a suitable vehicle. Other substances and matrices can be envisioned by practitioners of those arts that will fall within the scope of the present invention.  
         [0120]    In more specific embodiments, the outer implant  838 , 858  is configured so as to include an axially extending slot or slit  841 , 864  that is arranged and configured so as to permit adjustment of the diameter of the outer implant, for example to permit the outer implant to be expanded outwardly. Thus, bone sections can be placed with as tight a positioning as possible and the outer implant  838 , 858  can be placed in firmer or closer engagement with the vertebral bodies  820 , 822 . The structure forming the adjustment slit  841 , 864  includes any of a number of configurations, structures or arrangements that permit relative movement between the sides of the outer implant on either side of the adjustment slit. Such structures, arrangements and configurations include, but are not limited to an axially extending through aperture or an axially extending ship-lap type of joint where portions of the axially extending sides slidably overlap each other.  
         [0121]    There is generally down in FIGS.  14 A- 14 C, an inner tool  900  to be used, according to the systems and methods of the present invention. FIG. 14A shows the inner tool  900  positioned with the intervertebral disc space  906 . The inner tool  900  bears on its distal end, a shorter disc end  902  that is adapted for insertion within the intervertebral disc space  906  to allow for cutting a segment of the vertebral bodies  904  and  908  above and below it. FIG. 14B shows a perspective view of an inner tool  910  according to the systems and methods of the present invention. The distal end  912  thereof is adapted for cutting the cortical vertebral end plates that it abuts. FIG. 14C shows in more detail an embodiment of the cutting mechanism bone by the inner tool  916 . A cutting end  914  at the distal end of the tool  916  bears a set of stop cut blades shown here in the retracted position  920  and in the extended position  918 . Directing the blades from the retracted position  920  to the extended position  918  effects a cut in the adjacent bone (vertebral endplate, not shown). While the depicted embodiment of a tool can be advantageously employed in conjunction with the implant system according to these systems and methods other tools and, devices can be envisioned by skilled practitioners of these arts for cutting bone and for positioning an implant system all modification that fall within the scope of the present invention.  
         [0122]    [0122]FIG. 15 shows a lateral view of an embodiment of the tool system  1000  according to the present invention positioned in relation to the vertebral bodies  1014  and  1018 . In this view an inner tool  1002  is shown with its distal end positioned between the vertebral bodies  1014  and  1018 . An outer tool  1004  is shown in two positions, a position  1008  before driving it into the vertebral bodies  1014  and  1018  and a position  1020  after driving it into the vertebral bodies  1014  and  1018 . A blade  1022  of the outer tool  1004  is shown positioned at the anterior aspect of the vertebral body  1014  before the outer tool  1004  is driven into the vertebral body  1014 . In this position  1020  after driving the tool  1004  into the vertebral body  1018 , the blade  1024  is shown imbedded in the vertebral body  1018 , having cut it perpendicular to its anterior face. The inner tool  1002  can make bone cuts  1012  at right angles to the blade  1024  of the outer tool  1004 , thereby creating a bone slab  1010  that can be repositioned according to the systems and methods of the present invention. This bone slab  1010  (section) can be cut so as to allow for anterior vertebral distraction by making these slabs oblong rather than circular.  
         [0123]    It should be clear that the methods, systems, and devices of the invention are not limited to securing a pair of vertebrae, but rather any combination of multiple vertebrae segments. It also should be clear that the methods, systems, and devices are in no way limited to vertebrae segments. In particular, the invention enables securing any solid substrates particularly bone substrates, without use of protruding screws or plates. In this regard, FIG. 16 shows a bone-to-bone application using techniques of the invention. It also should be understood that the invention is applicable to a wide variety of fixation configurations, including bone-to-bone with a gap; bone-to-bone without a gap; bone-to-bone with bony spacers; and bone-to-bone with a non-bony spacer such as a metal, polymer, or a biodegradable maternal.  
         [0124]    Although a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.