CA2026718A1

CA2026718A1 - Device for the re-education of a limb

Info

Publication number: CA2026718A1
Application number: CA002026718A
Authority: CA
Inventors: Guy Grenouillet
Original assignee: Nivarox Far SA
Current assignee: Nivarox Far SA
Priority date: 1989-10-05
Filing date: 1990-10-02
Publication date: 1991-04-06
Also published as: AU6376590A; EP0421368B1; FR2652738B1; JPH03133454A; FR2652738A1; AU636660B2; EP0421368A1; ATE89155T1; DE69001599D1

Abstract

ABSTRACT OF THE DISCLOSURE

A device for the re-education of a limb comprising a motor element made of shape memory alloy, which possesses at least one shape memory state corresponding to a specific configuration, control means for bringing the motor element into the said shape memory state and mechanical attachment means for securing at least a part of the motor element to a part of the limb to be re-educated.

Description

2 ~ ~d ~J 7 ~
TITLE OF THE INVENTION

DEVICE FOR_THE RE-EDUCATION OF A LIMB

FIELD OF THE INVEN'rION
The invention relates to the medical or veterinary equipment sector, and more specifically to a device for the re-education of limbs comprising a motor element in shape memory alloy. This device is intended particularly for re~establishing the 0~ articular and/or muscular function of a limb following an accident, prolonged immobilisation or similar.
In the present text, the term "limb" shall be understood to describe any part of the human or animal body which comprises a muscle and/or a joint.

BACKGROUND OF~ THE INVENq~ION
It is a known fact that to recover the articular or muscular function of a limb that has suffered traumatism or~prolonged immobilisation, it is necessary to undertake re-education of this Iatter by subjecting it to programmes of specific movements.
Generally speaking, the re-education can be performed in two ways which may~be independent or complementary consisting either of the participation of a practitioner or of the use of mechanical apparatus specific to this re-education.
~ owever, in both cases the still convalescent patient must make frequent visits at appointed times to the practitioner or - 2 ~ r~l to special premises where the said re-education equipment is situated.
This therefore results on the one hand in the patient being fatigued, and on the other hand in time constraints that often 05 are badly suited to occupational activity.
Furthermore, features of the mechanical re-education apparatus used generally include relatively high cost and complex apparatus of heavy construction not easy to operate by the patient alone.

OBJECTS OF THE INVENTION
The object of the invention is therefore to overcome the disadvantages analysed above by providing a device for the re-education of a limb that is simple, lightweight, of low cost and easy to operate by the patient himself.

BRIEF SUMMARY OF THE INVENTION
For this purpose the object of the invention is a device for the re-education of a limb which, in accordance with the invention, comprlses at least one motor element made in shape memory alloy, ~he motor element possessing at least one shape memory state corresponding to a specific configuration, control means for bringing the motor element into the said shape memory state and means of mechanical attachment for securing at least a part of the motor element to a part of the limb to be re-educated.

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BRIEF DESCRIPTION OF THE INVENTIOM
In accordance with a preferred embodiment, these attachment means comprise an envelope accommodating at least a part o~ the limb to be re-eaucated and containing the motor elements. This envelope may be formed in particular by a sheath or belt of 05 fabric in the manner of a dressing.
It is known that shape memory alloys have the property of being capable of undergoing reversible transformation from a first crystallographic phase state of the austenitic type (high temperature HT) to a second crystallographic phase state of the 1~ martensitic type (low temperature LT ) and thus being capable of being educated to assume, under certain ~onditions, a confi~uration which is termed shape memory state, or memorised state.
In other words, if an object consisting of such an alloy is educated in such a way that it memorises a con~igu~ation in the austenitic phase state (~T), for example, and this object is subsequently deformed whilst it is in a martensltic phase state (LT), it remains in its deformed configuration. If this object is then heated to be brought to a temperature at which its phase state is austenitic (HT), it tends progressively to re-assume its non-deformed shape, i.e. the configuration corresponding to its memorised state.
With such alloys, the transition from one phase state to another occurs in one dir~ction as in the other within a temperature zone. The temperature at which the austenitic phase starts to appear when the alloy is heated is termed TAs and the , . . ' .

