GB2457740A

GB2457740A - A bone fastener for use in securing an intramedullary fixation device

Info

Publication number: GB2457740A
Application number: GB0806931A
Authority: GB
Inventors: Mohamed Khalid
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-10-08
Filing date: 2008-04-16
Publication date: 2009-08-26
Also published as: GB0806931D0

Abstract

An intramedullary rod 310 is inserted into a bone across a fracture 308 and is secured to the bone by means of a two-part fastener 330. The rod has a porous mesh region 313 and a reinforcing structure 320 which defines a windows 315 through which the fasteners may be inserted. Each bone fastener 330 comprises a first part 332 and a second part 334 which locate on opposite sides of the rod 310. The first part of the fastener is in the form of a punch and the second part is in the form of a dye which receives the part of the punch when the fastener is inserted. Both sections have a flange portion 346, 352 to contact with the outside surface of the bone 303.

Description

INTRAMEDULLARY FIXATION DEVICE AND A BONE FASTENER FOR USE

IN SECURiNG AN INTRAMEDULLARY FIXATION DEVICE The present invention relates to an intramedullary fixation device for keeping broken bones supported whilst they grow back together. More specifically, but not exclusively, the invention relates to an intramedullary rod for use in supporting broken bones following a fracture or osteotomy. The invention also relates to a bone fastener for securing an intramedullary rod in position across a bone fracture and to a method of inserting a bone fastener.

Often the tendon or arrangement of tendons in proximity to a fractured bone mean that it is difficult for the bone to be fixated by surgery without causing damage to one or more of the surrounding tendons.

For example, in the hand the proximal phalanges have an associated deep flexor tendon intimately related to a superficial flexor-tendon which both lie under the phalanx. Another tendon lies above the phalanx. It is important that these tendons are regularly mobilised to prevent any fibrous adhesions forming between the tendons and which may impair movement of the finger. It is therefore advantageous that the finger is mobilised as soon as possible after the fracture which some of the known methods of treating the fracture do not allow.

Known methods of treating fractures in the proximal phalanges may involve the splinting of the bones and joints on the exterior of the finger. Although this means *.... the bones of the fracture are supported and kept in alignment, movement of the finger *.

is restricted by this method and because the tendons are not being moved fibrous adhesions may form leading to stiffness of the finger when the splint is removed.

* 25 Physiotherapy after the splint is removed can help ease stiffness in the finger although in many cases full mobility may not be restored.

S. S*** * An alternative method is to use transfixing wires, such as K-wires * intramedullary across the fracture. The use of K-wires is more stable than using a splint, however, since the wires may extend over a joint in the bone the movement of the joint is still restricted and the same problems of stiffness of the finger as previously described may be experienced. In addition surgery is required to insert and then later remove wires from the hand.

Another known method is the use of a plate and screws fixator. Under surgery a plate is placed on the surface of the bone over the fracture and screws are placed through the plate and bone on either side of the fracture to hold the plate in place across the fracture. The screws are usually driven into the bone in a direction substantially perpendicular with respect to the plane of the surface of the bone. The problem associated with this method is that it is difficult to know how far to insert the screws into the bone. If they are inserted too far they protrude through to the other side of the bone and there is a risk they may rupture the sheaths of the underlying tendons, or the tendons themselves. Damage to the tendons may result in stiffness or loss of function of the finger. If the screws are not inserted sufficiently far the plate will not be firmly attached to the bone to keep the fracture fixated. Since the plate lies on the surface of the bone it must be inserted under the overlying tendon, which can be difficult and time consuming to do in surgery and again risks damage to the tendon.

Indeed the tendon is often intentionally split to facilitate placement of the plate. The surgery to fix the plate requires that an incision the length of the plate is made in the skin, which is undesirable since the healing of the skin impairs movement of the finger and may lead to scarring. Further it may be necessary that the plate is later removed, which would require additional surgery.

The problems outlined above which are experienced in fractures in the * ** proximal phalanges are also experienced in other areas of the body, for example the wrist where small bones are in very close proximity to tendons and are at a risk of I...

being damaged during fixation of the fracture. * S.

In larger bones, such as the tibia, fractures may be fixed using an *** * intramedullary rod. Typically, for the treatment of a fracture in the tibia a guide wire is inserted through and along the fractured bone from a location below the knee joint. A * reamer is then inserted to widen the hole through the bone and an elongate rod having a series of apertures near both ends of the rod is pushed through the hole in the bone across the fracture. After removing the guide wire and reamer, a jig moveable around the exterior of the leg is fitted to the top end or proximal end of the rod, which is the end nearest the knee, to assist with the insertion of bone fastener screws through the rod and bone to fixate the rod. Under x-ray, the surgeon attaches the jig to align the holes in the jig with the apertures near the top end/proximal end of the rod. The screws are then inserted from the exterior of the skin through the holes in the jig which guides the screws through the apertures in the rod and into the bone. For the apertures near the bottom, or distal, end of the rod the jig is not a useful device because it tends to sag and thus the holes in the jig do not correspond with the apertures in the rod. A jig can only be used accurately along a certain distance of the rod from the top (proximal) end of the rod. Typically, this distance is three times the diameter of the rod. The surgeon therefore has to drill holes in the bone free hand under x-ray control for affixing the distal end to the bone. Sometimes a targeting device with concentric circles together with a radiolucent drill is used to facilitate this difficult task. The screws must be inserted through the apertures perpendicular to the apertured surface of the rod. Even with the assistance of the targeting device and radiolucent drill it is no simple task and can be time consuming to align and insert the screws correctly into the apertures of the rod which is not desirable to the patient or the surgeon. A further problem with this arrangement is amount of debris which is produced when the rod is drilled in-situ intramedullary to receive the bone fastener screws. The debris can not only contaminate the fracture site but may provoke a foreign body reaction in the patient's body.

