WO2007122385A2

WO2007122385A2 - Fixator member

Info

Publication number: WO2007122385A2
Application number: PCT/GB2007/001372
Authority: WO
Inventors: Martin Arthur Elloy; Peter James Raffan
Original assignee: Fixator Innovations Limited
Priority date: 2006-04-13
Filing date: 2007-04-13
Publication date: 2007-11-01
Also published as: GB0607535D0; WO2007122385A3

Abstract

A mouldable fixator member for external fixing of bone fractures is made of thermoplastic, reinforced with fibre, can be moulded at 6O0C, is set rigid at body temperature but can be reheated and remoulded. It is used to fix a Fracture in combination with clamps and transfixion pins.

Description

FIXATOR MEMBER

The present invention relates to a fixator for use in external fixation of bone 5 fractures. In particular, the present invention relates to a fixator member and an external fixator comprising a fixator member, and to uses thereof.

Various different fracture repair systems are in common use to manage unstable fractures of weight bearing bones. These include external fixator IO systems using a scaffold of fixator members, e.g. metal rods or beams, and clamps, and internal fixator systems, for example the bone plate and screw system and the interlocking nail system.

The main advantages of the external fixator system are that it allows 15 adjustments to fracture alignment and loading during and after surgery. It is a system that can be applied without approaching the fracture site.. Also, the ability to use a minimally invasive, closed application technique preserves surrounding soft tissue, minimises damage to the bone's blood supply and optimises the biologic environment at the fracture site for bone healing, >0

The external fixator has two basic elements, regardless of the device or system used, the fixator transfixion pins that are attached to, normally by being screwed into, the bone and left protruding through the skin, and the rigid connecting beam or beams attached to the pins on the outside of the skin to >5 bear the load.

The pins are placed into or through sound bone on either side of the fracture site. However, the position of the pins is governed by the presence of muscle and other soft tissue, blood vessels and nerves. Wherever possible, the pins 50 are placed in 'safe corridors' in the soft tissue and may emerge from the skin at different angles and in different planes. To build the fixator frame, the beams must be routed around these pins and the clamps that attach the beams to the pins must accommodate beams and pins at various angles.

The majority of fixators use straight beams made of metal or carbon fibre reinforced thermoset polymers or metal tubes, connected to the pins with metal clamps. To achieve the necessary support for the fractured bone, the surgeon builds a frame to match the perceived stiffness required. As the required stiffness increases so does the complexity of the fixator frame. The result can be a heavy, awkward frame, which is susceptible to damage and is attached to the outside of a limb of a patient. The heavy, awkward fixator frame also interferes with the radiological examination of the fracture site.

Another approach, typically used in veterinary orthopaedics and non-weight bearing fractures in humans, such as hand fractures, is to use a cast-in-place acrylic beam. Here the pins are pushed through a flexible tube and acrylic resin is poured into the tube to harden around the pins.

This method provides a more flexible, cost effective, lightweight, radiolucent beam that accommodates pins at any angle in any plane. However, once set the resin can not be softened to adjust its shape and, as the pins are permanently set in the resin, they cannot be disconnected or adjusted until the entire assembly is removed.

Bone fixation systems are known in the art.

An example of a metal fixation rod is seen in US4969886. WO2005/013839 describes use of shape memory metal in implants designed for spinal fixation. These are not fixators, in that they are internal, not external, devices. The shape memory property is used to apply force to healing joints. FR2405063 describes fixation rods, made of a variety of plastics. They are designed to be sterilizable and said to have high heat stability.

EP1000585, GB2086231 and WO89/09031 all describe fixation systems which use hardenable fillers or polymers, either within or otherwise as part of the fixation support. Once hardened these can not be manipulated.

DE2440856 and US6096079 both relate to facial surgery. US6096079 describes use of a flexible metal bar to hold craniofacial bones. Similarly, DE2440856 describes fixing a fractures jaw using plastics tubing which is mouldable at room temperature.

It is, therefore, an object of the present invention to provide alternatives to the above and preferably seek to alleviate the above identified problems.

According to a first aspect of the present invention, there is provided a mouldable fixator member for external fixation of bone fractures.

