Patent Document

PRIORITY INFORMATION  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 10/600,368 filed Jun. 23, 2003, which, in turn, claims the benefit of U.S. Provisional Application Ser. No. 60/391,887, filed Jun. 27, 2002. The contents of both are hereby incorporated by reference herein in their entirety. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     The present invention relates to the field of suture removal. More particularly, the present invention provides a method, instrument, and kit for thermally cutting a suture which minimizes the tension placed on the suture during removal, thereby reducing pain, bleeding and tissue disruption.  
       BACKGROUND OF THE INVENTION  
       [0003]     Suture removal is an important part of wound repair in medicine. Internal sutures are absorbable so they are essentially “removed” by the body. External sutures or sutures on the surface of the body are nonabsorbable. Nonabsorbable sutures are advantageous, because they have a higher tensile strength than absorbable sutures. As such, they are the preferred suture for closure of external wounds. However, they carry with them the additional task of requiring manual suture removal.  
         [0004]     The removal of sutures is problematic for many doctors. Current suture removal techniques utilize standard instruments to manipulate and cut a stitch. This technique requires considerable tension on, and manipulation of, the stitch. The resulting pain, bleeding, and tissue disruption are uncomfortable and anxiety provoking for the patient and compromise the cosmesis of the wound repair. Lastly, the technique is time consuming for the physician.  
         [0005]     Current manual suture removal techniques rely on two methods. The first technique utilizes a suture removal kit containing a pair of forceps, scissors, and gauze pad. This technique consists of grasping the knot of the suture with the forceps and lifting the stitch enough to slip the scissors under the suture. The scissors then cut the stitch, which is then pulled out of the skin with the forceps. Unfortunately, the scissors generally have a blunt end, making it difficult to raise the stitch sufficiently off the skin to slip the distal tip of the scissors under the stitch. Additionally, the action of bringing the scissors blades together to cut the stitch creates significant tension on the suture. The gauze, included in the suture removal kit, is most aptly used to wipe away the blood which results from the manipulation necessary to remove the suture. The second current method for suture removal replaces the scissors with a thin knife but requires the same manipulation and results in similar tissue disruption and bleeding.  
         [0006]     It is accordingly an object of this invention to provide a method, instrument, and kit for suture removal which produces less tension in the suture than current methods.  
         [0007]     It is accordingly a further object of this invention to provide a method, instrument, and kit for suture removal which minimizes pain, bleeding and tissue disruption.  
         [0008]     It is a further object of this invention to provide a method, instrument, and kit for suture removal which allows sutures to be removed in less time than currently available methods and devices.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides a method, instrument, and kit for applying heat to the loop portion of a suture used to close a wound so as to melt the suture material, causing the loop to rupture. The cutting method disclosed and associated instrument allow the suture to be separated while producing less tension in the suture than current methods, thereby minimizing patient discomfort, tissue disruption and bleeding.  
         [0010]     In a preferred method of the instant invention; a resistive heating element is brought into contact with the loop of a suture used to close a wound. The heating element is placed under the suture loop (or stitch), preferably between the patient&#39;s skin and a knotted portion of the suture. Power is supplied to the heating element for a brief time, during which the element heats and melts the suture in contact therewith, causing the loop to rupture. Thereafter the suture is removed in the usual manner, i.e., using forceps or the like to extract the remaining suture material.  
         [0011]     Accordingly, the present invention provides a suture removal instrument comprising: 
        (a) an elongated body having a proximal handle portion and insulated distal portion;     (b) a first conductive member extending from the insulated distal portion of the elongated body, terminating in a wedge-shaped tip;     (c) a resistive heating element extending alongside the first conductive member and affixed at its distal end to the wedge-shaped tip;     (d) conduction means for supplying power to the heating element;     (e) activation means for controlling the supply of power to the heating element; and     (f) circuitry for providing power to the heating element as pulses of high current having a predetermined duration.        
 
         [0018]     The elongated body may serve as a handle for the operator to grasp and/or as a housing for the operating components, such as the power source, circuitry, conduction means and activation means. The elongated body may be formed from any suitable medical-grade material, such as plastic, metal, polycarbonate, polyvinyl chloride, and the like.  
