Abstract:
Disclosed is a dynamic cervical plate system that may be adjusted to length, locked in place to provide compression, and will automatically shorten its length to maintain compression. The system includes spinal cages coupled to the plate which provide intervertebral spacers for excised discs. The cervical plate system has a flat elongated shaft adapted to span the intervertebral space and has at least two screw receivers spaced along the length of the plate. The screw receivers each have screw holes for accepting the heads of bone screws. The spinal cage is coupled to the plate and interposed between the screw receivers.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of the filing date of U.S. Provisional Patent Application No. 61/049,209 filed on Apr. 30, 2008, the contents of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of orthopedic surgery and, particularly, to the area of spinal implants for stabilizing the spatial relationship of vertebrae. The device is designed for use in the cervical region of the spine though one skilled in the art may use the device in other regions of the spine and other skeletal fixations. 
     2. Description of the Prior Art 
     Spinal plates are well known in the orthopedic art for fixing bones or bone fragments in a pre-selected spatial orientation. The plates are usually attached to the bones or bone fragments by screws designed to make a secure and long lasting connection not affected by the loads caused by normal activities of the host. Gertzbein et al, U.S. Pat. No. 5,620,443, teaches an adjustable cervical connector composed of dual rods spanning the distance between adjacent vertebrae. The rods carry at least two slidable transverse connectors which are attached to the vertebrae by spikes and pedicle screws thereby fixing the relationship of the bones. The connectors are immobilized on the rods by clamps. 
     Richelsoph, U.S. Pat. No. 6,017,345, teaches a spinal plate spanning the distance between adjacent vertebrae. The plate has screw holes in each end. The pedicle screws are inserted through the holes and allow for some movement. 
     Shih et al, U.S. Pat. No. 6,136,002, teaches a similar device to that of Gertzbein with the clamps screwed onto the elongated rods. 
     Published Patent Application US 2003/0060828 A1 to Michelson teaches a cervical plate with at least two plate elements slidably connected together and fixed by a set screw. The contacting surfaces of the plate elements are formed with ratcheting to provide added security. 
     In all these prior art devices, the plate must be held in the selected position while the securing set screws or other fasteners are put in place and the final assembly is completed. Further, the prior art plates are not used in combination with spinal cages for filling the intervertebral space to compensate for removal of the spinal discs and to provide support for bone growth material and/or bone cement. 
     What is needed in the art is a dynamic cervical plate system that may be adjusted to length, locked in place to provide compression, and will automatically shorten its length to maintain compression. The system includes spinal cages coupled to the plate which provide intervertebral spacers for excised discs. 
     SUMMARY OF THE PRESENT INVENTION 
     Disclosed is a dynamic cervical plate system that may be adjusted to length, locked in place to provide compression, and will automatically shorten its length to maintain compression. The system includes spinal cages coupled to the plate which provide intervertebral spacers for excised discs. 
     Therefore, it is an objective of this invention to provide a cervical plate system with an elongated shaft adapted to span the intervertebral space and having at least two screw receivers spaced along the length of the plate. The screw receivers each have screw holes for accepting the heads of bone screws. A spinal cage is coupled to the plate and interposed between the screw receivers. 
     Another objective of this invention is to provide a locking mechanism that is manually operated simultaneously with the insertion of bone screws into the screw receiver to provide compression across the intervertebral space. 
     A further objective of this invention is to provide the locking mechanism with a retainer extending over the screw holes to prevent back out of the screws. 
     Yet another objective of this invention is to provide a guide rail on the plate shaft cooperating with the screw receivers and spinal cages to permit sliding connection between the screw receivers, cages and the plate shaft. 
