Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-09-23
2001-03-13
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S063000, C606S08600R, C606S057000, C606S105000, C606S058000
Reexamination Certificate
active
06200317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for moving a first object relative to a second object, which device comprises a first part, which can be fixed to said first object, and a second part, which can be fixed to said second object. Such a device may be used for moving bone portions relative to each other inside a human or animal body, whereby said first object is a first bone portion and said second object is a second bone portion.
Although the invention is not limited to medical applications, the present specification will describe the implementation of the invention for the movement of bone portions relative to each other inside a human body.
2. Description of Related Art
Devices are known wherein two bone portions are connected by means of pins to an elongation apparatus present outside the body, which moves the pins in such a manner that the desired movement is effected at the desired speed of the bone portions. One drawback of such external fixation devices is that they constitute a considerable physical and psychological burden for the patient, and that there is moreover a constant risk of infection in several places where the skin is pierced by pins.
Furthermore devices are known which can be implanted into the human body and which comprise a drive motor which moves the two bone portions to the desired extent relative to each other. Such a device is known from U.S. Pat. No. 5,415,660, which publication describes an elongation pin comprising two ends, which are each fixed to a bone portion, whilst the elongation pin is capable of telescoping out, thus elongating the pin. The drive motor used for said elongation thereby consists of a shape memory metal, whose shape is dependent on the temperature, as will be explained in more detail as yet.
A device for moving bone portions relative to each other, which is to be implanted into the body, must exhibit a high degree of reliability, which can be achieved by reducing the number of parts to a minimum. In addition to that the device must have small dimensions. Furthermore it may be necessary that the device is capable not only of moving the two bone portions in a direction away from each other, but also towards each other to a desired extent. The latter may for example be important if, for whatever reason, the bone portions have been moved too much or when it becomes necessary at a certain point in time to release or reverse the load being exerted on the tissue of the human body.
SUMMARY OF THE INVENTION
The object of the invention is to provide a device for moving objects such as bone portions relative to each other, which device exhibits a high degree of reliability, which is capable of generating large forces, and which is capable of moving the two objects both towards each other and away from each other.
In order to accomplish that objective the device is according to the invention provided with a first part comprising an elongated portion, along which the second part can move, which second part is provided with a clamping member, which is capable of clampingly engaging said elongated portion, and which comprises shape memory metal which gives the clamping member a clamping shape or a releasing (non-clamping) shape, depending on the temperature of the shape memory metal. Preferably the device is suitable for being implanted into a human or animal body, whereby said first object is a first bone portion and said second object is a second bone portion.
In one preferred embodiment said second part is provided with a first clamping member and with a second clamping member, which are each capable of clampingly engaging the elongated portion of said first part of the device some distance apart, whereby both clamping members comprise shape memory metal.
Shape memory metal is an alloy which may exhibit various phases, depending on the temperature. Such shape memory metal may for example consist of a TiNi alloy. The temperature ranges of the various phases are separated by a transition range. Said transition range can be adjusted to the desired value, for example round 37° C., the temperature of the human body, by a suitable selection of the composition and the treatment of the material. The phase above the transition range is the austenitic phase, and the phase below the transition range is the martensitic phase of the shape memory metal. A shape memory metal alloy can be produced and treated (trained) in such a manner that the material attempts to take a certain shape upon being heated to the austenitic phase. In addition to that it can be treated in such a manner that it attempts to take a different shape upon being cooled to the martensitic phase. The deformation may amount to several per cent. The term shape memory metal used herein is understood to mean the above-described bidirectional shape memory metal.
If the deformation is prevented or opposed by external means, high stresses will develop in the material, so that large forces can be exerted by the material. The stress that is developed is greatest in the austenitic phase, since the material has the highest modulus of elasticity in that phase.
By manufacturing the clamping members from shape memory metal it becomes possible to have a clamping member engage the elongated portion of the first part of the device at any random location, whereby the clamping member blocks relative movement of the first and the second part of the device in either direction.
In one preferred embodiment the elongated portion is substantially bar-shaped, and the clamping member is substantially ring-shaped, with said elongated portion being clampingly or releasingly surrounded by said clamping member. The ring-shaped clamping member thereby comprises an opening, through which the bar-shaped elongated portion, which is for example configured as a round pin, extends. Said opening has a particular dimension which depends on the temperature of the shape memory metal from which the ring is made, when the dimension is small, the bar-shaped portion is clamped down, and when the dimension is large, the ring encloses the bar-shaped portion with some play.
Preferably the first clamping member has its releasing shape at a particular temperature, namely the body temperature, whilst the second clamping member has its clamping shape at that temperature. As a result of that there will always be eon clamping member to perform its clamping action during the period that the device is present in the body, without being energized to do so.
The shape memory metal of each of the clamping members may be trained in such a manner that when the temperature rises above body temperature, the first clamping member whilst change from a releasing shape into a clamping shape, whilst the second clamping member will change from a clamping shape into a releasing shape. Both clamping members may thereby be provided with a heating element, which may be selectively energized.
In another preferred embodiment the clamping shape of the first clamping member is obtained by heating said member from the body temperature to a higher temperature, whilst the releasing shape of the second clamping member is obtained by cooling said clamping member from the body temperature to a lower temperature. The clamping action of a clamping member always takes place in the austenitic phase thereby, in which phase the shape memoy metal has a high modulus of elasticity. The heating of the shape memory metal from the body temperature to a higher temperature may take place in various manners. In one preferred embodiment said heating takes place by passing electric current through the metal.
In another preferred embodiment said heating takes place by means of a resistance foil, which completely or partially envelopes the shape memory metal. Said resistance foil generates heat when electric current is passed therethrough. The foil may be provided with an insulating layer on the outside, so that the generated heat can only escape to a limited extent, and consequently slowly, to the tissue present outside the resist
Aalsma Arthur Martinus Michael
Grootenboer Hendricus Johannes
Hekman Edsko Evert Geert
Stapert Jouwert Wilhelm Jacobus Lucas
Dorsey & Whitney LLP
Philogene Pedro
Universiteit Twente and Technologiestichting STW
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