Abstract:
Methods and devices for static or dynamic spine stabilization include an anterior plating system that allows longitudinal and pivoting motion of the plates and of the stabilized vertebras. In one embodiment a spine fixation assembly for connecting a first vertebra to a second vertebra includes a first plate configured to be attached to one or more locations of the first vertebra and a second plate configured to be attached to one or more locations of the second vertebra. The first plate is pivotally connected to the second plate and may also allow longitudinal and/or horizontal motion of the plates relative to each other.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 60/811,593 filed Jun. 7, 2006 and entitled “METHODS AND DEVICES FOR STATIC OR DYNAMIC SPINE STABILIZATION”, the contents of which are expressly incorporated herein by reference. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to methods and devices for static or dynamic spine stabilization, and more particularly to methods and devices including an anterior plating system that allows longitudinal and pivoting motion of the plates and therefore of the stabilized vertebras. 
       BACKGROUND OF THE INVENTION 
       [0003]    The human spine consists of individual vertebras (segments) that are connected to each other. Under normal circumstances the structures that make up the spine function to protect the neural structures and to allow us to stand erect, bear axial loads, and be flexible for bending and rotation. However, disorders of the spine occur when one or more of these spine structures are abnormal. In these pathologic circumstances, surgery may be tried to restore the spine to normal, achieve stability, protect the neural structures, or to relief the patient of discomfort. The goal of spine surgery for a multitude of spinal disorders especially those causing compression of the neural structures is often decompression of the neural elements and or fusion of adjacent vertebral segments. Fusion works well because it stops pain due to movement at the facet joints or intervertebral discs, holds the spine in place after correcting deformity, and prevents instability and or deformity of the spine after spine procedures such as laminectomies or corpectomies. 
         [0004]    Anterior decompression directly removes anterior compressive structures and is known to have improved results in these cases over indirect decompression afforded by laminectomies. Anterior discectomy and fusion or anterior corpectomy and fusion are most commonly performed in the cervical spine but there is increasing application in the thoracic and lumbar spine. 
         [0005]    In recent years, there is an increase in the use of plate fixation to stabilize the cervical spine after anterior decompression and fusion. (U.S. Pat. No. 6,402,756, U.S. Pat. No. 5,616,142, U.S. Pat. No. 5,800,433 and U.S. Publication No. 2002-0111630, U.S. Pat. No. 6,328,738) The goals of plate fixation include increased stability to allow for less reliance on rigid external orthosis such as hard cervical collars and halos for stability. It is thought that plates also increased the rate of fusion and decreased the incidence of graft complications such as graft extrusions and subsidence. One of the disadvantages of current anterior cervical plates includes the lack of graft subsidence and continuous graft loading which is believed to be advantageous for fusion. It is also difficult to place the plate in a straight line longitudinally between adjacent vertebras and plates are therefore often inadvertently placed at an angle. These technical difficulties often lead to a higher rate of complications including failure of the graft to fuse (pseudoarthrosis) and failure of the moveable (dynamic) mechanism to work, or failure of the plate-screw interface due to abnormal angular and rotational forces. 
         [0006]    The newest plating systems have been designed to allow motion between the segments to be fused either at the fixation points between the plate and the screws or as a sliding mechanism within the plate with the ends of the plate fixed to screws in the vertebral body. This new “dynamic” plating system is believed to offer superior fusion rates since it allows continuous graft loading and natural graft subsidence while acting as a block to anterior graft displacement. 
         [0007]    However, the limitations of dynamic plating systems include, potential failure of the moveable mechanism to work if the plates are placed at an angle between the vertebral bodies to be fused, lack of bidirectional movements during compression (neck flexion) and distraction (extension and lying supine), and lack of variable compression rates during sudden neck movements. Accordingly there is a need for an improved dynamic stabilization system that addresses the above-mentioned limitations. 
       SUMMARY OF THE INVENTION 
       [0008]    Methods and devices for static or dynamic spine stabilization include an anterior plating system that allows longitudinal and pivoting motion of the plates and of the stabilized vertebras. 
