Abstract:
A temperature sensing device for attachment to a powered surgical instrument operating a workpiece such as a bur. The device is a thermochromic element which may be embodied as a paint or a thermal insulating device. The device embodiment is in the form of a thermoplastic, elastomeric material which changes color at a predetermined temperature and is formed in a shape adapted to enable the device to be affixed to the distal end of the instrument, adjacent the collet connecting the workpiece to the instrument. The device is attached in a contiguous manner so frictional heat generated by moving parts of the instrument may be conducted through contiguous surfaces of the instrument and the device. The thermochromic element provides a visual indication of the temperature of a portion of the instrument when the temperature exceeds a predetermined level.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to powered surgical instruments. More particularly, the invention relates to temperature indicating elements for use with powered surgical instruments to provide a visual indication of the temperature of at least a portion of the surgical instrument. The invention also relates to thermal insulating devices for use with powered surgical instruments, these devices optionally including temperature indicating elements.  
           [0003]    2. Description of the Prior Art  
           [0004]    Powered surgical instruments are known for use during surgical procedures to operate a workpiece in some manner to perform the procedure. For example, a powered surgical instrument may be a handpiece, generally powered either electrically or pneumatically, in the form of a drill which rotates a drill bit or bur. Other handpiece instruments in the form of a saw operate a saw blade in either a reciprocating or oscillating manner. Various other types of powered surgical handpieces are known to move a tool or workpiece in various ways to perform surgical procedures.  
           [0005]    In some powered surgical instruments the workpiece (e.g. burr or drill bit, etc.) is rapidly rotated to, for example, debride or resect soft tissue or bone. The workpiece is locked into a collet at the distal end of the instrument for fixed attachment to the motor drive shaft in the instrument. The workpiece generally extends distally from the collet in alignment with the axis of the drive shaft. In some instances a bur guard or similar bearing-containing device is interposed between the workpiece and the handpiece in order to provide additional rotary bearing support between the workpiece and the handpiece. In all instances, the rapid movement of the workpiece relative to the stationary components of the handpiece creates heat-generated friction which ultimately passes via thermal conduction or radiation from the internal friction-generating components to the external surface of the handpiece or bur guard (or other component). The invention is described in terms of powered surgical instruments because manually operated instruments would not be expected to generate a great deal of frictional heat. Clearly, if a manual instrument did generate sufficient heat to cause concern, the invention would be equally applicable to such instruments.  
           [0006]    While powered surgical instruments are designed to be cleaned and sterilized after each use, it has been found that less than optimal cleaning and/or sterilization by users contributes to greater than normal generation of friction upon subsequent use and, consequently, greater than normal temperature rise in the components of the instrument and/or workpiece. In some instances, the heat generated by a powered surgical instrument may be so great as to make it unable to be held by a surgeon or may be so great as to cause injury to a patient. In particular, use of such potentially very hot instruments in small areas, such as during oral surgical procedures, raises the possibility that a patient will be burned inadvertently. It would, therefore, be desirable to provide some indication that a part of the surgical instrument is beginning to get hotter than intended. It would also be desirable to provide a way to protect the patient from sudden temperature increases of surfaces of powered surgical instruments likely to come in contact with the patient.  
           [0007]    It is accordingly an object of this invention to produce a temperature indicating device to provide an indication of the temperature of at least a portion of a powered surgical instrument.  
           [0008]    It is another object of this invention to provide a temperature indicating device for attachment to a specific portion of a powered surgical instrument to provide a visual indication of the temperature of that portion.  
           [0009]    It is also an object of this invention to provide a temperature indicating device for attachment at the distal end of a powered surgical instrument adjacent to the collet through which the workpiece passes.  
           [0010]    It is yet another object of this invention to provide a temperature indicating device capable of attachment to the distal end of an instrument at a location most clearly visible by a user.  
           [0011]    It is an additional object of this invention to produce a method for indicating a predetermined temperature of a portion of a surgical instrument.  
           [0012]    It is still another object of this invention to provide a thermal insulator device to be interposed between a patient and a potentially high temperature portion of a powered surgical instrument being used on the patient.  
           [0013]    It is also an object of this invention to provide such a thermal insulating device with a temperature indicating element to provide a visual indication of the temperature of the portion of the powered surgical instrument to which it is attached.  
         SUMMARY OF THE INVENTION  
         [0014]    These and other objects of the invention are achieved by the preferred embodiment disclosed herein which is a thermochromic indicating device for providing a visual signal indicative of a temperature change of at least a portion of a powered surgical instrument. The instrument has a proximal end and a distal end, the distal end being generally cylindrical and adapted to have an elongated workpiece extending distally therefrom. The indicating device is a generally cylindrical shell having an open proximal end and a closed, apertured distal end, a cylindrical wall with an axis and a predetermined axial length. The end wall enclosing the distal end has a workpiece-receiving aperture. The cylindrical wall is adapted to be received in contiguous engagement on the distal end of the instrument with the workpiece extending through said workpiece-receiving aperture. A temperature sensitive dye is embedded in the cylindrical shell to sense the temperature of the distal end of the instrument which is in contiguous engagement with the cylindrical shell. The dye changes color at a predetermined temperature to provide a visual indication of a change in the temperature of the device.  
