Abstract:
A surgical instrument and method for facilitating the capture of objects during surgery are provided. The surgical instrument comprises a flexible tube having a proximal tube end and a distal tube end, the flexible tube defining a cable passageway and being configured for insertion of at least a distal portion of the flexible tube into a body cavity of a patient. The surgical instrument further comprises a flexible cable having a proximal cable end and a distal cable end. At least a portion of the flexible cable is slidably disposed in the cable passageway. A snare loop having a loop member is attached to the distal cable end. The snare loop and the cable are adapted so that the snare loop can be selectively retracted within the cable passageway by sliding the flexible cable proximally within the cable passageway. The snare loop and the cable are also adapted so that at least a portion of the snare loop can be selectively extended from the distal tube end by sliding the flexible cable distally within the cable passageway. The loop member is adapted for selectively encircling and engaging at least a portion of an object in the body cavity. The system also comprises a steering tether having a proximal tether end and a distal tether end. The distal tether end is attached to the loop member so that application of a tensile force to the proximal tether end causes the snare loop to deform in a predetermined manner, thereby facilitating a maneuvering of the snare loop.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates generally to surgical instruments and more particularly to instruments such as snares that may be used for grasping and removing material during surgery.  
           [0002]    During surgery, there is often a need for the collection and removal of tissue specimens such as polyps or other material from a body cavity of the patient. The removal of such tissue is often accomplished through the use of a snare device or slip-knotted suture loop that is inserted into the patient through a cannula. The snare device is generally mounted to the end of a cable slidably disposed within a flexible tube. The user of the snare device must maneuver the end of the flexible tube and cable through the body cavity, which may have a number of convolutions such as in the case of an intestinal cavity. The snare must then be maneuvered so as to surround the material to be grasped and then cinched around the material, typically using an external actuation mechanism.  
           [0003]    The maneuverability of the snare device is generally limited to motion resulting from extension or retraction of the snare from the end of the flexible tube, extension or retraction of the flexible tube and the cable/rod and, under certain circumstances, rotation of the flexible tube and the cable/rod. This limited maneuverability can make it difficult to position the snare around the material of interest, particularly in areas where there is little room for repositioning of the tube and/or cannula.  
         SUMMARY OF THE INVENTION  
         [0004]    There is accordingly a need for a surgical instrument snare with an additional manipulation capability that facilitates the maneuvering of the snare to encircle material within a body cavity of a patient.  
           [0005]    Accordingly, an embodiment of the present invention provides a surgical instrument for facilitating the capture of objects during surgery. The surgical instrument comprises a flexible tube having a proximal tube end and a distal tube end, the flexible tube defining a cable passageway and being configured for insertion of at least a distal portion of the flexible tube into a body cavity of a patient. The surgical instrument further comprises a flexible cable having a proximal cable end and a distal cable end. At least a portion of the flexible cable is slidably disposed in the cable passageway. A snare loop having a loop member is attached to the distal cable end. The snare loop and the cable are adapted so that the snare loop can be selectively retracted within the cable passageway by sliding the flexible cable proximally within the cable passageway. The snare loop and the cable are also adapted so that at least a portion of the snare loop can be selectively extended from the distal tube end by sliding the flexible cable distally within the cable passageway. The loop member is adapted for selectively encircling and engaging at least a portion of an object in the body cavity. The system also comprises a steering tether having a proximal tether end and a distal tether end. The distal tether end is attached to the loop member so that application of a tensile force to the proximal tether end causes the snare loop to deform in a predetermined manner, thereby facilitating a maneuvering of the snare loop.  
           [0006]    Another aspect of the invention provides a surgical instrument for facilitating the capture of objects during surgery. The surgical instrument comprises a snare control module having a body with a distal body end and a proximal body end. The snare control module also has a control slide with a passage formed therein for slidable disposition of at least a portion of the body therethrough. The surgical instrument further comprises a flexible tube having a proximal tube end attached to the distal end of the body and a distal tube end. The flexible tube defines a cable passageway and is configured for insertion of at least a distal portion of the flexible tube into a body cavity of a patient. The surgical instrument still further comprises a flexible cable having a proximal cable end and a distal cable end. At least a portion of the flexible cable is slidably disposed in the cable passageway. The proximal cable end is connected to the control slide so that movement of the control slide toward the proximal body end causes proximal movement of the flexible cable within the cable passageway and movement of the control slide toward the distal body end causes distal movement of the flexible cable within the cable passageway. The instrument also comprises a snare loop having a loop member attached to the distal cable end. The snare loop and the cable are adapted so that the snare loop can be selectively retracted within the cable passageway by sliding the flexible cable proximally within the cable passageway and so that at least a portion of the snare loop can be selectively extended from the distal tube end by sliding the flexible cable distally within the cable passageway. The loop member is adapted for selectively encircling and engaging at least a portion of an object in the body cavity. The surgical instrument further comprises at least one steering tether having a proximal tether end and a distal tether end. The distal tether end of each of the at least one steering tether is attached to the loop member so that application of a tensile force to the proximal tether end causes the snare loop to deform in a predetermined manner, thereby facilitating a maneuvering of the snare loop.  
