Abstract:
An occipitocervical fixation system includes a plate for securing to the occiput and at least one pre-bent rod. The plate includes holes for receiving bone fasteners, and at least one clamping assembly for retaining a portion of a rod. The clamping assembly is selectively pivotable and lockable in place to fix the position of the rod.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is related to a system for stabilizing the spine. More particularly, the present invention is related to an occipitocervical fixation system that is mounted to both the occiput and spine.  
         BACKGROUND OF THE INVENTION  
         [0002]    Occipitocervical fixation has been achieved using a variety of techniques which generally provide stabilization of the base of the skull with respect to the neck. In order to promote fusion, for example, bone struts formed of autogenous ribs or curved iliac crest struts have been fixed to the occiput and spinous processes, cervical laminae, or facets. Wires are used to fix the struts in place until bone fusion occurs. The thickness of the occiput varies, however, and thus the occiput is typically wired in regions of greater thickness such as near the foramen magnum, at the nuchal line, and along the midline crest. Holes are drilled in the occiput to receive the wires that are also fed through holes in the struts. Although bone fusion occurs with this technique, the struts may be weak prior to fusion, and additional orthosis is applied such as with a halo vest or other hard collar until the struts can provide acceptably strong immobilization. Alternatively, metal struts may be used.  
           [0003]    Other techniques for occipitocervical fixation involve the use of other metal implants. One metal implant is a stainless steel, U-shaped device known as a Steinman pin. The threaded pin is bent to match the contour of the occipitocervical region, and fixed to the occiput and cervical laminae or facets using wires. The pin is generally symmetrically disposed about the spine, with the sides of the “U” creating a central region in which a bone graft can be disposed and further wired to the pin. When attached to the occiput and spine, the pin assumes an inverted-U configuration. Several holes are formed in the occiput so that the U-bend may be fixed in place.  
           [0004]    Additional metal implants include grooved or roughened titanium rods, smooth steel rods in the form of a Hartshill rectangle or Ransford loop, a Cotrel-Dubousset rod screw plate, and titanium frames have been employed.  
           [0005]    Despite these developments, there exists a need for an occipital plate and system for spinal stabilization in which the plate and rod components are separated to permit greater flexibility in installation by the surgeon. In particular, because a traditional unitary plate and rod system is bent in two planes in order to properly adjust it with respect to the occiput, such a unitary design presents difficulties in achieving the desired fit. devices Fixation is using wires that extend through holes formed in the occiput.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is related to an occipital plate that includes a Y-shaped plate portion having a front side and a back side, a central portion, two leg portions, and a plurality of bone screw holes in the central portion, the holes being configured and dimensioned to receive a bushing. The occipital plate also includes at least one clamping portion disposed on the front side proximate a free end of at least one of the leg portions, and the plate is bendable to conform to the an occiput. In one embodiment, the central portion includes an upper portion, a lower portion, and a grooved portion therebetween, the upper portion having one bone screw hole. The grooved portion is flexible to permit the upper portion to be disposed at an angle with respect to the lower portion. The leg portions and at least a portion of the central portion are disposed in nonparallel planes, and the planes may intersect at an angle of between about 160° and about 175°, and in one embodiment the planes intersect at an angle of about 170°.  
           [0007]    The clamping portion may include a pivot member and a clamp plate, the clamp plate being pivotable about the pivot member. The clamp plate may further include a hole, the pivot member being received in the hole. The pivot member also may include a tapered portion with serrations, and the leg portion may further include a tapered hole with serrations, with the serrations of the tapered portion positively engaging the serrations of the tapered hole. The diameter of the tapered hole increases from the back side to the front side, and the clamp plate is secured to the pivot member with a fastener. The leg portion additionally includes a rod-receiving first recess and the clamping plate additionally includes a rod-receiving second recess, with the first and second recesses generally opposing each other and the second recess being serrated. The bone screw holes in the lower portion may be disposed in a rectangular array, and at least one group of bone screw holes in the array may be disposed along a central axis of the plate extending between the leg portions. The bone screw hole in the upper portion may be disposed on the central axis, and at least two bone screw holes may be disposed coaxially. In one embodiment, the bushings permit polyaxial angulation, the plate is bendable along at least two generally parallel axes and/or at least two generally perpendicular axes.  
