Abstract:
An anterior cervical plate has a lower surface adapted to engage the cervical spine and a top surface. At least one location along the plate there are two transversely aligned bone screw holes. A locking element is pivotally mounted between these two bone screw holes for movement between an open position which uncovers the two bone screw holes and a locking position wherein the locking element at least partially covers each of the two bone screw holes. A positive positioning structure positively positions the locking element in the locking position.

Description:
FIELD OF THE INVENTION 
   This invention relates to an anterior cervical plate, and in particular it relates to such a plate with a new and improved locking element. 
   BACKGROUND OF THE INVENTION 
   It is known to provide an anterior cervical plate for attachment to the anterior of two or more cervical vertebrae for the purpose of immobilizing, stabilizing and/or aligning those vertebrae. The plates can be used for a variety of conditions including for example providing added strength and rigidity after fusion of adjacent vertebrae, securing vertebrae together where an intervening vertebrae has been removed and replaced, correcting spinal deformities, and correcting instability caused by trauma, tumors, advanced degenerative discs, infection or congenital or acquired deformities. 
   Cervical plates of the present type are generally elongated so as to span the distance between two, three, four or more vertebrae, as required in a given situation. The plates are generally curved transversely so as to fit the curvature of the vertebrae to which they are attached. Additionally, plates of this type are generally concave longitudinally thereof to match the curvature of the cervical spine. Cervical plates of this type are provided with holes for bone screws. Holes are drilled into the adjacent vertebrae by instruments which are known in the art, after which the cervical plate is attached by bone screws which pass through the holes in the cervical plate for securing the plate to the adjacent vertebrae. 
   Many cervical plates of the present type are known, each having various arrangements for securing the bone screws. Such arrangements are shown in prior U.S. Pat. Nos. 5,364,399; 5,549,612; 6,193,721; 6,224,602; 6,235,034; 6,383,186; and 6,454,771. Notwithstanding the development of the prior art to date, a need exists for improvements in arrangements for securing the bone screws in place after the bone screws have secured the cervical plate onto the adjacent vertebrae. 
   SUMMARY OF THE INVENTION 
   It is a purpose of the present invention to provide an anterior cervical plate of the type for attachment to cervical vertebrae for stabilizing, immobilizing and/or aligning those vertebrae, which plate has a new and improved arrangement for securing the bone screws in place after the cervical plate has been attached to the cervical vertebrae. 
   In accordance with the present invention, the cervical plate includes a number of bone screw holes for attaching the cervical plate to the vertebrae. Specifically, in accordance with the present invention there is provided at least one pair of adjacent bone screw holes, preferably transversely aligned, wherein the cervical plate has a locking element mounted between the adjacent bone screw holes and movable between a first, open position where it uncovers the two bone screw holes to permit insertion therethrough of the bone screws and a second, locking position whereat the locking element overlies at least a portion of each of the two bone screw holes, to lock those bone screws in place. The locking element of the present invention is intended essentially to prevent the screws from backing out, i.e., it is not intended to be a force exerting member to exert a downward force on tightened bone screws. 
   In accordance with one arrangement of the present invention, an elongated locking element is pivotally mounted on a surface area of the cervical plate between two adjacent bone screw holes. This locking element is movable to a first position whereat it completely uncovers the two adjacent holes so as to permit the insertion of bone screws therethrough. The locking element is then arranged to be pivoted to partially cover the two bone screw holes with the bone screws secured in place therebeneath. 
   The present invention provides various arrangements for effecting the pivotal connection between the plate and the locking element. In one arrangement the plate may have a raised boss onto which is pivotally mounted a locking element having an opening therethrough. In another arrangement the plate itself can have an opening and the locking element can have a raised boss on the lower side thereof which projects through the through hole in the plate. In another arrangement, the locking element can have a central opening and the plate can have a through hole, both of which cooperate with a third element, a post which passes through the opening and the through hole. 
