Abstract:
An expansible and retractable mechanism of the type disclosed in U.S. Pat. No. 5,924,175 and/or a medical grasper of the type disclosed in U.S. Pat. No. 5,906,622 in which (1) the fixed flexure elements are self-biased to move into the expanded condition thereof. The medical grasper is further characterized by  
     A method of forming an annularly expanding and retracting gripping and releasing mechanism providing a series of flexible tubes, comprising providing (1) a series of flexible tubes, (2) a corresponding series of wires, each of which includes a movable wire section and relatively short fixed wire section integrally connected with one end of the movable wire section by a kink configured so that the wire sections extend in longitudinally coextensive relation therefrom; (3) a series of tubular elements of thermoplastic material; and (4) a series of heat shrinkable sleeves assembling a distal end portion of each flexible tube with a fixed wire section, a tubular element and a heat shrinkable sleeve so that the fixed wire section extends along the exterior periphery of the flexible tube with the kink disposed outwardly of the distal end thereof. The tubular element is disposed in surrounding relation to the fixed wire section and the flexible tube and the heat shrinkable sleeve is disposed in surrounding relation to the tubular element. The method further comprises applying heat to the exterior of each heat shrinkable sleeve at a temperature sufficient to contract the sleeve and soften the thermoplastic material of the tubular element surrounded thereby so that the contraction of the sleeve molds the softened thermoplastic material into adhered contact with the exterior surfaces of the surrounded fixed wire section and flexible tube. A medical device made by the method which includes a short distal end portion of each of three wire receiving tubes having a fixed wire section extending along an exterior periphery thereof and a molded annular body of thermoplastic material surrounding the exterior periphery thereof in adhered relation thereto and to the fixed wire section extending therealong to retain the fixed wire section in fixed relation thereon. The medical grasper is further characterized by (1) the provision of a bendable section of the cannula assembly at the distal end thereof adjacent the gripping and releasing mechanisms in which the flexible tube sections thereof are contained in non-adhered relation by an overlying flexible sleeve and/or (2) the provision of a handpiece assembly capable of limiting the force of the pull that can be manually applied to retain a stone in gripped relation by allowing for a resiliently yielding movement after gripping has been accomplished.

Description:
[0001]    The subject matter of the application relates to improvements in medical extractors or graspers of the type disclosed in U.S. Pat. Nos. 5,906,622 and 5,924,175, the disclosure of both of which is hereby incorporated by reference into the present specification. The present application claims priority from provisional application 60/386,190 filed May 28, 2002, the disclosure of which is hereby incorporated by reference into the present specification. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The grasper disclosed in the &#39;622 patent comprises an elongated cannula assembly having an annularly expanding and retracting gripping and releasing mechanism at the distal end thereof and a moving assembly at the proximal end thereof. The gripping and releasing mechanism as described in both the &#39;622 patent and the &#39;175 patent includes an annular series of longitudinally fixed flexure elements and a corresponding series of longitudinally movable flexure elements. The moving assembly is operable to effect a relative movement between the flexure elements to move them between a retracted condition and an expanded condition defined by an annular series of transversely outwardly flexed fixed elements interconnected by an annular series of arcuately flexed portions of said flexure elements.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    The present invention embodies improvements in the medical extractor disclosed in the &#39;622 patent and the expanding and retraction mechanism of the patent. The feature of one improvement is to self bias the fixed flexure elements to move into the expanded condition thereof.  
           [0004]    Other improvements include (1) the provision of a bendable section of the cannula assembly at the distal end thereof adjacent the gripping and releasing mechanisms in which the flexible tube sections thereof are contained in non-adhered relation by an overlying flexible sleeve and (2) the provision of a handpiece assembly capable of limiting the force of the pull that can be manually applied to retain a stone in gripped relation by allowing for a resiliently yielding movement after gripping has been accomplished. Preferably, the handpiece is provided with a lock structure enabling the gripping action to be maintained within the limiting force while allowing the manual pull to be removed. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a fragmentary perspective view looking down on the distal end of the gripping and releasing mechanism and adjacent portion of the cannula assembly of a medical extractor embodying the principles of the present invention, the parts being shown in a closed position;  
         [0006]    [0006]FIG. 2 is a cross-sectional view of a moving assembly and adjacent portion of the cannula assembly of the medical extractor showing the parts in a closed position corresponding to the position of the parts shown in FIG. 1;  
         [0007]    [0007]FIG. 3 is a view similar to FIG. 1 showing the parts in an open position;  
         [0008]    [0008]FIG. 4 is a view similar to FIG. 2 showing the parts in an open position corresponding to the position of the parts shown in FIG. 3;  
         [0009]    [0009]FIG. 5 is a view similar to FIGS. 1 and 3 showing the parts in a stone gripping position;  
         [0010]    [0010]FIG. 6 is a view similar to FIGS. 2 and 4 showing the parts in a stone gripping position corresponding to the position of the parts in FIG. 5;  
         [0011]    [0011]FIG. 7 is an enlarged top plan view of the gripping and releasing mechanism of the present invention showing the same in a closed position;  
         [0012]    [0012]FIG. 8 is a fragmentary sectional view taken along the line  8 - 8  of FIG. 7;  
         [0013]    [0013]FIG. 9 is a perspective view illustrating an initial step in the assembly of the gripping and releasing mechanism according to the method of the present invention;  
         [0014]    [0014]FIG. 10 is a view similar to FIG. 9 illustrating a subsequent step in the assembly;  
         [0015]    [0015]FIG. 11 is a sectional view taken along the line  11 - 11  of FIG. 9;  
         [0016]    [0016]FIG. 12 is a sectional view taken along the line  12 - 12  of FIG. 10;  
         [0017]    [0017]FIG. 13 is a cross-sectional view taken along the line  13 - 13  of FIG. 8;  
         [0018]    [0018]FIG. 14 is a cross-sectional view taken along the line  14 - 14  of FIG. 8;  
         [0019]    [0019]FIG. 15 is a cross-sectional view taken along the line  15 - 15  of FIG. 8;  
         [0020]    [0020]FIG. 16 is a cross-sectional view taken along the line  16 - 16  of FIG. 8;  
         [0021]    [0021]FIG. 17 is a sectional view taken along the line  16 - 16  of FIG. 8 showing the position of the parts in an initial assembly condition;  
         [0022]    [0022]FIG. 18 is a cross-sectional view taken along the line  18 - 18  of FIG. 8;  
         [0023]    [0023]FIG. 19 is a sectional view taken along the line  19 - 19  of FIG. 2;  
         [0024]    [0024]FIG. 20 is a sectional view taken along the line  20 - 20  of FIG. 2;  
         [0025]    [0025]FIG. 21 is a sectional view taken along the line  21 - 21  of FIG. 2;  
         [0026]    [0026]FIG. 22 is a view similar to FIG. 2 showing a moving assembly of modified form constructed in accordance with the principles of the present invention;  
         [0027]    [0027]FIG. 23 is a view similar to FIG. 22 showing the position of the parts when in an initial unlocked position;  
         [0028]    [0028]FIG. 24 is a view similar to FIGS. 22 and 23 showing the parts in a position corresponding to the position of FIG. 4;  
         [0029]    [0029]FIG. 25 is a view similar to FIGS. 22 and 23 showing the parts in a position corresponding to the position of FIG. 6;  
         [0030]    [0030]FIG. 26 is an enlarged sectional view taken along the line  26 - 26  of FIG. 22;  
         [0031]    [0031]FIG. 27 is an enlarged sectional view taken along the line  27 - 27  of FIG. 22; and  
         [0032]    [0032]FIG. 28 is an exploded perspective view of replacement components useful in a modified form of device embodying the principles of the present invention;  
         [0033]    [0033]FIG. 29 is a view similar to FIG. 28 showing another form of the device embodying the principles of the present invention; and  
         [0034]    [0034]FIG. 30 is another modification within the present invention which is useful with the modified form shown in FIG. 29. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0035]    Referring now more particularly to FIGS.  1 - 21  of the drawings, there is shown therein a medical extractor, generally indicated at  10 , embodying the principles of the present invention. The medical extractor  10  as shown includes, in general, an elongated cannula assembly, generally indicated at  12 , having an expandable and retractable gripping and releasing mechanism, generally indicated at  14 , on the distal end thereof and a moving handpiece assembly, generally indicated at  16 , on the proximal end thereof. The moving assembly  16  is manually operable to expand and retract the gripping and releasing mechanism  14 . As shown, the cannula assembly  12  of the medical extractor  10  is capable of being inserted through the central passage of a conventional scope deployed within a patient with the gripping and releasing mechanism  14  extending within the patient outwardly of the distal end of the scope and the moving assembly  16  disposed inwardly of the proximate end of the scope exteriorly of the patient. The construction of the extractor  10 , as shown, can be made to pass through the central passage of a scope which measures three French.  
