Abstract:
An orthopedic bone plate constructed from shape memory material provides the ability to move from an open shape to a compressed shape and create compression on two bones or bone fragments to encourage healing. The plate may be any number of shapes, with two or more screws anchoring the plate to bone. The plate is affixed to bone in a sequence of steps that involve first placing the plate on an insertion tool, attaching drill guide tubes, placing the plate over bone, drill holes in bone, and then attaching the plate to the bone via screws. The insertion tool can then be removed at the surgeon&#39;s convenience allowing compression on the two bones.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to compressing plates and more particularly but not by way of limitation to a method and apparatus for the use of compressing plates to assist in osteosynthesis. 
         [0003]    2. Description of the Related Art 
         [0004]    Wire, staple, and plate fixation of bone have been used clinically for decades, In the last 20 years or so, nickel-titanium and shape memory materials have been used in orthopedics for their shape changing and superelastic properties. Shape memory devices feature martensitic and austenitic form, in which the addition of energy in the form of heat transforms the device from a temporary martensite state to a final austenite state at a defined temperature. The heat for transformation generally is categorized as being (1) room temperature activated (i.e. superelastic), (2) body temperature activated (i.e. body temperature), and (3) above body temperature activated (i.e. heated). The use of a shape memory plate, capable of transforming from a preliminary shape to a compressed final shape, presents unique challenges. If the plate is superelastic, then the plate is inclined to immediately transform at room temperature, making implantation and the use of screws difficult for a surgeon. If the plate is body temperature or heated, then the surgeon has to rely on either body heat, which is reduced during surgery due to the open wound, or an external heating source to transform the plate. For various reasons, many surgeons would prefer a superelastic shape memory plate. 
         [0005]    Accordingly, an apparatus and a method of surgical use for a shape memory plate that restrains the plate in an open position while screws are attached and then releases the plate to compress the bones and assist with osteosynthesis would provide an improvement in compressing plate surgeries. 
       SUMMARY OF THE INVENTION 
       [0006]    In accordance with the present invention, a fixation system includes a plate adapted for affixing between a first bone and a second bone and an insertion tool. The plate defines a central opening and is configurable between an open shape and a compressed shape. Once the plate has been moved to its open shape, the insertion tool inserts into the central opening and abuts the plate to retain the plate in its open shape. The insertion tool allows locating of the plate at the first bone and the second bone. After the plate has been affixed to the first and second bones, the insertion tool releases the plate allowing the plate to move from its open shape its compressed shape, thereby compressing the first bone with the second bone. 
         [0007]    The plate includes a first end portion defining a first screw hole and a second end portion defining a second screw hole. The plate further includes first and second arms disposed between the first and second end portions. such that the first and second end portions and the first and second arms define the central opening. The first and second arms expand to configure the plate in its open shape and contract to configure the plate in its compressed shape. 
         [0008]    The insertion tool includes a retention spacer that inserts into the central opening of the plate when the plate is in its open shape such that the retention spacer abuts the first and second end portions of the plate to retain the plate in its open shape. The insertion tool further includes a platform having a first guide hole that aligns with the first screw hole and a second guide hole that aligns with the second screw hole when the plate is in its open shape. 
         [0009]    The fixation system includes a first guide tube that inserts through the first guide hole of the platform and engages the first screw hole of the plate and a second guide tube that inserts through the second guide hole and engages the second screw hole of the plate. The fixation system also includes locating pins that insert through the first and second guide tubes for the purpose of creating pilot holes in the first and second bones. The locating pins further retain the plate at the first and second bones. The locating pins include marks that represent the depth of the locating pins within the first and second bones. 
         [0010]    The plate pre-loaded on the insertion tool may be delivered in a sterile package. Likewise, the first and second guide tubes coupled with the plate may be delivered in the sterile package along with the plate pre-loaded on the insertion tool. 