It has been proposed in WO 00/61018 (Depuy Orthopaedics, mc) to provide an * intramedullary nail or rod with opposing dynamization windows near the distal end into which a bio-resorbable spacer can be positioned. Screws are inserted into holes in * *** * the proximal end of the rod in the usual way whilst the distal end of the rod is secured using a bone fastener which is screwed into the spacer. As resorption of the spacer *:. occurs, stress is increasingly transmitted through the fracture site rather than through the rod. Such arrangements are reliant on the spacer being positioned in a window formed in the nail so as to be surrounded on all four sides by the metallic material of * the nail and on the use of a bio-resorbable material for the spacer. Bone healing is un-predictable and is dependent upon several factors like the age of the patient, extent of disruption of the bony and soft tissues, status of blood supply, infection etc. not all of which can be accurately predicted at the time of initial treatment of the fracture.

Therefore, although a useful concept in theory, such a device is rarely used in clinical practice because it is impossible to predict the precise amount of time required for the healing to take place and to match that with the time for resorption of the bio-resorbable material filling the window.

An object of the present invention is to provide apparatus and methods for the intramedullary fixation of bone fractures which mitigates or overcomes the problems associated with the aforementioned fixation techniques.

It is a further objective of the invention to provide an intramedullary rod which overcomes or at least mitigates some or all of the aforementioned problems with the

prior art.

It is a yet further object of the invention to provide an intramedullary rod in which a hole for receiving a bone fastener can be produced in-situ intramedullarly without drilling.

A further object of the invention is to provide an improved method of manufacturing an intramedullary rod.

A still further object of the device is to provide an improved bone fastener which can be secured to an intramedullary rod without pre-drilling a hole in the rod.

Another object of the invention is to provide an improved method of implanting an intramedullary rod across a break in a bone.

A further object of the invention is to provide an improved clamp which can 0S*S be used to insert a bone fastener through an intramedullary rod without the need to pre-drill a hole through the rod.

In accordance with a first aspect of the invention, there is provided a bone fastener as claimed in claim I. *..* Further optional features of the bone fastener in accordance with the first aspect of the invention are set out in the claims dependent on claim 1.

In accordance with a second aspect of the invention, there is provided an intramedullary rod as claimed in claim 14.

Further optional features of the intramedullary rod in accordance with the second aspect of the invention are set out in the claims dependent on claim 14.

In accordance with a third aspect of the invention, there is provided an intramedullary rod as claimed in claim 28.

Further optional features of the intramedullary rod in accordance with the third aspect of the invention are set out in the claims dependent on claim 28.

In accordance with a fourth aspect of the invention, there is provided a method of manufacturing an intramedullary rod in accordance with either of the second and third aspects of the invention as claimed in claim 30.

In accordance with a fifth aspect of the invention, there is provided a kit of parts comprising at least one bone fastener in accordance with the first aspect of the invention and an intramedullary rod in accordance with either of the second and third aspects of the invention, as claimed in claim 31.

Further optional features of the kit in accordance with the fifth aspect of the invention are set out in the claims dependent on claim 31.

In accordance with a sixth aspect of the invention, there is provided a method of implanting an intramedullary rod in accordance with either of the second and third aspects of the invention using a bone fastener in accordance with the first aspect of the invention, as claimed in claim 33.

In accordance with a seventh aspect of the invention, there is provided a *..... clamp for use in the method of the sixth aspect of the invention, as claimed in claim *. 34.

Further features of the clamp in accordance with the seventh aspect of the invention are set out in the claims dependent on claim 34. *..I

I

*:. Several embodiments of the invention will now be described, by way of example only with reference to the following drawings in which: Figure 1 shows a longitudinal cross section of a fractured proximal phalanx fixed with a known arrangement of plate and screws; Figure 2 shows a transverse cross section of the bone of Figure 1 along lines XX of Figure 1; Figure 3 is a perspective view of part of a first embodiment of an intramedullary rod in accordance with the invention; Figure 4 is a perspective view of a section of a porous mesh and reinforcing structure forming part of the intramedullary rod of Figure 3, shown in an enlarged scale; Figure 5 is a view similar to that of Figure 3 showing a modification to the intramedullary rod of Figure 3; Figure 6 is a schematic longitudinal cross sectional view showing an intramedullary rod secured across a fracture in a bone using bone fasteners in accordance with a first embodiment of a further aspect of the invention; Figure 7 is a schematic lateral cross sectional view showing an intramedullary rod secured in a bone using bone fasteners in accordance with an alternative embodiment of the further aspect of the invention; and; Figures 8 to 12 are perspective views of intramedullary rods in accordance with further embodiments of the invention.

In the following description, the same reference numbers, but increased by 100 in each case, will be used to identify features that are the same or which perform substantially the same function in each of the embodiments. * 0.