         [0009]    In general, in one aspect, the invention features a spine fixation assembly for connecting a first vertebra to a second vertebra including one or more guide wires, one or more fixation elements, a plate and one or more locking elements. One or more guide wires are configured to be inserted into one or more locations of the first vertebra and one or more guide wires are configured to be inserted into one or more locations of the second vertebra. One or more fixation elements are configured to be driven into the one or more locations of the first vertebra and one or more fixation elements are configured to be driven into the one or more locations of the second vertebra, respectively. Each of the fixation elements comprises a threaded body, a flange extending from an end of the threaded body, a threaded post extending from the flange and a through bore extending longitudinally through the threaded body the flange and the post, and the corresponding guide wire is dimensioned to pass through the through bore. The plate is configured to be placed over the threaded posts of the one or more fixation elements driven into the one or more locations of the first vertebra and over the threaded posts of the one or more fixation elements driven into the one or more locations of the second vertebra, and to overlay the vertebras. The plate comprises one or more apertures configured to receive the one or more fixation elements. One or more locking elements are configured to attach each of the posts of the one or more fixation elements to the plate, thereby securing the plate to the one or more fixation elements. 
         [0010]    Implementations of this aspect of the invention may include one or more of the following features. The plate comprises an hourglass shape and an hourglass central aperture and the hourglass aperture is configured to provide access and line of vision to the under laying first and second vertebras and to an intervertebral space between the first and second vertebras. The apertures are dimensioned to allow the posts to pass through and the flanges not to pass through, so that the plate sits on top of the flanges. The locking elements comprise threads dimensioned to engage threads in the posts. The first vertebra may be adjacent or not adjacent to the second vertebra. The first and second vertebras may be separated by at least a third vertebra and the plate is dimensioned to overlie the first, second and third vertebras. The spine assembly may further include one or more additional fixation elements configured to be driven into one or more locations of the third vertebra and wherein the plate comprises one or more additional apertures configured to receive the one or more additional fixation elements. 
         [0011]    In general in another aspect the invention features a spine fixation method for connecting a first vertebra to a second vertebra including the following steps. First, inserting one or more guide wires into one or more locations of the first vertebra and one or more guide wires into one or more locations of the second vertebra. Next, driving one or more fixation elements into the one or more locations of the first vertebra and one or more fixation elements into the one or more locations of the second vertebra, respectively. Each of the fixation elements comprises a threaded body, a flange extending from an end of the threaded body, a threaded post extending from the flange and a through bore extending longitudinally through the threaded body the flange and the post, and the corresponding guide wire passes through the through bore. Next, placing a plate over the threaded posts of the one or more fixation elements driven into the one or more locations of the first vertebra and over the threaded posts of the one or more fixation elements driven into the one or more locations of the second vertebra. The plate is configured to overlay the vertebras and comprises one or more apertures configured to receive the one or more fixation elements. Finally, attaching a locking element to each of the posts of the one or more fixation elements thereby securing the plate to the one or more fixation elements. 
         [0012]    In general in another aspect the invention features a spine fixation assembly for connecting a first vertebra to a second vertebra including a first plate configured to be attached to one or more locations of the first vertebra, a second plate configured to be attached to one or more locations of the second vertebra. The first plate is pivotally connected to the second plate. 
         [0013]    Implementations of this aspect of the invention may include one or more of the following features. The spine fixation assembly may further include one or more guide wires configured to be inserted into the one or more locations of the first vertebra and one or more guide wires configured to be inserted into the one or more locations of the second vertebra. One or more fixation elements are configured to be driven into the one or more locations of the first vertebra and one or more fixation elements are configured to be driven into the one or more locations of the second vertebra, respectively. Each of the fixation elements comprises a threaded body, a flange extending from an end of the threaded body, a threaded post extending from the flange and a through bore extending longitudinally through the threaded body the flange and the post, and the corresponding guide wire is dimensioned to pass through the through bore. The first plate is configured to be placed over the threaded posts of the one or more fixation elements driven into the one or more locations of the first vertebra and the second plate is configured to be placed over the threaded posts of the one or more fixation elements driven into the one or more locations of the second vertebra. The first and second plates comprise one or more apertures configured to receive the one or more fixation elements. The spine fixation assembly may further include one or more locking elements configured to attach each of the posts of the one or more fixation elements to the plates, thereby securing the plates to the one or more fixation elements. The first plate is also movable relative to the second plate along a longitudinal and/or a horizontal axis of the plates. These motions may be via a ratcheting mechanism. The plates may have triangular shape, rectangular shape, circular shape, semi-circular shape, oval shape, trapezoidal shape or elliptical shape. Each of the plates may comprise a central aperture configured to provide access and line of vision to the under laying first and second vertebras and to an intervertebral space between the first and second vertebras. The apertures are dimensioned to allow the posts to pass through and the flanges not to pass through, so that the plates sit on top of the flanges. The locking elements comprise threads dimensioned to engage threads in the posts. The first vertebra may be adjacent or not adjacent to the second vertebra. The first and second vertebras may be separated by at least a third vertebra and the plates are dimensioned to overlie the first, second and third vertebras. The spine fixation may further include a third plate configured to be attached to one or more locations of a third vertebra and the third plate is pivotally connected to the second plate. The third plate may be also movable relative to the second plate along a longitudinal or horizontal axis of the plates. 
