Abstract:
A surgical plate system including a surgical plate affixable to bone or other rigid tissue and a method for use of such a system. A connector body protruding from a secondary plate is matable in a receiver defined in a primary plate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to surgical plates used to join two or more areas of bone or other tissue, and particularly to a method and apparatus for placing an additional plate immediately adjacent to or overlapping an area to which a plate was previously affixed.  
         [0002]     Surgeons use surgical plates to immobilize a fractured bone to enable healing. Conventional surgical plates are integrally formed as rigid plates, and are secured to bone or other tissue by means of fasteners such as screws. A plate is placed approximately transversely to the fracture. Each end area of the plate is attached to bone, and the plate spans the fracture, so that fasteners are placed on either side of the fracture, allowing the plate to pull the fractured bone together and enable healing.  
         [0003]     Plates are also used to fuse vertebrae, which is often necessary to relieve debilitating pain or correct a deformity in the spine. To perform a typical spinal fusion, the disk between the vertebrae which are to be fused is removed and a bone graft is inserted in its place. A plate is then attached to the vertebrae, spanning the graft, and the plate immobilizes the vertebrae adjacent to the graft until the fusion is complete. Fasteners are used to attach the plate to both vertebrae, so that the plate spans the bone graft and immobilizes the area of the spine which is to be fused. A conventional plate may be generally rectangular and may have holes in its corners through which fasteners such as screws extend into the bone against which the plate is placed.  
         [0004]     Often, once a spinal fusion or fracture repair is made, especially in osteoporotic individuals, the patient experiences a complication called transition zone syndrome. Transition zone syndrome is a premature degeneration of a section of bone adjacent to a fusion or plate placement. The causes of transition zone syndrome are not well understood. It is hypothesized that increased stresses transferred to the adjacent segment of bone by the previous surgical procedure precipitate the premature degeneration. If transition zone syndrome occurs, an additional bone fracture or the weakening, damage, or rupture of a disk can occur immediately adjacent to the previous plate, requiring an additional repair immediately adjacent to the old plate. Unfortunately, such a repair is very difficult to perform using conventional methods. The old plate over time becomes embedded in tissue, and significant displacement of such tissue is required to gain access to the old plate, which conventionally must be unscrewed and pried off of the bone. This is difficult and potentially dangerous. Accordingly, when faced with the problem of a new injury adjacent to an old plate, surgeons may be unable to use conventional fasteners to affix the new plate to the bone. Surgeons may tie the new plate to the bone, but this is less effective than use of a screw or conventional fastener. Moreover, plates are intended to function as tension bands. Tension is force tending to separate the bones or fractured parts of bones longitudinally to the plate. Compression is force tending to compress the bones or fractured parts of bones. Plates are intended to strengthen or immobilize a bone or other tissue construct by maintaining tension rather than resisting compression. They are generally attached to the convex side of a curved long bone for example, and pull the fractured parts of the bone together. Therefore, a plate should be able to withstand axial tension, or force tending to separate bones held together by a plate longitudinal to the plate. A plate that is tied to the bone instead of screwed to the bone may not effectively withstand axial tension.  
         [0005]     What is desired, then, is to be able to attach a secondary plate to the area adjacent to a pre-existing plate in such a way as to preserve the secondary plate&#39;s function as a tension band without removing the pre-existing plate.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with a first aspect of the present invention, a plate system attachable to body tissue for interconnecting two adjacent areas of body tissue is provided in which a first plate having side margins and ends, said plate defining a receiver, is installed to support healing bone tissue. A secondary plate including a connector body shaped to matingly fit into the receiver is provided. The secondary plate may be added at a time subsequent to placement of the first plate and is attached to the first plate by the connector body and to the bone by fasteners such as screws.  
         [0007]     Another aspect of the invention is a method of surgically providing a support mechanism for adjacent body structures by applying a plate system to body tissue, wherein a first plate defines a receiver, matingly connectable with a connector body found on a second plate.  
         [0008]     In one embodiment of the method, the first plate is attached to bone by fasteners, then the secondary plate is attached to the first plate, by mating the connector body with the receiver, and is attached to the bone by fasteners.  
         [0009]     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0010]      FIG. 1  is a simplified front view of a section of spine to which is affixed a surgical plate embodying an aspect of the invention.  
         [0011]      FIG. 1A  is a section view taken on line  1 A- 1 A in  FIG. 1 .  
         [0012]      FIG. 2  is a front view of a section of spine to which is affixed a surgical plate such as that shown in  FIG. 1 , together with an isometric view of a special punch, and showing an area internal to the receiver of the plate cleaned of tissue by use of the punch.  
         [0013]      FIG. 3  is a front view of a section of spine to which are affixed a plate as shown in FIG. I and a secondary plate.  