         [0036]    The cannula assembly  12  and the gripping and releasing mechanism  14  constitute a subassembly of the extractor  10  which is preferably made in accordance with a method embodying the principles of the present invention. The starting materials used in practicing the method of the present invention to make the gripping and releasing mechanism  14  include (1) a series (three) of elongated flexible wire receiving tubular structures  18  and (2) a corresponding number of wires, generally indicated at  20 . Each wire  20  includes a relatively long movable wire section  22  and a relatively short fixed wire section  24  integrally connected with one end of the movable wire section  22  by a kink  26 . The starting materials also include (3) a corresponding number of tubular elements  28  of thermoplastic material; and (4) A corresponding number of heat shrinkable sleeves  30 .  
         [0037]    The tubular structures  18  shown in FIGS. 1, 3 and  5  are tubes made of a flexible, thin walled plastic material capable of stably withstanding relatively high temperatures and of resisting longitudinal stretch. The tubular structures  18  are sized to provide an interior diameter to slidably receive and closely confine an associated movable wire section  22  therein. A preferred example of a material which can be utilized to form the wire receiving tubular structures  18  is polyimide having a wall thickness of 0.0005″. Another exemplary material is (PEEK) Polyethyl ethyl keytone.  
         [0038]    The wires  20  are preferably made of a kink resistant metal, preferably a shape memory metal such as nitinol. Preferably, the kink  26  is formed in memory as an acute included angle between the fixed and movable wire sections  20  and  22  which extend co-extensively from the kink  26 . A preferred range being 80° to 45° with 50° being a preferred angle. An exemplary dimension for the nitinol wires is within the range 0.007″ to 0.0085″.  
         [0039]    As best shown in FIGS. 9 and 10, preferably, the fixed wire section  24  of each wire  20  has a free end portion thereof flattened, as by a squeezing action between two rollers, so as to provide a pair of spaced shoulders  31  facing toward the associated kink  26 . Preferably, the opposed exterior surfaces of each flattened portion are abraded, as indicated by the stippling in FIGS. 9 and 10, to enhance the adherence thereof to the thermoplastic material of the associated tubular element  28 .  
         [0040]    The tubular elements  28  are shown in FIGS. 9, 10 and  12 . A preferred material is high density polyethylene. The interior diameter size of the surrounding tubular elements  28  are oversize with respect to exterior diameter size of the wire receiving tubular structures  18 . The length of the tubular elements  28  is slightly in excess of the length of the heat shrinkable sleeves  30 , e.g. ¼ inch.  
         [0041]    Each heat shrinkable sleeve  30  is preferably somewhat oversize in diameter with respect to the tubular elements  28  and is formed of a material having a relatively high shrink temperature. A preferred material is PET—polyester resin, although other suitable materials may be utilized.  
         [0042]    Ultimately, the kinked wires  20 , the distal end portions of the wire receiving tubular structures  18 , the surrounding tubular elements  28 , and the heat shrinkable sleeves  30  are assembled so as to form the gripping and releasing mechanism  14 . In the assembly, a movable wire section  22  is disposed within each flexible tube  30  and a distal end portion of each flexible tubular structure  18  is assembled together with a fixed wire section  24 , a tubular element  28 , and a heat shrinkable sleeve  30  so that (1) the fixed wire section  24  extends along the exterior periphery of the flexible tubular structure  18  with the kink  26  disposed outwardly of the distal end thereof, (2) the tubular element  28  is disposed in surrounding relation to the fixed wire section  24  and the flexible tubular structure  18  and (3) the heat shrinkable sleeve  30  is disposed in surrounding relation to the tubular element  28  so that a short proximal end portion of the tubular element  28  (e.g. ¼ inch) extends beyond the proximal end of the heat shrinkable sleeve  30 . It is noted that the surrounding position of the tubular element  28  with respect to the fixed wire section  24  insures that the shoulders  31  of the flattened free ends of the fixed wire sections  24  are covered by thermoplastic material.  
         [0043]    Preferably, as shown in FIG. 10, each flexible tubular structure  18  is assembled with a fixed wire section  24 , a tubular element  28  and a heat shrinkable sleeve  30  in the positions indicated, heat is applied progressively to the exterior of the heat shrinkable sleeve  30  of the assembly at a temperature and for a time sufficient to cause the heat shrinkable sleeve  30  to shrink or contract around the coextensive portion of the associated surrounding tubular element  28 . The heat preferably is applied by a hot air blast at a temperature which will soften the thermoplastic material of the coextensive portion of the surrounding tubular element  28  causing it to flow into adhered contact with the exterior peripheries of the fixed wire section  24  and the distal end portion of the tubular structure  18 . Once the heat is removed and the components are allowed to cool, the thermoplastic material of the coextensive portions of the surrounding tubular elements  28  serves to adhere each fixed wire section  24  to the exterior periphery of the distal end portion of the associated wire receiving tubular structure  18 .  
         [0044]    The sequential heating of each heat shrinkable sleeve  30  as it is assembled, as shown in FIGS. 9 and 10, is, as aforesaid, preferred because only one assembly need be maintained in position at one time and then fixed in that position by the application of heat. However, it is within the broadest aspects of the present invention to complete all three assemblies and then effect the heating.  
