Abstract:
A spinal implant for insertion in the intervertebral space is formed as a hollow cage, wedge shaped in profile, with a lesser height leading end for a low profile entry. The cage has two open sides with a plurality of angled teeth along opposite longitudinal edges for engaging the end plates of adjacent vertebrae when the cage is rotated into position. One portion of the angled teeth is angled toward an end of the cage and another portion of the angled teeth is angled away from that end to provide a lock preventing the cage from migrating ventrally or dorsally from the spine. Upon rotation, the leading end has a greater height than the trailing end. Opposing side walls of the cage include recesses to facilitate rotation of the cage and minimize stress on adjacent vertebrae.

Description:
PRIORITY CLAIM 
       [0001]    This application is a continuation-in-part of application Ser. No. 11/741,249 filed on Apr. 27, 2007 entitled Spinal Implant, the contents of which are hereby expressly incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates to spinal implants inserted between adjacent vertebrae to stabilize the intervertebral space and correct the angle of the spine. The implant also facilitates fusion of the affected vertebrae. 
         [0004]    2. Description of the Prior Art 
         [0005]    The spinal cage is a well known device for insertion between vertebrae to provide support in lieu of the natural spinal disc. The cages may be of different shapes, including rectangle, cylinder and wedge, enclosing an interior filled with bone growth material, among other compositions, which promote the fusion of the vertebrae on each side of the cage. The cages are open structures which allow vascularization and bone in-growth. 
         [0006]    It is very important that these cages be prevented from migrating out of the prepared surgical site because any movement will prolong the fusion process and traumatize healthy tissue. 
         [0007]    U.S. Pat. No. 6,746,484 B1 to Liu et al illustrates such a wedge shaped cage with rectilinear ends. Liu et al is directed to proper placement of the cage so that the large and small ends of the wedge are support members and the interconnected sides facilitate fusion or bone growth. Distractors with screw-like threads are used to form a shaped bed in the end plates of the adjacent vertebrae to accept the cage. The cage has two open opposite long sides and two closed long sides. The filled cage is inserted into the prepared site and rotated 90 degrees so that the open sides will be in contact with the end plates of the adjacent vertebrae. The cage is held in place by compression between the vertebrae. 
         [0008]    U.S. Pat. No. 5,425,772 to Brantigan is directed to another wedge shaped implant similar to the cage described above. The surgical site is prepared by cutting slots in the adjacent vertebrae end plates and separating the end plates by distraction. The closed long sides have a series of sharpened ridges or teeth extending across the closed sides parallel to the ends. The teeth are shaped as elongated isosceles triangles for biting into the adjacent vertebrae surfaces when implanted. The valleys between the teeth are filled with bone growth material to promote fusion. After implantation, the distraction is released to reduce the space between the vertebrae and to seat the implant by compression. 
         [0009]    What is lacking in the prior art is a spinal cage which has a large open vertebral contact area for boney in-growth and a locking structure to prevent ventral and dorsal movement after implantation and a cage that can provide lordosis, mimicking the natural curvature of the spine. 
       SUMMARY OF THE PRESENT INVENTION 
       [0010]    Therefore, an object of this invention is to provide a spinal implant sized and shaped to support adjacent vertebrae in the proper angular and spatial relationship. 
         [0011]    It is another object of this invention to provide a spinal implant cage with a hollow interior to serve as a reservoir of bone growth material and to provide a large contact area between the material and the vertebrae. 
         [0012]    It is a further object of this invention to provide a plurality of angled teeth securing the cage to the end plates of the vertebrae and preventing migration of the implant from the implant site. 
         [0013]    It is yet another object of this invention to provide a method of implanting the cage by rotation of the cage to engage the angled teeth in the end plates of the vertebrae. 
         [0014]    It is a still further object of this invention to provide a wedge shape in which the major distraction distance shifts from the trailing end to the leading end as the cage is rotated. 
         [0015]    It is still yet an object of this invention to provide a method of facilitating the rotation of the cage by providing a recessed surface areas along the elongated side walls to minimize the stress placed on adjacent vertebrae as the cage is rotated. 
         [0016]    It is further still yet an object of this invention to provide a stop plate to prevent over rotating the cage to an undesirable position. 
