Abstract:
A spinal device for stabilizing adjacent vertebral bodies of the human spine. The device includes a combination of a screw and a member having a screw hole and a length sufficient to span a disc space between the adjacent vertebral bodies. The member has a portion that is bendable or deformable to prevent the outward excursion of the screw from the screw hole of the member.

Description:
[0001]    The present application is a continuation of application Ser. No. 13/180,990, filed; Jul. 12, 2011; which is a continuation of application Ser. No. 10/105,773, filed Mar. 25, 2002; now U.S. Pat. No. 7,976,566, which is a continuation of application Ser. No. 09/563,705, filed May 2, 2000, now U.S. Pat. No. 6,364,880; which is a continuation of application Ser. No. 09/126,585, filed Jul. 31, 1998, now U.S. Pat. No. 6,136,001; which is a continuation of application Ser. No. 08/926,334, filed Sep. 5, 1997, now U.S. Pat. No. 6,120,503; which is a continuation of application Ser. No. 08/589,787, filed Jan. 22, 1996, now abandoned; which is a continuation of application Ser. No. 08/219,626, filed Mar. 28, 1994, now abandoned; all of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to surgical interbody fixation devices and in particular to a surgically implantable device for the stabilization of adjacent vertebrae of the human spine undergoing spinal arthrodesis and for the prevention of the dislodgement of spinal fusion implants used in the fusion process. 
         [0004]    2. Description of the Related Art 
         [0005]    When a segment of the human spine degenerates, or otherwise becomes diseased, it may become necessary to surgically remove the affected disc of that segment, and to replace it with bone for the purpose of obtaining a spinal fusion by which to restore more normal, pre-morbid, spatial relations, and to provide for enhanced stability across that segment. Performing such surgery of the spine from an anterior (front) approach offers the great advantage of avoiding the spinal cord, dural sac, and nerve roots. Unfortunately, in entering the disc space anteriorly a very important band-like structure called the anterior longitudinal ligament, is violated. This structure physiologically acts as a significant restraint resisting the anterior displacement of the disc itself and acting as a tension band binding the front portions of the vertebrae so as to limit spinal hyperextension. 
         [0006]    Historically, various devices have been utilized in an attempt to compensate for the loss of this important stabilizing structure. These devices have assumed the form of blocks, bars, cables, or some combination thereof, and are bound to the vertebrae by screws, staples, bolts, or some combination thereof. The earliest teachings are of a metal plate attached to adjacent vertebrae with rood-type screws. Dwyer teaches the use of a staple-screw combination. Brantigan U.S. Pat. No. 4,743,256 issued on May 10, 1988, teaches the use of a block inserted to replace the disc, affixed to a plate then screwed to the vertebrae above and below. Raezian U.S. Pat. No. 4,401,112 issued on Aug. 30, 1993, teaches the use of a turnbuckle affixed to an elongated staple such that at least one entire vertebral body is removed, the turnbuckle portion is placed within the spine, and the staple extends both above and below the turnbuckle and engages the adjacent vertebrae to the one removed. 
         [0007]    Unfortunately, both staples and screws have quite predictably demonstrated the propensity to back out from the vertebrae. This is quite understandable as any motion, either micro or macro, tends to stress the interface of the metallic implant to the bone, and in doing so causes the bone to relieve the high stress upon it by resorbing and moving away from the metal. This entropic change is universally from the more tightened and thus well-fixated state, to the less tightened and less fixated state. For a staple, this is specifically from the more compressed and engaged state, to the less compressed and disengaged state. Similarly, screws in such a dynamic system loosen and back out. 
         [0008]    The potential consequences of such loosening and consequent backing out of the hardware from the anterior aspect of the vertebral column may easily be catastrophic. Because of the proximity of the great vessels, aortic erosions and perforations of the vena cava and iliac vessels have usually occurred with unfortunate regularity and have usually resulted in death. 
         [0009]    Therefore, the need exists for a device which is effective in restoring stability to a segment of the spine such as, but not limited to, the anterior aspect of the human spine and which will without danger remain permanently fixated once applied. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is directed to a spinal fixation device for stabilizing a segment of the human spine and for preventing the dislodgement of intervertebral spinal fusion implants, which remains permanently fixated to the spine once applied. The spinal fixation device of the present invention comprises a staple member made of a material appropriate for human surgical implantation and which is of sufficient length to span the disc space between two adjacent vertebrae. The staple member engages, via essentially perpendicular extending projections, the vertebrae adjacent to that disc space. The projections are sharpened and pointed so as to facilitate their insertion into the vertebrae and are segmented or ratcheted to prevent the staple member from disengaging and backing out once inserted. 
         [0011]    In the preferred embodiment of the spinal fixation device of the present invention, a portion of the staple member interdigitates with an already implanted intervertebral spinal fusion implant and the staple member is bound to the spinal fusion implant by a locking mechanism such as a screw with a locking thread pattern. The anchoring of the staple member via a locking mechanism to a spinal fusion implant protects the patient from the danger of the staple member itself disengaging and backing out. Further, if the spinal fusion implant is externally threaded, such as the spinal fusion implant taught by Michelson, U.S. Pat. No. 5,015,247 issued on May 14, 1991, then the staple member could only back out if the spinal fusion implant were free to rotate. However, the rotation of the spinal fusion implant in this instance is blocked by its connection to the staple member which is fixated across the disc space in such a way as to be incapable of rotation. Thus, the staple member is made safe against dislodgement by attachment to the spinal fusion implant and the stability of the spinal fusion implant is assured as it is also stabilized by the staple member and each works in connection with the other to remove the only remaining degree of freedom that would allow for the disengagement of either. 
         [0012]    The spinal fixation device of the present invention is broadly applicable to the anterior, posterior and lateral aspects of the spinal column, be it the cervical, thoracic or lumbar area. In particular, the use of a staple member spanning the disc space and engaging the adjacent vertebrae which is applied to the anterior aspect of the spine is of great utility in restraining those vertebral bodies from moving apart as the spine is extended and thus is effective in replacing the anterior longitudinal ligament of the patient. 
         [0013]    The spinal fixation device of the present invention provides the advantage of facilitating cross vertebral bony bridging (fusion via immobilization) which when achieved relieves all of the forces on the inserted spinal fusion implants. The spinal fixation device of the present invention may be coated with materials to promote bone fusion and thus promote the incorporation and ultimate entombment of the spinal fixation device into the bone fusion mass. The use of a bone fusion promoting material results in a speedier vertebra to vertebra fusion as bone may grow along the coated spinal fixation device bridging the two vertebrae so that the spinal fixation device acts as a trellis and supplies essential chemical elements to facilitate the bone fusion process. 
         [0014]    Another advantage provided by the spinal fixation device of the present invention is that as it is inserted it compresses the adjacent vertebrae together, thus increasing the compressive load on the spinal fusion implants or implants within the disc space, such compression being beneficial to fusion and further stabilizing the spinal fusion implants. 
