Abstract:
A Static Compression Device (SC device) for active, measurable compression of a spinal fusion graft is disclosed. The device attaches to adjacent vertebral bodies or other bone pieces works with a compression tool to apply compressive force to adjacent vertebral bodies or pieces of bone to assist fusion. Once compressed, the SC device locks to maintain the compression applied at surgery, while preventing further compression after surgery. In one embodiment, the compression device applies a desired, quantified, amount of force to allow the surgeon more control over the force applied to a cervical, thoracic or lumbar implant than previously available. The SC device may be used to compresses multiple adjacent vertebrae across adjacent bone graft(s) to facilitate fusion of these vertebrae to treat pain from damaged disks between vertebrae that impinge on the spinal cord and nerve roots. SC device may also apply compression across fractures to facilitate union.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a Divisional of application Ser. No. 14/525,095 filed Oct. 27, 2014, which is a Continuation-in-Part of application Ser. No. 13/709,864 filed Dec. 10, 2012, which is a Continuation of application Ser. No. 12/522,147 (now U.S. Pat. No. 8,328,853), filed Jul. 2, 2009, which is a US 371 National Stage Entry of PCT/US07/06830 filed Mar. 20, 2007, which claims the benefit of priority from Provisional Application Ser. No. 60/788,607 filed Apr. 3, 2006. Each of the aforementioned applications is incorporated herein by reference. 
         [0002]    This application is related to application Ser. No. 12/694,179 filed Jan. 26, 2010 (now U.S. Pat. No. 7,901,440) which is a Continuation of application Ser. No. 12/522,147 (now U.S. Pat. No. 8,328,853), filed Jul. 2, 2009, which is a US 371 National Stage Entry of PCT/US07/06830 filed Mar. 20, 2007, which claims the benefit of priority from Provisional Application Ser. No. 60/788,607 filed Apr. 3, 2006. Each of the aforementioned applications is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention is directed to devices and methods to compress two or more adjacent vertebrae across an adjacent bone graft to facilitate fusion of these vertebrae to treat pain produced by pressure from the disks between such vertebrae bulging and resulting in contact with and pressure on the spinal cord and adjacent nerve roots. 
         [0005]    2. Description of Related Art 
         [0006]    For nearly half a century, anterior cervical discectomy and fusion has been performed for individuals complaining of intractable upper extremity pain due to cervical disc herniation or bone spurs at single or multiple levels. This procedure has undergone several significant modifications since its inception. The introduction of the Smith-Robinson technique of using tricortical iliac crest bone graft, the technique of denuding vertebral endplates of cartilage described by Zdeblick et al., and the present use of cervical plates have all represented significant technical advances which have increased fusion rates and improved patient outcomes. Currently it is possible to expect greater than 85% good or excellent outcomes for individuals with appropriate indications who undergo this surgical procedure. 
         [0007]    However, several problems remain. Although fusion rates for one level anterior cervical fusion with autograft (patient&#39;s own bone) may approach 95%, these rates decrease significantly for each additional level incorporated in the fusion. Additionally, using autograft bone typically involves the use of a second incision, which significantly increases patient morbidity. Allograft bone (bone from another human) is a viable option, but has considerably lower fusion rates than autograft and is generally not considered a good choice in multiple level fusion surgery. 
         [0008]    The use of anterior cervical plates has been credited with increasing fusion rates in multiple level fusions. It is thought that the immediate stability provided by the plate provides a more favorable environment for fusion to occur. The vast majority of plates on the market provide for static stabilization of the vertebral body-graft construct (no compression, no dynamization). More recently dynamic plates have been introduced. These plates provide for passive dynamic compression of the vertebral body-graft construct. This compression occurs post-operatively when the weight of the patient&#39;s head loads the construct, allowing for passive compression of the graft to occur. Wolff&#39;s law (the concept that bone heals best under compression) suggests that the use of dynamic compression plates should lead to increased fusion rates. However, this has not been found to be the case. Several studies have indicated that dynamic compression plates do not lead to higher fusion rates than static plates. In addition, the possibility of uncontrolled settling over time which may lead to kyphosis (reversal of the normal curvature of the neck) has caused these plates to fall out of favor with many surgeons. 
         [0009]    Wolff&#39;s law is a well-accepted orthopedic principle, championed and reported in the trauma literature by the Swiss AO Foundation, a non-profit surgeon-driven organization dedicated to progress in research, development, and education in the field of trauma and corrective surgery. Several studies have shown that long bones heal best under rigid compression. This has led to the development of special compression plates that are currently widely used in surgical techniques of open reduction and internal fixation of fractures. 
         [0010]    It is believed that there is no plate on the market that truly invokes Wolff&#39;s law in spinal fusion surgery by providing rigid static loading of the graft-vertebral body construct. Mechanisms for achieving compression on adjacent vertebrae are known. But, most of these devices either utilize compression across individual screws (risking cut out due to lessened surface area) or attempt to achieve compression prior to the plate being applied (making this a cumbersome technique). 
       SUMMARY OF THE INVENTION 
       [0011]    The Static Compression Device (SC device) of the present invention allows for active, measurable compression of a fusion graft by the surgeon at the time of surgery. The SC device is attachable to adjacent vertebral bodies or other pieces of bone and has a device that applies compressive force to the adjacent vertebral bodies or other pieces of bone to assist fusion according to Wolff&#39;s law. The SC device has a locking mechanism that maintains the compression applied at surgery, but prevents further compression (settling) from occurring after surgery. So, the SC device allows the surgeon the ability to compress a segment or other adjacent pieces of bone, measure the applied compression, and to lock the segment or pieces of bone in the compressed position. In one embodiment of the invention, the pressure is applied to the SC device through a compression device that applies a desired and measurable amount of force. In this embodiment, the combination of the SC device with a pressure applying and measuring device allows the surgeon more control over the force applied to a cervical, lumbar or thoracic implant or implant applied to other pieces of bone than has previously been available. 
         [0012]    The SC device of the present invention in one embodiment compresses two or more adjacent vertebrae across an adjacent bone graft to facilitate fusion of these vertebrae to treat pain produced by pressure from the disks between such vertebrae, adjacent bone spurs or both bulging and resulting in contact with and pressure on the spinal cord and adjacent nerve roots or any other disorder of the spine. The vertebrae may be in the cervical, thoracic or lumbar spine. In fact, in various embodiments, the SC device may be used to apply measurable compression across any type of bony interface (e.g. fractures) to facilitate union. 
         [0013]    The SC device has four unique characteristics which together provide for static compression of the vertebral body-graft interface: [0012] The use of fixed angle screws to secure the SC device to the vertebral bodies; [0013] The use of a compression device to apply and measure the pressure applied to the vertebral bodies by the SC device; [0014] The technique of using active, static compression to assist the fusion process; and [0015] The use of a locking mechanism that maintains compression during the fusion process to facilitate bone growth. This SC device differs from currently known static plates by providing controlled loading (compression) of the graft at the time of surgery. The SC device also differs from currently known dynamic plates in that the compression achieved is “static” (rigid) and prevents further “dynamic” settling from occurring after the procedure is completed. The resulting major advantage of the SC device over previously known devices is that the SC device may significantly increase fusion rates (especially in multiple level cervical fusion) and maintain the anatomy of the cervical spine (preventing excessive compression leading to kyphosis). In fact, it is believed that using the SC device to provide static loading at each level in multiple level fusions may allow the use of allograft bone to approach fusion rates now only attainable by using autograft techniques. 
         [0014]    The invention will be described hereafter in detail with particular reference to the drawings. Throughout this description, like elements, in whatever embodiment described, refer to common elements wherever referred to and referenced by the same reference number. The characteristics, attributes, functions, interrelations ascribed to a particular element in one location apply to that element when referred to by the same reference number in another location unless specifically stated otherwise. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of one embodiment of the static compression device of the present invention. 
           [0016]      FIG. 2  is a top view of the static compression device of  FIG. 1 . 
           [0017]      FIG. 3  is a bottom view of the static compression device of  FIG. 1 . 
           [0018]      FIG. 4  is a side view of the static compression device of  FIG. 1 . 
           [0019]      FIG. 5  is a bottom end view of the static compression device of  FIG. 1 . 
           [0020]      FIG. 6  is a perspective view of the male plate of the static compression device of  FIG. 1 . 
           [0021]      FIG. 7  is a side view of the male plate of the static compression device of  FIG. 1 . 
           [0022]      FIG. 8  is a top view of the male plate of the static compression device of  FIG. 1 . 
           [0023]      FIG. 9  is a bottom end view of the male plate of the static compression device of  FIG. 1 . 
           [0024]      FIG. 10  is a perspective view of the female plate of the static compression device of  FIG. 1 . 
           [0025]      FIG. 11  is an end view of the female plate of the static compression device of  FIG. 1 . 
           [0026]      FIG. 12  is a bottom view of the female plate of the static compression device of  FIG. 1 . 
           [0027]      FIG. 13  is a perspective view of the interconnecting plate of the static compression device of  FIG. 1   
           [0028]      FIG. 14  is a top view of the interconnecting plate of the static compression device of  FIG. 1 . 
           [0029]      FIG. 15  is a perspective view of the static compression device of  FIG. 1  in an embodiment without the interconnecting plate. 
           [0030]      FIG. 16  is a perspective view of the static compression device of  FIG. 15  in an unlocked configuration. 
           [0031]      FIG. 17  is a perspective view of the static compression device of  FIG. 15  in a locked configuration. 
           [0032]      FIG. 18  is a perspective view of the locking clamp of the static compression device of  FIGS. 1 and 15 . 
           [0033]      FIG. 19  is a side view of the locking screw of the static compression device of  FIG. 1 . 
           [0034]      FIG. 20  is a perspective view of one embodiment of the compression tool of the present invention. 
