Patent Publication Number: US-2009222006-A1

Title: External fixator

Description:
FIELD OF THE INVENTION 
     The present invention relates to an external fixator for assisting healing of a fracture in a bone. 
     BACKGROUND OF THE INVENTION 
     Fracture of the distal end of the radius bone near the wrist is a relatively common injury. This injury is often referred to as a Colles fracture. A simple Colles fracture can be treated by merely realigning and immobilizing the fracture. More complex fractures may require the use of orthopedic devices to realign and reduce the fracture. 
     If wrist joint surfaces are damaged and not correctly realigned, the fracture may heal with an uneven joint surface, which can lead to accelerated wear and subsequent degenerative changes. 
     There are many methods used to realign or reduce fractures, such as a Colles fracture. One such method is ligamentotaxis. Ligamentotaxis relies on the attachment of ligaments, periosteum and other soft tissue attachments to the bone fracture fragments. By placing these soft tissue connections under tension the fracture is realigned or reduced. 
     Similarly, there are many methods of holding a reduced fracture in place after it has been realigned. One such method is external fixation, in which a device—usually comprising pins, rods, screws and/or other metal components—is attached percutaneously to pieces of bone, such that the device bridges the fracture. This type of device is commonly known as an external fixator. 
     In some cases of a Colles fracture, the external fixator is attached to the radius bone proximal to the fracture and to the metacarpal bones in the hand distal to the fracture. In this way, the fracture and the wrist joint are held in a fixed position during the healing process. However, fixing a joint in position can lead to increased stiffness of the joint and is undesirable. 
     Alternatively, an external fixator can be arranged such that the pins are inserted into the distal fragments of, for example, the fractured radius bone. This is a more desirable solution since mobility of the joint can be maintained during the healing process. However, when the distal fragments are small it can be difficult to hold the fracture in alignment by externally placed pins. This is particularly so when only one or two pins can be applied to hold the distal fragments in place and there are constraints on the direction in which they can be applied. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided an external fixator for assisting healing of a fracture in a bone, the external fixator comprising:
         a securing portion that defines a void; and   an elongate bracket portion extending from the securing portion, the bracket portion arranged to engage one or more first percutaneous bone fasteners locatable in the bone on a first side of the fracture;   whereby, in use, one or more second percutaneous bone fasteners are located in the bone on a second side of the fracture such that the second fasteners extend into the void of the securing portion, and the void can be filled with a cement compound to secure the second bone fasteners in place with respect to the securing portion.       

     Preferably, the securing portion is in the form of a loop. More preferably, the loop is a closed loop. 
     Preferably, part of the bracket portion forms a part of the securing portion. More preferably, the securing portion comprises an arcuate strip attached at each end to the bracket portion. Even more preferably, the arcuate strip is continuous with the bracket portion. 
     Preferably, the bracket portion comprises a plate having one or more holes extending therethrough for receiving the first bone fasteners. More preferably, the holes are arranged to extend through the plate transverse to the elongate direction of the bracket portion. 
     Preferably, each of the holes is provided with a threaded hole for receiving a threaded fastener to fix the respective first bone fastener in place, wherein the threaded hole is arranged to intersect with the respective hole. 
     Preferably, the second percutaneous bone fasteners are pins or rods, such as Kirschner wires. The pins or rods may be provided with a threaded portion for engaging bone. 
     In one embodiment, the external fixator further comprises at least one distractor comprising:
         a first coupling portion for coupling with the bracket portion;   a shaft attached to the first coupling portion; and   a pin clamp having a second coupling portion which engages the shaft such that the pin clamp is moveable along the length of the shaft, and one or more holes for receiving third percutaneous bone fasteners;   wherein, in use, the position of the pin clamp can be adjusted to provide distraction in the longitudinal direction of the shaft.       