         [0015]    A further advantage of the spinal fixation device of the present invention is that it may be used as an anchor such that a multiplicity of spinal fixation devices may then be interconnected via a cable, rod, bar, or plate, so as to achieve or maintain a multi-segmental spinal alignment. 
         [0016]    Alternatively, the spinal fixation device of the present invention could be made of resorbable materials, such as bio-compatible resorbable plastics, that resorb at an appropriate rate such that once the spinal fixation device is no longer needed (i.e. when spinal fusion is complete) the body would resorb the spinal fixation device. The spinal fixation device could be only in part resorbable such that the projections of the staple member would be non-resorbable and would remain incarcerated in the vertebrae and sealed off once the resorbable portion of the staple is resorbed by the body. 
         [0017]    As a further alternative, the spinal fixation device of the present invention could be made wholly of in part of ceramic and more particularly made of or coated with a ceramic such as hydroxyapatite that would actively participate in the fusion process. 
       OBJECTS OF THE PRESENT INVENTION 
       [0018]    It is an object of the present invention to provide a spinal fixation device having a staple member spanning the disc space and engaging two adjacent vertebrae of the spine to restrain the vertebrae from moving apart as the spine is extended; 
         [0019]    It is an another object of the present invention to provide a spinal fixation device that is effective in replacing the function of the anterior longitudinal ligament of a patient; 
         [0020]    It is a further object of the present invention to provide a means for protecting the patient from the danger of the spinal fixation device itself disengaging and backing out by its being anchored to an intervertebral spinal fusion implant; 
         [0021]    It is still another object of the present invention to provide a spinal fixation device that blocks the rotation of an intervertebral spinal fusion implant by its connection to the staple member which is fixated across the disc space in such a way as to be incapable of rotation thereby preventing the spinal fusion implant from backing out; 
         [0022]    It is yet another object of the present invention to provide a spinal fixation device that is broadly applicable to the anterior aspect of the spinal column, be it the cervical, thoracic or lumbar area; 
         [0023]    It is another object of the present invention to provide a spinal fixation device which may be applied longitudinally at any point about the circumference of the anterior aspect of the spine; 
         [0024]    It is also another object of the present invention to provide a spinal fixation device that stabilizes a surgically implanted spinal fusion implant and works in connection with the spinal fusion implant to prevent disengagement of either; 
         [0025]    It is another object of the present invention to provide a spinal fixation device that achieves cross vertebral bony bridging (fusion) which ultimately relieves all of the forces on inter-vertebral spinal fusion implants inserted within the disc space between two adjacent vertebrae, and provides for a permanently good result; 
         [0026]    It is another object of the present invention to provide a spinal fixation device that serves as an anchor, such that a multiplicity of these anchors may then be interconnected via a cable, rod, bar, or plate, so as to achieve or maintain a multi-segmental spinal alignment; and 
         [0027]    It is a further object of the present invention to provide a spinal fixation device that directly participates in the bony bridging of two adjacent vertebrae and participates in the spinal fusion process across those vertebrae. 
         [0028]    These and other objects of the present invention will become apparent from a review of the accompanying drawings and the detailed description of the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is a perspective side view of a segment of the spinal column having two spinal fusion implants shown partially in hidden line inserted across the disc space between two adjacent vertebrae with each spinal fusion implant having a spinal fixation device of the present invention shown partially in hidden line secured thereto, spanning across the disc space and inserted into the vertebrae. 
           [0030]      FIG. 2  is a perspective side view of a segment of the spinal column having two spinal fusion implants inserted across the disc space between two adjacent vertebrae. 
           [0031]      FIG. 3  is an elevational side view of a cylindrical threaded spinal fusion implant. 
           [0032]      FIG. 4  is an end view of the cylindrical threaded spinal fusion implant along lines  4 - 4  of  FIG. 3 . 
           [0033]      FIG. 5  is a perspective side view of a segment of the spinal column having two non-threaded spinal fusion implants with external ratchetings, shown in hidden line, inserted across the disc space between two adjacent vertebrae with each spinal fusion implant having a spinal fixation device of the present invention, shown partially in hidden line, coupled thereto, spanning across the disc space and inserted into the vertebrae. 
           [0034]      FIG. 6  is a perspective side view of a segment of the spinal column having two spinal fusion implants having truncated sides with external ratchetings shown in hidden line inserted across the disc space between two adjacent vertebrae with each spinal fusion implant having a spinal fixation device of the present invention shown partially in hidden line coupled thereto, spanning across the disc space and inserted into the vertebrae. 
           [0035]      FIG. 7  is a perspective side view of a segment of the spinal column having two spinal fusion implants having a knurled external surface shown in hidden line inserted across the disc space between two adjacent vertebrae with each spinal fusion implant having a spinal fixation device of the present invention shown partially in hidden line coupled thereto, spanning across the disc space and inserted into the vertebrae. 
           [0036]      FIG. 8  is a top plan view of the spinal fixation device of the present invention. 
           [0037]      FIG. 9  is a side view of the spinal fixation device of the present invention along lines  9 - 9  of  FIG. 8 . 
           [0038]      FIG. 10  is a cross sectional view taken along lines  10 - 10  of  FIG. 8  showing the top member of the spinal fixation device of the present invention. 
           [0039]      FIG. 11  is an enlarged fragmentary perspective side view of a projection of the spinal fixation device of the present invention taken along line  11  of  FIG. 9 . 
           [0040]      FIG. 12  is a cross sectional view of the spinal fixation device of the present invention inserted into the vertebrae and secured to the spinal fusion implant with the arrows showing the forces exerted, the rotational axis and the longitudinal axis of the spinal fusion implant. 
           [0041]      FIG. 13A  is a cross sectional view along line  13 - 13  of  FIG. 9  of the preferred embodiment of the projections of the present invention. 
           [0042]      FIGS. 13B ,  13 C,  13 D,  13 E, and  13 F are cross sectional views taken along line  13 - 13  of  FIG. 9  showing alternative embodiments of the projections of the spinal fixation device of the present invention. 
           [0043]      FIG. 14  is an enlarged elevational side view of the locking screw used to secure the spinal fixation device of the present invention to a spinal fusion implant. 
           [0044]      FIG. 15A  is a cross sectional view of a securing means for locking the locking screw of the present invention. 
           [0045]      FIG. 15B  is a cross sectional view of a first alternative embodiment of the securing means for locking the locking screw of the present invention. 
           [0046]      FIG. 15C  is a cross sectional view of a second alternative embodiment of the securing means for locking the locking screw of the present invention. 
           [0047]      FIG. 16A  is a perspective side view of the instrumentation used for driving the spinal fixation device of the present invention into the vertebrae. 
           [0048]      FIG. 16B  is a perspective side view of a first alternative embodiment of the instrumentation used for driving the spinal fixation device of the present invention into the vertebrae. 
           [0049]      FIG. 17A  is a perspective side view of an alignment rod used to align the spinal fixation device of the present invention. 
           [0050]      FIG. 17B  is a perspective side view of an alternative embodiment of the alignment rod having splines used to align the spinal fixation device of the present invention. 