         [0019]     The conductive member is shaped to facilitate insertion thereof into a suture loop. The tapered, wedge-shaped tip allows it to gently slide under the loop of the suture, between the patient&#39;s skin and a knotted portion of said suture. For example, the tapered tip may comprise a conical point. Alternatively, the tip may include one or more beveled surfaces which form a more or less wedge-shaped distal end.  
         [0020]     The resistive heating element is preferably a thin filament, formed from a material such as nichrome, tungsten, nickel, stainless steel or the like. The heating element preferably joins the tapered, wedge-shaped tip of the conductive member to form an acute angle with the adjacent surface of the tapered tip ranging from about 5 to about 40 degrees.  
         [0021]     The power source required to heat the resistive heating element may be carried by the suture removal instrument itself. For example, in a preferred embodiment, the power source comprises one or more batteries, for example, rechargeable batteries, contained within the elongated body. Alternatively, the elongated body may be fitted with a standard power cord and connector adapted for use with a conventional wall outlet.  
         [0022]     The circuitry ensures the heating of a heating element to a predetermined temperature suitable for thermally rupturing suture materials when the heating element resistance and source voltage fall within predetermined ranges. The circuit may be a timer circuit which connects power from the source to the heating element for a predetermined period of time. In a preferred embodiment the circuit supplies a predetermined amount of electrical energy to the heating element such that the element reaches a predetermined temperature, the circuit having a means for modifying its output based on the resistance of the element so as to achieve the predetermined energy value. In a preferred embodiment, the circuitry also has a timing means which prevents a second activation until a predetermined time has elapsed following a first activation so as to prevent heating of the conductive member distal tip to temperatures which could burn a patient.  
         [0023]     The conduction means for supplying power (typically electrical power) to the heating element may take any suitable form. Examples of suitable conduction means include, but are not limited to, wires, conductive structural components, electrodeposited metal coatings and the like.  
         [0024]     The activation means for controlling the supply of power to the heating element may take any suitable form. Examples of a suitable activation means include, but are not limited to, an actuator button, an on/off switch, and a foot pedal.  
         [0025]     The suture removal instrument optionally includes a second conductive member placed between the insulated portion of the elongated body and the resistive heating element. The second conductive member preferably extends from the insulated distal portion of the elongated body and is disposed next to the first conductive member in a parallel fashion. In operation, the conductive members are connected to the circuitry output so as to supply power to the heating element when the circuitry is activated. The conductive members do not heat up because they have a much larger cross-sectional area than the resistive heating element.  
         [0026]     In a particularly preferred embodiment, the suture removal instrument comprises an elongated body forming a handle, and a demountable distal tip assembly. The handle portion contains a power source, circuitry and an activation button. The distal end of the handle portion has a mounting means and conduction means for removably mounting the distal tip assembly to the handle portion. The distal tip assembly has an elongated insulated portion. First and second conductive members protrude distally from the insulated portion. It is conceivable that the heating filament could be integral with the conductive members, or that a single conductive member could be used, with the proximal end of the heating filament being connected directly to conduction means contained within the insulated portion of the elongated body.  
         [0027]     In a preferred embodiment, the first conductive member is longer than the second conductive member and has a tapered distal end. Both the conductive members are preferably formed from an easily machined metallic material, such as brass or stainless steel, and should have good thermal conduction properties. Both the members have a coplanar axis with each other and with the proximal handle portion. The distal end of the second element is affixed to the tapered distal end of the first elongated member by a thin resistive heating element. The thin resistive heating element forms an acute angle of about 5 to 40 degrees with the adjacent surface of the first elongated member. The first and second conductive members are connected to the power source and the activation button by a suitable conduction means discussed above. Because the conductive members have much larger cross-sections than the thin resistive heating element, the conductive members are not heated by the current. Because the element is energized for only a short period of time, heating of the conductive members by the filament is minimal.  
         [0028]     The present invention also contemplates a number of optional features.  
         [0029]     For example, the suture removal instrument of the present invention may optionally include a removably mounted magnifier assembly, optionally including a hinged lens for magnifying the distal end of the instrument and operative field of use.  
