Abstract:
A plate system used to maintain a generally fixed distance between vertebrae during the surgical repair of damaged vertebrae and/or the discs therebetween. The plate system is provided for use in conjunction with a cervical implant or alone. The system includes a plate which may be held in place with screws and nuts. The plate defines multiple apertures for the passage of the screws, one of which is a slot and as a result a single sized plate may be used for many different situations where the gap between adjacent vertebrae is varied. The plate also includes at least one cleat which provides and additional grip between the plate and vertebrae.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 60/456,787 filed on Mar. 21, 2003, currently pending, and incorporates its entirety herein. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention generally relates to prostheses for the spine and more specifically to a plate system to separate adjacent cervical vertebrae.  
         BACKGROUND OF THE INVENTION  
         [0003]    The spine is the central support column for the human body. The cervical region of the spine is located in the area of the neck and is comprised of cervical vertebrae separated by disks. A diseased spine suffers from deterioration of a vertebra, disk or both. Disks and vertebrae may also be damaged by physical causes as well. Surgical repair consists of fusing adjacent vertebrae together by means of a bone graft. It is necessary to keep the adjacent vertebrae spaced at a certain distance at the time the bone graft is growing and fusing the adjacent vertebrae together. Traditionally, this has been done mechanically. Typically, the systems are comprised of plates and screws or rods and screws.  
           [0004]    A problem with prior art mechanical devices of the plate and screw type is their lack of adjustability. A surgeon does not know until an incision is made and screws are set what the desired gap size between adjacent vertebrae should be, thus, a large inventory of plates must be kept. Some systems such as that described by U.S. Pat. No. 5,904,683 allow for some adjustment by tilting the set screws. However, a system which allows for a large amount of plate adjustment is desired so a doctor&#39;s inventory of plates may be kept small.  
           [0005]    Another problem with the prior art plate systems is that too many screws or too small of screws are used. Prior art which relies upon four or more screws has problems when part of one of the vertebra being screwed into is diseased or fractured. Alternatively, smaller screws have a problem with backing out of their set positions over time. What is desired is a minimum number of large screws which may be placed in multiple positions.  
           [0006]    Another problem with the prior art is that most plate inventions are not designed to work in tandem with implant devices. The result is a problem with the size to strength ratio of plate or rod or plate systems. Because they are designed to be used individually they often must be of a large size in order to guarantee separation of adjacent vertebrae. A drawback to these systems is that larger incisions must be made in order to install the systems and more bone screws must be used to secure the systems in place. Larger incisions and increased dissection lead to greater possibilities for dysphagia and/or recurrent nerve paralysis. What is desired is a plate system of reduced size which may be used in conjunction with other support structures such as cage or biscuit type implants.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention overcomes disadvantages in the prior art by providing an improved cervical system and method of holding spinal vertebrae apart. The system includes a cervical plate which is smaller and more universal than known plates. The plate may be used alone, but is preferably used in combination with known cervical implants, typically of a biscuit or cage type. The plate of the system also includes at least one cleat, which allows the number of screws used to hold the plate in position to be reduced and their sized increased.  
           [0008]    The invention provides in one aspect a plate for holding two vertebrae apart. The plate has at least two apertures, one being a slot. The plate includes interior and exterior faces and the cleat or cleats protrude from the interior face. Cancellous bone screws may be used to attach the plate to the vertebrae. The apertures within the plate pass over the trailing end of the screws and the plate secured using nuts which threadedly attach to the screws.  
           [0009]    The invention additionally provides a central beam integral within the plate which is aligned with the center of the spine when the plate is installed. This beam is continuous, avoiding any of the apertures defined by the plate, and provides superior strength where it is needed most.  
