Abstract:
A cervical bone plate includes a graft window that allows access to and/or visualization of a bone graft area of the cervical spine after attachment of the present cervical plate to the vertebrae. The window is preferably, but not necessarily, sized for maximum exposure of the graft area and/or the vertebral body without compromising plate strength, particularly with respect to federal standards for such devices. The window is centrally positioned on the plate and is sized to provide alignment of the plate onto the vertebrae at the base of the vertebra fastener or screw holes of the plate. In a dynamic form of this cervical bone plate, the graft window expands and contracts with respective expansion and contraction of the dynamic plate after attachment to the vertebrae (i.e. “dynamizes”). In another form, a three-component dynamic bone plate is configured such that a middle component accepts an identical end component at both ends of the middle component. The end component is a 180° interchangeable part. The middle component and the end component have cooperating configurations and complementarily configured grooves that allow sliding movement between the middle component and the end components. A two-pillar construction provides a central window.

Description:
[0001]     This U.S. non-provisional patent application claims the benefit of and/or priority to U.S. provisional patent application Ser. No. 60/531,657 filed Dec. 22, 2003 entitled “Static and Dynamic Cervical Plate Construct”, the entire contents of which is specifically incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to devices for the internal fixation of the spine particularly within the fields of orthopedics and/or neurosurgery such as spinal implants for holding vertebral bones fixed relative to one another and, more particularly, to static and/or a dynamic bone fixation implants for use in spinal surgical procedures for stabilizing the relative motion of, temporarily or permanently immobilizing, bones of the spine.  
         [0004]     2. Background Information  
         [0005]     Cervical plates have been used for more than 20 years to increase neck stability following single and multi-level cervical surgery. Cervical plates, implanted during surgery for reasons such as disease, trauma, defect, accident or the like, are used to stabilize one or more cervical vertebrae. Stabilization leads to a proper healing or a desired outcome. The cervical plate is mounted to one or more vertebrae during the surgery. Typically, screws are used to mount the cervical plate to the one or more vertebrae. It is important during the mounting process that the plate be properly aligned on the vertebrae for receipt of the mounting screws.  
         [0006]     In some instances, it is desirous to cause the fusion of two adjacent vertebrae. If this is the case, the surgeon makes a small incision in the front of the neck to reach the cervical spine. Tissues and muscles are retracted (spread apart) to reveal the proper level in the cervical spine. The cartilaginous material or disc between the two vertebrae is removed and the bone surface abraded to encourage a bleeding surface. Blood from the bleeding surfaces is desired in order for the bones to fuse. The space between the adjacent vertebrae is filled with bone graft. A cervical plate is then screwed into the superior (top) and inferior (bottom) vertebrae. This stabilizes the cervical spine to facilitate fusion and healing. With current cervical plates however, once the plate is secured over the graft area, the only manner of accessing the graft area is to remove the plate. Moreover, with current cervical plates, it is necessary to provide the bone graft material before mounting the plate.  
         [0007]     Heretofore, cervical plates were almost exclusively static, in that they have fixed dimensions. It has been realized that it is desirable in certain situations to allow shifting or slight movement between the plate-mounted vertebrae. The prior art is relatively devoid of dynamic cervical plates.  
         [0008]     It is thus evident from the above that what is needed is a cervical plate that allows access to a bone graft area of a cervical surgical site.  
         [0009]     It is thus evident from the above that what is needed is a cervical plate that is dynamic.  
         [0010]     This need and others are accomplished through application of the principles of the subject invention and/or as embodied in one or more various forms and/or structures such as are shown and/or described herein.  
       SUMMARY OF THE INVENTION  
       [0011]     According to an aspect of the invention, a bone plate is contoured to conform to the shape of typical vertebra or vertebrae when the bone plate is mounted to the vertebra or vertebrae. The bone plate, in one form, is contoured to conform to contours of one or more vertebrae upon anterior placement of the bone plate onto the one or more vertebrae. In one embodiment, the bone plate is contoured in two planes.  
         [0012]     According to another aspect of the invention, a cervical bone plate includes an opening or window that allows access to and/or viewing of a bone graft area of the spine after attachment of the cervical plate to the vertebrae. The window is preferably, but not necessarily, sized for maximum exposure of the graft area and/or the vertebral body without compromising plate strength, particularly with respect to federal standards for such devices. The window is centrally positioned on the plate. The graft window is also preferably sized to provide alignment of the plate onto the vertebrae at the base of the vertebra fastener or screw holes of the plate. In a dynamic form of this cervical bone plate, the graft window expands and contracts with respective expansion and contraction of the dynamic plate after attachment to the vertebrae (i.e. “dynamizes”).  
         [0013]     In one form of the invention, a three-component dynamic bone plate is configured such that a middle component accepts an identical end component at both ends of the middle component. The end component may be a 180° interchangeable part. The middle component and the end component have cooperating configurations and complementarily configured channels that allow sliding movement between the middle component and the end components. A two-pillar construction provides a central window.  
         [0014]     As well, in another form of the invention, there is provided a kit for assembling an n-level dynamic cervical plate. The kit includes an extension component and two, identical end components. The end components may be slidingly assembled to each other to provide a dynamic one level (1-L) cervical plate that includes a central window. The end components may be slidingly assembled to each end of the extension component to provide a dynamic two level (2-L) cervical plate that includes two central windows, one between each level. Moreover, the extension component is configured such that two or more extension components may be utilized, 180° rotated each relative to the other. End components may then be assembled to the open ends of the extension component.  