         [0030]     The suture removal instrument may also be provided with a distally projecting light assembly for illuminating the operative field, the light assembly preferably comprising one or more of light units mounted on the side of the distal portion of the handle assembly.  
         [0031]     In addition, the suture removal instrument of the present invention may include one or more indicator lamps, for indicating battery status and activation status, for example. Examples of suitable lighting means include light emitting diodes (LEDs) and incandescent lamps.  
         [0032]     The suture removal instrument of the present invention may further be outfitted with an alarm means, preferably mounted in the instrument handle, that emits an audible signal when current is delivered to the resistive heating element in the distal tip.  
         [0033]     The present invention also contemplates the provision of a charging cradle assembly for recharging the power source that coordinates with the suture removal instrument of the present invention, particularly receiving the proximal end of the elongated handle portion thereof.  
         [0034]     Finally, the present invention provides a suture removal kit comprising: 
        (i) an elongated body comprising a proximal handle portion and distal portion configured to receive an insulated distal tip assembly, the body housing a first, rechargeable power source; a conduction means for delivering power from the first power source to a heating element; an activation means for controlling the supply of power to the heating element; and circuitry for providing power to the heating element as pulses of high current having a predetermined duration;     (ii) one or more insulated distal tip assemblies having a generally wedge-shaped distal end, comprising (i) a first conductive member terminating in a tapered distal tip and (ii) a resistive heating element extending alongside the first conductive member and affixed at its distal end to the distal end of the tapered distal tip, the tip assembly detachably mountable to the distal end of the elongated body; and     (iii) a charging cradle connectable to a second, external power source for recharging the first power source housed within the elongated body.        
 
         [0038]     In a preferred embodiment, the suture removal kit of the present invention is provided with multiple, single use distal tip assemblies.  
         [0039]     In another preferred embodiment, the first power source comprises at least one rechargeable battery, optionally a removable battery pack. The charging cradle may be configured to receive either the elongated handle itself or the battery pack separately. The cradle may further be provided with one or more indicator lights, for indicating the status of the cradle and/or the first power source.  
         [0040]     These and other objects and features of the invention will become more fully apparent when the following detailed description is read in conjunction with the accompanying figures and examples. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]      FIG. 1  is an exploded view of a suture cutter constructed in accordance with the principles of this invention.  
         [0042]      FIG. 2  is a plan view of the assembled objects of  FIG. 1 .  
         [0043]      FIG. 3  is a side elevational view of the objects of  FIG. 2 .  
         [0044]      FIG. 4  is a distal axial view of the objects of  FIG. 2 .  
         [0045]      FIG. 5  is a perspective view of the objects of  FIG. 2 .  
         [0046]      FIG. 6  is a proximal axial view of the objects of  FIG. 2 .  
         [0047]      FIG. 7  is a plan view of the distal tip assembly of  FIG. 1 .  
         [0048]      FIG. 8  is a side elevational view of the objects of  FIG. 7 .  
         [0049]      FIG. 9  is a perspective view of the objects of  FIG. 7 .  
         [0050]      FIG. 10  is a distal end view of the objects of  FIG. 7 .  
         [0051]      FIG. 11  is an expanded side elevational view of the distal portion of the objects of  FIG. 7 .  
         [0052]      FIG. 12  is an expanded perspective view of the objects of  FIG. 11 .  
         [0053]      FIG. 13  is a plan view of the objects of  FIG. 11 .  
         [0054]      FIG. 14  is an expanded perspective view of a suture cutter constructed in accordance with the principles of this invention in use cutting a suture.  
         [0055]      FIG. 15  is an expanded perspective view of the objects of  FIG. 14 .  
         [0056]      FIG. 16  is an expanded side elevational view of the distal portion of the distal tip assembly of an alternate embodiment.  
         [0057]      FIG. 17  is an expanded side elevational view of the distal portion of the distal tip assembly of another alternate embodiment.  
         [0058]      FIG. 18  is an expanded plan view of the distal portion of the distal tip assembly of an alternate embodiment.  
         [0059]      FIG. 19  is a side elevational view of the objects of  FIG. 18 .  