           [0051]      FIG. 18  is a front perspective view of the drill template instrument. 
           [0052]      FIG. 19  is a perspective side view of the alignment rod attached to a spinal fusion implant inserted in the disc space between two adjacent vertebrae. 
           [0053]      FIG. 20  illustrates the step of drilling guide holes in the vertebrae adjacent to the spinal fusion implant with the drill template instrument of  FIG. 18 . 
           [0054]      FIG. 21  illustrates a step of the method of inserting the spinal fixation device of the present invention with the alignment rod attached to the spinal fusion implant and the spinal fixation device placed on the driver instrumentation. 
           [0055]      FIG. 22  illustrates a step of the short method of inserting the spinal fixation device of the present invention with the driver instrument engaging the splined alignment rod and a hammer for applying an impaction force and driving the driver instrument. 
           [0056]      FIG. 22A  is an enlarged fragmentary view of a projection being inserted into an insertion hole drilled within a vertebra shown in cross section taken along line  22 A of  FIG. 21 . 
           [0057]      FIG. 23  illustrates another step of the method of inserting the spinal fixation device of the present invention in which the spinal fixation device has been driven into the vertebrae and the driver instrumentation has been removed. 
           [0058]      FIG. 24  illustrates another step of the method of inserting the spinal fixation device of the present invention with the splined alignment rod being removed from the spinal fusion implant and the locking screw being inserted and secured the spinal fixation device to the spinal fusion implant. 
           [0059]      FIG. 25  is a top plan view of a first alternative embodiment of the spinal fixation device of the present invention. 
           [0060]      FIG. 26  is a top plan view of a second alternative embodiment of the spinal fixation device of the present invention. 
           [0061]      FIG. 27  is a perspective side view of a third alternative embodiment of the spinal fixation device of the present invention coupled to two spinal fusion implants and inserted in adjacent vertebrae of the spinal column. 
           [0062]      FIG. 28  is a top plan view of a fourth alternative embodiment of the spinal fixation device of the present invention inserted into the vertebrae of the spinal column having a spinal fusion implant inserted in the disc space. 
           [0063]      FIG. 29  is a top plan view of a fifth alternative embodiment of the spinal fixation device of the present invention inserted into the vertebrae of the spinal column having a spinal fusion implant inserted in the disc space. 
           [0064]      FIG. 30  is a perspective bottom view of the fourth alternative embodiment of the spinal fixation device of the present invention. 
           [0065]      FIG. 31  is a cross sectional view along lines  31 - 31  of  FIG. 29  showing the fifth alternative embodiment of the spinal fixation device of the present invention inserted into the adjacent vertebrae and coupled to a spinal fusion implant. 
           [0066]      FIG. 32  is a cross sectional view along lines  32 - 32  of  FIG. 29  showing the projections of the fifth alternative embodiment of the present invention with respect to a spinal fusion implant inserted within the disc space. 
           [0067]      FIG. 33  is a cross sectional view of a spinal fixation device of the present invention engaging two adjacent vertebrae and being attached to a spinal fusion implant, shown being used as an anchor for a multi-segmental spinal alignment means. 
           [0068]      FIG. 34  is an enlarged elevational side view of a threaded post used to connect the spinal fixation device of the present invention to a multi-segmental spinal alignment means. 
           [0069]      FIG. 35  is an exploded perspective view of a sixth alternative embodiment of the spinal fixation device of the present invention having independent projection members that are screws. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0070]    Referring to  FIGS. 1 and 2 , two identical spinal fixation devices of the present invention, each being generally referred to by the numerals  10  and  11 , respectively, are shown inserted into two vertebrae V adjacent to a disc D of a segment of the human spine. Each spinal fixation device  10  and  11  is shown coupled to identical spinal fusion implants  40  and  41  that have been surgically implanted in the disc space between adjacent vertebrae V. In this manner, the spinal fixation devices  10  and  11  stabilize a segment of the spine, prevent the dislodgement of the spinal fusion implant  40 , and remain permanently fixated to the spine once applied. The spinal fixation devices  10  and  11  are identical such that the description of one is equally applicable to the other. Thus, the description that follows will be directed to spinal fixation device  10 . 
         [0071]    Referring to  FIGS. 3-4 , the spinal fusion implant  40  such as, but not limited to, the spinal fusion implant described by Michelson, U.S. Pat. No. 5,0165,247 issued on May 14, 1991, is shown. The spinal fusion implant  40  is cylindrical in shape and has external threads  42  at its outer perimeter for engaging the bone of the vertebrae V adjacent to the disc D. The spinal fusion implant  40  has a trailing end  43  having a depression  44  and a threaded aperture  45  for engaging a portion of the spinal fixation device  10  and also for engaging a portion of an instrument used to insert the spinal fixation device  10  into the vertebrae V. 
         [0072]    Referring to  FIGS. 5-7 , it is appreciated that the spinal fixation devices  10  and  11  of the present invention are not limited in use with a threaded spinal fusion implant  40  and  41 , but may be used with different types of spinal fusion implants. For example, the spinal fixation devices  10  and  11  may be coupled to spinal fusion implants  40   a  and  41   a,  respectively, each having external ratchetings  42   a  instead of external threads  42  as shown in  FIG. 5 . Alternatively, the spinal fixation devices  10  and  11  may be coupled to spinal fusion implants  40   b  and  41   b,  respectively, each having a partially cylindrical shape with at least one truncated side  47  as shown in  FIG. 6 . As a further alternative, the spinal fixation devices  10  and  11  may be coupled to spinal fusion implants  40   c  and  41   c,  respectively, each having a knurled external surface  48  as shown in  FIG. 7 . It is also appreciated that the spinal fixation devices may be used with a variety of other bone fusion implants without departing from the scope of the present invention. 
         [0073]    Referring to  FIGS. 8-9 , in the preferred embodiment, the spinal fixation device  10  of the present invention comprises a staple member  12  having a substantially planar top member  14  which is of sufficient length to span one intervertebral disc D and to engage, via a plurality of essentially perpendicular extending projections  16  and  17 , the vertebrae V adjacent to that disc D. The top member  14  has a central opening  18  within a concentric, countersunk recess  19  for receiving therethrough a screw or similar coupling means for coupling the spinal fixation device  10  to the spinal fusion implant  40 . The top member  14  has an upper surface  20  having a pair of openings  22   a  and  22   b  for receiving the posts  88   a  and  88   b  of a driving instrument  80  which is described in greater detail below in reference to  FIGS. 16A and 16B . 
         [0074]    Referring to  FIG. 10 , a cross sectional view of the top member  14  is shown. In the preferred embodiment, the top member  14  is generally triangularly shaped and is radiused along curved side  24  and straight side  26 . The curved side  24  of the top member  14  is radiused at its upper edge  25  and at the upper edge  27  of straight side  26  to conform to the external curvature of the vertebrae V. In this manner, smooth surfaces are created at the upper edges  25  and  27  of the top member  14  that are contoured to the shape of the external curvature of the vertebrae V when the staple member  12  is in place. The smooth contoured surface of the upper edges  25  and  27  of the top member  14  prevent aortic erosions and perforations of the vessels proximate the vertebral column such as the vena cava and the iliac vessels which might otherwise result from friction. 