           [0015]    Another aspect of the invention is a device such as that described above, but without any thermochromic elements therein. Such a device would have insulating properties alone.  
           [0016]    Another aspect of the invention is a thermochromic element embodied in the form of a paint having thermochromic elements therein. Such an embodiment would not necessarily have the insulating properties of the previous embodiments.  
           [0017]    Another aspect of the invention is the method of operating a powered surgical instrument with the insulating and/or thermochromic elements described above. These methods comprise the steps of affixing the insulating and/or thermochromic elements to a selected portion of a powered surgical instrument as it is being used on a patient. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a side elevational view of a powered surgical instrument.  
         [0019]    [0019]FIG. 2 is a side elevational view of the instrument of FIG. 1 having attached thereto a temperature indicating device constructed in accordance with the principles of this invention.  
         [0020]    [0020]FIG. 3 is a cross-sectional view of the temperature indicating device of the invention taken along the lines  3 - 3  of FIG. 2.  
         [0021]    [0021]FIG. 4 is a front perspective view of FIG. 3.  
         [0022]    [0022]FIG. 5 is a side elevational view of an alternate powered surgical instrument.  
         [0023]    [0023]FIG. 6 is a side elevational view of the powered surgical instrument of FIG. 5 having a temperature indicating device attached thereto.  
         [0024]    [0024]FIG. 7 is a cross-sectional view of FIG. 6 taken along the line  7 - 7 .  
         [0025]    [0025]FIG. 8 is a front perspective view of FIG. 7. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    An example of a powered surgical instrument  10  is shown in FIG. 1. Instrument  10  includes a body  12  having a proximal end  14 , a distal end  16  and an operating on/off lever/switch. Proximal end  14  is attachable via an electrical connection (not shown) to which an electrical power cable (not shown) may be attached. Distal end  16  is provided with a collet mechanism  20  and a bearing-containing bur guard  22 . Workpiece  24 , shown in the form of a bur, is rotatably secured to the output shaft of a drive motor within body  12 . The shaft of workpiece  24  passes through bur guard  22  and collet  20  into engagement with the drive shaft (not shown). Collet  20  serves to rotatably lock workpiece  24  adjacent the drive shaft while bur guard  22  contains rotary bearings which provide additional support (especially for long burs) to maintain the axis of workpiece  24  in alignment with the axis of the output drive shaft of the motor within body  12 . The configuration shown in FIG. 1 is one prior art example of a surgical handpiece in combination with a workpiece.  
         [0027]    [0027]FIG. 2 shows the handpiece  10  of FIG. 1 assembled with a thermally insulating and temperature indicating element such as device  50  best seen in FIGS. 3 and 4. It will be understood that device  50  could be made without temperature indicating elements in which case it would have insulating properties only. Device  50  is made in the form of a cylindrical shell  52  having an open proximal end  54  and a closed distal end wall  56 . The inner diameter D (which may be slightly undersized to create a good fit on the bur guard) and inner length L of shell  50  are sized to fit on the corresponding distal portion of bur guard  22 . Aperture  58  in end wall  56  is sized to permit the shaft of workpiece  24  to pass therethrough without any contact. Device  50  thus is fixedly secured to, and in contiguous engagement with bur guard  22  while not impeding the movement of workpiece  24 .  
         [0028]    Device  50  is shaped to mate with a selected portion of the particular surgical instrument for which it is designed. If one desires to use a device such as device  50  on a different surgical instrument, or on a different portion of an instrument, the device just needs to be shaped accordingly to fit where intended. It would also be possible to attach a thermally insulating and temperature indicating device in any shape (flat, curved, etc.) with an auxiliary attachment mechanism (not shown) such as a screw or adhesive. The advantage of the cylindrical shape of the preferred embodiment is that it is functional and visible over a 360° range around the instrument.  
         [0029]    In the preferred embodiment, device  50  is integrally molded of an elastomeric material enabling it to be secured to the distal end of bur guard  22  with a simple friction fit ensuring contiguous engagement between the inner cylindrical surface of device  50  and the outer cylindrical surface of bur guard  22 . Contiguity facilitates good thermal conductivity between contiguous surfaces which in turn facilitate reliable temperature indication. It will be understood there is also contiguous contact between the end wall  56  and the corresponding end portion of bur guard  22  (not shown). In the preferred embodiment, device  50  is approximately 0.4 inches in length, with L=0.35 inches, D=0.222 inches, the thickness of wall  52  equal to 0.005 inches and the diameter of aperture  58  equal to 0.1 inches.  