         [0045]    In this way, there are formed at the distal end of the cannula assembly  12  three flexure elements  32 , each of which, as shown in FIG. 8, is comprised of the coextensive distal end portion of the associated wire receiving tubular structure  18 , a fixed wire section  24 , a surrounding body of molded thermoplastic material indicated at  34  in FIG. 8 and a coextensive surrounding short heat shrinkable sleeve  30  in a heat contracted condition defining the exterior molded shape of the body of thermoplastic material  34 . The three flexure elements  32  are fixed together at their proximal ends in a manner hereinafter to be described so as to constitute fixed flexure elements  32  of the gripping and releasing mechanism  14 . The distal portions of the movable wire sections  22  which move out of and are slidable within the fixed flexure elements  32  constitute movable flexure elements  36  of the gripping and releasing mechanism  14 .  
         [0046]    The fixing of the proximal ends of the fixed flexure elements  32  is preferably accomplished in conjunction with the assembly and making of the cannula assembly  12 .  
         [0047]    The subassembly resulting from the above procedures includes parts of the cannula assembly  12  with the gripping and releasing mechanism  14  connected at its distal end. The fixed and movable flexure elements  32  and  36  constitute fixed and movable parts of the gripping and releasing mechanism  14 . The main extent of the wire receiving tubular structures  18  are next contained together in coextensive relation to form the fixed structure of the cannula assembly  12  while the main extent of the movable wire sections  22  constitute the movable structure of the cannula assembly  12 . Thus, the connections of both the fixed structure or parts and the movable structure or parts between the distal end of the cannula assembly  12  and gripping and releasing mechanism  14  are essentially automatically made integral connections in that the portions of the flexible tubular structures  18  of the cannula assembly  12  form extensions of the distal portions forming the fixed flexure element  32  of the gripping and releasing mechanism  14  and the main portions of the movable wire sections  24  form extensions of the distal portions forming the movable flexure elements  36  of the gripping and releasing mechanism  14 .  
         [0048]    As best shown in FIGS. 8, 16 and  17 , the containing procedure involves the use of an elongated heat shrinkable outer sleeve  38  of a length sufficient to extend throughout the cannula assembly  12  and a series of elongated tubular elements  40  of a somewhat lesser length, as for example, approximately four inches less. The outer sleeve  38  is preferably formed of irradiated cross linked polyethylene and the tubular elements  40  are preferably of high density polyethylene.  
         [0049]    Each tubular element  40  of the series is positioned over a main proximal end portion of one of the tube extensions  18  and the outer sleeve  38  is positioned over the tubular elements  40  and the remaining uncovered distal sections of the tube extensions  18 . These distal sections of the tube extensions  18  provide a distal section of the cannula assembly  12  which is more flexible than the remainder. This flexibility characteristic is valuable when the medical device  10  is used to extract stones in the kidneys.  
         [0050]    As best shown in FIG. 8, the distal section of each tube extension  18  has mounted on the exterior periphery thereof a collapse preventing structure in the form of a coil of metal  41 . While the metal may be wire, a preferred form is a ribbon (e.g. 0.001″×0.003″) of stainless steel coiled with successive loops spaced slightly apart with the larger dimension disposed axially. Collapse prevention is desirable as this section of the cannula assembly  12  must undergo a somewhat severe 180° curvature when the device  10  is used to extract a kidney stone.  
         [0051]    As previously indicated, the fixing of the fixed flexure elements  32  is preferably accomplished in conjunction with the assembly of the cannula assembly  12 . The fixing procedure involves moving the proximal end portions of the tubular elements  28  extending from the sleeves  30  together and then surrounding the same with a distal end portion of the outer heat shrinkable sleeve  38 .  
         [0052]    It is now possible to effect a controlled progressive heating of the exterior periphery of the elongated heat shrinkable outer sleeve  38  starting at its distal end so that the distal end portion is first made to shrink and mold the thermoplastic material of the extensions of the tubular elements  28  into engaged relation to the exterior peripheries of the coextensive lengths of the wire receiving tubular structures  18 .  
         [0053]    The progressive heating of the next four inches of the elongated heat shrinkable sleeve  38  is such as to make the elongated heat shrinkable outer sleeve  38  to shrink but only to an extent sufficient to confine and contain the surrounded portions of the wire receiving tubular structures  18  and surrounding coils  41 .  
         [0054]    The progressive heating of the remainder of the elongated heat shrinkable outer sleeve  38  is accomplished at a temperature sufficient to shrink the elongated heat shrinkable outer sleeve  38  and soften and mold the thermoplastic material of the surrounded tubular elements  40  into adhered relation to the surrounded exterior peripheries of the wire receiving tubular structures  18 .  
         [0055]    In accordance with one feature of the present invention, the fixed flexure elements  32  are self-biased to move into the opened condition thereof by an appropriate heat treatment while held in a position preferably beyond the normal opened position. The term self-biased means biased by the materials which make up the fixed flexure elements  32 .  
         [0056]    A typical heat treatment involves first extending the movable wire sections  22  outwardly to maintain the fixed flexure elements  32  in the extended open position thereof and then placing the entire opened gripping and releasing mechanism  14  in an oven and maintaining it there at a temperature below the melting point of the thermoplastic material of the tubular elements  28  for a time period sufficient to impart a bias to the fixed flexure elements  32  to move into the open position thereof. An exemplary time is approximately twenty minutes and an exemplary temperature is approximately 230° F.  
         [0057]    It is noted that at the proximal end portion of the cannula assembly  12  of the subassembly, the three movable wire sections  22  extend outwardly of the proximal end of the wire receiving tubular structures  18  which are surrounded by a body of molded thermoplastic material  34 . The proximal ends of the movable and fixed parts of the cannula assembly  12  are then connected to movable and fixed parts respectively of the moving assembly  16 .  
         [0058]    It is now possible to effect a controlled progressive heating of the exterior periphery of the elongated heat shrinkable outer sleeve  39  starting at its distal end so that the distal end portion is first made to shrink and mold the thermoplastic material of the extensions of the tubular elements  28  into a molded body of thermoplastic material  34 ′, adhered relation to the exterior peripheries of the coextensive lengths of the wire receiving tubes  18 .  
         [0059]    The progressive heating of the next four inches of the elongated heat shrinkable tube  40  is such as to make the elongated heat shrinkable outer sleeve  39  to shrink but only to an extent sufficient to confine and contain the surrounded portions of the wire receiving tubes  18  and surrounding cores  41 .  
         [0060]    The progressive heating of the remainder of the elongated heat shrinkable outer sleeve  39  is accomplished at a temperature sufficient to shrink the elongated heat shrinkable outer sleeve  39  and mold the surrounded tubular elements  40 , as a molded body  45  of thermoplastic material into adhered relation to the surrounded exterior peripheries of the wire receiving tubes  18 .  