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temperature at which the formation of the phase is completed is termed TAf tTAf~ TAs~. In similar fashion, when the alloy is cooled, the martensitic phase transformation starting and finishing temperatures ar0 termed TMs and TMf respectively (TMf 05 ~ TMs).
Generally speaking, it is to be noted that TMs and TMf are appreciably lower than TAf and TAs respectively, the temperature zones [TAs, TAf] and [TMs, TMf] being governed by the composition of the alloy.
It is also to be noted that amongst these alloys, the Ti, Ni; Ti, Ni, x; and Cn, Al, X~ alloys are particularly interesting; X being one of the group of metallic doping additives.
Such alloys and their education procedure are described particularly in a NASA article SP 5110 published in 1972 and entitled "55 Nitinol, the alloy with a memory : its physical metallurgy properties and applications".
The incorporation of one or more motor elements formed of a shape memory alloy, for example in a dressing intended to~be intimately attached to a limb to be re-educated, with this element being subjected to alternate heating and cooling, thus allows a specific movement of the limb to be effected for the purpose of its re-education.
Preferably the conductive properties of the alloy will be ~5 used to produce heating of the motor element by the Joule effect, the control means being thus formed by a simple source of voltage to the terminals of which the motor element is connected.

_ 5 _ ~2 BRIEF DESCRIPTION OF THE DR~WINGS
Further advantages an~ features of the inv~ntion will appear in the course of the detailed description which follows, of embodiments given for the purpvse of illustration in association with the drawings, of which:
0~ - figure 1 is a view in longitudinal section representing diagrammatically a first embodiment of the device in accordance with the invention, equipped with its control means and placed on a finger in a first position;
- figure 2 is a similar view to figure 1, the control means having been omitted, whilst the finger is in a second position;
- figure 3 is a view in transverse sëction along the line III-III of figure 2;
- figure 4 is a view in longitudinal section representing diagrammatically a second embodiment of the device:in a cordance with the invention which is again equipped with its control means and placed on a finger in a first position;
- figure 5 is a similar view to figure 4, but partially representing the device in accordance with the invention and in a second position;
- figure 6 is a view in transverse section along the line IV-IV of figure 5;
- figure 7 is a plan view representing diagrammatically and without a control circuit a third ~mbodiment of the device in accordance with the invention; and ~ ~c~77 -- 6 ~
- figure ~ is a view in transverse section along the line VIII~VIII of figure 7.
The detailed description of the invention will be given within the conte~t of an application to the re-eauaation of the 05 joints of a finger, but it is clear that the invention is not restricted to the embodiments describ~d or envisaged. In particular, the device in accordance with the invention may be used to advanta~e for the r~-education of other limbs, and in such a case it will possess different configurations which will 1~ ~e made compatible with the shape of the limb on which it is to be fitted.

DETAILED pESCRIPTION OF THE INVENTION
Referring firstly to figures 1 to 3, a first embodiment is seen of the device for the re-education of a limb in accordance with the invention, marked througho~t by the reference number 1.
This device fitted on a finger 2 comprises a sheath ~
enveloping substantially the entirety of the finger to be re-educated.
This sheath 4, made for example of a woven element, comprises a motor element 6 in shape memory alloy connected to a circuit 8 forming the control means.
The motor element 6 is formed of a wi~e in shape memory a110y educated to have a one way effect and the memorised shape of which is the straight shape of the motor element 6 represented in figure 2.
The motor element 6 which is of circular cross-section, is ., ,: -. . . .

