WO2014122264A1

WO2014122264A1 - Bone reponator

Info

Publication number: WO2014122264A1
Application number: PCT/EP2014/052434
Authority: WO
Inventors: Kenneth BIHLET
Original assignee: Akershus Universitetssykehus Hf
Priority date: 2013-02-07
Filing date: 2014-02-07
Publication date: 2014-08-14
Also published as: GB201302143D0

Abstract

A bone reponator apparatus comprises: a fixed coupling 8 for connection to a first bone fragment 3 and a mobile coupling 10 for connection to a second bone fragment 4; wherein the mobile coupling 10 is for providing rotational and translational movement A, B, C, D of the second bone fragment 4 in first and second orthogonal planes; wherein the fixed coupling 8 is arranged to prevent movement of the first bone fragment 3 in the first and second planes; and wherein the mobile coupling 10 is arranged to permit rotational movement A about a normal to the first plane and translational movement B along the first plane whilst preventing rotational movement C about a normal to the second plane and translational movement D along the second plane, and to permit rotational movement C about the normal to the second plane and translational movement D along the second plane whilst preventing rotational movement A about a normal to the first plane and translational movement B along the first plane.

Description

BONE REPONATOR

The invention relates to a bone reponator apparatus and a method for the repositioning of bones, for example during treatment of fractures and arthrodesis.

When a bone is fractured or broken the parts of the bone can become spaced apart and/or misaligned. It is necessary to reponate (reposition the bone) before the bone is fixed to permit it to heal. Typically the reponation this is done by hand by a surgeon with an X-ray imaging system being used to determine when the bones are aligned. As an X- ray image is two dimensional it is necessary to take images from two orthogonal directions, with the patient stationary, in order to check for misalignment of the bone. Often it will be necessary to adjust the position of the bone several times, with intervening images being taken, before the surgeon can be satisfied that the bone fragments are correctly aligned and can be fixed in place by an appropriate fixation technique.

Bone fixation techniques typically involve the use of wires or pins that are usually drilled into bone and extend across gaps in the bone, such as the gaps caused by fractures. Smooth wire fixation uses wires that are smooth and without threading. Often the terms "Kirschner wire" or "K-wire" are used for these wires. Half pins can also be used for fixation in the bone. These half pins are wire like with a threaded portion at one end for screwing into the bone and a smooth portion at the other end. The wires or half pins hold parts of the bone in place allowing healing to occur. The wires or half pins can be held in place by clamps and external fixing wires or rods. A plaster cast or a joint bridging external fixation is frequently used to help immobilise the healing site and minimise movement of the wires and/or migration out of the bone.

A typical known arrangement uses an llizarov ring fixator in which tensioned wires penetrating the bone ends are locked into a ring at each bone end. The wires are clamped against the ring. Rods connect the two rings to form a cylindrical cage like structure.

Another typical arrangement will include wires and/or stiff half pins fitted into holes in the bone at the two ends of the bone and extending generally perpendicular to the bone, with a further external wire that is generally parallel to the bone and is joined via clamps to the other wires. The smooth wire fixation can be augmented by a plaster cast.

US 5752954 discloses one type of bone fixation device with fairly common general features, as shown in Figure 1. Pins 91 and 92 are inserted into the diaphysis 1 of a bone that is fractured in the vicinity of the epiphysis 2, which receives further pins 93 and 94. Two pins are shown in each bone fragment, but it is obviously possible to insert a larger number of bone pins. External fixation bars 81 , 82, 83, 84, 85 form a frame for the fixator. The pins 91 and 92 are held in a vice 104 whose jaws receive two bars 84 and 85 that constitute the lower part of the frame of the external fixator. Each of the pins 91 , 92, 93, 94 are held by an articulated clamp 200, which joins them to the respective external fixation bars. It will be noted that a bent bar may be employed, such as the bar 85.

GB 2033758 and US 2009/025086 disclose further examples of known fixation systems with US 2009/02586 disclosing a clamp for holding wires or half pins, and GB

2033758 disclosing an arrangement of clamps and rods used to secure two or more bone fragments together. The clamping device of GB 2033758 has links or joints each comprising two or more link members with mating flat surfaces in which are spaced longitudinal bores parallel to such surfaces for receiving bone rods or nails and/or connecting rods. The clamping devices also having transverse bores to receive screws for clamping the link members together to hold the various rods. The links or joints can hold the rods at various angles and in various arrangements.

