FR2783702A1 - Self-locking prosthesis for bone insert has heat activated anchor flanges formed on central core - Google Patents

Abstract

The self locking bone prosthesis (3) has flanges (4) formed of titanium nickel alloy which is of shape memory or super elastic characteristics, mounted on a central core (5). The flanges expand after insertion due to the heat of the body to lock into the medullary canal. The flanges are cut from the core or attached to it.

Description

DEVICE

SELF-LOCKING

FOR PROSTHESES

  The present invention relates to a self-locking device implantable in bone elements and usable more particularly in orthopedics or osteosynthesis. A large number of parts are known which are intended to be implanted in bone elements to constitute implants proper or even reinforcing parts. All of these parts have the common characteristic of having to maintain a rigid mechanical connection between the part and the bone in which they are implanted over time. In the rest of the text, we will simply call

  such "implantable parts">.

  It is known (FR 85 19365) to constitute a self-locking medical prosthesis, the stem of which is intended to be inserted into a bone, made of a biologically compatible material and split over its entire width and over part of its length so as to form at least two separate branches (Figure IA), the rod material being a shape memory material having a martensitic transformation temperature lower than the temperature of the human body. Such a known self-locking medical prosthesis can be used in the following way: (a) the part is brought to a temperature below ambient temperature, for example at around 0 ° C., while being deformed to be brought into a configuration in which the two branches, 1 and 2, are brought together, the part thus retaining this configuration as long as it is maintained at this temperature; (b) the part is implanted in a bone by being threaded through a hole

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  formed in the bone with a certain play between the part and the bone; (c) then the temperature of the human body then brings the part definitively up to around 37 C, which automatically causes the deformation of the part which tends to resume its initial configuration, that is to say a configuration in which the two branches , 1 and 2, move apart (Figure IB), which generates a radial clamping force, F, outward, final, which causes a

blockage of the part in the bone.

  Such a known self-locking prosthesis has the drawback, as indicated in FIGS. 1A and 1B which illustrate the prior art, that the two branches, 1 and 2, cause, when they open or move apart one on the other, outwardly directed radial forces F which are not distributed uniformly over the entire length of the branches. In Figure 1 C, there is shown a diagram which is intended to illustrate the distribution of these radial forces over the length of the branches of the prosthesis. It can be seen that a large part A of the free end of the branches cannot be used to cause significant radial forces. It can also be seen that the most important radial forces F are distributed at the level of the base B of the branches, which has the drawback that the bone can burst or be damaged in the area B which corresponds to these most important forces. It is precisely in this

  end region of the bone that the bone is most fragile.

  From this known structure of a self-locking prosthesis such as that shown in FIGS. 1A and 1B, it could be envisaged to constitute the branches of the prosthesis so that their shapes, when they are in the separated position, one of the other correspond to an outwardly curved shape, that is to say that the free end parts of the two branches deviate from one another very much while the intermediate parts or the base parts of the of them

  branches do not deviate at all or deviate very little.

  Even if we thus plan to play on the shape of the branches in order to improve the distribution of forces

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  radial, this distribution remains relatively unsatisfactory

  because always irregular along the length of the branches.

  On the other hand, the metallic mass which constitutes these branches

  is relatively large for sufficient radial forces.

  The invention therefore relates specifically to a self-locking device implantable in a bone element and characterized in that it comprises on its external surface protuberances (fins or o0 variants) made of shape memory alloy or superelastic which go, by the temperature of the human body or by an external contribution of heat, expand

in order to block a prosthesis.

  An object of the present invention is to provide such a device having a specific shape (or shapes) which allows the part to be able to create substantially constant outward radial forces.

along the entire length of the room.

  Another object of the present invention is to provide such a device, the structure of which allows the part to be easily arranged so that the diagram of the radial forces as a function of the

  position along the workpiece can be freely distributed.

  Another object of the present invention is to provide such a device in which the quantity of shape memory material can be relatively small while allowing the formation of

  large radial forces over the entire length.

  These and other objects, features and advantages of the present invention

  will be better understood during the detailed description

  examples of embodiments which will follow, illustrated by the appended figures among which:

  FIGS. 1A and 1B are a diagrammatic representation

  than of a device of the prior art which here is applied

than a hip prosthesis.

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  FIG. 1C is a diagram, still with reference to the prior art, representing the location of the radial forces F. FIG. 2 is the overall representation of the application of the invention. Figure 3 shows the device in position

  closed, fins blocked against the central body.

  Figure 4 shows the same device but

  this time with the illustration of the opening of the fins.

  Figure 5 is intended to show the part and its

  fins manufactured in a single piece.

  Figure 6 shows the same part but manufactured not in a single piece but by adding parts

to a central part.

  Figure 7 shows a sectional view of the device.

  Figures 8 and 9 are variants, in section, of the

  system arising from this invention.

  Figure 10 illustrates the installation of the device

in a bone.

  With reference to these figures, the device claimed according to the invention consists of an element 3 (Figure 2) comprising on its outer surface fins or scales 4 attached to the

central body 5 by their base 6.