         [0015]     The present invention also provides a cervical plate construct comprising a plate formed as a single piece in the case of a static plate, and formed as two or more sections in the case of a dynamic plate, a minimum of four bone screws, and one or more locking covers depending on the level of the cervical plate. The present cervical plate may be formed as a single level plate or a multi-level plate while still retaining the characteristics described and shown herein.  
         [0016]     The dynamic plate in accordance with the principles of the subject invention provides for pure vertebral body translation without creating guesswork with respect to screw positioning. The dynamic plate may be fabricated in 1-L or multi-L configurations. Moreover, the dynamic plate utilizes a dual pillar style of plate adjustment. In one form, the dynamic plate is formed of two identical sections situated at 180° relative to one another. The section has two legs, one defining a configured channel or bore therein, and the other having a like configured arm that fits into the channel.  
         [0017]     The present invention provides advantages over the teachings of the prior art with respect to cervical plating technology. The principles accompanying the present invention allows the fixation plate to be used with greater accuracy. This may ultimately increase the efficacy of an established procedure. For instance the present invention provides a window within the center area of the plate. This allows viewing of graft material during and after placement. This is accomplished by utilizing a dual pillar configuration for both the static and dynamic plates, and for all levels (1-L, ML) of fixation plates.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the inventions will be better understood by reference to the following description of embodiments of the inventions taken in conjunction with the accompanying drawings, wherein:  
         [0019]      FIG. 1  is a perspective view of an exemplary embodiment of a one-level (1-L) static bone fixation plate fashioned in accordance with the principles of the present invention;  
         [0020]      FIG. 2  is a bottom view of the one-level (1-L) static bone fixation plate of  FIG. 1 ;  
         [0021]      FIG. 3  is a perspective view of the one-level (1-L) static bone fixation plate of  FIG. 1  but having a cover thereon fashioned in accordance with an aspect of the present invention;  
         [0022]      FIG. 4  is a perspective view of the one-level (1-L) static bone fixation plate of  FIG. 1  having a contoured cover thereon fashioned in accordance with an aspect of the present invention;  
         [0023]      FIG. 5  is a perspective view of an exemplary embodiment of a two-level (2-L) static bone fixation plate fashioned in accordance with the principles of the present invention;  
         [0024]      FIG. 6  is a sectional view of the 2-L static bone fixation plate of  FIG. 5  taken along line  6 - 6  thereof;  
         [0025]      FIG. 7  is a sectional view of the 2-L static bone fixation plate of  FIG. 5  taken along line  7 - 7  thereof;  
         [0026]      FIG. 8  is a perspective view of a 2-L construct including the 2-L static bone fixation plate of  FIG. 5  with bone plate screws and bone screw retention clips;  
         [0027]      FIG. 9  is an enlarged perspective view of the bone screw retention clip depicted in  FIG. 8 ;  
         [0028]      FIG. 10  is a perspective view of an exemplary embodiment of a one-level (1-L) dynamic bone fixation plate fashioned in accordance with the principles of the present invention, the 1-L dynamic plate shown in an almost fully open or fully dynamic state;  
         [0029]      FIG. 11  is a perspective view of an exemplary embodiment of a two-level (2-L) dynamic bone fixation plate fashioned in accordance with the principles of the subject invention, the 2-L dynamic plate shown with each end plate portion of the 2-L dynamic plate in exploded view relative to an intermediate plate portion of the 2-L dynamic plate;  
         [0030]      FIG. 12  is a perspective view of an exemplary embodiment of another 2-L dynamic bone fixation plate fashioned in accordance with the principles of the subject invention, the 2-L dynamic plate shown with end plate portions thereof in an exploded position relative to an intermediate plate portion thereof in accordance with the principles of the subject invention; and  
         [0031]      FIG. 13  is an enlarged sectional view of an exemplary constraining mechanism that may be utilized in the present dynamic plates. 
     
    
       [0032]     Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent various embodiments of the invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the invention. Also, the exemplifications set out herein illustrate various embodiments of the invention, but such exemplifications are not to be construed as limiting the scope of the invention in any manner.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     Referring to  FIGS. 1 and 2 , there is depicted an exemplary one level (1-L), static cervical plate generally designated  100 , of which  FIG. 1  is lateral perspective view of the plate  100  and  FIG. 2  is a bottom plan view of the plate  100 . The plate  100  is characterized by a body  102  formed of a suitable material such as is known for the manufacture of cervical plates, for example titanium, a titanium alloy or the like. The body  102  is generally rectangular in shape and slightly curved on the underside thereof in order to mimic the natural curvature of a vertebra. Such curvature may be in one or two planes. The body  102  may be manufactured in various sizes to accommodate vertebra of different sizes.  
         [0034]     The body  102  has an opening, window, void or the like  104  (collectively hereinafter, window) in a middle, center or central portion of the body  102  bounded by surface  107 . While the window  104  may be formed in various configurations, it is preferable that the window extend essentially from proximate to adjacent bone screw bores  106  that are situated on ends  121 ,  123  of the 1-L plate  100 . In the exemplary plate  100 , the window  104  is configured in a somewhat oblong shape defining a first peak  111  and a second peak  113 . As developed more fully below, the elongation of the window allows for better alignment of the plate  100  on the vertebra by the surgeon. The window  104  itself provides visualization of the bone graft abutment to the posterior section of the plate while in situ. The opening  104  defines a first leg  103   a  and a second leg  103   b  to the body  102  that extend between ends  121  and  123  of the body  102 . The length (l) is longer then the width (w) of the opening  104 . The length (l) is elongated or extended to span essentially between the edges of each screw bore  106 .  