   Another feature of the present invention is the provision of a structure to positively position the locking element in its locking position. For this purpose, a protrusion on either the bottom of the locking element or the surface of the plate can be arranged to be snap fitted into a recess or indentation in the other of the cervical plate or locking element. Preferably, the protrusions will be in the form of bumps on the surface of the plate and the indentions will be in the form of recesses on the bottom of the locking element, wherein the bumps and recesses are aligned to positively position the locking element when it is in its locking position. The bottom of the locking element may include recessed ramps which ride over the bumps as the locking element is initially turned from its open position to its locking position. The bumps would then ride up the recessed ramps and then snap into place in the recesses when the locking element has reached its locking position. 
   Turning of the locking element between its open and locking positions can be accomplished by using a tool, and for this purpose the locking elements are provided with a pair of openings, offset relative to the pivot axis, to receive such a tool. 
   The present invention is applicable to cervical plates of a virtually limitless number of configurations. Cervical plates are generally referred to by the number of levels that they overlie, wherein the word “level” refers to the number of intervening intervertebral spaces that are spanned. Thus, for example, a three level cervical plate would span the four vertebrae beyond and between the three intervertebral spaces. The plate can be connected at some places by a single central bone screw through a single central bone screw hole instead of by the two adjacent bone screw holes which include the locking element of the present invention. In virtually all configurations, an opening will be provided between adjacent vertebrae for viewing the intervening intervertebral space. 
   In any configuration the cervical plate would almost always be attached to the upper and lower vertebrae. Connections of the cervical plate between the upper and lower vertebrae would depend on the level of the cervical plate and the nature of the surgery performed on the spine adjacent to the cervical plate. For example, if the surgery involved replacing only the discs and leaving the vertebrae intact in a three or four level cervical plate, then screws might be attached to the intermediate vertebrae. However, a long plate such as a three level or four level plate would more likely be used after a corpectomy, wherein the intervening vertebrae and discs would have been removed and replaced with a bone plug/graft or a mesh/cage implant. In these cases, it is unlikely that screws would be attached between the upper and lower vertebrae, although it might be desirable to place one or two screws into a bone plug/graft. 
   Thus, it is an object of the present invention to provide a new and improved anterior cervical plate. 
   It is another object of the present invention to provide a new and improved locking element in combination with a cervical plate for locking a pair of bone screws in adjacent bone screw openings of the plate. 
   These and other objects of the present invention will be apparent from the detailed description to follow, together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     There follows a detailed description of preferred embodiments of the present invention which are to be read together with the drawings wherein: 
       FIG. 1  is a top plan view of an anterior cervical plate in accordance with the present invention; 
       FIG. 2  is a bottom plan view of  FIG. 1 ; 
       FIG. 3  is a top plan view of the locking element of  FIG. 1 ; 
       FIG. 4  is a bottom plan view of the locking element of  FIG. 1 ; 
       FIG. 5  is a cross sectional view taken along line  5 - 5  of  FIG. 1 ; 
       FIG. 6  is a cross sectional view taken along line  6 - 6  of  FIG. 1 ; 
       FIG. 7  is a cross sectional view taken along line  7 - 7  of  FIG. 1 ; 
       FIGS. 8 ,  9 ,  10  and  11  show four different shaped anterior cervical plates, all of which are designed to employ the features of the present invention; 
       FIG. 12  is a top plan view of an anterior cervical plate showing another embodiment of the present invention; 
       FIG. 13  is a bottom plan view of  FIG. 12 ; 
       FIG. 14  is a top plan view of the locking element of  FIG. 12 ; 
       FIG. 15  is a bottom plan view of the locking element of  FIG. 12 ; 
       FIG. 16  is a bottom perspective view of the locking element of  FIG. 12 ; 
       FIG. 17  is a view taken along line  18 - 18  of  FIG. 12 , but showing certain elements in a partially assembled state; 
       FIG. 18  is a cross sectional view taken along line  18 - 18  of  FIG. 12 ; 
       FIG. 19  is an exploded view which is taken along a plane represented by plane  18 - 18  of  FIG. 12  but showing a modification of the present invention; 
       FIG. 20  illustrates the embodiment of  FIG. 19 , but during a subsequent state of assembly; 
       FIG. 21  shows the modification of  FIGS. 19 and 20  in the fully assembled state; and 
       FIG. 22  is a schematic view showing an anterior cervical plate which would in the final form include the features of the present invention, but showing the plate in relation to vertebrae and discs of the cervical spine. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the figures, like elements are represented by like numerals throughout the several views. 