           [0008]    The present invention is also related to an occipitocervical fixation system including an occipital plate having at least one rod clamp portion and a plate portion with at least one hole for receiving a bone screw, the rod clamp portion having a post, a clamp plate with a hole for receiving the post, and a fastener for tightening the clamp to the post. The system also includes at least one bone screw and at least one rod, with the rod being retained between the plate portion and the clamp plate and being pivotable about the post.  
           [0009]    Furthermore, the present invention is related to a pre-bent rod for attachment to an occipital plate including a straight section, a bent section, and a serrated clamping section, with the straight section and the serrated clamping section being disposed substantially perpendicular to each other, and the serrated clamping section and the bent section being disposed at an angle of about 45° with respect to each other. In one embodiment, the serrated clamping section is generally cylindrical and includes circumferential serrations about an angular range of between about 90° and 180°. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Preferred features of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein:  
         [0011]    [0011]FIG. 1 shows a front view of an occipital plate according to the present invention;  
         [0012]    [0012]FIG. 2 shows a side view thereof;  
         [0013]    [0013]FIG. 3 shows a partial cross-sectional side view of a hole in the occipital plate of FIG. 1 taken along line III-III;  
         [0014]    [0014]FIG. 4 shows another front view of the occipital plate of FIG. 1 without clamping plates attached thereto;  
         [0015]    FIGS.  4 A- 4 B show front views of additional embodiments of occipital plates without clamping plates attached thereto;  
         [0016]    [0016]FIG. 5 shows a partial cross-sectional side view of a leg portion of the occipital plate of FIG. 4 taken along line V-V;  
         [0017]    [0017]FIG. 6 shows a partial front view of part of a leg portion of the occipital plate of FIG. 4;  
         [0018]    [0018]FIG. 7 shows a side view of the occipital plate of FIG. 4; FIG. 8 shows a post according to the present invention;  
         [0019]    [0019]FIG. 9 shows a side view of the occipital plate of FIG. 7 with a post inserted therein;  
         [0020]    FIGS.  11 - 14  show a top view, bottom view, side view, and partial cross-sectional view, respectively, of a clamping plate according to the present invention; FIGS.  15 - 18  show a perspective view, top view, partial cross-sectional view through line XVII-XVII, and partial cross-sectional view through line XVIII-XVIII, respectively, of a bushing for use with the present invention;  
         [0021]    [0021]FIGS. 19 and 19A show a front view of a first embodiment of a right pre-bent rod and a left pre-bent rod, respectively, according to the present invention;  
         [0022]    [0022]FIG. 20 shows a side view of the pre-bent rod of FIG. 19;  
         [0023]    [0023]FIG. 21 shows a side view of the serrated clamping section of FIG. 20;  
         [0024]    FIGS.  22 - 23  show a front view and a side view of a second embodiment of a pre-bent rod according to the present invention;  
         [0025]    [0025]FIG. 24 shows an occipital plate with first and second embodiments of the pre-bent rods of FIGS.  19 - 23 ;  
         [0026]    FIGS.  25 - 26  show a front view and a partial cross-sectional side view of another embodiment of an occipital plate according to the present invention;  
         [0027]    FIGS.  27 - 29  show a front view side view, and partial cross-sectional side view of yet another embodiment of an occipital plate according to the present invention; and  
         [0028]    FIGS.  30 - 31  show perspective view of additional embodiments of occipital plates according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    Referring initially to FIGS.  1 - 3 , an occipital plate  10  according to the present invention is shown. In the preferred embodiment, occipital plate  10  is generally Y-shaped with a pair of rod supporting arms  12 ,  14  and a central extension  16  along with a main portion  17 . Holes  18  extending from the front surface  11  to the back surface  13  are provided for receiving bone fasteners (not shown) for fixation of occipital plate  10  to the occiput. Preferably, as shown in FIG. 3, holes  18  are each provided with an expansion head bushing  20  to permit relative angulation of a locking screw or other bone fastener received therein. A grooved region  22  is provided along central extension  16  to facilitate bending of plate  10 . In the preferred embodiment, plate  10  may be bent along grooved region  22 . In an alternate embodiment, central extension  16  and grooved region  22  may be removed from plate  10 . Preferably, grooved region  22  has a thickness that may be accommodated in a rod cutter as used with the rods of the present invention. A clamp assembly  24 ,  26  is provided proximate the free end of each rod supporting arm  12 ,  14 , respectively, for clamping a portion of a rod against occipital plate  10 . Preferably, spinal rods are positionable in clamp assemblies  24 ,  26 , by insertion from the top portion  21 of the assemblies. Alternatively, the rods may be inserted from a side portion  23  of the assemblies. In addition, although the preferred embodiment includes two clamp assemblies,  24 ,  26 , a number other than two may be provided. Rod supporting arms  12 ,  14  may also be bent, for example near points  12 ′,  14 ′.  