     
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of the spinal cage of this invention; 
           [0018]      FIG. 2  is a top plan view of the cage of  FIG. 1 ; 
           [0019]      FIG. 3  is a side plan view of the cage of  FIG. 1 ; 
           [0020]      FIG. 4  is an exploded perspective of another embodiment of the cage of this invention; 
           [0021]      FIG. 5  is a perspective view of another embodiment of the spinal cage of this invention; 
           [0022]      FIG. 6  is a top view of the cage of  FIG. 5 ; 
           [0023]      FIG. 7  is a side plan view of the cage of  FIG. 5 ; 
           [0024]      FIG. 8  is a partially exploded view of the spinal cage of  FIG. 5  including radiopqaue rods; 
           [0025]      FIG. 9  is a perspective view of another embodiment of the spinal cage invention; 
           [0026]      FIG. 10  is a top view of the spinal cage of  FIG. 9   
           [0027]      FIG. 11  is a partially exploded view of the spinal cage of  FIG. 9  including radiopqaue rods; 
           [0028]      FIG. 12  is another perspective view of the spinal cage shown in  FIG. 9 ; 
           [0029]      FIG. 13  is another top view of the spinal cage shown in  FIG. 9 ; and 
           [0030]      FIGS. 14 and 15  are end views of the spinal cage shown in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0031]    The spinal implant is formed as a cage  10  with a hollow interior  30 , as shown in  FIG. 1 , surrounded by an open framework. The cage shown in  FIGS. 1 ,  2 , and  3  has an overall shape of a wedge with a smaller end wall  14  and a larger end wall  15 . As shown in  FIGS. 1 and 4 , the leading end  15  is longer than trailing end  14 . Elongated sidewalls  12  and  16  connect the ends and are disposed diametrically opposite to each other. Sidewall  12  has apertures  18  and  19  which communicate with the interior  30 . Sidewall  16  is a mirror image of sidewall  12  and includes apertures  20  and  21 . The apertures in the sidewalls may be the same size or different sizes, as shown. The apertures contribute to the integration of the implant into spine. The cage may be made of surgical stainless steel, titanium, other metallic alloys, ceramics, polymeric material or combinations thereof that are bio-compatible and have sufficient strength to support adjacent vertebrae in desired spatial relationship with proper curvature of the spine. 
         [0032]    Along the longitudinal periphery of the sidewall  12  is a series of teeth terminating in a sharpened apex. On one portion of the periphery the teeth  24  and  26  are angled away from the small end  14 . In the other portion of the periphery of sidewall  12 , the teeth  25  and  27  are angled toward the small end wall  14 , as shown in  FIG. 3 . The periphery of sidewall  16  is similarly shaped with the teeth  22  angled away from the small end wall  14  and the teeth  23  angled toward the small end wall  14 . The angled teeth gain purchase in the bone and act as a ratchet to prevent relative movement between the implant and the end plates of the adjacent vertebrae. The opening  30  between the periphery of side walls  12  and  16  communicates with the hollow interior of the cage. When the cage is filled with bone growth and/or other material, this large opening on either side of the cage provides a large contact area to promote boney in growth, vascularization and fusion of the adjacent vertebrae. 
         [0033]    The end smaller wall  14 , shown in  FIG. 1 , has an oblong opening  31  which mates with an implant tool (not shown) used to manipulate the implant for permanent positioning in the spine. The longer end wall  15  has a threaded opening  32  opposite the opening  31  to which the implant tool may be removably connected. These openings,  31  and  32 , may be reversed. 
         [0034]    The manipulation would normally include insertion through a percutaneous opening in the patient&#39;s back and sliding the implant into a prepared site between lumbar vertebrae. The longer end wall  15  is the leading end with the smooth width of one of the sidewalls contacting the upper vertebrae and the other sidewall contacting the lower vertebrae. To this end, the sidewalls  12  and  16  are bowed outwardly in an arc increasing the volume of the hollow interior and reducing the area of sliding contact with the vertebral end plates. Also, the end walls  14  and  15  may be rectilinear with the sidewalls connecting the opposite sides of the rectangles so that the implant has a low profile during insertion within the prepared spinal site. The low profile leading end is shown in the insertion phase in  FIG. 2 . 
         [0035]    Once within the spinal site, the implant is rotated approximately 90 degrees to orient the width of the sidewalls of the implant more or less parallel with the longitudinal axis of the spine and engage the teeth with the end plates of the adjacent vertebrae. The rotation results in increasing the profile of the cage at the leading end and reducing the profile at the trailing end, as shown by a comparison of  FIG. 2  and  FIG. 3 . 
         [0036]    The implant tool is then removed. The hollow interior  30  of the cage may then be filled with a composition including bone growth material, bone cement, bone particles, and other structural or pharmaceutical components, alone or in combination. In the alternative, the interior of the cage may be filled with the desired material before insertion into the patient. In the final position, the bone growth material is in contact with the end plates of the vertebrae through the large openings on both sides of the implant. 