   An anterior cervical plate of the type with which the present invention is concerned attaches to the anterior surface of a plurality of cervical vertebrae to perform a number of different functions including stabilizing, aligning and immobilizing two or more adjacent vertebrae. These will be described generally with respect to the diagrammatic view of  FIG. 22 . This figure shows four adjacent vertebrae V 1 , V 2 , V 3  and V 4  separated by intervertebral discs D 1 , D 2  and D 3 , respectively. Cervical plates are defined by “levels” wherein the term “level” designates the number of intervertebral disc spaces which are traversed by the cervical plate. Thus for example the cervical plate  90  shown in  FIG. 22  spans three different intervertebral spaces D 1 , D 2  and D 3  between vertebral bodies V 1 , V 2 , V 3  and V 4  so that the embodiment shown therein is a three level plate. Cervical plates can come in a longer size, i.e., up to four levels or of course in smaller sizes, i.e., two levels or one level. For convenience, the invention is described throughout the present specification with respect to one level and two level cervical plates. It is to be understood that strictly for purposes of illustration  FIG. 22  shows the cervical plate  90  against what appears to be an essentially normal spine. In practice, however, as discussed above, when the cervical plate is attached, it will be subsequent to surgery that may have replaced some or all of the intermediary discs and vertebrae with a corpectomy to remove vertebrae which is replaced with a bone graph/plug or a mesh/cage implant or the like. 
   A cervical plate can have different openings serving different purposes. In  FIG. 22  the pair of holes  100  are provided for attaching two bone screws to the upper and lower vertebrae adjacent thereto is the form of bone screw holes to which the locking element of the present invention will be applied. However, in combination with bone screw holes  100 , the cervical plate can have other bone screw holes such as simple holes  101  which are shown in  FIG. 22  for attachment if desired, between the upper and lower bone screw holes  100 . Between the attachments to the vertebral bodies the cervical plates are provided with openings  102  which serve as windows to view into the interior of the intervertebral spaces. There will generally be at least one such window opening in the vicinity of each intervertebral space. As is known, anterior cervical plates of this type, in the various configurations, can be used to stabilize, immobilize and/or align the cervical spine following a number of different problems. For example, intermediate disc or discs can be removed and replaced by a cage, mesh or bone graph/plug or allograft/autograft. In addition to removal of the discs, the intermediate vertebrae can also be removed. The cervical plate can also be used to correct instability of the cervical spine caused by trauma, tumors, advanced degenerative discs disease, cervical deformities caused by lordosis or kyphosis or other conditions. 
     FIGS. 1-7  illustrate a first embodiment of the present invention. These figures illustrate an anterior cervical plate  10  which has first, second and third recessed areas  11 ,  12  and  13  for receiving bone screws through holes  17 ,  18 ;  19 ,  20 ; and  21 ,  22 , respectively. Between the recessed areas  11 ,  12  and  13  are provided web areas  15  and  16 , respectively, each including a window opening  28  and  29 , respectively, for viewing the intervertebral space adjacent thereto, as described above. In practice, each of the pair of bone screw holes would have a locking element  30  mounted therebetween. For purposes of illustration, in the first embodiment, i.e.,  FIGS. 1 ,  2  and  5 - 7 , the top recessed area  11  includes a locking element  30  in the open position, the bottom recessed area  13  shows a locking element  30  in the locking position and the middle recessed area  12  does not show any locking element, so as to illustrate the recessed area there below. 