         [0014]    In general in another aspect the invention features a spine fixation method for connecting a first vertebra to a second vertebra including attaching a first plate to one or more locations of said first vertebra and then attaching a second plate to one or more locations of said second vertebra. The first plate is pivotally connected to said second plate. 
         [0015]    Among the advantages of this invention may be one or more of the following. The improved spine fixation system allows motion between the segments to be fused away from the fixation points. The dynamic fixation system provides bidirectional motion between the fused segments during compression (neck flexion) and distraction (extension and lying supine). The plates are allowed to pivot and/or slide longitudinally and/or horizontally relative to each other at a point between the fused segments. The plates can be placed at an angle relative to each other. This new dynamic plating system offers superior fusion rates since it allows continuous graft loading and natural graft subsidence while acting as a block to anterior graft displacement. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Referring to the figures, wherein like numerals represent like parts throughout the several views: 
           [0017]      FIG. 1  is a front perspective view of a top loading, one-level, fixed cervical fusion plate connecting two adjacent vertebras; 
           [0018]      FIG. 2  is a front perspective view of the cervical fusion plate of  FIG. 1 ; 
           [0019]      FIG. 3  is an exploded view of the cervical plate of  FIG. 2 ; 
           [0020]      FIGS. 4A ,  4 B,  4 C,  4 D depict the steps for attaching the cervical plate of  FIG. 1  to the vertebras; 
           [0021]      FIG. 5  is a front view of the cervical fusion plate of  FIG. 1 ; 
           [0022]      FIG. 6  is a front perspective view of a top loading, one-level, pivoting cervical fusion plate connecting two adjacent vertebras; 
           [0023]      FIG. 7  is an exploded view of the cervical plate of  FIG. 6 ; 
           [0024]      FIG. 8A  depicts the counterclockwise pivoting motion of the top plate of  FIG. 6 ; 
           [0025]      FIG. 8B  depicts the clockwise pivoting motion of the top plate of  FIG. 6 ; 
           [0026]      FIG. 9  is a front perspective view of a top loading, one-level, dynamic cervical fusion plate connecting two adjacent vertebras; 
           [0027]      FIG. 10  is an exploded view of the cervical plate of  FIG. 9 ; 
           [0028]      FIG. 11A  depicts the upward motion of the top plate of  FIG. 9 ; 
           [0029]      FIG. 11B  depicts the downward motion of the top plate of  FIG. 9 ; 
           [0030]      FIG. 12A  depicts the counterclockwise motion of the top plate of  FIG. 9 ; 
           [0031]      FIG. 12B  depicts the clockwise motion of the top plate of  FIG. 9 ; 
           [0032]      FIG. 13  is a front perspective view of a top loading, two-level, fixed cervical fusion plate connecting three adjacent vertebras; 
           [0033]      FIG. 14  is an exploded view of the cervical plate of  FIG. 13 ; 
           [0034]      FIG. 15  is a front perspective view of a top loading, two-level, pivoting cervical fusion plate connecting three adjacent vertebras; 
           [0035]      FIG. 16  is a perspective view of the cervical plate of  FIG. 15 ; 
           [0036]      FIG. 17  is a perspective view of a top loading, two-level, dynamic cervical fusion plate connecting three adjacent vertebras; 
