Patent Publication Number: US-2011060372-A1

Title: Bone fixing device

Description:
FIELD OF THE INVENTION 
     The present invention relates to bone fixing devices for fixing bone pieces together and also to a method of fixing bone pieces together. 
     BACKGROUND 
     A common procedure in orthopaedic surgery is fixing bone pieces together. Often the bone pieces were originally one continuous bone piece which has separated either intentionally, for example in a re-alignment procedure, or unintentionally, as in the case of a fracture. Alternatively, it may be desirable to fix two or more bone pieces together such as when performing arthrodeses or joint fusions. 
     In almost all cases of such bone connections it is essential for the cut or fractured bone surfaces to be held together in close mutual confrontation. This intimacy of contact is usually referred to as compression. To form a strong bond between the bone pieces it is necessary for the bone surfaces to be held in well fitted contact during healing or union. In practice the simplest way of ensuring this contact is, where practical, to apply a compressive load to the bone portions in a direction substantially normal to the severed bone faces. 
     A known method to apply such a compressive loading is using bone screws. A first type of bone screw has a head attached to one end of a threaded shaft. The screw is screwed into the bone such that the head applies a compressive force directly to the bony cortex (or surface) of one of the pieces of bone to be held together. 
     A second type of bone screw comprises a shaft having two threaded portions separated by a shank devoid of thread. The two threaded portions are threaded in the same directions, but have a different pitch. Accordingly, as the screw is tightened a compressive load is applied to the bone faces. 
     One alternative to bone screws are bone plates. These are in various configurations, but are most commonly longer in one direction than in the other. A series of holes are provided in the plate in a single row along the longest direction. The plate is positioned across the fissure between the bone pieces such that longer dimension is generally orthogonal to the fissure. Bone screws with heads are screwed through the holes in the plate and into the bone. The plate holes can be elongated in the line of the longer dimension of the plate. If the screws are placed eccentrically away from the fissure, the bone surfaces will be drawn together on tightening. 
     In some such plates, the holes are provided with internal threads to engage complementary threads on the heads of the bone screws. Thus, the screws are locked to the plate. 
     In a further alternative, staples can be used to fix severed bone pieces together. Some staples can apply compression by virtue of their structure. Others can be tightened in various ways so as to bring about compression of the bone surfaces. 
     Each of the above mechanisms for fixing bone pieces together suffer from a number of deficiencies. For example, in practice it may not be possible to insert a screw in an appropriate direction due to the anatomical location of the pieces of bone to be fixed. Similarly, it may not be possible to use a bone plate due to size constraints and/or surgical access. 
     Staples can be difficult to use in that the bone can be split if the staple is too large. In addition, staples can remove themselves from the bone leaving an unstable fixation. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a bone fixing device for fixing bone pieces together, the bone fixing device comprising:
         a pair of spaced-apart fixing portions, each having at least one hole dimensioned such that a fastener can extend therethrough; and,   a pair of substantially rigid connecting members extending between the fixing portions, the connecting members being deformable without substantially losing rigidity,   whereby, in use, each fixing portion is fixed to one or more of the bone pieces by the fasteners such that the connecting members extend across one or more fissures between the bone pieces, and the connecting members are simultaneously deformed such that the fissures are closed with the bone pieces held in compression.       

     According to a second aspect of the present invention, there is provided a modular system for fixing bone pieces together, the modular system comprising at least two bone fixing devices, each bone fixing device comprising:
         a pair of spaced-apart fixing portions each having at least one hole dimensioned such that a fastener can extend therethrough; and,   a pair of substantially rigid connecting members extending between the fixing portions, the connecting members being deformable without losing rigidity,   whereby, in use, at least one of the fixing portions of each bone fixing device can be concentrically overlapped with a fixing portions of another bone fixing device such that a fastener can extend through the holes of the overlapped fixing portions.       