         [0060]      FIG. 20  is a perspective view of the objects of  FIG. 18 .  
         [0061]      FIG. 21  is an expanded plan view of the distal portion of the distal tip assembly of another alternate embodiment.  
         [0062]      FIG. 22  is a side elevational view of the objects of  FIG. 21 .  
         [0063]      FIG. 23  is a perspective view of the objects of  FIG. 21 .  
         [0064]      FIG. 24  is an expanded plan view of the distal portion of the distal tip assembly of another alternate embodiment.  
         [0065]      FIG. 25  is a side elevational view of the objects of  FIG. 24 .  
         [0066]      FIG. 26  is a perspective view of the objects of  FIG. 24 .  
         [0067]      FIG. 27  is an expanded plan view of the distal portion of an alternate embodiment of the distal tip assembly of the present invention.  
         [0068]      FIG. 28  is a side elevational view of the objects of  FIG. 27 .  
         [0069]      FIG. 29  is a perspective view of the objects of  FIG. 27 .  
         [0070]      FIG. 30  is a block diagram of circuitry for controlling power supplied to the heating element.  
         [0071]      FIG. 31  is a perspective view of a charging cradle for recharging the power source of a preferred embodiment.  
         [0072]      FIG. 32  is a perspective view of the charging cradle of  FIG. 31  in use. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0073]     In the context of the present invention, the following definitions apply:  
         [0074]     The term “suture” is used to refer both to the fine thread or other material used surgically to close a wound or join tissues and to the stitch so formed.  
         [0075]     The term “distal” refers to that end or portion which is situated farthest from the hand of the operator and closest to the body of the patient when the device is in use.  
         [0076]     The term “proximal” refers to that end or portion situated closest to the hand of the operator and farthest away from the body of the patient when the device is in use.  
         [0077]     The accompanying figures, described in detail below, illustrate aspects of the invention but are in no way intended to limit the scope of the present invention.  
         [0078]     Referring to the figures showing a suture cutter  10  constructed in accordance with the principles of this invention,  FIG. 1  depicts an exploded view of suture cutter  10 , cutter  10  having a first, proximal assembly  12  forming a handle, a second magnifier assembly  14 , and a third, distal tip assembly  16 . Handle portion  12  has a distal end  20  having a cylindrical portion  22  having a plurality of axial ribs  24  and a distal ridge  26  having a diameter slightly larger than cylindrical portion  22 . Distal end  20  has a distal-most surface  28  in which are first connector socket  30  and second connector socket  31 . Magnifier assembly  14  has a mounting ring  32  having a gap  34  and a cylindrical inner surface  36  having a diameter approximately equal to that of cylindrical portion  22  of distal end  20  of handle  12 , and a plurality of axial grooves  38  corresponding and complementary in size and shape to ribs  24  of cylindrical portion  22  of distal end  20  of handle  12 . Ring  32  is made from a suitable polymeric material. Ring  32  is mounted to distal end  20  of handle assembly  12 , gap  34  allowing ring  32  to elastically deform to pass over distal ridge  26  so that ring  32  removably mounts to cylindrical portion  22  of distal end  20 . Ring  32  is angularly positionable about axis  40  of cylindrical portion  22 . Distal tip assembly  16  has a distal end  42  and a proximal end  44 , proximal end  44  having a first axial connector piece  46  and a second axial connector piece  48 . Distal tip assembly  16  is removably mounted to distal end  20  of handle assembly  12 , with first connector piece  46  mounting to first connector socket  30 , and second connector piece  48  mounting to second connector socket  31 .  
         [0079]     Friction between connector piece  46  and socket  30  and between connector piece  48  and connector socket  31  maintains the positional relationship between handle assembly  12  and distal tip assembly  16 , as well as provides electrical connectivity therebetween. In other embodiments, a fastening means may be provided to maintain the positional relationship. For instance, distal tip assembly  16  may be removably mechanically fastened to handle assembly  12  using screws, clips, or the like; alternatively, assemblies  12  and  16  may be provided with mating interlocking features such as slots and ribs, threaded portions, or the like. Electrical connectivity between assemblies  12  and  16  may take the form of mating pairs of contacting concentric cylindrical surfaces, planar surfaces, protrusions, or the like in other embodiments.  
