WO1994015544A1

WO1994015544A1 - Device for fixing a prosthesis to a bone

Info

Publication number: WO1994015544A1
Application number: PCT/EP1993/003702
Authority: WO
Inventors: Yuval Bromberg; Josef Flomenblit; Itzhak Binderman; Sergei Melbard
Original assignee: A. Bromberg & Co. Ltd.; Cohn, Michael
Priority date: 1993-01-06
Filing date: 1993-12-27
Publication date: 1994-07-21
Also published as: AU5834494A; IL104313A0

Abstract

A device (11) for fixing a prosthesis to a bone (24) has a first member (12) adapted for connecting to the prosthesis and has a second member (13) adapted for anchoring the device (11) in the bone (24). At least a substantial part of the second member (13) is made of a shape memory material which is capable of changing its shape between a first and a second state as a result of an appropriate temperature range. The second member (13) consists of a plurality of discrete wall members (18) having each one end (19) integral with said first member (12) and another, free end (20). In the said first state the wall member (18) is defined together a shape resembling that of a prismatic or cylindrical tube, and in said second shape, the free ends (20) of the wall members (18) become more distanced from one another, whereby the fixation device (11) becomes anchored in a bone (24).

Description

DEVICE FOR FIXING A PROSTHESIS TO A BONE

FIELD OF THE INVENTION

The present invention concerns a device for retaining a prosthesis in a bone, based on the properties of shape memory materials. The present invention also concerns a method for fixing a prosthesis to a bone using such device.

The term "shape memory material", refers to a material made of plastic or metal which, after plastic deformation, has the ability to revert to its shape prior to deformation upon appropriate temperature change, i.e. change of temperature beyond a certain specific conversion temperature. The most common materials of this kind are shape memory alloys which are composed of various metallic materials some of which will be detailed below.

BACKGROUND OF THE INVENTION Modern dentistry, orthopedics, neurosurgery, otology and ophthalmology make use of various prostheses that have to be firmly fixed to a bone. The prostheses are secured to the bone by appropriate fixation

SUBSTITUTE SHEET elements anchored in the bone. Usually these fixation elements are held by press fitting into a prior drilled bore or by being self-tapped.

In order to ensure a firm grip of the fixation element to the bone tissue, it has to be inserted as deep as possible into the bone, usually not less than 6 mm deep. This creates a problem in flat bones such as jaw or skull bones.

Shape memory alloys found applications in various medical devices, including such intended for anchoring a prosthesis in a bone. Use of shape memory alloys for such purposes has been disclosed in U.S. Patents 4,921,499; 4,170,990 and 4,468,201.

GENERAL DESCRIPTION OF THE INVENTION

The present invention provides a fixation device which does not require deep-drilled bores for fixation and is thus particularly suitable for retaining a prosthesis in a flat bone or cortical bone (hard bone shell).

The device of the present invention can be easily inserted and retracted from a drilled bore without damaging the surrounding bone tissue.

While the fixation element of the present invention is principally suitable for use in all types of bones, a particularly preferred use is in a flat bone such as in the jaw and skull bones.

The present invention provides a fixation device for fixing a prosthesis in a bone having a first member adapted for connecting to the prosthesis and having a second member adapted for anchoring the device to the bone, the device being characterized in said second member, having the following features:

(i) at least a substantial part thereof is made of shape memory material being capable of changing its shape between a first and a second state as a result of an appropriate temperature change;

SUBSTITUTE SHEET (ii) it consists of a plurality of discrete wall members having each one end integral with said first member and another, free end; in said first state the wall members define together a shape resembling that of a prismatic or cylindrical tube, and in said second state, the free ends of the wall member become more distanced from one another; and

(iii) the wall members having a rough external surface.

The present invention further provides a method for anchoring a prosthesis in a bone comprising:

(a) providing a fixation device of the kind specified above; (b) forming a bore in the bone of a diameter allowing insertion of said second member in said first state but ensuring tight fit thereof in said second state, the bore being of a length allowing it to accommodate the entire length of said second member;

(c) providing a temperature so that said second member assumes its said first state and inserting said second member into said bore;

(d) changing the temperatures so that said second member assumes its said second state, whereby the fixation device becomes fixed in the bone; and

(e) connecting the prosthesis to said first member. In accordance with one embodiment of the present invention, the wall members diverge from one another in said second state defining together a shape resembling that of a cone.