           [0037]      FIG. 18  is an exploded view of the cervical plate of  FIG. 17 ; 
           [0038]      FIGS. 19A ,  19 B,  19 C depict the steps of modifying the two-level, dynamic cervical fusion plate of  FIG. 17  to dynamically attach it to a fourth vertebra; 
           [0039]      FIG. 20  is another embodiment of a top loading, one-level, dynamic cervical fusion plate connecting two adjacent vertebras; and 
           [0040]      FIG. 21  is another embodiment of a top loading, one-level, dynamic cervical fusion plate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    Referring to  FIG. 1 ,  FIG. 2  and  FIG. 3 , an anterior one-level fixed cervical fusion system  90  includes a top loading, one-level fixed cervical plate  100  that connects two adjacent vertebras  82  and  84 . The fixed cervical plate  100  is attached to the vertebras  82  and  84  via four screws  130   a ,  130   b  and  130   c ,  130   d , respectively. The fixed cervical plate  100  has an hourglass shape and an hourglass shaped aperture  102  centered in the middle of the plate  100 . Aperture  102  provides visibility and access to the vertebras  82 ,  84  and disc  62  below the plate  100 . Plate  100  also has four holes  162   a ,  162   b ,  162   c  and  162   d  located in the four corners of the plate. Holes  162   a ,  162   b ,  62   c ,  162   d  are dimensioned to receive the four screws  130   a ,  130   b ,  130   c ,  130   d , respectively. 
         [0042]    Referring to  FIG. 4A ,  4 B,  4 C,  4 D, the process for attaching the plate  100  to the adjacent vertebras  82 ,  84  includes the following steps. First, four k-wires  140   a ,  140   b  and  140   c ,  140   d  are inserted into the vertebras  82  and  84 , respectively ( 182 ). Next, four screws  130   a ,  130   b  and  130   c ,  130   d  are driven into the vertebras  82  and  84 , respectively, using the four k-wires  140   a ,  140   b , and  140   c ,  140   d , as guides respectively ( 184 ). Each screw has a threaded body  131 , a flange  132  on top of the threaded body  131  and a threaded post  133  extending upwards from the flange  132 . The threaded body  131  is driven into the vertebra while the flange  132  and the threaded post  133  remain above the vertebra. Next, the four holes  162   a ,  162   b ,  162   c ,  162   d  of the plate  100  are aligned with the four threaded posts  133   a ,  133   b ,  133   c ,  133   d , respectively, and the plate  100  is top-loaded onto the screws  130   a ,  130   b ,  130   c ,  130   d  and lands onto the screw flanges  132   a ,  132   b ,  132   c ,  132   d  ( 186 ). The diameter of the screw flanges  132   a - 132   d  is larger than the diameter of holes  162   a - 162   d , respectively, and the diameter of the screw posts  133   a - 133   d  is smaller than the diameter of holes  162   a - 162   d , respectively. This geometric dimensioning allows the screw posts to pass through the plate holes while the plate stays on top of the flanges. Finally, four locking nuts  160   a ,  160   b ,  160   c ,  160   d  are screwed onto the threaded posts  133   a ,  133   b ,  133   c ,  133   d , respectively, thereby securing the plate  100  onto the screws  130   a ,  130   b ,  130   c ,  130   d  ( 188 ). 
         [0043]    In one example, plate  100  has a height  91  of 30 mm, a width  93  of 17 mm and the aperture  102  has a height  92  of 15 mm, as shown in  FIG. 5 . The plate  100  may be made of metal such as stainless steel or titanium, plastic, bioabsorbable material and ceramic. 