Figure 1 shows a longitudinal cross sectional view of a known means of fixing a fracture in the hand of a proximal phalanx 1. The drawings show a simplified L: sketch of the tendon and bone arrangement in the fractured proximal phalanx as seen from the side of a finger. Above the fractured bone 3 there is a tendon 2 and below the fractured bone 3 there are two tendons 4. Once the broken bone has been manipulated *... . so that the two parts are aligned, a plate 5 is affixed across the fracture along the top surface 3a of the bone by means of screws or pins 6. The plate 5 is fitted under the tendon 2 during surgery which can be tricky and time consuming. Using x-ray imaging, screws or pins 6 are inserted through apertures (not shown) in the plate 5 and bone 3 either side of the fracture to fixate the plate to the bone. The screws or pins 6 are inserted in a direction substantially perpendicular with respect to the apertured surface of the plate 5. If the screws/pins 6 extend too far through the bone 3 so that the tendons 4 or sheaths of the tendons (not shown) are damaged by the pins or screws, stiffness and possible loss of function of the finger can result.

Figure 2 shows a transverse cross section of the phalanx along line XX of Figure 1. Here the plate 5 is shown attached to the bone 3 by screws/pins 6. The screws/pins are inserted perpendicular to the surface of the bone as in Figure 1. In this arrangement they could potentially damage the underlying tendons if they are too long.

Figures 3 and 4 illustrate a first embodiment of an intramedullary rod 110 in accordance with one aspect of the invention.

The rod 110 has an elongate body comprising two spaced, elongate beams or casing portions 112. The volume between the casing portions is filled by a porous material 113 comprising a porous structure produced from the same base material as the casing portions 112. In this embodiment, the porous structure 113 is in the form of a mesh. The casing portions 112 are substantially solid and so relatively dense when compared with the porous structure 113. Preferably, the casing portions 112 and the porous mesh structure 113 are produced from a bio-compatible material. It is particularly advantageous if the casing portions and mesh are produced from a bio-compatible metallic material such as titanium, stainless steel or cobalt chrome, for example. The substantially solid casing portions 112 and the porous mesh 113 will be * clearly distinguished from one another other when viewed using x-ray imaging owing * to the differences in radio density between the regions. The pore size, shape and density of the porous structure 113 can be selected as appropriate to the application * but in one embodiment the porous structure consists of a mesh that is comprised of filaments having a diameter of about 100.tm and which are spaced by 100tm to 500j.tm (microns).

The porous mesh 113 is able to receive bone fastener screws which can be screwed directly into and held by the mesh 113. Alternatively, holes may be drilled or otherwise formed in the porous mesh to receive the screws whilst the rod is in-situ intramedullary. However, it is an advantage that the holes can be formed at any desired angle through the porous material 113 and need not extend perpendicularly to the surface of the rod as in the prior art. With a conventional intramedullary rod or nail with a solid metallic body, it is not possible to drill holes in the rod whilst it is in-situ intramedullary because too much heat and debris is generated. However, because the porous mesh material 313 is of a lower density than the solid material used in the prior art rods, holes can be fonned in the mesh without generating unacceptable levels of heat or debris.

As shown in Figure 3, the rod 110 may be circular in lateral cross-section and the spaced casing portions 112 can be arcuate. However, the rod 110 can be any suitable shape in lateral cross section. To increase the torsional strength of the rod 110, a reinforcing structure is also provided. In the present embodiment, the reinforcing structure comprises a plurality of beams 120 which interconnect opposing arcuate end regions 114 of the casing portions 112. The beams 120 are considerably thicker than the wires or filaments that make up the porous mesh 113 and give added structural rigidity to the rod. In a particularly advantageous arrangement, the beams are shaped to form part of a double helix running the length of the rod. Figure 4 illustrates the mesh 113 and the doubly helix configuration of the beams 120.

Typically the beams 120 will be the same thickness as the casing portions and are an integral part of the casing portions 112 where the two overlap. The double helix configuration is particularly beneficial in resisting torsion.

The porous material 113 fills the core of the rod between the casing portions 112 as well as a series of windows 115 defined between the opposing arcuate ends 114 of the casing portions and the reinforcing beams 120. The casing portions 112 and beams 120 are arranged so that windows 115 are provided in alignment on either side of the rod in generally diametrically opposing positions. When viewed using x-ray imaging, the mesh filled windows will be clearly distinguished from the casing S. S*** portions and the beams, allowing the surgeon to position the rod and insert bone S. fastener screws into the mesh through an appropriate window.

The shape of the windows 115 is determined by the size and spacing of the casing portions and/or their position on the circumference relative to the double helix configuration of the reinforcing beams. In the embodiment shown in Figure 3, the casing portions are aligned relative to the double helix so that the windows 115 coincide with the point at which the helixes cross one another. Figure 5 illustrates a modified embodiment of a rod 210 in which the position of the casing portions 212 has been moved relative to the double helix so that the windows 215 align with a mid-point where the spacing between the helixes is at its maximum. By comparing Figures 3 and 5, the effect of re-positioning the casing portions 112, 212 relative to the double helix on the shape and number of the windows 115, 215 can be seen. Thus in the Figure 3 embodiment, the rod 110 has a fewer number of longer, generally rectangular shaped windows 115. In contrast, the rod 210 as shown in Figure 5 has an increased number of shorter windows 215 which have a truncated triangular shape.