           [0010]    The invention, in the aspects described above, provides the advantage of a physical support device which prevents the collapse of adjacent vertebrae in the event a bone graft is unsuccessful. Further the invention provides a plate having superior strength which may be used for a wide variety of gap sizes between adjacent vertebrae. These and other features, aspects and advantages of the present invention will be fully described by the following description, appended claims, and accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0011]    [0011]FIG. 1 a  is a side view of a uniplate cervical system attached to spinal vertebrae;  
         [0012]    [0012]FIG. 1 b  is a front view of a uniplate cervical system attached to spinal vertebrae;  
         [0013]    [0013]FIG. 1 c  is a side view of a uniplate cervical system attached to spinal vertebrae used in conjunction with a cervical implant;  
         [0014]    [0014]FIG. 2 a  is a side view of a cancellous bone screw;  
         [0015]    [0015]FIG. 2 b  is an end view of the cancellous bone screw;  
         [0016]    [0016]FIG. 2 c  is a cross sectional view of the cancellous bone screw;  
         [0017]    [0017]FIG. 2 d  is a cross sectional detail view of a portion of the screw of FIG. 2 c;    
         [0018]    [0018]FIG. 3 is a side view of a distracter;  
         [0019]    [0019]FIG. 4 a  is a top view of a cervical plate;  
         [0020]    [0020]FIG. 4 b  is a cross sectional view of one portion of the cervical plate;  
         [0021]    [0021]FIG. 4 c  is a cross sectional view of another portion of the cervical plate;  
         [0022]    [0022]FIG. 4 d  is a side view of the cervical plate;  
         [0023]    [0023]FIG. 4 e  is a perspective view of the cervical plate;  
         [0024]    [0024]FIG. 4 f  is isolated view of a cleat from the cervical plate;  
         [0025]    [0025]FIG. 5 a  is a top view of a cervical plate with multiple cleats;  
         [0026]    [0026]FIG. 5 b  is a cross sectional view of one portion of the cervical plate of FIG. 5 a;    
         [0027]    [0027]FIG. 5 c  is a cross sectional view of another portion of the cervical plate of FIG. 5 a;    
         [0028]    [0028]FIG. 5 d  is a side view of the cervical plate of FIG. 5 a;    
         [0029]    [0029]FIG. 5 e  is a perspective view of the cervical plate of FIG. 5 a;    
         [0030]    [0030]FIG. 5 f  is an isolated view of a cleat from a cervical plate of FIG. 5 a;    
         [0031]    [0031]FIG. 6 a  is a side view of a locking nut;  
         [0032]    [0032]FIG. 6 b  is a top view of the locking nut; and  
         [0033]    [0033]FIG. 6 c  is a perspective view of the locking nut. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0034]    Referring to the drawings, FIGS. 1 a  and  1   b  illustrate a preferred uniplate cervical system  30 , as will be described in greater detail below, which includes two cancellous threaded bone screws  40 , a cervical plate  60  with at least one stabilizing cleat or projection  70  (a stabilizing cleat can be any bump, spike or other protuberance that furnishes a grip), and mounting apertures  64  and  66 , one of which may be a slot. FIG. 1 c  shows an alternate embodiment of a uniplate cervical system which additionally includes a cervical implant  90 , comprising a cage or biscuit device to keep adjacent vertebrae spaced consistently.  
         [0035]    As schematically represented in FIG. 1 a,  two cancellous threaded bone screws  40  are used to attach the system  30  to damaged vertebrae  110 , or vertebrae between which a disc  100  has been damaged. A cancellous screw is any type of fastener in which the threads are designed to penetrate a soft substrate as opposed to a hard substrate, such as metal.  
         [0036]    As shown in FIG. 2 a  each bone screw  40  has a leading end  42  and trailing end  43 . Preferably the bone screw  40  has a length in a range from about 8 to about 30 millimeters omitting the trailing end  43 . The trailing end  43  has a different surface configuration (threads, etc.) than the remainder of the bone screw  40 . The first turn  44  of the thread at the leading end  42  of the bone screw  40  may have a tapered crest which prevents the bone screw  40  from backing out of its set position after being screwed into the bone. The leading end  42  of the bone screw  40  may have a cone point  45  which is rounded at the tip. A main body section  41  of the bone screw includes threads  46 . The surface of trailing end  43  of the bone screw  40  may also be threaded on the exterior with a thread (different from the main body thread) which allows a distracter adapter  50  shown in FIG. 3 to be attached to the bone screw  40  easily. Alternatively, the surface of the trailing end  43  could include flats which allow a clamp to be applied for attachment. Referring to FIG. 2 b,  the interior of the trailing end  43  of the bone screw  40  may also be machined allowing the bone screw  40  to be driven into place with a tool. The interior of the bone screw  40  may be machined leaving a void with hexagonal sides. However, square sides or internal threads may also be used for connection to a driving tool.  