These systems use clamps with pairs of jaws, where the wires, half pins or rods are inserted between the pairs of jaws and the jaws are tightened to secure them in place in interlocking arrangements. The rods and clamps form a cage like structure around the limb. When reponating the bone prior to fixation the pins or rods would typically already be attached to the bone. The surgeon can use the external parts of the pins to manipulate the bone fragments and when the bone is in place then the pins can be fixed by the selected clamping arrangement.

However there remain difficulties in manipulation of the patient and it is still possible for patient movement to misalign the bones again without the surgeon noticing. Moreover the attachment of the pins in the bone to the external clamping mechanism can be complicated and this can once again result in undesirable misalignment of the bones during fixation. Misaligned bones can result in significant later medical problems for the patient. The need for repeated X-ray imaging when reponating and also to check alignment during and after fixation can result in an undesirably high radiation exposure for the patient and for the surgeon and other medical personnel.

Viewed from a first aspect, the present invention provides a bone reponator apparatus comprising: a fixed coupling for connection to a first bone fragment and a mobile coupling for connection to a second bone fragment; wherein the mobile coupling is for providing rotational and translational movement of the second bone fragment in first and second orthogonal planes; wherein the fixed coupling is arranged to prevent movement of the first bone fragment in the first and second planes; and wherein the mobile coupling is arranged to permit rotational movement about a normal to the first plane and translational movement along the first plane whilst preventing rotational movement about a normal to the second plane and translational movement along the second plane, and to permit rotational movement about the normal to the second plane and translational movement along the second plane whilst preventing rotational movement about the normal to the first plane and translational movement along the first plane.

With this apparatus the alignment of the bone fragments can readily be corrected by movements in the two orthogonal planes in two stages, with the corrections applied in the first stage being maintained during corrections in the second stage. The mobile coupling may be considered to have two modes of operation wherein in a first mode corrections in a first plane are permitted whilst movement in the second plane is not permitted, and in a second mode corrections in a second plane are permitted whilst movement in the first plane is not permitted. The rotational and translational movements in each plane might be made simultaneously, or the mobile coupling could be arranged to make these movements separately, for example to permit rotation in one plane whilst preventing translation in the same plane and vice versa, with no movement in the other plane being permitted as described above. The preferred fixed coupling is capable of preventing all movement of the first bone fragment relative to the mobile coupling, and may also be capable of preventing movement of the bone in absolute terms.

The apparatus may include a mechanism for clamping parts of the mobile coupling in order to selectively prevent movement in the first plane or in the second plane, and to hence allow operation in the first mode and second mode described above. For example, a screw fitting may be used to clamp moveable parts together and hence prevent movement. The clamping mechanism in preferred embodiments will, in the first mode, be arranged to prevent rotational and translational movement in the first plane whilst allowing rotational and/or translational movement in the second plane and, in the second mode, be arranged to prevent rotational and translational movement in the second plane whilst allowing rotational and/or translational movement in the first plane. Preferably the clamping mechanism is such that, when it is released, both rotational and translational movement is permitted in the corresponding plane. This means that the apparatus can be easily operated by a surgeon with the use of possibly even just one hand to release and engage the clamp and one hand to manoeuvre the bone fragment. The clamping mechanism may be arranged to be released or engaged with the use of just one hand. It will be appreciated that there could also be a fixed mode where no movement at all is permitted, which could be used when moving the patient and/or when the bone has been fully aligned and should be fixed in place. The reponator apparatus may further include a mechanism for mounting the couplings to an operating table and/or imaging system such that the fixed coupling does not move relative to the operating table and/or imaging system and the mobile coupling can move the second bone fragment relative to the operating table and/or imaging system with the rotational and translational movements set out above. Preferably the mechanism for mounting the couplings is arranged to align the first and second planes with orthogonal imaging planes of the imaging system. The imaging system may for example be an X-ray intensifier.