           [0035]      FIG. 21  is a perspective view of the embodiment of the compression tool of  FIG. 20  from the opposite side of the view of  FIG. 20 . 
           [0036]      FIG. 22  is a perspective view of the preferred embodiment of the compression tool of the present invention with cannula for receiving a screwdriver. 
           [0037]      FIG. 23  is a close up perspective view of the distal end of the compression tools of the present invention. 
           [0038]      FIG. 24  is a perspective view of another embodiment of the compression tool of the present invention. 
           [0039]      FIG. 25  is a side view of the embodiment of the compression tool of  FIG. 24 . 
           [0040]      FIG. 26  is an exploded perspective view of the turnbuckle of the embodiment of the compression tool of  FIG. 24 . 
           [0041]      FIG. 27  is an exploded perspective view of the compression tool of  FIG. 24 . 
           [0042]      FIG. 28  is a perspective view of an embodiment of the static compression device of the present invention. 
           [0043]      FIG. 29  is a perspective view of the static compression device of  FIG. 28  without the locking screw in place. 
           [0044]      FIG. 30  is a side view of the locking screw of the static compression device of  FIG. 28 . 
           [0045]      FIG. 31  is a cross-sectional perspective view of the static compression device of  FIG. 28  without the locking screw in place. 
           [0046]      FIG. 32  is a perspective view of the static compression device of  FIG. 28  without an alternate embodiment of the locking screw in place. 
           [0047]      FIG. 33  is a perspective view of an alternate embodiment of the static compression device. 
           [0048]      FIG. 34  is an end view of the female plate of the static compression device of  FIG. 33  with the locking screw and cam in place. 
           [0049]      FIG. 35  is a perspective view of the locking screw and cam of the static compression device of  FIG. 33 . 
           [0050]      FIG. 36  is a perspective view of one embodiment of the static compression device of the present invention. 
           [0051]      FIG. 37  is a top view of the static compression device of  FIG. 36 . 
           [0052]      FIG. 38  is a bottom view of the static compression device of  FIG. 36 . 
           [0053]      FIG. 39  is a side view of the static compression device of  FIG. 36 . 
           [0054]      FIG. 40  is a bottom end view of the static compression device of  FIG. 36 . 
           [0055]      FIG. 41  is a top end view of the static compression device of  FIG. 36 . 
           [0056]      FIG. 42  is a perspective view of the male plate of the static compression device of  FIG. 36 . 
           [0057]      FIG. 43  is a side view of the male plate of the static compression device of  FIG. 36 . 
           [0058]      FIG. 44  is a bottom view of the male plate of the static compression device of  FIG. 36 . 
           [0059]      FIG. 45  is a perspective view of the female plate of the static compression device of  FIG. 36 . 
           [0060]      FIG. 46  is an end view of the female plate of the static compression device of  FIG. 36 . 
           [0061]      FIG. 47  is a bottom view of the female plate of the static compression device of  FIG. 36 . 
           [0062]      FIG. 48  is a perspective view of the male plate and female plate of the static compression device of  FIG. 36  in an interconnected relationship. 
           [0063]      FIG. 49  is a perspective view of the male plate and female plate of the static compression device of  FIG. 36  in an interconnected relationship and with the locking plate in place. 
           [0064]      FIG. 50  is a perspective view of the male plate and female plate of the static compression device of  FIG. 36  in an interconnected relationship and with the locking plate and locking screw in place. 
           [0065]      FIG. 51  is a top view of the static compression device of  FIG. 36  with the male plate interconnected to the female plate and with the locking plate in place and in the uncompressed position. 
           [0066]      FIG. 52  is a top view of the static compression device of  FIG. 36  with the male plate interconnected to the female plate and with the locking plate in place and in the compressed position. 
           [0067]      FIG. 53  is a bottom view of the locking plate of the static compression device of  FIG. 36 . 
           [0068]      FIG. 54  is a side view of the locking screw of the static compression device of  FIG. 36 . 
           [0069]      FIG. 55  is a perspective view of an alternate embodiment of the static compression device. 
           [0070]      FIG. 56  is a perspective view of the static compression device of  FIG. 55  with the guide plate shown in phantom. 
           [0071]      FIG. 57  is a perspective view of a series of trial spacers and corresponding handle of one aspect of the present invention. 
           [0072]      FIG. 58  is a perspective view of an embodiment of the static compression device designed to be used in the thoracic or lumbar region of the spine. 
           [0073]      FIG. 59  is a perspective view of an embodiment of the static compression device designed to be used to treat fractures. 
           [0074]      FIG. 60  is a perspective view of an embodiment of the static compression device designed to be used to treat fractures. 
           [0075]      FIG. 61  is a top perspective view of an alternative embodiment of the static compression device for treating spinal fractures. 
           [0076]      FIG. 62  is a bottom perspective view of the embodiment of  FIG. 61  of the static compression device for treating spinal fractures. 
           [0077]      FIG. 63  is a top perspective view of the end plate of the embodiment of  FIG. 61  of the static compression device for treating spinal fractures. 
           [0078]      FIG. 64  is a bottom perspective view of the end plate of the embodiment of  FIG. 61  of the static compression device for treating spinal fractures. 
           [0079]      FIG. 65  is a top perspective view of the center plate of the embodiment of  FIG. 61  of the static compression device for treating spinal fractures. 
           [0080]      FIG. 66  is a bottom perspective view of the center plate of the embodiment of  FIG. 61  of the static compression device for treating spinal fractures. 
           [0081]      FIG. 67  is a top perspective view of the lock screw of the embodiment of  FIG. 61  of the static compression device for treating spinal fractures. 
           [0082]      FIG. 68  is a top perspective view of an alternative embodiment derived from the embodiment of  FIG. 61  having additional levels for treating spinal fractures of multiple vertebrae. 
           [0083]      FIG. 69  is a top perspective view of another alternative embodiment derived from the embodiment of  61  also having additional levels for treating spinal fractures of multiple vertebrae. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0084]    The SC device  10  in a preferred embodiment shown in  FIGS. 1-14 and 18  has five main parts, a male plate  12 , a female plate  14 , an interconnecting plate  15 , a locking clamp  16  and a locking screw  18  that, in combination with standard cancellous bone screws (not shown) fix the SC device  10  to the patient&#39;s vertebrae. The SC device  10  has a top side  20 , a bottom side  22  and opposed medial sides  24 . 
         [0085]    The male plate  12  has a male main body  26  and a central protrusion  28  extending away from the male main body  26 . The central protrusion  28  has a top surface  30 , a longitudinal axis  32 , a bottom surface  33  and parallel sides  36 . Central protrusion  28  also has a threaded hole  35  in the top surface  30 . 
         [0086]    The male plate  12  also has a pair of side protrusions  29  extending away from the male main body  26  on opposite sides of the central protrusion  28 . Each of the side protrusions  29  has an inner surface  37  and an outer surface  39 . The inner surfaces  37  are directed toward the central protrusion  28  and are preferably curved in a concave fashion to mate with the outer surfaces  63  of the left guide  58  and right guide  60  of the interconnecting plate  15  or the female plate  14  as will be described hereafter. 
         [0087]    The male main body  26  is relatively flat with a top side  34  and a bottom side  36  and, in a preferred embodiment, has two screw receiving holes  38 . The screw receiving holes  38  each have a bowl-shaped basin  40  on the top side  34  to receive the heads of the screws  43  and a throughhole  42  through which the main body of the screws  43  pass to come into contact with the vertebral body. The throughholes  42  are configured in a manner that allows the cancellous bone screws  43  to be rigidly fixed to the plate once inserted in bone. The method of fixing the screws  43  to the plate may utilize any number of mechanisms well understood in the art that allow the screws  43  and the male plate  12  to maintain a rigid relationship once the screws  43  are inserted in bone. 
         [0088]    The bottom side  36  of the male plate  12 , female plate  14  and interconnecting plate  15  is preferable roughened, thereby allowing the bottom side  22  of the SC device  10  to “grip” the vertebral body when the bottom side  22  of the SC device  10  is brought into contact with and secured to the vertebral body by the interaction of the screws  43  and the body of the SC device  10  as described herein. 
         [0089]    As mentioned, the male plate  12  has a central protrusion  28  with a top surface  30  and a longitudinal axis  32 . Central protrusion  28  is dimensioned to mate with and secure the male plate  12  with the interconnecting plate  15  or the female plate  14  as will be described in detail hereafter. Where the interconnecting plate  15  is used, the combined length of the central protrusion  28  on the male plate  12  and the central protrusion  28 ′ on the interconnecting plate  15  will be slightly longer than the distance the SC device  10  is intended to provide compression over. 
         [0090]    Central protrusion  28  has a boss  44  extending entirely through it approximately parallel to the top surface  30  that is designed to mate with a relief cut  62  in the interconnecting plate  15 /female plate  14 . 
         [0091]    The interconnecting plate  15  combines the features of the male plate  12  and the female plate  14  on its opposite ends. As a result, on one end of interconnecting plate there is a central protrusion  28 ′ essentially as described in connection with the central protrusion  28  of male plate  12 . On the opposite end of interconnection plate  15 , there is a protrusion receiving channel  56  essentially as described hereafter in connection with the protrusion receiving channel  56  of female plate  14 . In addition, interconnecting plate  15  has at least a pair of screw receiving holes  38  essentially as described in connection with the screw receiving holes  38  of the male plate  12 . 