         [0044]    Referring to  FIG. 6  and  FIG. 7 , an anterior one-level pivoting cervical fusion system  80  includes a top loading, one-level pivoting cervical plate  100  that connects two adjacent vertebras  82  and  84 . The pivoting cervical plate  100  is attached to the vertebras  82  and  84  via four screws  130   a ,  130   b  and  130   c ,  130   d , respectively. The pivoting cervical plate  100 , includes a triangular shaped top subplate  110  and a triangular shaped bottom subplate  120 . The top subplate  110  is closest to the head of the patient and has an apex  111  facing down toward the bottom subplate  120 . The bottom subplate  110  is closest to the patient&#39;s feet and has an apex  121  facing up toward the top subplate  110 . The apex  111  of the top subplate  110  is pivotably connected to the apex  121  of the bottom subplate  120  at point  150 , via a pivoting pin  152  that protrudes from the top surface of the apex  111  of the top subplate  110 . The bottom subplate  120  has a hole  153  formed at the apex  121  for receiving the pivoting pin  152 . A pivot cap  154  secures the top subplate  120  onto the pivot pin  152  while allowing the two subplates  110 ,  120  to pivot relative to each other counterclockwise  155   a  and clockwise  155   b  by a few degrees, as shown in  FIG. 8A , and  FIG. 8B , respectively. Each of the top and bottom subplates  110 ,  120 , has two holes  162   a ,  162   b  and  162   c ,  162   d , respectively, at the two corners opposite their respective apexes  111 ,  121 . Holes  162   a ,  162   b ,  162   c ,  162   d  are dimensioned to receive the four screws  130   a ,  130   b ,  130   c ,  130   d , respectively. The subplates  110 ,  120  are top loaded onto the posts of the four screws  130   a ,  130   b ,  130   c ,  130   d , and are secured onto the flanges of the four screws  130   a ,  130   b ,  130   c ,  130   d , with four locking nuts  160   a ,  160   b ,  160   c ,  160   d , respectively, as described in  FIG. 4D . The triangular subplates  110 ,  120  have central apertures  112 ,  122 , that provide visibility and access to the vertebras  82 ,  84  and disc  62  below them. 
         [0045]    Referring to  FIG. 9 ,  FIG. 10  and  FIG. 11A , an anterior one-level dynamic stabilization system  70  includes a top loading, one-level dynamic plate  100  that connects two adjacent vertebras  82  and  84 , shown in  FIG. 6 . The dynamic plate  100  is attached to the vertebras  82  and  84  via four screws  130   a ,  130   b  and  130   c ,  130   d , respectively. The dynamic cervical plate  100 , includes a triangular shaped top subplate  110  and a triangular shaped bottom subplate  120 . The top subplate  110  slides down and pivots relative to the bottom subplate  120  via a ratchet and pivot mechanism  155 , respectively. The top subplate  110  is closest to the head of the patient and has an apex  111  facing down toward the bottom subplate  120 . The bottom subplate  110  is closest to the patient&#39;s feet and has an apex  121  facing up toward the top subplate  110 . The apex  111  of the top subplate  110  is pivotably connected to the apex  121  of the bottom subplate  120  at point  155 , via a pivoting pin  152  that protrudes from the top surface of the apex  111  of the top subplate  110 , shown in  FIG. 7 . The bottom subplate  120  has an elongated hole  153  formed at the apex  121  for receiving the pivoting pin  152 , shown in  FIG. 11A  and  FIG. 11B . The elongated hole  153  includes a ratchet mechanism for providing the sliding motion of the top subplate  110  relative to the bottom subplate  120 . The ratchet mechanism allows for one-way movement  156  of the top subplate  110  toward the bottom subplate  120 , shown in  FIG. 11A  and  FIG. 11B . In one example, the sliding movement has a span of 2 mm at 0.03 mm increments. In this embodiment, the bottom subplate  120  is not able to slide relative to the top subplate  110 . A ratchet cap  151  secures the ratchet mechanism and the top subplate  120  onto the pivot pin  152  while allowing the two subplates  110 ,  120  to pivot relative to each other counterclockwise  155   a  and clockwise  155   b  by a few degrees, as shown in  FIG. 12A , and  FIG. 12B , respectively. Each of the top and bottom subplates  110 ,  120 , has two holes  162   a ,  162   b  and  162   c ,  162   d , respectively, at the two corners opposite their respective apexes  111 ,  121 . Holes  162   a ,  162   b ,  62   c ,  162   d  are dimensioned to receive the four screws  130   a ,  130   b ,  130   c ,  130   d , respectively. The subplates  110 ,  120  are top loaded onto the posts of the four screws  130   a ,  130   b ,  130   c ,  130   d , and are secured onto the flanges of the four screws  130   a ,  130   b ,  130   c ,  130   d , with four locking nuts  160   a ,  160   b ,  160   c ,  160   d , respectively. The triangular subplates  110 ,  120  have central apertures  112 ,  122 , that provide visibility and access to the vertebras  82 ,  84  and disc  62  below them. 