   Referring to  FIG. 1  and the bottom plan view of  FIG. 2 , the plates include spikes  41 ,  42  for initially engaging the vertebrae when the cervical plate is first mounted thereon. Some operators prefer to use a fixation pin in addition to the spikes  41 ,  42 , and for this purpose the cervical plate  10  is provided with openings  23  and  24  at the top and bottom thereof, respectively. 
   Referring to  FIGS. 1 ,  6  and  7 , the lower bone screw holes  21  and  22  each have a bone screw  35  therein, each having a bone screw socket  36  for receiving a screwdriver for securing the bone screws into the bone. Referring to  FIGS. 6 and 7 , in a manner known per se, the screws can be driven into the bone over a range of transverse angles D, as shown in  FIG. 6 , or longitudinal angles C, as shown in  FIG. 7 . Normally the range of the angles C and D is approximately 15°. Referring to  FIGS. 5 and 7 , the cervical plates would generally be curved in both the transverse and the longitudinal direction. The radius of curvature of the plate in the transverse direction would be approximately 24 mm, as represented by arrow A, in order to fit the curvature of the vertebral bodies. Referring to  FIG. 7 , the radius of curvature of the cervical plate in the longitudinal direction would be approximately 200 mm, as represented by arrow B. 
   A feature of the present invention is an elongated locking element  30  which is mounted so as to move between an open position as shown at recessed area  11  of  FIG. 1  and a locking position as shown at the lower recessed area  13  of  FIG. 1 . Referring to  FIGS. 3 and 4 , the locking element  30  includes a central hole  31  for engaging the boss  27  on the cervical plate  10  and additional openings  32  and  33  offset from the pivot axis for receiving a tool to assist in turning the locking element  30  between its open and locking positions. To positively position the locking element  30  in its locked position, a pair of bumps  25  and  26  on the cervical plate are positioned to engage recesses  44  and  46 , as shown in  FIG. 4 , on the bottom of the locking element  30 . To facilitate movement of the locking element over the bumps  25  and  26 , the bottom of the locking element  30  includes recessed inclined ramps  45  and  47  which are deep enough to initially ride over the tops of the bumps. The ramps stop short of the recesses  44  and  46  so that as the locking element  30  is turned, the bumps  25 ,  26  will ride up the ramps and then snap into place in the recesses  44  and  46 . 
   The embodiment of  FIGS. 1-7  illustrates a first arrangement for attaching the locking element to the boss  27 . It is noted that the center boss  27  in recessed area  12  is essentially frustoconical. When it is desired to attach a locking element  30  to a boss  27 , the locking element is placed thereon after which the top of the boss  27  is swaged, as shown at  27   a  in  FIGS. 5 ,  6  and  7 , so as to prevent removal of the locking element while allowing it to pivot thereabout. 
     FIGS. 8 ,  9 ,  10  and  11  are intended to show various shapes of anterior cervical plates, each intended for a different level and/or showing a different connection and some such as  FIG. 9  and  FIG. 11  showing simple bone screw holes for attachment to certain intervening vertebrae. 
   Cervical plate  50  of  FIG. 8  is a two level cervical plate having pairs of bone screw holes at the two ends thereof which would in practice incorporate the features of the present invention and including a window opening  50   a  for viewing the intervertebral space therebetween.  FIG. 9  illustrates another cervical plate  51  which also would include the features of the present invention at the pairs of holes at the top and bottom thereof. This is a two level cervical plate having viewing holes  51   a  for viewing the intervertebral spaces and a simple central bone screw hole  51   b .  FIG. 10  illustrates a three level cervical plate  52  having the pair of bone screw holes which could receive the locking element of the present invention at all four connections to the vertebrae, and showing window opening  52   a  for viewing the three intermediate intervertebral spaces.  FIG. 11  shows a cervical plate  53  which is the same one previously described with respect to  FIG. 22 , and having three viewing windows  53   a  and two simple bone screw holes  53   b.    
     FIGS. 12-18  illustrate another embodiment of the present invention which is identical in all respects to the embodiment of  FIGS. 1-12  with respect to the features of the locking element (and other than the fact that some of the embodiments of  FIGS. 1-12  show different shapes and arrangements of cervical plates), except for a different arrangement for connecting the locking element to the cervical plate. 