     According to a third aspect of the present invention, there is provided a method of fixing bone pieces separated by a fissure, comprising the steps of:
         (a) providing at least one bone fixing device having a pair of spaced-apart fixing portions each having at least one hole being dimensioned such that a fastener can extend therethrough and a pair of deformable connecting members extending between the fixing portions;   (b) fixing one of the fixing portions to one bone piece using a fastener and the other fixing portion to another bone piece using another fastener such that the connecting members extend across the fissure; and,   (c) simultaneously deforming the connecting members such that the fixing portions are drawn together.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be more easily understood, embodiments will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1 : is a plan view of a bone fixing device according to a first embodiment of the present invention; 
         FIG. 2 : is a side view of the bone fixing device of  FIG. 1 ; 
         FIG. 3 : is a plan view of the bone fixing device of  FIG. 1  showing a method of use of the device; 
         FIG. 4 : is a plan view of the bone fixing device of  FIG. 1  positioned across a fissure; 
         FIG. 5 : is a side view of the bone fixing device of  FIG. 4 ; 
         FIG. 6 : is a plan view of the bone fixing device having been used to close the fissure of  FIG. 4 ; 
         FIG. 7 : is a side view of the bone fixing device of  FIG. 6 ; 
         FIG. 8 : is a plan view of two bone fixing devices according to a second embodiment of the present invention; 
         FIG. 9 : is a side view of the bone fixing device according to the second embodiment; 
         FIG. 10 : is a side view of the bone fixing device according to a third embodiment of the present invention; 
         FIG. 11 : is a plan view of a bone fixing device according to a fourth embodiment of the present invention; 
         FIG. 12 : is a plan view of a bone fixing device according to a fifth embodiment of the present invention; 
         FIG. 13 : is a plan view of a bone fixing device according to a sixth embodiment of the present invention; and 
         FIG. 14 : is a plan view of a bone fixing device according to a seventh embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 7  show schematically a bone fixing device  10  according to a first embodiment of the present invention. The bone fixing device  10  has two fixing portions, in the form of annuli  12 , each having a hole  14  for receiving a fastener, such as a bone screw  16 . Two spaced apart substantially rigid connecting members  18  extend between the two annuli  12 . In this embodiment the connecting members  18  are substantially parallel prior to deformation in use. The connecting members  18  join with the annuli  12  on the circumference of the annuli  12  so that the outer lateral dimensions of the connecting members are about the same as the outer diameter of the annuli  12  prior to deformation in use. 
     The connecting members  18  can be deformed, such as by using a pair of pliers, substantially without losing their rigidity, from the initial position (as shown in  FIG. 1 ) such that the connecting members  18  are mutually separated. The separation will cause the annuli  12  to be drawn towards one another (as indicated by the broken lines  10 ′ in  FIG. 3 ). The connecting members  18  will substantially maintain their position after deformation, and consequently the annuli  12  will also maintain their position closer together than prior to the deformation. 
     As shown in  FIGS. 4 and 5 , the bone fixing device  10  can be positioned across a fissure F between two bone pieces B. Each of the annuli  12  is attached to a respective one of the bone pieces B using a fastener in the form of a bone screw  16 . Once the bone fixing device  10  is in place, the connecting members  18  can be deformed such that the annuli  12  are drawn together. As the connecting members  18  are deformed, the bone pieces B will also be drawn together closing the fissure F, as shown in  FIGS. 6 and 7 . Further deformation of the connecting members  18  will generate a compressive force on the bone pieces B at the contacting surfaces. 
     While the fissure F is shown as a single gap between the bone pieces B, it will be appreciated that there could be two or more fissures between the bone pieces B. For example, one or more bone pieces may be intercalated between the bone pieces B to which the fixing portions are attached. 
     As shown in  FIG. 1 , each of the connecting members  18  may be provided with a necked portion  20 . Each of the necked portions  20  is a point of reduced resistance to deformation. The connecting members  18  will therefore bend most readily at the necked portions  20 . 