         [0075]    In the preferred embodiment of the spinal fixation device  10 , the top member  14  has a width ranging from 6.0 mm to 28.0 mm, with 10.0 mm being the preferred width, and having a thickness in the range of 2.0 mm to 4.0 mm, with 3.0 mm being the preferred thickness. The staple member  12  is made of material appropriate for human surgical implantation including all surgically appropriate metals such as but not limited to, titanium, titanium alloy, chrome molybidium alloys, stainless steel; or non-metallic materials including permanent or resorbable substances or composites, carbon fiber materials, resins, plastics, ceramics or others. 
         [0076]    Further, the staple member  12  of the present invention may be treated with, or even composed of, materials known to participate in or promote in the fusion process or bone growth. The spinal fixation device  10  may be coated with materials to promote bone fusion and thus promote the incorporation and ultimate entombment of the spinal fixation device  10  into the bone fusion mass. The use of a bone fusion promoting material such as, but not limited to hydroxyapatite, hydroxyapatite tricalcium phosphate or bone morphogenic protein, results in a speedier vertebra V to vertebra V fusion as bone may grow along the coated spinal fixation device  10  bridging the two vertebrae V so that the spinal fixation device  10  acts as a trellis and supplies essential chemical elements to facilitate the bone fusion process. 
         [0077]    Referring again to  FIG. 9 , the projections  16  and  17  are positioned at opposite ends of the top member  14  and depend downwardly and extend perpendicularly from the bottom surface  30  of the top member  14 . The projections  16  and  17  each terminate in a distal end  32  that is pointed and sharpened to facilitate the insertion of the projections  16  and  17  into the vertebrae V. 
         [0078]    The staple member  12  is most effective when the interprojection distance I between projections  16  and  17  is at least 4.0 mm and preferably 6.0 mm greater than the diameter of the particular spinal fusion implant  40  for which the spinal fixation device  10  is being used so that at least 2.0 mm and preferably 3.0 mm of bone from the vertebrae V will be present between the spinal fusion implant  40  and each of the projections  16  and  17 . Typically, intervertebral spinal fusion implants have a diameter that ranges from 12.0 mm to 28.0 mm, therefore, the interprojection distance I typically will range from 18.0 mm to 34.0 mm for most applications. 
         [0079]    In the preferred embodiment, the projections  16  and  17  comprise a series of segmented and ratcheted portions  34 . The segmented and ratcheted portions  34  provide for a “one way” insertion of the staple member  12  to prevent the backing-out of the projections  16  and  17  once they are inserted into the bone of the vertebrae V. In the preferred embodiment, each segmented and ratcheted portion  34  of the projections  16  and  17  is conical in shape and the diameter of each segmented and ratcheted portion  34  increases in the direction from the distal end  32  toward the top member  14  so that the projections  16  and  17  resemble a stack of cones. The segmented and ratcheted portions  34  are spaced approximately 2.0 mm to 4.0 mm apart, with 3.0 mm being the preferred distance between each segmented and ratcheted portion  34 . 
         [0080]    Referring to  FIG. 11-12 , in the preferred embodiment of the spinal fixation device  10 , in order to further facilitate the insertion of the projections  16  and  17  into the vertebrae V, the distal end  32  of each projection  16  has an eccentric, incline-planed inner surface  36  as shown in  FIG. 11 . The eccentric, incline-planed inner surface  36  of each of the projections  16  and  17  create a force F which pushes the bone of the vertebrae V toward the spinal fusion implant  40  as the staple member  12  is inserted into each of the vertebrae V as shown in  FIG. 12 . 
         [0081]    Referring to  FIGS. 13A-13F , in the preferred embodiment of the spinal fixation device  10 , the projections  16  and  17  are cylindrical in shape having a circular cross section as shown for projection  16  in  FIG. 13A . Alternatively, the projection  16   a  may have a triangular cross section as shown in  FIG. 13B ; the projection  16   b  may have a square cross section as shown in  FIG. 13C ; the projection  16   c  may have a rectangular cross section as shown in  FIG. 13D ; the projection  16   d  may have a trapezoidal cross section as shown in  FIG. 13E ; or the projection  16   e  may have a cross section with a configuration as shown in  FIG. 13F . 
         [0082]    In the preferred embodiment, the projections  16  and  17  each have a diameter of approximately 2.0 mm to 4.0 mm, with 3.0 mm being the preferred diameter at the widest point. The projection  16  and  17  each have a length ranging from 16.0 mm to 28.0 mm, with 22.0 mm being the preferred length when the spinal fixation device  10  is implanted in the direction of the anterior aspect of the vertebra V to the posterior aspect of the vertebrae V. Alternatively, it is appreciated that the projections  16  and  17  each could have a longer length depending on the diameter of the vertebrae V in which the projections  16  and  17  are implanted. 
         [0083]    Referring again to  FIG. 9 , the top member  14  of the staple member  12  has a central bar  35  extending from the center of its bottom surface  30 , for interdigitating and mating to an already implanted intervertebral spinal fusion implant  40 . In the preferred embodiment, the central bar  35  has a thickness in the range of 0.5 mm to 1.5 mm, with 0.5 mm being the preferred thickness. 
         [0084]    Referring to  FIG. 1 , the central bar  35  is configured so that it complements and engages the depression  44  at the insertion end  43  of the spinal fusion implant  40 . Once engaged to the depression  44 , the bar  35  interdigitates with the depression  44  of the spinal fusion implant  40  to lock and prevent the rotation of the spinal fusion implant  40 . 
         [0085]    Referring to  FIG. 14 , in the preferred embodiment, the staple member  12  is secured to the spinal fusion implant  40  by a screw  60  having threaded end  61  with a locking thread pattern  62  and screw head  64 . The locking thread pattern  62  has a reduced pitch at the bottom of the threaded end  61  such that the screw  60  is self-locking. However, it is appreciated that the threaded pattern  62  may be any of the means for locking a screw well known by those skilled in the art. 
         [0086]    Referring to  FIGS. 2 and 8 , the threaded end  61  of the screw  60  passes through the central opening  18  of the top member  14  and the threaded pattern  62  threads into the threaded aperture  45  of the spinal fusion implant  40 . The screw head  64  fits within the countersunk recess  19  of the top member  14  such that the screw head  64  is at or below the plane of the upper surface  20  of the top member  14 . In the preferred embodiment, the central opening  18  has a diameter ranging from 4.5 mm to 5.5 mm, with 5.0 mm being the preferred diameter. The countersunk recess  19  has a diameter in the range of 6.0 mm to 8.0 mm with 7.0 mm being the preferred diameter. 
