Tissue distractor
First Claim
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1. A mechanism for powering an auto-extensible tissue distractor comprising:
- an elongate member having a proximal end, a distal end, and a longitudinal axis;
at least one movable device movably mounted on the elongate member for movement therealong in a direction away from the proximal end towards the distal end, said movable device comprising;
a first crawler portion operatively engaged with the elongate member and having a first non-return means for preventing movement of the first crawler portion at least in a direction towards the proximal end;
a second crawler portion operatively engaged with the elongate member and disposed nearer the distal end than the first crawler portion, the second crawler portion having a second non-return means for preventing movement of the second crawler portion at least in a direction towards the proximal end;
piezoelectric drive means adapted to undergo elongation by a discrete incremental amount in an elongation direction upon application of a selected voltage potential thereto and at a rate of elongation dependent upon the rate of increase of the voltage applied thereto, the piezoelectric drive means being operatively mounted between the first and second crawler portions with its elongation direction aligned substantially parallel to the longitudinal axis of the elongate member so that, upon applying the selected voltage potential thereto at a predetermined rate of increase of applied voltage with the first non-return means preventing the first crawler portion from moving in a direction towards the proximal end of the elongate member and with the second non-return means permitting movement of the second crawler portion towards the distal end, the piezoelectric drive means undergoes elongation and the second crawler portion is caused to move at a predetermined rate of elongation a distance corresponding to the incremental amount towards the distal end, and so that, upon removal of the selected voltage from the piezoelectric means with the second non-return means preventing the second crawler portion from moving towards the proximal end and with the first non-return means permitting the first crawler portion to move towards the distal end, the piezoelectric drive means reverts to its original length and thereby moves the first crawler portion a distance along the elongate member towards the distal end corresponding to the incremental amount;
voltage generating means for applying a voltage potential to the piezoelectric means; and
control means for repeatedly applying the selected voltage potential at the predetermined rate of increase of applied voltage to the piezoelectric means to cause the movable device to move in incremental steps along the elongate member in a controlled manner.
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Abstract
A mechanism for powering an auto-extensible tissue distractor, e.g. a bone fixator, is described in which a movable device is caused to move in small incremental steps of a few μm each along an elongate member towards its distal end under the influence of one or more piezoelectric actuators.
136 Citations
29 Claims
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1. A mechanism for powering an auto-extensible tissue distractor comprising:
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an elongate member having a proximal end, a distal end, and a longitudinal axis;
at least one movable device movably mounted on the elongate member for movement therealong in a direction away from the proximal end towards the distal end, said movable device comprising;
a first crawler portion operatively engaged with the elongate member and having a first non-return means for preventing movement of the first crawler portion at least in a direction towards the proximal end;
a second crawler portion operatively engaged with the elongate member and disposed nearer the distal end than the first crawler portion, the second crawler portion having a second non-return means for preventing movement of the second crawler portion at least in a direction towards the proximal end;
piezoelectric drive means adapted to undergo elongation by a discrete incremental amount in an elongation direction upon application of a selected voltage potential thereto and at a rate of elongation dependent upon the rate of increase of the voltage applied thereto, the piezoelectric drive means being operatively mounted between the first and second crawler portions with its elongation direction aligned substantially parallel to the longitudinal axis of the elongate member so that, upon applying the selected voltage potential thereto at a predetermined rate of increase of applied voltage with the first non-return means preventing the first crawler portion from moving in a direction towards the proximal end of the elongate member and with the second non-return means permitting movement of the second crawler portion towards the distal end, the piezoelectric drive means undergoes elongation and the second crawler portion is caused to move at a predetermined rate of elongation a distance corresponding to the incremental amount towards the distal end, and so that, upon removal of the selected voltage from the piezoelectric means with the second non-return means preventing the second crawler portion from moving towards the proximal end and with the first non-return means permitting the first crawler portion to move towards the distal end, the piezoelectric drive means reverts to its original length and thereby moves the first crawler portion a distance along the elongate member towards the distal end corresponding to the incremental amount;
voltage generating means for applying a voltage potential to the piezoelectric means; and
control means for repeatedly applying the selected voltage potential at the predetermined rate of increase of applied voltage to the piezoelectric means to cause the movable device to move in incremental steps along the elongate member in a controlled manner. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
(i) the rate of increase of d.c. voltage potential with time applied to the piezoelectric drive means thereby to determine the rate of extension thereof;
(ii) a functional relationship involving the rate of increase of the d.c. voltage potential applied to the piezoelectric drive means and also the load sensed by the load cell;
(iii) the maximum d.c. voltage potential to be applied to the piezoelectric drive means thereby to determine the size of each said incremental step;
(iv) the maximum load sensed by the load sensor permitted to be applied by or to the piezoelectric drive means thereby to determine the load imposed on the bone callus and associated soft tissue;
(iv) the maximum time period during which the movable device is permitted to move thereby to determine the maximum distance through which the movable device is permitted to move along the elongate member;
(v) the maximum distance through which the movable device is permitted to move along the elongate member.
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26. A mechanism according to claim 1, in which the incremental steps range from about 5 μ
- m to about 120 μ
m.
- m to about 120 μ
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27. A mechanism according to claim 26, in which the incremental steps range from about 40 μ
- m to about 80 μ
m.
- m to about 80 μ
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28. A mechanism according to claim 1, in which the control means is arranged to cause the movable device to move along the movable member at a rate of about 1 mm per day.
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29. An auto-extensible tissue distractor fitted with a mechanism according to claim 1.
Specification