In some applications, the reinforcing structure 120, 220 can be omitted provided the casing portions 112, 212 and the porous material can be configured to provide sufficient structural strength and rigidity. Alternatively, the casing portions 112, 212 could be omitted so that the rod comprises only the porous material 113, 213 and the reinforcing beam structure 120, 220. Indeed, in some applications, the whole rod could be constructed entirely of the porous material 313 with no outer casing portions or support structure.

Intramedullary rods 110, 210 in accordance with the invention can be used in conjunction with a lag screw to reduce a fracture or osteotomy. Lag screws are used to reduce an oblique fracture or osteotomy by drawing the two sections of bone together * under compression. Typically, a clearance bore is drilled through one section of bone and a smaller diameter bore is drilled in the other section of bone. A lag screw is inserted through the clearance bore, across the break and is screwed into the smaller a *.

: * 25 diameter bore formed in the other section of bone. The lag screw is then tightened to draw the two sections together, reducing the fracture or osteotomy. Whilst a single lag screw is useful for holding the two sections of bone in compression, it is unable to I.....

resist rotational forces. Thus a lag screw is usually used in combination with device to S..

neutralise rotational forces. One example of a neutralisation device is a side plate which is fixed to the exterior of the bone sections across the fracture site with all the attendant difficulties discussed previously.

Advantageously, an intramedullary rod 110, 210 in accordance with the invention can be used in conjunction with a lag screw to resist relative rotation of the bone sections. The rod 110, 210 is inserted across the fracture site and a lag screw inserted to reduce the fracture, with the lag screw passing through aligned windows 115, 215 on either side or a though a gap between the two outer casing portions. The end regions of the rod can then be fixed to their respective bone sections as described previously to resist rotational forces. In some cases, it may be preferable to fix one end region of the rod 110, 210 to its respective bone section before the lag screw is inserted. Because the windows 115, 215 are spaced along the whole length of the rod 110, 210, the surgeon has a high degree of freedom in positioning the rod, the lag screw and bone fastening screws or pins. This method of combining a lag screw' for providing stability and compression at the fracture site and an intramedullary device locked at either end to prevent flexural as well as rotational stability is possible because of the unique design of the intramedullary rod 110, 210 in accordance with the invention through which it is possible to insert a bone fastener or lag screw at an oblique angle.

The intramedullary rods 110, 210 as described above in relation to Figures 3 to can be manufactured from powdered metal using selective laser melting or selective laser sintering. Selective laser melting is a known process by which metal powder is melted by an intensive infrared laser beam to form a desired geometry layer by layer.

Preferably, the metallic powder is bio-compatible such as titanium, including titanium alloys such as Ti6AI4V, Cobalt chrome, or stainless steel (ex. 31 6L). By using this * *b . method of manufacture, the casing portions, porous mesh and reinforcing beams are * 4** * -s constructed from the same base material as an integral component providing increased structural integrity. A further advantage of this method of construction is that the rod *:. 110, 210 can be formed from a single bio-compatible material which has been proven to be safe for intramedullary devices and therefore trusted by many surgeons.

Nevertheless, the rods 110, 210 may be coated with a biologically inert material such as Teflon (RTM) PTFE to prevent bony in-growth into the rod and in to the mesh in particular. Alternatively, coatings like Titanium carbo-nitide (TCN), Diamond like carbide (DLC), or Plasma Electrolytic Oxidation (PEO) may be used to increase the hardness of the implant.

Whilst the porous material 313 is shown as having a uniform grid like mesh structure, this is not essential and the porous material 313 can have any suitable structure which provides the desired level of porosity and other mechanical properties.

The term "porous metallic material" is used herein to refer to a material having engineered inter-connected porosities as opposed to random, isolated non-engineered pores such as those created in the manufacturing process of certain metals, most commonly due to the formation of gas bubbles during cooling of molten metal. Porous metallic materials are known for use in a number of different applications including filtration, manufacture of light but high strength aircraft parts etc. and can be manufactured from metal powders using a variety of known powder metallurgy techniques, including those discussed above. In most applications, the porous material is expected to have porosity in the range of 40% to 90%, and more particularly in the range of 50% to 80%. A material having porosity in the range of 60% to 70% and pore size distribution range of 200-500 micro-meter is especially preferred. The non-porous parts of the intramedullary rod 310, such as the casing portions 312, which are described herein as being substantially solid, may in fact contain pores, particularly where they are formed from a metallic material. However, these pores are not engineered and generally speaking not interconnected and so the material in these regions is relatively dense when compared with the porous material. In this regard, the ability to engineer the porous material to determine its porosity and mechanical $S ** * * characteristics is important. It should also be noted that the size and spacing of the * S..

S * pores can be varied within a given porous region of the rod.

Intramedullary rods in accordance with the invention can be produced in a range of sizes depending on the size of bones with which they are to be used. For an * intramedullary rod for use in fixating the phalanx, a rod having a diameter of 3mm iv....

would be typical though the diameter could be in the range of 2 to 4mm. In a rod 110, 210 as described above having a diameter of 3mm, the casing portions would typically have a thickness of 0.5mm and the beams forming the reinforcing structure have a thickness of 0.5mm, the same as the casing portions. The double helix on which the beams are positioned have a pitch of 3mm with a 2.5mm gap at the widest part.