         [0030]    As shown in FIG. 4, preferably occipital plate  10  includes seven fastener holes  18 , with six of the holes  18  aligned in a 2×3 rectangular array. Three holes  18  are aligned along line  28  while three holes  18  are aligned along line  30 , with lines  28 ,  30  being parallel to each other. In addition, while three holes  18 are aligned along central line  32 , two holes are aligned long each of lines  34 ,  26 . Lines  32 ,  34 ,  36  are parallel to each other and perpendicular to lines  28 ,  30 . In addition, grooved region  22  is aligned along a line  38  which is parallel to lines  28 ,  30 .  
         [0031]    As shown in FIGS. 4A and 4B, additional hole patterns may be used with the occipital plates of the present invention. For example, in FIG. 4A, occipital plate  10 ′ includes four holes  18  that are disposed adjacent line  32 , such that the plate may be bent along line  32  without bending along holes  18 . In addition, this permits bone screws inserted in holes  18  to be angulated toward the midline  32  of the plate. In FIG. 4B, occipital plate  10 ″ includes a triangular array of holes  18  with one hole along line  28 ′ and another hole along line  30 ′.  
         [0032]    Referring particularly to FIGS.  5 - 6 , occipital plate  10  includes holes  38 ,  40  in lower portions  42 ,  44  respectively. Holes  38 ,  40  are configured and dimensioned to receive clamping posts, as will be described. Rod-receiving recesses  46 ,  48  are generally V-shaped, with each leg of the “V” extending at an angle θ 1  with respect to a line  50  extending through V-notch  52  and the center of hole  40 , and further aligned parallel to lines  32 ,  34 ,  36 . In the preferred embodiment, angle θ 1  is between about 60° and about 80°, and more preferably about 70°. Arcuate stepped-in portions  54 ,  56  are disposed along the lowermost regions of rod supporting arms  12 ,  14 , and preferably extend through a total angle of about 80° and about 120°, and more preferably about 100°, symmetrically with respect to line  50 . As shown in FIG. 5, holes  38 ,  40  are preferably tapered with a first diameter D 1  on front surface  11  being smaller than a second diameter D 2  on back surface  13 .  
         [0033]    With reference to FIG. 7, central extension  16  is disposed along a plane  60 , while rod supporting arms  12 ,  14  are disposed along a plane  62 . Planes  60 ,  62  are not coplanar, and form an angle θ 3  with respect to each other that is preferably between about 160° and about 175° , and more preferably about 170°.  
         [0034]    Turning to FIGS.  8 - 10 , a post  64  is shown. One post  64  is placed in each hole  38 ,  40  such that the tapered head  66  rests in the hole. Preferably, taper head  66  tapers at an angle θ 4  of between about 5° and 15° and more preferably about 10° with respect to the central axis  70  of post  64 , and this taper angle is also present in holes  38 ,  40 . A post  64  installed in a hole  38  is shown in FIGS.  9 - 10 . Preferably, head  66  is provided with serrations that interlock with serrations on the inside surface of a hole  38 ,  40  so that a positive mechanical engagement can be achieved to assist in locking a post  64  in place with respect to the occipital plate  10 . Post  64  also includes a body portion  68 , which preferably is at least partially threaded for receiving a nut or other like-threaded fastening device.  
