Abstract:
A spinal fusion implant for implantation between adjacent vertebrae is formed in the approximate shape of a hollow cube. The device has an upper section and a lower section separated by a distractor all of which are relatively movable. The sidewalls of the upper section and the lower section terminate in inclined planes so that the sections move away from each other as the wedge shaped distractor increases the height of the device.

Description:
RELATED APPLICATIONS 
     This application is a continuation in part of U.S. patent application Ser. No. 10/776,663 filed Feb. 10, 2004 now U.S. Pat. No. 7,211,112. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of orthopedic surgery and, more particularly, to implants to be placed between vertebrae in the spine. 
     2. Background of the Invention 
     Spinal stabilization is one approach to alleviating chronic back pain caused by displaced disk material or excessive movement of individual vertebrae. Conventional stabilization techniques include fusing two or more vertebrae together to circumvent or immobilize the area of excessive movement. Normally, the vertebral disk material which separates the vertebrae is removed and bone graft material is inserted in the space for interbody fusion. In addition to or, in place of, the bone graft material, a spinal implant may be inserted in the intervertebral space. 
     The conventional surgical approach for stabilization has been posteriorly for ease of access to the spine and to avoid interfering with internal organs and tissue. Usually the implant site is prepared to maintain natural lordosis and to accept a certain sized implant within certain pressure limits. This requires considerable time and skill by the surgeon. 
     DESCRIPTION OF THE PRIOR ART 
     U.S. Pat. No. 6,562,074 to Gerber et al issued May 13, 2003 discloses a spinal insert which can be manipulated to adjust the height of the implant through links connected to the upper and lower plates. 
     U.S. Pat. No. 6,120,506 issued Sep. 19, 2000 to Kohrs et al discloses a lordotic implant and a tap for use in preparing the vertebrae. The implant is designed to be inserted between the non-parallel end plates of adjacent vertebrae and maintain the natural lordotic angle of the spine. This is done through the use of a threaded tapered plug inserted in a tapped hole in the direction required by the lordosis of the spine. The implant is hollow and has radial apertures for accommodating bone graft material. 
     U.S. Pat. No. 6,015,436 issued Jan. 18, 2000 to Shoenhoeffer discloses a tubular spinal implant. The implant is hollow and has radial apertures for interbody fusion through bone growth material. The device is placed between adjacent vertebrae with the opposite ends of the tube contacting the opposing vertebrae. The opposite ends are threaded together to form the hollow tube. 
     SUMMARY OF THE INVENTION 
     The implant of this invention has a main body having upper and a lower sections with mating sidewalls relatively movable along an inclined ramp. The inclined ramp forms a wedge movable between inclined sidewalls of the main body sections. The main body sections and the inclined ramp form a hollow cube-shaped structure with common open sides. The implant is inserted in an extended thin mode between adjacent vertebrae and the ramp is inserted between the sections through one end. The body sections are connected at the other end by a link which permits the sections to move vertically away from each other for increasing the height of the implant and engaging the opposing surfaces of adjacent vertebrae. The adjacent vertebrae are forced apart as the height of the implant increases. The spinal fusion device may be used unilaterally or bilaterally. 
     Accordingly, it is an objective of the instant invention to teach a posterior surgical approach for placement of an adjustable spinal implant for interbody fusion allowing the implant to be inserted through a small incision and increased in size in situ. 
     It is another objective of the instant invention to teach a spinal implant which allows the surgeon to provide for lordosis intraoperatively and to distract through the implant. 
     It is a further objective of the instant invention to teach a spinal implant having increased contact area in the disk space. 
     It is yet another objective of the instant invention to teach an implant facilitating interbody fusion through bone graft or an ingrowth-type implant. 
     Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective of the spinal fusion implant of this invention in the thin mode; 
         FIG. 2  is a perspective of the spinal fusion device of this invention in the deployed mode; 
         FIG. 3  is a side view, partially in section, of the implant of  FIG. 2 ; 
         FIG. 4  is an end view in perspective another embodiment of the implant of this invention in the thin mode; 
         FIG. 5  is a perspective of the spinal fusion device of  FIG. 4  of this invention in the deployed mode; and 
         FIG. 6  is a side view, partially in section, of the implant of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The spinal fusion device  10  is inserted in the intervertebral space in the insertion mode, shown in  FIG. 1 , to replace damaged, missing or excised disk material. This extended position allows the leading end of the implant to be inserted in a small intervertebral space without the necessity of excising structurally sound bone. The upper section  11  has a top surface  12  for engaging the end plate of a vertebra and the lower section  13  has a bottom surface  14  for engaging the end plate of an adjacent vertebra. The top surface  12  and the bottom surface  14  are planar to provide a large contact area with each vertebra. Each contact surface has a roughened finish to provide better purchase on the end plates of the vertebrae. As shown, the top and bottom surfaces have a series of lands and grooves  15 ,  16 ,  17  and  18  though other stippled treatment may be employed. Of course, the device may be rotated about its longitudinal axis 180 degrees so that the upper section becomes the lower section and vice versa. 
