Patent Publication Number: US-2009218321-A1

Title: Shape Memory Implant Heating Device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to devices for heating shape memory transformable surgical clamps used in implanted surgical applications. More particularly, the present invention relates to a device for heating nickel/titanium alloy shape memory implant clamps, which includes a cordless, portable, variable power source. 
     2. Description of Related Art 
     Heating or cooling shape memory transformable surgical clamps are initially supplied in an open configuration at ambient temperature. After surgical placement, a quantity of heat is then provided to close the clamp and thus provide tissue support. In other configurations, the clamp can be transformed back to its original shape by cooling. Hence, the surgical implant can be made to release its fixation to the tissue. Various configurations of implants are available. In practice, surgical constraints require these surgical devices (or implants) to be manufactured to extremely restrictive specifications. 
     In the surgical context, it is desired that a heating or cooling device to be able to transform many different types of clamps, whether they be mono-cortical or bicortical, bipode or quadripode clamps, and irrespective of their cross sectional shape or size, or the amount of shape memory metal used in their design. Many prior art designs are limited in the variety of clamps they can transform. It is also desired that a heating or cooling device include a reliable and effective safety system to prevent accidental bone necroses due to excessive heating or cooling applied by the device. Many prior art devices fail to include reliable safety systems. A common problem with the heating devices used to transform shape memory alloy implants is the inability to see the implant transform. The legs of these implants are imbedded in bone or tissue and in some cases do not move when transformed, but rather begin to exert forces on the tissue. Many prior art devices are not capable of determining when enough energy has been transferred to the implant so it transforms completely but does not get so hot as to damage the surrounding tissue. 
     While devices are available that can provide the heating required to transform the implants in a surgical setting, it has become evident that in some surgical settings, surgeons need a cordless device, that is less constraining than the presently available AC wall current powered devices. Similarly, it is sometimes necessary to have multiple heating devices or heating device having various sizes of power sources available at a particular surgical institution. These systems must be ready for multiple emergency surgeries with little prior notice. For example, at large trauma centers, or at military evacuation hospitals, many simultaneous trauma cases may be presented after long periods of little or no trauma activity. Hence, there is a need for inexpensive presterilized heating systems that could be stored with the surgical implants to be ready at a moment&#39;s notice. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is a device for heating heat-transformable shape memory implants used in surgery applications. The device includes a case having an interior chamber and exterior surfaces. The case is configured to be hand-held by a user. The device also includes a variable electronic power supply contained within the interior chamber of the case. The variable electronic power supply includes a predetermined size and quantity of batteries. The variable electronic power supply is varied by varying the predetermined size and quantity of batteries according to the characteristics of the shape memory implants. The device further includes conductive electrodes extending from the case. The conductive electrodes are electrically joined with the electronic power supply in the interior chamber of the case via an electrical connection to form a power circuit. A user activated switch is joined with the electronic power supply. The user activated switch is accessible from one of the exterior surfaces of the case and is configured to activate and deactivate the power circuit. 