     Still another objective of this invention is to provide a ratchet mechanism on the shaft and screw receivers to permit post operative one-way movement shortening the distance between the screw receivers and maintaining compression across the intervertebral space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective of the cervical plate system, spinal cages and screw receivers of this invention; 
         FIG. 2  is a side view of the cervical plate and screw receivers of  FIG. 1 ; 
         FIG. 3  is a perspective of the spinal cage of this invention; 
         FIG. 4  is an end view of the spinal cage of  FIG. 3 ; 
         FIG. 5  is a top view of the spinal cage of  FIG. 3 ; 
         FIG. 6  is a side view of the spinal cage of  FIG. 3 ; 
         FIG. 7  is a side view of a second embodiment of a cervical plate system; 
         FIG. 8  is a top view of the second embodiment; 
         FIG. 9  is a perspective view of the second embodiment; 
         FIG. 10  is an exploded view of the second embodiment; 
         FIG. 11  is a cross sectional side view of the second embodiment; 
         FIG. 12  is a cross sectional end view of the second embodiment; 
         FIG. 13  is a bottom view of the second embodiment illustrating the engagement tabs; 
         FIG. 14  is a cross sectional side view illustrating the engagement tabs; 
         FIG. 15  is a bottom perspective view illustrating the positioning of the engagement tabs; 
         FIG. 16  is a perspective view of the connector plate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The cervical plate  10  has an elongated flat shaft  11  that is made in different lengths but must be of a length to span, at least, the distance between two vertebrae. The plate  10  has a lateral bar  12  fixed to one end and a free end. The bar has countersunk apertures  20 ,  20 ′ on each side of the elongated flat shaft for capturing the head  61  of bone screws  60 . Permanently mounted to the plate is a retainer clip  40  having ears  18 ,  18 ′. The clip  40  is resilient and extends under the plate parallel but outside the periphery of the lateral bar  12  then rises vertically to the top of the flat shaft  11  and extends across the bone screw apertures  20 ,  20 ′. The portion that extends across the countersunk apertures  20 ,  20 ′ are the ears  18 ,  18 ′ for retaining the bone screws  60  to prevent back-out. The retainer clip  40  is resilient enough to allow flexing while the heads  61  of the bone screws  60  are seated in the aperture then is released on top of the screw heads  61 . In one embodiment, the ears  18 ,  18 ′ have wedges  50  which engage the edges of the screw heads  61  as the screws are tightened to further lock the screws  60  in place. 
     The bottom of the flat shaft  11  has a row of teeth  15  formed across the longitudinal axis of the plate  10 . The teeth are angled to form a ratchet allowing one-way movement of a bar, such as  13  or  14 , from the free end toward the lateral bar  12  at one end of the plate  10 . In some instances, the teeth  15  may be cut normal to the shaft. Along each longitudinal side of the flat shaft are parallel grooves  23  extending from the free end toward the lateral bar. 
     Slidably attached to the free end of the flat shaft  11  is at least one movable bar  13  but two are preferred. The second bar  14  is of similar construction as the bar  13 . Bar  13  and bar  14  have similar structure therefore; reference to elements of one bar is the same as the other. 
     The slidable bar  13  has a distal surface which engages the vertebrae and is convexly curved to closely fit the curvature of the vertebrae. The slidable bar  13  has apertures  20  and  20 ′ near each end with a depression there between. The depression is approximately the same depth as the thickness of the flat shaft  11  to provide a low profile to the assembled cervical plate  10 . The opposite edges of the depression have shoulders  26  that slide within the longitudinal groves  23  in the flat shaft. This provides a close association between the surface of the bar depression and the ratchet teeth  15  of the plate  10 . 
     Attached to movable bar  13  is a retainer clip  42  having clip ears  17 ,  17 ′. The retainer clip  42  has an elongated hollow body with an oval shape. The sides of the oval follow the edges of the depression so that clip ears  17 ,  17 ′ are on the proximal surface of the movable bar  13 . At least one side of the clips ( 40 ,  42 ,  44 ) is welded or otherwise permanently attached to the respective side of the bars ( 12 ,  13 ,  14 ). The rounded ends of the oval of the retainer clips form the screw retainers. The pawl portions of the retainer clips extend across the flat shaft  11  engaging the teeth  15  to form the ratchet. 
     In the preferred embodiment, the retainer clips  42  and  44  have a flange that extends above the surfaces of the bars to provide a counter force to the bottom portion for engaging of the teeth  15  of the ratchet on the flat shaft  11 . Of course, the clips may have pawls on both sides of the bar. By flexing the clip with an instrument, the flange can be disengaged from the ratchet teeth  15  for initial adjustment. 
     As shown in  FIGS. 3 through 6  the spacers  27  have a top connector  28  having a planar base plate  29  and parallel upstanding flanges  30  which are undercut forming rails  31 . An aperture  38  passes through the base plate and communicates with the hollow interior. The rails  31  slide along the groves  23  in the longitudinal edges of the flat shaft  11 . The body of the spacers  27  is of open construction with a series of bars  32 ,  33 ,  34 ,  35  forming an open and interconnected framework about a hollow center  36 . The hollow center may be filled with bone growth materials, bone particles, and/or bone cement to facilitate boney ingrowth into the intervertebral space strengthening the fusion of the several vertebrae. 
     The connector  28  and the spacer  27  may be unitary or separable. As shown in  FIG. 3  and  FIG. 4 , the connector may be permanently or separately formed and fastened to the spacer  27  by screws or brads  37 . In one embodiment, the connectors, alone, could be slidably mounted on the flat shaft  11  between the bars  12 ,  13 , or  14  as a pre-assembly. The spacers would be placed between the vertebrae, as necessary. The connectors and the spacers brought together and attached as a final assembly, in situ. Otherwise, the assembled spacers and connectors are placed between vertebrae and the plate is slidably adjusted for best placement of the bone screws in adjacent vertebrae. 
