GB2387117A

GB2387117A - Shape memory circlip for fixing elements to a bone

Info

Publication number: GB2387117A
Application number: GB0207990A
Authority: GB
Inventors: Paul Mason
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-04-06
Filing date: 2002-04-06
Publication date: 2003-10-08
Also published as: GB0207990D0

Abstract

Apparatus for securing a bone graft 12, plate or other element on or in a human or animal bone 14 which comprises one or more belts or circlips 10 of shape memory alloy. Preferably the circlip is resiliently deformable, returning to its original form when released or heated. The circlip may have an arcuate shape, varying thickness, radii or length and one or more holes, grooves or protuberances to permit blood flow or for additional fixtures. The circlip may be made from Nickel-Titanium shape memory alloy, single memory one-way or super-elastic. A plurality of circlips may be joined together concentrically with a bar. Methods of using the circlip to secure a bone graft, plate or other element on or in a bone have also been claimed, including heating the circlips with hot liquid such as saline or passing an electrical current through them.

Description

1 23871 17

Name Of Irlventon: The Morngton Buckle

CIRCLIP

1. This invention relates to a circlip and in particular to a circlip for use intracorporeally in a human or animal patient.

2 During orthopacdic surgery involving the fixation of damaged bone, circlage wiring is used commonly in order to achieve this. In addition, allografts (both traditional and synthetic) would require securing to the bone and again a circlage technique is used.

A typical example would be; when a hip prosthesis (a femoral portion of a hip replacement) fails, it is normally due to loosening of the stem within the femur. In extreme cases, the prosthesis may cause thinning of the bone to the point where the stem would protrude through the bone and this can be a site of fracturing. Such an event can be associated with significant pain for the patient.

3. In this case, the patient will undergo revision surgery to replace prosthesis and to repair the femur. The defect in the bone is usually repaired with a bone graft and the stem is then re-cemented into the femur. In other cases, a hole (or window) is drilled into the femur so that the surgeon may clear cement debris from within the femur.

Such a defect in the bone will need closure by using a bone graft 4. It is obviously necessary to secure the bone graft in place in either of the above circumstances and the method currently used is known as "circlage wiring, in which a length of stainless steel wire is wrapped around the femur and pulls the bone graft on to the defect The ends of the wires are then twisted together to the point where the graft is securely held in the defect.

5. However, there are a number of drawbacks associated with the circlage wire method.

Firstly, it is difficult to ensure that the correct taut is applied when twisting the ends of the wire and often the wire snaps due to cold working. Sometimes this occurs at the time of operation and sometimes this can occur later. Further, the method of placing the wire all the way around the bone and graft can be difficult, tedious and occasionally dangerous. (A blood vessel or nervous structure may be damaged). The tool used to achieve this comprises a hooked tube which, when passed, may damage surrounding tissues.

6. We have now devised an arrangement, which seeks to overcome the problems outlined above. In accordance with a first aspect of the present invention, there is an apparatus provided for securing a bone graft/plate or other apparatus to a human or animal bone. The apparatus comprises one or more belts or circlips of shape memory alloy adapted so that it can be placed over the graft or plate or other element and then heated to secure the graft 7. In accordance with a second aspect of the present invention, there is provided apparatus for securing a bone graft, plate or other element to a bone within a human or animal body, the apparatus comprising one or more belts or circlips of shape memory alloy adapted to be deformed, placed over said graft, plate or other element on or in said bone and then released such that said one or more belts or circlips return to their original form and secure said graft, plate or other element to the bone.

8. Thus, in its broadest sense, the present invention provides apparatus for securing a bone graft, plate or other element to a bone within a human or animal body, the apparatus comprising one or more belts or circlips of shape memory alloy adapted to be placed over said graft, plate or other element on or in said bone to secure said graft, plate or other element to the bone.

9. The or each circlip is beneficially generally accurate (such as generally semicircular) and preferably of Nickel-Titanium (Ni-Ti) shape memory alloy and more preferably of single memory one-way or superelastic Ni-Ti.

10. In use, with one embodiment of the present invention, each circlip is placed over, for example, a bone graft and then heated so that it reverts to a predetermined shape or adopts the precise circumferential shape of the adjacent graft and bone. In this case, each circlip may be heated in a number of different ways. For example, a hot saline solution may be applied thereto.

Alternatively, an electrical current could be allowed to pass through it; the resistance of shape memory alloys (a particular class of materials which is known in the art of metallurgy, for example nickel-titanium) is relatively high (much higher than that of stainless steel, for example) so they can be heated using a relatively Live level voltage. In one specific embodiment of the invention, each circlip may be wanned to approximately 61 C. 11. In accordance with another embodiment of the present invention, the or each circlip is resiliently deformable, so that it can be deformed to a configuration which enables it to be placed over, for example, a bone graft and then released so that it reverts to it's original shape and clasps the graft thinly to the bone.

12. The or each circlip may have holes, grooves or protuberances to avoid restricting blood flow to the bone and/or to provide for additional fixing facilities, such as screws, pins or the like. The surface(s) of the or each circlip may be smooth or uneven. Circlips generally may, of course, be provided in various lengths, shapes and widths to accommodate different sizes of bone and different applications.

13. The or each circlip of the present invention may have an uneven profile i.e. generally accurate shape but unevenly so. Each circlip may also be of a varying thickness and/or radii along its width and/or length according to specific applications and requirements. 14. In the case where the apparatus comprises a number of belts or circlips for use together, the circlips can be joined together by means of a central bar or strip to which the circlips are disposed, usually concentrically.

15. It will be understood that the circlip can be used in either human or animal patients and, for example, may have an application in the treatment of fractures in race horses as well as in human fracture and joint replacement surgery.