It will be understood that the exact nature of the mechanism for moving the mobile coupling can vary provided that it permits the required types of movement of the bone fragment. In preferred embodiments the mechanism of the mobile coupling comprises pivoting and sliding joints. The mechanism of the mobile coupling may be completely mechanical and actuated manually by the surgeon. Alternatively the apparatus may be arranged for automatic and/or remote actuation of the rotational and translational motions, for example by using suitable electronic or electro-mechanical actuators. In one example embodiment the mobile coupling includes two pins mounted in slots, which can permit a translation along the slot and a rotation about the pin, with one pin and slot being oriented to allow for movement in the first plane, and the other pin and slot being oriented to allow for movement in the second plane. The pins may be provided with clamping devices to fix them and prevent movement, for example a screw clamp.

Preferably the first and second planes both extend radially relative to the longitudinal axis of the bone, which would hence be parallel with a line of intersection of the two planes. It will be appreciated that the apparatus may be provided with an articulated mechanism for mounting to an operating table or imaging system whereby the apparatus can be adjusted to align the axes of movement with the patient and with the axes of the imaging system.

The apparatus is preferably arranged for a movement of the bone fragments relative to one another along the longitudinal axis of the bone. This allows for the fracture to be overstretched by moving the bone fragments apart prior to the correction of angulation and sideways alignment. Once the correction of angulation and sideways alignment is completed then the overstretching can be reversed.

The translational movements along the first and second planes may be movements along one line in each plane. It will be appreciated that it is not essential to allow full freedom of movement in the two planes provided that a linear movement along one line is permitted, with this line being non-parallel with the line of intersection of the planes. This line of intersection would typically be parallel to the longitudinal axis of the bone. However, it is preferred for a translation to be permitted along a line that is generally normal to the line of intersection of the orthogonal planes. This maximises the correctional effect of the movement for a given absolute translational movement. The translational movements in one or both planes may be restricted to a movement generally along the line that is normal to the line of intersection of the orthogonal planes, but it is advantageous to have a greater degree of freedom of movement including the ability to move the bone fragments toward and away from one another along the line of intersection of the orthogonal planes.

Preferably therefore the mobile coupling is arranged to provide two dimensional translational movement along one of or each of the orthogonal planes. This allows for overstretching of the fracture or closing of the distance between bone fragments during the alignment of the bone in the first and second planes.

In one preferred embodiment the mobile coupling may be arranged to provide a movement of the second bone fragment along the longitudinal axis of the bone whilst no rotational or translational movement is permitted in the two orthogonal planes. This means that whilst the angulation and translation of the bone is fixed in the two orthogonal planes the surgeon can overstretch the fracture and/or reverse the overstretching of the fracture. As an alternative to movement of the mobile coupling along the longitudinal axis of the bone to overstretch the fracture and/or reverse the overstretching of the fracture it is also possible to allow for a movement of the fixed coupling along the longitudinal axis of the bone. Thus the fixed coupling may be arranged to provide translational movement along the longitudinal axis of the bone.

The reponator apparatus may further include a pivot or turntable mechanism for rotational alignment of the bone fragments about the longitudinal axis of the bone. This then allows mechanical and controlled adjustment of the rotation of the bone.

Viewed from a second aspect, the invention provides a method comprising use of the apparatus described above for reponation of a bone in the human or animal body.

Viewed from a third aspect the invention provides a method of reponation of a bone in the human or animal body comprising: attaching a first bone fragment to a fixed coupling of a reponator apparatus; and attaching a second bone fragment to a mobile coupling of the reponator apparatus; wherein the mobile coupling is for providing rotational and translational movement of the second bone fragment in first and second orthogonal planes; wherein the fixed coupling is arranged to prevent movement of the first bone fragment in the first and second planes; and wherein the method comprises: aligning the two bone fragments in the first plane by rotational movement of the second bone fragment about a normal to the first plane and translational movement of the second bone fragment along the first plane whilst preventing rotational movement about a normal to the second plane and translational movement along the second plane, and then aligning the two bone fragments in the second plane by rotational movement of the second bone fragment about the normal to the second plane and translational movement of the second bone fragment along the second plane whilst preventing rotational movement about the normal to the first plane and translational movement along the first plane.