The present invention therefore provides a fixator member, which can be moulded to a desired shape in order that it may be connected to a plurality, and sometimes all, of the pins attached to a fractured bone. It can then if needed be reheated and remoulded - the fixator is not thermosetting but thermoplastic. The fixator member can be attached irrespective of the angle of projection or plane of the pins from the bone because it can be moulded into a shape, which is coincident with the shafts of the pins. The use of a fixator member according to the present invention thus negates the need for a large number of straight fixator rods and crossing members, as required by the prior art devices, to allow connection of a fixator rod to each of the pins. The result is a much lighter and less bulky arrangement around the fracture site. Furthermore, the time taken to implement an external fixator comprising a fixator member of the present invention can be greatly reduced. The fixator member of the present invention can be moulded such that it may be attached to all of the pins, or, if it is more practical, two or more fixator members of the present invention may be used in place of a larger number of straight fixator rods of the prior art.

As such, there is provided a mouldable external fixator member, preferably one that can be moulded by hand. There is also provided an external fixator comprising at least one mouldable external fixator member. There is further provided a mouldable fixator bar, rod or beam for external fixation of bone fractures - again, both preferably mouldable by hand.

Preferably, the fixator member is mouldable at high temperatures but rigid at lower temperatures. In preferred embodiments, the fixator member is mouldable above about 60°C but set hard below about 40⁰C. This allows the fixator member to be moulded into a desired shape at the high temperature and the desired shape maintained thereafter once it has cooled. The fixator member is preferably set hard such that it is able to support the weight borne by the fractured bone, on its own or in combination with one or more additional fixator members.

In use of an example of the invention, the fixator is heated to about 60⁰C, at which temperature it can be moulded by hand by an operator - e.g. a surgeon. It is then moulded in situ so that its shape enables pins to be attached to bone around a fracture site and attached to the fixator. It is then cooled to about ambient temperature and sets hard. Ambient temperature will vary but is generally below typical body temperature of about 37⁰C - the fixator is hence set hard at body temperature. The fixator is

Preferably, the fixator member comprises a thermoplastic polymer. In one embodiment, the fixator member comprises polycaprolactone. In preferred embodiments, the fixator member is reinforced. Preferably, the fixator member is reinforced with fibre, and this can be for example carbon fibre and/or glass fibre. The amount of fibre can vary, and the fixator member can comprise for example from about 5 to 80% by weight carbon fibre and/or glass fibre. Further preferably the fixator member comprises 5 to 50% by weight carbon fibre and/or glass fibre.

Polymer of the fixator can be fibre filled or fibre reinforced in accordance with known use of reinforcing fibre. Thus, in a further embodiment, the fixator member comprises one or more layers of fibre. Preferably, the fixator member comprises fibre running in at least two different directions. Alternatively, the fixator comprises fibre running in the same direction. In another embodiment, the fixator member comprises two or more layers of fibre, wherein the fibres of at least one layer lie in different directions to the fibres of at least one other layer.

A particularly preferred embodiment of the invention is a fixator member, made of thermoplastic polymer reinforced with from 5 to 50% fibre, mouldable at 60°C and set hard at 37°C.

More generally, fixator members of the invention are suitably made of a fibre - filled (preferably carbon fibre-filled) mouldable thermoplastic. This can comprise polycaprolactone, with suitably from 5-80% weight carbon fibres. In a specific embodiment, the invention uses carbon fibre - filled polycaprolactone.

