System and method for force, displacement, and rate control of shaped memory material implants

Abstract

An energy delivery device controls the transformation of the microstructure of shape memory material. A surgeon can use the energy delivery device to control the rate of implant shape change, the extent of implant shape change, as well as the force exerted on the surrounding tissue. The energy delivery device allows for the fine control of force when fixating osteoporotic bone and rate of bone transport when working near the spinal cord. The energy delivery device models or measures the heating profile of the implant and provides the surgeon a method to control the extent of microstructure phase transformation so that the rate, force or extent of implant shape change can be controlled individually or together. The invention is an implant controlled with an energy delivery device that transforms the microstructure of a shape memory material through heat generation in the implant. The implant is manufactured so that the energy delivery device achieves an implant temperature that controls the conversion of the microstructure for one of a plurality of members.

Description

FEDERALLY SPONSORED RESEARCH [0001] Not applicable FIELD OF THE INVENTION [0002] The present invention relates to instrumentation and a method of controlling in vivo shape changes in devices formed from memory materials that change shape when heated. In particular, the present invention relates to surgical instrumentation, used to control the rate of shape change and forces imparted to the surrounding tissue by memory material implants during medical use. BACKGROUND-DISCUSSION OF THE PRIOR ART [0003] Shape memory alloys such as nitinol have been well known since their development by Buehler and Wiley (U.S. Pat. No. 3,174,851) in 1965. Other metals, such as AuCd, FePt3, beta Brass and InTI, exhibit shape memory behavior. These materials have the property of changing shape in response to a change in material temperature. This shape change potential is imparted into the memory metal device through a series of heat treatments. [0004] The transition temperature range is imparted to the m...

AI Technical Summary

Problems solved by technology

These heat-initiated changes cause gross changes in the shape of the implant formed from the memory metal.

The prior art associated with resistive heating of memory alloys have not recognized the need for the control of the rate of shape change and magnitude of forces applied by the implant to the surrounding tissue.

In this case, there was no force control of the implant due to the body temperature transition point of the metal, which resulted in the implant applying the maximum potential force to the surrounding tissue.

The prior art is at a significant disadvantage to the subject invention in the field of orthopaedics due to the lack of a method and system to control the rate and maximum shape change force exerted on the surrounding tissue.

Though these methods and devices control thermal injury to tissue and extent of shape change they are significantly limited in musculoskeletal applications.

This implant heating strategy results in a predetermined degree of shape change but no control of its force or rate of shape change.

This strategy significantly limits implant design because in many musculoskeletal uses solid stable bone structures may not allow the implant to change shape only to provide compressive forces.

Thus the heating device of Krumme can not control either rate of shape change or force exerted on the surrounding tissue.

Because the implant is fully activated, the heating device of Alfidi can not control the force exerted on the surrounding tissue.

Thus the implant sizes that can be heated through their transition temperature is limited.

Furthermore the inability to control heat energy delivery time teaches away from controlling the rate of memory-metal-implant shape changes so as to protect vital structures.

This instrument limits the use of the shape memory implant.

Furthermore, many uses would not be realized due to the bulk and functional requirements of the instrument needed to control the closing force and rate of the implant.

Flot provides “predetermined quantities of heat, each corresponding to a given size of clamp” but does not provide a plurality of heat energies to a single style clamp to control the force applied to bone or its rate of closure.

These limitations of the prior art have caused memory metals to be limited in use in orthopaedics.

Memory alloy implants have found use as simple two and four leg staples but have not reached the potential of implants that can be manipulated with precise control to change their shape and move bony structures.

The lack of surgeon control of forces applied to bone is of significant concern in osteoporotic bone and thus with implants and heat energy sources described in the prior art.

Furthermore the quick shape changing movement of implant and bony structures described under the prior art could pinch and injury the spinal cord.

This inability to adjust the implants' shape-changing response within the martensitic to austenitic transformation temperature range to control its force and closure rate has discouraged the clinical use of these systems.

In osteoporotic bone an implant that closes with too much force may create fracture.

In displaced fractures of healthy bone, implant forces exerted by its shape change may be too low to pull the fracture line closed.

The lack of control, of the peak and residual forces by the inventions of the prior art, has significantly impeded the adoption of musculoskeletal implants that changed shape.

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