         [0080]     The means for mounting magnifier assembly  14  to handle assembly  12  may be modified in other embodiments. For instance, ribs  24  of cylindrical portion  22  of distal end  20  of handle  12 , and grooves  38  of inner surface  36  of ring  32  may be eliminated, and the diameter of inner surface  36  made somewhat smaller than the diameter of cylindrical portion  22  so that the frictional force between surface  36  and portion  22  is sufficient to maintain angular positioning therebetween. In other embodiments, the magnifier assembly  14  may be removably mounted to handle  12  by other mechanical means, such as mating protrusions and sockets, or mechanical fasteners, such as screws or clips.  
         [0081]     Referring now to  FIGS. 2 through 6  showing suture cutter  10 , magnifier assembly  14  and distal tip assembly  16  are removably mounted to distal end  20  of handle assembly  12 . Handle  12  has a proximal end  50  having a proximal-most surface  52  in which are electrical connectors  54 . Upper surface  56  of handle  12  has protruding therefrom activation button  58 , first indicator lamp  60 , and second indicator lamp  62 . Near distal end  20 , illumination lamps  64  face toward the distal end  42  of cutter  12 . In a preferred embodiment, lamps  64  are light emitting diodes (LEDs). In another, they are incandescent lamps. Ring  32  of magnifier assembly  14  has mounted thereto positioning linkage  65  having at its distal end magnifying lens  66 . Linkage  65  allows lens  66  to be positioned and pivoted so as to allow distal end  42  of distal tip assembly  16  to be viewed in magnification through lens  66 .  
         [0082]     Referring now to  FIGS. 7 through 12 , distal tip assembly  16  has a body  70  made of a suitable dielectric material. In a preferred embodiment body  70  is made of a polymeric material. First connector piece  46  forms the proximal end of first conductive piece  74 ; second connector piece  48  forms the proximal end of second conductive piece  72 . In a preferred embodiment body  70  is molded around conductive pieces  72  and  74 . Distal end  42  of assembly  16  is generally wedge-shaped when viewed in a side elevational view as in  FIG. 8 , the wedge being formed by the distal portion of first conductive piece  74  and heating element  76 . Heating element  76 , formed from a material such as nichrome, tungsten, nickel, stainless steel or the like, has a distal end  78  affixed to distal end  77  of first conductive piece  74 . Proximal end  80  of element  76  is affixed to distal end  82  of second conductive piece  72 . Distal end  82  of second conductive piece  72  is displaced proximally distance  84  from distal end  77  of first connector piece  74 . In a preferred embodiment, distal portion  86  of element  76  forms a first wedge angle  88  with first conductive piece  74 . Proximal portion  90  of element  76  forms a second wedge angle  92  with first conductive piece  74 . In a preferred embodiment proximal end  80  of element  76  is affixed to distal end  82  of second conductive piece  72 , such as by crimping, piece  72  being made of a malleable, low resistivity material, such as brass. Also in a preferred embodiment distal end  78  of element  76  is affixed to distal end  77  of first conductive piece  74 , such as by crimping, piece  74  also being made of a low resistivity material, such as brass. In other embodiments, conductive pieces  72  and  74  are made from stainless steel, nickel, or other suitable corrosion resistant alloys, or of assemblies having an electrically conductive portion of a first material, and second portion made of a suitable material such as, for instance, a ceramic or polymeric material, or a corrosion resistant metal. In other embodiments, element  76  may be affixed to conductive pieces  74  and  72  by welding, brazing or soldering. Distal end  77  of first conductive piece  74  has a tapered distal-most portion  79  having a more or less conical shape having an included angle  94  and an axis  96  offset distance  98  from axis  100  of distal end  77  of conductive piece  74 . Included angle  94  is less than twice first wedge angle  88  so that element distal portion  86  contacts tapered distal-most portion  79  of conductive piece  74  only at the point of attachment. When viewed in a plan view as shown in  FIG. 13 , tapered portion  79  of distal end  77  of first conductive piece  74  forms a wedge having an included angle  94  equal to included angle  94  of the conical shape of tapered portion  79  of conductive piece  74 .  