Filled polycaprolactone containing carbon fibres can be prepared by known methods. In a typical method, polycaprolactone from a commercial source is melted and poured over a mat of carbon fibres, suitably at from 5 to 80% more suitably to 50%, preferably 10 to 40% by weight, which are hence incorporated into the reinforced polymer matrix. The carbon fibres can be a mixture of short and/or long fibres. Fibres can be woven for increased strength e.g. to resist torsional, axial and/or bending forces, especially at +/- 45 degrees. A specific polymer for use in the invention can be prepared in accordance with the methods disclosed in US-A-20040054372, the contents of which is incorporated herein, using carbon fibres instead of glass fibres. The carbon fibre - filled mouldable thermoplastic is preferably built up from laminated layers of carbon fibre mat. Each mat preferably has fibres running in two directions, further preferably at right angles to each other, for example, longitudinal and horizontal. Every second layer is preferably laid at about 45 degrees to the layer below. In other words, fibres in the first layer preferably run longitudinal and horizontal, in the second layer the fibres preferably run at about 45 degrees in both directions in relation to the first layer, in the third layer the fibres preferably run in substantially the same direction as the first layer, and in the fourth layer the fibres are again preferably at about 45 degrees, and so on. This pattern has been shown to be particularly effective, however, it will be envisaged that other patterns may be suitable. In particular, the carbon fibre - filled mouldable thermoplastic could be built up from carbon fibre mat having more horizontal and longitudinal layers, or more about 45 degree layers, or no about 45 degree fibres.

As detailed above, the polymer is preferably polycaprolactone. However, other suitable alternatives may be used, for example biocompatible polyethylene or nylon. Use of these polymers tend to result in a higher softening temperature and may be cheaper to manufacture.

In preferred embodiments, the strength of the fibre - filled thermoplastic is tailored to the required strength of its application, which may depend for example on the bone being fixed and the size and weight of the patient. For example, if the fixator is to be used for a fractured bone which would normally bear a high weight, the fixator member will generally be provided with a greater strength than that required for a fractured bone which would normally bear a low weight.

In general, the fixator member of the invention preferably has a longitudinal strength of at least about 50, more preferably about 70 GPa. The fixator member suitably has a minimum lateral strength of about 20 or about 40 GPa. The fixator member suitably has a shear strength of at least about 20 or about 40 GPa. Again generally, the fixator member has a minimum ultimate tensile strength (UTS) of about 130 MPa.

Preferably, the fixator member has a minimum fatigue strength of about 120 to 160 MPa, more preferably about 140 MPa.

Preferably, a fixator member of the invention has a minimum bending stiffness about 1Nm per degree of movement, more preferably about 1.5Nm or 2Nm per degree of movement. Preferably, a fixator member has a fatigue strength of about 1 million cycles bending at a minimum of about 6Nm.

The above discussed strength parameters are preferably achieved at below about 4O⁰C and at about 100% humidity in physiological saline.

It is further optional that the fixator member comprises magnetic material, which can be incorporated into polymer of the fixator or which is separate from the polymer and enclosed within the polymer. In one embodiment, the fixator member comprises polymer containing from 1 to 30% by weight of magnetic material, for example magnetic metal or magnetic metal particles - we have made polymer containing about 4% by weight ferrite particles. The magnetic material can be a coil of magnetic metal either outside the polymer or within the polymer, and optionally both outside and within. In another embodiment of the invention, illustrated in examples below, we have made a fixator comprising a magnetic metal coil encased within the polymer. The coil can be or different pitch. The coil can be close coiled or open coiled. In an example shown below a close coiled spring is illustrated.

An advantage of including the magnetic material is that the fixator member can be heated by induction heating, enabling easy heating to moulding temperatures, and heating that can be performed in situ and with reduced or no risk of heat damage to surrounding tissue or equipment.

An additional advantage of the presence of the coil is the strength conferred on the resultant composite fixator member.

Another particularly preferred embodiment of the invention is a fixator member, made of thermoplastic polymer reinforced with from 5 to 50% fibre and containing from 1 to 30% by weight magnetic metal or magnetic metal particles, mouldable at 60°C and set hard at 37⁰C. A further particularly preferred embodiment of the invention is a fixator member, comprising a coil of magnetic metal made of thermoplastic polymer reinforced with from 5 to 50% fibre and containing from 1 to 30% by weight magnetic metal or magnetic metal particles, mouldable at 60⁰C and set hard at 37°C.