The method may further include mounting the couplings to an operating table and/or imaging system such that the fixed coupling does not move relative to the operating table and/or imaging system and the mobile coupling can move the second bone fragment relative to the operating table and/or imaging system with the rotational and translational movements set out above. Preferably the step of mounting the couplings includes aligning the first and second planes with orthogonal imaging planes of the imaging system. The imaging system may for example be an X-ray intensifier.

The method may comprise clamping parts of the mobile coupling in order to selectively prevent movement in the first plane or in the second plane, and to hence allow operation in the first mode and second mode described above. For example, a screw fitting may be used to clamp moveable parts together and hence prevent movement. The clamping mechanism can be used as described above in relation to the apparatus of the invention.

Preferably the first and second planes are in a radial direction relative to the longitudinal axis of the bone. The method may further include movement of the bone fragments relative to one another along the longitudinal axis of the bone.

The method may comprise the use of an apparatus as set out above.

Preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying figures in which:

Figure 1 illustrates an example of a known bone fixation apparatus;

Figure 2 is a schematic diagram showing a bone reponator apparatus;

Figures 3a to 3c illustrate stages of reponation of a bone viewed from a first direction;

Figures 4a to 4c illustrate stages of reponation of a bone viewed from a second direction, orthogonal to the first direction;

Figure 5 is a perspective view of another bone reponator apparatus with simulated bone fragments and simulated X-ray imaging planes;

Figure 6 shows the apparatus of Figure 5 in a different view; Figure 7 illustrates the same apparatus with the fracture stabilising rod and reponator start-off positioning rod removed;

Figure 8 shows the apparatus of Figure 5 after correction for bone position and angulation in a first plane;

Figure 9 shows the result of a further correction in a second plane;

Figure 10 illustrates the apparatus of Figure 5 with a fully aligned pair of simulated bone fragments; and

Figure 1 1 shows the same apparatus with the fracture stabilising rod re-fitted and the aligned bone fragments ready for disconnection from the reponator.

By way of example the preferred embodiment is described with reference to a notional fracture where the bone is split into two fragments 3, 4 as shown schematically in the Figures. The bone reponator apparatus, as shown schematically in Figure 2 or as depicted in Figures 5 to 1 1 , makes use of pins 6 or similar elements fixed into the bone fragments. The term bone fragment as used herein is intended to refer to any part of a damaged bone requiring realignment with other parts of the damaged bone, for example during treatment of fractures or arthrodesis. The pins 6 can be joined to the bone in conventional fashion and should preferably be appropriately positioned for use in a later bone fixation system.

The reponator apparatus consists generally of a fixed coupling 8 for connection to a first bone fragment 3 and a mobile coupling mechanism 10 for connection to a second bone fragment 4. The selection of which bone fragment 3, 4 should be fixed can be made by the surgeon based on the nature of the damage to the bone and the condition of the patient. In the embodiment of Figure 2 the rotational alignment of the bone fragments about the longitudinal axis of the bone, which would be the z-axis as shown in Figure 2, is done by the surgeon prior to connection of the couplings 8, 10. This can be carried out via conventional clinical judgment using anatomical landmarks. The fixed coupling 8 is immovably mounted with reference to an imaging system and may for example be rigidly connected to an operating table or other patient support system to which the imaging system is attached. The fixed coupling 8 is used to ensure that first bone fragment 3 does not move during manipulation of the second bone fragment 4.

The mobile coupling mechanism 10 can be implemented in various ways. The important functional features are provided by a basic exemplary mechanism in Figure 2, which is described below with reference to three orthogonal axes that in this example have a z-axis aligned with the longitudinal axis of the bone along with orthogonal x and y-axes that extend radially relative to the longitudinal axis of the bone. This simple system permits movement along one line in each of two orthogonal planes by means of translational movements along the orthogonal x and y-axes. The mechanism consists of: a pivoting joint 12 joined to the bone fragment 4 by the pins 6, a rod 14 mounted for translating and rotating movement at a joint 16, with the joint 16 itself being mounted for translating movement on a rod 18, which is fixed in relation to the x and y axes as represented by mounting point 19.