         [0087]    Referring to  FIGS. 15A ,  15 B, and  15 C, an enlarged cross sectional view of three different embodiments of a securing means  65  for locking the screw  60  once it is threaded to the spinal fusion implant  40  are shown. In  FIG. 15A , the securing means  65  comprises a notch  66  in the surface  20  of the top member  14  which is preferably made of metal. Once the screw  60  is threaded and securely tightened to the spinal fusion implant  40 , a chisel C is used to bend a portion  67  of the top member  14  into the central opening  18  and against the screw head  64  so as to prevent the outward excursion and any unwanted loosening of the screw  60 . 
         [0088]    In  FIG. 15B , a second embodiment of the securing means  65   a  is shown comprising a central score  66   a  concentric with the central opening  18 . A screw  60   a  having a slot  61   a  in the screw head  64   a  is threaded and securely tightened to the spinal fusion implant  40 . An instrument T is partially inserted into slot  61   a  after which an impaction force F.sub.1 is applied to the instrument T to spread apart the screw head  64   a  in the direction of the arrows A so that the screw head  64   a  becomes deformed from the impaction force F.sub.1 and fits within the central score  66   a.  Once the screw head  64   a  is in the central score  66   a,  the outward excursion of the screw  60   a  is prevented by the top lip  68  of the central score  66   a.    
         [0089]    In  FIG. 15C , a third embodiment of the securing means  65   b  is shown comprising a screw  60   b  having a screw head  64   b  with a slightly flanged portion  69   b  near the top and a slot  61   b.  The central opening  18  has along its circumference a recess  66   b  for receiving the flanged portion  69   b  of the screw head  64   b.  The securing means  65   b  relies on the natural resiliency of the metal screw head  64   b  such that when the screw  60   b  is being driven by a screw driver, the screw head  64   b  flexes in the direction of the arrows B. In this manner, the flanged portion  69   b  of the screw head  64   b  slides along the interior of the central opening  18  so that the screw head  64   b  is below the top lip  68   b  of the recess  66   b.  Once the screw driver is removed from the screw  60   b,  the screw head  64   b  returns to its natural state in the direction opposite to the arrows B so that the flanged portion  69   b  is within the recess  66   b.  The outward excursion of the screw  60  is thus prevented by the top lip  68   b  which blocks the screw head  64   b  by catching the flanged portion  69   b.    
         [0090]      FIGS. 16A-18  show the instrumentation used for installing the spinal fixation device  10 . Referring to  FIG. 16A , a driving instrument  80  used for inserting the spinal fixation device  10  into the vertebrae V is shown having a hollow tubular shaft  82  which terminates at one end to a bottom flat member  84  and terminates to a top flat member  86  at the other end. The bottom flat member  84  is preferably configured so that it conforms to the shape of the top member  14  of the staple member  12 . 
         [0091]    The driving instrument  80  has a pair of short posts  88   a  and  88   b  extending from the bottom flat member  84 . The posts  88   a  and  88   b  are oriented on the bottom flat member  84  so as to correspond to the position of the openings  22   a  and  22   b  in the upper surface  20  of the top member  14  of the staple member  12 . Each of the posts  88   a  and  88   b  fit into each of the openings  22   a  and  22   b  and keep the staple member  12  aligned on the bottom flat member  84  of the driving instrument  80 . It is appreciated that the openings  22   a  and  22   b  in the top member  14  may be depressions within the surface  20  of the top member  14  or may be holes that pass through the top member  14 . In the preferred embodiment, the openings  22   a  and  22   b  gave a diameter ranging from 1.5 mm to 3.5 mm, with 2.5 mm being the preferred diameter. 
         [0092]    Referring to  FIG. 16B , an alternative embodiment of the driving instrument  80 ′ which is used for inserting into the vertebrae V the spinal fixation device  210 , described in detail below in reference to  FIG. 26 , is shown having a hollow tubular shaft  82 ′ which terminates at one end to a bottom flat member  84 ′ and terminates to a top flat member  86 ′ at the other end. The bottom flat member  84 ′ is rectangular in shape so that it conforms to the shape of the top member  214  of the spinal fixation device  210 . 
         [0093]    The driving instrument  80 ′ has a pair of short posts  88 ′ a,    88 ′ b,    88 ′ c  and  88 ′ d  extending from the bottom flat member  84 ′. The posts  88 ′ a - 88 ′ d  are oriented on the bottom flat member  84 ′ so as to correspond to the position of the openings  222   a - 222   d  of the spinal fixation device  210 . Each of the and keep the spinal fixation device  210  aligned on the bottom flat member  84 ′ of the driving instrument  80 ′. 
         [0094]    Referring to  FIG. 17A , an alignment rod  70  comprising a cylindrical shaft  72  having a smooth exterior surface  73  and a threaded end  74  may be threadably attached to the threaded aperture  45  of the spinal fusion implant  40  is shown. The alignment rod  70  fits through the central opening  18  of the spinal fixation device  10  and is used to properly align the projections  16  and  17  on each side of the spinal fusion implant  40  prior to engaging the vertebrae V. Further, the alignment rod  70  also serves as a guide post for the drilling template instrument  50  described in greater detail below. 
         [0095]    Referring to  FIG. 17B , as an alternative embodiment of the alignment rod  70 , a splined alignment rod  70 ′ that has a finely splined surface  72 ′ along its longitudinal axis and a threaded end  74 ′ that may be attached to the threaded aperture  45  of the spinal fusion implant is shown. 
         [0096]    Referring to  FIG. 18 , a drilling template instrument  50  for creating a pair of insertion holes  53   a  and  53   b  in each of the vertebrae V for receiving each of the projection  16  and  17  respectively is shown. The drilling template instrument  50  has a template  52  with a central aperture  54  therethrough and guide passages  55  and  56  for guiding a drill bit  51  of a drilling tool. Attached to the template  52  is a handle  58  which angles away from the template  52  so as not to obstruct the line of sight of the surgeon and to allow easy access to the template  52  and easy access to the guide holes  55  and  56  for the drill bit  51 . Extending from the center of the bottom surface of the template  52  is a central member  59  (similar in structure and function to the central bar  35 ) for mating to an already implanted intervertebral spinal fusion implant  40 . The central member  59  interdigitates with the depression  42  of the spinal fusion implant  40  so that the template  52  is properly oriented about the spinal fusion implant  409  and the guide holes  55  and  56  are properly oriented with respect to the vertebrae V adjacent to the spinal fusion implant  40 . The alignment rod  70  serves as a guide post for the drill template instrument  50  as it fits through the central aperture  54  of the template  52  and aligns the template  52  with respect to the spinal; fusion implant  40  and insures that it is coaxial. The central aperture  54  of the drilling template instrument  50  is smooth so that if it is placed over a splined alignment rod  70 ′ the drilling template instrument  50  may be easily rotated about the splined alignment rod  70 ′ into position such that the central member  59  is able to mate and interdigitate with the depression  44  of the spinal fusion implant  40 . 
