Abstract:
An adjustable occipital plate includes a central body portion having a plurality of arms extending therefrom in a generally Y-shaped configuration. Two of the arms include elongate slots for slidably receiving retaining members therein. Each retaining member includes a U-shaped channel for receiving a spine rod and a set screw. The central body portion and one arm include openings for receiving bone screws therein. Each of the arms may be angled with respect to the central body portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 12/578,274, filed on Oct. 13, 2009, which claims priority to, and the benefit of, U.S. Provisional Patent Application No. 61/195,825, filed Oct. 10, 2008. The entire contents of each of these prior applications are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to devices for bone fixation. More particularly, the present disclosure relates to an occipital plate for cervical fixation. 
         [0004]    2. Background of Related Art 
         [0005]    The occipitocervical junction, which comprises the occiput, atlas, and axis, represents a unique and complex interface between the cranium and the rostral cervical spine. More than 50% of the rotation and flexion-extension of the head and neck occurs in that region. In addition, the osseous articulations and their ligamentous support structures must resist force in eight axes of rotation. These include flexion, extension, bilateral lateral bending; and bilateral rotation, distraction, and axial loading. Instrumentation constructs not only must resist forces in all of these vectors, but also must resist the significant lever arm created by the suboccipital bone and the cervical spine, which meet at a 50° angle. Any instrumentation construct designed for use in this region must, therefore, have adequate dimensions to interface with the osseous structures of the spinal structures as well as have sufficient rigidity and purchase to resist these forces until bone fusion can occur. Great flexibility must be afforded to allow for the multiple anatomical variations seen in this region. 
         [0006]    In the early 1900s occipitocervical instability and lesions located at the occipitocervical junction were considered inoperable and terminal. Since the first description of an occipitocervical fusion by Forrester in 1927, multiple methods of fusion in this region have been described. Descriptions of simple onlay bone grafts with halo immobilization; wire, pin, or hook constructs; rigid metallic loops and rectangles fixed to the bone with either screws or wires; and most recently, plate or rod constructs with screws have all been described. In general, the evolution of this technology has focused on providing increasingly more rigid constructs to facilitate bone fusion and to minimize the need for and duration of external immobilization. 
         [0007]    A common technique for fixing occipitocervical instability is the use of an inverted Y-shaped screw plate. Using this technique, the plate is secured to C1-2 with transarticular screws and to the suboccipital bone with paramedian screws. The suboccipital bone varies in thickness, with a mean thickness of about 14 mm. Screws must be carefully selected to provide adequate purchase, yet avoid cerebellar injury. Utilizing the maximum screw length possible is critical, because shorter screws do have reduced resistance to pullout. If stabilization is required below the C1-2 level, then lateral mass screws can be placed through additional holes in a longer plate to include these levels as well. A bone graft is again added to promote fusion. The Y-shaped plate, in combination with transarticular screws, is an economically favorable alternative. Immediate postoperative stabilization is achieved and very low rates of pseudoarthrosis have been reported. 
       SUMMARY 
       [0008]    The present disclosure relates to an adjustable occipital plate having a central body portion and a plurality of arms extending therefrom in a generally Y-shaped configuration. The central body portion and at least one of the arms include an opening for threadably receiving a bone screw. Each arm may be joined to the central body portion by a bendable joint that allows each arm to be individually angled with respect to the central body portion. 
         [0009]    Further, at least one of the arms includes an elongate slot for slidably receiving a retaining member or screw housing. The screw housing includes a shank having threads formed thereon and a head. The head includes a pair of opposed upstanding walls defining a U-shaped channel therebetween that is configured and adapted for receiving a portion of a spine rod. The upstanding walls include threads for threadably engaging threads of a set screw. Once the spine rod is positioned relative to the occipital plate and a portion of the spine rod is disposed in the U-shaped channel, the set screw is threaded into the screw housing, thereby securing the spine rod to the occipital plate. The at least one arm including the elongate slot further includes a channel disposed on one side. The channel is configured and dimensioned for slidably receiving a nut therein. The nut is threadably engaged with the threads on the shank of the screw housing, thereby retaining the screw housing to the respective arm of the occipital plate. The screw housing may be welded to the nut and may also be rotatable in the elongate slot since the nut may be rotatable within the channel. 
         [0010]    A plurality of bone screws is insertable through the openings of the occipital plate. In one embodiment, the screws are formed from a harder material than the occipital plate. As such, when the bone screws are threaded into the openings, a lip of each opening deforms such that the bone screw is affixed to the occipital plate and resists backing out from the occipital plate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments of the presently disclosed occipital plate are described herein with reference to the accompanying drawings, wherein: 
           [0012]      FIG. 1A  is a top elevational view of the presently disclosed occipital plate with rods coupled to retaining members; 
           [0013]      FIG. 2A  is a top elevational view of the occipital plate of  FIG. 1  with bone fasteners disposed in openings of the occipital plate; 
           [0014]      FIG. 2B  is a side view of the occipital plate of  FIG. 2A ; 
           [0015]      FIG. 3  is an end view of the occipital plate of  FIG. 1  with the rods removed; 
           [0016]      FIG. 4A  is a top view of a rod coupled a retaining member; 
           [0017]      FIG. 4B  is a side cross-sectional view of the rod and retaining member of  FIG. 4A  taken along section line  4 B- 4 B; and 
           [0018]      FIG. 5  is a side, part cross-sectional view of an arm and the retaining member of the occipital plate of  FIG. 2B . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Various embodiments of the presently disclosed occipital plate for cervical fixation will now be described in detail with reference to the drawings, wherein like reference numerals identify similar or identical elements. In the drawings and in the description that follows, the term “proximal,” will refer to the end of a device or system that is closest to the operator, while the term “distal” will refer to the end of the device or system that is farthest from the operator. In addition, the term “cephalad” is used in this application to indicate a direction toward a patient&#39;s head, whereas the term “caudad” indicates a direction toward the patient&#39;s feet. Further still, for the purposes of this application, the term “medial” indicates a direction toward the middle of the body of the patient, whilst the term “lateral” indicates a direction toward a side of the body of the patient (i.e. away from the middle of the body of the patient). The term “posterior” indicates a direction toward the patient&#39;s back, and the term “anterior” indicates a direction toward the patient&#39;s front. Additionally, in the drawings and in the description that follows, terms such as front, rear, upper, lower, top, bottom, and the similar directional terms are used simply for convenience of description and are not intended to limit the disclosure attached hereto. 
