Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2002-03-15
2004-03-16
Milano, Michael J. (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S058000
Reexamination Certificate
active
06706042
ABSTRACT:
This invention relates to tissue distractors, more particularly to a mechanism for powering an auto-extensible tissue distractor, such as a bone fixator.
Since the turn of the last century when Ilizarov discovered that new bone and soft tissue is regenerated under the effect of slow and gradual distraction, external fixation has been utilised in the treatment of various bone conditions. Limb length differences resulting from congenital, developmental, post-traumatic or post-surgical causes may be treated in this manner. The procedure also lends itself to the treatment of congenital deformities, post-traumatic bone deformities, non-healing fractures and bone loss from tumour, trauma or infection.
Traditionally an external bone fixator has been used which comprises a framework of metal rings connected by rods, whereby each ring is connected to the bone by a plurality of wires under tension or by pins. Titanium pins may be used to support the bone. Presently, a wide variety of designs of fixator are available and are suitable for withstanding the forces imposed by the full weight of the patient.
In surgical limb lengthening, the bone is subjected to osteotomy so as to sever it into two or more parts before the fixator is attached to the severed parts of the bone. In the course of the operation the surgeon will attach at least one pair of pins to each of the severed parts of the bone and then join the pins externally of the patient's limb by means of a rod or rods. Generally there is at least one rod on each side of the limb. Just a few days after surgery the patient is encouraged to resume normal use of the limb in order to maintain joint flexibility and to facilitate muscle growth to match the osteogenesis.
Approximately one week after the surgery to fit the fixator, manual adjustments are commenced in order to lengthen the rods equally so as to separate the severed ends of the bone at a rate of about 1 mm per day. An increase of more than about 1 mm per day results in a slowing of the osteogenesis and an increase of less than about 1 mm per day can result in premature consolidation.
In surgical limb straightening the bone can be severed completely or partially. If the bone is completely severed, then the rod or rods on one side of the limb may be lengthened at a greater rate than the rod or rods on the other side thereof. Alternatively the bone can be partially severed according to a technique known as open wedge osteotomy, in which case a bone fixator may be needed only on the side of the bone in which the cut has been made by the surgeon.
It has further been found that osteogenesis proceeds more satisfactorily if frequent small adjustments in bone length are made by distraction rather than larger less frequent adjustments of bone length. Hence adjustments of about 0.25 mm every 6 hours are recommended. This places a burden upon the patient and carer to conform to a routine which can be very disruptive to day to day life.
It is very common for patients to experience a great deal of pain each time that the fixator is incrementally lengthened. This can make the four times daily lengthening procedure a traumatic experience both for the patient and for the patient's carer, particularly if the patient is a young child. Since the entire bone lengthening or straightening process can last from three to six months this can impose a continuing great strain not only on the patient but also on those caring for the patient. Moreover this procedure tends to lead to very high complication rates so that it is not uncommon for the complication rate to be as high as about 200% which means that each patient on average experiences at least two incidents during a course of bone lengthening or straightening treatment requiring a return to hospital, possibly for further surgery.
Another problem with external bone fixators is that there is a significant risk of infection arising at the site of each pin or wire.
It has been proposed to utilise gradual motorised distraction in which a typical procedure could involve applying a very small incremental lengthening over 1000 times per day which still achieves an average bone lengthening rate of about 1 mm per day.
It would be desirable to provide an auto-extensible tissue distractor, such as a bone fixator, which can effect substantially continuous distraction of bone or other living tissue throughout the day, even while the patient is asleep, thereby avoiding for the patient the pain associated with a several times daily incremental lengthening of the bone or other tissue. It would also be desirable to provide a bone fixator of sufficiently compact size to enable its use as an internal bone fixator, either attached surgically to the outside of the patient's bone or even to the inside the patient's bone, whereby the fixator can remain in situ after the bone lengthening or straightening process has been completed. It would be further desirable to provide a bone fixator which effects continuous bone distraction and which is suitable for external use or for implantation within or adjacent the bone to be lengthened.
The present invention accordingly seeks to provide a mechanism for use with a tissue distractor which enables tissue distraction to be effected substantially continuously throughout the day and night during the entire tissue distraction process. It further seeks to provide a mechanism for powering an auto-extensible bone fixator. It also seeks to provide such a mechanism which can be used with an external fixator. Another objective of the invention is to provide a mechanism for powering an auto-extensible internal tissue distractor. In addition the invention seeks to provide an auto-extensible bone fixator which avoids for the patient the pain associated with a four times daily incremental lengthening of about 0.25 mm by effecting substantially continuous bone distraction throughout the patient's waking hours (and possibly also during the patient's sleeping hours). A further objective of the invention is to provide a mechanism for powering a tissue distractor, such as a bone fixator, so as to cause it to extend in a series of very small increments so as to avoid, for a patient fitted with the tissue distractor, the experience of pain associated due to the extension of the tissue distractor. Yet another objective of the invention is to provide a compact bone fixator which can be used as an internal bone fixator, for example by being attached surgically to the outside of the patient's bone or by being implanted inside the patient's bone. In addition the invention seeks to provide a compact design of bone fixator which effects substantially continuous bone distraction and which is suitable for external use or for implantation within or adjacent a bone to be surgically lengthened or straightened. An additional objective is to provide an auto-extensible mechanism for a bone fixator which can automatically lengthen at an essentially continuous and controllable rate while measuring both the rate of lengthening and also the load being imposed on the bone being lengthened and its associated soft tissue.
According to the present invention there is provided 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
Baxter Jessica R
Finsbury (Development) Limited
Greer Burns & Crain Ltd.
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