         [0061]    In accordance with one feature of the present invention, the fixed flexure elements  32  are biased to move into the opened condition thereof by an appropriate heat treatment while held in a position preferably beyond the normal opened position.  
         [0062]    It is noted that at the proximal end portion of the cannula assembly  12  of the subassembly, the three movable wire sections  22  extend outwardly of the proximal end of the wire receiving tubes  18  which are surrounded by a body of molded thermoplastic material. The proximal ends of the movable and fixed parts of the cannula assembly  12  are then connected to movable and fixed parts respectively of the moving assembly  16 .  
         [0063]    While the moving assembly  16  may assume any known configuration, one embodiment of a moving assembly  16 , constructed in accordance with the principles of the present invention, which may be utilized is shown in FIGS. 1, 3,  5  and  13 - 16 . As shown, the fixed part or fixed structure of the moving assembly  16  includes a cylindrical housing member  42  having a longitudinal slot  43  extending substantially therethrough from a distal or forward end thereof and a cap assembly generally indicated at  44 , fixed at the distal end of the housing member  42  which serves to connect the fixed part of the moving assembly  16  with the fixed part of the proximal end of the cannula assembly  12 . The movable part of the moving assembly  16  includes a slide structure, generally indicated at  46 , mounted within the cylindrical housing member  42  for longitudinal sliding movement in opposite directions.  
         [0064]    In accordance with the principles of the present invention, a motion transmitting mechanism, generally indicated at  48 , serves to connect the moving parts of the moving assembly  16  and cannula assembly  12 . In accordance with the principles of the present invention, the motion transmitting mechanism  48  is constructed and arranged to enable (1) a manual movement of the moving part of the moving assembly  16  in one direction through an opening stroke to effect movement of the movable part of the gripping and releasing mechanism  14  through an opening stroke into a stone receiving open position, and (2) a manual movement of the moving part of the moving assembly  16  in an opposite direction through a gripping stroke to effect movement of the movable part of the gripping and releasing mechanism  14  through a gripping stroke toward a closed limiting position to establish a gripping relation with a stone and (3) further a manual movement of the moving part of the moving assembly  16  toward the closed limiting position to effect the application of a limiting resiliently yielding force to the movable part of the gripping and releasing mechanism  14  to maintain the gripping relation with the stone.  
         [0065]    In accordance with the principles of the present invention, the slide structure  46  includes a releasable locking mechanism, generally indicated at  50 , which cooperates with structure of the housing member  42  to releasably lock the moving part of the moving assembly  16  against movement in the aforesaid one direction when the moving part has been moved a predetermined distance in the opposite direction beyond the gripping stroke to maintain the gripping relation by the applied limiting force without the necessity to maintain manual engagement of the moving part of the moving assembly  16 .  
         [0066]    Also in accordance with the principles of the present invention, the moving assembly  16  preferably includes a stop structure, generally indicated at  52 , configured and positioned in a normal operating position to determine a normally operable opening limiting position for the moving part of the moving assembly  16 . The stop structure  52  is operable to be moved out of the normal operation position thereof to enable the moving part of the moving assembly  16  to have an increased opening stroke under emergency conditions.  
         [0067]    The connection between the movable parts of the moving assembly  16  and the cannula assembly  12  includes an elongated metal tube  54  of hypodermic needle stock which forms the proximal end of the movable part of the cannula assembly  12 . As shown, the metal tube  54  preferably constitutes the inner tube of a pair of telescopic tubes which also includes an outer metal tube  56  forming the proximal end of the fixed part of the cannula assembly  12 .  
         [0068]    The inner metal tube  54  is configured to receive therein the outwardly extending proximal ends of the three movable wire sections  22  and to have the wire sections  22  fixedly secured with respect thereto. While the mode of securement could be by a mechanical fastener arrangement, a preferred mode is simply to allow a drop of a viscous adhesive to move within the tube  54  by capillary action into surrounding relation to the wire sections  22  therein so as to effect an adhesive fixed securement. The adhesive securement is preferably accomplished with the gripping and releasing mechanism  14  in the closed limiting position thereof and the inner metal tube  54  spaced from the proximal end of the fixed part of the cannula assembly  12  a distance determined by the increased operative stroke of the movable part of the moving assembly  16 .  
         [0069]    The connection between the fixed part of the moving assembly  16  and the fixed part of the cannula assembly  12  is accomplished after the aforesaid securement of the inner metal tube  54 . Initially, the outer metal tube  56  is moved rearwardly over the proximal end of the fixed part of the cannula assembly  12 . Preferably, the exterior surface of the outer metal tube  56 , which is exemplarily made of stainless steel, is sand blasted so that it will adhesively adhere to a heated plastic contacted therewith.  
         [0070]    As best shown in FIGS. 1, 3 and  5 , it is preferable that the outer metal tube  56  forms an insert in a molding operation which serves to form over a central portion of the outer metal tube  56  near its forward end a molded plastic body  58  constituting a part of the cap assembly  44 .  
         [0071]    The inner metal tube  54  is also preferably formed with a molded plastic body  60  of U-shaped cross-sectional configuration adhered to its rearward end which constitutes a part of the motion transmitting mechanism  48 .  
         [0072]    The slide structure  46  includes a central section  62  of generally inverted U-shaped cross-sectional configuration as best shown in FIGS. 14 and 15, with the legs of the U having exterior arcuate surfaces to conform with the interior cylindrical surface of the slotted cylindrical housing member  42 . The opposite ends of the central slide section  62  are integrally formed with forward and rearward end walls  64  and  66  respectively. The forward end wall  64  is centrally apertured to provide an opening  68  configured and positioned to slidably support the outer metal tube  56  therein.  
         [0073]    The slide structure  46  includes a forward section  70  which extends forwardly of the forward end wall  64 . The forward slide section  68  is of cylindrical configuration having an exterior periphery which slidably cooperates with the cylindrical interior periphery of the slotted cylindrical housing member  42 .  
         [0074]    The slide structure  46  also includes a rearward section  72  which includes a part of the releasable locking mechanism  50 . As best shown in FIGS. 1, 3,  5  and  13 , the releasable locking mechanism  50 , like the sections  62 ,  64  and  66  of the slide structure  46  is formed as a molded plastic part. The slide structure  46  including the part of the releasable locking mechanism  50  forms a two-piece molded structure. It is within the broadest aspects of the present invention to make this two-piece structure as one molded part.  
         [0075]    As shown in FIG. 13, the rearward slide section  72  is of U-shaped cross-sectional configuration and the associated part of the releasable locking mechanism  50  is in the form of a lever member generally indicated at  74 . The lever member  74  is pivotally connected with the rearward slide section  72  as by a pair of integral stub shaft elements  76  which snap into receiving openings formed in the central upper portion of the rearward slide section  72 .  