     In operation, the vertebrae are manipulated into the desired position and the spacers placed as required to compensate for removal of bone and/or disc material. The plate  10  is placed on the spine and the connectors  28  and the bars  13  and  14  are adjusted to provide some compression on the site to assist in the grafting of the spine. The connectors  28  are slid along the plate  10  until registered with the tops of the spacers  27 . The connectors  28  can then be attached to the spacers  27 . As the bars are slid along the shaft, the shoulders of the bars  13  and  14  and the grooves on the shaft maintain a close fit between the pawls and the teeth  15  on the flat shaft  11  shaft requiring the pawls to be deflected by the teeth. Once the bars are in the desired location and the flanges seated in the teeth  15 , the ratchet prevents retrograde movement of the bars away from the head. The bone screws are driven into the spine. As the screw heads  61  engage the apertures the clip retainers  40 ,  42 , and  44  are flexed to permit the screw heads  61  to seat in the apertures  20  and released to block back-out. 
       FIGS. 7 through 16  show a second embodiment of the invention. Bone plate  110  that includes a flat shaft  111  including three lateral bars;  112 , 113 , and  114  are mounted thereon. Flat shaft  111  is made in varying lengths however it has a length at least sufficient to span the distance between two adjacent vertebrae. The bone plate  110  has a fixed lateral bar  113  located between two moveable lateral bars  112  and  114 . Each lateral bar has countersunk apertures  120  and  120 ′ on each side of the flat shaft  111  for capturing the head  161  of bones screws  160 . Permanently mounted to flat shaft  111  is a retainer clip  142  having retaining clip ears  117  and  117 ′. The retaining clip is resilient and extends under the flat shaft  111  parallel but outside the periphery of the lateral bar  113  and then rises vertically to the top of the plate and extends across the bone screw apertures  120  and  120 ′. Retainer clip ears  117  and  117 ′ extend across countersunk apertures  120  and  120 ′ for retaining the bone screws  160  and preventing them from backing out. The retainer  142  is resilient enough to allow flexing while the heads of the bone screws are being seated in the aperture and then subsequently released on to the top of the screws heads when the screws are seated within the aperture. 
     The bottom of the flat shaft  111  has two rows of teeth  115  formed across the longitudinal axis of the flat shaft, one at each end of the flat shaft. The teeth  115  are angled to form a ratchet allowing one-way movement of the lateral bars  112  and  114  towards the fixed lateral bar  113 . Lateral bars  112  and  114  have similar structure therefore reference to elements of one bar is the same as the other. Movable lateral bars  112  and  114  have a distal surface which engages the vertebrae and are convexly curved to fit the curvature of the vertebrae. Each of lateral bars  112  and  114  has an internal passageway  130  located between its distal and proximal surfaces. Internal passageway  130  is sized to closely conform to the external dimensions of the flat shaft  111  at each end. The ends of flat shaft  111  are somewhat reduced in size from the remainder of the flat shaft  111 . The proximal surface of flat shaft  111  also includes a longitudinally extending projection  132 ; the ends which conform in size to a complimentary recess  134  formed in each of the proximal surface of the lateral bars  112  and  114 . Attached to movable bar  112  is a retainer clip  140  having retainer clip ears  118  and  118 ′. Attached to movable bar  114  is a retainer clip  144  having retainer clip ears  116  and  116 ′. The retainer clips  140  and  144  each have an elongated hollow body with an oval shape. The sides of the oval follow the edges of bar so that the retainer clip ears  118  and  118 ′ are on the proximal surface of the moveable bar  112  and retainers clip ears  116  and  116 ′ are on the proximal surface of movable bar  114 . Each of the retaining clip ears prevent the screws from backing out. The pawl portion of the retaining clips  140  and  144  extend across the flat shaft  111  engaging the teeth  115  formed at each end thereof to from the ratchet. The retaining clips  140  and  144  each have a flange that extends above the surface of the associated movable bars to provide a force for engaging the teeth  115  formed on the bottom surface on each end of the flat shaft  111 . By flexing the retainer clip with an instrument, the flange can be disengaged from the teeth  115  for initial adjustment. 
     While not illustrated, the spacers  27  disclosed above and shown in  FIGS. 3 through 6  can be used in the bone plate arrangement  110  disclosed in  FIGS. 7 through 16 . In this arrangement the upstanding flanges and rails on the top connectors are configured to be operatively connected to rail  111 . 
     It is well known that as the site heals and the adjacent vertebrae begin to graft together and as a result of the forces of gravity, there is some reduction in the span between the vertebrae. As this occurs, the dynamic cervical plate can accommodate the reduction and maintain some compression because the shaft will move in the bars resulting in the clips moving from one ratchet tooth to the next automatically shortening the intervertebral distance. 
     A number of 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.