         [0035]    Referring to FIGS.  11 - 14 , a clamp plate  72  for use as a part of a clamp assembly  24 ,  26  is shown. Clamp plate  72  includes a hooked serrated portion  74  for engagement with a longitudinal rod, and further includes a central pivoting hole  76  in which a post  64  is received. A leg  78  of each clamp plate  72  is received in an arcuate stepped-in portion  54 ,  56  of a rod supporting arm  12 ,  14 . Front edge  80  of clamp plate  72  is disposed at an angle θ 5  with respect to top edge  82 , and preferably angle θ 5  is about 45°. Back edge  84  is disposed at an angle θ 6  with respect to rear edge  86 , and preferably angle θ 6  is about 38°. Outer and inner sides  88 ,  90 , respectively, are substantially parallel with respect to each other. Edge  92  is disposed at an angle θ 7  with respect to edge  93 , with angle θ 7  preferably being about 22°.  
         [0036]    Turning briefly to FIGS.  15 - 18 , a bushing  20  for use with the present invention is shown. Bushing  20  has an upper surface  116 , a lower surface  118 , and a sidewall  120 . Sidewall  120  has an exterior surface  122  configured and dimensioned for polyaxial rotation within a through hole  18 . As a result and as described in more detail below, a fastener inserted through a bore  124 , which is defined by an interior surface  126  of bushing  20  and extends through both upper and lower surfaces  116 ,  118 , can be inserted at a wide variety of orientations relative to occipital plate  10 . In an exemplary embodiment, bushing  20  has a frustospherical shape. Alternatively, bushing  20  can have a frustoconical shape. With either shape, bore  124  can extend through the central longitudinal axis perpendicular to the parallel upper and lower surfaces  116 ,  118 .  
         [0037]    Bushing  20  includes slots  128  located on sidewall  120 . Slots  128  allow sidewall  120  to expand outwardly against through hole  18 . This outward expansion locks bushing  20  at the selected orientation relative to the axis of through hole  18 . In order to enhance the locking effect upon expansion, exterior surface  122  of sidewall  120  and/or the periphery of through holes  18  can be provided with ridges  130 . Ridges  130  provide an additional mechanism to resist motion of bushing  20  relative to occipital plate  10  once sidewall  120  has expanded outwardly. Although bushing  20  is shown having four slots, any number of slots, including one, can be used as long as the chosen number of slots provides for outward expansion of sidewall  120 . Slot  128   a  extends from upper surface  116  through lower surface  118  while the rest of slots  128  do not extend through to lower surface  118 . Slots  128  all extend from upper surface  116  of bushing  20 .  
         [0038]    In the preferred embodiment, pre-bent rods suitable for use with the present invention are shown in FIGS.  19 - 21 . Each rod  140  includes a straight section  142  for running generally parallel to the spine, a bent section  144 , and a serrated clamping section  146 . Sections  142 ,  146  are substantially perpendicular to each other, while sections  144 ,  146  are disposed at an angle θ 8 , with respect to each other. Preferably, angle θ 8 , is between about 40° and about 50°, and more preferably approximately 45°. As shown in FIG. 21, serrated clamping section  146  includes serrations  148  about a portion of its circumference. When bent section  144  is aligned with vertical line  150 , and section  146  is centered at the intersection of perpendicular lines  150 ,  152 , it can be seen from FIG. 21 that serrations  148  only extend through an angle θ 9  from line  152 . Preferably, angle θ 9  is between about 30° and about 50°, and more preferably about 41°. Moreover, serrations  148  are present along the circumference of section  146  of rod  148  through a total angular range θ 10  as measured from center point  154 . Preferably, θ 10  is between about 90° and 180°, and more preferably θ 10  is about 156°.  
         [0039]    The pair of rods used with occipital plate  10  are typically mirror images of each other. For example, a rod  140  would be used with right clamp assembly  26  while a mirror image of rod  140 , as shown in FIG. 19A, would be used with left clamp assembly  24 .  
         [0040]    In an alternate embodiment shown in FIGS.  22 - 23 , pre-bent rod  160  includes a straight section  162  for running generally parallel to the spine, a transition section  164 , and a serrated clamping section  166 . Sections  162 ,  166  are substantially perpendicular to each other, while sections  164 ,  166  are disposed at an angle θ 11  with respect to each other. Preferably, angle θ 11  is between about 40° and about 50°, and more preferably approximately 45°.  
