Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. Ser. No. 10/985,598, filed Nov. 10, 2004, and U.S. Ser. No. 11/040,779, filed Jan. 21, 2005, which are hereby incorporated by reference herein in their entireties. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates broadly to surgical implants. More particularly, this invention relates to a bone fracture fixation system. 
     2. State of the Art 
     Fracture to the metaphyseal portion of a long bone can be difficult to treat. Improper treatment can result in deformity and long-term discomfort. 
     By way of example, a Colles&#39; fracture is a fracture resulting from compressive forces being placed on the distal radius, and which causes backward or dorsal displacement of the distal fragment and radial deviation of the hand at the wrist. Often, a Colles&#39; fracture will result in multiple bone fragments which are movable and out of alignment relative to each other. If not properly treated, such fractures may result in permanent wrist deformity and limited articulation of the wrist. It is therefore important to align the fracture and fixate the bones relative to each other so that proper healing may occur. 
     Alignment and fixation of a metaphyseal fracture (occurring at the extremity of a shaft of a long bone) are typically performed by one of several methods: casting, external fixation, pinning, and plating. Casting is non-invasive, but may not be able to maintain alignment of the fracture where many bone fragments exist. Therefore, as an alternative, external fixators may be used. External fixators utilize a method known as ligamentotaxis, which provides distraction forces across the joint and permits the fracture to be aligned based upon the tension placed on the surrounding ligaments. However, while external fixators can maintain the position of the wrist bones, it may nevertheless be difficult in certain fractures to first provide the bones in proper alignment. In addition, external fixators are often not suitable for fractures resulting in multiple bone fragments. Pinning with K-wires (Kirschner wires) is an invasive procedure whereby pins are positioned into the various fragments. This is a difficult and time consuming procedure that provides limited fixation if the bone is comminuted or osteoporotic. Plating utilizes a stabilizing metal plate typically placed against the dorsal side of a bone, and screws extending from the plate into holes drilled in the bone fragments to provide stabilized fixation of the fragments. 
     In some cases, a relatively proximal diaphyseal portion as well as the distal metaphyseal portion of the radius may be fractured. In these cases, fragment plates are often used in conjunction with the distal radius plate. There is a disadvantage, however, in using two plates rather than one. It results in unsupported bone between the two implants. The resultant load supported by the bone between the plates in a concentrated manner. Thus, it would be desirable to provide an integrated implant which shares the load across the entire implant for distal and mid-shaft fractures. 
     U.S. Pat. No. 5,190,544 to Chapman et al. describes a modular plating system including a metaphyseal plate and a diaphyseal plate which are interconnected via a dovetail slot and then secured to the bone with cortical bone screws to lock the plates together. The integrity of such a system is subject to loosening in the event the bone screws loosen their engagement with the bone, e.g., through micromotion. Furthermore, if the bone is of poor quality, e.g., as a result of multiple fractures along the bone portion underlying the components, integrity between the components may never be accomplished. In addition, the metaphyseal component which receives an end of the diaphyseal fragment plate is significantly thicker (approximately 75% percent thicker) and wider (approximately 35% wider) than the fragment plate, providing an undesirably thick metaphyseal plate and creating a potentially irritating transition in two dimensions from the metaphyseal plate to the diaphyseal plate where the metaphyseal plate ends. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a modular fixation system. 
     It is another object of the invention to provide a modular fixation system that desirably aligns and stabilizes multiple bone fragments in a fracture to permit proper healing. 
     It is also an object of the invention to provide a modular fixation system which does not rely on the bone for locking the modular components together. 
     It is a further object of the invention to provide a modular fixation system which will not irritate the tissue. 
     It is an additional object of the invention to provide an improved fixation system which accommodates the anatomical structure of the metaphysis and diaphysis of the radius. 
     In accord with these and other objects, which will be discussed in detail below, a fracture fixation plate system for the radius according to the invention includes a plurality of different sized distal radius plates (e.g., volar plates or dorsal plates) and a plurality of different sized fragment plates. The distal radius plates are generally T-shaped having a head and a stem substantially transverse thereto. The end of the stem is provided with a mating structure whereby an end of a fragment plate can be coupled to the distal radius plate. The surgeon can select an appropriate size distal radius plate and an appropriate size fragment plate and secure them together prior to implant to form a unified distal radius and fragment plate customized for the patient. This overcomes the disadvantage of using separate distal radius and fragment plates and allows for a wide variety of different sizes while using the minimum number of components. It is an important aspect of the invention that the distal radius plate and fragment plate be joined without reliance on the bone to join them. Otherwise, the tight interface and coupling between the plates could be compromised based on the quality of the bone, which may be fractured beneath the location of the coupling or which may be osteoporotic. In order to secure the distal radius plate and fragment plate together independent of the bone, set screw holes are provided at both ends of the fragment plates. In addition, suitable mating structure is provided at the end of the radius plate stem, e.g., a slot with an unthreaded orthogonal set screw hole. The two plates are mated by inserting an end of the fragment plate into the slot at the end of the distal radius plate stem, then inserting a set screw through the orthogonal set screw hole to engage the threaded set screw hole in the end of the fragment plate. 
     Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of a distal radius volar plate according to the invention; 
         FIG. 2  is a bottom perspective view of the volar plate; 
         FIG. 3  is top perspective view of a fragment plate according to the invention; 
         FIG. 4  is an enlarged broken bottom perspective view of an end of the fragment plate; 
         FIG. 5  is an enlarged broken top perspective view of an end of the fragment plate; 
         FIG. 6  is a top perspective view of the volar plate with the fragment plate inserted into the slot at the end of the volar plate stem; 
         FIG. 7  is an enlarged broken top perspective view showing the mating of the volar plate and the fragment plate with a set screw; and 
         FIG. 8  is an enlarged perspective view of the set screw. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to  FIGS. 1 and 2 , a distal radius volar fixation plate (or generally an ‘end’ plate or metaphyseal plate)  10  includes a distal head portion  12  and a proximal stem portion  14 . In a preferred embodiment, the plate  10  corresponds to the plate described in previously incorporated U.S. Ser. No. 10/985,598. However, other metaphyseal plates for different bones or different locations on the radius bone can be used. 
     The head portion  12  of the volar fixation plate  10  shown has a plurality of alignment holes  16  which are dimensioned to closely accept K-wires in a fixed angle relationship and two longitudinally offset rows  17   a ,  17   b  of screw holes  18  for receiving fixation elements therethrough. In a preferred embodiment, the screw holes  18  are threaded, and as such are specifically adapted to receive locking screws and pegs which lock relative to the plate. 
     The stem portion  14  has at least one alignment hole  20  dimensioned to closely accept a K-wire and may optionally include one or more (two as illustrated) bone screw holes  22 ,  24 . That is, the stem may be substantially shorter than shown and does not need to include a bone screw hole. The free end of the stem portion  14  includes a slot  26  and an orthogonal set screw hole  28  intersecting the slot. As shown in the Figures, the slot  26  is open to the proximal end of the stem portion, and preferably is also open on the bottom side of the stem portion as well. 
     From the Figures, it will be appreciated that the top side ( FIG. 1 ) of the volar plate  10  has a topography of curved surfaces and recesses surrounding some of the holes to provide a low profile when seated on the anatomical bone surface. The bottom side ( FIG. 2 ) of the head portion  12  is likewise constructed to conform with the anatomy, while the stem portion  14  presents a smooth surface. A portion of the bottom of the head portion  12  lies in a first plane and the stem portion  14  lies in a second plane. A neck  30  transitions betweens the two planes. The angle between the two planes is preferably approximately 25 degrees. 
     The alignment holes and the bone screw holes are used as described in previously incorporated U.S. Ser. No. 10/985,598. The slot  26  and the set screw hole  28  are used in conjunction with a fragment plate and a set screw as described in more detail below. 
     Turning now to  FIGS. 3-5 , an exemplary fragment plate (or diaphyseal plate)  40  according to the invention is illustrated. The fragment plate  40  is an elongate plate having a first end  42  and a second end  44 . A plurality of bone screw holes  46 ,  48 ,  50 ,  52 ,  54 ,  56  are spaced along the length of the plate for receiving bone screws, and a threaded set screw hole  58 ,  60 ,  62 ,  64 ,  66 ,  68  is arranged adjacent each bone screw hole. More particularly, such screw holes are preferably any of the screw holes and associated locking systems described in previously incorporated U.S. Ser. No. 11/040,779, filed Jan. 21, 2005, for the reasons and advantages provided therein, although any suitable bone screw hole may be used. 
     As illustrated, the shape of the fragment plate  40  and the arrangement of holes are preferably longitudinally symmetrical about a mid point  70 . Each set screw hole is provided on a side of a bone screw hole closer to an end of the fragment plate than the midpoint of the plate, with a set screw hole  58 ,  68  specifically being located at each end of the plate. As seen best in  FIGS. 4 and 5 , the ends  42 ,  44  of the plate are tapered as well as rounded. The taper occurs over a significant length which permits both a bone screw hole  46 ,  56  and a set screw hole  58 ,  68  to be located in the tapered ends  42 ,  44  of each plate. Comparing  FIGS. 4 and 5  with  FIGS. 1 and 2 , it will be appreciated that the ends  42 ,  44  of the plate  40  are shaped and dimensioned to fit neatly into the slot  26  of the volar plate  10  with the set screw hole  58 ,  68  of the plate  40  aligning with the set screw hole  28  of the plate  10 . This is illustrated more clearly in  FIG. 6 . The taper at the end of the fragment plate  40  permits the remainder of the fragment plate and the stem  14  of the end plate  10  to have substantially the same width, e.g., approximately 0.43″ for a distal radius fixation system. It is noted that both ends  42 ,  44  of the fragment plate preferably have the same shape and features. Thus either end  42 ,  44  may be inserted into the slot  26  of the plate. 