It will be understood that the exact nature of the mechanism can vary provided that it permits the required types of movement of the bone fragment 4. The mechanism of Figure 2 is merely an illustrative example. Another mechanism is described below with reference to Figures 5 to 1 1. A larger number of mechanical parts could be used to provide greater rigidity. The mechanism should also include clamps or locking devices for fixing the parts of the mechanism in place. This is so that the position of the bone can be fixed to permit the external fixing clamps to be attached (for example a mechanism as in Figure 1 ) and, perhaps more importantly, to restrict the movement of the bone fragment during a second stage correction after a first stage correction has been completed, as discussed below.

The reponator should be arranged to provide for movement generally along the longitudinal axis of the bone to overstretch the fracture followed by correctional movement of one bone fragment relative to another bone fragment as set out below, with the notation referring to corresponding arrows in Figures 2 to 4. Thus, after an initial movement along the longitudinal axis of the bone the reponator should allow for the following correctional movements:

(i) rotational movement A about a normal to a first plane;

(ii) translational movement B along the first plane;

(iii) rotational movement C about a normal to a second plane;

(iv) translational movement D along the second plane; and

(v) translational movement E along a longitudinal axis of the bone, which would typically be parallel to the line of intersection of the first and second planes.

In the arrangement of Figure 2 the translational movement is embodied by a sliding movement along first and second orthogonal axes. Preferably the first and second axes are in a radial direction relative to the longitudinal axis of the bone as set out above and as shown in Figure 2. However some variation can be tolerated and might be necessary depending on the injury that is being treated, since access to certain bones can be restricted. It is required that movements A and B occur with the bone fragment fixed in place in relation to movements C and D, and that the movements C and D occur with the bone fragment fixed in place in relation to movements A and B. Ideally the mobile coupling should also be fixed in place with reference to the movement E as well, during all of movements A to D. It is not essential for the rotation to occur prior to translation, so the movements A and B and correspondingly the movements C and D can occur in any order, with the first movement being selected by the surgeon according to their preference and based on the nature of the damage to the bone. It is also not necessary for the mechanism to require separation of the rotational and translational movements in each of the orthogonal planes. So movements A and B could occur at the same time and likewise movements C and D could occur at the same time. When the rotational and translational movements are separated then it is preferred to correct angulation first since it is much easier to judge a movement to correct dislocation once the bone is correctly angled. The selection of which pair of A and B or C and D to perform first can also be made by the surgeon.

The reponator splits the movements based on two orthogonal planes (using movements along orthogonal axes x and y in this example) to thereby permit a two stage reponation which can be monitored by an X-ray image (or equivalent imaging system) in two orthogonal planes. It is typical to have X-ray intensifiers that can take an image in plan and in side elevation when the patient is laid on an operating table or similar. The imaging system and reponator should be arranged so that the bone can be viewed along the two orthogonal planes for the motions A to D, which would be the x-z and y-z planes in this example.

Figures 3a to 3b show an example sequence of movements to reponate a bone using the apparatus of Figure 2 with the bone viewed along the y-axis, looking toward the x-z plane. For clarity the couplings 8, 10 are omitted. At the start of the procedure the bone fragment 4 has been moved away from the bone fragment 3 in the direction of the z- axis to thereby overstretch the fracture and it is misaligned both by angulation and dislocation. The angulation is corrected by a rotation A about the y-axis as indicated in Figure 3a and the dislocation is corrected by a translation B along the x-axis as in Figure 3b. As noted above these two corrections could be performed in the reverse order or at the same time. The end result is a bone that, when viewed along the y-axis, is aligned both in angulation and sideways position as shown in Figure 3c. The mechanism of the mobile coupling 10 is fixed in relation to the other possible movements C to E and hence the overstretching of the fracture is still present in Figure 3c. Figures 4a to 4b show the subsequent sequence of movements with the bone viewed along the x-axis looking toward the y-z plane. During these movements the mobile coupling mechanism 10 is arranged to prevent movement in rotation A about the y-axis and translation B along the x-axis. As a result the corrections applied in Figures 3a to 3c will not be disturbed. The angulation is corrected by a rotation C about the x-axis as indicated in Figure 4a and the dislocation is corrected by a translation D along the y-axis as in Figure 4b. As noted above these two corrections could be performed in the reverse order or at the same time. The end result is a bone that, when viewed along the x-axis, is aligned both in angulation and sideways position as shown in Figure 4c. Since movement is restricted in the plane orthogonal to the x-axis then there can be no movement when viewing along the y-axis. As a result the bone fragments 3, 4 would also be aligned when viewed along the y axis. The bone is hence completely aligned in both of the two orthogonal planes and no more rotation or translation in the x or y directions is required.