         [0011]    A first bone is affixed with a second bone as follows. A plate in its open shape couples with an insertion tool. A first drill guide tube engages a first screw hole of the plate, and a second drill guide tube engages a second screw hole of the plate. The insertion tool locates the plate onto first and second bones. A first locating pin inserts through the first drill guide tube and drills into the first bone. A second locating pin inserts through the second drill guide tube and drills into the second bone. The first locating pin removes from the first drill guide tube, and the first drill guide tube disengages from the plate. A first screw inserts through the first screw hole of the plate and into the first bone. The second locating pin removes from the second drill guide tube, and the second drill guide tube disengages from the plate. A second screw inserts through the second screw hole of the plate and into the second bone. The insertion tool decouples from the plate such that the plate moves to its compressed shape. 
         [0012]    Other objects, features, and advantages of the present invention will become evident to those of ordinary skill in the art in light of the following. Also, it should be understood that the scope of this invention is intended to be broad, and any combination of any subset of the features, elements, or steps described herein is part of the intended scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  provides an isometric view of a shape memory plate in an initial stretched shape. 
           [0014]      FIG. 2  provides an isometric view of the shape memory plate in a final compressed shape. 
           [0015]      FIG. 3  provides an isometric view of a drill guide tube. 
           [0016]      FIG. 4  provides a side view of the drill guide tube. 
           [0017]      FIG. 5  provides an isometric view of a locating pin. 
           [0018]      FIG. 6  provides an isometric view of a screw. 
           [0019]      FIG. 7  provides an isometric view of an insertion tool. 
           [0020]      FIG. 8  provides a side view of the insertion tool. 
           [0021]      FIG. 9  provides a top view of the insertion tool. 
           [0022]      FIG. 10  provides an isometric view of the shape memory plate in its stretched shape affixed to the insertion tool with drill guide tubes in place. 
           [0023]      FIG. 11  provides a bottom view of a shape memory plate in a stretched shape affixed to an insertion tool with drill guide tubes in place. 
           [0024]      FIG. 12  provides an isometric view of the shape memory plate situated on two bones and affixed in its stretched shape to the insertion tool with drill guide tubes in place. 
           [0025]      FIG. 13  provides an isometric view of the shape memory plate situated on two bones and affixed in its stretched shape to the insertion tool with drill guide tubes and locating pins in place. 
           [0026]      FIG. 14  provides an isometric view of the shape memory plate situated on two bones and affixed in its stretched shape to the insertion tool with one drill guide tube and locating pin in place and one screw being inserted. 
           [0027]      FIG. 15  provides an isometric view of the shape memory plate situated on two bones and affixed in a stretched shape affixed to the insertion tool with one screw in place and one screw being inserted. 
           [0028]      FIG. 16  provides an isometric view of the shape memory plate situated on two bones and affixed in a stretched shape to the insertion tool with two screws in place. 
           [0029]      FIG. 17  provides an isometric view of the shape memory plate in its final compressed shape affixed to two bones by two screws, and released to create compression. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0030]    As required, a detailed embodiment of the present invention is disclosed herein; however, it is to be understood that the disclosed embodiment is merely exemplary of the invention, which may be embodied in various forms. It is further to be understood that the figures are not necessarily to scale, and some features may be exaggerated to show details of particular components or steps. 
         [0031]      FIG. 1  illustrates an orthopedic plate  10 . The plate can be fabricated from a shape memory material such as nitinol (nickel-titanium), or any other elastic material capable of deforming and rebounding to an original shape. The plate  10  is shown in a constrained and stretched open shape  100 . In the preferred embodiment, the plate  10  includes a body portion  16  defining a screw hole  11  and a body portion  17  defining a screw hole  12 . Nevertheless, one of ordinary skill in the art will recognize that the plate  10  may include more or less body portions and screw holes depending upon the type of surgery. The screw holes  11  and  12 , or any number of screw holes, can be smooth, tapered, or threaded as necessary to engage a screw. In the preferred embodiment, the screw holes  11  and  12  are shown with threads. The plate  10  also includes moveable arms  13  and  14  formed integrally with and between the body portions  16  and  17 . Nevertheless, one of ordinary skill in the art will recognize that the plate  10  may include more moveable arms depending upon the type of surgery. The moveable arms  13  and  14  and the end portions  16  and  17  define therebetween a central opening  15 , which has been elongated when the plate  10  resides in its open shape  100 . The central opening  15  may be any shape, as long as it allows two or more moveable arms  13  and  14  space to move between open and compressed positions. 