         [0092]    The purpose of the interconnecting plate  15  is to allow the SC device  10  to be secured to three or more adjacent vertebrae and allow the SC device  10  to apply compression across these vertebrae to facilitate healing as described herein. As a result, a single interconnecting plate  15  may be placed between the male plate  12  and the female plate  14  and attached to the vertebra between the vertebrae that the male and females plates  12 ,  14  are attached to. Alternately, several interconnecting plates  15  can be connected end to end (i.e., the protrusion receiving channel  56  of one interconnecting plate  15  receives the central protrusion  28 ′ of an adjacent interconnecting plate  15  and the process continues until all the interconnecting plates  15  are joined together) to form an interconnecting span with a male plate  12  and a female plate  14  attached to the ultimate ends of this chain of interconnecting plates  15 . In this embodiment of the invention, each of the interconnecting plates  15  would have screw receiving holes  38  allowing each interconnecting plate  15  to be attached to a single vertebra by bone screws  43 . In a variant of this embodiment, a single interconnecting plate  15  could have several sets of screw receiving holes  38  so that this single interconnecting plate  15  could be attached to several adjacent vertebrae or could span a previously fused segment. 
         [0093]    The female plate  14  has a female main body  52  with a bottom side  54  and a protrusion receiving channel  56 . Protrusion receiving channel  56  is formed between a left guide  58  and a right guide  60  that extend away from the female main body  52 . Left guide  58  and right guide  60  each have an inner surface  61 , an outer surface  63 , a bottom surface  65  and a top surface  67 . Left guide  58  and right guide  60  are basically rectangular in cross-section with inner surfaces  61  being preferably essentially planar and with outer surfaces  63  being essentially outwardly curved with a series of ridges  71  extending outwardly. On the bottom surface  65  of the left and right guides  58 ,  60  facing the protrusion receiving channel  56 , there is a relief cut  62  machined to accept the boss  44  on the central protrusion  28 ′ of the interconnecting plate  15  or the male plate  14 . 
         [0094]    Protrusion receiving channel  56  is dimensioned to snugly receive the central protrusion  28 ′ with the locking clamp  16  in place on the central protrusion  28 ′ as will be described hereafter so that the central protrusion  28 ′ is “captured” and held in the protrusion receiving channel  56  by physical contact between the outer surface of the locking clamp  16  and the inner surfaces of the left guide  58  and right guide  60  as well as by the interaction between the central protrusion  28 ′ and the boss  44  on the inferior aspect of the central protrusion  28 ′ and relief cut  62 . 
         [0095]    The outer surfaces  63  of the left and right guides  58 ,  60  contact the inner surfaces  37  of the side protrusions  29  under the influence of the locking clamp  16 , as will be described hereafter, to securely locate the female plate  14  with respect to the interconnecting plate  15  and the interconnecting plate  15  with the male plate  12 . 
         [0096]    The female plate  14 , also in a preferred embodiment, has two screw receiving holes  82 . These screw receiving holes  82  receive standard cancellous bone screws  43  that are threaded into the bone of the vertebrae. In similar fashion to screw receiving holes  38 , the screw receiving holes  82  also have a bowl-shaped basin  84  on the upper surface  78  to receive the heads of the bone screws  43  and a throughhole  86  through which the main body of the bone screws  43  pass to come into contact with the vertebral body. The throughholes  86  are configured in a manner that allows the cancellous bone screws  43  to be rigidly fixed to the plate once inserted in bone by the interaction of the screws  43  with the basins  84 . The method of fixing the screws  43  to the female plate  14  may utilize any number of mechanisms well understood in the art that allow the screws  43  and the female plate  14  to maintain a rigid relationship once the screws  43  are inserted in bone. 
         [0097]    The SC device  10  has a locking mechanism  88 . Locking mechanism  88  converts “active” compression applied by the surgeon using the compression device  90  described below interacting with the device  10  at the time of surgery to “static” compression after surgery. The locking mechanism  88  also provides rigid fixation to the SC device  10  to optimize bone healing and preventing further settling from occurring. 
         [0098]    The locking mechanism  88  in one embodiment includes locking clamp  16  and locking screw  18 . The locking clamp  16  has a top surface  92  with a hole  93  extending through it, a bottom surface  94 , parallel sides  96 , a longitudinal axis  97  and an inner channel  99  between the parallel sides  96  and below the top surface  92 . The inner width of the inner channel  99  of the locking clamp  16  (i.e., the inside distance between the parallel sides  96 ) is such that the locking clamp  16  will fit snugly over the central protrusion  28 . The width of the locking clamp  16  (i.e., the distance between the parallel sides  96 ) is such that the locking clamp  16  will fit snugly between the left and right guides  58 ,  60  in the protrusion receiving channel  56 . 
         [0099]    A single large locking screw  18 , dimensioned to rotate freely within the hole  93  of the locking clamp  16 , activates the locking mechanism  88 . In the embodiment of the invention shown in  FIGS. 1-19 , the locking screw  18  has a head  106 , a body  108  and a distal end  110  opposite the head  106 . The head  106  has a larger cross-sectional diameter than the threaded body  108 . The body  108  is threaded at least on the distal end  110  to correspond to the threads of the threaded hole  35  in the protrusion  28 . 
         [0100]    The parallel sides  96  of locking clamp  16  preferably have a series of ridges  46  and valleys  48 , preferably placed substantially perpendicular to the longitudinal axis  97  and tapered from top to bottom, to locate and affix the locking clamp  16  to the inner surfaces of the left guide  58  and right guide  60  of the interconnecting plate  15  and female plate  14 . Through this configuration, the ridges  46  and valleys  48  on the sides  96  of the locking clamp  16  preferably contact and engage with the inner surfaces of left and right guides  58 ,  60  in frictional or mechanical contact to precisely locate and affix the locking clamp  16  within the protrusion receiving channel  56 . Because the series of ridges  46  and  48  are tapered, as the series of ridges  46 ,  48  are moved into contact with and engage the inner surfaces of left and right guides  58 ,  60 , this engagement adds compressive force to the adjacent vertebral bodies through the SC device  10 . The locking clamp  16  is preferably made of a material that is harder than the material of the interconnecting plate  15  or the female plate  14 . 
         [0101]    The present invention also includes a compression device  90  ( FIGS. 20-23 ) that allows the surgeon to provide active, controlled compression between the two sliding components of the SC device  10  (male plate  12  and female plate  14 ) at the time of surgery. This compression device  90  allows the surgeon to accurately measure the force applied across the graft by the SC device  10  and allows the surgeon to stop compressing when a predetermined amount of force has been obtained. Since both the male plate  12  and the female plate  14  are each connected to adjacent vertebral bodies by two fixed angle bone screws  43 , this provides for even, surgeon-controlled compression across the interbody graft. 
         [0102]    The compression device  90  has two arms  114 ,  116  that each have a handle  118 ,  120  at one end and a foot  122 ,  124 , located at a distal end  126 ,  128 , respectively. The arms  114 ,  116  are connected via a pivot  130  that connects the respective arms  114 ,  116  and allows them to move in scissors-like movement with respect to each other. By connecting the arms  114 ,  116  through a pivot  130 , a surgeon squeezing the handles  118 ,  120  moves the distal ends  126 ,  128  together. By connecting these distal ends  126 ,  128  to the device  10 , a surgeon squeezing the handles  118 ,  120  together is able to apply compression to the SC device  10  and thus to adjacent vertebral bodies through the interaction of the feet  122 ,  124  and the male plate  12  and female plate  14  as will be explained hereafter. 
         [0103]    Each foot  122 ,  124  of the compression device  90  engages the male plate  12  or female plate  14  (or interconnecting plate  15 ), respectively, to apply pressure to move the male plate  12  and female plate  14  toward each other as the physician squeezes the handles  118 ,  120  together. In the embodiment of compression device  90  and SC device  10  shown in  FIG. 23 , the distal ends  126 ,  128  of feet  122 ,  124 , respectively, are shaped with pins  132  that protrude from the distal ends  126 ,  128 . 
         [0104]    In the embodiment shown in  FIGS. 21-23 , pins  132  protrude from adaptor plates  134  having throughholes  136 . Adaptor plates  134  are secured to the distal ends  126 ,  128  of feet  122 ,  124 , respectively by screws  138  that pass through throughholes  136 . The distal ends  126 ,  128  of feet  122 ,  124 , respectively each have a threaded secure hole  140  that receives a screw  138 . In this way, adaptor plates  134  are secured to the distal ends  126 ,  128  of feet  122 ,  124 , respectively. The adaptor plates  134  may be removed and replaced with hooks protruding from the distal ends  126 ,  128  of feet  122 ,  124 , respectively, that each engage a slot on the outermost aspects of the male and female plates  12 ,  14  placed or formed in the top side  34  of the male plate  12  and the top surface  78  of the female plate  14 . This enables the ends of compression device  90  to be modular (i.e., replaceable so that the appropriate end for a desired application can be placed on the compression device  90 ) with respect to using different techniques to achieve compression. 
         [0105]    The male plate  12  and female plate  14  each have a notch  142 ,  144 , respectively, located on opposite ends of the SC device  10  and shaped to receive the pins  132  in a snug, conforming fashion so that compression applied to the feet  122 ,  124  by squeezing the handles  118 ,  120  together is transferred from the distal ends  126 ,  128  to the male plate  12  and female plate  14 , respectively, through the interaction of the pins  132  with the notches  142 ,  144 . 
         [0106]    In an alternate embodiment of the invention, the distal ends  126 ,  128  of feet  122 ,  124 , respectively, again engage the male plate  12  and the female plate  14 , respectively, through pins  132 . However, in this embodiment, the notches  142 ,  144  are located in the outer edge of the top surfaces  26  and upper surface  78  of the male plate  12  and female plate  14 , respectively, sized and shaped to receive the pins  132  in a snug fashion so that compression applied to the feet  122 ,  124  by squeezing the handles  118 ,  120  together is transferred from the pins  132  to the male plate  12  and female plate  14 , respectively, through the notches  142 ,  144 . 