     Preferably, the shaft is threaded and the second coupling portion has a threaded hole which engages the thread of the shaft such that rotation of the shaft causes movement of the pin clamp along the length of the shaft. Preferably the shaft is longitudinally fixed to the first coupling portion and axially rotatable relative to the first coupling portion. 
     Preferably, the first coupling portion has a projecting stud that is received in a complementary hole in the bracket portion to couple the distractor to the bracket portion. 
     Preferably, the complementary hole is one of a plurality of like complementary holes. 
     According to a second aspect of the present invention, there is provided a method for holding in place a fracture in a bone, the method comprising the steps of:
         providing an external fixator according to the first aspect;   securing one or more first bone fasteners percutaneously in the bone on the first side of the fracture;   fastening the bracket portion to the first bone fasteners;   securing one or more second bone fasteners percutaneously in the bone on the second side of the fracture, such that the second bone fasteners extend through the void defined by the securing portion; and   filling the void with a cement compound and allowing the cement compound to set so as to secure the second bone fasteners in place with respect to the external fixator.       

     After the cement compound has set, exposed ends of the second bone fasteners may be trimmed if desired. 
     In an embodiment the method further comprises realigning or reducing the fracture by moving the bone on the second side of the fracture prior to allowing the cement compound to set. Preferably the realignment or reduction occurs prior to filling the void with the cement compound. Even more preferably the realignment or reduction occurs prior to securing the second bone fasteners in the bone. 
     Preferably, the step of realigning or reducing the fracture further comprises providing one or more distractors, and for each distractor:
         securing one or more third percutaneous bone fasteners to a piece of bone in the direction to be distracted;   securing a clamp of the distractor to the third bone fasteners;   attaching a coupling portion of the distractor to the bracket portion; and   adjusting the position of the clamp with respect to the bracket portion to attain the desired distraction and realignment or reduction of the fracture.       

     Preferably, once the cement compound is set the distractors are removed from the bracket portion and the third bone fasteners removed. 
     According to a third aspect of the present invention, there is provided an external fixator kit for assisting healing of a fracture in a bone, the external fixator kit comprising:
         an external fixator comprising;   a securing portion that defines a void, and   an elongate bracket portion extending from the securing portion;   one or more first percutaneous bone fasteners locatable in the bone on a first side of the fracture and arranged to engage the bracket portion in use;   one or more second percutaneous bone fasteners locatable in the bone on a second side of the fracture such that the second fasteners extend into the void of the securing portion; and   a cement compound for filling the void so as to secure the second bone fasteners in place with respect to the securing portion.       

     According to a fourth aspect of the present invention, there is provided a distracter comprising:
         an elongate bracket portion arranged to engage one or more first percutaneous bone fasteners locatable in bone on a first side of a bone fracture;   a first coupling portion for coupling with the bracket portion;   a shaft attached to the first coupling portion; and   a pin clamp having a second coupling portion which engages the shaft such that the pin clamp is moveable along the length of the shaft, and one or more holes for receiving further percutaneous bone fasteners locatable in bone on a second side of the bone fracture;   wherein, in use, the position of the pin clamp can be adjusted to provide distraction in the longitudinal direction of the shaft.       

    
    