Reinforcement with fibre and use of magnetic material can be used in combination. Further embodiments of the invention comprise polymer which is fibre-reinforced and which contains magnetic particles or a magnetic metal coil. As illustrated in examples below, a fixator member of the invention comprises a core of close coiled wire of magnetic material surrounded with randomly orientated short reinforcing fibres. In another embodiment shown in the examples, the fixator member has an externally wound coil of magnetic wire encompassing polymer which contains randomly orientated short fibres. In a still further embodiment, also shown below, a fixator member has both internal and external coils, wound in opposite senses inside and surrounding polymer which contains short, randomly orientated fibres. The fixator member can also additionally comprises an inner reinforced core or section. In these embodiments, a fixator member comprises an inner core, for example comprising fibre such as carbon fibre, surrounded by thermoplastic polymer and optionally containing a magnetic metal coil or being partially filled with magnetic metal particles. Alternatively, or in addition to the inner core, it is preferred that the fixator member comprises an outer reinforced section. Preferably, a fixator member is provided which comprises an inner section reinforced with a first type of fibre and an outer section reinforced with a second type of fibre. The first type of fibre may be glass fibre, and the second type of fibre may be carbon fibre, or vice versa.

In preferred embodiments, the fibres or the coil elements extend along substantially the entire length of the fixator member.

In accordance with its conventional uses, the fixator member is generally in the form of a rod or bar shape. Preferably, the fixator member comprises a substantially circular cross section. In preferred embodiments, the fixator member has a diameter of between about 5 mm and about 20 mm. For example, the fixator member may preferably have a diameter of around 6.5 mm. The diameter of the fixator member is preferably tailored to the size of the bone being fixed as is known in this art.

According to a further aspect of the present invention, there is provided a fixator for external fixing of bone fractures, the fixator comprising:

(a) a fixator member as described above, and

(b) a plurality of connectors for attachment of the fixator member to a plurality of pins attached to a fractured bone.

According to another aspect of the present invention, there is provided a kit for fixing bone fractures, the kit comprising: (a) a fixator member as described above, and

Preferably, the kit further comprises:

(c) a plurality of pins for attachment to a fractured bone.

According to a further aspect of the present invention, there is provided a method of fixing a fractured bone, the method comprising: - (i) attaching pins to the fractured bone either side of a fracture site;

(ii) heating a mouldable fixator member according to the invention;

(iii) moulding the fixator member to be coincident with the pins attached to the bone;

(iv) cooling the fixator member to become rigid; and (v) connecting the fixator member to the pins.

Preferably, the fixator member is moulded to be coincident with all the pins. In one embodiment, two or more fixator members are heated, moulded, cooled and connected to the pins. In preferred embodiments, the cooled fixator member or members are able to support substantially the entire load of the fractured bone.

The fixator member or members are preferably heated by immersion in hot water, or by hot air, or by induction heating. They are preferably heated in situ, enabling heating and moulding to take place conveniently for the user, typically a surgeon. Through use of a thermoplastic having the properties described, the fixator member can in use be heated, moulded to a desired shape and then cooled to set it hard. It can then be re-heated and its shape adjusted, for example to accommodate a particular pin location. It can be reheated and remoulded in situ, in close proximity to the pins and the bone being fixed. If a further change to the shape is needed then, again, it can be reheated and remoulded.

Preferably, the fixator member or members are cooled by the application of water or saline. Alternatively, the fixator member or members may simply be allowed to cool.

Conveniently, the fixator member or members are connected to the pins via connectors.

The thickness of the fixator member will generally depend upon the weight, which the external fixator will be required to bear. However, in typical, embodiments the fixator member will have a diameter of around 5 mm to 15 mm, preferably around 5 mm to 10 mm, more preferably around 6.5 mm. For large animals, for example an exotic animal (say in a zoo) the fixator member may have a thickness of up to 20mm or more.

The length of the fixator member is preferably tailored to the length of the fractured bone and the fracture. In preferred embodiments, the fixator member is provided at a standard length and can then be cut to size by a surgeon.

Methods of softening the fixator member preferably include by induction heating of the magnetic components in the construct or of the carbon fibres, e.g. with a suitably shaped water cooled coil attached to an induction heating machine or other suitable equipment, by hot water, by hot air, or by other methods known in the art. By using induction heating or by electricity conducted within the carbon fibres, the softening temperature can be extended upwards and in excess of 100°C. This increases the choice of thermoplastics available, for example nylons and polyethylenes, and thus can result in a stiffer fixator member at room temperature at a lower cost. In embodiments of the invention that take advantage of induction heating, the high temperature at which the fixator member is mouldable is 70°C or more, and can be 80°C or more.