     Another aspect of the invention is a system for heating a heat-transformable. shape memory surgical device. The system includes a sealed, sterilizable housing, which is configured to be hand-held by a user, a thermal probe for heating the shape memory surgical device, the thermal probe being connected with the housing, a variable electronic power supply contained within the housing, the variable electronic power supply including a predetermined size and quantity of batteries, wherein the variable electronic power supply is varied by varying the predetermined size and quantity of batteries according to the characteristics of the shape memory surgical device, and a printed circuit board positioned within the housing. The printed circuit board includes a system controller having a power circuit for controlling the receipt and distribution of heating power from the variable electronic power supply to the thermal probe, a feedback circuit for measuring a condition of the shape memory surgical device via the thermal probe, and a control circuit for receiving data from the feedback circuit and adjustably controlling an amount of heating power that the power circuit distributes to the thermal probe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       For the purpose of illustrating the invention, the drawings show a form of the invention that is presently preferred. However it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: 
         FIG. 1  is a transparent isometric side view of a device according to one embodiment of the present invention; 
         FIG. 2  is a partial side-section view of one embodiment according to the present invention; 
         FIG. 3  is side sectional view of a handheld battery-powered device according to one embodiment of the present invention; 
         FIG. 4  is an enlarged partial view of an electrode tip according to one embodiment of the present invention; and 
         FIG. 5  is an enlarged partial view of an electrode tip according to one embodiment of the present invention 
     
    
    
     DETAILED DESCRIPTION  
     Referring now to the drawings in which like reference numerals indicate like parts, and in particular, to  FIG. 1 , one aspect of the present invention is a device  20  for heating heat-transformable shape memory implants (not shown) used in surgery applications. In one embodiment, device  20  includes a case  22  that contains a variable electronic power supply  24  that is joined with conductive electrodes  26  and controlled by a user activated switch  28 . In use, electrical current is generally supplied automatically when contact is made between conductive electrodes  26  and the shape memory implant. 
     Case  22  includes an interior chamber  30  and exterior surfaces  32 . Case  22  is generally configured to be hand-held by a user and typically fabricated from materials, e.g., metals and plastics, etc., that can be sterilized by a variety of means, e.g., bulk processes such as ethylene oxide gas or gamma ray ionization. 
     Variable electronic power supply  24  is contained within interior chamber  30  of case  22 . Variable electronic power supply  24  includes a predetermined size and quantity of batteries  34 . The strength or maximum amount of power available from variable electronic power supply  24  is varied or adjusted by varying the predetermined size and quantity of batteries  34  according to the characteristics of the shape memory implants, e.g., in accordance with the amount of power required to transform a particular shape memory implant. To minimize the possibility of tissue necrosis, the adjustment of variable electronic power supply  24  is configured so that the amount of heat delivered to a given shape memory implant cannot cause the temperature of the implant to exceed a maximum value, e.g., 55° C. 
     Conductive electrodes  26  extend from case  22  and are electrically joined with variable electronic power supply  24  in interior chamber  30  of case  22  via an electrical connection  36  to form a power circuit  38 . Conductive electrodes  26  include a tip  40 , which can be formed from a conductive material to supply the shape memory implant (not shown) with electrical current through which it is heated due to the electrical resistance of its material. Electrical or thermal conductivity between tip  40  and the shape memory implants may be improved by using a more conductive material, or plating with a more conductive material. Tips  40  can be fashioned of a conductive material with ends that have sharp ridges to provide a non-slip contact between the implant and the tip or the tip can be saddle-shaped to help prevent the tips from slipping on the surface of the implant. In one embodiment, the conductive material is one of gold, aluminum, silver, and a combination thereof. In another embodiment, tip  40  is formed from a resistive material to supply the shape memory implant (not shown) with electrical current through which it is heated due to the electrical resistance of its material. The resistive material can be one of carbon, graphite, and a combination thereof. In another embodiment, conductive electrodes  26  can be spanned by a resistive wire or ribbon  42  through which electric current is passed. When resistive wire  42  is brought into contact with a shape memory implant and the user activates the current, the shape memory implant is heated by conduction with the resistive wire or ribbon. 
     User activated switch  28 , which is generally positioned so as to be accessible from one of exterior surfaces  32  of case  22 , is joined with variable electronic power supply  24 . User activated switch  28  is typically configured to activate and deactivate power circuit  38 . 