     The device  10  has two extreme positions and is adjustable infinitely between those positions, eg., in the insertion mode, the extended position of the leading end of the structure has a height  20  approximately the same as the height of the sections and a length approximately twice the length of one section, as shown in  FIG. 1 . In the increased height mode, the expanded position, shown in  FIG. 2 , the height  19  is the sum of the height of the individual sections with the distractor  42  and the length is approximately the same as the length of a section. 
     The fusion device  10  may be made of conventional materials used for surgical implants, such as stainless steel and its many different alloys, titanium, and any other metal with the requisite strength and biologically inert properties. Polymeric materials with adequate strength and biological properties may also be used in the construction of the fusion device. 
     The upper section  11  is formed with an end wall  21  a top surface  12  and depending sidewalls  22  and  23 . The sidewalls terminate in an inclined plane  24  which extends from the end wall  21  to the top surface  12 . The top surface  12  has a large aperture  25  therethrough to provide for bone ingrowth. The top surface  12  has a narrower groove  26  extending along the sidewalls  22  and  23 . The groove  26  engages the flange  43  of distractor  42  to guide the relative movement of the sections maintaining the distractor  42  and the depending sidewalls in alignment. The link  40  has a bore  27  with internal threads  28  to cooperate with the threads  41  on the link  40 . 
     The bottom surface  14  of the lower section  13  has a large aperture  30 , as shown in  FIG. 1 , to facilitate bone ingrowth after implantation. The lower section  13  is a U-shaped channel with opposed upstanding sidewalls  31  and  32  projecting from the bottom surface. The side walls  31  and  32  have a short end  33  and a long end  34 . The sidewalls  31  and  32  terminate in an inclined plane extending from the short end  33  toward the long end  34 . The upstanding walls each have a groove  35  along the edge of the inclined plane. The movement of the flange  44  through the groove  35  contributes to the alignment of the distractor  42  and lower section as they move relative to each other. 
     The ends of the inclined planes of the upstanding and depending walls are smooth ramps to provide ease in the relative sliding contact between the distractor and upper and lower section surfaces. Other embodiments of the complementary surfaces may provide additional or substitute guidance to maintain the upper and lower sections in alignment during movement of the contacting surfaces of the inclined planes, such as, the ends of the inclined planes may be sloped across the thickness of the side walls or a stepped ramp may be used. 
     The ramp or distractor  42  is dimensioned to be inserted into the trailing end of the interior cavity between the upper section and the lower section of the spinal infusion device  10 , as shown in  FIG. 1 . An end wall  36  is dimensioned to close the opening formed in the trailing end between the upper section  11  and the lower section  13  by the depending and upstanding sidewalls. The upper surface of the plug has an inclined ramp on each side to accommodate the inclined plane  24  of the depending walls  22  and  23  of the upper section. The end wall  36  has a larger circumferential end dimensioned to extend to the outer periphery of the upper and lower sections to make a smooth trailing end outer surface. Extending from the end wall  36  into the cavity of the hollow structure  10  is the body  47  of the distractor  42 . The body is connected to the end wall  36  by two rails  48  and  49  leaving the central area open for bone ingrowth. The end plug  36  has a bore  61  aligned with bore  60  in link  40 . The bore  61  has a larger countersunk bore  63  in the end wall  36 . These bores are aligned with the threaded tube  29  attached to the link  40 , as shown in  FIG. 3 . 
     The leading ends of the upper and lower sections are formed with a vertical slot  64 . Link  40  includes an upper flange  65  and a lower flange  66  of a size and shape to slide within the vertical slot  64  as the distractor  42  moves into the central cavity foreshortening the implant and increasing the distance between the leading ends of the sections. The threaded tube  29  surrounds the bore  60  and extends toward the bore  61 . A jack screw  67  is inserted through bore  61  engaging the threads in the tube  27 . As the jack screw  67  is tightened, the ramp is drawn toward the leading end of the implant and the leading ends of the upper and lower sections slide apart along flanges  65  and  66 . 
     The spinal fusion device is inserted in the disk space between adjacent vertebrae in the extended position with the top surface in contact with the end plate of one vertebra and the bottom surface in contact with the end plate of an adjacent vertebra. The surgeon turns the jack screw  67  causing the upper and lower sections to move along the complementary inclined plane to shorten the fusion device and increase the distance between the end plates of the adjacent vertebrae. The adjustment may continue until the optimum distance between vertebrae has been reached. At this time, the jack screw may be removed and replaced by a bolt (not shown) of sufficient length to retain the upper and lower sections together. 
     In  FIGS. 4 ,  5  and  6 , another embodiment of the implant  10  is illustrated with integral brackets on the upper and lower sections for engaging adjacent vertebrae. Each bracket has apertures therethrough for placing bone screws into the adjacent vertebra. The bone screws add stability to the implant and provide additional security to prevent dislodgement of th implant under normal activity. 
     The upper section has a bracket  70  attached to the trailing end wall. As shown, the bracket extends normal to the top surface  12  in a direction away from the distractor  42 . The lower section  13  has a bracket  71  attached to the trailing end wall and extending in the opposite direction from the lower section. Each bracket  70 ,  71  is shown with countersunk apertures  72 ,  73 ,  74  and  75 . Bone screws  76 ,  77 ,  78  and  79  are inserted into the apertures and threaded into the vertebrae. 
     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.