         [0107]    The compression device  90  also preferably has a gauge  146  that allows the physician to measure the compression force being applied to the SC device  10 , and thus to the vertebral bodies, by the squeezing together of the handles  118 ,  120 . The gauge  146 , by quantifying the deflection of the handles  118 ,  120  when they are squeezed together, gives an accurate measurement of force applied across the SC device  10 . In the embodiment of the compression device  90  shown in  FIG. 20 , gauge  146  includes an arm  148  attached to pivot  130  and located between handles  118 ,  120 . The arm  148  preferably has a circular, oval, square or rectangular cross-section and a horizontal and a vertical component  149 ,  151 , respectively. The arm  148  has indicia  150  located on at least a portion of the horizontal component  149 . 
         [0108]    The gauge  146  has an indicator  152  that is an annular spacer located along the horizontal component  149  of arm  148 . The indicator  152  has a central opening  154  sized to be approximately the same size and shape as the cross-sectional size and shape of the horizontal component  149  of arm  148  so that indicator  152  is attached to the horizontal component  149  by sliding the horizontal component  149  through the first central opening  154 . A frictional fit between the first central opening  154  and the horizontal component  149  holds the indicator  152  in position on the horizontal component  149 . 
         [0109]    As mentioned above, when the handles  118 ,  120  are squeezed together, the resulting amount of deflection of the handles  118 ,  120  is directly related to the force applied by the physician as he or she squeezes the handles  118 ,  120  together. Because the vertical component  151  of the arm  148  is rigidly attached to the pivot  130 , as the handles  118 ,  120  move together as a result of being squeezed, the horizontal component of the arm  148  and its associate indicator  152  does not move. As a result, the handle  120  will be deflected along the horizontal component  149  of the arm  148  and along the indicia  150  located on the horizontal component  149 . By observing the location of the handle  120  with respect to the indicia  150  on the horizontal component  149 , the amount of force applied to handles  118 ,  120  and, therefore to the distal ends  126 ,  128  of feet  122 ,  124 , is indicated. When the distal ends  126 ,  128  are placed in functional contact with the notches  142 ,  144  of the male plate  12  and female plate  14 , the gauge  146  indirectly measures the compression being applied to the graft, and allows the surgeon to stop compressing once a predetermined force has been achieved. 
         [0110]    By placing the indicator  152  at a desired location on the horizontal component  149  of arm  148 , the physician can squeeze the handles  118 ,  120  together until the handle  120  moves into contact with the indicator  152 . At this point, the physician knows that the desired amount of force has been applied to the compression device  90  and thereby to the SC device  10  to the graft. 
         [0111]    In another embodiment of the compression device  90  shown in  FIG. 22 , gauge  146  again includes an arm  148 . But, in this embodiment, the arm  148  is connected to a rigid arm  156  located on the outside of handle  118 . Rigid arm  156  is attached to handle  118  near the pivot  130 . Arm  148  extends from the rigid arm  156  in the direction that handle  118  moves when it is squeezed together with handle  120  and may extend through a slot in handle  118  or may be formed around handle  118  so that arm  148  extends toward handle  120 . In this embodiment as well, indicator  152  is located between handles  118 ,  120 . 
         [0112]    As mentioned above, when the handles  118 ,  120  are squeezed together, the resulting amount of deflection of the handles  118 ,  120  is directly related to the force applied by the physician as he or she squeezes the handles  118 ,  120  together. Because the arm  148  is rigidly attached to the rigid arm  156 , as the handle  118 ,  120  move together as a result of being squeezed, the arm  148  and its associate indicator  152  does not move. As a result, the handle  118  will be deflected along arm  148  and along the indicia  150  located on arm  148 . By observing the location of the handle  118  with respect to the indicia  150  on arm  148 , the amount of force applied to handles  118 ,  120  and, therefore to the distal ends  126 ,  128  of feet  122 ,  124 , is indicated. When the distal ends  126 ,  128  are placed in functional contact with the notches  142 .  144  of the male plate  12  and female plate  14 , the gauge  146  indirectly measures the compression being applied to the graft, and allows the surgeon to stop compressing once a predetermined force has been achieved. Again, by observing the location of the handle  118  versus the indictor, the surgeon will know that the desired amount of force has been applied to the compression device  90  and thereby to the SC device  10  to the graft. 
         [0113]    An alternative embodiment of the compression device  90  is referred to as the static compensating compressor  590  and shown in  FIGS. 24-27 . The static compensating compressor  590  utilizes a force indicator  592  and a method to measure static compressive forces applied by the patient&#39;s own anatomy to allow the surgeon to factor the patient&#39;s own static compressive forces out to ensure the correct value of the absolute compression applied through the SC device  10  to the vertebral bodies. The static compensating compressor  590  includes a turnbuckle  594  that uses a threaded nut  596 , threaded inserts  598 , along with a series of compression springs  600  and guide rods  602 , collectively known as the distraction mechanism  604 , to allow the surgeon to apply a measurable distraction force (a force in the opposite direction to the compressive force) to unload the vertebral segment. By unload, we mean to take compression pressure, usually applied by the patient&#39;s own muscles and ligaments, off the vertebral segments. Once compression pressure on the vertebral segment has been unloaded from the vertebral segment, a null point (i.e., a point where there is no compression or distraction force on the vertebral bodies) is established and therapeutically useful compression can be applied to the vertebral segment at a known rate. 
         [0114]    The force indicator  592  has a central processing unit (CPU)  606  and a display  608  to determine and indicate the amount of force applied in either compression or distraction to the SC device  10  and a zeroing function that allows the surgeon to compensate for static anatomical compression. The force indicator  592  also includes a strain gauge  610 . The force indicator  592  is a simple electronic device that measures the resistance across the strain gauge  610  that is secured to one of the arms  114 ,  116  of the compressor  90  and then uses the CPU  606  to determine, by formula or through a lookup table, and indicate the amount of force applied by the compressor  90  and then indicate this amount of force on the display  608 . The CPU  606  may be an application specific integrated circuit (ASIC), a digitally based central processing unit or discrete components. 
         [0115]    The display  608  is preferably attached to one of the handles  118 ,  120  of the arms  114 ,  116  and the CPU  606  and the display  608  are preferably combined into a single unit. However, either or both the CPU  606  and the display  608  may be located remotely from the static compensating compressor  590  and the CPU  606  and the display  608  may be located separately from each other. 
         [0116]    The strain gauge  610  is preferably located on a distal end  126 ,  128  of a respective arm  114 ,  116  of the compression device  90  although the strain gauge may be located anywhere on an arm  114 ,  116  or on the pivot  130 . As the physician applies compression through the compression device  90  to the SC device  10  and thus to the vertebral bodies by squeezing the handles  118 ,  120  of the compression device  90  together, the distal ends  126 ,  128  will flex or bend slightly. The strain gauge  610  measures this flexing or bending of the distal ends  126 ,  128  and communicates the value to the CPU  606  where the force value, once determined, indicates the amount of force applied to the SC device  10 , and thus to the vertebral bodies, as is well understood in the art. 
         [0117]    As mentioned above, the static compensating compressor  590  is able to apply distraction pressure to the vertebral bodies through the use of a turnbuckle  594  ( FIG. 26 ). The threaded nut  596  has a pair of threaded holes  612 . The threaded holes  612  are threaded in opposite directions (i.e., with right and left handed threads) as is well understood in turnbuckles. The threaded inserts  598  each have a threaded end  614  and a non-threaded end  616  to which a guide rod  602  is attached. The guide rods  602  are preferably attached to the non-threaded ends  616  through springs  600  that have a low spring force. Springs  600 , when used, apply a low biasing force to the turnbuckle  594  to remove looseness in the connection between the turnbuckle  594  and the arms  114 ,  116 . In another embodiment, the guide rods  602  may be attached directly to the non-threaded ends  616 . The threaded inserts  598  are also each threaded on their threaded ends  614  in opposite directions (i.e., with right and left handed threads) and are mated with the threaded holes  612  of the threaded nut  596  so that as the threaded nut  596  is rotated in a first direction, the threaded inserts  598  are drawn into the threaded holes  612  and as the threaded nut  596  is rotated in a second direction, the threaded inserts  598  are moved out of the threaded holes  612 . As a result, as the threaded nut  596  is rotated in a first direction, the turnbuckle  594  expands in length and as the turnbuckle  594  is rotated in a second direction opposite the first direction, the turnbuckle contracts in length. 
         [0118]    The turnbuckle  594  is preferably attached between and applies a preload to the handles  118 ,  120  of the arms  114 ,  166  of the compressor  90 . However, the turnbuckle  594  may also be attached between and apply a preload to the distal ends  126 ,  128  of the arms  114 ,  166  of the compressor  90 . In either embodiment, the turnbuckle  594  is fitted between the arms  114 ,  116 , either between the handles  118 ,  120  or distal ends  126 ,  128  preferably in slots  618 , secured with pins  620  or other suitable retaining devices well understood in the art. In a variant of this embodiment, the pins  620  could be quick release pins, allowing the turnbuckle  594  to be quickly removed once the null point is found, as explained below, so that the compressor  90  would be used thereafter without the turnbuckle  594 . 
         [0119]    Once the turnbuckle  594  is attached to the arms  114 ,  116 , by turning the threaded nut  596 , the turnbuckle  594  expands or contracts (depending on the direction the threaded nut  596  is rotated) thereby applying a preload in either a compression or distraction direction to the arms  114 ,  166  of the compressor  90  and thus to the SC device  10  and ultimately to the vertebral bodies. This preload allows the vertebral segment that the SC device  10  is spanning to become unloaded or lifted. By “lifted” or “lift-off” we mean that a distraction force has been applied to the vertebral segment by the compressor  90  and SC device  10  to the point where the distraction force is equal to the anatomical compression force applied to the vertebral segment by the patient&#39;s own muscles and ligaments. At this point, called the null point, there is a net zero force applied to the affected vertebral segment so that the affected vertebral bodies separate or “lift-off” of each other slightly which separation is visually ascertained by the physician. 