In accordance with another embodiment, the wall members assume a prismatic or cylindrical tubular shape similar to that in the first state but of a larger diameter.

The device of the invention is particularly suitable for fixing prostheses to flat bones, e.g. fixing an artificial tooth to a jawbone, a hearing aid to the skull, etc.

SUBSTITUTE SHEET The length of the wall members may typically be essentially equal to or more than the thickness of the bone in case of flat bones, or than the thickness of a cortical bone shell in case of other types of bones. At times it is desired to have wall members which consist of a major portion having essentially a length equal to said thickness and in addition, terminal portion at their free end, being straight with the major portion at said first state and which bend radially in said second state, forming together a corona beyond the distal part of the bone or the bone shell, as the case may be. The outer surface of the wall members are rough so as to increase the friction between them and the bone tissue and/or allow it to cooperate with the growing bone tissue so as to firmly secure the device in situ. For example, the external surface of the wall members may have a plurality of bulges, teeth, annular ribs, threads, etc. Additionally, the wall members may have a coating comprising minerals, polymers, etc. The first member may be connected to a prosthesis by any of a number of means known er se, such as by screw engagement, by a male- female type engagement and the like.

Said substantial part of said second member is made of a shape memory material, such as shape memory alloy or shape memory plastics of non-bornane series. Shape memory alloys are generally preferred and include binary alloys such as Ti-Ni, known as Nitinol™ (Unitek Cor., U.S.A.) and various tertiary alloys such as TiNiCo, TiNiCu, TiNiPd, TiNiAu, TiNiFe, TiNiCr, TiNiV, TiNiNb, CuAINi, and CuZnAl.

Typically, the device is devised so that said second member assumes its said first state in cool temperature and upon heating, e.g. to body temperature, it deforms to said second state. Upon cooling of such a device, e.g. close to or below 0°C, it assumes its said first state in which it can be inserted into a prior drilled bore, and then, after heating for example above 28°C, it assumes its second state whereby it becomes tightly fitted inside the bore. If it is desired to remove the device, it may be cooled again, thereby assuming its first state in which it can be removed.

The diameter of the bore is usually made to be somewhat less than the maximal diameter which can be assumed by the second member in said second state. Thereby, in view of the super-elastic properties of shape memqry alloys, the tight fit will remain even where the diameter of the bore increases over time, due to reabsorption of surrounding bone tissue.

The invention will now be illustrated by several non-limiting specific embodiments with reference to the Figures in the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a side cross-sectional view of a device in accordance with one embodiment of the invention in a first state, with a second state superimposed by dotted lines; Fig. 2 shows a cross-section of a device through lines 2-2 of Fig. 1;

Fig. 3 shows the device in accordance with the embodiment of Fig.

1 fixed in a bone;

Fig. 4 shows a side cross-sectional view through a device in accordance with a modification of the embodiment of Fig. 1 in a first state, with the second state superimposed by dotted lines;

Fig. 5 shows the device of Fig. 4 in situ in a bone; Fig. 6 shows a side cross-sectional view of a device in accordance with another embodiment of the invention in a first state, with the second state superimposed by way of dotted lines; and Fig. 7 shows a cross-section through lines 7-7 in Fig. 6.

DESCRIPTION OF SPECIFIC EMBODIMENTS Reference is first made to Figs. 1-3 showing a device generally designated 11 comprising a first member 12 adapted for connect¬ ing to a prosthesis and a second, anchoring member 13.

The first member 12 has a central bore 14 which is screw- threaded in its side walls 15 allowing a screw engagement with a prosthesis (not shown). The first member 12 has shoulders 16 intended to serve as a limit for insertion of the device into the bone.

The second member 13, as can be seen in Fig. 2, consists of six wall members 18 defining together a shape resembling a cylindrical tube, and having each one end 19 integral with the first member and another, free end 20. The wall members 13 have on their external surface a plurality of annular projections 21.

The wall members 18 are made of a shape memory alloy such as Nitinol™, consisting of 50.6% titanium and 49.90 nickel, and can thus change their shape between a first and a second state as a result of an appropriate temperature change. In a first state, at a temperature ≤0°C, wall members 18 assume together a shape resembling that of a cylindrical tube, and in the second state at a temperature ≥28°C, the wall members diverge from one another and assume together a shape resembling that of a cone, as shown in Fig. 1 by way of dotted lines.