     
       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 schematic plan view of an external fixator according to a first embodiment of the present invention; 
         FIG. 2  is a side view of the external fixator of  FIG. 1 ; 
         FIG. 3  is a perspective view of an external fixator with a distractor according to a second embodiment of the present invention; 
         FIG. 4  is a side view of the distractor of  FIG. 3 ; and 
         FIG. 5  is a perspective view of an external fixator according to a third embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show an external fixator  10  according to a first embodiment of the present invention. The fixator  10  comprises a bracket portion  12  and a securing portion in the form of a closed loop  16  continuous with the bracket portion  12 . The fixator  10  is shaped so as to extend along an elongate axis L. In use, the fixator  10  is attached to a bone B such that the elongate axis L is aligned generally with the direction of the bone B. 
     The bracket portion  12  is provided with three holes  18  which are arranged perpendicular to the elongate axis L. The holes  18  are arranged to receive one or more of a first type of bone fasteners, such as rods  20 , in a clearance fit. Each hole  18  is provided with a corresponding hole  22  that extends through part of the bracket portion  12  and intersects with the side of the respective hole  18 . The holes  22  are internally threaded to receive a grub screw  24 . 
     The loop  16  is arranged so that a one or more of a second type of bone fasteners, such as Kirschner wires or thin pins  26 , can be arranged to extend through the void on the inside of the loop  16  and into distal fragments of the bone B. As shown in the figures, the pins  26  can be arranged in many different orientations. A surgical cement compound, such as (poly)methylmethacrylate—also known as PMMA, is used to fill the volume of the void enclosed by the loop  16  and secure the pins  26  in position relative to the fixator  10 . 
     In use, the surgeon has the freedom to select the number of pins  26  to be inserted into the bone fragments. In addition, the pins  26  can be oriented to suit the particular fracture, provided that the pins  26  extend through the loop  16 . 
       FIGS. 1 and 2  show the fixator  10  applied to the distal end of a radius bone B across a fracture F. As mentioned above, the distal radius fracture is a common injury. The rods  20  are secured in the proximal portion of the bone B and the pins  26  are secured in fragments of the distal portion of the bone B. 
     In use, the rods  20  are secured percutaneously to the proximal portion of the bone B and the bracket portion  12  is then fastened to the rods  20 . The location of the rods  20  is selected to correspond with the relative position of the holes  18  and such that the fixator  10  extends across the fracture F. The pins  26  are similarly secured percutaneously to the fragments of bone at the distal end of the bone B after the fracture is reduced. Clearly, the location and orientation of each pin  26 , as well as the number of pins  26  used, will be selected for the particular fracture F. Finally, the cement compound (not shown) is used to fill the void enclosed by the loop  16  and secure the pins  26  in place relative to the fixator  10 . Once setting of the cement has occurred, free ends of the pins  26  may be trimmed if desired. 
     The fixator  10  has been shown using rods  20  with a threaded portion that engages the bone B. However, it will be appreciated that alternate fixing methods may be used. 
     One advantage of the fixator according to the present invention is that the joint can remain active whilst the fracture is healing. Mobility during the healing process can help to reduce stiffness of the joint in the long term. 
       FIG. 3  shows an external fixator  110  according to a second embodiment of the present invention. The fixator  110  comprises a bracket portion  112  and a securing portion in the form of a loop  116  continuous with the bracket portion  112 . The fixator  110  is shaped so as to extend along an elongate axis. In use, the fixator  110  is attached to a bone such that the elongate axis of the fixator  110  is aligned generally with the direction of the bone. 
     The bracket portion  112  is provided with three holes  118  which are arranged perpendicular to the elongate axis. The holes  118  are arranged to receive rods  120  in a clearance fit. Each hole  118  is provided with a corresponding hole that extends through part of the bracket portion  112  and opens into the side of the respective hole  118 . The holes are internally threaded to receive a grub screw (not shown in  FIG. 3 ). 
     The loop  116  is arranged so that a one or more of a second type of bone fasteners, such as Kirschner wires or thin pins  126 , can be arranged to extend through the loop  116  and into distal fragments of the bone B. As shown in the figures, the pins  126  can be arranged in many different orientations. A surgical cement compound is used to fill the void enclosed by the loop  116  and set the pins  126  in position relative to the fixator  110 . 
     It has been shown that the principle of ligamentotaxis, which is obtained by longitudinal traction (or distraction), can be useful in realigning or reducing some fractures, such as distal radial fractures. To provide distraction, the fixator  110  further comprises a distractor  130 , as shown in  FIG. 4 , which comprises a coupling portion  132 , a threaded shaft  134  and a clamp, such as pin clamp  136 . The pin clamp  136  is provided with two holes  138  for receiving distractor pins  140 , and an internally threaded hole  142 . The direction of the holes  138  and the direction of the threaded hole  142  are transverse. The threaded shaft  134  extends through the threaded hole  142 . 