         [0041]    Pre-bent rods  140 ,  160  are shown retained in clamp assemblies  24 ,  26 , respectively, in FIG. 24. Although the pair of rods used with occipital plate  10  are typically mirror images of each other, for illustrative purposes only, one of each rod  140 ,  160  is shown. As seen particularly with regard to clamp assembly  24 , clamp plate  72  rotates about post  64 , and may be fixed in place using a nut  168 . Rod receiving recesses  46 ,  48  are used to further lock a rod  140 ,  160  in place.  
         [0042]    Alternate embodiments of occipital plates are shown in FIGS.  25 - 31 . First referring to FIGS.  25 - 26 , similar to occipital plate  10 , occipital plate  200  includes seven holes  18  for receiving bone fasteners. However, in this embodiment, holes  18  are disposed about four parallel lines  202 ,  204 ,  206 ,  208  instead of three. In addition, as shown particularly in FIG. 26, pre-bent rods are clamped to occipital plate  200  using set screws  210  extending through a U-shaped or C-shaped section  216 , and which are disposed about an axis  212  that may be aligned with or slightly offset from the center of a rod held in region  214 . Another embodiment is shown in FIGS.  27 - 29 , in which an occipital plate  250  is provided with nine holes  18  disposed about four parallel lines  254 ,  256 ,  258 ,  260 . As with occipital plate  200 , sections  262  are provided for clamping spinal fixation rods to occipital plate  250 . A threaded set screw (not shown) is threadably received in like-threaded hole  264 , which is preferably aligned along an axis  266  disposed at an angle  012  with respect to plate wall  268 . Preferably, angle θ12 is between about 50° and about 70°, and more preferably about 60°. Again, threaded hole  264  aligns a set screw to be offset from the center of a rod seated in region  270  and centered about point  272 .  
         [0043]    Additional embodiments of occipital plates are shown in FIGS.  30 - 31 . Notably, expansion head screws  282  are shown installed or partially installed in plate holes  18 . Occipital plates  280 ,  300  include notched regions  284 ,  302 , respectively, to facilitate bending. Also, side clamping assemblies  286 ,  304  receive rods  290 ,  308  that are fixed with a set screw extending in holes  288 ,  306 , respectively. Preferably, side clamping assemblies  286 ,  304  are angulated such that rods  290 ,  308  are disposed at an angle of between about 20° and about 30°, and more preferably about 25° with respect to the plane of the plate prior to bending.  
         [0044]    In some preferred embodiments of the present invention, cylindrical rods with a diameter of 3.5 mm are used as the spinal rods or pre-bent rods. In alternate embodiments, straight rods may be used and oriented accordingly by a surgeon using a rod bender.  
         [0045]    In the occipital plate designs disclosed herein, screw holes have been positioned along the midline of the plate for use at the midline of the occiput, since the bone thickness there is greater than on the sides. In some embodiments, the screw holes may be angled about 12° to facilitate access to the screws with a screwdriver, and to enhance pull-out strength of the screws due to the wedge effect. Although expansion head screws are preferred, other non-locking screws may be used. Arc shaped cuts between the clamping assemblies or arrangements of each plate allow the placement of a bone graft. In the preferred embodiment, occipital plate  10  is formed of titanium. Preferably, the shape of the occipital plate facilitates polyaxial bending thereof.  
         [0046]    The number of holes provided in an occipital plate of the present invention for receiving bone screws may be varied, as may the pattern of the holes and the relative alignment. Other screw hole shapes such as an oval shape, and other hole sizes may be used, as well as alternative means for locking screws. Bushings may not be included in some embodiments. Alternative fasteners for attaching an occipital plate to bone include staples and wires.  
         [0047]    While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein.  
         [0048]    Further, it should be understood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains. For example, the C-shaped clamping sections of some embodiments of the occipital plate may instead include full-circle regions for receiving rods. In another embodiment, a sleeve for receiving the rods may extend across some or the entire the length of the occipital plate. In yet another embodiment, two smaller occipital plates are provided for securement to the occiput, with each plate having a single clamp assembly and receiving one rod. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is accordingly defined as set forth in the appended claims.