In said first state, second member 13 can be inserted into a prior drilled bore which should have a diameter somewhat larger than the external diameter of the annular projections 21. As can be seen in Fig. 3, after insertion second member 13 which is at body temperature, assumes its cone-shaped second state and in that state projections 21 tightly press against wall 22 of bore 23 in bone 24. As can be seen in Fig. 3, the diameter of bore 23 is such that the wall members do not diverge to their full extent shown in Fig. 1 and thus maintain a potential to diverge more in case the bore's diameter will increase at a later stage as a result of reabsorp- tion of the surrounding bone tissue.

Attention is now being directed to Figs. 4 and 5 showing a modification of the embodiment of Figs. 1-3. In this embodiment all like elements have been given the same reference numeral as in the embodiment of Figs. 1-3 with a prime indication. The difference between device 11' of this embodiment is in the terminal portion 26 at the free end of each wall member. The terminal segments are designed to be straight with respect to the remaining portions of the wall members in said first state and radially bend in said second state. The terminal segments constitute the portion which protrudes beyond the distal part of the bone in case of flat bones, or beyond the cortical bone into the trabecular bone. When bending, all the terminal segments form together a corona which aids in anchoring of the device as shown in Fig. 5. Attention is now being made to Figs. 6 and 7 showing another embodiment of the invention. Here again, like elements have been given like numbers as those in the embodiment of Fig. 1 with a two-prime indication. The difference between the device 11" in Figs. 6 and 7 and the device 11 in Fig. 1 is that rather than diverging, the wall members 18" in the embodiment of Figs. 6 and 7 assume in the second state, as shown by way of dotted lines, a cylindrical shape of a larger diameter than that assumed by them in the first state. This increased diameter ensures tight fitting of the second member 13" of the device 11" inside the bore in the bone.

Claims

CLAIMS:

1. A fixation device for fixing a prosthesis in a bone having a first member adapted for connecting to the prosthesis and having a second member adapted for anchoring the device in the bone, the device being characterized in said second member having the following features:

(i) at least a substantial part thereof is made of a shape memory material being capable of changing its shape between a first and a second state as a result of an appropriate temperature change; (ii) it consists of a plurality of discrete wall members having each one end integral with said first member and another, free end; in said first state the wall members define together a shape resembling that of a prismatic or a cylindrical tube, and in said second state, the free ends of the wall members become more distanced from one another; (iii) the wall members having a rough external surface.

2. A device according to Claim 1, wherein said wall members of said second member, diverge from one another in said second state, to form a shape resembling that of a cone.

3. A device according to Claim 1, wherein said wall members assume in said second state a cylindrical or prismatic shape similar to that they assume in said first state, but of a larger diameter.

4. A device according to Claim 1, wherein the wall members have external annular projections.

5. A device according to Claim 1, wherein the wall members comprise a terminal portion being straight with respect to the remaining portion of the wall members in said first state and radially bending in said second state.

6. A method for anchoring a prosthesis in a bone comprising: (a) providing a fixation device having a first member adapted for connecting to the prosthesis and having a second member adapted for anchoring the device in the bone; at least a substantial part of said second member being made of a shape memory material being capable of changing its shape between a first and a second state as a result of an appropriate temperature change; said second member consisting of a plurality of discrete wall members, having each a rough external surface and having one end integral with said first member and another, free end; in said first state the wall members define together a shape resembling that of a prismatic or cylindrical tube, and in said second state, the free ends of the wall members become more distanced from one another;

(b) forming a bore in the bone of a diameter allowing insertion of said second member in said first state but ensuring tight fit thereof in said second state, the bore being of a length allowing it to accommodate the entire length of said second member;

(c) providing a temperature so that said second member assumes its said first state and inserting said second member into said bore; -

(d) allowing the temperature to change so that said second member assumes its said second state, whereby the fixation device becomes fixed in the bone; and

(e) connecting the prosthesis to said first member.

7. A method according to Claim 6, wherein said first state is assumed by said second member at a temperature below body temperature, and upon heating of the device, said second member assumes its second state.