         [0046]    Referring to  FIG. 13  and  FIG. 14 , an anterior two-level fixed cervical fusion system  60  includes a top loading, two-level fixed cervical plate  100  that connects three adjacent vertebras  82 ,  84 , and  86 . The fixed cervical plate  100  is attached to the vertebras  82 ,  84  and  86  via six screws  130   a ,  130   b ,  130   c ,  130   d ,  130   e , and  130   f . The fixed cervical plate  100  has a shape of two adjacent hourglasses that are merged together. The plate  100  has two hourglass shaped apertures  105 ,  106  centered in the top and bottom of the plate  100 . Apertures  105 ,  106  provide visibility and access to the vertebras  82 ,  84 ,  86  and disc  62  below the plate  100 . Plate  100  also has six holes  162   a ,  162   b ,  162   c ,  162   d ,  162   e  and  162   f  located in the four corners and center of the plate. Holes  162   a ,  162   b ,  62   c ,  162   d ,  162   e ,  162   f  are dimensioned to receive the six screws  130   a ,  130   b ,  130   c ,  130   d ,  130   e ,  130   f , respectively. Six locking nuts  160   a ,  160   b ,  160   c ,  160   d ,  160   e ,  160   g  are screwed onto the threaded posts of the screws, thereby securing the plate  100  onto the screws. The process of attaching the plate  100  to the adjacent vertebras  82 ,  84 ,  86  is as described above. 
         [0047]    Referring to  FIG. 15  and  FIG. 16 , an anterior two-level pivoting cervical fusion system  200  includes a top loading, two-level pivoting cervical plate  100  that connects three adjacent vertebras  82 ,  84 , and  86 . The pivoting cervical plate  100  is attached to the vertebras  82 ,  84  and  86  via six screws  130   a ,  130   b ,  130   c ,  130   d ,  130   e , and  130   f  . The pivoting cervical plate  100 , includes a triangular shaped top plate  220   a , a diamond shaped middle subplate  210  and a triangular shaped bottom plate  220   b . The top subplate  220   a  pivots relative to the middle subplate  210  around pivot point  255   a . The bottom subplate  220   b  pivots relative to the middle subplate  210  around pivot point  255   b . The top subplate  220   a  is closest to the head of the patient and has an apex facing down towards the top apex of the middle subplate  210 . The bottom subplate  220   b  is closest to the patient&#39;s feet and has an apex facing up toward the bottom apex of the middle subplate  210 . The apex of the top subplate  220   a  is pivotably connected to the top apex of the middle subplate  210  at point  255   a . The apex of the bottom subplate  220   b  is pivotably connected to the bottom apex of the middle subplate  210  at point  255   b . The pivoting mechanism is similar to the mechanism in  FIG. 6  and it allows the top and bottom subplates  220   a ,  220   b  to pivot relative to the middle subplate  210  counterclockwise and clockwise by a few degrees. Each of the top and bottom subplates  220   a ,  220   b , has two holes  262   a ,  262   b  and  262   e ,  262   f , respectively, at the two corners opposite their respective apexes, and the middle subplate  210  has two holes  262   c ,  262   d  in its middle corners. Holes  262   a ,  262   b ,  262   c ,  262   d ,  262   e ,  262   f  are dimensioned to receive six screws  230   a ,  230   b ,  230   c ,  230   d ,  230   e ,  230   f , respectively. The subplates  220   a ,  220   b ,  210  are top loaded onto the posts of the screws and are secured onto the flanges of the screws with locking nuts  260   a ,  260   b ,  260   c ,  260   d ,  260   e ,  260   f , respectively. The triangular subplates  220   a ,  220   b  have central apertures  213   a ,  213   b  and the middle subplate  210  has two central apertures  212   a ,  212   b , that provide visibility and access to the vertebras  82 ,  84 ,  86  and discs below them. The process of attaching the plate  100  to the adjacent vertebras  82 ,  84 ,  86  is as described above. 