         [0037]    The cancellous bone screw  40  may be made of a titanium alloy, preferably Ti-6AI-4V, but may be any material possessing superior strength and which is compatible with the human body. Referring to FIG. 2 a,  the bone screw  40  may be also of any size and of any known type that is suitable for use in securing bone material. Preferably, however, the bone screws have a main body  41  minor diameter not exceeding 3.5 millimeters.  
         [0038]    The uniplate cervical system  30  further comprises a cervical plate  60  as shown in FIGS. 1 a - c,  and  4   a - e  which holds two vertebrae apart at a desired distance. FIGS. 5 a - e  show an alternate embodiment of the cervical plate  160  having a different size and including multiple cleats  170 . Referring to FIGS. 4 a - e,  the cervical plate  60  is shown as a generally rectangular shaped piece having an interior side  61  and an exterior side  62 , rounded edges  63  and being bowed along its width, but may be other shapes. Preferably, the bow of the cervical plate  60  is defined by an angled radius of curvature of about 27 millimeters. The thickness of the cervical plate  60  is preferably about 1.6 millimeters  
         [0039]    The cervical plate  60  defines two mounting apertures  64  and  66  through which the trailing ends  43  of bone screws  40  pass when the uniplate cervical system  30  is installed. Round aperture  64  is substantially the same size as the diameter of the trailing end  43  of the bone screw  40  such that there is no substantial play in the fitting between the bone screw  40  and the cervical plate  60 . The round aperture  64  may be countersunk which improves seating of a locking nut  80  further reducing any chance for movement of the cervical uniplate system  30  when in place and secured. The round aperture  64  is preferably countersunk at about 66 degrees. The round aperture  64  is preferably offset, at its center, from a centerline “CL” passing from a leading edge to a trailing edge of the cervical plate  60 . The cervical plate  60  also defines an aperture  69  for the mounting of a cleat  70 . This aperture  69  may or may not be threaded. The cleat aperture  69  is preferably located along the same transverse axis as the center of the round aperture  64 . The cleat aperture  69  is preferably offset from the cervical plate centerline “CL”.  
         [0040]    The aperture  66  is a slot having a predetermined length, a width substantially the same size as the diameter of the trailing edge  43  of the bone screw  40  and rounded ends with a radius substantially the same size as the radius of the trailing edge  43  of the bone screw  40 . The perimeter of the aperture  66  may be countersunk to allow improved seating of a locking nut  80 . The slotted cervical plate  60  allows a surgeon to address multiple situations, where the desired gap between vertebra varies, while carrying a small inventory of plates. Further benefit is derived from the small amount of vertebral settling that the aperture  66  allows. Should settling occur, the screw  40  will slide in the aperture  66  within the plate  60 , rather than pull out from the vertebra. The aperture  66  may be of any appropriate length, but preferably has a length of 2.8 millimeters (see designation “x”) from the radial centers of each rounded edge. Alternatively, aperture  66  may be a circular aperture similar to aperture  64 .  
         [0041]    In use, the apertures  64  and  66  are placed along a common axis (“CA”) which is parallel to, but offset from the central axis of the patient&#39;s spine as shown in FIG. 1 b.  Thus, when mounted, the beam  68  (co-linear with centerline “CL”) inherent in the cervical plate  60  which is also co-linear with the spine&#39;s central axis, is devoid of any holes or formations, resulting in a region of superior strength where it is most desired. Placement of the bone screws  40  and cervical plate apertures  64  and  66  may be on either side of the spine&#39;s central axis, thus giving a surgeon greater flexibility to avoid attachment to weak or deteriorated bone.  
         [0042]    Referring back to FIGS. 4 a - e,  the size of the cervical plate  60  may be of any appropriate size required to perform its function. However, preferably the size of the cervical plate  60  from leading edge to trailing edge may be within a range of about 28 millimeters to about 43 millimeters. The width of the cervical plate  60  preferably is between 10 and 14 millimeters. The portion of reduced width in the central region of the cervical plate preferably between 6 and 10 millimeters. The nominal size of the cervical plate  60  is measured from the center of the round aperture  64  to the center of the aperture  66  and may be in a range from about 18 to about 32 millimeters.  
         [0043]    One cleat  70  protrudes from the interior side  61  of the cervical plate  60  and may be embedded within a vertebra when the system  30  is installed. Referring to FIG. 4 f,  each cleat  70  preferably tapers to a sharp point from its anterior to its posterior end. Alternatively, the cleat  70  may be a tapering rectangular solid or any other shape that can grip a structure comprised of bone. The cervical plate  60  is preferably made of titanium alloy (Ti-6AL-4V), but may be made of any material possessing superior strength which is compatible with the human body. The cervical plate  60  can be passivated and given a #10 glass bead finish. The cleat  70  is manufactured out of any common material used in the bone grafting art. Cleat  70  is usually a separate piece that is threaded into the cervical plate  60 , but may also simply be press fit into cervical plate  60 .  
