WO2010131020A1

WO2010131020A1 - Extraction tool

Info

Publication number: WO2010131020A1
Application number: PCT/GB2010/050656
Authority: WO
Inventors: Aman Sharma
Original assignee: Cambridge University Hospitals Nhs Foundation Trust
Priority date: 2009-05-12
Filing date: 2010-04-22
Publication date: 2010-11-18
Also published as: GB2470200A; GB0908150D0

Abstract

The invention provides an extraction tool which is arranged to remove a hollow medical device from a subject. The tool comprises an elongate member, having at an end region thereof a body region comprising at least one wall-engaging means configured to engage an inner wall of a medical device, into which, in use, the tool is inserted. The invention also provides a kit for removing a hollow medical device from a subject, and methods of removing such devices from subjects.

Description

EXTRACTION TOOL

This invention relates to an extraction tool, particularly, but not exclusively, an extraction tool for the removal of hollow medical devices from the body of a subject. The extraction tool may in particular, but again not exclusively, be arranged to remove intramedullary nails. The invention may also provide a kit containing an extraction tool and a hammer configured to engage with the extraction tool, and uses and methods of extracting medical devices from a patient.

Fractured bones, particularly those that may be thought of as long, frequently require stabilisation to allow satisfactory healing. One means of achieving such stabilisation is through the use of an intramedullary nail, a hollow metal rod which is inserted into the marrow canal. The nail is fixed into position with the help of bolts, which are inserted through the bone, generally at both end regions of the nail. Any gross movements of the fractured portions of bone are thus prevented while at the same time allowing slight movements that are known to assist in the healing process. Intramedullary nails can typically be left in position inside the bone for extended periods, in some cases even permanently. The benefit of stabilising the bone must however be weighed against the increased risk of complications such as infection and soft tissue irritation associated with the nail remaining in situ for extended periods. In addition, the nail can move within the bone over time, which can result in pain and discomfort as the nail impinges on neighbouring joints. Other potential problems are breakage of the nail and nonunion of the fractured bone. It can therefore be desirable to remove the nail in the event of such complications or to prevent complications in the future.

Moreover, the presence of a nail can be detrimental to the bone, should it be injured in a further accident. Procedures to remove intramedullary nails are carried out in 30 - 60% of patients after the fracture has healed. Different methods currently exist for the removal of intramedullary nails. One method relies on insertion of a wire through what may be thought of as a central canal of the hollow nail. The wire is fitted with a terminal hook, such that when the wire is fully inserted, the hook protrudes from the distal end of the nail. The hook is then used to grasp the distal edge of the nail and force is applied to the wire to remove the nail from the bone.

Another system uses intramedullary nails that have an internal screw thread at their proximal end; which again may be thought of as at a terminal portion. A hammer device with a matching thread is screwed into the end of the nail and the hammer is used to dislodge the nail.

However, both the wire and internal screw thread systems suffer from the same problem: while the nail in inside the healing bone, it is common for bone tissue to grow into the open ends of the nail. This in-growth is particularly common if the nail remains in position for extended periods of time. As a result it may be impossible, or at least difficult, to push the hooked wire through the distal opening of the nail as it is blocked by growing bone tissue. Similarly, bone tissue may infiltrate the threading at the proximal end of the nail making it impossible, or at least difficult, to attach the hammer device for removal. In each case, ingrowth of bone tissue increases the duration of the operation, leading to increased risk to the patient and increased use of hospital resources. Moreover, attempting to use either system under these conditions can result in undesirable additional trauma to the bone and surrounding tissue, which is also likely to lead to an increased recovery time for the patient.

Growing bone tissue is capable of tightly bonding to the nail while it is in situ within a bone. Significant levels of force, in the region of 6-7kN, may therefore be required to dislodge the nail from the bone. If care is not taken during the extraction process, application of these forces can result in refracturing of the bone, breakage of the nail or damage to the surrounding soft tissue. This is particularly relevant to the hooked wire extractor where force is by definition applied to only one side of the nail. This asymmetrical traction may cause breakage of the nail which further complicates the extraction process and may damage the bone. An example of an existing extraction device is given in US 5,766,180.