The overstretching of the fracture can then be reversed by a movement E along the z-axis. The reponation is then completed and the bone fragments can be secured in place using any suitable clamping arrangement. This can be done whilst the bone fragments remain fixed in place by the reponator apparatus and hence there is no risk of inadvertently moving the bone out of alignment during fixation. The bone fragments 3, 4 will then be aligned and stably connected together in order to allow for healing of the bone.

As an alternative to movement of the mobile coupling 10 along the third orthogonal axis to reverse the overstretching of the fracture it is also possible to allow for a movement of the fixed coupling 8 along the third orthogonal axis. With this alternative the fixed coupling 8 would be mounted for sliding movement along the third orthogonal axis and would be provided with a clamp or locking mechanism to fix it in place and prevent movement during the angulation and dislocation corrections of Figures 3 and 4.

Figures 5 to 1 1 show a further example of a mechanism for providing the required reponation movement. The bone reponator apparatus is illustrated with simulated bone fragments and simulated X-ray imaging planes. Wooden blocks 3, 4 act as the first and second bone fragments 3, 4 and these will be referenced herein as simulated bone fragments 3, 4. As with the previous example the simulated bone fragments 3, 4 are connected by pins 6 to a fixed coupling 8 and a mobile coupling 10. The fixed coupling 8 is connected to the first simulated bone fragment 3 and the mobile coupling mechanism 10 is connected to the second simulated bone fragment 4. Further connecting rods and articulated joints are used to connect the pins 6 to the mechanism of the couplings 8, 10. It will be appreciated that the exact form of these rods and joints is not particularly limited, provided that they rigidly connect the bone fragments to the couplings and can be joined to the bone in a fashion that is appropriate for the condition of the patient undergoing treatment.

The reponator apparatus is shown with simulated X-ray imaging planes 22 and 24, which are orthogonal planes that are in alignment with the planes of adjustment of the mobile coupling 10. The X-ray images are simulated by shadows 20 and 26 cast on the planes 22 and 24 by vertical and horizontally directed light sources. A first shadow 26 shows the vertical translational and rotational alignment of the simulated bone fragments 3, 4 and a second shadow 20 shows the horizontal translational and rotational alignment of the simulated bone fragments 3, 4. When both of the shadows 26, 20 appear to show aligned bone fragments then the bone fragments will be completely aligned. In practice the optical light would be replaced by an X-ray source and images equivalent to the shadows 26, 20 would be provided by an X-ray intensifier.

As with the example described above the mobile coupling 10 allows for a rotation A about a normal to a first plane and a translational movement B along the first plane. The first plane is aligned with a vertical plane 24 of the imaging system and hence the first shadow 26 shows the alignment in the first plane. Similarly a rotation C and a translational movement D (not shown) are permitted in a second plane, which in this case is aligned with the horizontal plane of the imaging system.

In contrast to the simple example above, which allowed for translation along only one axis, the mechanism of Figures 5 to 1 1 allows for two dimensional movement and simultaneous rotational movement. With reference to the movement B in the first plane it will be see that this is achieved by the use of two slotted plates 32 aligned with the arrows. The slotted plates 32 run along the first plane and hence allow for translational movement in the first plane only. A pin 34 joins the two slots together and allows for rotation of one plate relative to the other. There is a screw clamp mechanism that, when tightened, will prevent rotation or sliding of the pin 34 in the slotted plates 32. When the clamp is loosened then both sliding and rotation is possible. The rotation is restricted to be about a normal to the plane of the plates and slots and hence forms the rotation A. A similar mechanism with two slotted plates 36, a pin 38, and a screw clamp is placed orthogonal to the mechanism for the first plane and permits two dimensional translational movement in the second plane as well as the rotation C. This mechanism 36, 38 is not fully visible in all of the Figures and is best viewed in Figures 6 to 1 1.