         [0083]     Handle portion  12  optionally contains at least one battery which is charged by a suitable charging means, for example, a charging cradle, connected to the at least one battery by connectors  54  in proximal-most surface  52 . In other embodiments charging may be accomplished through electromagnetic coupling with an external charger and connectors  54  may be eliminated. First indicator light  60  indicates the battery condition. The at least one battery is connected to circuitry having a means for providing high current output when activated. The circuitry output is connected via a connecting means to electrical connectors  30  and  31  in distal-most surface  28  of handle  12 , and, via connector pieces  46  and  48  of tip assembly  16  to conductive pieces  74  and  72  respectively. In this manner, the output of the circuitry is supplied to heating element  76  when the circuitry is activated, activation occurring when button  58  is depressed. The circuitry of handle  12  also has a current control means therein, such that activation of the circuitry causes voltage to be supplied to heating element  76  for a period of time determined by the current control means. In a preferred embodiment the time is about 0.1 to 1 seconds, or more preferably between 0.1 and 0.5 seconds. During the time that voltage is supplied to heating element  76 , second indicator lamp  62  is illuminated and an audio signal is emitted by a means within handle  12 . The circuit of handle  12  further contains a timing means such that a second activation of the device is prevented for a predetermined period of time after a first activation. In a preferred embodiment the period between activations is about 1 to 5 seconds, and more preferably between 1 and 3 seconds.  
         [0084]     Referring now to  FIGS. 14 and 15  showing suture cutter  10  in use, magnifier  66  is aligned so as to allow magnified viewing of distal end  42  of tip assembly  16 , lights  64  providing supplemental illumination to the region. Wound  110  is closed by sutures  112 . Tapered distal-most portion  79  of first conductive piece  74  is inserted into the loop of stitch  114  and advanced until suture  114  is in contact with heating element  76 , whereupon activation button  58  is depressed. Depressing button  58  causes voltage to be supplied to heating element  76  causing element  76  to heat thereby melting the portion of suture  114  in contact with element  76  causing it to rupture. First activation light  62  is lit, and a means within handle  12  emits an audible signal during heating of element  76 . Cutter  10  is then repositioned so that tapered distal-most portion  79  of first conductive piece  74  is inserted under stitch  116  in the same manner as for stitch  114 . Stitch  116  is then cut in the same manner as stitch  114 . When all the stitches are cut, they are removed in the conventional manner, using a forceps or other grasping device.  
         [0085]     The temperature of heating element  76  is non-uniform throughout its length. Conductive pieces  72  and  74  have large thermal masses and high thermal conductivity as compared to element  76 . Because of this, heat flows from element  76  into conductive pieces  72  and  74 , thereby causing cooling of filament  76  in portions of element  76  adjacent to conductive pieces  72  and  74 . Heat flow from element  76  into conductive pieces  72  and  74  also heats up the portions of these pieces adjacent to filament  76 , particularly distal portion  77  of first conductive piece  74  which has less thermal mass than the distal portion of second conductive piece  72 . Tapered distal-most portion  79  of first conductive piece  74  undergoes the most heating. The temperature at a given location on filament  76  is determined by its distance from conductive pieces  72  and  74 , the voltage applied to element  76 , and the length of time that the voltage is applied. At the first instant that voltage is applied to filament  76 , the temperature in the filament is quite uniform and the distal portions of conductive pieces  72  and  74  have only a slight temperature increase, as little heat transfer from filament  76  to conductive pieces  72  and  74  has occurred. Increasing the voltage applied to a given heating element will increase the temperatures; however, at the first instant of activation, the temperature distribution along the filament length is uniform. When voltage is applied for longer periods of time to a heating element, such as element  76 , the temperature of the element increases until it reaches equilibrium, wherein the rate of radiant and convective heat losses from the element then being equal to the electrical power input. The temperature distribution in the element  76 , however, becomes increasingly non-uniform. Portions adjacent to conductive pieces  72  and  74  are cooler because of conductive heat loss to the conductive pieces. Distal portions of conductive pieces  72  and  74  are heated by this conductive transfer of heat. Suture cutter  10  cuts sutures using the portion of distal portion  86  in close proximity to distal portion  77  of first conductive piece  74 .  