         [0097]    Referring to  FIGS. 19-24 , the spinal fixation device  10  of the present invention is inserted in the following manner: At least one spinal fusion implant  40  is surgically implanted so that it is substantially within the disc space between two adjacent vertebrae V and engages at least a portion of each of the two adjacent vertebrae V. Once the spinal fusion implant  40  is in place, the alignment rod  70  is attached to the threaded aperture  45  of the spinal fusion implant  40 . The alignment rod  70  serves as a guide post for the drilling template instrument  50  as it fits through the central aperture  54  of the template  52  and aligns the template  52  coaxially with respect to the spinal fusion implant  40 . 
         [0098]    Referring to  FIG. 20 , once the template  52  is properly aligned and the drilling template instrument  50  is seated so that the central member  59  interdigitates with the spinal fusion implant  40 , the insertion holes  53   a  and  53   b  are drilled in each of the adjacent vertebrae V with a drilling instrument having a drill bit  51  with a diameter that is substantially smaller than the diameter of each the projections  16  and  17  of the staple member  12 . 
         [0099]    Once the drilling of the insertion holes  53   a  and  53   b  is completed, the drill template instrument  50  is removed from the spinal fusion implant  40  and from the alignment rod  70 . The alignment rod  70  is left in place attached to the threaded aperture  45  of the spinal fusion implant  40 . 
         [0100]    Referring to  FIG. 21 , the staple member  12  is placed onto the driving instrument  80  used for driving and fixing the staple member  12  into the vertebrae V so that the bottom flat member  84  and the posts  88   a  and  88   b  are aligned with the top member  14  and the depressions  22   a  and  22   b  of the top member  14 . The alignment rod  70  serves as a guide post for the staple member  12  as it fits through the central opening  18  of the staple member  12  and aligns the staple member  12  coaxially with respect to the spinal fusion implant  40 . 
         [0101]    Referring to  FIG. 22 , once the staple member  12  is properly placed onto the bottom flat member  84  of the driving instrument  80 , the staple member  12  and the driving instrument  80  are aligned with respect to the alignment rod  70  so that the alignment rod  70  passes through the central opening  18  of the staple member  12  and is inserted into the central hollow portion  89  of the driving instrument  80 . The staple member  12  and the driving instrument  80  are then lowered along the alignment rod  70  so that the sharp distal end  32  of each of the projections  16  and  17  comes into contact with the external surface of the vertebrae V and is aligned with the previously drilled insertion holes  53   a  and  53   b.    
         [0102]    As shown in  FIG. 22A , it is preferred that the insertion holes  53   a  and  53   b  be drilled so that when the projections  16  and  17  are inserted into the holes  53   a  and  53   b,  the incline planed inner surface  36  of each of the projections  16  and  17  contacts the inner wall W of the insertion holes  53   a  and  53   b  that is closest to the spinal fusion implant  40 . In this manner a compression force F is created as each of the projections  16  and  17  of the staple member  12  is inserted into insertion holes  53   a  and  53   b,  respectively, compressing the bone of the vertebrae V toward the spinal fusion implant  40 . 
         [0103]    Referring to  FIG. 23 , the staple member  12  is then driven into the vertebrae V by applying a high impaction force to the driving instrument  80  with a hammer H or other impacting means against the top flat member  86  of the driving instrument  80 . The staple member  12  is driven into the vertebrae V such that the projections  16  and  17  are moved forward into the insertion holes  53   a  and  53   b,  respectively, until the bottom surface  30  of the top member  14  of the staple member  12  comes to rest against the surface of the vertebrae V. 
         [0104]    Referring to  FIGS. 23-24 , the driving instrument  80  is lifted away from the alignment rod  70  so that the alignment rod  70  is no longer within the central hollow portion  89  of the driving instrument  80 . The alignment rod  70  is unthreaded from the threaded aperture  45  and is removed from the spinal fusion implant  40 . The staple member  12  is secured to the spinal fusion implant  40  with the locking screw  60  which has a threaded pattern  62  with a reduced pitch. The reduced pitch of the locking screw  60  locks the locking screw  60  to the spinal fusion implant  40  with minimal turning of the locking screw  60  and prevents any unwanted loosening. Further, any of the three embodiments of the securing means  65 ,  65   a  or  65   b  described above in reference to  FIGS. 15A-15C  may be used to further prevent any unwanted loosening and outward excursion of the screw  60 . 
         [0105]    Referring back to  FIG. 12 , once the staple member  12  is driven into the vertebrae V and is secured to the spinal fusion implant  40 , the spinal fusion implant  40  is prevented from rotating along its rotational axis R by its connection to the staple member  12  which is fixated across the disc space between the vertebrae V. The staple member  12  is prevented from backing out from the vertebrae V along the longitudinal axis L by its connection to the spinal fusion implant  40  and by the segmented and ratcheted portions  34  of the projections  16  and  17 . In this manner, the staple member  12  and the spinal fusion implant  40  interact to prevent the dislodgement of each other from the vertebrae V in which they are implanted. Thus, the staple member  12  is made safe against dislodgement by attachment to the spinal fusion implant  40  and the stability of the spinal fusion implant  40  is assured as it is also stabilized by the staple member  12  and each works in connection with the other to remove the only remaining degree of freedom that would allow for the disengagement of either. In addition, the incline planed inner surface  36  at the distal end  32  of the projections  16  and  17  forces bone toward the spinal fusion implant  40  along force lines F to further secure the spinal fusion implant  40  and further prevent the dislodgement of the spinal fusion implant  40 . 
         [0106]    It is appreciated by those skilled in the art that when the bone of the vertebrae V is sufficiently soft, a shorter method (hereinafter referred to as the “Short Method”) of inserting the spinal fixation device  10  is possible by omitting the steps of drilling the insertion holes  53   a  and  53   b  prior to inserting the staple member  12  into the vertebrae V. 
         [0107]    Referring to  FIG. 22 , in the Short Method, the splined alignment rod  70 ′ that is finely splined along its longitudinal axis is used instead of the alignment rod  70 . Once the splined alignment rod  70 ′ has been attached to the spinal fusion implant  40 , the staple member  12  may be placed over the splined alignment rod  70 ′ so that the splined alignment rod  70 ′ passes through the aperture  18  and into the central aperture  89  of the driving instrument  80 . The central aperture  89  of the driving instrument  80  is correspondingly splined to the splines of the splined alignment rod  70 ′ so that the staple member  12  can be aligned with respect to the spinal implant  40 . The alignment of the staple member  12  and the driving instrument  80  is maintained as the corresponding splines of the central aperture  89  interdigitate with the splines of the splined alignment rod  70 ′ and prevent the rotation of the staple member  12  about the splined alignment rod  70 ′. The prevention of rotation about the splined alignment rod  70 ′ is especially important when the Short Method is used to insert the spinal fixation device  10 , as no insertion holes  53   a  and  53   b  have been drilled in the vertebrae V. The staple  12  can be driven directly into the vertebrae V by the application of a high impaction force to the driving instrument  80  as described above and shown in  FIG. 22 . 