         [0014]      FIG. 3A  is a sectional view taken along lines  3 A- 3 A in  FIG. 3 .  
         [0015]      FIG. 4  is a top view of an alternate embodiment of the plate system disclosed herein.  
         [0016]      FIG. 5  is a top view of a second alternate embodiment of the plate system disclosed herein.  
         [0017]      FIG. 6  is a top view of a third alternate embodiment of the plate system disclosed herein.  
         [0018]      FIG. 7  is a top view of a long bone fracture to which are affixed a plate as shown in FIG. I and a secondary plate. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]     Referring now to  FIGS. 1-1A  of the drawings which form a part of the disclosure herein, a surgical plate  2  is integrally formed from a rigid material and is attachable to rigid body tissue such as bone. The plate  2  may be attached to vertebrae or a long bone  64  such as a femur (see  FIG. 7 ). The plate  2  has a body  4  including side margins  6  and end  8 . The plate  2  is manufactured using techniques known in the art and may be made of biocompatible material, such as titanium, titanium alloy, or stainless steel. The plate  2  should be relatively light in weight but should be strong enough to withstand expected amounts of tension in use. It should be relatively thin and generally planar or may be slightly curved as shown in  FIG. 1A , to conform to the shape of bone to which it is intended to be attached. The plate  2  may have a thickness  7  of 2.5 mm for example, although the thickness  7  is determined depending on where it is designed to be placed. It has receptacles  12  to accommodate fasteners  10  such as screws, nails, or tacks and can include a conventional locking mechanism (not shown) to immobilize them once they are installed. The receptacles  12  can preferably accommodate up to 15 degrees of variation in fastener angle in order to allow the vertebrae being fused together to subside, or move closer to one another, as healing occurs.  
         [0020]     The plate  2  includes a receiver  14  in one or both ends  8 . The receiver  14  is shaped such that a relatively narrow channel  16  extends to a larger bay  18 . The difference in width between the channel  16  and bay  18  is defined by a shoulder angle  20  (see  FIG. 2 ) between the sides of the channel  16  and surfaces  19  defining the bay  18 . The shoulder angle  20  should be less than 145° and must be less than 180°, and the surfaces  19  are preferably perpendicular to the general plane of the plate  2 . The shoulder angle  20 , relatively narrow channel  16 , and larger bay  18  allow a secondary plate  22  with a connector body  24  sized and shaped to fit matingly with the receiver  14  to lock in place so that the construct resists tension in a direction axial to the plate along line  67  (see  FIG. 7 ), so that the plates cannot be pulled apart once the plates are connected. The specific shape of the receiver may vary. It may be characterized by a narrow channel  104  and a round bay  102  ( FIG. 5 ), a triangular bay  124  ( FIG. 6 ), a bar-shaped bay such that the channel and bay form a T-shape  74  ( FIG. 4 ), or other variations.  
         [0021]     When a surgical procedure is performed to create spinal fusion, such as a fusion of two or more cervical vertebrae, the disk  26  between two adjacent vertebrae  28   b ,  28   c  is removed, a bone graft  30  is inserted, and a plate  2  is affixed to the vertebrae such that it spans the graft  30  and immobilizes the vertebrae relative to the graft. The immobilized vertebrae  28   b ,  28   c , then fuse together with the graft  30 , as a result of biological action, and tissue will eventually grow tightly adjacent the ends  8  and side margins  6 . The plate  2  is affixed to the vertebrae  28   b ,  28   c  in the same manner in which conventional surgical plates are implanted, using fasteners  10  placed preferably in each of the corners  34  defined generally by the intersection of the side margins  6  and ends  8 .  