   For convenience,  FIGS. 12-18  use the same numerals as in  FIGS. 1-7  for identical parts. Different numerals are used with respect to the modified locking element. As seen in  FIGS. 12 and 13 , in this case the recessed areas  11 ,  12  and  13  which receive the locking element include a through hole  65  instead of raised boss  27 . The locking element  55 , as shown in  FIGS. 14-16 , instead of having the opening  31  in the center thereof, has a raised boss  62  on the bottom thereof. This locking element  55  includes tool receiving holes  56  and  57  which are similar to holes  32  and  33  of  FIGS. 1-7 . In a manner similar to the embodiment of  FIGS. 1-7 , in this locking element  55  there are provided recesses  58  and  60  for cooperating with bumps  25  and  26  and recessed ramps  59  and  61  for riding up over the bumps and allowing the bumps to snap into place into the recesses  58  and  60 , precisely as described above with respect to  FIGS. 1-7 . 
   Referring to  FIG. 17 , the through hole  65  has a chamfer  65   a  at the bottom thereof.  FIG. 17  illustrates the locking element  55  with a boss  62  still of the shape as shown in  FIGS. 15 and 16 , extending through the opening  65 . The assembly process, however, is completed by swaging the lower end of the boss  62  as shown at  62   a  in  FIG. 18  to secure the locking element  55  onto the plate  54  while allowing it to pivot relative to the plate  54 . 
     FIGS. 19-21  illustrate the anterior cervical plate  54  taken along plane  18 - 18  of  FIG. 12  but showing a modified attachment between the locking element and the cervical plate. Referring to  FIG. 19 , the locking element is of the type  30  shown in  FIGS. 1-7  with an opening  31  therein. The plate is of the type  54  shown in  FIGS. 12-17  with a through hole  65  having a chamfer  65   a . In this embodiment, a tapered post  70  is inserted up through the through hole  65  such that its conical surface engages the chamfer  65   a  with the upper end of post  70  located above the upper surface of locking element  30  as shown in  FIG. 20 . The post  70  is then fixed to the plate at its bottom and swaged at the top as shown at  70   a  in  FIG. 21  in order to allow the locking element  30  to pivot relative to the cervical plate  54 . 
   Although the operation of the present invention will be apparent from the preceding discussion, for convenience the operation will be summarized herein. First, after the problem of the cervical spine has been surgically repaired, the anterior cervical plate is placed against the anterior of the cervical vertebrae. Initially it is held there by the spikes  41 ,  42  and/or by fixation pins passing through the openings  23 ,  24 . The method of preparing the holes in the vertebral bodies for the bone screws is well known, conventional and need not be further described herein. 
   At the recessed areas which include the locking element of the present invention, the screws are tightened to the point where their upper surfaces are at or slightly below the level of the recessed areas so that the locking elements, when pivoted to the locking position, will prevent the screws from backing out but not exert an inward force thereon. The bone screws for the holes adjacent the locking elements are inserted and attached when the locking element  30  or  55  is in the open position as shown at the top of  FIGS. 1 and 12 . After the bone screws are tightened in place, a tool (not shown) engages the openings  32  and  33  or  56  and  57  to turn the locking element clockwise. On the bottom of the locking element, ramps  44 ,  47  or  59 ,  61  on the bottom of the locking element will ride up the bumps  25 ,  26  until the locking element moves to its locking position as shown at the bottom recessed area  13  of  FIGS. 1  and  12 . At this point the bumps  25  and  26  have snapped into their respective recesses  44  and  46  for locking element  30  and  58  and  60  for locking element  55 . A preferred material for the cervical plate would be implantable Titanium alloy, Ti-6 Al-4V per ASTM F-136. 
   Although the invention has been described in considerable detail with respect to preferred embodiments, it will be apparent that the invention is capable of numerous modifications and variations, apparent to those skilled in the art, without departing from the spirit and scope of the invention.