         [0020]    Referring initially to  FIG. 1 , an occipital plate or adjustable occipital plate  100  is illustrated. The adjustable occipital plate  100  includes a central portion  110  having an opening  108  therethrough. The opening  108  is generally circular and includes a generally circular lip  107 . In addition, the adjustable occipital plate  100  includes a first arm  102  and a second arm  104  extending from the central body portion  110  at an angle thereto. A third arm  106  also extends from the central body portion  110  such that the first arm  102 , the second arm  104 , and the third arm  106  define a generally Y-shaped configuration of the adjustable occipital plate  100 . In one embodiment, the adjustable occipital plate  100  is formed from commercially pure titanium. A deformable joint  114  is located between the central portion  110  and each of the arms  102 ,  104 , and  106 . The joint  114  may be formed such that each of the arms  102 ,  104 , and  106  are bendable with respect to the central portion as shown by directional arrows A in  FIG. 3 . Thus, the arms  102 ,  104 , and  106  may be bent relative to the central portion  110  and define acute angles with respect thereto. Each arm  102 ,  104 , and  106  may be individually bent without regard to the remaining arms. 
         [0021]    With additional reference to  FIGS. 2A and 2B , each of the first and second arms  102 ,  104  includes an elongate oval slot  112 , while the third arm includes openings  108 . Each of the openings  108  is configured for receiving a bone screw  30  therein. Bone screw  30  includes a shank  32  extending from a head. The head of the bone screw  30  preferably includes threads  36  having a first pitch and the shank  32  includes threads  34  having a second pitch that may be different from the first pitch of threads  36 . In one embodiment, the bone screw  30  is formed from a titanium alloy (e.g. Ti-6A1-4V) or another material that is harder than the material used to form the occipital plate  100 . In this configuration, when the bone screw  30  is installed in the opening  108 , the threads  36  of the head of the bone screw engage the lip  107  of the opening. Since the bone screw  30  is formed from harder material than that of the lip  107 , the lip  107  deforms, thereby securing the bone screw  30  and plate  100  to each other. In this arrangement, the bone screw  30  resists backing out of the opening  108 . This type of screw locking arrangement is disclosed and shown in U.S. Pat. No. 6,322,562 to Wolter, the entire contents of which are hereby incorporated by reference herein. 
         [0022]    The oval slots  112  are configured for receiving a screw housing  50  therein. In this configuration, the screw housings  50  are repositionable throughout a plurality of positions along a length of the oval slots  112 . A spinal rod  20  is coupled to each of the screw housings  50 . 
         [0023]    Referring additionally to  FIGS. 4A ,  4 B, and  5 , each screw housing  50  includes a head  40  having upstanding walls with internal threads  42  that define a U-shaped channel  44  therebetween. The U-shaped channel  44  is configured for receiving the spinal rod  20  therein. The internal threads  42  of the head  40  are configured for engaging external threads of a set screw  52 . Each screw housing  50  is secured to its respective oval slot  112  by a nut  56 . 
         [0024]    Further still, the screw housing  50  includes a shank  54  having threads thereon for engaging the threading of the nut  56 . Once assembled, the shank  54  is welded to the nut  56 . Since the nut  56  is round, it is able to rotate in a channel  115  that is located on the underside of the oval slot  112 , thereby allowing the screw housing  50  to rotate relative to its respective arm  102 ,  104 . As such, the screw housing  50  is easily repositionable and rotatable for accommodating the spinal rod  20 . The channel  115  allows the nut  56  and the screw housing  50  to slide along the length of the oval slot  112  without the nut  56  separating from the channel  115 . Once the screw housing  50  is in its desired position, the physician installs the spinal rod  20  in the U-shaped channel  44  of the screw housing  50 . After the spinal rod  20  is positioned in the U-shaped channel  44 , the physician threads the set screw  52  into the head  50  and tightens the set screw  52  which causes the nut  56  and rod  20  to be tightened against an upper surface of the respective arm  102 ,  104  to hold the spinal rod  20  in position. Finally, the physician installs one or more other bone screws  30  into the openings  108  and secures the adjustable occipital plate  100 . Thus, the spinal rod  20  and screw housing  50  construct is secured to the occiput region of the patient&#39;s cranium. 
         [0025]    Each of the embodiments described above are provided for illustrative purposes only. It will be understood that various modifications may be made to the embodiments of the presently disclosed vertebral body staple. By way of example only, it is contemplated that the rod receiving portion of the housing may include a taper lock for locking the rod relative to the housing, rather than a set screw design as shown, A suitable taper lock configuration may be adapted from the taper lock design shown in International Patent Application Number PCT/US/2008/080682 filed on Oct. 22, 2008 and published as international application WO 2009/055407, the entire contents of which are incorporated herein by reference. Therefore, the above description should not be construed as limiting, but merely as exemplifications of embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the present disclosure.