Also visible in Figure 5 is a fracture stabilising rod 28. Such a rod 28 is typically fixed to the patient once the bone pins 6 have been inserted to allow the patient to be moved without risk of inadvertent movement of the fractured bone. Figure 6 shows the apparatus of Figure 5 from a different angle where a further rod 30 is visible. This is a reponator start-off positioning rod 30 and it is used to fix the mobile coupling 10 in a desired starting position. When both the fracture stabilising rod 28 and the reponator start- off positioning rod 30 are in place the patient can be safely joined to the reponator couplings 8, 10 and manoeuvred into a suitable position for reponation. The fracture stabilising rod 28 and reponator start-off positioning rod 30 can then be removed as shown in Figure 7. At this point the bone fragments are held in place since the two pin connections 34, 38 on the mobile coupling 10 are clamped in position.

Correction of the bone position can then begin, guided by the X-ray image as represented by the shadows 26, 20. Figure 8 shows the results of movements A and B in the first plane. To allow these movements the clamping action of the pin 34 is released and the slotted plates 32 are slid and rotated relative to one another. It will be seen that the first shadow 26 in Figure 8 shows that the simulated bone fragments 3, 4 are aligned in the vertical plane. However the second shadow 20 shows misalignment in the horizontal plane. The pin 34 is fixed in place again to prevent further movement in the first plane and the pin 38 is released to allow for rotation C and translation D by rotating and sliding the slotted plates 36 for horizontal correction of the position of the bone fragments 3, 4. The simulated bone fragments 3, 4 can then be aligned in both planes, as shown in Figure 9.

The next step is to correct for overstretching of the fracture by movement E in the direction of the longitudinal axis of the bone. With this apparatus it is possible to do this by loosening any one of the pins 34, 38 and using the two dimensional adjustment to make a movement in the direction of arrow E only. Alternatively a separate sliding connection can be provided to allow for the overstretching to be corrected.

Figure 10 illustrates the final result, with a fully aligned pair of simulated bone fragments 3, 4 and hence fully aligned images in both orthogonal planes as demonstrated by the two shadows 26, 20. The final step is to re-fit the fracture stabilising rod 28 whilst the bone fragments are clamped in place by the mobile coupling 10. Figure 1 1 shows the fracture stabilising rod 28 re-fitted to pins 6 via the external fixation clamps. The patient can then be released from the reponator apparatus with the now aligned fracture safely held by the fracture stabilising rod 28.

In a further alternative embodiment, which is not illustrated in the drawings, the reponator apparatus further includes a pivot or turntable mechanism for rotational alignment of the bone fragments 3, 4 about the third orthogonal axis, which would typically be the longitudinal axis of the bone (the z-axis of Figure 2). This then allows mechanical and controlled adjustment of the rotation of the bone. The pivot or turntable mechanism of this alternative embodiment has a clamp or locking mechanism to prevent movement whilst angulation and sideward dislocation is being corrected in the other two axes. This correction can be carried out as shown in Figures 3 and 4, preferably after an initial correction for rotation of the bone, with a final correction for rotation of the bone then being performed prior to reversing the overstretching of the fracture to bring the bone fragments into contact ready for healing.

As noted previously, whilst smooth wires or rods are described in relation to the preferred embodiment and shown schematically in the Figures, the invention also extends to the use of the reponator apparatus for other alternatives used in bone fixation including threaded wires, rods, pins, half pins and so on. Furthermore, it will be appreciated that the mechanism utilised for the required rotational and translational movement of the bone can be varied. Any appropriate mechanism can be used to provide this movement. The use of the x, y and z notation for the axes and planes described herein is arbitrary and of course any appropriate set of orthogonal planes could be used.