The invention is suitable for application to animals, including humans, and birds, including small animals and birds.

The thermoplastic used in the fixator member of an embodiment comprises polycaprolactone, with suitably from 5-80% weight carbon fibres. Filled polycaprolactone containing carbon fibres can be prepared by known methods. In one method, used to make a fixator shown in the examples, polycaprolactone from a commercial source is melted and pultruded over a core of a close coiled wire spring. Another coil of wire or fibres is pulwound over the extruding rod. The wire elements, bound together with the fibres, provide torsional stiffness to the construct as well as a magnetic media to facilitate induction heating. In another method, polycaprolactone from a commercial source is melted and poured over a mat of carbon fibres, suitably at from 5 to 80% more suitably to 50%, preferably 10 to 40% by weight, which are hence incorporated into the reinforced polymer matrix. The carbon fibres can be a mixture of short and/or long fibres. Fibres can be woven for increased strength e.g. to resist torsional, axial and/or bending forces, especially at about +/- 45 degrees. A specific polymer for use in the invention can be prepared in accordance with the methods disclosed in US-A- 20040054372, the contents of which is incorporated herein, using carbon fibres instead of glass fibres if desired.

The carbon fibre - filled mouldable thermoplastic used for forming the fixator member is preferably built up from laminated layers of carbon fibre mat. Each mat preferably has fibres running in two directions, further preferably at right angles to each other, for example, longitudinal and horizontal. Every second layer is preferably laid at about 45 degrees to the layer below. In other words, fibres in the first layer preferably run longitudinal and horizontal, in the second layer the fibres preferably run at about 45 degrees in both directions in relation to the first layer, in the third layer the fibres preferably run in substantially the same direction as the first layer, and in the fourth layer the fibres are again preferably at about 45 degrees, and so on. This pattern has been shown to be particularly effective, however, it will be envisaged that other patterns may be suitable. In particular, the carbon fibre - filled mouldable thermoplastic could be built up from carbon fibre mat having more horizontal and longitudinal layers, or more about 45 degree layers, or no about 45 degree fibres. If a core or external spring element is incorporated fibres may be chopped to a length sufficient to adequately bridge the coils.

As an alternative to carbon fibre, glass fibre can also be used and prepared in the same way as the carbon fibre above. As a further alternative, any suitable reinforcement fibre known in the art may be used, for example aramid. The fibres should be capable of withstanding the process temperatures and be compatible with the matrix polymer.

The fibres can be provided as straight, long carbon fibres, as braided fibres, chopped fibres, or as a mixture of the two. The fibres may be provided substantially in alignment with a longitudinal axis of the fixator member.

Alternatively, the fibres may be provided substantially perpendicular to a longitudinal axis of the fixator member or at an angle between perpendicular and in alignment with the longitudinal axis. In a further embodiment, fibres can be provided of varying alignment with the longitudinal axis. The fibres can also be provided such that they extend along the entire length of the fixator member.

As detailed above, the polymer is preferably polycaprolactone. However, other suitable alternatives may be used, for example polyethylenes, polypropylenes, polydienes or nylon. Use of these polymers will result in a higher softening temperature and will be cheaper to manufacture.

In preferred embodiments, the fixator member comprises up to twelve layers, or more of fibre mat, preferably between 5 and 7 layers of fibre mat. The number of layers used depends upon the size of the fixator member required. In this connection, more layers will be used for larger, stronger fixator members and maybe fewer layers for smaller fixator members.

The fixator member may be prepared using compression moulding.

Another preferred embodiment the fixator member is formed by pultruding chopped fibre reinforced polymer over a spring of magnetic metal. In this embodiment fibres or a metallic filament may be pulwound over the extrusion.

As an alternative to the use of magnetic filaments in the construct, a magnetic filler e.g. ferrite, in particular form may be added to the polymer.