         [0108]    Once the staple member  12  is driven into the vertebrae V, the steps of the longer method described above are used to secure the spinal fixation device to the spinal fusion implant  40  are the same. The Short Method of inserting the staple member  12  reduces the amount of time required to insert and secure the spinal fixation device  10  of the present invention and thus reduces the overall duration of the spinal fixation surgical procedure. 
         [0109]    While the present invention has been described with respect to its preferred embodiment, it is recognized that alternative embodiments of the present invention may be devised without departing from the inventive concept. 
         [0110]    For example, referring to  FIG. 25 , a first alternative embodiment of a spinal fixation device  110  having a staple member  112  with a top member  114  generally in the shape of an elongated oval having two curved sides  124   a  and  124   b  is shown. In this alternative embodiment, the curved sides  124   a  and  124   b  have upper edges  125   a  and  125   b,  respectively, that are radiused to conform to the external curvature of the vertebrae V thereby creating smooth contoured surfaces as described above for the spinal fixation device  10 , the preferred embodiment of the present invention. The top member  114  has openings  122   a  and  122   b  in the upper surface  120  of the top member  114  and has two projections  116  and  117  depending downwardly from the bottom surface  130  of the top member  114  at opposite ends of the staple member  112 . The projections  116  and  117  are the same as the projections  16  described above for the preferred embodiment. 
         [0111]    Referring to  FIG. 26 , a second alternative embodiment of the spinal fixation device  210  having a staple member  212  is shown with a top member  214  that is generally rectangular  5  in shape and has an upper surface  220  with openings  222   a,    222   b,    222   c,  and  222   d.  The top member  214  has four projections  216 ,  217 ,  218 , and  219  depending from its bottom surface at each of its corners. The projections  216 - 217  are the same as the projections  16  and  17  described above in the preferred embodiment. The stop member  2145  has four straight sides  228   a,    228   b,    228   c,  and  228   d  having upper edges  225   a,    225   b,    225   c,  and  225   d,  respectively, that are radiused to conform to the external curvature of the vertebrae V create a smooth surface as described above for the preferred embodiment. The driving instrument  80 ′ shown in  FIG. 16B  is used to insert the spinal fixation device  210 . 
         [0112]    Referring to  FIG. 27 , a third alternative embodiment of the spinal fixation device  310  having a staple  312  with a top member  314  that is generally triangular is shown. The top member  314  has two projections  316  and  317  depending from the bottom surface of the top member  314  that engage the vertebrae V. Extending from the center of the bottom surface of the top member  314  is a central member  390  which is similar to the central bar  35  of the preferred embodiment of the spinal fixation device  10  in that the central member  390  interdigitates with the depression  44  of the spinal fusion implant  40 . However, the central bar  390  also has an extension arm  392  that extends laterally from the top member  314  to span the diameter of an adjacent spinal fusion implant  41 . The extension arm  392  interdigitates with the depression  44  of the spinal implant  41 . The extension arm  392  has a central aperture  394  for receiving a screw  60   b  used to couple the extension arm  392  to the spinal fusion implant  41 . In this manner, a single spinal fixation device  310  is capable of interdigitating with two adjacent spinal fusion implants  40  and  41  to clock and prevent the rotation and any excursion of the spinal fusion implants  40  and  41 . The fixation of two spinal fusion implants  40  and  41  is possible while leaving no protruding metal, such as the top member  314 , on the side of the spine where the vessels are located in close approximation to the vertebrae as is the case with the L 4  and L 5  vertebrae where the vessels are located over the left side of those vertebrae. It is appreciated that any of the securing means  65 - 65   b,  described above may be used to lock the screw  60   b  to the extension arm  392 . 
         [0113]    Referring to  FIG. 28 , a fourth alternative embodiment of the spinal fixation device  410  having a staple member  412  with a top member  414  that is generally triangular in shape is shown in the installed position. The top member  414  is wider and larger than top member  14  as it is used with an implant  440  having a large diameter in the range of 22.0 mm to 28.0 mm. The top member  414  needs to be wider when used with implant  440  in order to provide a central bar  435  of sufficient length to interdigitate and mate with the depression  444  of the implant  440  in order to prevent its rotation. Further, the top member  414  is tapered at portion  416  so as not to cause erosion or pressure against the vessels that may be present in the area of the spine adjacent to the portion  416  of the top member  414 . 
         [0114]    Referring to  FIGS. 29-32 , a fifth alternative embodiment of the spinal fixation device  510  with a staple member  512  having a generally rectangular top member  514  is shown. The staple member  512  is similar in structure to the staple  212  described above except that the top member  514  has multipronged projection blades  516  and  517  depending from its lower surface  530  as shown in  FIG. 30 . The multipronged projection blades  516  and  517  have the same function and similar structure as the projections  16  and  17  described above and include segmented and ratcheted portions  534  which are similar in design are function to segmented and ratcheted portions  34 . The multipronged blade projections  516  and  517  offer the added advantage of increasing the strength and stability of the staple member  514  once it is inserted into the bone of the vertebrae V providing a greater area of engagement of the staple member  512  to the vertebrae V. 
         [0115]    The lower surface  530  has knobs  532  and  534  extending therefrom for engaging and interdigitating with a spinal implant  540  having an insertion end  541  with openings  542  and  544  for receiving knobs  532  and  534  respectively. 
         [0116]    Referring to  FIGS. 31 and 32 , the spinal fusion implant  540  is shown inserted within the disc space between two adjacent vertebrae V. The spinal implant  540  is generally rectangular in shape. The multiprong blade projections  516  and  517  have a width that is approximately equal or slightly less than the width of the spinal fusion implant  540 . Once inserted, the spinal fixation device  510  compresses the bone of the vertebrae V towards the spinal fusion implant  540  as discussed above in reference to  FIG. 12 . The spinal fixation device  510  may be secured to the spinal fusion implant  540  with a screw  60  as discussed above. 
         [0117]    The spinal fixation device  510  having a staple member  512  is the preferred embodiment of the present invention for use with a multi-segmental spinal alignment means  600  described in greater detail below in that the staple  512  provides a more solid anchoring means that can resist greater torsion forces resulting from the application of the multi-segmental spinal alignment means  600  to align the spine. 
         [0118]    Alternatively, for all of the embodiments described above, the spinal fixation device  10  of the present invention could be made of resorbable materials, such as bio-compatible resorbable plastics, that resorb at an appropriate rate such that once the spinal fixation device  10  is no longer needed (i.e. when spinal fusion is complete) the body would resorb the spinal fixation device  10 . One such resorbable material is polygalactone, however any other resorbable plastic or other material safely usable within the human body are also within the scope of the present invention. 
         [0119]    Further, the spinal fixation device could be only in part resorbable such that the projections  16  and  17  of the staple member  12  would be non-resorbable and would remain incarcerated in the vertebrae V and sealed off once the resorbable portion of the staple is resorbed by the body. 