     It will be appreciated that one or more neck portions  20  may be provided in each of the connecting members  18 . 
     The holes  14  in each of the annuli  12  may have a frusto-conical portion  22 , for receiving the head of a bone screw  16 , and a cylindrical portion  24  for receiving part of the shaft of the bone screw  16 . 
       FIGS. 8 to 10  show two bone fixing devices  110  and  210  according to second and third embodiments respectively. In the second embodiment  110 , shown in  FIG. 9 , two fixing portions, in the form of annuli  112 , are provided between which two connecting members  118  extend. 
     In the third embodiment  210 , shown in  FIG. 10 , two fixing portions, in the form of annuli  212 , are provided between which two connecting members  218  extend. As shown in  FIG. 8 , an annulus  212  of the bone fixing device  210  overlaps an annulus  112  of the bone fixing device  110  such that the holes  114 ,  214  of the respective annuli  112 ,  212  are concentric. Accordingly, the shaft of a bone screw (not shown) can extend through the holes  114 ,  214 . 
     In this way, two or more bone fixing devices can be arranged to form a modular fixing system  150 . The modular system  150  can be used to connect, and hold in compression, more than two bone pieces. Alternatively, the modular system  150  can be used to provide compression between two bone pieces which are separated by a nonlinear fissure. Alternatively or additionally, the modular system  150  may be used to provide at least bi-directional compression of bone pieces across a fissure. 
     In the modular fixing system  150 , the overlapped annuli  112 ,  212  cooperate to receive and locate the bone screw which would fasten the bone fixing devices  110 ,  210  to the bone piece. The hole  214  in the annulus  212  is frusto-conical in shape, while the hole  114  in the annulus  112  is cylindrical in shape. Therefore, the hole  214  is dimensioned to receive the head of a bone screw and the hole  114  is dimensioned to receive the shaft of a bone screw. 
     The combined thickness of the annuli  112 ,  212  is approximately equal to the thickness of the annulus  12  of the bone fixing device  10 . Thus, the thickness profile of the modular system  150  is substantially the same as that of the bone fixing device  10 . It may be noted that the thickness of the annuli  112 ,  212  is approximately half the thickness of the respective connecting members  118 ,  218 . 
     It will be apparent to the person skilled in the art that it may be necessary to provide a washer  124 ,  224  for the respective bone fixing devices  110 ,  210  such that an annulus  112 ,  212  in the modular system  150  which is not overlapped with another annulus can receive and locate a bone screw. Accordingly, each washer  126 ,  226  is provided with a hole  128 ,  228  which complements the annulus  112 ,  212  of the respective bone fixing device  110 ,  210 . 
     While not illustrated in the figures, it will also be apparent that an alternative embodiment of bone fixing device could be provided having two annuli, one of the type illustrated in  FIG. 9  and the other of the type illustrated in  FIG. 10 . 
       FIG. 11  shows schematically a bone fixing device  310  according to a fourth embodiment of the present invention. 
     The bone fixing device  310  has two fixing portions. One fixing portion is in the form of an annulus  312  having a hole  314  for receiving a fastener such as a bone screw  16 . The second fixing portion in the form of two conjoined annuli  313  such that there are two holes  315 , each for receiving a fastener. Two connecting members  318  extend between the two fixing portions  312 ,  313 , the connecting members  318  being deformable to draw the two fixing portions  312 ,  313  toward one another. 
     The bone fixing device  310  having a fixing portion in the form of the conjoined annuli  313  can be used to join three bone pieces together, for example, in an operation to fuse the scaphoid, trapezoid and trapezium bones in a patient&#39;s wrist. This operation is performed where arthritis in this joint has resulted in instability. 