         [0076]    The lever member  74  includes a digitally engageable arm portion  78  extending forwardly and upwardly from the central transverse pivotal axis of the lever member  74  provided by the stub shaft elements  76 . The forward free end of the digitally engageable arm portion  78  extends upwardly through the slot A of the housing member  42  and overlies a ledge formation  80  integrally molded in the upper rearward portion of the central slide section  62 . The free end of the arm portion  72  includes upwardly and rearwardly facing thumb engaging surface  84  for moving the lever member  74  in a clockwise direction, as viewed in FIGS. 1, 3 and  5 , about its pivotal axis and the slide structure  46  forwardly within the housing member  42 .  
         [0077]    Formed integrally on the central slide section  62  forwardly of the ledge formation  80  is a digitally engageable hump shaped portion  86  extending upwardly through the slot  43  of the housing member  42 . The hump portion  86  provides an upwardly and forwardly facing thumb engaging surface  88  for moving the slide structure rearwardly within the housing member  42 .  
         [0078]    The lever member  74  includes an integrally rearwardly extending arm portion  90  having a forwardly facing locking surface  92  for releasably engaging a rearwardly facing locking surface  97  of a ramp element  96  formed integrally on the interior periphery of the housing member  42  as a part of the releasable locking mechanism  50 . The lever member  74  is biased to move into a locking position wherein the locking surfaces  92  and  94  are engaged by a spring arm  98  formed integrally thereon and extending forwardly and downwardly from the pivotal axis. A free end of the spring arm  98  engages the central portion of the U-shaped section of the rearward slide section and slides therealong as the spring arm  98  flexes during the pivotal movement of the lever member  74  between the locking position and a releasing position wherein the locking surfaces are disengaged. Instead of the integral spring arm  98 , a separate metal spring could be used.  
         [0079]    The central slide section  62  forms a part of the motion transmitting mechanism  48  which also includes a compression coil spring  100 . The coil spring  100  is initially assembled over the forward end of the inner metal tube  54  and then the forward end of the inner metal tube  54  is fed forwardly through the forward end wall opening  68  until the trailing surface of the U-shaped molded plastic body  60  on the inner metal tube  54  moves past the leading surface of the rearward end wall  66  and moves within the central slide section  62  into an operative position therein, as shown in FIGS. 1, 3 and  5 . As can be seen in the operative position, the trailing surface of the plastic body  60  and the leading surface of the rearward end wall  66  are in abutting engagement and the coil spring  100  is compressed between the molded plastic body  58  and forward end wall  64 .  
         [0080]    The proximal ends of the movable wire sections  22  extending from the distal end of the fixed part of the cannula assembly  12  are then inserted within the forward end of the inner metal tube  54  so that a predetermined space is left between the forward end of the inner metal tube and the proximal end of the fixed part of the cannula assembly  12 . The proximal ends of the movable wire sections are then fixed within the inner metal tube  54  by any suitable means, as for example, a drop of viscous adhesive can be fed to the forward end of the inner metal tube  54  and allowed to wick therein by capillary action and then allowed to cure or set. Epoxy is an exemplary adhesive.  
         [0081]    After the inner metal tube  54  has been assembled in the slide structure  46  and adhered to the proximal ends of the movable wire sections  22 , the outer metal tube  56  with its molded plastic body  58  is moved over the cannula assembly  12  into telescoping relation to the inner metal tube  54 . Here again, a drop of viscous adhesive, such as epoxy, serves to fix the outer metal tube  56  to the cannula assembly  12  in predetermined spaced relationship equal to the aforesaid increased opening stroke. This completes a subassembly wherein the lever member  74  is pivoted to the rearward slide section  72  which may be accomplished as a last step or before. The subassembly is then fed axially into the forward open end of the slotted cylindrical housing member  42  until a rearwardly facing end surface of the slide section  72  engages a forwardly facing stop surface  101  formed in the housing member  42 , as shown in FIG. 4.  
         [0082]    The molded plastic body  58  includes a projecting slot entering portion  102  which enters the forward end of the slot  43  in engaged relation to the slot defining surfaces as the axial movement of the subassembly proceeds. The molded plastic body  58  also includes a rearwardly facing arcuately shaped flat surface  104  which engages the forward end surface of the housing member  42  when the subassembly reaches its operative position. Next, a cap member  106  forming a part of the cap assembly  44  is fed axially over the cannula assembly  12  and into operative position. In its operative position, the cap member  106  abuttingly engages the molded plastic body and is fixed to the forward exterior periphery of the slotted housing member  42 . The securement as shown is a threaded securement although a snap action or glued securement could be utilized.  
         [0083]    It will be noted that the stop structure  52  includes a thin arcuate stop element  108  extending rearwardly from the slot entering portion  102  in a position to be engaged by a forwardly facing surface  110  of the slide structure  46  forming another part of the stop structure  52 . The axial position of the stop element  108  determines the normal opening stroke and its length determines the increased opening stroke. It is noted that the arcuate thin configuration of the stop element  108  enables it to be easily cut off by a scalpel or scissors when necessary.  
       Operation  
       [0084]    As previously indicated, the medical device  10  is made to cooperate with a scope. When used as a kidney stone extractor, typically, the scope will be entered into the kidney through the urinary canal. The medical device  10  with the gripping and releasing mechanism  14  and moving assembly  16  in the closed positions thereof, as shown in FIGS. 1 and 2, is fed through the central passageway of the scope. When the gripping and releasing mechanism  14  extends outwardly of the distal end of the passageway of the scope, the operator grasping the housing member  42  in one hand moves his thumb forwardly on the thumb engaging surface  84  of the digitally engageable arm position  82 . Since the slide structure  46  is restrained against forward movement by the interengagement of locking surfaces  92  and  94 , the arm portion  82  moves downwardly into engagement with the ledge formation  80  which effects a clockwise movement of the lever member  74  about its pivotal axis. The clockwise movement of the lever member  74  moves the stop surfaces  92  and  94  into a disengaged relationship and the spring arm  98  into a flexed or stressed relationship. With the stop surfaces  92  and  94  disengaged, the slide structure  46  can now move forwardly within the housing member  42  as the thumb pushes forwardly. The forward movement of the rearward end wall  66  of the slide structure  46  by virtue of its abutting relationship with the rearwardly facing surface of the inner metal tube molded plastic body  60  moves the inner metal tube  54  forward in telescopic relation into the outer metal tube  56  which is fixed to the housing member  42  and to the fixed part of the cannula assembly  12 . Since the movable wire sections  22  are fixed within the inner metal tube  54 , they, in turn, are moved forwardly. Since each movable wire section  22  is contained throughout its length by a wire receiving tube  18 , the distal end portions of the movable wire sections constituting the movable flexure elements  36  of the gripping and releasing mechanism  14  move outwardly of the distal ends of the wire receiving tubular structures  18 . When the slide structure  46  has been moved from the closed limiting position thereof forwardly toward its opened limiting position through an operative opening stroke, as shown in FIG. 4, the gripping and releasing mechanism will have been moved toward the open limiting position thereof into an expanded condition as defined by an annular series of transversely outwardly flexed fixed flexure elements  32  interconnected by an annular series of arcuately flexed portions of the movable flexure elements  36 . The extent of the operative opening stroke is dependent upon the size of the stone to be extracted, but is normally limited by the engagement of the slide structure  46  with the stop surface  110  of the stop element  108 , as shown in FIG. 4.  