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encased in an electrically and thermally insulating synthetic material 10 (figure 3) such as a silicone or the like.
As clearly visible in figures 1 to 3, the motor element 6 is incorpoxated within a wall of th~ sheath 4 and extends parallel 05 to its longitudinal axis substantially over the entire length of the sheath.
Of course, in accordance with one embodiment the motor element may be placed and attached on an outer sur~ace of the sheath, for example by means of a self-adhesive tape or the like.
In the embodiment shown, the motor element is located on the top of the finger when the device is in place on the finger, but it is to be understood that depending on the education of the motor element situated in the sheath 4 and the shape of the section of this element, the device may be placed in such a way that the motor element is located underneath or on the sides of the finger.
Moreover, the motor element 6 has a proximal extremity 12 and a distal extremity 14 connected respectively by means of two conventional electrical connectors 16, 18 to the control circuit 8. It is to be noted that the electrical connectors 16, 18 are similarly coated with an electrically insulating material, and preferably this is the same material as that coating the motor element 6.
The circuit 8 forming the contro1 means comprises in series, a direct current supply 20, a switch 22, a device 24 for varying the strength of the voltage circulating in the circuit and :
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circuit breaking means 26. The circuit 8 also comprises monitoring means 28 connected in parallel to the switch 22 and to the device 24.
Advantageously the drive circuit 8 may be formed using 05 commercially available integrated circuit components, the monitoring means 28 comprising in particular a microprocessor _combined with programmable memory. In one embodiment the moni toring means 28 compr~se timing means for programmin~ and/or monitoring automatically tile r~-~uuca~i~n cycles.

The operation of the device in accordance with the invention is as follows:
Firstly it is to be noted that the device descxibed above only permits, with a one way effect educated motor element, what is termed "active" re-education. "Active" re-education implies re-education requiring an effort on the part of the patient who must attempt to perform a movement without any external aid. In the example described it involves re-educating the joints of a finger with the patient being asked to bend his finger.
The finger 2 is encompassed in the sheath 4 which is, for example, in a position corresponding to the finger extended position (figure 2), and in the example illustrated has the memorised shape of the motor element 6. The motor element is at this moment in a martensitic crystallographic phase state (low temperature or T C TMs). The patient bends his finger to bring ~5 it into the position shown in figure 1, at the same time deforming the motor element 6. Once the finger is bent and the mot~r element deformed, the patient closes the contro1 circuit 8 by means of the switch 22. This closure causes current to pass through the motor element and as a consequence causes it to heat up by the Joule effect, so that the ~emperature of the motor element rises. ~s soon as this temperature exceeds the 05 temperature TAs, i.e. the temperature at which the austenitic crystallographic phase (high temperature) starts to form, the motor element 6 becomes progressively deformed to re-assume its memorised state (figure 2) as soon as the motor element reaches a temperature substantially higher than TAf.
At this moment, the control circuit can be switched off by the patient or, should the occasion arise, by the monitoring means so that the motor element cools down and its crystallographic phase state passes from the austenitic state to the initlal martensitic state. At this moment a new cycle can be initiated.
It may easily be understood therefore that in a first phase the patient makes an effort to bend his finger and that in a second phase the motor element 6 solid with the sheath 4 forces the finger into a straight position~
A repetition of this cycle a large number of times enables the patient to pexform, without ex$ernal aid, simply and at his own speed, the re-education of his afflicted limb.
In the embodiment represented in figures 1 to 3, a wire in alloy Ti - Ni of the 50-50 type has been used, the wire being of diameter D = 2 mm approximately and the circuit being powered by a supply of about 3 volts. This has enabled a motive force Fm of the order of 3.5 N to be obtained.
For information, with the alloy used the following phase `, . ' , .

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transition temperatures are obtained:
TAs = 60C; TAf = 90C; TMs = 60C; TMf = 40C.
Of course the force that is supplied by the motor element to the limb to be re-educated may ~ary according to the limb one 05 wishes to re-ed~cate and in this respect it is to be noted that this motive force is substantially proportional to the dimensions of the motor element used. It is therefore self evident that to obtain the same motive force, it is possible to replace a single motor element by a number of motor elements of smaller dimensions and acting in the same way.
To prevent the patient feeling uncomfortable as a result of an excessive temperature in the heating up of the motor element, between the motor element and the sheath it is possible to provide an additional layer made of thermally insulating material (not shown).
Referring now to figures 4 to 6, a second embodiment is shown of a device in accordance with the invention in which the elements identical with those described previously are given the same reference numbers.
In this second embodiment, the device 1 comprises two motor elements 40, 42 formed of a shape memory alloy and made in the manner of a strip of substantially rectangular cross-section.
These two motor elements encompassed in an electrically and thermally insulating material are incorporated in diametrically opposed walls of the sheath 4 and the latter is placed on the finger in such a way that they are respectively located under and on top of the finger. As already described in the first 2~2~7~