         [0120]    Once lift-off has been determined, and consequently, the null point established, a button is pushed on the display  608 , on the CPU  606  itself or otherwise, including remotely, to alert the CPU  606  that strain measured by the strain gauge  610  at that point is the null point. As a result, the CPU  606  directs the display  608  to indicate a zero reading at that point. 
         [0121]    At this point, the turnbuckle  594  is preferably removed from the compressor  90 . As the turnbuckle  594  is removed, the patient&#39;s anatomical compression force will be applied to the affected vertebral segment. This compression force will be transferred through the SC device  10  to the compressor  90  where the strain gauge  610  will measure the anatomically applied compression force and the CPU  606  will direct the display  608  to indicate the anatomically applied compression force. Thereafter, the surgeon applies an additional compressive force to the SC device  10  which additional compressive force will be sensed by the strain gauge  610  combined with the compressive force applied by the patient&#39;s own anatomy. As a result, the CPU  606  will determine the total compressive force applied to the vertebral segment (i.e., the summation of the patient&#39;s own anatomical compressive force and the compressive force being applied by the physician by the compressor  90 ) which total compressive force is displayed on the display  608 . The physician then applies the additional compressive force to the vertebral segment until a desired total compressive force for maximum therapeutic value is obtained. 
         [0122]    If the force indicator  592  is set to a null point before distraction pressure is applied to the vertebral segment by the turnbuckle  594 , the force indicator  592  will also indicate the distraction pressure applied to the vertebral segment by the turnbuckle  594 . At the point where lift-off occurs, the display  608  will indicate the amount of distraction pressure being applied by the turnbuckle  594  which equals the amount of compression force that is applied by the patient&#39;s own anatomy. This amount of compression force is also potentially valuable information in that the amount of compression force anatomically applied by the patient may be used by the physician to determine the overall health and strength of the patient&#39;s inherent anatomical compression mechanism. Thereafter, the physician may set the force indicator  592  to zero as described above to indicate the null point for the application of compression force also as described above. 
         [0123]    In a variant to the embodiments of the compression device  90  described above, a small cannula  158  is attached to the compression device  90  at the pivot  130 . The cannula  158  is directed downward toward the SC device  10 . This cannula  158  is intended to receive a special screwdriver  160  that activates the locking mechanism  88  of the SC device  10  when the desired compression is achieved. The screwdriver  160  is inserted through the cannula  158  into the loosened locking mechanism  88  as the compression device  90  engages the male plate  12  and female plate  14 . Thus, it is possible for the surgeon to maintain compression across the graft with one hand on the compression device  90 , to determine the degree of compression achieved on the SC device  10  by visualizing the compression gauge  146 , and to activate the locking mechanism  88  of the SC device  10  with the other hand, causing the SC device  10  to become a rigid construct and preventing further movement of the vertebral bodies from occurring. 
         [0124]    Alternately, the physician may use the screwdriver  160  without inserting it through the cannula  158  or may use the screwdriver  160  in an embodiment of the compression device  90  that does not include a cannula  158 . Further, in any of the embodiments of the compressor  90 , the compressor  90  may be disposable or reusable. 
         [0125]    One mechanism of fixing the bone screws  43  to the male plate  12  at a rigid predetermined angle is described as follows. As mentioned above, bone screws  43  fix the male plate  12 , the female plate  14  and the interconnecting plate,  15 , if present, to the vertebral bodies. The bone screws  43  may be machined, as is common for such screws, with two separate sets of threads, one on the shaft of the screw  43 , the second set on the head of the screw  43 . These threads are distinct from each other in that they have different pitches and distinct outer diameters. The pitch and outer diameter of the threads on the shaft of the screw  43  are that of a standard cancellous bone screw. In order to engage the main male plate  12 , the diameter of the head  45  of the bone screw  43  head is significantly larger than the diameter of the threads on the shaft of the bone screw  43 . However, the threads on the bone screw  43  are smaller in outer diameter and tighter in pitch than the bore of the screw receiving holes  38 . These threads are machined to engage threads of similar pitch and diameter in the screw receiving holes  38  of the male plate  12 . 
         [0126]    The screw receiving holes  38  are machined to project the screw  43  into the vertebral body at a predetermined angle determined to be most advantageous for fixing the SC device  10  to the vertebral bodies. Thus, by engaging the threads on the head  45  of the screw  43  with those in the screw receiving hole  38 , the screw  43  projects into the vertebral body at the predetermined angle and maintains a rigid fixed relationship with the male plate  12 . 
         [0127]    The interaction between the bone screws  43  and the SC device  10  described above is one of the many ways that bone screws  43  can be connected to the SC device  10 . However, it is well understood in the art that there are other commercially available ways to connect devices like the SC device  10  to vertebrae that could also be used. As a result, it is intended that any method of connecting the SC device  10  to vertebral bone so that there is a rigid fixed relationship between the SC device  10  and the bone may be used with the SC device  10  of the present invention. 
         [0128]    The mechanism of fixing the screws  43  to the female plate  14  at a rigid predetermined angle is similar to the mechanism for fixing the screws  43  to the male plate  12  at a rigid predetermined angle as described above. Again, the bone screws  43  are machined, as is common for such screws, with two separate sets of threads, one on the shaft of the screw  43 , the second set on the head of the screw  43 . These threads are distinct from each other in that they have different pitches and distinct outer diameters. The pitch and outer diameter of the threads on the shaft of the screw  43  are that of a standard cancellous bone screw. In order to engage the female plate  14 , the inner diameter of the screw head  45  is significantly larger than the inner diameter of the threads on the shaft. However, the threads on the screw head  45  are smaller in outer diameter and tighter in pitch than the bore of the screw receiving holes  82 . These threads are machined to engage threads of similar pitch and diameter in the screw receiving holes  82  of the female plate  14 . The screw receiving holes  82  are machined to project the screw  43  into the vertebral body at a predetermined angle. Thus, by engaging the threads on the head  45  of the screw  43  with those in the screw receiving holes  82 , the screw  43  projects into the vertebral body at the predetermined angle and maintains a rigid fixed relationship with the female plate  14 . 
         [0129]    The SC device  10  as described in the embodiment above has the option of using fixed angle screws. However, variable angle screws  43  may be used with the SCD device  10  as long as when these screws  43  are placed through the male plate  12 , female plate  14  or interconnecting plate  15  into bone, their relationship with the respective plate  12 ,  14  or  15  becomes rigid. There are numerous methods of attaching bone screws to plates well understood in the art, all of which may be used with this device. It is important that the relationship between the screws and the plates  12 ,  14 ,  15  becomes rigid once the screws are placed in order to avoid “toggle” of the screws during the compression maneuver. “Toggle” must be avoided, because if it occurs, actual compression may be significantly less than measured. 
         [0130]    Most currently available non-adjustable plates have the option to place screws into the bone at a variety of different angles to obtain optimum purchase. While this is necessary to position static plates, it is not necessary in the SC device  10 . In fact the sliding capability that the SC device  10  has in the unlocked arrangement renders the common use of variable screws superfluous. Nevertheless, any type of screw may be used with the SC device  10  as long as a mechanism exists for rigidly fixing the screw to the plate. 
         [0131]    The importance of having screws  43  that are rigidly fixed to the male plate  12  and female plate  14  at a predetermined angle is that compression occurs through the entire SC device  10  (the sliding components of the SC device  10  (male plate  12  and female plate  14  and the two rigidly attached screws), rather than through the screws individually. Also, as mentioned, the bottom side  36  of the male plate  12  and the bottom side  54  of the female plate  14 , and of the interconnecting plate  15  if present, are roughened, allowing the SC device  10  to “grip” the vertebral body. These characteristics in combination provide for a much larger surface area to compress against (the contact of the bottom side  36  and bottom side  54  on the anterior surface of the vertebrae as well as the two rigidly fixed bone screws in the male plate  12  and female plate  14 , respectively). This results in a much more even compression against the entirety of the interbody graft and minimizes the potential for screw cutout or bony failure. 
         [0132]    For purposes of illustrating the operation of locking mechanism  88  of the invention in the embodiment shown in  FIGS. 1-14 , a variant of the embodiment described above will be used. In this variant, shown in  FIGS. 15-17 , there is no interconnecting plate  15 . Instead, the male plate  12  and female plate  14  intermesh directly through the interaction of the central protrusion  28  and side protrusions  29  of the male plate  12  and the left and right guides  58 ,  60  of the female plate  14 . In describing the operation of the SC device  10 , it is to be understood that the concepts described apply as well to the interaction between the male plate  12  and one end of the interconnecting plate  15  and the interaction between the opposite end of the interconnecting plate  15  and the female plate  14 . 
         [0133]    In use, the central protrusion  28  is inserted into the protrusion receiving channel  56  ( FIG. 15 ). Because protrusion receiving channel  56  is dimensioned to receive central protrusion  28  with the locking clamp  16  in place, central protrusion  28  is precisely located and retained within the protrusion receiving channel  56 . In this position with the locking clamp  16  in place on the top surface  30  of central protrusion  28 , the ridges  46  and valleys  48  on the parallel sides  96  of locking clamp  16  come into loose contact with the inner surface  61  of left guide  58  and right guide  60  of the female plate  14 . ( FIG. 15 ) The locking screw  18  is passed through the screw hole  93  so that its distal end  110  comes into contact with and is threaded into the threaded hole  35  a sufficient amount to locate the distal end  110  of the locking screw  18  in the threaded hole  35  but not a sufficient amount to deform the locking clamp  16 . 
         [0134]    Bone screws are passed through the screw receiving holes  38  and  82  and into the vertebral bone. These bone screws are screwed into the vertebral bone until the heads of the bone screws seat into the basins  40 ,  84  of the male plate  12  and female plate  14 , respectively. 