         [0048]    Referring to  FIG. 17  and  FIG. 18 , an anterior two-level dynamic stabilization system  205  includes a top loading, two-level dynamic cervical plate  100  that connects three adjacent vertebras  82 ,  84 , and  86 . The dynamic cervical plate  100  is attached to the vertebras  82 ,  84  and  86  via six screws  230   a ,  230   b ,  230   c ,  230   d ,  230   e , and  230   f  The dynamic cervical plate  100 , includes a triangular shaped top plate  220   a , a diamond shaped middle subplate  210  and a triangular shaped bottom plate  220   b . The top subplate  220   a  slides and pivots relative to the middle subplate  210  around pivot point  250   a  via a ratchet and pivot mechanism, as described above in  FIG. 9 . The bottom subplate  220   b  slides and pivots relative to the middle subplate  210  around pivot point  250   b  via a ratchet and pivot mechanism as described for the embodiment of  FIG. 9 . The top subplate  220   a  is closest to the head of the patient and has an apex facing down toward the top apex of the middle subplate  210 . The bottom subplate  220   b  is closest to the patient&#39;s feet and has an apex facing up toward the bottom apex of the middle subplate  210 . The apex of the top subplate  220   a  is slidably and pivotably connected to the top apex of the middle subplate  210  at point  255   a . The apex of the bottom subplate  220   b  is slidably and pivotably connected to the bottom apex of the middle subplate  210  at point  255   b . The ratchet and pivoting mechanism is similar to the mechanism in  FIG. 9  and it allows the top and bottom subplates  220   a ,  220   b  to slide by about 2 mm and pivot relative to the middle subplate  210  counterclockwise and clockwise by a few degrees. Each of the top and bottom subplates  220   a ,  220   b , has two holes  262   a ,  262   b  and  262   e ,  162   f , respectively, at the two corners opposite their respective apexes, and the middle subplate  210  has two holes  262   c ,  262   d  in its middle corners. Holes  262   a ,  262   b ,  262   c ,  162   d ,  262   e ,  262   f  are dimensioned to receive six screws  230   a ,  230   b ,  230   c ,  230   d ,  230   e ,  230   f , respectively. The subplates  220   a ,  220   b ,  210  are top loaded onto the posts of the screws and are secured onto the flanges of the screws with locking nuts  260   a ,  260   b ,  260   c ,  260   d ,  260   e ,  260   f , respectively. The triangular subplates  220   a ,  220   b  have central apertures  213   a ,  213   b  and the middle subplate  210  has two central apertures  212   a ,  212   b , that provide visibility and access to the vertebras  82 ,  84 ,  86  and discs below them. 
         [0049]    In the embodiment of  FIG. 19A ,  19 B and  19 C, an anterior two-level dynamic stabilization system  205  is already in place and the patient needs to have the next level of vertebra stabilized. In this case, the top subplate  220   a , is removed and is replaced with a diamond shaped sub-plate  310 , shown in  FIG. 19B . Next, the top subplate is re-installed on the top of the diamond subplate  310 , as shown in  FIG. 19C . The attachment of the diamond shaped subplate  310  to the middle subplate  210  is not dynamic, i.e., it allows pivoting but not sliding, whereas the connection of the top subplate  220   a  to the diamond shaped subplate  310  is dynamic. 
         [0050]    Other embodiments are within the scope of the following claims. For example, the bottom subplate may be able to slide relative to the top subplate in the dynamic stabilization system of  FIG. 9 . The motion of the top subplate  110  relative to the bottom subplate  120  may be vertical  156 , horizontal  157 , pivoting  155  and any combinations thereof, as shown in  FIG. 21  and  FIG. 8A-8B . The plate  100  may be placed onto the cervical bone first and then may be attached to the bone by screwing the screws  130   a ,  130   b ,  130   c ,  130   d  through the holes  162   a ,  162   b ,  162   c ,  162   d , into the bone and then securing the screws onto the plate  100  with the locking nuts  160   a ,  160   b ,  160   c ,  160   d , respectively. The screws  130   a ,  130   b ,  130   c ,  130   d  may be multi-axial screws with locking housings and “starfish” shape locking nuts that locks into the screw housings. Alternatively, the screws may have a spherically shaped head on the screw with textured surface that allows for angular mounting with a concaved spherically shaped hole or chamfered shaped hole with textured surface in the plate. Then a threaded bolt would be screwed onto the top of the spherically shaped head and lock the system together. Alternatively, multi-axial and oversized holes are formed in the plate and “starfish” shaped locking nuts lock the screws onto the plate. The subplates may have other shapes including rectangular (shown in  FIG. 20 ), square, circular, oval or polygonal. 
         [0051]    Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.