       FIG. 6  shows the end  42  of the plate  40  inserted into the slot  26  of the plate  10 . The tapered and rounded end  42  of the plate  40  is shaped and dimensioned to fit neatly into the slot  26  of the volar plate  10  with the threaded set screw hole  58  of the plate  40  aligning with the unthreaded set screw hole  28  of the plate  10 . When the two plates are arranged as shown in  FIG. 6 , a set screw  80  is inserted into the hole  28  as shown in  FIG. 7 . When so inserted, the set screw  80  is threaded into the threaded set screw hole  58  in the plate  40 . This secures the two plates together so that they function as a single piece. It is an important aspect of the invention that the distal radius plate and fragment plate be joined without reliance on the bone to join them. Otherwise, the tight interface and coupling between the plates could be compromised based on the quality of the bone, e.g., where such bone is fractured beneath the location of the coupling or where the bone is osteoporotic. 
     The presently preferred set screw  80  has a frustoconical head  82  from which depends a threaded stem  84 . The head  82  has a hex socket  86  adapted to receive a driver (not shown). The set screw provides a secure lock between the two plates independent of the bone. 
     By having a threaded set screw hole  58 ,  68  located near each end of the fragment plate, each such hole can be used to lock the fragment plate to the volar plate, or may alternatively be used to lock an adjacent bone screw in a bone screw hole  46 ,  56  in place. 
     In accord with the invention, the end plate  10  at the slot  26  and the fragment plate  40  are substantially similar in thickness, preferably within approximately 30% of each other, and more preferably approximately 26% (end plate=0.145″ and fragment plate=0.115″). The relatively close thicknesses are possible, for one reason, in that the end plate does not need to support the compressive forces of bone screws at that location. Rather, as discussed above, the set screws are used which exert a substantially smaller force on the upper thinner portion of the end plate. 
     According to an important aspect of the invention, the plates  10  and  40  are arranged in a kit containing several different size plates  10  and several different size fragment plates  40 . According to the presently preferred embodiment, three different size volar plates are provided: standard, wide, and narrow. A plurality of different length fragment plates are also provided. The fragment plates may be straight or curved. For example, the plate may be curved in the plane of the plate to match the radius of curvature of the volar side of the radius bone, e.g., r=23 inches over approximately eighty percent of the length of the plate. The fragment plates can be used alone or in combination with the volar plates. When used together, distal and mid-shaft fractures can be covered with one integral plate (i.e. the two plates coupled to each other as shown in  FIG. 7 ). Thus, the loads are shared by the combined plate rather than the bone between two plates. The load is thereby spread out rather than concentrated on the bone between two plates. The modularity of the different size plates allows for the assembly of a wide variety of combinations using only a few different sizes. For example, three different width volar plates packed together with five different length fragment plates can be used to construct fifteen different size combination plates using only eight different size pieces. 
     According to an alternate embodiment of the invention, the volar plate is not required to include a socket for receiving an end portion of the fragment plate. Rather, a discrete coupler with sockets at two of its sides can be provided between the volar and fragment plates. The coupler operates to “splice” together the metaphyseal volar plate and the diaphyseal fragment plate. The advantage is that the volar plate for use in the system can be a standard component without modification, and can therefore be used alone without the fragment plate. Thus, the surgical tray will need fewer of the more expensive volar plates. In addition, the coupler allows “splicing” of multiple diaphyseal fragment plates together to make one extra long plate. 
     There have been described and illustrated herein embodiments of a fixation plate, and particularly plates for fixation of distal radius fractures. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while particular preferred materials, dimensions, and relative angles for particular elements of the system have been disclosed, it will be appreciated that other materials, dimensions, and relative angles may be used as well. Further, while the invention has been described with respect to distal volar radius plates, the invention may include other ‘end’ plates suitable in size and shape for placement at other metaphyseal locations, e.g., the dorsal side of the distal radius, the humerus, the femur and the tibia. In addition, end plates having shapes other than a ‘T’ may also be used, such as lateral and medial columns (generally ‘L’-shaped), and plates having a flared or forked head, provided such end plates are dimensioned and configured for placement at the metaphysis. In addition, while a particular number of screw holes in the end plate and fragment plate have been described, it will be understood a different numbers of screw holes may be used. Also, fewer or more threaded holes (for pegs or locking screws) may be used. In addition, while a particular preferred angle between the head and stem of the volar plate has been disclosed, other angles can also be used. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope.

Technology Category: 1