         [0035]     The window/leg configuration creates a “dual pillar” like support foundation for plate strength as between the first and second ends  121 ,  123 , such as against twisting or flexing. The size and configuration of the window  104  (forming two legs or a dual pillar configuration) provides an easy bone screw placement and/or allows for bone graft viewing. Each leg  103   a / 103   b  preferably, but not necessarily, has the same cross-sectional profile. Moreover, the cross-sectional profile of each leg is preferably, but not necessarily, consistent throughout its length between ends  121 ,  123 . Furthermore, the legs  103   a / 103   b  have the same height profile as the overall plate body  102 .  
         [0036]     The ends  121  and  123  each have two bone screw bores  106  each one of which is disposed on corners of the respective ends. The four bone screw bores  106  are preferably, but not necessarily, aligned to correspond to vertices of a rectangle, the rectangle preferably, but not necessarily, being a scaled version of the rectangular body  102 . The scaled rectangle forming a pattern for placement of screw bores on a patient&#39;s vertebra. The ends  121  and  123  each have an outer contour that defines a notch  109 . Each bone screw bore  106  is sized, configured and/or situated such that a portion thereof is adjacent a proximate portion of the opening  104 .  
         [0037]     Each bone screw bore  106  has a ledge  105  formed in the interior thereof. The ledge  105  is configured to capture an undersurface of a head of a bone screw. As such, each ledge  105  is somewhat dish-shaped to accommodate the complementary shape of the undersurface of the bone screw head. Each ledge  105  is also angled to allow the inserted bone screw to achieve a proper orientation during implantation. The bone screw bores  106  are configured to utilize various types of bone screws such as fixed angle screws, emergency screws, and variable angle screws, examples of which are incorporated herewith through the parent provisional application. Moreover, the bore/ledge allows variable bone screw angulation while fixing or mounting the plate to the vertebrae. Such angulation is up to 30° cephalad—caudal, and 20° lateral—medial.  
         [0038]     The body  102  further includes two bores  108  each one of which is situated proximate (here shown as between) bone screw bore pairs  106  of each end  121  and  123 . Each bore  108  is configured to receive a boss or fastening device/portion of a bone screw retainer device, cover plate, retention clip, or the like such as described herein for preventing rotation and/or backout of a bone screw that has been implanted.  
         [0039]     Referring to  FIG. 3 , there is depicted the 1-L static cervical plate  100  of  FIGS. 1 and 2 , but shown with one embodiment of a bone screw anti-backout, rotation inhibitor and/or releasable locking mechanism, embodied as a cover, plate or the like  110 . The cover  110  is situated on the plate  100  so as to cover the graft window  104  and at least partially the heads of the implanted bone screws. The cover  110  is used with the plate  100  to provide an embodiment of a 1-L static cervical plate construct. After the plate  100  has been implanted through use of bone screws, such as via the procedure described herein, the cover  110  may be placed onto the body  102 . This covers the opening  104 , and most of the screw bores  106 . The cover  110  is essentially flat, thus having a low profile.  
         [0040]     The cover  110  moreover surrounds the window  104  and most of each bone screw bore  106  (which would be most of a bone screw head when so installed). This helps to keep, retain or releasably lock the bone screws from backing out and/or turning. The cover also will provide protection against potential graft migrating out of the inter-vertebral space post operatively. The cover further will allow for post-operative visualization via radiograph. The cover  110  includes two cover bosses  112  that are configured to provide a snap fit into plate bores  108  when installed, such that the cover  110  is retained on the plate  100 . While normal use will not cause the cover  110  to separate from body  102 , a simple tool may allow removal of the cover  110 .  
         [0041]     The cover  110  is exemplary of the type of covers that may be used as bone screw locking mechanisms with the 1-L static cervical plate  100 . As such, covers  110  may be manufactured in various sizes to accommodate various sizes of cervical plates  110 . The cover  110  is also fabricated from a biocompatible material like the material for the plate  100 . The plate  100  may also accommodate other styles of covers.  
         [0042]      FIG. 4  depicts an alternative cover  114  (bone screw locking mechanism and/or graft window/area cover) for the 1-L static cervical plate  100  of  FIG. 1 . The cover  114  includes two bosses  116  that are configured to be snap fit received in the plate bores  108  thus retaining the cover  114  onto the plate  100 . The cover  114  extends over the opening  104  of the plate from over the leg  103   a  to over the leg  103   b , and over each screw bore  106  of the body  102 .  
         [0043]     In this embodiment, the cover  114  includes a depression or concavity  120  that is configured like the opening  104  in order to extend into the opening  104  when the cover  114  is installed. Moreover, the cover  114  includes four screw bore depressions or concavities  118  each of which is configured to extend into one of the bone screw bores  106  of the body  102  of the plate  100 . The covers or cover plates may be fashioned from an alloy of metals, titanium, a titanium alloy, PEEK, or suitable biocompatible material.  
         [0044]     While none of  FIGS. 1-4  show a bone screw in use with the plate  100 , it should be appreciated that the plate  100  is able to utilize various types of bone screws such as were set forth in the corresponding provisional application, incorporated above. Briefly, the plate  100  may utilize a polyaxial bone screw, a fixed bone screw, and an emergency bone screw.  
         [0045]     Referring now to  FIGS. 5-7 , there is depicted an exemplary embodiment of a two level (2-L) static cervical plate, generally designated  150 , incorporating the dual or twin pillar configuration for each level thereof such as described with reference to the 1-L plate  100 . The 2-L plate is designed to span between and be anchored to three vertebrae with a central window in accordance with the present principles between each fastening juncture thereof. The windows formed by the dual pillar configuration. As indicated in  FIGS. 6 and 7  by the curved arrow relative to a horizontal line (representing a centerline of the plate  100 ) illustrates two planes of curvature that the plate  100  may have mimicking the curvatures of vertebrae. As such, a particular length and/or thickness cervical plate may also be manufactured with varying curvatures.  