One of the problems encountered with the use of small intramedullary rods is the difficulty of drilling through them mechanically as there is a tendency for the drill bit to jump. Additionally, debris is produced which may provoke a foreign body reaction in the patient's body. To address this problem, holes may be formed through the mesh material 113 in-situ using a laser. Use of a laser or optical drill to form a hole rather than a mechanical drill bit means there is no risk ofjumping and damaging the surrounding bone or tissue or the rod itself Any suitable laser can be used including Erbium, YAG, Infrared or CO2 lasers for example. However, it is preferred that the laser is an ultra short pulse laser rather than a continuous wave laser because less heat is generated and transferred into the target and surrounding material. A further advantage of using ultra short pulse laser is that the spectral characteristics of the plasma emission generated by a material as it vaporises can be analysed to differentiate between different materials using a spectroscope. Thus emitted light from the plasma can be collected and analysed by a spectroscope to provide feedback control of the laser to ensure that only the target materials are removed. The device can, therefore, be calibrated to differentiate between bone, the rod and surrounding tissue. For example, when forming a bore for a lag screw, the device can be controlled so that it produces a bore through the first bone section, the mesh region and the second bone section only.

Use of ultra short pulse laser for optical dental drilling has been proposed in US patent No. 5720894 assigned to the Regents of the University of California. The * reader should refer to this document for a more detailed explanation of the process and feedback control using spectral analysis. The contents of this patent are hereby * incorporated by reference.

Figure 6 illustrates schematically an alternative bone fastener 330 in *** * accordance with a further aspect of the invention which can be used to secure an intramedullary rod having a porous region in position, without the need to drill or *. 30 otherwise form a hole in the rod prior to insertion of the fastener.

Figure 6 shows in longitudinal cross section a bone 303 having a fracture 308.

An intramedullary rod 310 is inserted into the bone across the fracture 308 and is secured to the bone on either side of the fracture by means of a two-part bone fastener, indicated generally at 330. The rod 310 is similar to the embodiments 110, 210 described above and has porous mesh region 313 and a reinforcing structure 320 which defines windows 315 through which the fasteners can be inserted into the porous region. The rod 310 may also have casing portions made from a substantially solid material which partially surround the porous material 313 but these are not shown in Figure 6.

Each bone fastener 330 comprises a first part 332 and a second part 334 which parts locate on opposite sides of the rod 310. In the present embodiment, the first part 332 is in the form of a punch having a portion for insertion into the rod and the second part 334 is in the form of a dye which receives part of the punch when the fastener is inserted.

The punch 332 has a head portion 336 and an elongate pin portion 338 projecting from the head portion for insertion through a porous region 313 of the rod 310. The pin has a tapered distal end 340 to assist in the pin being pressed through the rod as will be described in detail below. The head portion comprises a cylindrical main body 342 which locates in a hole 344 formed in the bone on one side of the rod 310. The head portion 332 also has a flange portion 346 having a larger diameter than the main body 336 and which abuts an outer surface of the bone 303 when the fastener 330 is fully fitted.

The dye 334 comprises a cylindrical main body 348 which locates in a hole 350 formed in the bone on the opposite side of the rod 310 from the hole 344. A flange 352 is provided at the outer end of the dye main body for contact with the outer * surface of the bone 303 when the fastener 330 is fully fitted. A bore 354 extends centrally through the dye to receive a distal end region of the pin portion 338 To locate an intramedullary rod 310 using a two part bone fastener 330 in * accordance with the invention, the rod 3 10 is first located intramedullarly across the * 30 fracture using known methods such as over a guide wire or simply inserted as a solid rod and advanced to the desirable position under X-ray control. Typically, a small incision is made through the skin and the soft tissues by the side of the bone into the fractured bone 303 and a guide wire inserted through the fractured bone across the fracture and into the other part of the fractured bone. A reamer is then inserted over the guide wire to widen the holes through the bone. The reamer is taken off at this stage. If a cannulated rod is being used it can then be passed over the guide wire whereas if a solid rod is being used the guide wire is taken off as well and the Intramedullary rod advanced under X-ray control. The fixator rod 310 can then be inserted into the holes in the confronting ends of the bone across the fracture and orientated such that the rod 310 is positioned with the windows 315 at which the porous mesh 113 is exposed aligned laterally of the bone.

The rod 310 is then fixed in place by means of the bone fasteners 330. Under x-ray imaging the windows 315 containing the porous region 313, which is radiolucent compared to the reinforcing beams 320 and the casing portions, will show up as a darker region between whiter regions indicating the position of the beams 320 and the casing portions. Thus the surgeon will be able to see clearly where the bone fasteners may be inserted.