         [0085]    With the gripping and releasing mechanism  14  in its expanded condition, as shown in FIG. 3, the physician can then manipulate the open gripping and releasing mechanism  14  into surrounding relation to the stone within the kidney to be extracted. As soon as this stone surrounding relationship is established, the physician engages a thumb on the thumb engaging surface  88  of the hump shape portion  86  of the slide structure  46  to pull the slide structure  46  rearwardly with the housing member  42 . The rearward movement of the slide structure  46  is transmitted to the inner metal tube  54  and hence movable wire sections  22  through the compressed coil spring  100  which is engaged between the forward end wall  64  and the inner tube molded plastic body  60 . The rearward movement of the proximal end portions of the movable wire sections  22  with the inner metal tube  54  causes the movable flexure elements  36  of the gripping and releasing mechanism to move through a gripping stroke during which the movable flexure elements  36  are moved inwardly into the fixed flexure elements  32  to progressively retract the gripping and releasing mechanism  16  from its expanded condition into gripping relation to the stone, as shown in FIG. 5.  
         [0086]    It will be noted that the strength of the coil spring is chosen so as to enable the physician to apply a digitized force in the gripping direction to effect an effective gripping relationship while limiting the transmission of an excessive digitized force to the movable wire sections  22  by yielding so as to allow continued rearward movement of the slide structure  46  unaccompanied by movement of the inner metal tube  54  and contained movable wire sections  22 . The yielding force is chosen as one which can be readily applied so that a continuous rearward movement of the slide structure  46  will take place after the gripping stroke to move the slide structure  46  into its closed limiting position where the spring arm  98 , stressed by the clockwise pivotal movement of the lever member  74  as the arm portion  90  rides up the ramp element  96 , biases the lever member  74  to pivot in a counter clockwise direction as the arm portion  90  becomes free to move downwardly to engage locking surfaces  92  and  94 . When the lever member  74  reaches this locking position, coil spring  100  has been compressed into a stressed condition transmitting a force to the inner metal tube and movable wire sections  22  which retains the movable flexure elements  36  of the gripping and releasing mechanism  16  in gripping relation to the stone. In this way, not only are the gripping forces which can be applied limited by a desirable gripping force releasably lockingly retained enabling the physician&#39;s hands to be released from the housing member  42  as the scope is withdrawn with the gripped stone in the gripping and releasing mechanism.  
         [0087]    After withdrawal, the gripped stone can be released by simply digitally moving forwardly on the thumb engaging surface  84  to expand the gripping and releasing mechanism  14  and release the stone, after which the slide structure  46  can be returned to its closed limiting position.  
         [0088]    When the gripping and releasing mechanism  14  is disposed in gripping engagement with a stone within the kidney and for some reason, it becomes desirable to release the stone and the operative opening stroke provided is insufficient to effect release, the physician can simply cut off the stop element  108  with a scalpel or scissors to provide an increased operative stroke which can be sufficient to effect release.  
         [0089]    Referring now more particularly to FIGS.  22 - 27 , there is shown therein a modified form of moving handpiece assembly, generally indicated at  128 , which can be utilized in lieu of the moving handpiece assembly  16 . The fixed part or fixed structure of the moving assembly  128  includes a pair of cooperating or mating housing half shell members  142 . The part of shell members  142  when mated together provide rearward exterior surfaces  143  defining a hand grip section, a central upper slot  144 , and a forward portion  145  which fixedly connects with a fixed part of the cannula assembly  12 . The movable part of the moving assembly  128  includes a slide structure, generally indicated at  146 , mounted within the mated housing shell members  142  for longitudinal sliding movement in opposite directions. The slide structure extends outwardly of the mated housing shell members  142  through a slot  144 ′ formed therein.  
         [0090]    In accordance with the principles of the present invention, a motion transmitting mechanism, generally indicated at  148 , serves to connect the moving parts of the moving assembly  128  and cannula assembly  12 . In accordance with the principles of the present invention, the motion transmitting mechanism  148 , as before with the motion transmitting mechanism  48 , is constructed and arranged to enable (1) a manual movement of the moving part of the moving assembly  128  in one direction through an opening stroke to effect movement of the movable part of the gripping and releasing mechanism  14  through an opening stroke into a stone receiving open position, and (2) a manual movement of the moving part of the moving assembly  128  in an opposite direction through a gripping stroke to effect movement of the movable part of the gripping and releasing mechanism  14  through a gripping stroke toward a closed limiting position to establish a gripping relation with a stone and (3) further a manual movement of the moving part of the moving assembly  128  toward the closed limiting position to effect the application of a limiting resiliently yielding force to the movable part of the gripping and releasing mechanism  14  to maintain the gripping relation with the stone.  
         [0091]    In accordance with the principles of the present invention, the slide structure  146  includes a releasable locking mechanism, generally indicated at  150 , which cooperates with structure of the mated housing shell members  142  to releasably lock the moving part of the moving assembly  128  against movement in the aforesaid one direction when the moving part has been moved a predetermined distance in the opposite direction beyond the gripping stroke to maintain the gripping relation by the applied limiting force without the necessity to maintain manual engagement of the moving part of the moving assembly  128 .  
         [0092]    Also in accordance with the principles of the present invention, the moving assembly  128  preferably includes a stop structure, generally indicated at  152 , configured and positioned in a normal operating position to determine a normally operable opening limiting position for the moving part of the moving assembly  128 . The stop structure  152  is operable to be moved out of the normal operation position thereof to enable the moving part of the moving assembly  128  to have an increased opening stroke under emergency conditions.  
         [0093]    As before, the connection between the movable parts of the moving assembly  128  and the cannula assembly  12  includes an elongated metal tube  154  of hypodermic needle stock which forms the proximal end of the movable part of the cannula assembly  12 . As shown, the metal tube  154  preferably constitutes the inner tube of a pair of telescopic tubes which also includes an outer metal tube  156  forming the proximal end of the fixed part of the cannula assembly  12 .  
         [0094]    The inner metal tube  154  is configured to receive therein the outwardly extending proximal ends of the three movable wire sections  22  and to have the wire sections  22  fixedly secured with respect thereto. While the mode of securement could be by a mechanical fastener arrangement, a preferred mode is simply to allow a drop of a viscous adhesive to move within the tube  154  by capillary action into surrounding relation to the wire sections  22  therein so as to effect an adhesive fixed securement. The adhesive securement is preferably accomplished with the gripping and releasing mechanism  14  in the closed limiting position thereof and the inner metal tube  154  spaced from the proximal end of the fixed part of the cannula assembly  12  a distance determined by the increased operative stroke of the movable part of the moving assembly  128 .  
         [0095]    The connection between the fixed parts of the moving assembly  128  and the cannula assembly  12  is accomplished after the aforesaid securement of the inner metal tube  154 . Initially, the outer metal tube  156  is moved rearwardly over the proximal end of the fixed part of the cannula assembly  12 .  