         [0046]     The plate  150  is defined by a body  152  that may be considered as having a middle portion or section  167 , a first end portion or section  166  on one side of the middle portion  167 , and a second end portion or section  168  on another side of the middle portion  167 . The middle portion  167  defines a fastening, mounting or attachment portion that is adapted to be attached to a central vertebra of a three vertebrae fusion. The end portions  166  and  168  also define a fastening, mounting or attachment portion that is adapted to be attached to separate outer vertebra of the three vertebrae fusion. As such, and keeping with the principles set forth herein with respect to the 1-L static plate  100 , the static 2-L plate  150  includes dual (two) openings, windows, voids or the like  153  and  155 , one opening for each level or between each end portion  166 ,  168  and the middle portion  167 . Each window  153  and  155  is centrally, located defines leg pairs (pillars)  164   a / 164   b  and  165   a / 165   b.    
         [0047]     The opening  153  is disposed in the middle, center or central portion of the area between the end portion  166  and the middle portion  167 , being bounded by surface  154 . The window  153  is configured in an exemplary fashion as an elongated oval that extends from just adjacent to a portion of each screw bore  157  of the end portion  166  (proximate the reception bore  160  of the end portion  166 ) to just adjacent to a portion of each screw bore  161  of the middle portion  167  (proximate the reception bore  160  of the middle portion  167 ).  
         [0048]     The opening  155  is disposed in the middle, center or central portion of the area between the end portion  168  and the middle portion  167 , being bounded by surface  156 . The opening  155  is configured as an elongated oval that extends from just adjacent to a portion of each screw bore  157  of the end portion  168  (proximate the reception bore  160  of the end portion  168 ) to just adjacent to a portion of each screw bore  161  of the middle portion  167  (proximate the reception bore  160  of the middle portion  167 ).  
         [0049]     The elongation of the openings  153 ,  155  allow for alignment of the plate  150  during surgery and mounting thereof by the surgeon. The size and configuration of the openings  153 ,  155  (forming two legs or a dual pillar configuration) provides easy bone screw placement and/or allows for bone graft viewing.  
         [0050]     Each leg pair  164   a / 164   b  and  165   a / 165   b  preferably, but not necessarily, has the same cross-sectional profile. As well, each leg  164   a/b  and  165   a /b preferably, but not necessarily has the same cross-sectional profile. Moreover, the cross-sectional profile of each leg is preferably, but not necessarily, consistent throughout its length between the middle portion  167  and end portions  166  and  168 . Furthermore, the legs  164   a/b  and  165   a/b  have the same height profile as the overall plate body  152 .  
         [0051]     The ends  166  and  168  each have two bone screw bores  157  each one of which is disposed on corners of the respective ends and at least partially defining the fastening portions. The ends  166  and  168  each have an outer contour that defines a notch. Each bone screw bore  106  is sized, configured and/or situated such that a portion thereof is adjacent a proximate portion of its respective opening  153 ,  155 . Each bone screw bore  157  has a ledge  158  formed in the interior thereof. Each ledge  158  is configured to capture an undersurface of a head of a bone screw. As such, each ledge  158  is somewhat dish-shaped to accommodate the complementary shape of the undersurface of the bone screw head. Each ledge  158  is also angled to allow the inserted bone screw to achieve a proper orientation during implantation. The bone screw bores  157  are configured to utilize various types of bone screws as described above. Additionally, the bone screw bores  157  are configured to utilize various types of bone screws such as fixed angle screws, emergency screws, and variable angle screws, examples of which are incorporated herewith through the parent provisional application. Moreover, the bore/ledge allows variable bone screw angulation while fixing or mounting the plate to the vertebrae. Again, such angulation may be up to 30° cephalad—caudal, and 20° lateral—medial.  
         [0052]     The middle portion  167  also has two bone screw bores  161  disposed as pairs of screw bores in like manner to the other screw bores at least partially defining the fastening portion. Each bone screw bore  161  is sized, configured and/or situated such that a portion thereof is adjacent a proximate portion of an opening  153 ,  155 . Each bone screw bore  161  has a ledge  162  formed around the interior thereof. Each ledge  162  is configured to capture an undersurface of a head of a bone screw. As such, each ledge  158  is somewhat dish-shaped to accommodate the complementary shape of the undersurface of the bone screw head. Each ledge  158  is also designed to receive the inserted bone screw in a fairly straight manner to achieve a proper orientation during implantation. The bone screw bores  161  are configured to utilize various types of bone screws like those above.  
         [0053]     The body  152  further includes two bores  160  each one of which is situated between bone screw bore pairs  157  of each end portion  166  and  168 . An additional like bore  160  is positioned in the middle portion  167 . Each bore  160  is configured to receive a boss or fastener of a bone screw retainer device, cover plate, retention clip, or the like.  
         [0054]     Referring to  FIG. 8 , there is depicted an exemplary 2-L static cervical plate construct  159 . The 2-L static cervical plate construct  159  includes the 2-L static cervical plate  150 , bone screws  180 , and bone screw locking, retainer or retention clips, tabs or the like  170  (clips). Some of the bone screws  180  are depicted in various orientations relative to the plate  150  to illustrate the ability of the plate  150  to allow such variable orientations. The construct  159  utilizes releasable bone screw locking means, anti-backing, retainer, retention or retaining clips or tabs  170  that attach onto and between pairs of screws  180 , particularly the pairs of screws for each body section  166 ,  167 ,  168 . The clips  170  also attach to the plate body  152 . The clips  170  aid in preventing the backing out or rotation of the bone screws thus providing locking of the bone screws and to the cervical plate.  