     Referring now to  FIG. 2 , in another embodiment conductive electrodes  26  can be conductive tubular electrodes  44 . Each of conductive tubular electrodes  44  has a tubular body  46 , an internal compression spring  48  positioned within the tubular body, and conductive tips  50 . Conductive tips  50  can be rod-shaped and are configured to slide within tubular body  46 . Tubular body  46  can be molded into case  22  of device  20  by an insulating material (not shown). Internal compression springs  48  can be inserted between conductive tips  50  and tubular body  46 , within the tubes to provide a certain amount of give or flexibility between the tips and body of device  20 . Without flexibility, a user would be required to hold device  20  perfectly still, with no up or down or angular motion while current was being applied to the implant. Internal compression spring  48  is retained at least partially within tubular body  46  by crimps (not shown) in the tubular body. Conductive tips  50  can include roughened conductive pads  52  and generally are configured so as to move independently of one another. Each of conductive tips  50  is typically retained at least partially within tubular body  46  by crimps (not shown) in the tubular body. With this tip design, device  20  does not have to be held in perfect alignment with the implant to insure contact between conductive tips  50  and an implant surface. 
     Referring now to  FIG. 3 , another aspect of the present invention is a system  60  for heating a heat-transformable shape memory surgical device (not shown). In one embodiment, system  60  is contained in a sealed, sterilizable handheld housing  62 . System  60  includes a printed circuit board  64  including a system controller  66 , both of which are contained in housing  62 . System controller  66  is connected with a thermal probe  68 , which extends from housing  62 , for heating the shape memory surgical device. A variable electronic power supply  69 , which is contained within housing  62 , provides power for heating the shape memory surgical device. 
     Housing  62  is generally sealed such that it is sterilizable and can withstand the conditions of an autoclave without damaging any of its internal components such as system controller  66 . The components of system  60  generally form a handheld device in the form of housing  62 . 
     Thermal probe  68 , which is used to heat the shape memory surgical device, is connected with housing  62  via printed circuit board  64  and extends from an end  70  of the housing. Referring now to  FIG. 4 , in one embodiment, thermal probe  68  is formed from a pair of electrodes  72 , which are used to apply an electric current to the shape memory surgical device. Electrodes  72  cause the shape memory surgical device to be heated by its resistance to electric current, rather than by heat conduction or radiation. As described in greater detail below, thermal probe  68  may also be defined by thermal contacts other than conventional electrodes such as electrodes  72 . 
     A current sensing wire  74  may be joined with each of electrodes  72  to measure the current flow between a tip  76  of each electrode and the shape memory surgical device. Electrodes  72  may be formed from conductive materials such as gold, aluminum, silver, or a combination thereof. Alternatively, electrodes  72  may be formed from resistive materials such as carbon, graphite, or a combination thereof. 
     In one embodiment, as illustrated in  FIG. 4 , electrodes  72  formed from two graphite rods  78 , both of which are covered by an insulating material  80 , may be placed in close contact to each other. Current sensing wires  74  are attached to each of rods  78 . Current sensing wires  74  are insulated from each other and graphite rods  78  except at their point of contact with rods adjacent each tip  82 . Current sensing wires  74  are used to measure the current flow close tips  82 . Electrodes  72  may be formed into a cylindrical shape using an insulation  84  to facilitate placement into a surgical site. 
     Referring now to  FIG. 5 , in one embodiment, a resistive wire or ribbon  85  may be joined with and extend between electrodes  72 . A current is passed through wire or ribbon  85 . Wire or ribbon  85 , rather than electrodes  72 , is brought into contact with the shape memory surgical device to heat the device. 
     Referring again to  FIG. 3 , printed circuit board  64  is typically positioned within housing  62  to ensure it is protected during sterilization. Printed circuit board  64  includes system controller  66 , which is generally defined by a power circuit (not shown) for controlling the receipt and distribution of heating power to each thermal probe  68 , a feedback circuit (not shown) for measuring a condition of the shape memory surgical device via the thermal probe, and a control circuit (not shown) for receiving data from the feedback circuit and adjustably controlling an amount of heating power that the power circuit distributes to the thermal probe. If thermal probe  68  includes electrodes  72 , system controller  66  will control the flow of electrical current to the electrodes. 