     In such a fusion operation, the conjoined annuli  313  is fixed to both the trapezoid and trapezium bones by inserting bone screws  16  through each of the holes  315  and into a respective one of the trapezoid and trapezium bones. The annulus  312  is fixed to the scaphoid bone by inserting a bone screw  16  through the hole  314  and into the scaphoid bone. The connecting members  18  are then be simultaneously separated to draw the conjoined annuli  313  and the annulus  312  together. Compressive loads between both the scaphoid and trapezoid bones and the scaphoid and trapezium bones will be applied by the bone fixing device  310 . Over time the trapezoid and trapezium bones will fuse with the scaphoid bone. 
       FIG. 12  shows schematically a bone fixing device  410  according to a fifth embodiment of the present invention. The bone fixing device  410  has two fixing portions, both generally in the form of an annulus  412  having a hole  414 . Fasteners can be used to secure each of the annuli  412  to a bone piece. 
     Two connecting members  418  extend between the two annuli  412  such that each connecting member  418  is joined to each annulus  412  at a point remote from the opposing annulus  412 . Accordingly, in their initial states, the annuli  412  of this bone fixing device  410  has a smaller separation when compared with the annuli  12  of the bone fixing device  10 , when both bone fixing devices  10 ,  410  are provided with connecting members  18 ,  418  of the same length. 
     In use, the connecting members  418  can be simultaneously deformed such that the two annuli  412  are drawn together. Accordingly, a compressive load will be generated on the two bone pieces. 
     Clearly, the ease with which the connecting members can be deformed is at least partially dependent on the length of the connecting members. In addition, the maximum deflection of the fixing portions is also at least partially dependent on the length of the connecting members. The arrangement of the fixing portions  412  and the connecting members  418  allows the bone fixing device  410  to have a reduced overall length (and thus a reduced separation of the fixing portions  412 ) without shortening the length of the connecting members  418 , when compared with the bone fixing device  10  of  FIG. 1 . 
       FIG. 13  shows schematically a bone fixing device  510  according to a sixth embodiment of the present invention. The bone fixing device  510  has two fixing portions  512 ,  513  both generally in the form of an annulus having a hole  514 . Fasteners, such as bone screws  16 , can be used to secure each of the fixing portion  512  to a bone piece. 
     Two connecting members  518  extend between the two fixing portions  512 ,  513 . The first fixing portion  512  is joined to each connecting member  518  at a point remote from the second fixing portion  513 . The second fixing portion  518  is joined to each connecting member  518  at a point near to the first fixing portion  512 . 
       FIG. 14  shows schematically a bone fixing device  610  according to a seventh embodiment of the present invention. The bone fixing device  610  has two fixing portions, each in the form of two conjoined annuli  612  such that there are two holes  614  in each fixing portion. The holes  614  are able to receive a fastener such as a bone screw  16 . Two connecting members  618  extend between the two fixing portions  612 , the connecting members  618  being deformable to draw the two fixing portions  612  toward one another. 
     As shown in  FIG. 14 , the two holes  614  in each fixing portion are separated longitudinally with respect to the bone fixing device  610 . In use, the load applied to each bone piece by the respective fixing portion is distributed between the two bone screws in each of the conjoined annuli  612 . More than two holes could be incorporated at either or both ends of the device, either in line as shown in  FIG. 14  or at an angle to the long axis of the device as shown in  FIG. 11 . 
     It will be understood to persons skilled in the art that modifications may be made without departing from the scope of the invention. For example, alternative embodiments of bone fixing devices may be conceived having combinations of the fixing portions described above in connection with the accompanying figures. In addition, alternative forms of fixing portions may be conceived which accommodate alternate forms of fastening means. 
     It will also be appreciated that, while the embodiments described above generate a compressive load on the respective bone pieces by separation of the connecting members, it is possible that a compressive load may be generated by pinching together the connecting members. It may also be possible to deform the connecting members in other ways providing that the fixing portions are drawn generally towards one another to generate a compressive load. 
     In the claims of this application and in the description of the invention, except where the context requires otherwise due to express language or necessary implication, the words “comprise” or variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.