         [0055]     Additionally referring to  FIG. 9 , a clip  170  is depicted. The clip  170  has been enlarged for clarity. The clip  170  is formed of a biocompatible material preferably, but not necessarily, the same material as the cervical plates and/or cover plates. The clip  170  is defined by a body  171  having a first prong  176  on one end thereof, a second prong  178  on a second end thereof, and a boss structure  172 . The body  171  is sized such that the prongs  176  and  178  span the distance between bone screw heads. The boss structure  172  is defined by a post  173  that extends from the underside of the body  171 . The post terminates in a rim  174  and includes one or more slots  175 . The post  173  is configured to be received in the clip post (boss) bore  160  of the body  152  of the plate  150  (and other such situated bores in the other plates described herein) thus releasably retaining or locking the clip  170  to the plate  150 .  
         [0056]     Each prong  176 ,  178  is adapted to be received in a bone screw head socket. It should be appreciated, that the use of clips  170  is not limited to static 2-L plates as shown, but may be used with static 1-L plates, static multi-level plates, and dynamic plates of all levels. The clip  170  is provided in various sizes in order to be used with plates of various sizes, since the span between bone screw heads may be different for different size plates. The clip  170  also has a low profile (thickness) so as to remain relatively flat against the plate  150 .  
         [0057]     The diameter of the post  173  is slightly less than the diameter of the receiving bore in the plate (e.g. bore  160  of plate  150 ) so that the receiving bore may receive the post. The rim  174 , however, defines a diameter that is oversized for the receiving bore in the plate. The notches or slots  175  allow the ends of the post  173  to slightly compress, reducing the effective diameter of the rim  174 , causing the rim  174  to pass through the receiving bore. Once the rim  174  is through the receiving bore, the post  173  returns to its uncompressed state such that the end  177  of the rim  174  contacts the underside of the plate, preventing the clip  170  from pulling out of the receiving bore without a special tool or the like. The resilient boss  174  is thus configured to be releasably, but snugly snap or press fit received into an appropriate plate bore.  
         [0058]     The interaction of the clip  170  with the plate  150  and the bone screw pairs is best seen in  FIG. 8 , and particular attention is drawn to the end portion  168  of the plate  150  of  FIG. 8 . Each bone screw  180  has a head or head portion  181 . Each head  181  includes a socket  182  formed therein. The socket  182  is preferably, but not necessarily, configured in a polygonal pattern. Other configurations may be used. Each corner  182  of the polygon pattern (socket configuration) is rounded such that the span of the ends of the prongs  176 ,  178  fits into two rounded corners  182 . In this manner the prongs  176  and  178  lock the bone screws from rotation. Moreover, rotation of either bone screw of the bone screw pair fitted with a clip  170  will slightly rotate the clip in the plane of the plate  150  thus binding the clip against each other. The clip  170  is also releasably locked to the plate  150 .  
         [0059]     The boss  172  of the clip  170  is situated in the bore  157  (snap-fit received). One prong  176  extends into the socket  182  of the head  181  of the upper bone screw  180  while the other prong  178  extends into the socket  182  of the head  181  of the lower bone screw  180 . The prongs interact with the polygon socket of the head to limit rotation of a screw. The first and second configured flanges  176 ,  178  are configured to be press or snap fit received in the bone screw head socket.  
         [0060]      FIG. 10  depicts an exemplary embodiment of a dynamic 1-L cervical plate generally designated  200 , in accordance with the present principles. The dynamic 1-L plate  200  is shown in exploded form to better illustrate the manner in which the dynamic plate is assembled, joined and/or is dynamic or dynamizes. The dynamic 1-L plate  200  is characterized by a first section  202  and a second section  204  that when assembled or together provides an opening, void or window  117 . The size of the opening  117  is variable depending on the position of the two sections  202 ,  204  relative to one another. Each section  202 ,  204  defines a U-shape or portion that slidingly mates with one another to provide dynamization when attached. This sliding motion is unconstrained such that it smoothly transitions between various positions without ratchets or the like. The sections  202 ,  204  each provide a fastening portion, one for each vertebra. The window  217  exposes an area between the vertebrae. It should be appreciated that the configuration of such mating may be modified and/or deviate from that shown.  
         [0061]     The first section  202  has a body  203  supporting two bone screw bores  206  which, while not shown, may include configured ledges such as the configured ledges  158  of bone screw bores  157  of plate  150  (see, e.g.  FIG. 5 ) for variable bone screw angulation as described above. The first section  202  also includes first and second legs  208  and  211 . The first leg  208  has a configured channel  209  extending therein. The second leg  211  also has a configured channel  210  extending therein. While not necessary, the first and second channels  209 ,  210  are preferably the same configuration, but may be of one each such that the device is 180° rotatable and be the same.  
         [0062]     The second section  204  has a body  205  supporting two bone screw bores  218 , which, while not shown, may include configured ledges such as the configured ledges  158  of bone screw bores  157  of plate  150  (see, e.g.  FIG. 5 ). The second section  204  also includes first and second configured arms  214 ,  216 . The first configured arm  214  is configured and/or dimensioned in like manner to the channel  209  and thus to be slidingly receivable into the configured channel  209 . The second configured arm  216  is also configured and/or dimensioned in like manner to the channel  210  and thus to be slidingly receivable into the configured channel  211 . The arms  214 ,  216  are of a length to be fully received in the respective channel  209 ,  211  so the ends of the legs  208 ,  210  abut the ends of the arms  214 ,  216 . In this manner, the dynamic 1-L plate  200  of  FIG. 10  provides relative movement between the two sections or components  202 ,  204 .  