           [0007]    Yet another aspect of the invention provides a method of securing an object disposed within a body cavity of a patient using a surgical instrument of the invention. The surgical instrument has a flexible tube having distal and proximal tube ends and defining a cable passageway, a flexible cable having proximal and distal cable ends and being slidably disposed in the cable passageway, a snare loop attached to the distal cable end, the snare loop and the cable being adapted so that the snare loop can be selectively retracted within the cable passageway by sliding the flexible cable proximally within the cable passageway and so that at least a portion of the snare loop can be selectively extended from the distal tube end by sliding the flexible cable distally within the cable passageway, and a steering tether having a proximal tether end and a distal tether end, the distal tether end being attached to the snare loop. The method comprises inserting the distal end of the flexible tube and the snare loop into the body cavity through a cannula while retaining the proximal tether end outside the body cavity. The method further comprises maneuvering the distal end of the flexible tube through the body cavity until the snare loop is positioned adjacent the object. The method still further comprises placing the steering tether in tension by pulling on the proximal tether end and applying a tensile force to the steering tether sufficient to cause the snare loop to deform in an efficacious manner to facilitate positioning of the snare loop around at least a portion of the object. The method still further comprises maneuvering the snare loop to encircle at least a portion of the object.  
           [0008]    Other objects and advantages of the invention will be apparent to one of ordinary skill in the art upon reviewing the detailed description of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a partially sectioned view of a surgical instrument according to an embodiment of the invention;  
         [0010]    [0010]FIG. 2 is a perspective view of a snare loop of the surgical instrument illustrated in FIG. 1;  
         [0011]    [0011]FIG. 3 is a view of the surgical instrument of FIG. 1 partially inserted into a body cavity through a cannula;  
         [0012]    [0012]FIG. 4 is a view of the surgical instrument of FIG. 3 with its snare loop deployed;  
         [0013]    [0013]FIG. 5 is a perspective view of a snare loop of a surgical instrument according to the invention illustrating a step in a sequence of encircling a polyp with the snare loop;  
         [0014]    [0014]FIG. 6 is a perspective view of a snare loop of a surgical instrument according to the invention illustrating another step in a sequence of encircling a polyp with the snare loop;  
         [0015]    [0015]FIG. 7 is a perspective view of a snare loop of a surgical instrument according to the invention illustrating another step in a sequence of encircling a polyp with the snare loop;  
         [0016]    [0016]FIG. 8 is a perspective view of a snare loop of a surgical instrument according to the invention illustrating another step in a sequence of encircling a polyp with the snare loop;  
         [0017]    [0017]FIG. 9 is a partially sectioned view of a surgical instrument according to an embodiment of the invention;  
         [0018]    [0018]FIG. 10 is a perspective view of a snare loop of the surgical instrument illustrated in FIG. 9;  
         [0019]    [0019]FIG. 11 is a view of the surgical instrument of FIG. 9 partially inserted into a body cavity through a cannula;  
         [0020]    [0020]FIG. 12 is a view of the surgical instrument of FIG. 11 with its snare loop deployed;  
         [0021]    [0021]FIG. 13 is a perspective view of a snare loop of a surgical instrument according to the invention illustrating a step in a sequence of encircling a polyp with the snare loop;  
         [0022]    [0022]FIG. 14 is a perspective view of a snare loop of a surgical instrument according to the invention illustrating another step in a sequence of encircling a polyp with the snare loop;  
         [0023]    [0023]FIG. 15 is a perspective view of a snare loop of a surgical instrument according to the invention illustrating another step in a sequence of encircling a polyp with the snare loop;  
         [0024]    [0024]FIG. 16 is a perspective view of a snare loop of a surgical instrument according to the invention illustrating another step in a sequence of encircling a polyp with the snare loop;  
         [0025]    [0025]FIG. 17 is a partially sectioned view of a surgical instrument according to an embodiment of the invention; and  
         [0026]    [0026]FIG. 18 is a perspective view of a snare loop of the surgical instrument illustrated in FIG. 17.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    The present invention provides a surgical instrument that includes a steering tether that allows a surgeon to remotely manipulate a snare loop to maneuver the snare loop in position around an object or tissue inside a body cavity of a patient.  