         [0030]    The polymeric material from which device  50  is formed is, in the preferred embodiment, a polypropylene compound which, if temperature indicating properties are desired, additionally contains a conventional thermochromic dye which changes color depending upon the temperature of the device. The material is a mixture of a first polypropylene material containing a red dye which is not notably temperature sensitive and a second polypropylene material containing a blue dye which is temperature sensitive. While many different thermochromic dyes are known and available in many colors and temperature ranges, the preferred embodiment utilizes a microencapsulated leuco dye which changes from a color to clear at the selected temperature. As the temperature of the blend of first and second polypropylene material changes, the resultant color of the blend, which is normally purple at room temperature changes (in varying degrees, depending upon temperature) to bright pink or red. Since the color change visually indicates an undesirable temperature increase which indicates some unintended, friction-generating element in the instrument, any color change should be interpreted as an indicator signaling that the instrument should not be used until it has been repaired. The polymeric material from which device  50  is made is a proprietary thermoplastic resin compound Colorcomp® M-1000, color # BL5-778-1 TCH available from LNP Engineering Plastics, Inc., 251 South Bailey Road, Thorndale, Pa. The temperature range at which the color changes may be varied, depending upon the proprietary formulation of the colorant in the polypropylene, although in the preferred embodiment the selected temperature range is from approximately 135° F., at which point the color change begins to occur, to approximately 150° F., at which point a full color change could be expected. Leuco dyes are not extremely precise in the temperature at which they change color, but because the invention is intended as a gross indicator of heat, precision is not essential. It should be noted that while the color change may occur at the aforementioned temperatures, the insulation properties of the material mitigate the potential for patient burns because of its poor heat transferability (i.e. specific heat value). Additionally, the color of the material of the device varies in a gradient through a cross-section causing color changes before the outside surface of the device reaches the same temperature as the internal surface.  
         [0031]    While the thermochromic material is, in the preferred embodiment, embedded in device  50 , it will be understood that thermochromic material could simply be mixed with a paint or similar medium to be painted on the device or otherwise topically applied or associated with the device (the term “associated” is used to mean the thermochromic material could be on or in the device). It could even be made to read “HOT” or other words at a given temperature.  
         [0032]    It will be understood that device  50  may be made disposable and may be made in a variety of shapes and sizes in order to enable it to be secured to a variety of powered surgical instruments and at a variety of locations on a given powered surgical instrument. For example, another prior art powered surgical instrument is shown in FIG. 5 as instrument  70  having a proximal end  72  and a distal end  74 . Instrument  70  has an on/off lever/switch  76 , a collet mechanism  78  and a bur guard  80 . Instrument  70  is operated pneumatically and has a pneumatic connection  82  adjacent proximal end  72  although, while it will be noted that bur guard  80  has a frustoconical distal tip  84 , in all other respects the general operation of instrument  70  is similar to that instrument  10  in that instrument  70  also rotates a workpiece (not shown). Because of the frustoconical shape of the distal tip of bur guard  80 , a thermoplastic device  90 , best seen in FIGS. 6, 7 and  8  must have a corresponding frustoconical internal shape. Thus, device  90  has a frustoconical wall  92  adjacent a cylindrical wall  94  and sections  92  and  94  are bounded by open ends  96  and closed end wall  98 , respectively. End wall  98  contains a workpiece-receiving aperture  100 . In all other respects the operation of temperature device  90  is similar to that of temperature indicating device  50 .  
         [0033]    While the temperature indicating embodiments of the invention have been described in terms of a thermochromic element to be applied via a paint medium or a device such as a shell adapted to contiguously fit a cylindrical bur guard, it will be understood that the temperature indicating element may be attached to the powered surgical instrument at any desired location which may be a potential heat source or where a temperature indication is desired. For example, if a particular instrument has two components which are movable relative to each other so that friction generated heat may be produced and transferred by conduction or radiation from one component to the other, a temperature indicating element could be used. In this circumstance the element could be in the form of a device attached in contiguous relationship (using techniques described above or any suitable attachment mechanism) to a place on the instrument adjacent, but not necessarily contiguous to the source of heat. Indeed, the source of heat need not be frictional, and it will be understood that any heat source (chemical, thermal radiation, etc.) serving to produce potentially detrimental effects may be monitored by a temperature indicating element as described above. The monitoring may even be accomplished with the indicating element spaced away from the heat source, provided that heat is ultimately transferred by some means to the device in order to activate the thermochromic material.  
         [0034]    It will be understood by those skilled in the art that numerous improvements and modifications may be made to the preferred embodiment of the invention described herein without departing from the spirit and scope thereof.