         [0032]      FIG. 2  illustrates the same plate  10 , except in a compressed shape  101 , which is the original fabrication shape of the plate  10 . In this shape, the screw holes  11  and  12  can remain circular or change shape if it is desired that they bind upon screws. By application of some energy source, from room temperature, body temperature, or external, the moveable arms  13  and  14  have changed shape from the open shape  100  to the compressed shape  101 . In the compressed shape  101 , the moveable arms  13  and  14  have contracted and along with the end portions  16  and  17  define a central opening  15  of a different contracted shape than the elongated shape of the open shape  100 . 
         [0033]    The plate  10  begins in the compressed shape  101  and through application of an external force, the plate is moved from its compressed shape  101  to its open shape  100 . In particular, the application of an external force causes the moveable arms  13  and  14  to stretch and expand, elongating the plate  10  and thus the central area  15  into the open shape  100 . After application of some energy source, from room temperature, body temperature, or external, the moveable arms  13  and  14  contract and shrink, contracting the plate  10  and thus the central area  15  into the compressed shape  101 . 
         [0034]      FIGS. 3  and illustrate a drill guide tube  20 . The drill guide tube  20  can be made from metal or plate, and has an inner cannulation of diameter  21  and an outer surface  22 . A shoulder  23  is a location where a large outer surface  22  reduces to a new small outer surface  24  of smaller diameter. The screw threads  25  extend from the small outer surface  24 , and are of the same thread characteristics needed to mate with the screw holes  11  and  12  of the plate  10 . 
         [0035]      FIG. 5  illustrates a locating pin  30 . The locating pin  30  can be manufactured of any material; in the preferred embodiment, it is made from medical grade metal. The locating pin  30  has cutting flutes  31  for cutting through bone. A shank  32  of the locating pin  30  is of a diameter that will fit into the inner cannulation  21  of the drill guide tube  20 . A short sizing line  33  is an ink or engraved mark on the surface of the locating pin  30  to define a certain depth for drilling of a pilot hole. Similarly, a long sizing line  34  is also a mark for defining depth of a pilot hole, only it encircles the circumference of the locating pin  30 . 
         [0036]      FIG. 6  illustrates a screw  40  designed to attach the plate  10  to a bone. In the preferred embodiment, the screw  40  has two threaded sections, shank threads  41  and head threads  42 . The shank threads  41  are designed to engage bone once inserted into a pilot hole created by the locating pin  30 . There is any number of thread characteristics related to pitch, diameter, and threads per inch that will accomplish this purpose. The head threads  42  are designed to engage the screw holes  11  and  12  of the plate  10 . 
         [0037]      FIGS. 7-9  illustrate an insertion tool  50 . The insertion tool  50  consists of a handle  51 , a shaft  52 , a platform  53 , and a retention spacer  56 . The handle  51  can be any shape such that it ergonomically fits a surgeon&#39;s hand. The shaft  52  can be any length or angle as required to position the platform  50  on a desired bone surface. In some applications, the shaft  52  might not be needed at all, and could thus be eliminated from the insertion tool  50 . The platform  53  is a solid material such as metal or plastic, designed to space drill guide holes  54  and  55  to the proper separation distance, as well as retain the plate  10  in the open shape  100 . Thus, the drill guide holes  54  and  55  of the platform  53  correspond to the separation distance of the screw holes  11  and  12  of the plate  10  when it is in the open shape  100 . The retention spacer  56  is designed to substantially match the length of the central opening  15  of the plate  10  when the plate  10  resides in its open shape  100 , and is made from a solid material such as plastic or metal. In this preferred embodiment, the retention spacer  56  is rectangular shape. The shape of the retention spacer  56  is not critical, as long as theretention spacer  56  fits within the central opening  15  when the plate  10  resides in its open shape  100  and includes raised side portions  18  and  19  that abut the end portions  16  and  17  such that the retention spacer  56  holds the plate  10  in the open shape  100 . 