Claims

CLAIMS:

1. A bone reponator apparatus comprising:

a fixed coupling for connection to a first bone fragment and a mobile coupling for connection to a second bone fragment;

wherein the mobile coupling is for providing rotational and translational movement of the second bone fragment in first and second orthogonal planes;

wherein the fixed coupling is arranged to prevent movement of the first bone fragment in the first and second planes; and

wherein the mobile coupling is arranged to permit rotational movement about a normal to the first plane and translational movement along the first plane whilst preventing rotational movement about a normal to the second plane and translational movement along the second plane, and to permit rotational movement about the normal to the second plane and translational movement along the second plane whilst preventing rotational movement about the normal to the first plane and translational movement along the first plane.

2. An apparatus as claimed in claim 1 comprising a mechanism for mounting the couplings to an operating table and/or imaging system such that the fixed coupling does not move relative to the operating table and/or imaging system and the mobile coupling can move the second bone fragment relative to the operating table and/or imaging system.

3. An apparatus as claimed in claim 2, wherein the mechanism for mounting the couplings is arranged to align the first and second planes with orthogonal imaging planes of the imaging system.

4. An apparatus as claimed in claim 1 , 2 or 3, arranged so that, in use, the first and second planes extend in a radial direction relative to the longitudinal axis of the bone.

5. An apparatus as claimed in any preceding claim, wherein the mobile coupling has a first mode of operation where corrections in the first plane are permitted whilst movement in the second plane is not permitted, and a second mode of operation where corrections in the second plane are permitted whilst movement in the first plane is not permitted, and wherein in the first mode simultaneous rotational and translational movements in the first plane are permitted, and in the second mode simultaneous rotational and translational movements in the second plane are permitted.

6. An apparatus as claimed in claim 5, comprising a mechanism for clamping parts of the mobile coupling in order to selectively prevent movement in the first plane or in the second plane, and to hence allow operation in the first mode and second mode.

7. An apparatus as claimed in any preceding claim, wherein the apparatus is arranged for a movement of the bone fragments relative to one another along the longitudinal axis of the bone.

8. An apparatus as claimed in claim 7, arranged such that, in use, the longitudinal axis of the bone can be aligned with the line of intersection of the two orthogonal planes.

9. An apparatus as claimed in any preceding claim further comprising an imaging system arranged to take images of the bone in orthogonal planes aligned with the first and second planes.

10. An apparatus as claimed in any preceding claim wherein mobile coupling allows the translational movement in the first plane and/or second plane to be a two dimensional movement in that plane.

11. A method comprising use of the apparatus described above for reponation of a bone in the human or animal body.

12. A method of reponation of a bone in the human or animal body comprising: attaching a first bone fragment to a fixed coupling of a reponator apparatus; and attaching a second bone fragment to a mobile coupling of the reponator apparatus; wherein the mobile coupling is for providing rotational and translational movement of the second bone fragment in first and second orthogonal planes;

wherein the method comprises: aligning the two bone fragments in the first plane by rotational movement of the second bone fragment about a normal to the first plane and translational movement of the second bone fragment along the first plane whilst preventing rotational movement about a normal to the second plane and translational movement along the second plane, and then aligning the two bone fragments in the second plane by rotational movement of the second bone fragment about the normal to the second plane and translational movement of the second bone fragment along the second plane whilst preventing rotational movement about the normal to the first plane and translational movement along the first plane.

13. A method as claimed in claim 12 comprising: mounting the couplings to an operating table and/or imaging system such that the fixed coupling does not move relative to the operating table and/or imaging system and the mobile coupling can move the second bone fragment relative to the operating table and/or imaging system with the rotational and translational movements set out above.

14. A method as claimed in claim 13, comprising mounting the couplings relative to an imaging system, wherein the step of mounting the couplings includes aligning the first and second planes with orthogonal imaging planes of the imaging system.

15. A method as claimed in claim 12, 13 or 1214 wherein the first and second planes are in a radial direction relative to the longitudinal axis of the bone.

16. A method of reponation substantially as hereinbefore described with reference to Figures 2 to 4c or Figures 5 to 1 1 of the accompanying drawings.

17. A reponator apparatus substantially as hereinbefore described with reference to Figures 2 to 4c or Figures 5 to 1 1 of the accompanying drawings.