         [0037]      FIG. 4  illustrates another embodiment of the cage which may have a rectilinear shape and radiopaque markers useful during the surgical implantation to locate the forward and rear ends of the cage in relation to the spine for proper placement of the cage. The end walls  14  and  15  each have an opening  61  connecting to a bore  63  along one edge, respectively. Radiopqaue rods  64  and  65  are secured in the bores. During the surgical procedure of implantation, the proper positioning of the implant may be monitored by flouroscope. 
         [0038]    With regards to the rotation, the peripheral surfaces of the sidewalls  12  and  16  on top  11  and bottom  13  portion of the cage  10  alternatively includes recesses.  FIG. 5  shows first recess  80  and second recess  81 . First recess  80 , is located on the top portion  11  of the cage  10  and is preferably cut into the exterior surface of the peripheral sidewall  16 . The first recess  80  extends from substantially the small end  14  to substantially the large end  15 . The second recess  81  is an inverse mirror image of the first recess  80  except on the second recess  81  is located on the bottom portion  13  of the cage  10 . More specifically, each recess  80  and  81  includes a pair of opposing faces, defining a carved out open area  82  there between. Because the first recess  80  and the second recess  81  is carved out within the hollow opening  30  the surface area of the opening  82  contains a hollow opening to promote boney in growth, vascularization and fusion of the adjacent vertebrae. The opening  82  may be of a concave, convex, or planar shape. The edge of the recesses preferably slope at an angle of 45 degrees from the centerline CL of the cage, however, it is contemplated that the recesses may vary in angle from 1 degree to 89 degrees from the centerline CL. The recesses are designed to help aid in rotation of the cage. The amount of surface area in contact with the top vertebrae during rotation is decreased with the grooves thus reducing the frictional forces working against the rotation and making the rotation easier. In addition, the spaced traversed between adjacent vertebrae is reduced as the cage is rotated into position thereby minimizing the stress applied to the vertebrae. 
         [0039]      FIG. 6  shows a top view of spinal cage  10  illustrating the groove  81  on elongated side wall  12 . 
         [0040]      FIG. 7  shows a side view of spinal cage  10  illustrating groove  81  and opening  82  on elongated side wall  12 . 
         [0041]      FIG. 8  shows a partially exploded perspective view of the spinal cage  10  with groove  80  on elongated side wall  16  further including radiopqaue markers  64  and  65 . 
         [0042]      FIGS. 9 through 14  show an alternative embodiment with a stop-plate  90  and  91  on the top portion  11  and bottom portion  13  of the cage  10 , specifically the elongated sidewall  12  and elongated sidewall  16  towards the larger end wall  15 , respectively. The stop-plate is configured to make contact with the top vertebrae and act as a guide to prevent from over rotation of the cage  10 . Because the desired rotation of the cage  10  is 90 degrees the stop-plates  90  and  91  are oriented at right angles from the top portion  11  to prevent over rotation. The body of the stop-plates  90  and  91  are sloped, having a concave cross-section to promote easy transition when the cage is manipulated into position with sidewalls parallel to the longitudinal axis of the spine. Stop plates  90  and  91  can likewise be incorporated to each of the spinal cages  10  previously described. In this embodiment the cage  10  includes a bridging element  70  located on the top portion  11  and bridging element  72  located on the bottom portion  13 . Bridging element  70 , located on the top portion  11 , traverses the hollow interior  30  and extends in a diagonal fashion from end  14  adjacent side wall  12  to end wall  15  adjacent side wall  16 , as shown in  FIG. 9 . Bridging element  72 , located on the bottom portion  13 , traverses hollow interior  30  and extends in a diagonal fashion from end  14  adjacent side wall  16  to end wall  15  adjacent side wall  12 , as shown in  FIG. 15 . Bridge members  70  and  72  are each provided with teeth that are in alignment with the teeth formed on the top and bottom peripheries of the elongated side walls  12  and  16 . The profile of the teeth on the side walls  12  and  16  and bridging elements  70  and  72  that are in alignment have identical profiles. 
         [0043]    The cage  10  may be constructed as a molded, cast or machined unitary structure or as a construct of components. The end walls and the sidewalls may be separate elements connected together by welding, adhesives, heat and pressure, or other fastening. The teeth may be integral with the sidewalls or separate pieces attached to the periphery of the sidewalls. 
         [0044]    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. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment but only by the scope of the appended claims.