Alternative methods of manufacture may also be used and may depend upon the amount of fixator member to be produced. For example, when it comes to bulk manufacture, the 'wetting out' process may be modified, or an alternative method used, and compression moulding may be replaced by another method such as pultrusion, which is cheaper than compression moulding. Further examples of suitable methods of production include pultrusion of commingled fibres where fibres of both the polymer and reinforcement are consolidated and formed into a profile, and direct melt pultrusion where reinforcement fibres are impregnated with polymer melt and consolidated into a profile.

Further, different methods of manufacture may preferably be used depending upon the nature of the fixator member being produced. For example, pultrusion may preferably be used for straight fixator members, with another method such as compression moulding preferably used for shaped fixator members.

Preferably the fixator member is substantially straight. Alternatively, the fixator member comprises a pre-determined shape for fitting the profile of pins projecting from a bone having a fracture for which there is a predetermined pattern of pins. It is also envisaged that the fixator member can be moulded into the correct shape immediately prior to attachment to the pins.

In use of an example of the invention, the bone is identified and fixator member of suitable dimension, made of the thermoplastic, selected. If no suitably sized fixator member is available then a larger fixator member can be cut down to size. It is hence not necessary to provide to the surgeon a large inventory of differently sized fixator members. Instead, a larger section of the fixator member can be cut once the size needed for the particular fracture is known, and this can be done during the course of an operation.

The fixator member is manipulated into the desired shape either before or after attachment of pins to the fractured bone. Typically, the fixator member is heated during the operation, or it can be heated prior to the operation and then maintained in a mouldable state. The fixator member may cool to some extent during handling and whilst it is being positioned. However, the fixator member, once heated to a temperature at which it can be moulded, will retain mouldability as the temperature decreases. If the temperature drops such that the fixator member can no longer be moulded then local application of heat, for example using hot water or induction heating or. electrically with electrodes, can increase the mouldability so the surgeon can complete the process of shaping the fixator member. The fixator member once correctly positioned can be allowed to cool or can actively be cooled, for example using a cooling liquid such as water or saline solution or other solution suitable for use during surgery. The fixator member then becomes rigid and is rigid and sufficiently strong to support the bone at room temperature.

An external fixator comprising the fixator member, clamps and pins can be used alone or in conjunction with other devices for securing bone fractures. For example, the external fixator may be combined with bone plates, an intramedulary pin or intramedulary biocompatible composite rod.

According to a further aspect of the present invention, there is provided use of" a thermoplastic, mouldable polymer as hereindescribed in the manufacture of an external fixator member.

An example of the present invention will now be described in detail with reference to the accompanying drawings, in which: -

Figure 1 shows a known external fixator of the type having a plurality of straight metal rods;

Figure 2A shows a first view of a fixator member and connectors according to the present invention;

Figure 2B shows a second view of a fixator member and connectors according to the present invention;

Figure 3A show a schematic cross section of a fixator member according to the present invention wherein the fixator member is reinforced with carbon fibre uniformly throughout its cross section;

Figure 3B shows a schematic cross section of a fixator member according the present invention wherein the fixator member is reinforced with carbon fibre at an outer section; Figure 3C shows a schematic cross section of a fixator member according to the present invention wherein the fixator member is reinforced with glass fibre uniformly throughout its cross section;

Figure 3D shows a schematic cross section of a fixator member according the present invention wherein the fixator member is reinforced with glass fibre at an outer section;

Figure 3E shows a schematic cross section of a fixator member according to the present invention wherein the fixator member is reinforced with a mixture of carbon fibre and glass fibre uniformly throughout its cross section;

Figure 3F shows a schematic cross section of a fixator member according to the present invention wherein the fixator member is reinforced with carbon fibre at an outer section and with glass fibre at an inner section; and

Figures 3G and 3H show schematic' isometric views of a fixator member that has both internal and external wound elements of magnetic metal with interspersed random fibre reinforcement and continuous longitudinal core fibres.