According to a first aspect of the invention, there is provided an extraction tool arranged to remove a hollow medical device from a subject, the tool comprising an elongate member, having at an end region thereof, a body region comprising at least one wall-engaging means configured to engage an inner wall of a medical device, into which, in use, the tool is inserted.

The invention provides a tool intended to allow simpler and more controlled removal of medical devices that are within a subject. In some embodiments, the tool may be arranged to remove a tubular medical device. In such embodiments, tubular is deemed to be any cross-section and not just circular in cross section.

The or each wall-engaging means is advantageous as it grips the medical device and allows force applied to the tool to be transferred to a device in which the tool is fitted.

One of the tool's applications may be in the removal of intramedullary nails from human or animal bones. In this context, the tool has the advantage that it engages with the inner wall of an intramedullary nail rather than the terminal portions of the nail, which can be covered by growing bone tissue. In order to function, the tool is inserted into the proximal opening of an intramedullary nail so that the cam can engage with an inner wall of the nail at any point along the length of the nail. The tool has the further advantage that it may be used to remove more than one part of the nail, or other medical device, if the nail or other device has broken into multiple portions.

In one embodiment, the elongate member comprises a flexible rod, which may allow the body region of the tool to be inserted into a medical device more readily and indeed may allow the tool to be inserted into curved, or at least not straight, medical devices. Intramedullary nails often follow an oblique angle typically toward one end; and as such flexibility of the elongate member may therefore be advantageous in helping the tool extend around such a curved nail.

As such, the elongate member may be constructed of a material that is flexible while being of sufficient strength to withstand the forces generated during the extraction process. For example, the elongate member may be fabricated from stainless steel, aluminium, tantalum, chromium cobalt alloy or any other suitable metal or metal alloy. Alternatively, it can be fabricated from ceramics, carbon fibre, nano-carbon composites, medical grade silicone, polyethylene composites and zirconium oxide composites.

In other embodiments, the elongate member may comprise a flexible cable. Such an embodiment may be appropriate when the guiding function of a rigid rod member is not required, for example when the body region does not need to be deeply inserted into a medical device.

In one embodiment, the wall-engaging means may comprise one or more cams. A cam may be suited as a wall-engaging means because it is asymmetrical. This asymmetry may allow it to be arranged to protrude from the body region to limited extent during insertion of the tool into a medical device but to a greater extent when the tool is required to engage with the wall of a medical device during extraction. The or each cam may be pivotably mounted upon a rod connected to the body region of the tool. The or each wall-engaging means may be fabricated from a material such as stainless steel, which may be hardened, titanium, other combinations of metals or metal alloys, polyethylene, medical grade silicone, a ceramic material, or another suitable material which would generally be a medical grade material.

In other embodiments, the or each wall-engaging means may be fabricated from urethane or similar material. Such embodiments, may find particular application, but not be limited to, fields outside of orthopaedics, such as coronary artery stent removal.

In one embodiment, the or each wall-engaging means (preferably the or each cam) may be arranged to be unidirectional, such that they engage with a medical device when rotating in one direction and generally they are arranged such that they rotate in a direction outwith of the tool when the tool is withdrawn from the medical device. Consequently, the or each wall-engaging means may be arranged such that insertion of the tool into a medical device causes the wall-engaging means to rotate into the body region of the tool. Such an arrangement is advantageous as it allows the tool to be inserted into medical device but prevents the tool from being withdrawn from the device.

The or each wall-engaging means (preferably the or each cam) may be located within a recess in the body region of the tool. A wall of the recess may be arranged to limit rotation of the or each wall-engaging means in at least one direction; i.e. to provide a limit to the rotation of the or each wall-engaging means.