The holes 344, 350 are drilled in the bone on either side of the rod 310 in alignment with a window 315. The dye 334 is inserted into one of the holes 350 so that an inner end abuts an outer surface of the rod 310. The punch 332 is inserted through the other hole 344 until the tapered end 340 contacts the porous mesh 313 on the opposite side of the rod 310 from the dye. Pressure is then applied to the punch 332 and dye 334 pressing them together so that the pin passes through the porous mesh 313 forming a hole. When the punch 332 is fully inserted, a distal end region of the pin protrudes from the opposite side of the rod 310 and is received in the bore 354 of the dye so that the two are interlocked. With the bone fastener fully inserted, the flanges 346, 352 contact the outer surface of the bone. The inner surfaces of the flanges 356 may be provided with fins or other formations (not shown) which dig into the bone assist in holding the fastener 330 in position. Typically, one end of the rod 310 is secured in position using a first bone fastener 330 before the holes 344, 350 are drilled to locate the other end of the rod 310 using a second bone fastener 330 but the precise order of the steps taken may vary.

The punch 332 and dye 334 may be compressed between the jaws of a clamp like device (not show) which may be mechanically, hydraulically, pneumatically or electronically driven. In a particularly preferred embodiment, the punch and dye are loaded into the jaws of the clamp device which is then used to position the punch and dye in the holes 344, 350 and to compress them together.

The punch 332 and dye 334 are preferably manufactured from a bio-compatible metallic material such as titanium, including titanium alloys such as Ti6A14V, Cobalt chrome, or stainless steel (ex. 31 6L). The punch in particular needs to be sufficiently strong and to have sufficient hardness to enable it to be driven through the porous mesh 315. The punch 332 may be coated to increase its hardness.

Any suitable coating can be used such as Titanium carbo-nitride (TiCN), which is a ceramic coating having an indentation hardness measured using the Vickers test of about 2, 500 VH or a carbide coating with a VH of 1,400 or more, for example. The punch and die may also be heat treated or subjected to Kolsterising, which is a process involving diffusion of carbon into the work piece surface without the formation of chromium carbides. Such treatment can increase the indentation hardness of the material.

The hardness of the punch 332, the porosity, malleability and ductility of the porous material 313 are configured to ensure that the punch can be inserted through the mesh to form a substantially rigid fixation without creating excessive debris or heat. One advantage of the arrangement as described is that the porous material 313 is compressed about the pin as it is inserted, which improves the rigidity of the final assembly. It is a further advantage that no, or only minimal, metallic debris is created * ** in-situ as the rod does not have to be drilled. * * * * S.

*. 25 The bore 354 in the dye 354 is configured to be a close, possibly interference, * * fit about the main cylindrical portion of the pin 338. Whilst the bore 354 is shown as extending all the way through the dye in Figure 6, this is not essential and the bore *..

* could be a closed bore or recess. However, means for enabling air within the closed bore or recess may be provided to ensure the pin can be fully inserted into the dye.

This could take the form of a small air release hole to connect the closed bore or recess to atmosphere or one or more grooves could be provided in the surface of the closed bore or recess.

In an alternative arrangement, part of the dye 354 may also be arranged to enter the porous material 313 of the rod. In one such alternative embodiment (not shown), the pin portion 338 of the punch has longer tapered end portion 340 than that shown in Figure 6. The dye 334 in this embodiment has a portion which extends into the porous material 313 when frilly fitted. This portion of the dye has an internal bore that is tapered to correspond with the taper on the pin so that the two form a substantially cylindrical rod when assembled.

The bone fasteners 330 and rod 110 will generally remain in-situ once fitted.

However, in the event that the rod 310 or fasteners 330 need to be removed, the punch 332 and the dye 334 can be provided with formations to which a tool or tools can be attached to enable them to be drawn apart. As illustrated in Figure 6, the head 336 of the dye can be provided with a threaded hole 352 into which a fixture may be screwed.

A similar arrangement can be provided in the dye so that a tool can be attached to the two fixtures to draw the punch 332 and the dye 334 apart. Alternatively, the head portions of the punch 332 and dye 334 may have recesses or other shaped formations which can be gripped by a suitable tool or tools to enable them to be separated.

Figure 7 illustrates schematically an alternative embodiment of a two part bone fastener 430 in accordance with the further aspect of the invention. In this embodiment, both parts of the fastener 432, 434 comprise a tapering punch portion, the two punches being inserted through the bone 403 into the porous material 413 from either side. The punches 432, 434 can be advanced such that their tips are brought close together or meet towards the centre of the rod 410. Figure 7 is a *. 25 schematic representation of the punches 432, 434 which shows them as being * ** essentially conical in shape. In practice the actual shape of the punches may vary and they could each have a head portion and flange with a tapering pin portion similar to *** the punch 332 described above in relation to Figure 6. Where the bone fastener 430 comprises a pair of tapering punches, the pore size in the porous material 413 can be designed in such a way as to have larger pores towards the surface and progressively smaller pores and hence denser material towards the core of the rod.

Use of the two-part bone fastener 330, 430 in conjunction with an intramedullary rod 310, 410 having a suitable porous region 313, 413 through which the punch can be inserted enables a bone fastener to be inserted without pre-drilling the rod in a one step operation which both forms a hole through the rod and inserts the bone fastener. In some applications, one end of the rod may be secured using conventional techniques, in which case a porous region need only provided at the other end. For example, where a rod in accordance with the invention is to be used to treat a fracture in a proximal phalange, the proximal end of the rod may have a pre-drilled hole and a jig used to drill corresponding holes in the bone in the known manner. The proximal end can then be secured in place using a bone fastener 330, 430 in accordance with the invention, or a conventional bone fastener screw or pin. The distal end of the rod, for which the jig cannot be used, being located using a bone fastener 330 in accordance with the invention which is pressed through a porous region of the rod as described above.