As shown in figure 1 , known external fixators require a plurality of straight fixator rods 1 , which are usually metal, in order to support a plurality of pins 2 attached to a fractured bone 3 at required varying angles of projection. The pins are connected to the fixator rods via clamps 6. Due to the requirement of a plurality of straight fixator rods, it is also necessary to provide a plurality of cross members 4 to link and hold the fixator rods in a rigid scaffold around the fractured bone. Even with the provision of only two straight fixator rods, as shown in figure 1 , complex, bulky and heavy scaffold is required around the fractured bone. As the number of pins and variety of projection angles increases, the number of fixator rods and cross members required also increases. This can result in an even more complex scaffold, which, as discussed above, is hugely inconvenient for the patient, the physician and the radiographer.

As shown, in figure 2, in one embodiment of the present invention there is provided a mouldable fixator member 5 for use with connectors 6, e.g. clamps, which attach the mouldable fixator member to pins 2 attached to the fractured bone 3.

The fixator member can be provided in any suitable shape, but is here provided as a straight bar which is then moulded to the desired shape: once a surgeon has decided upon how many pins to attach to the bone and their angle of projection from the bone, the fixator member is heated to its moulding temperature and then moulded such that all the pins projecting from the bone can be attached to the fixator member. Once the fixator member has been moulded to the correct shape, it is allowed to cool to a temperature at which it becomes rigid before being attached to the pins. Alternatively, the fixator member can be attached to the pins whilst still mouldable and then allowed to cool. Once cooled, the fixator member is sufficiently rigid or hard to support the weight borne by the fractured bone. Alternatively, the fixator member is attached to the pins whilst still in a mouldable state, thus ensuring that all of the pins are supported in the desired angle. In such a way, it is also possible to make adjustments to the shape of the fixator member to optimise the support provided by the fixator member. The fixator member may be attached directly to the pins, for example via holes formed in the fixator member, or may be attached to the pins via connectors such as clamps commonly used in the art. In this respect, the fixator member can also be prepared with one or more pre-existing holes. For particularly complicated fractures where a large variety of angles of projection of pins is required, more than one fixator member of the present invention is used. This is still advantageous over known systems in which a larger number of fixator rods and cross members would have been required.

The illustrated fixator member is mouldable at high temperatures (at 60°C and above) but rigid at room temperature. This enables a user to heat the fixator member, e.g. by immersion in hot water, mould the fixator member in situ into the required shape and then cool the fixator member by. application e.g. of water or saline, setting the fixator member rigid.

Once the fixator member has cooled and become rigid, it is still possible to make adjustments to the shape and positioning of the fixator member by heating small sections. Fixator member that contains magnetic particles can be heated by induction heating. Thus, if it is felt that not enough support is being provided to one of the pins by the fixator member this can be easily corrected.

Figures 3A to 3H show embodiments of the invention in which different reinforcement of the fixator member is achieved through use of carbon fibre uniformly throughout its cross section (3A), carbon fibre at an outer section (3B), glass fibre uniformly throughout its cross section (3C), glass fibre at an outer section (3D), a mixture of carbon fibre and glass fibre uniformly throughout its cross section (3E), and carbon fibre at an outer section and with glass fibre at an inner section (3F).

Figures 3A to 3F show a variety of fibre arrangements dispersed within the fixator member 5. The examples shown relate to the use of carbon fibre 8 (Fig 3A, 3B), glass fibre 9 (Fig 3C, 3D), or a mixture of the two 8, 9 (Fig 3E, 3F). In figures 3B and 3D where the fibres are restricted to an outer section of the fixator member, the centre 10 of the fixator member may be left as un- reinforced polymer, or provided with a hollow core. Figures 3G and 3H show a construct comprising a close coiled spring surrounded by chopped fibre reinforced polymer . As an option an external counter-wound spring may be added and/or a core of continuous fibres. In further examples, the density of each fibre within the polymer may be different. Furthermore, the fibres may be provided at varying densities throughout the cross section. The pattern of fibre dispersal within the fixator member will depend upon the type of bone and/or fracture that the fixator member is to support, with differing arrangements providing differing degrees of strength to the fixator member.

Accordingly, there is provided a new type of external fixator which minimally impedes radiographs, is light and easy to manage, does not result in a complicated scaffold structure around a healing bone and can provide a significant cost saving over external fixation devices known in the art.