         [0063]     Referring to  FIG. 11 , there is depicted an exemplary embodiment of a dynamic two level (2-L) plate generally designated  230  formed in accordance with an aspect of the subject invention. The dynamic 2-L plate  230  is shown in exploded form to better illustrate the manner in which the dynamic plate is assembled, joined and/or is dynamic or dynamizes. This also illustrates how the middle plate component  250  may be used with itself to form n-levels of cervical plates with end components (i.e. two end plate components  232  for attachment to beginning and end vertebrae, and n middle plate components  250  defining the n-levels for attachment to n number of middle vertebrae), and moreover with each level providing dynamization (internally dynamizing). Thus, each internal or middle section is dynamizing as between themselves, not just the end plate components relative to a middle portion. The dynamic 1-L plate  200  is characterized by a first section  202  and a second section  204  that when assembled or together provides an opening, void or window  117 . The size of the opening  117  is variable depending on the position of the two sections  202 ,  204  relative to one another. Each section  202 ,  204  defines a U-shape or portion that slidingly mates with one another to provide dynamization when attached. This sliding motion is unconstrained such that it smoothly transitions between various positions without ratchets or the like. The sections  202 ,  204  each provide a fastening portion, one for each vertebra. The window  217  exposes an area between the vertebrae. It should be appreciated that the configuration of such mating may be modified and/or deviate from that shown.  
         [0064]     As such, the dynamic plate  230  has extended windows or openings formed by the dual pillar structure and, more particularly, has two windows formed by two dual pillar structures. The dynamic plate  230  is a two level (2-L) plate that is composed of three components which are shown in exploded view relative to one another in  FIG. 11 . The plate  230  is formed of a middle plate component  250  and two end plate components  232   a  and  232   b . The two end plate components  232   a  and  232   b  are identical. A 180° reversal of an end component  232 , in conjunction with the configuration of the middle component  250 , allows the dynamic 2-L plate to utilize only two different pieces. Therefore, kits to provide n-level plates would come with two end plate components, and a plurality of middle plate components.  
         [0065]     End component  232   a  is defined by a body  233   a  having bone screw bores  235   a  and configured ledges  234   a  such as described above. A retention bore  236   a  for a locking clip  170  or cover plate boss is provided between the two bone screw bores. The body  233   a  defines a first leg  238   a  having a configured channel or cutout  237   a  therein. The shape of the channel  237   a  provides lateral and up/down stability to a joining or mating piece of the middle component  250 . Thus, the configuration of the channel may be changed as appropriate under the present principles. In this particular form, the channel  237   a  is configured akin to a dovetail. A second leg  244   a  of the body  233   a  is configured akin to the channel  237   a  dovetail. It should be observed that the end components  232   a  and  232   b  may be joined or assembled into a dynamic 1L plate without the use of the middle component  250  since the leg  244   b  (identical to leg  244   a ) will be received in leg channel  237   a  while the leg  244   a  will be received in leg channel  237   b  (identical to leg channel  237   a ).  
         [0066]     The end component  234   b  is defined by a body  233   b  having bone screw bores  235   b  and configured ledges  234   b  such as described above. A retention bore  236   b  for a retention clip or cover boss is provided between the two bone screw bores. The body  233   b  defines a first leg  238   b  having a configured channel or cutout  237   b  therein. The shape of the channel  237   b  provides lateral and up/down stability to a joining or mating piece of the middle component  250 . Thus, the configuration of the channel may be changed as appropriate under the present principles. In this particular form, the channel  237   b  is configured akin to a dovetail. A second leg  244   b  of the body  233   b  is configured akin to the channel  237   b  dovetail.  
         [0067]     The middle or expansion component  250  is defined by a body  252  having two bone screw bores  254  having head seats  255 , and a boss bore  256 . The body  252  also includes a first leg  258  having a configured channel  260  therein. The channel  260  receives the configured leg  244   a  of the section  232   a  (or flange  272  of another expansion component) and is thus configured appropriately. A second leg  262  of the body  252  includes a configured flange  264  that is configured to be received in the channel  237   a  of the section  230  (or a channel  268  of another expansion component) and is thus configured appropriately. A third leg  270  includes the configured flange  272  receivable in the channel  237   b  of the section  232   b  (or in the channel  260  of another expansion component). A fourth leg  266  of the body  252  includes the channel  268  that receives the configured flange  244  of the section  230  or the flange  264  of another expansion device. This structure and/or interrelationship of the middle component  250  to itself and to the end components  232 , provides the ability to assemble N-level, dynamic plates. The 2-L dynamic plate  230 , when assembled, defines first and second windows, voids or openings  275 ,  277  between the middle component  250  and each end component  232 . The legs and flanges when assembled each have the same cross-section. The truncated triangle cross-section provides loading stability.  
         [0068]      FIG. 12  depicts another exemplary embodiment of a dynamic two-level cervical plate, generally designated  300 , that is a variation of the dynamic two-level cervical plate  230  but which incorporates the features and/or functions of the plate  230 . As such, the 2-L plate  300  has components that can be assembled to form a 1-L plate or an n-level plate. The plate  300  is formed of a middle component  302  and first and second identical end components  304   a ,  304   b . Like plate  230 , the dynamic plate  300  has extended windows or openings formed by dual pillar structures. The dynamic plate  300  is a two level (2-L) plate that is composed of three components which are shown assembled in  FIG. 11 . The plate  300  is formed of a middle plate component  302  and two end plate components  304   a  and  304   b . The two end plate components  304   a  and  304   b  are identical. A 180° reversal of an end component  304 , in conjunction with the configuration of the middle component  302 , allows the dynamic 2-L plate to utilize only two different pieces.  