         [0120]    Referring to  FIGS. 33 and 34 , as a further application, the spinal fixation device  510  of the present invention may be used as an anchor for a multi-segmental spinal alignment means  600 , such that a multiplicity of spinal fixation devices may then be interconnected via a cable, rod, bar, or plate, so as to achieve or maintain any desired multi-segment spinal alignment. In the preferred embodiment, the multi-segmental spinal alignment means  600  comprises more than one spinal fixation device  510  of the present invention placed in series along the spine such that each spinal fixation device  510  spans one disc D and engages two adjacent vertebrae V. The spinal fixation device  510  is preferred over the other embodiments of the present invention in that it has a greater area of engagement with the vertebrae V so as to provide a solid anchoring means for the multi-segmental spinal alignment means  600 . However, it is appreciated that other embodiments including but not limited to those described herein may be utilized as anchoring means for the multi-segmental spinal alignment means  600 . 
         [0121]    When used as an anchor, each spinal fixation device  510  interdigitates with and is connected to a spinal fusion implant  610  having an insertion end  612 , an interior chamber  614  and is inserted in the disc space between the two adjacent vertebrae. The spinal fusion implant  610  has a threaded blind hole  620  for receiving a threaded post  622  therein. The blind hole  620  has a casing that is made of strong surgically, implantable material such as, but not limited to titanium. The casing  624  extends from the insertion end  612  of the spinal fusion implant  610  into the interior central chamber  614 . The insertion end  612  has a rigid construction that is capable of withstanding high torsion forces resulting from the tensioning of the multi-segmental spinal alignment means to align segments of the spine. In the preferred embodiment, the insertion end  612  of the spinal fusion implant has an end portion  626  that closes the insertion end  612 . The end portion is substantially thicker than the rest of the spinal fusion implant  610  and in the preferred embodiment, the end portion  626  has thickness ranging from 1.5 mm to 4.0 mm, with 2.5 mm being the preferred thickness. 
         [0122]    Referring to  FIG. 34 , the threaded post  622  has a threaded end  628  with a locking thread pattern that is substantially longer than the locking thread pattern  62  of the screw  60  described above and a head portion  630  having a hole  632  for receiving a rod  634  or a cable therethrough. The head portion  630  has a rounded exterior surface to prevent any damage such as aortic erosion to the vessels in the area adjacent to the spine. In the preferred embodiment the threaded post has a diameter ranging from 3.0 mm to 6.0 mm, with 4.5 mm being the preferred diameter and has a length ranging from 15.0 mm to 25.0 mm, with 20.0 mm being the preferred length. The head portion  630  extends at a height above the top member  514  of the spinal fixation device  510  of approximately 8.0 mm to 16.0 mm, with 12.0 being the height preferred once it is threadably attached to the spinal fusion implant  610  such that it does not significantly protrude from the spinal column into the tissue and vessels adjacent thereto. 
         [0123]    Once the threaded post  622  is attached to the spinal fusion implant  610 , the head portion  630  of each threaded post  622  are connected to one another by the rod  634  having a sufficient diameter to fit through the hole  632  of each head portion  630 . The rod  634  has at least a portion thereof that is threaded so that a plurality of lock nuts  638  may be used to secure the rod  634  to the head portions  630 . The lock nuts  638  may also be used as length adjusting means to adjust the length of the rod  634  between head portions  630  so that segmental portions of the spine may be held closer together or held further aport for the purposes of aligning the spine. It is appreciated that a plurality of multi-segmental spinal alignment means  600  may be placed in series either on one side or on opposite sides of the spine, such that one side of the spine may be extended while the other side may be held stationary or may be compressed in order to achieve proper spinal alignment. The multi-segment spinal alignment may be maintained by keeping the rod tensioned with the lock nuts  638  or by any other means well known by those skilled in the art. It is also appreciated that in place of a rod  634  a cable, a plate or any other means well known by those skilled in the art may be used to interconnect the multi-segmental spinal alignment means. 
         [0124]    Referring to  FIG. 35 , a sixth alternative embodiment of the spinal fixation device of the present invention is shown and generally referred to by the numeral  710 . The spinal fixation device  710  comprises a top member  714  that is similar to the top member  14  described above, except that it does not have projections  16  and  17  extending from the bottom surface. Like numbers are being used to designate identical features of the top members  14  and  714 . 
         [0125]    In the top member  714 , instead of having projections  16  and  17 , independent projection members  716  and  717  in the form of screws are used to secure the top member  714  of the spinal fixation device  710  to the vertebrae V of the spine. The projection screw members  716  and  717  each terminate in a sharp distal end  720  and  722  respectively, have a threaded portion  723 , and have screw heads  724  and  726  for engaging a screw driver or similar driving instrument. 
         [0126]    The top member  714  has a hole  728  on one end and a hole  730  at its other end through which each of the projection screw members  716  and  717  respectively, may pass. The projection screw members  716  and  717  pass through the holes  728  and  730  to engage the vertebrae V. Each of the holes  728  and  730  has a concentric counter sunk recess  732  for receiving and seating the screw heads  724  and  726  of the projection screw members  716  and  717  so that the screw heads  724  and  726  are flush or below the top surface  20  of the stop member  714  once inserted into the vertebrae V. 
         [0127]    As the projection screw members  716  and  717  are threaded, they can be rotationally advanced into the vertebrae instead of by way of an impaction force such that the potential for damage to the vertebrae V is reduced. The threads of the threaded portion  723  follow one another as the projection screw members  716  and  717  are being screwed into the bone such that the integrity of the vertebrae V is preserved. Also, as the projection screw members  716  and  717  are independent from the top member  714 , the penetration depth of the spinal fixation device  710  into the bone of the vertebrae V may be easily altered by selecting different sized projection screw members  716  and  717  appropriate for the particular vertebrae being fused. Further, it is possible to configure the holes  728  and  730  in the top member  714  such that the projection screw members  716  and  717  may be inserted into the vertebrae V from a number of different angles relative to the top member  714 . 
         [0128]    Adjacent and proximate to each of the holes  728  and  730  are threaded openings  740  and  742 , respectively, for receiving locking screws  744  and  746  respectively. Each of the locking screws  744  and  746  have a head portion  750  and a locking thread portion  754  for threadably and lockably engaging the threaded openings  740  and  742 . The locking screws  744  and  746  are attached to the top member  714  after the projection screw members  716  and  717  have been inserted into the vertebrae V. At least a part of the head portion  750  and  752  blocks and preferably makes contact with the screw projections  716  and  717  to prevent any unwanted loosening and outward excursion of the screw projections  716  and  717 . 
         [0129]    It is appreciated that the projection members  716  and  717 , instead of being threaded screws, may have a number of other configurations such as, but not limited to, the configurations of the projections described above for the various embodiments of the present invention. If the projections members  716  and  717  are ratcheted instead of being threaded, they can be driven into the vertebrae V with a driving instrument and impaction force as described above for the method of the present invention. 
         [0130]    While the present invention has been described with respect to its preferred embodiment and a number of alternative embodiments, it is recognized that additional variations of the present invention may be devised without departing from the inventive concept and scope of the present invention. 
         [0131]    
       27