  Still with reference to the invention, the fins 4 are made of metal in shape memory, that is to say with an alloy such that the fins after being constrained along the central body (Figure 3) go through of a change in temperature, deploy (Figure 4) to return to their original shape which was open. These same

  fins 4, to perform the same functions as described below

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  above, may be made of superelastic alloy or any biocompatible material capable of giving them, by virtue of their elasticity, the possibility of being constrained firstly then, secondly, of being deployed by developing and retaining sufficient force to be

block in a bone.

  With reference to the invention, these fins 4 can be cut either from a metal block which then constitutes the central body (Figure 5). The fins 4 are then detached by machining, of course keeping them attached to the central body 5

by their base 6.

  A variant (Figure 6) consists in attaching to the central body 5 fins 4 always made of memory metal or other suitable metal. These fins can be, for example, a sheet in which the fins have been detached by punching, stamping ... In this case, the sheet folded back on itself into a cylinder for example can either be fixed strongly on the body central (Figure 6) or be left hollow to, for example, slide a rod as in some models of finger or toe prostheses or all prostheses requiring such sliding. It is also possible to have on the central body 5 inserts supporting the fins 4. Indeed, given the cost of shape memory metal, if it seems conceivable to manufacture a small prosthesis, for example for a finger, it is need to find cheaper solutions for larger prostheses such as the hip or knee while keeping

the benefits of the invention.

  Another variant according to the device of one invention can be found in the shape of the fins. These, instead of moving radially perpendicularly (Figure 7) relative to the central body (5), will expand circularly. Firstly (Figure 8), the fins 7 are kept compressed around the central axis 8. Then, after installation (Figure 9), the fins 7 still through heat will expand in the tunnel dug into the bone and block the prosthesis. Well

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  obviously, the same possibilities are claimed as described above with regard to the fins from a solid central body or cut from sheet metal for example and

  reported on the said central part.

  Furthermore, with reference to the invention, and to its adaptation, it is obvious that the arrangement, the shape, the length or the width of the fins can be different or even on the same part, in order to adapt to the requirements thereof with regard to the radial forces to be applied at such or such point of the prosthesis in order to bring to the surgeon, and to the patient, all the benefits which he can expect from this new device. Because if we take the very foundation of said invention, it is necessary to remember that it is based on the need to overcome the drawbacks described above compared to the known rod for example, which does not exert the right pressures

  in the right places.

  Furthermore, it is essential to remember that the major drawback of a prosthesis fixed in a bone has always been the loosening of the latter. In order to avoid this problem, multiple solutions have been proposed such as adding a "cement" or strengthening the prosthesis or prostheses with no screws. To date, all these solutions are still in use, which suggests, and this is the opinion of orthopedic surgeons, that none has given better results than the others. It is necessary to know indeed, and this is of capital importance in the development of the invention, that when one introduces a foreign body into the medullary canal of a bone, this one over time reacts in " fleeing "literally before this foreign body from which the phenomenon of loosening. In the light of FIG. 1B, one can easily imagine the drawbacks for the patient wearing such a prosthesis who feels that it "floats" without

  omit the pains and helplessness thus engendered.

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  Also, advantageously, the object of the invention (Figure 2) is intended to overcome these drawbacks without forgetting that it can only facilitate the task of the surgeon who, as in the current case of placement in force of a cementless prosthesis, must work very precisely. In fact, the fins will automatically block the prosthesis, even though the tunneling in the medullary part of the bone would not have been carried out very precisely. Without forgetting, that given that over time, all prostheses, whether they were

  put in force or with cement, tend to loosen.

  Here, thanks to the fins which, due to the temperature of the human body, will always retain all of their expansion properties, the fins will therefore constantly catch up with the "play" that could take place between the prosthesis and the spinal canal of the bone. 'This implantable device, which can be applied to all prostheses (hip, knee, joint of all kinds (Figure), even dental implant), is not limited to the embodiments which have been described here only by way of nonlimiting examples, but the invention extends to all the imaginable variants which remain in the spirit and in the

general framework of the invention.

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Claims (4)

  1) Self-locking device for implantable prosthesis characterized in that it comprises fins 4 made of titanium-nickel (shape memory or superelastic alloy) disposed on the central body 5, which, once placed in the medullary canal go, by the temperature of the human body or by the supply of heat, expand in order to block the said prosthesis in a bone (Figure 10).   2) Self-locking device for implantable prosthesis according to claim 1 characterized in that it comprises   fins over all or part of the length of the part.   3) Self-locking device according to claims 1 and 2   comprising fins 4 either of different lengths or widths, or of different shapes, or of   different forces or all combined.   4! Self-locking device according to any one of   claims 1,2 and 3 comprising fins 4 or   cut in the mass (Figure 3, 4 and 5) is reported (Figure 6) by any means on the central body 5, the latter being or not solid or hollow titanium-nickel alloy. ) Self-locking device according to any one of   claims 1,2, 3, 4, characterized in that the   fins 4 have a shape such that it expands circularly (7,8) but always with the aim of   block a prosthesis in a bone (Figure 1 0).   6) Self-locking device according to claim 1 characterized in that the titanium alloy operates at different temperatures.