     The control circuit typically includes an automatic-cutout circuit (not shown) for terminating the distribution of heating power to thermal probe  68  after a specific amount of time or upon the occurrence of a predetermined condition. System  60  may also incorporate one or more digital microprocessors (not shown) for determining a proper temperature and time to heat the shape memory surgical device so that the temperature generated in the shape memory surgical device does not exceed a predetermined maximum value. The one or more digital microprocessors are in cooperation with the control circuit. The shape memory surgical devices are typically designed to be shape transformed at specific temperatures, usually between 45 and 50 degrees Celsius. The control circuit ensures that system  60  heats the shape memory surgical devices to a temperature slightly higher than that needed for shape transformation, but no more. A temperature limit allows the implant to be shape transformed, but not induce tissue necrosis from over heating. 
     System  60  includes variable electronic power supply  69  for supplying heating power to the power circuit and system in general. Variable electronic power supply  69  typically includes a predetermined size and quantity of batteries  86  contained within housing  62 . Variable electronic power supply  69  can be adjusted or varied by varying the predetermined size and quantity of batteries  86  according to the characteristics of the shape memory surgical device. In one embodiment, system  60  is configured to include sensors (not shown) or another mechanism for supplying heating power automatically when thermal probe  68  is brought into contact with the shape memory surgical device. 
     System  60  may include manual switches such as a momentary switch  90  and a multi-position switch  92 , which are positioned on housing  62 . Momentary switch  90  allows a user to manually activate the system. Multi-position switch  92  allows a user to manually set the amount of time or the amount of current to be delivered to the shape memory surgical device. Visual and audible signaling features such as an LED  94 , piezo beeper  96 , and a digital or analog readout  98  alert a user when a certain condition has occurred, e.g., the desired temperature of the shape memory surgical device was achieved, a predetermined amount of operation time elapsed, the device moved to a desired shape, or a predetermined amount of current passed through the device. 
     Prior to use of system  60 , the appropriate size and number of batteries  86  are selected according to the size and material of the shape memory surgical device to be transformed. In use, system  60  is operated by first selecting a position of multi-position switch  92  appropriate for the size of the shape memory surgical device to be transformed. Moving multi-position switch  92  to one of several shape memory surgical device size positions illuminates LED  94 . LED  94  indicates power is available to the unit. 
     Next, tip  76  of thermal probe  68  is placed in contact with one side of the shape memory surgical device. When electrodes  72  are placed in contact with the shape memory surgical device, current sensing wires  74  sense the completion of the circuit. Upon completion of the conductivity circuit, a user presses momentary switch  90  and current is supplied to electrodes  72  for a number of seconds until an audible signal from piezo beeper  96  is heard. At this time, LED  94  changes color indicating that both contact is being made with the shape memory surgical device and the power circuit is delivering a specific current to tip  76 . LED  94  changes back to its original color at the end of the heating sequence. Current sensing wires  74  are provided to more precisely measure the current at each of tips  76 . After a specific amount of time has passed, the power circuit stops delivering current. 
     The shape memory implants are designed to be shape transformed at specific temperatures, usually between 45° C. and 50° C. This heating device describe here will be used to heat the implants to a temperature slightly higher than that needed for shape transformation. Device  20  will limit the current, and hence the temperature of the shape memory implants, via the inherent current limit that a specific choice of battery can deliver. The current supplied will allow the implant to be heated to be shape transformed, but not induce tissue necrosis from over heating. The use of an electrode tip design in device  20  will cause the implant to be heated by its resistance to electric current, rather than by heat conduction or radiation. In use, a surgeon would observe the implant as it is heated by device  20  and transforms its shape. A careful choice of battery capacity for each implant size would be used to keep the heating device from generating too great a temperature. While this scheme is less sophisticated than that of providing the device with a timer, or other control circuit, it is the simplest and least expensive embodiment, thus satisfying the need for a low cost device that can be provided to the surgeon presterilized for single patient use. 
     Although the invention has been described and illustrated with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention. Accordingly, other embodiments are within the scope of the following claims.