16. Exemplary embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which: O Figure 1 is a schematic diagram illustrating a method of securing a bone graft according to the prior art.

Figure 2 is a schematic diagram illustrating apparatus according to a first exemplar embodiment of the present invention.

O Figure 3 is a schematic diagram illustrating a method of using the apparatus of Figure 2.

O Figure 4 is a schematic diagram illustrating apparatus according to a second exemplary embodiment of the present invention.

and Figure 5 is a schematic diagram illustrating apparatus according to a third exemplar embodiment of the present invention.

17.Figure 1 Referring to Figure 1 of the drawings, according to current practice, a bone graft (100) is applied over a hole in a bone (102) and a stainless steel wire (104) is wrapped around the bone (102) and the graft (1OOJ, and secured by twisting the ends of the wire (104) together, as shown. This is known as the circlage wire method.

18.Figure 2 Referring to Figure 2 of the drawings, in its simplest form, the apparatus of the present invention may comprise a generally semicircular or arcuate circlip (10) of nickel titanium alloy, having a substantially equal width and thickness along its length. In use, referring to Figure 3 of the drawings, a circlip (10) is placed over a bone graft (12), as shown, and secured to clasp the graft firmly to the bone (14).

19. This may be achiev.ed.by marry different means. accor.cling to the inventiom In accordance with one embodiment of the invention, the circlip (10) is resiliently deformable. In this case, it may be deformed to increase its radius SO that it can be placed over the graft, and then released so that it returns to its original form and clasps the graft (12) fly to the bone (14).

In accordance with another embodiment of the invention, the circlip (10) is provided of a size and configuration to allow it to be placed over the graft t-12) with or without deformation thereof being required) and then heated (in one embodiment to approximately 61 C) using, for example, hot saline solution or by allowing an electrical current to pass through it In this case, the application of heat to the circlip It O.). causes it to either revert to its original shape (if deformation thereof was required to place it over the graft (12) and/or adopt the precise circumferential shape of the adjacent graft (12) and bone (141, so as to securely clasp the graft (12) firmly to the bone (14).

20. Of course, more than one such circlip (10) can be used if required, as shawl Referring to Figure 4 of the drawings, the circlip (10) may have a variable width along its length, as shown, and may also include one or more apertures (16) to allow for additional fixing facilities, such as screws or pins, to be used.

21. Figure 5 Referring to Figure 5 of the drawings, a plurality of circlips (10) may be connected together substantially concentrically by means of a bar tiS) or strip, as shown. However, many other methods of connecting such circlips together are envisaged and the invention is not intended to be limited in this regard.

22. Embodiments of the present invention have been described above by way of examples only with reference to Figures 2 to 5 of the drawings. It wit} be apparent to a person skilled in the art that modifications and variations can be made to the described embodiments without departing from the scope of the invention as defined by the appended claims

Claims

s CL=MS 1. Apparatus for securing a bone graft, plate or other element to

a bone within a human or ammal body, the apparatus comprising one or more belts or circlips of shape memory alloy adapted to be placed over said graft, plate or other element on or in said bone to secure said graft, plate or other element to the bone
2. Apparatus for securing a bone graft, plate or other element to a bone within a human or animal body, the apparatus comprising one or more belts or circlips of shape memory alloy adapted to be deformed, placed over said graft, plate or other element on or in said bone and then released such that said one or more belts or circlips return to their original form and secure said graft, plate or other element to the bone.
3. Apparatus for securing a bone graft, plate or other element to a bone within a human or animal body, the apparatus comprising one or more belts or circlips of shape memory alloy adapted to be placed over said graft, plate or other element on or in said bone and then heated to secure said graft, plate or other element to the bone.
4. Apparatus according to any one of claims 1 to 3, wherein the or each circlip is generally accurate.
5. Apparatus according to any one of the preceding claims, wherein the or each circlip is of Nickel-Titanium (Ni-Ti) shape memory alloy, and more preferably of single memory one-way or super-elastic Ni-Ti.
6. Apparatus according to any one of the preceding claims, wherein the or each circlip is resiliently deformable.
7. Apparatus according to any one of the preceding claims, wherein the or each circlip includes one or more holes, grooves andlor protuberances to avoid restricting blood flow to the bone and/or to provide for additional fixing facilities, such as screws, pins or the like.
8. Apparatus according to any one of the preceding claims, wherein the or each circlip is of a varying thickness and/or radii along its width and/or length.
9. Apparatus according to any one of the preceding claims, comprising a plurality of belts or circlips joined together, preferably substantially concentrically.
10. A method of securing a bone graft, plate or other element to a bone within a human or animal body, the method comprising the steps of providing one or more belts or circlips of shape memory alloy, and placing said one or more belts or circlips over said graft, plate or other element on or in said bone to secure said graft, plate or other element to the bone.
11. A method of securing a bone graft, plate or other element to a bone within a human or animal body, the method comprising the steps of providing one or more belts or circlips of shape memoir alloy, deforming said one or more belts or circlips and placing said one or more belts or cirdips over said graft, plate or other element on or in said bone, and then releasing said one or more belts or circlips such that it or they return to their original form and secure said graft, plate or other element to the bone.
12. A method of securing a bone graft, plate or other element to a bone within a human or animal body, the method comprising the steps of providing one or more belts or circlips of shape memory alloy, placing said one or more belts or circlips over said graft, plate or other element on or in said bone and then heating said one or more belts or circlips to secure said graft, plate or other element to the bone.
13. A method according to claim 12, wherein said one or more belts or circlips are heated by applying a hot liquid, such as saline solution, thereto.
14. A method according to claim 12, wherein said one or more belts or circlips are heated by passing an electrical current there through.