         [0135]    The compression device  90  is then used to apply the desired compression to the SC device  10 . The pins  132  are placed in the notches  142 ,  144  and the handles  118 ,  120  are squeezed together. As a result, compression pressure is applied to the male plate  12 , female plate  14  and interconnecting plate  15  if present, and thereby to the vertebral bone through the bone screws. 
         [0136]    As mentioned above, where a gauge  146  is present, the amount of compressive force applied to the device  10  can be ascertained. 
         [0137]    As shown in  FIGS. 16 and 17 , when the male plate  12  is moved into an intermeshing position with the female plate  14  and the appropriate amount of compression is applied to the SC device  10  through the compression device  90 , the screwdriver  160  is coupled to the head  106  of the locking screw  18 . The screwdriver  160  is rotated so that the threaded body  108  of locking screw  18  is threaded into the threaded hole  35 . The locking screw  18  is then screwed further onto the central protrusion  28  on the male plate  12  so that the head  106  contacts the top surface  92  of the locking clamp  16 . 
         [0138]    Once the head  106  has contacted the top surface  92 , further rotation of the locking screw  18  will cause the head to be forced into the material of the top surface  92  of the locking clamp  16 . This will cause the locking clamp  16  to interfere so that the parallel sides  96  will be forced into engaging and locking contact with the inner surfaces  61  of the left and right guides  58 ,  60  on the female plate  14  or the interconnecting plate  15 . This outward compression from the interference fit is transferred through the left and right guides  58 ,  60  to cause engaging and locking contact between the outer surface  63  of the left and right guides  58 ,  60  and the inner surface  37  of the side protrusions  29 . The interaction between the head  106  and the screw hole  35  locks the locking clamp  16  against the right and left guides  58 ,  60 . Once male plate  12  is secured with respect to the female plate  14 , the compression device  90  is removed. As a result, the compression applied to the SC device  10  through the compression device  90  will be locked to the vertebral bone through the male plate  12  and female plate  14  (and interconnecting plate  15  if used) because these various components are locked in a fixed relationship to each other. 
         [0139]    An alternate embodiment of the locking mechanism  88  is shown in  FIGS. 28-32  and is described as follows. In this embodiment there is no locking clamp  16  and the locking screw  18  ( FIG. 30 ) is large in diameter and is tapered from the head  106  to the distal end  110  so that the diameter of the head  106  is significantly larger than the diameter of the distal end  110 . In addition, the diameter of head  106  of the locking screw  18  is greater than the width of the central protrusion  28 . Further, the threaded hole  35  of the central protrusion  28  of the male plate  12  is fashioned in a threaded tapered fashion so that the locking screw  18  fits into the threaded hole  35 . In this embodiment the central protrusion  28  may include a slot  41  through which the threaded hole  35  passes to allow maximal deformation of the central protrusion  28  along the length of the central protrusion  28 . 
         [0140]    Thus, when appropriate compression has been applied to the vertebral bodies by the SC device  10 , the locking mechanism  88  is engaged by advancing the locking screw  18  into the threaded hole  35 . The advancement of the locking screw  18  into the threaded hole  35  deforms the outer aspect of the central protrusion  28  which surrounds the threaded hole  35  thereby causing this portion of the central protrusion  28  to expand and interfere with the inner surface  61  of left guide  58  and right guide  60  of the female plate  14 . The presence of the slot  41  helps the deformation of the outer aspects of the central protrusion  28  by making it easier for the two sides of the central protrusion  28  to move away from the threaded hole  35  under the influence of the locking screw  18 . This outward compression from the interference between expanded central protrusion  28  and left and right guides  58 ,  60  is transferred through the left and right guides  58 ,  60  to cause engaging and locking contact between the outer surfaces  63  of the left and right guides  58 ,  60  and the inner surface  37  of the side protrusions  29 . 
         [0141]    It should be noted that the SC device  10  is a modular and expandable device. The characteristics of this device allow it to be disassembled in vivo and expanded to immobilize adjacent vertebral segments (or other bone pieces or segments) by the insertion of one or more interconnecting plates  15  to form an interconnecting span as described above. 
         [0142]    Thus, should subsequent surgery be required, as for example, in the case of adjacent segment disease (the segment adjacent to a fused segment undergoing accelerated degeneration), it is not necessary to expose the entirety of the SC device  10  and remove it to extend the fusion to the adjacent segment (as is the case with nearly all current plates). Instead, an end portion of the SC device  10  (e.g., either the male plate  12  or female plate  14 ) may be removed (leaving the remainder of the SC device  10  intact), the fusion completed and the SC device  10  simply expanded to include the newly fused segment by inserting one or more interconnecting plate  15 , then reapplying the end portion (either the male plate  12  or female plate  14 , respectively) of the SC device  10  to the newly fused vertebrae, applying compression as explained herein and locking and securing the SC device  10 . 
         [0143]    An alternate embodiment of the SC device  10  is shown in  FIGS. 33-35 . In this embodiment, the locking screw  18  of the locking mechanism  88  is modified to include a cam  162  that rotates around the locking screw  18  below the head  106  ( FIG. 35 ). Further, the edges of channel  80  form a track  164  ( FIG. 34 ) dimensioned to receive and constrain the cam  162  within the track  164  in a relatively conformal manner. In addition, in this embodiment of the locking mechanism  88 , there is no locking clamp  16  and the central protrusion  28  does not have the protrusion ridges  50 . 
         [0144]    Cam  162  is relatively disk shaped with elongated opposed outer edges  166 . The outer edges  166  resemble somewhat a “V” with the bottom of the V being farther from the body  108  than the open mouth of the V which rotates around the body  108  of locking screw  18 . The locking screw  18  in this embodiment rotates freely with respect to cam  162 . However, the cam portion can be rotated into contact with and engage the track  164  when rotated 90 degrees about the body  108 . When the locking screw  18  is in the unlocked position, the male plate  12  is inserted into the protrusion receiving channel  56 . With the cam  162  rotated so that the cam  162  does not contact the track  164 , the cam  162  and the locking screw  18  move easily into the channel  80 . Then the male plate  12  and the female plate  14  are moved to the desired position relative to each other, the cam  162  is rotated 90 degrees so that the cam  162  contacts the wall of the track  164  where such frictional contact prevents the male plate  12  from moving relative to the female plate  14 . In addition, though both the locking screw  18  and the female plate  14 , including the track  164  are preferably made of titanium, the locking screw  18  is of a significantly harder grade. In this way, as the locking screw  18  is rotated 90 degrees, because the cam  162  is present and has a cam shape, the cam  162  is forced into the track  164 , effectively deforming the cam  162  and forming a “cold weld” with the track  164 . In this way, a rigid, permanent fixation between the locking screw  18  and the male plate  12  to which it is attached and the female plate  14  through track  164  is achieved and compression is maintained. The SC device  10  in this embodiment is also designed to work with the compression device  90 . 
         [0145]    An alternate embodiment of the SC device  10  in a preferred embodiment shown in  FIGS. 36-54  also has a male plate  12  and a female plate  14 . In addition, the SC device  10  in this embodiment also has a locking plate  316  and a locking screw  318  that, in combination with standard cancellous bone screws (not shown) fix the SC device  10  to the patient&#39;s vertebrae. This SC device  10  has a top side  320 , a bottom side  322  and opposed medial sides  324 . 
         [0146]    The male plate  12  has a male main body  326  and a protrusion  328  extending away from the male main body  326 . The protrusion  328  has a top surface  330  and a longitudinal axis  332 . The male main body  326  is relatively flat with a top side  334  and a bottom side  336  and, in a preferred embodiment, has two screw receiving holes  338 . The screw receiving holes  338  each have a bowl-shaped basin  340  on the top side  334  to receive the heads of the screws and a throughhole  342  through which the main body of the screws pass to come into contact with the vertebral body. The throughholes  342  are machined to have a rigid relationship with the bone screws as will be described hereafter. 
         [0147]    The bottom side  336  of male plate  12  is preferably roughened, thereby allowing the bottom side  336  of male plate  12  to “grip” the vertebral body when the bottom side  336  is brought into contact with and is secured to the vertebral body by the interaction of the screws and the male main body  326  as described above. 
         [0148]    As mentioned, the male plate  12  has a protrusion  328  with a top surface  330  and a longitudinal axis  332 . Protrusion  328  is dimensioned to mate with and secure the male plate  12  with the female plate  14  as will be described in detail hereafter. The length of protrusion  328  along the longitudinal axis  332  is chosen to be slightly longer than the distance the SC device  10  is intended to provide compression over. 
         [0149]    Protrusion  328  has a slot  344  extending entirely through it approximately perpendicular to the top surface  330 . Protrusion  328  also has a series of alternating ridges  346  and valleys  348 , collectively protrusion ridges  350 , located on a portion of its top surface  330 . Ridges  350  are preferable angled slightly with respect to the longitudinal axis  332  for a purpose to be explained hereafter. 
         [0150]    The female plate  14  has a female main body  352  with a bottom side  354  and a protrusion receiving channel  356 . Protrusion receiving channel  356  is comprised of a left channel  358 , a right channel  360  and a connecting piece  362 . Left channel  358  is basically “C” shaped with a top piece  370 , bottom piece  372  and an outer piece  374 . Although left channel  358  has been described as having a top piece  370 , bottom piece  372  and outer piece  374 , left channel  358  is preferable a single contiguous piece although it could be made of these separate segments connected together. 
         [0151]    Right channel  360  has a top piece  370 , a bottom piece  372  and an outer piece  374 . Although right channel  360  has been described as having a top piece  370 , bottom piece  372  and outer piece  374 , right channel  360 , like left channel  358 , is preferably a single contiguous piece although it could be made of these separate segments connected together. 