The tool may comprise control means connected to the or each wall-engaging means, generally arranged so as to cause the or each wall-engaging means to rotate when a force is applied to the control means. As such, the position of the or each wall-engaging means may be adjusted by the control means. The control means may comprise a control wire. Advantageously, the control wire may be arranged to allow the or each wall-engaging means to be retracted such that the tool may be withdrawn from the medical device.

The control means (preferably, a control wire) may be arranged to extend along (i.e. run) for substantially the length of the elongate member. In some embodiments, the control means may connect the wall-engaging means to a push lever. As such, movement of the push lever is arranged to control the movement of the or each wall-engaging means.

In one embodiment, the or each wall-engaging means is configured to rotate between a retracted, non-engaging position and an extended, engaging position. In one embodiment, the or each wall-engaging means is configured to rotate from a retracted, non-engaging position to an extended, engaging position.

In cross-section, the or each wall-engaging means may have the shape of a circle that is flattened on one side. The wall-engaging means may be mounted eccentrically on the rod. This eccentric rotation and flattened shape of the wall- engaging means may combine to allow the wall-engaging means to adopt the two positions with respect to the body region of the tool.

In the retracted position, the wall-engaging means may be arranged to rest against an inner wall of the body region with its flattened side, such that there is substantially none of the wall-engaging means protruding from the body region. If the wall-engaging means is however rotated into or at least toward the extended position, the eccentric point of rotation causes it to protrude from the body region and enables it to make contact with the inner wall of a medical device into which the tool has been inserted. In one embodiment, the unidirectional movement of the or each wall-engaging means allows insertion of the tool into a medical device but results in the device being engaged by the wall-engaging means upon withdrawal of the tool. Prior to insertion of the tool into a device, the wall-engaging means may be placed in their retracted position although insertion of the tool into a medical device may tend to cause the or each wall-engaging means to adopt the retracted position. If a control wire is fitted then it may be used to cause the wall-engaging means to adopt the retracted position. Such a tool, may be inserted into a medical device allowing the tool to be placed in the best position for extraction of that device. Once the correct location of the tool has been reached relative to the medical device, retraction of the tool generally causes the wall-engaging means to move to or at least towards the extended position such that they engage with the inner wall of the device.

Generally, the or each wall-engaging means will be arranged such that increasing the force of extraction, increases the force with which the wall-engaging means engage with the inner wall of the medical device. The or each wall-engaging means may be mounted relative to a wall of the recess such that once substantially in the extended position, the wall-engaging means engages that wall of the recess. Such an arrangement can help the wall-engaging means apply significant force against a medical device in which it is inserted and limits over-rotation of the wall-engaging means which would reduce the force that the wall-engaging means would be capable of generating.

In other embodiments, the or each wall-engaging means is resiliently biased towards their extended position. This may be achieved for example by constructing the wall-engaging means to be spring-loaded. As the spring expands, it may be arranged to urge the wall-engaging means to rotate towards the extended position. As such, the wall-engaging means and spring are generally arranged such that when the wall-engaging means is placed into its retracted position, the spring is compressed. Therefore, as the tool is inserted into a tubular medical device, the or each wall-engaging means would be pushed into their retracted position within the recess of the body portion. Once insertion of the tool is stopped and the direction of movement is reversed for extraction, the wall- engaging means will be urged into their extended position by the or each spring to assist gripping of the wall of the device. Thus, the springs will help to ensure that the or each wall-engaging means engages the walls of a medical device rather than simply relying on the forces generated by movement of the tool relative to the medical device. The or each spring may be a coil spring.

In one embodiment, the tool comprises two or more cams. Such an arrangement may be advantageous to help force applied to the tool during the extraction process to be more effectively transferred to the medical device and may prevent rotation of the tool within the medical device which may increase the chance of failure of the tool.

In further embodiments, at least a first cam may be provided on a substantially opposite side of the body portion of the tool from a second cam. This may be advantageous since it helps to overcome the problem of applying forces to the device asymmetrically, which may result in reduced effectiveness of the tool or even in its breakage.