         [0022]     After the procedure is completed, the patient may experience a subsequent fracture, rupture, or deformity of a disk adjacent to the fused vertebrae. This subsequent injury may require further repair employing a surgical plate immediately adjacent to the first plate. In this event, the injured disk is removed, and the first plate is prepared for attachment of the secondary plate. A punch  40  specially shaped to fit matingly within the receiver is used to remove tissue which has subsequently formed within the receiver  14 , as shown in  FIG. 2 . The punch  40  has a handle  56  which permits the surgeon to apply pressure manually or by use of a mallet to chisel away any tissue accumulated within the receiver  14 . The punch has sharp edges  54  which facilitate the removal of tissue. Other tools commonly used for scraping or chiseling may also be used to remove accumulated tissue. Once sufficient tissue has been removed, a secondary plate  22  is installed, as shown in  FIG. 3 . The secondary plate  22  includes receptacles  12  for fasteners  10 . The secondary plate has a connector body  24  which is shaped to fit matingly within the receiver  14  of the plate  2 , the connector body  24  including a narrow neck portion  52  corresponding with the channel  16  of the receiver  14  and wider head  48  corresponding with the bay  18  of the receiver in shape and size. The connector body  24  is inserted into the receiver  14  and fasteners  10  are used to fasten the secondary plate to the vertebrae on either side of the new fusion. Preferably at least one fastener such as a screw  33  is placed through the connector body  24 , fastening the secondary plate  22  to one of the fused vertebrae  28 b to which the original plate  2  is also attached so that the plates are aligned to be coplanar as shown in section view in  FIG. 3A , so that the surfaces  19  of the bay  18  facing away from the end  8  are aligned with and face toward the surface  25 . Further fasteners  32   a  are used to attach the main body  42  of the secondary plate  22  to the vertebra  28   a  on the other side of the graft  30  so that the secondary plate spans the new vertebra to be fused. Once the connector body  24  is mated with the receiver  14 , the plate system can withstand axial tension because the plates are interconnected and cannot be separated by force in an axial direction, indicated by the arrow  69  in  FIG. 3A . The shoulder angle  20  of the receiver channel  16  and bay  18  corresponds with the shoulder angle of the neck  52  and head  48  of the connector body  24  so that the two plates interlock and cannot be pulled apart. Thus the interconnection between the mated plates can withstand axial tension. As shown in  FIGS. 3 and 3 A the fastener  33  maintains the connector body  24  in a coplanar relationship with the receiver  14 . The first plate  2  is anchored by corner fasteners  32 . When the connector body and receiver are coplanar, tension forces cause the corresponding surfaces  19  on the sides of the bay  18  which face away from the end  8  of the first plate to press against opposed corresponding surfaces  25  of the connector body  24 , allowing the plate system to resist tension.  
         [0023]     The fit between the connector body  24  and the receiver  14  is relatively tight, with approximately one-half to one millimeter of gap  50  between the two components. In this way, the fit is tight enough to permit the plate construct to function as a tension band, but the fit is loose enough to allow the placement of the transition plate notwithstanding the accumulation of tissue in the receiver  14  and possible incomplete removal with the punch  40 . The receiver  14  and connector body  24  can take a variety of shapes.  FIGS. 4, 5  and  6  show alternative shapes.  
         [0024]      FIG. 4  shows an alternate embodiment of the plate system in which the plate  68  has a rounded T-shaped receiver  75  including a narrow channel  76  and the secondary plate  72  has a rounded T-shaped connector body  78  including a bar shaped head  80 . The shoulder angle  70  defined by the intersection between the channel  76  and the bay  74  is approximately 90 degrees. A fastener  84  is placed in the connector body  78  to hold it in generally coplanar alignment with the receiver  75  in the plate  72 .  
         [0025]      FIG. 5  shows yet another alternate embodiment of the plate system in which the plate  100  has a round receiver  108  including a round bay  102  and a narrow channel  104 , and the secondary plate  90  has a connector body  98  with a round head  96  with a narrow neck  92 . The shoulder angle  106  defined by the intersection between the channel  104  and the head  102  is between 100 degrees and 120 degrees. A fastener  94  is placed in the connector body  96 , to hold it in generally coplanar alignment with the receiver  108  in the plate  100 .  
         [0026]      FIG. 6  shows another alternate embodiment of the plate system in which the plate  122  has a receiver  126  with a narrow channel  128  and a triangular shaped bay  124 , and the secondary plate  110  has a connector body  116  with a triangular head  120  and narrow neck  112 . The shoulder angle  114  defined by the intersection between the channel  128  and the bay  124  is between 100 degrees and 170 degrees. A fastener  118  is placed in the connector body  116  to hold it in generally coplanar alignment with the receiver  126  in the plate  122 .  
         [0027]      FIG. 7  shows a long bone  64  with a fracture  58  spanned by a plate  2 . Subsequent to installation of the surgical plate  2  the patient has developed transition zone syndrome, a secondary transition zone fracture  60  has occurred next to the pre-existing plate  2 . To repair the secondary, transition zone fracture  60 , a secondary plate  22  has been installed and spans the second fracture  60 . The punch  40  is used to remove tissue from the area of the receiver  14  (see  FIG. 2 ). The secondary plate  22  is installed by inserting the connector body  24  into the receiver  14  and attaching it to the bone  64  with fasteners  10 . The connector body  24  includes at least one fastener  33  to hold it in generally coplanar alignment with the receiver  14  in the plate  2 . Because of the fastener  33  in the connector body, fasteners are placed in either side of the new fracture, better enabling the plate system to perform its immobilization function as a tension band.  
         [0028]     The plate system can be used to immobilize any bone or rigid tissue found in the human or any mammalian body, where conventional plates may be used.  
         [0029]     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.