         [0038]      FIGS. 10-11  illustrate an assembly showing the plate  10 , the two drill guide tubes  20 , and the plate insertion tool  50 . The plate  10  is in the open shape  100  in this configuration. The small outer surface  24  of the drill guide tubes  20  pass through the drill guide holes  54  and  55  that are located on the platform  53  of the insertion tool  50 . The screw threads  25  on the drill guide tubes  20  are screwed into the holes  11  and  12  of the plate  10 . The retention spacer  56  is positioned in the central opening  15  of the plate  10  such that the ends of the retention spacer  56  abut the end portions  16  and  17  resulting in the retention spacer  56  maintaining the plate  10  in its open shape  100 . The screw threads  25  on the drill guide tubes  20  are screwed into the holes  11  and  12  of the plate  10 . 
         [0039]      FIGS. 12-17  illustrate a method of use for a shape memory plate to fixate two bones or bone fragments in a surgery. The surgical procedure begins with the surgeon trying to fixate a first bone  71  and a second bone  72 . As illustrated in  FIG. 12 , the plate  10  in the open shape  100  as a result of the insertion of theretention spacer  56  into the central opening  15  is positioned on top of a bone fusion interface  73 , which lies between a first bone  71  and a second bone  72 . The screw holes  11  and  12  of the plate  10  are positioned so that the screw hole  11  is over the first bone  71  and screw hole  12  is over the second bone  72 . In the preferred method, the plate  10  positioned in its open shape  100  is centered over the fusion interface  73  between the first bone  71  and the second bone  72 . The drill guide tubes  20  are screwed into the plate  10 , passing through the platform  53  of the insertion tool  50 . 
         [0040]    After positioning the assembly as shown in  FIG. 12 , the surgeon uses two locating pins to temporarily anchor the plate  10  in place and measure screw lengths. As illustrated in  FIG. 13 , the two locating pins  30  which have been drilled into place pass through the drill guide tubes  20 , through the platform  53  of the insertion tool  50 , through respective screw holes  11  and  12  of the plate  10 , and then into respective first and second bones  71  and  72 . The short and the long sizing lines  33  and  34 , respectively, can now be used to assess the depth of a screw  40  to anchor the plate  10 . 
         [0041]    At this time, the surgeon would be ready to screw the plate  10  to the first and second bones  71  and  72 . As illustrated in  FIG. 14 , the plate  10  is positioned in its open shape  100  over the first and second bones  71  and  72  as well as centered over the fusion interface  73 . One of the drill guide tube  20  remains attached to the plate  10 , while the other drill guide tube  20  has been removed from the plate  10  and the platform  53  of the insertion tool  50 . At this point, the insertion tool  50  remains attached to the plate  10  with the retention spacer  56  residing within the central opening  15  of plate  10 . The screw  40  is screwed into the screw hole  11  of the plate  10 . To reach the screw hole  11 , the screw  40  passes through the screw hole  54  of the insertion tool  50 . The head threads  42  of the screw  40  mate with the screw hole  11  of the plate  10 . Once the screw  40  is fully in place, one side of the plate  10  will be anchored to the first bone  71 . 