In one embodiment, the surface of the wall-engaging means comprises friction- enhancing properties. Such friction-enhancing properties may include the surface of the wall-engaging means being provided with one or more of teeth, ridges, serrations or the like. Such friction-enhancing properties can help to increase friction between the tool and the medical device in which the tool in inserted.

The external surface of the body region of the tool may also comprise friction- enhancing properties. As a result, friction between the medical device and both the wall-engaging means, as well as the surface of the body region in contact with the medical device will be increased. Said surface of the body region can therefore contribute to the transmission of force from the tool the medical device. Such an embodiment may in particular, but no exclusively, find advantage in embodiments having a single wall-engaging means since forces can be applied more symmetrically in tools comprising a single wall-engaging means.

The proximal end of the tool may be configured to connect to a mallet, slap- hammer, other force imparting means or the like. As such, the tool may comprise a threaded portion to which the force imparting means may be attached. However, the tool may comprise other mechanical mechanisms for attaching the force imparting means such as alignable holes in conjunction with a pin, pins in conjunction with corresponding channels, or the like.

This may be advantageous in that the hammer, mallet or force imparting means may be firmly attached to the tool so that at least a significant portion of the force applied to the force imparting means will be transmitted to the tool thereby increasing the efficiency of the extraction process and reduced the risk of damaging the tool. Further a slap-hammer, mallet or other force imparting means designed for this purpose may form a linear continuation of the tool and as such force should therefore be applied to the tool in substantially the same direction as the direction of removal which is likely to further increase the efficiency of the process.

The tool may be arranged to remove an intramedullary nail or rod. In other embodiments, the tool may be arranged to remove a stent, or other tube arranged to carry fluids. According to a second aspect of the invention, there is provided a kit comprising an extraction tool according to the first aspect of the invention and force applying means configured to engage with the extraction tool.

According to another aspect of the invention, there is provided a kit comprising an extraction tool according to the first aspect of the invention and a hammer configured to engage with the extraction tool.

The kit may also comprise one or more intramedullary nails, or other medical devices for which the extraction tool is arranged to be used.

According to a third aspect of the invention, there is provided an extraction tool according to the first aspect, for removing a hollow medical device from a subject.

According to a fourth aspect of the invention, there is provided a method of removing a hollow medical device from a subject, the method comprising the steps of:

(a) inserting an elongate member of the extraction tool according to the first aspect into a hollow medical device, (b) engaging at least one wall-engaging means with an inner wall of the medical device, and (c) withdrawing the tool and the device from the subject.

AU of the features described herein (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined with any of the above aspects in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figure IA shows a section through an intramedullary nail extraction tool embodiment of the invention;

Figure IB shows magnified view of the portion of the body region of the embodiment shown in Figure 1 showing details of a cam assembly;

Figure 2 shows a side view of a further embodiment of the invention comprising springs to bias rotational movement of a cam;

Figure 3 shows a side view of further embodiment of the invention comprising two cams on opposite sides of a body region;

Figure 4 shows a simplified diagrammatic side view of an intramedullary nail extraction tool embodiment of the invention with recesses for cams; and

Figure 5A and 5B demonstrate the use of an intramedullary nail extraction tool embodiment of the invention in situ within a medical device.

Referring first to Figure IA, an extraction tool, and in particular a nail extraction tool, is shown generally as 1. It comprises an elongate member 2, a body region 3 and a handle bar 11. The end region of the elongate member 2 proximal to the handle 11 comprises a screw thread 12 arranged to secure a slap-hammer thereto. The elongate member 2 and body region 3 are constructed from separate components and connected by a joint 13. The body region 3 comprises a rounded distal end 4.

Within an end region of the body region 3 a recess 15 is provided and in which a wall-engaging means 5 is provided. In this embodiment and those shown in subsequent figures, the wall-engaging means comprises a cam. A magnification of Figure Ia is shown in Figure Ib and shows the cam 5 and the recess in more detail. The cam 5 is pivotably mounted on a rod όwhich is mounted on the body region 3 across the recess (i.e. into the plane of the paper as seen in Figure 1). A portion of the surface of the cam 5, which will in use engage with a medical device, comprises teeth or serrations 7 which provide friction enhancing properties to increase force that can be applied to a medical device. The part of the body region 3 which is substantially on the opposite side from where the cam is provided, comprises teeth or serrations 7a in order to increase the friction between the body region 3 and a wall of a medical device.