embodiment, each element 40, 42 is connected through the intermediary of electrical connectors to a control circuit 44.
This control circuit 44 differs from the circuit described in association with figures 1 and 2 by comprising means 46 for 05 alternately energising motor element 40 and motor element 42.
These means 46 are formed by a f1ip-f1Op connected on the one hand to the power supply 20 and on the o~hex hand to the electrical connector 18 of each motor element, the rocker switch 46 being furthermore connected to the monitoring means 28.
The two motor elements 40, 42 are in this case one way effect educated and possess different memorised shapes in the sense that for example, the memorised shape (high temperature or austenitic phase) of the motor element 40 is bent or "crooked"
(figure 4j whereas the memorised shape of the motor element 42 is straight (figure 3~.
Thus when the motor elements 40, 42 are energised alternately, they act in opposite directions so that an alternating movement of the finger between its bent positlon (figure 3) and its extended position can be obtained.
With this suitable control of the device, it is thus possible to undertake in a simple way a re~education that may be termed "passive", i.e. without the patien~ providing any effort to initiate these movements.
In this case, the monitoring means 28 a~e programmed so that the motor elements 40, 42 are energised systematically in succession and never simultaneously~
It is similarly understood that these monitoring means 28 ~ ~ C~ ~3 t~

comprise timing means like those described in association with figures 1 to 3 for performing ~e-education cycles aaapted to each patient.
O~ course, passive re-education with the aia of such a OS device can be performed by replacing the two . one way effect educated motor elements 40, 42 by a single motor element in alloy with two way.~effects educated shape.memory.
Finally referring to figures 7 and 8, a third embodiment is seen of the device in accordance with the invention in which a single motor element 6 is incorporated in a strip of fabric 48 provided on one of its faces with an adhesive material 50 in the manner of a dressing. The motor element ~ is of course connected to a control circuit (not shown~ of the type of that described in association with figures 1 to 3.
In accordance with one embodiment, the adhesive material 50 can be replaced by other means of being attached to the limb to be re-educated, such as in particular by straps with buckle fasteners, straps with Velcro fastening, or simllar.
It is to be noted that advantageously such an embodiment permits the same device to be fitted on limbs of different shapes, sizes and sections.
It is to be noted that in all the embodiments described above, the control circuit preferably includes a fuse forming circuit-breaking means 26 for the event of a short-circuit occurring in the device.
Finally, it will be noted that such a device has the advantage of being capable of being used in an autonomous :

manner, i.e. without any association with a fixed point of reference such as a building or similar, and whatever the location of the limb to be re~educated~

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Claims

1. A device for the re-education of a limb, having at least one motor element made of shape memory alloy, the said motor element possessing at least one shape memory state corresponding to a specific configuration, control means for bringing the motor element into the said shape memory state and mechanical attachment means for securing at least a part of the motor element to a part of the limb to be re-educated.

2. A device in accordance with Claim 1, wherein the attachment means comprises an envelope accommodating at least a part of a limb to be re-educated, each motor element being incorporated in the envelope.

3. A device in accordance with Claim 1, wherein the attachment means comprises an envelope having the configuration of a sheath for accommodating at least a part of a limb to be re-educated and by each motor element being attached to an external face of the envelope.

4. A device in accordance with Claim 1, wherein each motor element is formed of a profiled element at least partially coated with an electrically and thermally insulating synthetic material.

5. A device in accordance with Claim 1, wherein the control means comprises a direct current source of electrical energy connected to the extremities of each motor element.

6. A device in accordance with Claim 5, wherein the control means furthermore comprises a switch connected between the direct current electrical energy source and one extremity of each motor element.

7. A device in accordance with Claim 5, wherein the control means furthermore comprises means for varying the strength of the current passing through each motor element.

8. A device in accordance with Claim 1, which also comprises timing means automatically monitoring the expired time between two successive operations of switching-on each motor element.

9. A device in accordance with Claim 1, which furthermore comprises circuit-breaking means for the event of overheating of each motor element.

10. A device in accordance with Claim 1, wherein each motor element is made of one way effect educated shape memory alloy.

11. A device in accordance with Claim 1 which comprises two motor elements located on either side of the limb to be re-educated and acting in opposing directions.

12. A device in accordance with Claim 11, which comprises means for energising only one motor element at a time.