         [0096]    As best shown in FIGS. 1, 3 an  5 , it is preferable that the outer metal tube  156  is used an insert in a molding operation which serves to form over a portion of the outer metal tube  156  at its forward end a molded plastic body  158 . A tube  159  is then preferably heat shrunk in a position to adhere to the exterior surface of the plastic body  158  and an adjacent exterior surface of the sleeve  40  defining the proximal fixed portion of cannula assembly  12 .  
         [0097]    The inner metal tube  154  is also preferably formed with a molded plastic body  160  of piston-like configuration adhered to its rearward end which constitutes a part of the motion transmitting mechanism  148 .  
         [0098]    As best shown in FIGS. 26 and 27, the slide structure  146  includes a main central section  162  of generally rectangular exterior configuration to conform with the interior rectangular shaped surfaces of the housing shell members  142  when mated so as to enable the slide member  146  to be moved with a rectilinear movement forwardly and rearwardly therewithin. The slide member  146  opens forwardly from its rear end so as to form a forward cylindrical chamber  164  closed at its forward end by a forward end wall  166 . The forward end wall  166  is centrally apertured to provide an opening  168  configured and positioned to slidably support the outer metal tube  156  therein.  
         [0099]    The slide member  146  includes a rear section  170  having an upper slot  172  extending throughout the same and an interior configuration, which, as best shown in FIG. 27, is rectangular.  
         [0100]    As best shown in FIGS.  22 - 24 , the releasable locking mechanism  150  includes a pusher member  174 , having a rectangular exterior configuration which slidably fits within the interior configuration of the rearward section  170  of the slide member  146  for movement therewith longitudinally and with respect thereto in forward and rearward directions.  
         [0101]    It will be understood that slide member  146  is mounted in the position shown with respect to the outer metal tube  156  and piston body  160  prior to affixing the inner metal tube  154  to the proximal ends of the movable wire sections  22  as aforesaid. In addition, a coil spring  176  is initially fed over the outer metal tube  156  to engage rearwardly of the forward end wall  166  of the slide member  146 . Coil spring  176  forms a part of the motion transmitting mechanism  148 .  
         [0102]    The pusher member  174  is slidable within the rearward section  170  from the rear. However, before effecting this connection, a second coil spring  177  is fed within the hollow rearward section  170  so as to engage at its forward end with the central section  162  of the slide member  146  and at its rearward end within forwardly facing recesses in the pusher member  174 .  
         [0103]    The pusher member  174  includes a digitally engageable portion  178  extending upwardly through the upper slot  172  and the slot  144  provided by the mating housing shell members  142 .  
         [0104]    Formed integrally on the central slide section  162  extending upwardly through the slot  144  provided by the mated housing shell members  142  is a digitally engageable puller portion  180 . The puller portion  180  provides an upwardly and forwardly facing thumb engaging surface for moving the slide member  146  rearwardly within the mated housing shell members  142 .  
         [0105]    The releasable locking mechanism  150  also includes a locking element, generally indicated at  182 , which, as shown, is in the form of a rivet or separable two headed pin fastener. The locking element  182  includes a fixed head  184  formed on one end of a pin or shaft  186  and a second head  188  which is either after formed, as a conventional rivet head, or is capable of screwing into an internal thread in the opposite end of the pin  186 .  
         [0106]    The shaft  186  of the locking element  182  is arranged to extend through a pair of aligned longitudinally extending slots  190  having depending recesses  192  at their rear ends formed in the mating housing shell members  142 , a pair of aligned vertically elongated openings  194  in the side walls of the rearward section  170  of the slide member  146  and a diagonal opening  196 . The diagonal slot  196  could be straight, however as shown, it is of arcuate configuration defined on an upper side by a downwardly facing arcuate surface  198  and on a lower side by an upwardly facing arcuate surface  200 .  
         [0107]    The components of the motion transmitting mechanism  148  and the components of the releasable locking assembly  150  are assembled in the manner previously indicated and then mounted with respect to one of the housing shell members  142  having the locking element shaft  186  extending through the recess  192  of the slot  190  therein with the fixed head  184  in engagement with the adjacent exterior surface thereof. The mounting is accomplished by simply moving the components in the position shown in FIG. 22 laterally so that the locking element shaft  186  extends through the lower portion of the vertically elongated openings  194  in the slide member  146  and the forward end of the arcuate opening  196  in the pusher member  174 . The other housing shell member  142  can then be moved into mating relation after which the second head  188  is added to the free end of the shaft  186 . Finally, it is preferable that the two mated housing shell members  142  are heat fused together.  
         [0108]    The moving handpiece assembly  128  is operated like the moving handpiece assembly  16  previously described except that the initial unlocking movement is accomplished by a rectilinear push forward of the pusher member  174  rather than a pivotal movement of the pivoted pusher member  74 .  
         [0109]    With respect to the locking action of the pusher member  174 , it will be noted that the locking pin  186  is held within the recesses  192  of the slots  190  and the lower portion of the vertically elongated openings  194  by virtue of the engagement of the section of downwardly facing arcuate surface  198  at the forward end of the opening  196 , which, in turn, is held in that position by the strength of coil spring  177  biasing the pusher member  174  rearwardly.  
         [0110]    When the pusher member  174  is digitally moved forward by the operator&#39;s thumb pushing on pusher portion  178 , the pusher member  174  is allowed to move forwardly by the compression of the coil spring  177 . As the pusher member  174  moves forward, the upwardly facing arcuate surface  200  of the pusher member opening  196  engages the locking pin  186  and cams it upwardly so that it moves to the upper portion of the vertically elongated openings  194  and into alignment with the slots  190 . When this condition is reached, as shown in FIG. 23, the surface defining end the rearward end of the slot  196  of the pusher member  174  engages the pin  186  whose longitudinal movement results in a longitudinal movement of the slide member  146 . In this position, it is preferable that the two thumb engaging portions  177  and  180  do not meet in such a way as to pinch the operator while it is desirable that the pusher almost engage if not engage the piston  160 .  
         [0111]    Once the pusher member  174  has reached this unlocked position shown in FIG. 23, continued forward movement will move the slide member  146  forward with respect to the mated housing shell members  142  and the inner metal tube  154  carrying the movable wire sections  22  forward with respect to the fixedly retained outer metal tube  156 . It will be noted that when the operator releases the push on the pusher member  174 , the coil spring  177  is ineffective to move the pusher member  174  rearwardly because the engagement of the locking pin  186  with the surfaces  200  defining the lower extent of the slot  194  prevents the upper arcuate surfaces  198  from camming the pin  186  downwardly. However, as soon as the slide member  146  is returned to its starting position and the locking pin  186  is moved in slot  190  over recess  192 , coil spring  177  becomes effective to move the pusher member  174  rearwardly because arcuate surface  198  can now move the pin  186  downwardly into the recess  192 .  