In the Figure the cam 5 is shown part way between a retracted position in which it is retracted into the recess 15 and as such does not engage a medical device into which the tool is inserted; i.e. a non-engaging position. However, it will be seen that the cam can rotate further in a clock-wise direction (as shown in the Figure) in order that the serrations 7 extend further in a horizontal direction (with reference to the Figure) from the body region 3. When the cam 5 engages a wall of the recess it is fully extended to what may be termed an extended, or engaging position.

It will be seen that the cam 5 and its mounting on the rod 6 are arranged such that insertion of the tool (i.e. movement in a downward direction in the Figure) into a device will tend to cause the cam to move toward the retracted position. Withdrawal of the tool from a medical device (i.e. in an upward direction in the Figure) will tend to cause the cam to move toward the extended position and as such will cause the force with which the cam 5 engages a device into which it is inserted to increase as the device is withdrawn.

A control wire 9 is attached to the cam 5 at point 8 and is run from the body region 3 to the handle bar 11. In some embodiments, the control wire may be provided within the elongate member 2. However, in Figure 1 the control wire is shown running adjacent the elongate member 2. If the control wire is pulled then the cam 5 is forced to rotate towards the retracted position; ie in an anticlockwise manner as viewed in the picture. As such, use of the control wire 9 can allow the tool 1 to be withdrawn from a medical device into which it is inserted by preventing the cam to engage an inner wall of the medical device.

In some embodiments, the cam 5 is connected to a push lever 10 by means of a control wire 9 thereby allowing the cam 5 to be rotated toward the retracted position by operation of the push lever 10.

Figure 2 shows a second embodiment and like parts have been referred to with the same reference numerals as Figure 1. Movement of the cam 5 in this embodiment is biased towards the extended position by means of a spring 19, which in this embodiment is a coil spring. Further springs are shown adjacent the handle bar 11 and arranged to bias the control wire 9 in order such that tension is not applied to the cam 5. Other embodiments may have only some of these springs and in one embodiment, only the coil spring 19 is provided.

This embodiment also shows an alternative form of construction of the tool 1 where the elongate member 2 and the body region are made of one single piece of material with a gradual transition region 14 between the two, rather than comprising two separate pieces joined together. In other embodiments, the elongate member 2 may have the same, or at least similar, diameter to the body region 3.

In Figures 1 and 2, the elongate member 2 and the body region 3 are shown as being circular in cross section. The skilled person will appreciate that this is not essential to the invention and that other cross sections are suitable. For example, either or both of the elongate member 2 and the body region 3 may be any of the following: triangular, square, pentagonal, hexagonal, octagonal, or the like. Figure 3 shows an embodiment of the tool 1 comprising two cams 5, 50 on substantially opposite sides of the body region 3. Again, like parts of the tool have been referred to by the same reference number as the previous embodiments. The first cam 5 is connected to the push lever 10 by control wire 9, while the second cam 50 is joined to the lever 10 by control wire 90.

A simplified diagram of an alternative embodiment is shown in Figure 4 in which parts have been omitted for ease of reference. Multiple recesses 18 — 21 enable multiple cams to be fitted to the tool.

Figure 5A and 5B demonstrate use of the device in extracting a hollow medical device. In both Figures, the distal portion of the tool comprising the body region 3 is shown within a cut-away section of a hollow medical device 22. In use, the tool will be inserted into the medical device 22 with the cam in its retracted position 23. As discussed above, movement of the tool 1 in a downward direction as shown in the Figure will tend to cause the cam 5 to move toward the retracted position. Further, the control wire (not shown for ease of reference) may be utilised in order to maintain the cam 5 in the retracted position. The tool is therefore free to move within the device as shown in Figure 5A.