As discussed above, the shape and size of an intramedullary rod in accordance with the invention can be varied to suit a rage of applications. The whole body of the rod may be manufactured from a porous material or the rod may have outer casings which are substantially solid with a porous region extending between the casing portions over the whole length of the rod. In a different arrangement, the rod may have one or more discreet regions comprising a porous material along its length with material in the remainder of the rod being substantially solid. In one embodiment, the rod has a main body region formed from a material which is substantially solid and at least one end region comprising a porous material. The end region may comprise only * the porous material or it may have outer casing regions made of a substantially solid material which partially surround the porous material on opposing sides. The main body region may be solid or it may be in the form of a hollow tube of relatively dense material. In yet another arrangement, the body of the rod may have spaced dense * casing portions running along the length of the rod covering opposing sides and partially encasing a region of porous material at either. In this arrangement, the space *S..*.

between the casing portions is empty between the end regions. The rod may be S..

cannulated.

Figures 8 to 12 illustrate four possible configurations for an intramedullary rod in accordance with the invention. The configurations shown are exemplary only and those skilled in the art will understand how the design of the rod may be varied. The rods 510, 610,710, 810, 910 as shown in Figures 8 to 12 all have a similar overall construction having a flattened oval shape in lateral cross section with one end of the rod being angled relative to the remainder of the rod. However the rods could be straight or any other suitable shape for location in the particular bone being treated.

The rod 510 as shown in Figure 8 has a main body portion 554 and a region 556 at either end which contains a porous material 513. In the embodiment shown in Figure 8, the end regions 556 have outer casing portions 512 made of a substantially solid material which partially surround the porous material 513 on opposing sides.

However, the porous material 513 is exposed on either side of the rod between the casing portions so that a bone fastener can be inserted through the porous material 513. The main body region 554 may be solid or it may be in the form of a hollow tube made from a substantially solid material. As shown in Figure 8, one end of the rod has a pre-drilled hole 557 formed through the porous material 513 to enable that end to be secured in position using aug in the known manner. In an alternative embodiment, the end region with the pre-drilled hole 557 can be formed entirely of a substantially solid material and may be a continuation of the main body portion so that the rod 510 has only one end region 556 containing the porous material 513.

The rod 610 shown in Figure 9 is essential identical to the rod 510 in Figure 8, except that neither end region 656 has a pre-drilled hole for a bone fastener.

The intramedullary rod 710 as shown in Figure 10, is similar to the rod shown in Figure 8, except that the end regions 756 have no outer casing portions but are * 25 comprised entirely of the porous material 713. In this embodiment, the properties of * ** the porous material are configured to ensure that it has the required mechanical * ** strength without the casing portions. As with the rod 510, the rod 710 as shown in Figure 10 has a pre-drilled hole 757 for a bone fastener in one end region. The end region 756 having the pre-drilled hole could be formed from a relatively dense material so that only one end region 756 is porous.

The intramedullary rod 810 in Figure 11 is identical to that as shown in Figure except that neither end region 856 has a pre-drilled hole for receiving a bone fastener.

Figure 12 illustrates on a slightly larger scale a further alternative embodiment of an intramedullary rod 910 in accordance with the invention. In this embodiment, the rod has an elongate body comprising spaced casing portions 912 made of a relatively dense material, which will usually be substantially solid. At the end regions 956 of the rod, the casing portions partially surround a porous material 913. Between the end regions 956, the rod is hollow. Although not shown, a pre-drilled hole maybe formed through the porous material 913 in one of the end regions 956.

As with the previously described embodiments, the porous material 513, 613, 713, 813, 913 may have a mesh like structure and the rods 510, 610, 710, 810, 910 may be manufactured from powdered metal using selective laser meting or selective laser sintering. Preferably, the metallic powder is bio-compatible and may be any of those discussed in relation to the previous embodiments. A reinforcing structure may be incorporated into the porous regions of the rods 510, 610, 710, 810, 910. The reinforcing structure may take the form of beams similar to those 120, 220 described above in relation to the rods 110, 210 as shown in Figure 3 to 5.

The phalanx has been used as an example of the type of bone which may benefit from the invention, however, it must be understood that the invention can also be used in other bones, for example wrist, forearm, arm and shoulder bones where precise insertion of bone fasteners through the bone and fixator is required.

Whereas the invention has been described in relation to what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed arrangements but rather is intended to cover various modifications and equivalent constructions included within the spirit and scope of the invention.

S S..