         [0152]    Connecting piece  362  connects the left channel  358  to the right channel  360  at the respective bottom pieces  372 . In the preferred embodiment, connecting piece  362  is integrally formed with the bottom pieces  372  although it could be made of these separate segments connected together. Connecting piece  362  has a threaded hole  376  that extends into connecting piece  362 . 
         [0153]    Protrusion receiving channel  356  is dimensioned to snugly receive the protrusion  328  so that the protrusion  328  is “captured” and held in the protrusion receiving channel  356  by relatively conformal physical contact between the outer surface of the protrusion  328  and the inner surfaces of the left channel  358 , right channel  360  and connecting piece  362 . 
         [0154]    The female main body  352  also has an upper surface  378  and a channel  380  formed in the upper surface  378  between the left channel  358  and the right channel  360 . Channel  380  extends entirely through the upper surface  378 . 
         [0155]    The female plate  14 , also in a preferred embodiment, has two screw receiving holes  382 . These screw receiving holes  382  receive standard cancellous bone screws (not shown) that are threaded into the bone of the vertebrae. In similar fashion to screw receiving holes  338 , the screw receiving holes  382  also have a bowl-shaped basin  384  on the upper surface  378  to receive the heads of the bone screws and a throughhole  386  through which the main body of the bone screws pass to come into contact with the vertebral body. The throughholes  386  are machined to provide a rigid relationship with the bone screws. The SC device  10  has a locking mechanism  388 . The locking mechanism  388  includes locking plate  316  and locking screw  318  as well as the ridges  346  and valleys  348  on the top surface  330  of protrusion  328  of the male plate  12  and the threaded hole  376  and channel  380  of female plate  14  as described below. Locking mechanism  388  converts “active” compression applied by the surgeon using the compression device  90  described above interacting with the SC device  10  at the time of surgery to “static” compression after surgery. The locking mechanism  388  also provides rigid fixation to the SC device  10  to optimize bone healing and preventing further settling from occurring. 
         [0156]    The locking plate  316  has a top surface  392 , a bottom surface  394  and parallel sides  396 . The bottom surface of locking plate  316  preferably has a series of ridges  398  and valleys  400 , collectively locking ridges  402 , of similar dimensions to the ridges  346  and valleys  348  of the protrusion  328  to locate and affix the locking plate  316  to the protrusion  328  as will be described hereafter. In a most preferred embodiment of the invention, the ridges  346  and valleys  348  of the protrusion  328  and the ridges  398  and valleys  400  of the locking plate  316  are angled slightly with respect to the longitudinal axis  332 . Through this configuration, the ridges  398  and valleys  400  of the bottom surface  394  of the locking plate  316  preferably contact and engage with the ridges  346  and valleys  348  of the protrusion  328  in frictional or mechanical contact to precisely locate and affix the locking plate  316  to the protrusion  328 . Further, as shown in  FIGS. 42 and 48-53 , because the protrusion ridges  350  and the locking ridges  402  are angled, as the locking plate  316  is moved from one side of the channel  380  to the other, as the locking ridges  402  seat with the protrusion ridges  350 , the male plate  12  is moved into compression with the female plate  14 . This compression is transferred through the male plate  12  and female plate  14  to the vertebral bone. 
         [0157]    The width of the locking plate  316  (i.e, the distance between the parallel sides  396 ) is such that the locking plate  316  will fit snugly into the channel  380  formed in the upper surface  378  of the female plate  14  of the SC device  10  but still allow the locking plate  316  to move in a direction perpendicular to the parallel sides  396  within the channel  380 . 
         [0158]    Locking plate  316  has a slot  404 . Slot  404  is aligned with channel  344  of the protrusion  328  and allows a locking screw  318 , as explained hereafter, to pass through both the slot  404  and mate with the threaded hole  376  as described hereafter. Slot  404  is also dimensioned to conformally mate with the head  406  of screw  318  so that contact between the head  406  and slot  404  as the locking screw  318  is threaded into threaded hole  376  moves the locking ridges  402  into contact with the protrusion ridges  350 . 
         [0159]    A single large locking screw  318 , dimensioned to rotate freely within the slot  404  of the locking plate  316 , activates the locking mechanism  388 . In the embodiment of the invention shown in  FIGS. 36-54 , the locking screw  318  has a head  406 , a threaded body  408  and a distal end  410  where the head  406  has a larger cross-sectional diameter than the threaded body  408 . 
         [0160]    In use, the protrusion  328  is inserted into the protrusion receiving channel  356  ( FIGS. 39 and 48 ). Because protrusion receiving channel  356  is dimensioned to conformally receive protrusion  328 , protrusion is precisely located and retained within the protrusion receiving channel  356 . Locking plate  316  is placed on the top surface  330  of protrusion  328  within the channel  380  so that the protrusion ridges  350  come into contact with the locking ridges  402  ( FIG. 49 ). The locking screw  318  is passed through the slot  404  so that its distal end  410  comes into contact with and is threaded into the threaded hole  376  a sufficient amount to locate the distal end  410  of the locking screw  318  in the threaded hole  376  but not a sufficient amount to secure the locking ridges  402  of the locking plate  316  into secure contact with the protrusion ridges  350  ( FIGS. 50-51 ). 
         [0161]    Bone screws are passed through the screw receiving holes  338  and  376  and into the vertebral bone. These bone screws are screwed into the vertebral bone until the heads of the bone screws seat into the basins  334 ,  378  of the male plate  12  and female plate  14 , respectively. 
         [0162]    The compression device  90  is then used to apply the desired compression to the SC device  10 . The pins  132  are placed in the notches  442 ,  444  and the handles  118 ,  120  are squeezed together. As a result, compression pressure is applied to the male plate  12  and female plate  14  and thereby to the vertebral bone through the bone screws. As mentioned above, where a gauge  146  is present, the amount of compressive force applied to the SC device  10  can be ascertained. Once the desired amount of compressive force is applied to the SC device  10 , the screwdriver  160  is coupled to the head  406  of the locking screw  318 . The screwdriver  160  is rotated so that the threaded body  408  of locking screw  318  is threaded into the threaded hole  376 . In this process, the locking ridges  402  are brought into secure contact with the protrusion ridges  350 . But, to secure an optimum fit between the locking ridges  402  and the protrusion ridges  350 , it may be necessary to move the locking plate  316  from side to side within the channel  380  until they mate optimally and impart a compression on the male plate  12  and female plate  14  ( FIG. 52 ). Once this optimal mating occurs, the screwdriver  160  is rotated further. The interaction between the head  406  and the slot  404  locks the locking plate  316  against the protrusion  328 . Locking screw  318  is tightened into the threaded hole  376  so that the male plate  12  is securely positioned with respect to the female plate  14 . Once male plate  12  is secured with respect to the female plate  14 , the compression device  90  is removed. 
         [0163]    Another alternate embodiment of the SC device  10  is shown in  FIGS. 55-56 . In this embodiment, the SC device  10  is as described above except that the SC device  10  has a spring mechanism  168  integral between the ends of the male plate  12  and female plate  14  that provides a near constant force applied to a fixed vertebral segment (or segments) through a standard buttressing or tension band construct. Spring mechanism  168  has three parts, a relatively flat spring plate  170 , guide pins  184 ,  186  and a guide plate  172 . Spring plate  170  has ends suitable for attaching to bone via one or more bone screws. 
         [0164]    Spring  178  is preferably a plurality of flexible members that resist being moved in a lateral direction, in this case, in the direction of moving the one plate end  174  away from the other plate end  176 . In a preferred version of this embodiment, the spring  178  is a plurality of flat serpentine shaped members made of a spring metal such as spring steel. However, the spring  178  could also be made of a single member that has spring-like attributes and could be made of materials other than metal so long as the elements of spring  178  possess the ability to resist stretching according to a linear restoring force (i.e., follows Hooke&#39;s law). 
         [0165]    Guide plate  172  reinforces spring plate  170  and provides over extension protection as well as flexion/extension moment buffering. Over extension protection is provided by guide pins  184 ,  186  attached to spring plate  12  via slots and limit the extension of the spring  178 . Flexion/extension is controlled by the guide plate  172  in close contact with the spring plate  12 . 
         [0166]    This embodiment of SC device  10  allows the SC device  10  to settle into position on the vertebral bone and minimize the deflection of the male plate  12  and the female plate  14  without a drastic reduction in the SC device  10 ′s ability to provide a consistent tension force. Further, after the SC device  10  is implanted, the surgeon can determine the actual level of compression by measuring the overall change in length of the construct and applying Hooke&#39;s law to determine the relative rate of compression. 
         [0167]    Another feature of an embodiment of the invention shown in  FIG. 57  is that of a series of trial spacers  202  that include a strain gauge capable of measuring compressive strain through electromagnetic techniques as are well understood in the art. These spacers  202  are preferably cylindrical in shape with a handle which allows them to be inserted between the vertebral bodies. The spacers are machined to have the approximate dimensions of the bone graft which is to be placed between adjacent vertebrae (in the disc space once the disc has been removed). This embodiment also includes a handle  204  attached to the spacer  202  in order to allow the surgeon ease in facilitating insertion and extraction of the spacer  202 . The cylinders of the spacer  202  are preferably machined in height increments (e.g. one millimeter) in order to accommodate a variety of disc space heights. 
         [0168]    The spacer  202  serves two purposes. First, it enables the surgeon to “size” the disc space in order to place an appropriate sized graft, in the same manner that many allograft spacers currently have “trials”. Second, each spacer  202  has the characteristics of a strain gauge which is able to directly measure the “passive” force applied to that spacer  202  by the adjacent vertebral bodies, once the spacer  202  is inserted. In this way the surgeon may estimate the approximate “passive” force which would be applied to a similar sized bone graft. The total force applied to that graft, then, would be the sum of the passive force applied to the graft (as measured by the spacer of similar dimensions) and the active force applied by the surgeon through the compression device  90 . Thus, by using the strain-gauge spacer  202  in conjunction with the compression device  90 , the surgeon may obtain an accurate assessment of total force applied to the graft. This is beneficial in that it allows further study of the “optimal” force which must be applied in order to reliably achieve fusion. 