When the correct position is reached as in Figure 5B then downward movement of the tool is stopped. For clarity, the relative dimensions of the tool have been reduced when compared to the medical device. However, the dimensions of the tool are such that the cam 5 engages inner wall of the medical device such that withdrawal of the tool causes the cam to move toward the extended position. The relative dimensions of the tool and medical device will determine whether the cam 5 reaches the extended position (and contacts a wall of the recess) or whether the available space within the tool will prevent the cam 5 from extending this far. Force can then be applied to the tool in order to extract the medical device. In the embodiments shown this force is applied using a slap hammer that has been connected to the top of the tool via the screw thread 12.

The skilled person will appreciate that features may be taken from any one of the embodiments described above and applied mutatis mutandis to other of the embodiments of the invention.

Claims

1. An extraction tool arranged to remove a hollow medical device from a subject, the tool comprising an elongate member, having at an end region thereof a body region comprising at least one wall-engaging means configured to engage an inner wall of a medical device, into which, in use, the tool is inserted.

2. A tool according to claim 1, wherein the elongate member comprises a flexible rod or cable, which allows the body region of the tool to be inserted into a medical device.

3. A tool according to any preceding claim, wherein the or wall-engaging means is unidirectional, such that it is configured to engage with the medical device when rotating in one direction relative to the body region.

4. A tool according to claim 3, wherein the unidirectional nature of the or each wall-engaging means allows insertion of the tool into a medical device with the or each wall-engaging means in their retracted position but results in the device being engaged upon withdrawal of the tool with the wall-engaging means in or at least towards an extended position.

5. A tool according to any preceding claim, wherein the or each wall-engaging means is configured to rotate between a retracted, non-engaging position and an extended, engaging position.

6. A tool according to any preceding claim, wherein the or each wall-engaging means is arranged such that increasing the force of extraction, increases the force with which the wall-engaging means engages with an inner wall of the medical device.

7. A tool according to any preceding claim, wherein the tool comprises control means connected to the or each wall-engaging means, generally arranged so as to cause the or each wall-engaging means to rotate when a force is applied to the control means.

8. A tool according to claim 7, wherein the position of the or each wall- engaging means can be adjusted by the control means.

9. A tool according to either claim 7 or claim 8, wherein the control means comprises a control wire.

10. A tool according to any one of claims 7-9, wherein the control means connects the wall-engaging means to a push lever.

11. A tool according to any preceding claim, wherein the or each wall-engaging means is resiliently biased towards an extended position.

12. A tool according to any preceding claim, wherein the wall-engaging means comprises one or more cams.

13. A tool according to any preceding claim, wherein the wall-engaging means comprises two or more cams.

14. A tool according to claim 13, wherein each pair of cams is configured to engage with the inner surface on substantially opposite sides of a medical device in which it is inserted.

15. A tool according to any preceding claim, wherein the surface of the or each wall-engaging means comprises friction-enhancing properties.

16. A tool according to claim 15, wherein the friction-enhancing properties include the surface of the wall-engaging means being provided with one or more of teeth, ridges, serrations or the like.

17. A tool according to any preceding claim, wherein the proximal end is configured to be connected to a mallet or slap-hammer or other force applying means.

18. A tool according to any preceding claim, wherein the tool is arranged to extract an intramedullary nail.

19. A tool according to any preceding claim, wherein the tool is arranged to extract a stent or other tube arranged to carry fluids.

20. A kit comprising an extraction tool according to any preceding claim and a force applying means configured to engage with the extraction tool.

21. A kit according to claim 20 which comprises one or more intramedullary nails which the extraction tool is arranged to be used with.

22. An extraction tool according to any one of claims 1 -19, for removing a hollow medical device from a subject.

23. A method of removing a hollow medical device from a subject, the method comprising the steps of:

(a) inserting an elongate member of the extraction tool according to any one of claims 1-19 into a hollow medical device,

(b) engaging at least one wall-engaging means with an inner wall of the medical device, and (c) withdrawing the tool and the device from the subject.