         [0044]    An alternate embodiment of the invention, cervical plate  160  is shown in FIGS. 5 a - e  and includes multiple cleats  170 . This plate  160  also defines multiple apertures  164  and  166  for the passage of mounting screws. The second cleat  170  is located with its center along a transverse axis which passes through the center of the aperture  166 .  
         [0045]    Locking nuts  80  are known and screwed onto the trailing ends  43  of the cancellous bone screws  40  and act to lock the cervical plate  60  or  160  in place. Referring to FIGS. 6 a - c  a locking nut  80  may be hexagonal shaped with a chamfered end allowing superior engagement with the countersunk area of the cervical plate  60  thus disallowing relative movement. The nut  80  may be made of titanium alloy, but may be made of any strong material which is compatible with the human body. Locking nuts  80  may be of the type sold by a company called Spiralock Corporation located in Madison Heights, Mich.  
         [0046]    Referring to FIGS. 1 a  and  1   b,  the uniplate cervical system  30  is shown being attached to two vertebrae in the cervical section of the human spine. The spine may be accessed anteriorally. A limited discectomy is performed to identify the orientation of the space between the two mounting vertebrae. In no preferred order, prior to insertion of the plate, a single cancellous bone screw  40  is screwed into the vertebra adjacent to the altered disc and a second bone screw  40  is attached to the second adjacent vertebra. The screws  40  are offset from the central axis of the spine, but are placed such that their centers are on a line substantially parallel to the central axis. A distraction adapter  50  screws onto the machine thread or clamps to each bone screw  40 . The adapter  50  may be any tool which has an end to mate with the cancellous bone screw  40  and is of a sufficient length to extend outside of the body. Distracter adapter  50 , shown in FIG. 3 may have an internal female machine thread  52  at one end, although this may also be a hexagonal shaped adapter or a clamp. Distracter adapter  50  also has a machined opposite end,  54  which may be in a hexagonal shape, so as to allow connection to a distracter tool. A distracter tool, such as a Caspar distracter, is connected to each distracter adapter  50 . A surgeon applies force to the distracter tool to separate the vertebrae apart. The use of cancellous threaded screws  40  allows for more force to be applied through the distracter tool than was possible with prior art.  
         [0047]    A partial or complete discectomy is performed and bone graft material is placed between the spaced vertebrae. Additionally or alternatively, an anterior weight-sharing device or cervical implant may be placed between the spaced vertebrae. A typical cervical implant is shown in U.S. Pat. No. 6,635,086 to Lin or U.S. Pat. No. 6,193,755 to Metz-Stavenhagen et al. Distracter tool and distracter adapters  50  are removed from the cancellous screws  40  allowing cervical plate  60  to be put in place. The appropriate sized cervical plate  60  is chosen after the distance between the cancellous screws  40  is measured. A benefit of having aperture  66  be a slot upon the cervical plate  60  is that one plate  60  can be used for a variety of distances between the cancellous screws  40 . Thus, a smaller inventory of cervical plates  60  is required in the surgeon&#39;s inventory. The trailing ends  43  of the two cancellous bone screws  40  protrude through the mounting apertures  64  and  66  of the cervical plate  60  when it is in position. Chamfered nuts  80  are applied to the ends of the cancellous screws  40  to lock the cervical plate  60  in place.  
         [0048]    Due to the presence of cleat  70  or  170 , the plate may be placed and secured to the vertebrae without any additional screws being inserted into the vertebrae. This results in a much faster and streamlined medical procedure and also results in fewer, larger holes that need be created in bone tissue that usually is already damaged in some way.  
         [0049]    Although the invention has been shown and described with reference to certain preferred and alternate embodiments, the invention is not limited to these specific embodiments. Minor variations and insubstantial differences in the various combinations of materials and methods of application may occur to those of ordinary skill in the art while remaining within the scope of the invention as claimed and equivalents. Use of the term “or” herein is the inclusive, and not the exclusive use. The preferred embodiments described above are not in any way intended to limit the invention as claimed below.