         [0086]     It is essential that suture cutter  10  rapidly and efficiently melt a suture so as to cut it, yet at the same time not burn the patient. Accordingly, it is essential that heat transfer from heating element  76  to conductive distal portion  77  of first conductive piece  74  be minimized. This is accomplished by applying a high current, supplied by circuitry inside handle  12  to filament  76 , for a short period of time so as to maximize filament temperature while minimizing conductive heat loss. When the power to element  76  ceases, the element cools through conduction of heat from element  76  to distal portions of conductive pieces  72  and  74 . Because a voltage pulse is supplied to the filament for a brief period of time to melt suture, the amount of heat energy in the filament is minimized. The thermal mass of the distal ends of conductive pieces  72  and  74  is much greater than that of filament  76 . Because of these factors, the temperature rise of the distal end of conductive piece  74 , especially of tapered region  79  is insufficient to cause patient discomfort due to contact with region  79 . The minimum time between activations produced by the timing means within handle  12  ensures that heat conduction from distal portion  77  of conductive piece  74  decreases the temperature of distal portion  77  so that subsequent activation does not cause sufficient temperature rise in portion  77  to cause patient discomfort.  
         [0087]     The wedge shape of distal portion  42  of tip assembly  16  when viewed in side elevation ( FIG. 11 ) and when viewed in plan view ( FIG. 13 ) allows cutter  10  to penetrate the loop of a suture with distal-most portion  79  of first conductive piece  74 , and advance within the loop until filament  76  contacts the suture and cutting is accomplished. In the embodiment previously herein described, element  76  has linear proximal and distal portions. Embodiments having elements  76  with other shapes are contemplated. For instance,  FIG. 16  shows a tip assembly  16  having an element  76  with a curvilinear shape.  FIG. 17  shows a tip assembly  16  with an element  76  having a single linear portion. In both of these embodiments the element  76  and first conductive piece  74  form a wedge when viewed in side elevation. Other element shapes may be used provided they have a distal portion  78  which forms a taper or wedge shape with conductive piece  74  when viewed in side elevation.  
         [0088]     Distal-most portion  79  of first conductive piece  74  also has a wedge shape when viewed in side elevation ( FIG. 11 ) and when viewed in plan view ( FIG. 13 ) which allows cutter  10  to penetrate the loop of a suture with distal-most portion  79  of first conductive piece  74 , and advance within the loop until filament  76  contacts the suture and cutting is accomplished. In the embodiment previously herein described, distal-most portion  79  has a more or less conical shape. Embodiments having portion  79  formed to other tapered shapes are contemplated as well. For instance,  FIGS. 18 through 20  show an alternate embodiment having a distal portion  77  and distal-most portion  79  formed from a sheet material folded to form seam  120  in top surface  122  of first conductive member  74 , distal end  78  of filament  76  being crimped in seam  120 . Distal-most portion  79  is formed of angled surface  124  and cylindrical radii  126  formed by the folding process. Portion  79  has a tapered distal end  128  when viewed in plan view ( FIG. 18 ).  FIGS. 21 through 23  show a modification of the embodiment of  FIGS. 18 through 20 . A secondary coining or trimming operation forms tapered portion  130  having an included angle  132  when viewed in a plan view ( FIG. 21 ). Referring now to  FIGS. 24 through 26  showing yet another embodiment, distal-most portion  79  of first conductive piece  74  is formed from a sheet material folded to form seam  120  in top surface  122  of first conductive member  74 , distal end  78  of filament  76  being crimped in seam  120 . Distal-most portion  79  is formed by angled or beveled surface  140  best seen in  FIG. 25 , and angled surfaces  142  best seen in  FIG. 24 . In yet another embodiment, shown in  FIGS. 27 through 29 , first conductive member  74  has a tubular construction, distal end  78  of filament  76  being positioned in a slot  150  in the upper distal portion of member  74 .before the end of the member is crimped to form a pair of laterally opposed, parallel planar surfaces  152  spaced distance  154  apart. Beveled surface  156  forms a wedge shape at distal-most portion  79  of member  74 , Distal-most portion  79 , because of its wedge shape and narrow width  154 , slips easily into the loop of a suture, even one of a small size.  