         [0069]     End components  304   a/b  is defined by a body  333   a/b  having bone screw bores  335   a/b  and configured ledges  334   a/b  such as described above. A retention bore  336   a/b  for a retention clip or cover boss is provided between the two bone screw bores. The body  333   a/b  defines a first leg  338   a/b  having a configured mating structure thereon. The body  333   a/b  also defines a thickened second let  340   a/b  that has a channel for receiving a like configured leg portion of the middle component  302 , the shape of which provides lateral and up/down stability to a joining or mating piece of the middle component  302 . Thus, the configuration of the channel may be changed as appropriate under the present principles. It should be observed that the end components  304   a  and  304   b  may be joined or assembled into a dynamic 1L plate without the use of the middle component  302 .  
         [0070]     The middle or expansion component  302  is defined by a body  352  having two bone screw bores  354  having head seats  355 , and a boss bore  356 . The body  352  also includes a first thickened leg  358  having a channel therein that is configured to receive the configured leg  338   a  of the end component  304   a  (or flange  366  of another middle component  350 ) and is thus configured appropriately. A second leg  364  of the body  352  includes a flange that is configured to be received in the channel structure  340   a  of the end component  304   a  (or a channel  366  of another middle component) and is thus configured appropriately. A third leg  372  includes configured flange receivable in the channel structure  340   b  of the end section  232   b  (or in the channel of another middle component). A fourth leg  366  of the body  352  includes a channel structure that receives the configured flange  338   b  of the end component  304   b  or the flange of another middle component. This structure and/or interrelationship of the middle component  302  to itself and to the end components  304 , provides the ability to assemble N-level, dynamic plates. The 2-L dynamic plate  300 , when assembled, defines first and second windows, voids or openings  308 ,  310  between the middle component  302  and each end component  304 . The legs and flanges when assembled each have the same cross-section.  
         [0071]     The various dynamic plates of the present invention are assembled from a number of end and middle components depending on the desired plate level. The various components are slidingly interconnected to one another. It should be appreciated that once assembled, the plate components, while slidable with respect to each other, have a disassembly stop or constraining mechanism or device such that the plate components will not disassemble once assembled. The disassembly constraining mechanism constrains or limits the length of travel of the leg assemblies (slidingly connected legs of the plate components) of the two plate components relative to one another in a disassembled direction of travel.  
         [0072]     To this end and referring to  FIG. 13 , there is depicted an exemplary disassembly constraining mechanism for the present dynamic plate components. Particularly,  FIG. 13  illustrates an enlarged portion of two slidingly interconnected legs  380 ,  382  of any two assembled dynamic plate components according to the principles of the present invention. Leg  380  may be a configured leg with a channel or groove, while the leg  382  is a configured leg with a flange, or vice versa such as described herein. When referring to  FIG. 13 , however, the arm  380  will arbitrarily considered a configured channel arm and the arm  382  necessarily considered the configured flange arm. It should also be appreciated that distances and lengths are not necessarily to scale and/or in proportion with one another.  
         [0073]     The channeled arm  380  has a detent  384  within the groove (the underside per  FIG. 13 ) of the arm  380 . The detent  384  extends a distance from the groove surface into the are  385  and is preferably, but not necessarily, in the form of a right triangle having a sharp to rounded apex. The flanged arm  382  includes a notched or cutout area or portion  385  bounded by a ledge  388 . A detent  386 , again preferably, but not necessarily in the form of a right triangle having a sharp to rounded apex, is situated within the area  385 .  
         [0074]     During assembly, the detent  386  is to the left of detent  384 . While the height of the detents are such that the apex of each detent extends beyond the apex of the other detent, as the two detents  384 ,  386  meet their angled or ramped surfaces meet. Continued travel allow the ramps to slide relative to another. The small overlap in detent height thus allows the detent  384  to reside in area  385  once full assembly has taken place. In one direction of travel, the detent  384  will contact ledge  388 , while in the other direction the difference in detent height creates a stop. Of course, other types of stop mechanisms may be employed that allow assembly but prevents disassembly or makes disassembly extremely difficult.  
         [0075]     The cervical plates described above are intended for anterior screw fixation to the cervical spine (C2 through T1) for various conditions such as at least the conditions of spondylolisthesis, fracture, spinal stenosis, and tumor. Moreover, it should be appreciated that the configuration(s) and/or principles of the 1-L dynamic plate(s) described herein are applicable to and/or may be used in the various 2-L dynamic plates also described herein. As well, 2-L dynamic plate configurations described herein may be used in the 1-L plates described herein. This is particularly true with respect to the various leg or projection configurations and the sliding connectivity thereof.  
         [0076]     Each plate is preferably, but not necessarily, formed from titanium (e.g. titanium 6A1-4V ELI per AASTM F-136). Other suitable metals, ceramics may be used if appropriate.  
         [0077]     In general, the preferred embodiment of the present cervical plates will embody curvature in two planes (sagittal and coronal) to more closely resemble the anatomical aspects of the spine. The cervical plates may be provided without curvature or with curvature in one plane as necessary. The plates are made in various sizes (e.g. 14 mm through 110 mm) to accommodate various spines. The plates have a nominal thickness of about 1.8 mm to 3.0 mm and a width of about 18 mm. The plates are configured to accept bone screws having a diameter of about 4.0 through 4.5 mm. Moreover, the bone screw holes of the plates are configured to accommodate both static and variable angle bone screws. This is accomplished by use of a unique pocket design of the bone screw holes. The bone screws are affixed using a typical screw driver (e.g. hexalobullar driver, ×10).  