         [0042]    Referring to  FIG. 15 , once the first screw  40  has been screwed into place in the first bone  71 , the remaining drill tube  20  is removed from the plate  10  and the platform  53  of the insertion tool  50 , and a second screw  40  is screwed into the screw hole  12  of the plate  10 . The second screw  40  passes through the screw hole  55  of the insertion tool  50 . After both the first and second screws  40  have been screwed into place, the insertion tool  50  remains positioned relative to the plate  10  such that the retention spacer  56  is in the central opening  15  of plate  10  as illustrated in  FIG. 16 . The plate  10  thus is screwed to the first bone  71  and the second bone  72  and centered over the bone fusion interface  73 . 
         [0043]      FIG. 17  illustrates the final step in the implantation of the plate  10  in the first bone  71  and the second bone  72 . The insertion tool  50  is removed from the plate  10  due to the extraction, rotation, pulling, and/or or jiggling of the retention spacer  56  from the central opening  15  of the plate  10 . The first and second screws  40  are positioned, respectively, in the screw holes  11  and  12  of the plate  10 , and thus anchor the plate  10  to the first bone  71  and the second bone  72 . With the retention spacer  56  removed, the shape memory plate  10  can now respond to room temperature, body temperature, or external energy input and transform in shape from its open shape  100  to its compressed shape  101 . In particular, the moveable arms  13  and  14  decrease in length resulting the first central opening  15  transitioning in shape to the second new central opening  18 . While the moveable arms  13  and  14  transform the plate  10  in this preferred embodiment, one of ordinary skill in the art will recognize that there are any number of designs, orientations, shapes, and numbers of moveable arms that would create the same transformation effect. Upon the transitioning of the plate  10  to its compressed shape  101 , compression is created between the first bone  71  and the second bone  72  at the bone fusion location  73 . 
         [0044]    Summarizing the implantation, the surgeon selects a shape memory plate implant pre-loaded onto an insertion tool. The plate can also be pre-loaded with drill guide tubes, or those can be attached during surgery. The surgeon positions the plate at the juncture of two bones to be fused or fixated, and uses locating pins to temporarily hold the plate to the bones. The surgeon then removes one locating pin and drill guide tube, replaces it with a screw to hold one side of the plate in place, and then removes the second locating pin and drill guide tube to allow the second screw to be placed. 
         [0045]    The ingenuity of this system is as follows. A shape memory plate that creates compression has to be held open until both sides of the plate are anchored in bone, lest the compressive force be released too early. This can be accomplished initially with an insertion tool that props open the plate. However, the plate has to be anchored to the bone before the insertion tool can be removed, to preserve the compressive force until the surgeon is ready. This then requires that the screws pass through the insertion tool in some way. The aforementioned method for implantation accomplishes these objectives. Furthermore, this method allows the surgeon to select the timing of the application of compressive force. A surgeon could potentially implant more than one plate, and leave the insertion tools in place, only to release them at the appropriate time. This sequence could allow more complex surgeries to take place. Furthermore, since the presence of the insertion tool can hide or obscure the visibility of the plate from the surgeon, the two locating pins insure that the plate remains properly oriented on the bones. 
         [0046]    To use this shape memory plate, a medical device company or hospital could pre-load certain elements of the system prior to surgery. The shape memory plate  10  must be stretched from its compressed shape  101  shown in  FIG. 2 , to its open shape  100  shown in  FIG. 1 . The plate must then be held open via an insertion tool, such as insertion tool  50 , which restrains the plate  10  in an open shape  100 . This then allows for a method of preparation of the plate. Plate  10  is stretched from compressed shape  101  to open shape  100 . Plate  10  is placed on insertion tool  50 . Drill guides  20  can optionally be attached prior to surgery or at the time of surgery. It is also contemplated that the pre-loaded plate could be delivered in a sterile package. 
         [0047]    Although the present invention has been described in terms of the foregoing preferred embodiment, such description has been for exemplary purposes only and, as will be apparent to those of ordinary skill in the art, many alternatives, equivalents, and variations of varying degrees will fall within the scope of the present invention. That scope, accordingly, is not to be limited in any respect by the foregoing detailed description; rather, it is defined only by the claims that follow.