         [0089]     The temperature of heating element  76  is determined by the voltage supplied to the element, the length of time that the voltage is supplied, and by the resistance of the element. The resistance of distal tip assembly  16  will vary due to manufacturing tolerances on the diameter and length of heating element  76 , and due to variations in the attachment of the element  76  to conductive pieces  72  and  74 . In some cases the resistance may also vary with repeated activations due to resistance changes in the attachments. Accordingly, a circuit within proximal portion  12  conditions the power supplied to element  76  so that element  76  is heated to a predetermined temperature even though battery voltage and element resistances vary within predetermined ranges.  
         [0090]     Referring now to  FIG. 30 , circuit  200  for conditioning and controlling power supplied to heating element  76  has a voltage source  202 , in this preferred embodiment two Nickel-Metal Hydride (NiMH) batteries, which is applied to a DC to DC voltage converter  204  which puts out voltage at a predetermined level. The output of converter  204  is supplied to timer circuit  206  and current controller  208 . Current controller  208  supplies current to heating element  76  such that element  76  achieves a predetermined temperature. In a preferred embodiment current controller  208  determines the resistance of the element  76  by sensing the voltage across the element when power is supplied to the element. Current controller  208  supplies power to the element  76  until a predetermined energy value is reached, the value being the product of the voltage, current and time. Because the electrical energy is converted to thermal energy by heating element  76 , the heating of element  76  is repeatable even though the resistance of the element may vary. In another embodiment current controller  208  varies the voltage supplied to element  76  based on the resistance of element  76  so as to supply a predetermined amount of energy. In yet another embodiment, used with heating elements  76  in which the resistance is closely controlled, power at a predetermined voltage is supplied to element  76  for a predetermined length of time.  
         [0091]     When filament  76  has been energized, timer  206  prevents a second activation for a predetermined time period so as to allow heat from element  76  to dissipate in conductive pieces  72  and  74 , and for conductive piece  74  to cool so that subsequent activation of the device does not cause the temperature of distal end  77  of piece  74  to rise to a level which would cause patient discomfort or harm.  
         [0092]     An exemplary charging cradle for recharging the batteries within handle  12  is shown in  FIG. 31 . Charging cradle  300  has a pocket  302  formed in surface  304 , pocket  302  being shaped to receive and position proximal end  50  of handle  12  therein such that pins  306  are received by connectors  54  making an electrical connection thereto. Electrical cable  308  connects to an external voltage source. By means conventional in the art, charging cradle  300  supplies voltage to handle  12  so as to charge batteries therein. First indicator light  310  illuminates to indicate that charger  300  is connected to a power source. Second indicator light  312 , when handle  12  is positioned in pocket  302  (see  FIG. 32 ), indicates the condition of the batteries in handle  12 , light  312  having a first condition when the batteries are not fully charged, and a second condition when the batteries are fully charged. Charging cradle  300  may be placed on a horizontal surface such as a table top, or mounted to a wall using fasteners placed in holes  314 . In another embodiment cradle  300  supplies power to handle  12  electromagnetically so that pins  306  and connectors  54  of handle  12  are not required. In yet another embodiment, handle  12  has a removable battery pack which is placed in charging cradle  300  for recharging.  
         [0093]     Thermal suture cutter  10  consisting of handle  12 , single-use distal tip assemblies and optional magnifier assembly, together with charging cradle  300  form a system for cutting sutures for removal. Components may be sold separately or as a kit, the kit containing all elements required for suture cutting, including a plurality of distal assemblies  16 .  
         [0094]     The disclosure of each publication, patent or patent application mentioned in this specification is specifically incorporated by reference herein in its entirety.  
         [0095]     The invention has been illustrated by reference to specific examples and preferred embodiments. However, it should be understood that the invention is intended not to be limited by the foregoing description, but to be defined by the appended claims and their equivalents.

Technology Category: 1