It will be appreciated that the examples of the invention discussed above are for illustrative purposes only and should not be construed to limit the scope of the invention. Various alterations and modifications to the examples described above will be envisaged by the skilled person whilst still falling within the scope of the invention.

Claims

1. A mouldable fixator member, for external fixing of bone fractures.

2. A fixator member according to claim 1 , which is non-thermosetting and which is mouldable at high temperatures but rigid at lower temperatures.

3. A fixator member according to claim 2, mouldable above about 60°C but set hard below about 40°C.

4. A fixator member according to any preceding claim, comprising a thermoplastic.

5. A fixator member according to claim 4, comprising polycaprolactone.

6. A fixator member according to any preceding claim, wherein the fixator member is reinforced.

7. A fixator member according to claim 6, comprising an inner reinforced section.

8. A fixator member according to claim 6 or 7, comprising an outer reinforced section.

9. A fixator member according to any of claims 6 to 8, reinforced with fibre. .

10. A fixator member according to claim 9, comprising one or more layers of fibre.

11. A fixator member according to claim 9 or 10, comprising fibre running in at least two different directions.

12. A fixator member according to claim 9 or 10, comprising fibre running in a single direction.

13. A fixator member according to claim 11, comprising two or more layers of fibre, wherein the fibres of at least one layer lie in different directions to the fibres of at least one other layer.

14. A fixator member according to any of claims 9 to 13, wherein the fibres extend substantially the entire length of the fixator member.

15. A fixator member according any of claims 1 to 14, reinforced with carbon fibre and/or glass fibre.

16. A fixator member according to claim 15, comprising from 5-80% by weight carbon fibre and/or glass fibre.

17. A fixator member according to claim 16, comprising 5-50% by weight carbon fibre and/or glass fibre.

18. A fixator member according to claims 1 to 15 comprising a spring-like metal core.

19. A fixator member according to claims 1 to 15 comprising a spring-like outer coating.

20. A fixator member according to claim 18 or 19 in which the spring like member is made of a magnetic material.

20. A fixator member according to claims 18 or 19 in which the spring like member is made of steel.

21. A fixator member according any previous claim in which the polymer has added particles of a magnetic material.

22. A fixator member according to any preceding claim in the shape of a rod or bar.

23. A fixator member according to any preceding claim comprising a hollow core.

24. A fixator member according to any preceding claim, comprising nylon, a polydiene and/or a polyethylene.

25. A fixator member according to any preceding claim having a substantially circular cross section.

26. A fixator member according to any preceding claim having a diameter of between about 5 mm and about 20 mm.

27. A fixator for external fixing of bone fractures, the fixator comprising

(a) a fixator member according to any preceding claim, and

28. A kit for fixing bone fractures, the kit comprising

(a) a fixator member according to any of claims 1 to 26 and

29. A kit according to claim 28 further comprising

(c) a plurality of pins for attachment to a fractured bone.

30. A method of fixing a fractured bone, the method comprising: - (i) attaching pins to the fractured bone either side of a fracture site; (ii) heating a mouldable fixator member according to any of claims 1 to 26; (iii) moulding the fixator member to be coincident with the pins attached to the bone;

31. A method according to claim 30, further comprising reheating the fixator member, remoulding the fixator member and then cooling the fixator member.

32. A method according to claim 30 or 31 , wherein two or more fixator members are heated, moulded, cooled and connected to the pins.

33. A method according to any of claims 30 to 32, wherein the cooled fixator member or members support substantially the entire load of the fractured bone.

34. A method according to any of claims 30 to 33, wherein the fixator member or members are heated by immersion in hot water, or by hot air, by induction heating or by conduction of electricity.

35. A method according to any of claims 30 to 34, wherein the fixator member or members are cooled by the application of water or saline.

36. A method according to any of claims 30 to 35, wherein the fixator member or members are connected to the pins via connectors.

37. Use of a thermoplastic, mouldable polymer in the manufacture of an external fixator member.

38. A fixator member substantially as described herein with reference to figures 2A, 2B and 3A to 3H.