         [0078]     Once the plate has been installed with the appropriate bone screws, the bone screws may be locked via several methods. In one method, a single locking plate locks a pair of screws. The locking plate includes a center post that locks into a cover plate bore in the plate, and which has two configured flanges that are received in the head of the screw. In another form, the cover includes integral locking flanges for the bone screws. The cover and/or locking flanges are preferably made of PEEK, plastic, alloy or titanium.  
         [0079]     A plate may be utilized as follows. A plate is placed onto the anterior aspect of a vertebral body of the cervical spine by inserting a 4.0 mm cancellous bone screw or a 4.3 mm expansion screw through the cephalad holes and into the vertebral body. The screw or expansion screws are then inserted into the caudal holes in the plate and inserted into the vertebral bodies of the cervical spine. The locking mechanisms are then inserted in a single step over the entire plate (e.g. a cover), or two locking mechanism are inserted over each set of screws (cephalad and caudel). The locking mechanisms will snap into place.  
         [0080]     The present invention also provides for dynamically fusing the cervical spine of a patient via various methods, particularly, but not necessarily, utilizing a cervical plate as described herein. One such method includes the opening of an access aperture in the patient to permit access to an appropriate area of the cervical spine of the patient. A vertebral disc is removed between each vertebrae (level) as appropriate (e.g. one disc for a 1-L, two discs for a 2-L, etc.). Bone graft is then sized for placement into the space where the spinal disc has been removed. A dynamic cervical plate, such as any described herein, is selected for implanting onto the spine (vertabrae). The selected dynamic cervical plate is sized to allow for the best anatomical settling (motion), e.g. between 0 and 4 mm, of the vertebral bodies. The selected and sized dynamic plate is placed over the inserted bone graft(s) onto the vertebrae. The graft(s) is then visualized through the window(s) within the dynamic plate for proper fitment. Each section is accomplished in sequence for proper fitment. The plate is secured onto the spine by bone screws placed through the bone screw bores within the plate components or segments. After each bone screw is attached, a locking mechanism is installed onto/over the bone screws/plate. The aperture is then closed.  
         [0081]     Another method of dynamically fusing the cervical spine includes providing a dynamic cervical plate wherein the end components of the provided dynamic cervical plate move relative to one another utilizing multiple projections (e.g. legs) sliding into or over one another according to the principles of the present invention. Another method of dynamically fusing the cervical spine includes providing a dynamic cervical plate wherein the end components of the provided dynamic cervical plate move relative to a middle segment/component utilizing multiple projections (e.g. legs) sliding into or over one another according to the principles of the present invention. Another method of dynamically fusing the cervical spine includes providing a dynamic cervical plate wherein the middle segments/components of the provided dynamic cervical plate move relative to one another utilizing multiple projections (e.g. legs) sliding into or over one another according to the principles of the present invention. Each plate providing a central graft window as provided herein for each level thereof.  
         [0082]     Moreover, any of the methods, such as those immediately above, may include the providing of an n-level dynamic cervical plate, plate construct, or plate kit, wherein the end segments are 180° interchangeable, middle segments are 180° interchangeable, the end segments and the middle segments are 180° interchangeable, the end segments and the middle segments move 0 to 4 mm independent of the movement of one another, and/or the movement of the end segments and the middle segments is unconstrained.  
         [0083]     The subject invention provides several key attributes that other plates and/or plate systems do not including:  
         [0084]     1. The curvatures placed on the window portion of the plate allow the surgeon to align the plate more accurately to the vertebral body.  
         [0085]     2. The curvatures placed on the window portion of the plate allow the surgeon to place bone screws more accurately because the bottom of the screw holes mate with a top of the plate window. This provides a positive visual indication that the plate is situated properly.  
         [0086]     3. The screw holes have a unique geometry allowing a simple change of screws to utilize the plate as a variable angle screw/plate construct or as a fixed angle screw plate construct.  
         [0087]     4. The plate construct may utilize an optional bone screw locking mechanism. The optional screw locking mechanism is a single-piece, snap on cover that is preferably, but not necessarily, made of PEEK or Titanium.  
         [0088]     5. In one form, the optional screw locking mechanism attaches into the cervical plate by one of the midline holes. The locking mechanism will cover two screws at one time and lock into the plate using a pronged shaft. Radial projections (propeller like structures) have teeth on the extended ends that mate with the corresponding screws. The teeth lock into the lobes within the screw preventing them from both turning and backing out. This mechanism, like the other, snaps into place but remains removable with the proper instrument.  
         [0089]     6. The dynamic plate form of the present invention will allow the fused vertebral bodies to settle onto the graft centered between them. This new dynamic plate and technique will allow fused segments to move, settle or subside which will provide for more constant bone-graft-bone contact. The present dynamic plate design allows the settling to occur in an anatomical fashion, due to plate curvatures. The bodies will translate in stabilized directions on two separate planes (pure translation).  
         [0090]     7. The present invention provides the ability to control subsidence of the plate. This is important in order to prevent the plate from migrating into the healthy adjacent disc space. Moreover the present invention aids in preventing the destruction of the host endplate or the graft from unmitigated settling that may lead to pseudarthrosis. It should be appreciated that the above description is only exemplary of the principles of the subject invention. Therefore, other embodiments are contemplated and within the present scope.  
         [0091]     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, of adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and that fall within the limits of the appended claims.