         [0112]    Referring now more particularly to FIG. 28, there is shown thereon a modified wire receiving tubular assembly, generally indicated at  212 , which can be utilized in lieu of the assembly provided by the series of tube  18 , coils  41 , tubular elements  40  and outer sleeve  39 . The tubular assembly  212  includes a series of relatively short tubular structures  214  in the form of composite tubes (e.g. 4½ inches), a slightly shorter heat shrinkable sleeve  216 , preferably made of irradiate crosslinked polyethylene, and a relatively long three lumen extrusion structure  218  preferably made of PET.  
         [0113]    Each tubular structure  214  is formed of a metal coil  220  of a construction similar to the coils  41  previously described. A short distal fixed flexure element defining portion of each coil  220  is covered with a heat shrinkable sleeve  222  preferably made of an elastomeric material as, for example, Pebax®. The remaining proximal portion of each coil  220  is coated, as indicated at  224 , with a more longitudinally stable material, as, for example, polyimide.  
         [0114]    The coated proximal end portions of the coils  220  are inserted within distal end portions of lumens  226  formed in the extrusion structure  218  and then suitably secured therein as by gluing or otherwise.  
         [0115]    Next, the elastomeric material covered distal end portions of the coils  120  are assembled with movable wire sections  22 , flattened and abraded fixed wire sections  24 , tubular elements  28  and heat shrinkable sleeve  30  in the manner previously described.  
         [0116]    It will be noted that the lumens  226  of the extrusion structure  218  serve to contain and keep oriented the movable wire sections  22  while this assembly is carried out. The longitudinal extent of the coils  220  is sufficient to enable the person performing the assembly to effect the linear angular displacements of the distal wire ends necessary to complete the assembly.  
         [0117]    After this assembly is completed, the formed flexure elements  32  are fixed together by first moving the extruded proximal end portions of the tubular elements  28  together and then extending (1) the distal end portion of the heat shrinkable sleeve  216  over the assembled tubular element end portions and (2) the proximal end portion of the heat shrinkable sleeve  216  over the distal end portion of the extrusion structure  218 . Heat is then applied progressively to the exterior of the heat shrinkable sleeve  216  starting at the distal end portion thereof to shrink the same and mold the softened thermoplastic material of the tubular elements  28  into adhered relation to the exterior peripheries of the distal end portions of the coated portions of the coils  220 . The heating progresses through the main central portion of the sleeve  216  so as to reduce it to confine the contained coated coils  220  but in an non-adhered relationship. The heating progresses finally to the proximal end portion of the sleeve  216  which is shrunk into adhered relation to the exterior surface of the extrusion structure  218 .  
         [0118]    The modification of FIG. 28 is simpler to assemble. The use of elastomeric material covered coils rather than tubes  18  as part of the fixed flexure elements  32  enables a greater amount of self bias to be imparted to the fixed flexure elements  32  during heat treatment since the covered coils  41  do not resist the bias to the same extent as the polyimide tubes  18 . On the other hand, the PET extrusion structure  118  and the combination of the polyethylene sleeve  216  and polyimide coated sections of coils  220  provide a desired comparable longitudinal stability and lateral flexibility.  
         [0119]    Referring now more particularly to FIG. 29, there is shown therein another modification of the fixed tubular structure of the cannula assembly  12  embodying the principles of the present invention. This modification involves substituting for the three lumen tubular member  218 , a single lumen tubular member, generally indicated at  228 . The single lumen tubular member is in the form of a composite laminate which includes a central reinforcing braid  230  sandwiched between inner and outer tubular layers  232  and  234  of a suitable plastic material.  
         [0120]    An exemplary material for the braid  230  is stainless steel or Kevlar®. The plastic material of the layers  232  and  228  can be a wide variety of different materials, such as polyethylene, polyester, nylon, as preferred material being polytetraflouroethylene for its favorable low friction characteristics.  
         [0121]    When the single lumen tubular member  228  is used, the integral extensions of the movable wire sections  22  are extended within the single lumen of the member in side by side relation. While this construction is within the contemplation of the invention, it is preferred to gather a main proximal portion of the side by side wire sections  22  into abutting relation and adhere them in abutting relation by heat shrinking a heat shrinkable sleeve or tube of a suitable plastic material. The sleeve begins at a distal point space in the proximal direction from the proximal ends of the tubes  214  a distance sufficient to accomplish the movement of the movable cannula structure required to open the gripping and releasing mechanism  14  to the maximum extent. At the proximal ends of the three movable wire sections  22 , a piston rod section  236  provides a continuation of the movable cannula structure which is connected by heat shrinking the heat shrinkable sleeve in surround relation thereto. The heat shrinkable sleeve may be formed of a wide variety of plastic materials, such as (polyethylene, polyester, nylon, a preferred material being polytetraflourethylene for its desirable frictionless characteristics.  
         [0122]    The heat shrinkable sleeve is shown in heat shrunken condition as a heat shrunken sleeve  238  in FIG. 30 disposed in surrounding relation adhered to the movable wire sections  22  and the piston rod section  236 .  
         [0123]    The piston rod section  236  extends beyond the proximal end of the heat shrunken sleeve  238  and has a spring biased piston member  240  formed integrally at its proximal end. Preferably, the entire integral part comprising the piston rod section  236  and piston member  240  is formed of metal, e.g. stainless steel. It is connected into (1) the handpiece assembly  16  in place of the inner metal tube  56  and piston element. The single lumen tubular member  228  is disposed in surrounding relation to the heat shrunken sleeve  238 . The proximal end portion of the single lumen member  228  is connected in (1) the handpiece assembly  16  in place of the outer metal tube  56  and (2) the handpiece assembly  128  in place of the outer metal tube  186 .  
         [0124]    It is also within the contemplation of the present invention to utilize the slidably cooperating single lumen tubular member  228  and heat shrunken sleeve  238  as the entire fixed and movable parts of the cannula assembly  12 . This modification involves simply the elimination of the covered proximal portions  224  of the coils  220  and spacing the distal end of the heat shrunken sleeve  238  from the proximal ends of the elastomeric covered coils  220 - 222  at the proximal end of the joint of the gripping and releasing mechanism  14 .  
         [0125]    In this embodiment, the distal end portion of the single lumen tubular member  228  enters into the joint at the proximal end of the gripping and releasing assembly  14  by first inserting the distal end portion of the single lumen tubular member  228  over the extending tubular elements  28  and then heat shrinking a short heat shrinkable tube (not shown) thereover so that the distal end of the single lumen tubular member  228  molds the soften thermoplastic material in adhered contact as aforesaid. Thereafter, the heat shrunken tube (not shown) is stripped from the joint in accordance with known procedures.  
         [0126]    In this embodiment, as well as the one shown in FIG. 2, the entire tubular structures  214  or the proximal portions  220 - 224  thereof could be replaced by polyimide or Peek tubes.  
         [0127]    It thus will be seen that the objects of this invention have been filly and effectively accomplished. It will be realized, however, that the foregoing preferred embodiments of the present invention have been shown and described for the purposes of illustrating the structural and functional principles of the present invention and are subject to change without departure from the spirit and scope of the appended claims.