         [0169]    In all the embodiments shown, the SC device  10  is a unique device that utilizes Wolff&#39;s law to compress two or more adjacent cervical vertebrae while fusion between the vertebrae occurs by allowing static, rigid compression to be applied to interbody graft in the cervical spine. Static, rigid compression has definitively been shown to increase bony union in a long bone fracture model. Lumbar interbody fusions have been shown to heal at a higher rate than intertransverse fusions, presumably because of the constant loading of the graft. No other currently available cervical device allows for active, static compression. 
         [0170]    It should be noted that use of the SC device  10  is by no means limited to use in the cervical spine. Any of the aforementioned embodiments, in a somewhat larger version or having a curved bottom side  22  ( FIG. 58 ) as will be clear to those skilled in the art, may be used for the same or similar purposes in the thoracic or lumbar spine, or in instances where static compression is desired outside of the spine (e.g., and without limitation, bone fractures, as for example, of long bones like the femur or bones of the skull, hip or scapula) ( FIG. 59 ). 
         [0171]    In the thoracic spine a larger version of the SC device  10  may be placed on the side of the thoracic spine (as opposed to the front) in order to facilitate approach to the thoracic spine and to avoid large vascular structures that reside immediately in front of the thoracic spine. 
         [0172]    In the lumbar spine, a larger version of the SC device  10  may be placed either on the side of the spine to facilitate exposure and avoid vascular structures or directly on the front of the spine, especially at the lumbosacral junction. It is believed that in order to obtain anterior fusion at L5-S1, it is important to have a fully contoured SC device  10  ( FIG. 58 ) that is simply comprised of a male plate  12  and a female plate  14  with a curved bottom side  22  matching the curvature of the vertebral segments in the L5-S1 region. 
         [0173]    As mentioned above, the SC device  10  may be used to obtain union of fractures, nonunions, osteotomies and other bony defects in regions other than the spine. In the embodiment suited for use with other bones, the SC device  10  should be sized appropriately to the bone and have the option of placing more than two screws  138  on either side of the defect where union is desired ( FIG. 59 ). The SC device  10  allows for maximum utilization of Wolff&#39;s Law to facilitate healing in that reproducible measurable compression is applied in each of these scenarios to obtain bony union. 
         [0174]      FIG. 60  is a perspective view of an embodiment of the static compression device designed to be used to treat fractures. The reference numerals correspond to elements described in other embodiments above. Reference numerals designed with a prime symbol simply refer to the same element disposed in a different structural configuration. 
         [0175]    An alternative embodiment  700  of the static compression device for treating spinal fractures is illustrated in top perspective view in  FIG. 61 , with bottom perspective view in  FIG. 62 . Each device  700  has a first end plate  702 , a center plate  704 , and a second end plate  706 , the second end plate  706  being of the same design as the first end plate  704 ; end plates  702 ,  706  are illustrated in more detail in top perspective view in  FIG. 63  and bottom perspective view in  FIG. 64 , and center plates  704  are illustrated in more detail in top perspective view in  FIG. 65  and bottom perspective view in  FIG. 66 . Each end plate  702  has a cavity portion  703  that surrounds a protrusion portion  716 ,  718  of center plate  704  and is attached to the center plate  704  with a lock screw  708 ,  710 , illustrated in more detail in  FIG. 67 ; lock screws  708 ,  710  engage with threads  712 ,  714  in protrusion portions  716 ,  718  of center plate  704 . Protrusion portions  716 ,  718  have multiple valleys  720 ,  722  adapted to engage multiple ridges  724  of end plates  702 ,  706 . The multiple valleys  720 ,  722  engage the multiple ridges  724  when the end plates are drawn into contact with the center plate protrusion portions  718   718  by tension of tightened lock screw  708 ,  710 . In an alternative embodiment, the valleys are on the end plates  702 ,  706  in similar location, and the ridges are on the protrusion portions  718 ,  716  of the center plate. 
         [0176]      FIG. 68  is a top perspective view of an alternative embodiment  800  derived from the embodiment of  FIG. 61  but having additional levels for treating spinal fractures of multiple vertebrae. In the embodiment of  FIG. 68 , an end plate  802  engages a protrusion portion (hidden by end plate  802 ) of a daisy-chain plate  804  and is secured to the protrusion portion by lock screw  806 . The daisy-chain plate  804  differs from the center plate  704  in that one protrusion portion, such as protrusion portion  718  is replaced by an equivalent  808  of a cavity portion  703  of an end plate  702 . In embodiment  800 , multiple daisy-chain plates  804 ,  810  may be used as shown, or a series of one or more daisy-chain plates may have a cavity portion engaging a protrusion portion of a center plate like center plate  704  and an end plate like end plate  706  as illustrated in  FIG. 69 . In the embodiment  800  illustrated, where two daisy-chain plates  804 ,  810 , are illustrated, an end plate  814  having a protrusion portion (concealed within cavity portion  812  of daisy chain plate  810 ) instead of a cavity portion is used to terminate the string of plates. 
         [0177]    In the embodiments of  FIG. 61-69 , in order to retain end plates, center plates, and daisy-chain plates together and simplify handling during surgery, pins  730  ( FIG. 62 ) are driven into holes  732  ( FIG. 66 ) of the center plate, the pins engaging in slots  734  ( FIG. 62 ) of the end plate cavity portion  703 . Similarly, cavity portions  808  of daisy-chain plates  804  and engaging protrusion portions of daisy chain plates and/or end plate  814  are pinned together ( FIG. 69 ), although these pins are not visible in the top view of  FIG. 69 . These pins serve to limit relative motion of the plates. 
         [0178]    As with the other embodiments, the embodiments of  FIG. 61-69  have two holes  760  in each of end plates  702 ,  706 ,  802  center plate  704 , and daisy-chain plates  804  such that screws may be inserted in holes  760  to attach the plates to bone. Each hole has an interior circumferential slot (not shown) into which an optional snap ring  762  may be fitted. In an embodiment having pre-attached screws, screws are used that have a head, a distal threaded portion, and a proximal unthreaded portion near the head having diameter less than an outer diameter of the distal threaded portion such that a screw can be inserted into each hole  760  and retained with snap ring  762 . In embodiments having pre-attached screws, the proximal unthreaded portion is sufficiently long that the device can be placed on bone and the screws inserted into tapered holes in bone. 
         [0179]    In each device of the embodiments of  FIG. 61-69 , a notch  770 , recess, or hole is provided in at least two plates, and in some embodiments all plates, of the device such that a separate device, such as that of  FIG. 22 , can be coupled to the plates and applied to exert compressive force on the plates, thereby sliding the protrusions of each male plate into cavities of the mating female plates into a compressed position, and thus applying compressive forces on the bones or bone fragments to which they are attached, before tightening lock screws  708 ,  718  to hold the plates in compressed position. The embodiments of  FIG. 61-69  illustrate a notch  770  in end plates for this purpose, other embodiments, including variations of the embodiments of  FIG. 61-69 , may have additional holes, hooks, or notches in both the end plates and intermediate plates so that compressive forces can be applied across plate-to-plate boundary, representing a bone-to-bone boundary, individually. 
         [0180]    The SC device  10  described herein has the following four unique characteristics which together provide for static compression of the vertebral body-graft interface:
       The use of fixed-angle screws to secure the SC device  10  to the vertebral bodies;   The use of a compression device to apply and measure the pressure applied to the vertebral bodies by the SC device  10 ;   The technique of using active, static compression to assist the fusion process; and   The use of a locking mechanism  88  that maintains compression during the fusion process to facilitate bone growth. These four characteristics of the SC device  10  are not currently found in any other spinal device. As a result, it is believed that the SC device  10  in any of the disclosed embodiments provides an optimal environment for spinal fusions to consolidate while preventing frequent non-unions and occasional deformities seen with the use of current dynamic plates.       
 
         [0185]    The SC device  10  in several embodiments has been described in detail above. However, it is to be understood that the specific features of the various components may be modified as will occur to those skilled in the art and still fall within the parameters of the invention. For example, the specific cross-sectional shape of the protrusion  28 , left and right guides  58 ,  60  and side protrusions  29  may be modified so long as these components interlock with each other as described herein. Further, the shape of the locking clamp  16  may be modified so long as it is able to be deformed to force frictional or mechanical contact between the various components as described above. 
         [0186]    Further, the invention has been described as having a protrusion  28  with side protrusions  29  on a male plate  12  or interconnecting plate  15  and a left guide  58  and right guide  60  on a female plate  14  or interconnecting plate  15 . It is clear that the invention could also be practiced with the male plate  12  or interconnecting plate  15  having a single protrusion  28  with the female plate  14  or interconnecting plate  15  still having the left guide  58  and right guide  60 . Also, the SC device  10  could have two or more protrusions  28  on the male plate  12  or interconnecting plate  15  with a corresponding number of protrusion receiving channels  56  to receive these protrusions  28  and a corresponding number of locking clamps  16 . 
         [0187]    The present invention has been described in connection with certain embodiments, configurations and relative dimensions. It is to be understood, however, that the description given herein has been given for the purpose of explaining and illustrating the invention and are not intended to limit the scope of the invention. For example, complimentary versions of the mating aspects of the SC device  10  could be formed and still be within the scope of the invention. In addition, it is clear that an almost infinite number of minor variations to the form and function of the disclosed invention could be made and also still be within the scope of the invention. Consequently, it is not intended that the invention be limited to the specific embodiments and variants of the invention disclosed. It is to be further understood that changes and modifications to the descriptions given herein will occur to those skilled in the art. Therefore, the scope of the invention should be limited only by the scope of the claims.