S

Claims

Claims 1. A bone fastener for securing an intramedullary rod to a bone, the bone fastener comprising two parts, a first part for location on one side of an associated intramedullary rod and a second part for location on an opposing side of the rod, at least the first part comprising a portion for insertion into the rod.
2. A bone fastener as claimed in 1, in which the portion is a punch for insertion into the material of the rod.
3. A bone fastener as claimed in claim 2, in which at least a part of the punch portion is tapered.
4. A bone fastener as claimed in any one of claims I to 3, in which the second part also comprises a portion for insertion into the rod.
5. A bone fastener as claimed in claim 4, in which the portion of the second part is a punch for insertion into the material of the rod.
6. A bone fastener as claimed in claim 5, in which at least part of the punch portion on the second part is tapered.
7. A bone fastener as claimed in any one of claims 1 to 4, in which the second part has a hole or recess for receiving at least part of the portion of the first part.
8. A bone fastener as claimed in claim 7, in which the portion of the first part * 20 comprises a pin having a tapered free end. * * ****
9. A bone fastener as claimed in any one of the previous claims, in which the first part comprises a head portion having a main body for location in a hole in the ** bone and a flange for contact with an exterior surface of the bone.
10. A bone fastener as claimed in any one of the previous claims, in which the second part comprises a main body for location in a hole in the bone and a flange for contact with an exterior surface of the bone.
11. A bone fastener as claimed in claim 9 or claim 10, in which the flange has formations configured to dig into the bone when the fastener is fully inserted.
12. A bone fastener as claimed in any one of the previous claims, in which the first and second parts are manufactured from a bio-compatible metallic material such as titanium, titanium alloy, or stainless steel.
13. A bone fastener as claimed in claim 15, in which at least part of at least one of the first and second parts is coated or otherwise treated to increase its hardness.
14. An intramedullary rod having an elongate body, at least one region of the body comprising a porous material.
15. An intramedullary rod as claimed in claim 14, in which the porous material has a porosity in the range of 40% to 90%, and more preferably in the range of 50% to 80%, and yet more preferably in the range of 60% to 70%.
16. An intramedullary rod as claimed in claim 15, in which the porous material has a pore size distribution range of 50-500 micro-meters.
17. An intramedullary rod as claimed in any one of claims 14 to 16, in which the porous material is a porous metallic material.
18. An intramedullary rod as claimed in any one of claims 14 to 17, in which the porous material comprises a mesh.
19. An intramedullary rod as claimed in any one of claims 14 to 18, in which at least one region comprising the porous material is provided at one end of the S...: body.
20. An intraniedullary rod as claimed in claim 19, in which two regions comprising the porous material are provide, one at either end of the body.S.....S
21. An intramedullary rod as claimed in claim 19 or claim 20, in which the remainder of the body is substantially solid.
22. An intramedullary rod as claimed in claim 19 or claim 20, in which the remainder of the body comprises a tube formed of a substantially solid material.
23. An intramedullary rod as claimed in claim 19 or claim 20, in which the body comprises a pair of spaced casing portions made of a relatively dense material, the casing portions partially surrounding a region of porous material at either end of the rod, the body being hollow between the end regions.
24. An intramedullary rod as claimed in any one of claims 14 to 18, in which the region of the body comprising the porous material extends the whole length of the rod.
25. An intramedullary rod as claimed in any one of claims 14 to 22 or 24, in which the at least one region of the body comprising the porous material also comprises spaced casing portions formed of a substantially solid material, the casing portions partially surrounding the porous material such that the porous material is exposed on opposing sides of the rod between the casing portions.
26. An intramedullary rod as claimed in claim 25, in which the at least one region of the body comprising a porous material further comprises reinforcing beams extending between end regions of the spaced casing portions, the beams and casing portions defining windows on opposing sides of the rod through which the porous material is accessible.
27. An intramedullary rod as claimed in any one of claims 14 to 26, in which the body is formed from powdered metal. * *
28. An intramedullary rod manufactured from powdered metal, the rod comprising an elongate body, at least part of the body comprising a mesh-like porous if 25 structure accessible from opposing sides of the rod.
29. An intramedullary rod as claimed in claim 27 or claim 28, in which the body is formed from powdered titanium alloy, Cobalt chrome or stainless steel.
30. A method of manufacturing the intramedullary rod as claimed in any one of claims 27 to 29, the method comprising forming the rod from powdered metal using selective laser melting
31. A kit comprising at least one bone fastener as claimed in any one of claims 1 to 13 and an intramedullary rod as claimed in any one of claims 14 to 29.
32. A kit as claimed in claim 31, in which the fastener and rod are configured such that the portion of at least one of the parts of the fastener can be pressed through the porous material of the rod.
33. A method of implanting an intramedullary rod across a break in a bone, the method comprising: a. providing an intramedullary rod in accordance with any one of claims 14 to 29; b. providing a bone fastener in accordance with any one of claims 1 to 13; c. locating the rod intramedullary across a break in the bone; d. forming holes in the bone on opposing sides of the rod in alignment with a region of the rod comprising porous material; e. locating a first part of the bone fastener in one of the holes so that the portion protrudes towards the porous material; f. locating a second part of the bone fastener in the other hole in the bone; g. compressing the first and second parts of the fastener together so that the portion is pressed through the porous material of the rod.
34. A clamp for use in the method of claim 33, the clamp comprising a pair of * jaws for location on either side of the bone, the jaws having means for engaging with the first and second parts of the bone fastener and means for *** * 25 bring the jaws together to press the portion through the rod.
35. A clamp as claimed in claim 34, in which the jaws are adapted to receive and hold the first and second parts of the bone fastener.
36. A bone fastener substantially as herein described, with reference to and as illustrated in Figure 6 or Figure 7of the accompanying drawings.
37. An intramedullary rod substantially as herein described, with reference to and as illustrated in Figures 3 & 4, or Figure 5 or any of Figures 8 to 12. * ** ** * * ** I... * * * ** * * * *** *S *** * **.S*S. * * * S..S