     The coupling portion  132  is attached to an end of the threaded shaft  134  in a swivel joint arrangement. Thus, the threaded shaft  134  can freely rotate with respect to the coupling portion  132 . The opposite end of the threaded shaft  134  is provide with a head  144  that is shaped such that a tool can be used to effect rotation of the threaded shaft  134 . The coupling portion  132  has a protruding stud  146  that engages a complementary hole (not shown) in the bracket portion  112 . 
     In use, the distractor pins  140  can be applied percutaneously through the soft tissue of the hand into, for example, the second metacarpal bone. The pin clamp  136  of the distractor  130  is then attached to the exposed portions of the distractor pins  140 . The coupling portion  132  is then attached to the bracket portion  112 . The position of the pin clamp  136  along the threaded shaft  134  and relative to the fixator  110  is adjusted by rotation of the threaded shaft  134  until the desired longitudinal distraction is attained and the fracture reduced. Subsequently, the pins are placed through the void and across the fracture and the cement compound is applied to fill the void defined by the loop  116 . Once the cement compound has set, the distractor  130  is removed from the bracket portion  112 . 
       FIG. 5  shows an external fixator  210  according to a third embodiment in the present invention. The fixator  210  comprises a bracket portion  212  and a securing portion in the form of a loop  216  connected to the bracket portion  212 . In this embodiment the bracket portion  212  is an elongate rod which in use is arranged so that its length is generally aligned with the direction of a bone in need of healing. 
     The bracket portion  212  is provided with a clamp  221  which receives a percutaneous bone fastener  220 . The second bone fastener  220  shown is also clamped to the bracket portion  212  but for clarity purposes the clamp is not shown. The bracket portion  212  is provided with a hole  231  adjacent to the loop  216  for receiving protruding stud  146  of a distractor  136  should it need to be used. In this embodiment the loop  216  is generally kidney shaped. It can be seen that six percutaneous bone fastening pins  226  are used. The loop  216  is shown with cement  240  securing the pins  226  in place. The cement  240  is shown partially cut away. 
     It will be understood to persons skilled in the art of the invention that many modifications may be made without departing from the scope of the invention. For example, the fixator of the present invention may be provided with one or more holes in the bracket portion to receive the rods. Clearly, in use a surgeon may choose to use fewer rods than can be accommodated in the bracket portion, provided that the fixator is secured to the proximal portion of the bone. 
     The fixator may be further provided with a one or more membranes, mesh or similar on one or both sides of the loop  16 . Accordingly, the void enclosed by the loop  16  and in particular the cement can be physically contained by the loop and the membranes or mesh. The membranes can be perforated to allow the pins to pass through the loop or the holes in the mesh perform this role. The cement can then be applied into the void defined by the loop and the membranes or mesh. The mesh or membrane(s) can assist to hold the pins in place while the cement sets. The holes in the mesh or markings on the membrane(s) can operate as a positioning guide. 
     While the closed loop  16  in the figures is shown to be generally circular, it will be appreciated that the loop can be provided in a number of shapes. For example, tear drop shaped. 
     The fixator is shown in  FIGS. 1 to 3  as comprising a bracket portion in the form of a narrow plate. Furthermore, the loop is shown as being an arcuate strip joined at each end to the bracket portion, such that a closed loop is formed. It will be appreciated that alternative embodiments of the fixator may be provided, in which, for example, the bracket portion is in the form of a wire frame, a rod or a rigid tube of suitable material that is rigidly attached to a securing portion in the form of a ring. In this alternative embodiment, conventional pin/rod clamps may be used to secure the rods to the wire frame, rod or rigid tube. 
     The securing portion need not be a closed loop. The loop may be formed by two discontinuous arms, such that an opening is provided in the loop. In an embodiment in which the arms are made of a deformable material, the size of the void defined by the loop can be increased or decreased as desired. In use, any gap between the arms can be filled with the cement compound. 
     It will be appreciated that many alternative cement products may be used, such as, for example, a Calcium Phosphate (CaP) cement compound. The cement should be substantially inflexible once set. 
     It is recognized that ligamentotaxis in two (or more) planes can be of benefit in the reduction or realignment of a fracture. Accordingly, it will be appreciated that a plurality of distractors  130  may be used to achieve distraction in specific directions. 
     The coupling portion  132  has been shown as having a stud which is received in a hole in the bracket portion. However, it will be appreciated that alternative coupling arrangements can be employed. For example, the coupling portion  132  could be secured to the bracket portion  112  by a clamp. 
     The shaft  134  is in threaded engagement with threaded hole  142 , however it will be appreciated that other mechanisms can be employed to move the pin clamp  136  along the length of the shaft  134 , such as a rack and pinion. 
     While embodiments of the fixator have been described in connection with a fracture to the distal end of the radius bone, it will be appreciated that the fixator may be used to facilitate the healing of fractures in other bones of humans or animals. 
     Throughout this specification, 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.