         [0028]    [0028]FIGS. 1 and 2 illustrate a surgical instrument  100  according to an embodiment of the invention. The surgical instrument  100  includes a snare control module  110  that is used to control the deployment and retraction of a snare loop  150  from a flexible tube  132 . The snare loop  150  is formed from a resilient loop member  152 . The loop member  152  has first and second ends  154 ,  156  that are attached to a flexible cable  134  at its distal end  138 . The resilient loop member  152  may take the form of a wire, cable or band formed from metal or a resilient surgical plastic. The resilient loop member  152  may also be a suture material attached to a biasing member or material. The resilient loop member  152  may be formed from an electrically conductive material for use as a cauterization loop. The loop member  152  may be attached to the cable  34  in any conventional manner such as bonding or welding.  
         [0029]    The flexible cable  134  is slidably disposed within a flexible tube  132  formed from a polymer or other material suitable for use in surgical applications. The flexible tube  132  has an inside diameter sized to accommodate the cable  134  and the snare loop  150 . In particular, the tube  132  is sized so that the snare loop  150  can be easily retracted into the distal end  133  of the tube  132  when the cable  134  is moved proximally relative to the tube  132  and extended out of and from the tube  132  when the cable is moved distally relative to the tube  132 .  
         [0030]    The snare loop  150  is formed so that when freed from the flexible tube  132 , it will form a substantially elliptical loop that can be used to encircle an object. As the ends  154 ,  156  of the resilient loop member  152  are drawn into the flexible tube  132 , the loop member  152  is cinched to a smaller and smaller loop. If an object is encircled by the loop member  152 , the loop member  152  can be tightened around the object to secure the snare loop  150  to the object. If no object is encircled, the snare loop  150  may be drawn within the flexible tube  132 .  
         [0031]    The loop member  152  may be formed so as to include an extension  158  that extends outward from the distal end of the elliptical loop formed by the loop member  152 . Such an extension can be used to facilitate the capture and retrieval of certain objects.  
         [0032]    The snare control module  110  may be used to control the retraction and extension of the snare loop  150  from the tube  132 . The snare control module  110  has a generally cylindrical body  112 , a control slide  122 , an actuation rod  128  and a tube connector  130 . The body  112  of the snare control module  110  is formed by two frame members  114 ,  116  and a proximal end portion  118 . The frame members  114 ,  116  and the end portion  118  may be integrally formed into a single body structure. The frame members  114 ,  116  define a central frame opening  117  that runs diametrically through the body  112 .  
         [0033]    The control slide  122  has a central portion  123  having a cylindrical passage  125  formed therethrough. The cylindrical passage  125  is sized to slidably accommodate the body  112  within the cylindrical passage  125 . This allows the control slide  122  to be reciprocated along the body  112 .  
         [0034]    The proximal end  135  of the flexible tube  132  is attached to the distal end of the body by a hollow, cylindrical connector  130 . Alternatively, the tube  132  may have a flange (not shown) at its proximal end  135  that can be used to hold the proximal end  135  in place within the connector  130 . The connector  130  may be attached to the body  112  by internal threads configured to mate with external threads on the frame members  114 ,  116 .  
         [0035]    An actuation rod  128  is attached at one end to the proximal end  136  of the cable  134  and at its other end to an actuation rod pin  129  attached to the central portion  123  of the control slide  122 . The actuation rod pin  129  is positioned diametrically across the cylindrical passage  125  within the central frame opening  117  so that it does not impede the reciprocal motion of the control slide  122 . When the control slide  122  is moved toward the proximal end of the body  112 , the actuation rod  128  also moves in this direction, which, in turn, moves the proximal end  136  of the cable  134  proximally relative to the flexible tube  132 . When the control slide  122  is moved away from the proximal end of the body  112 , the actuation rod  128  moves the proximal end  136  of the cable  134  distally relative to the flexible tube  132 .  
         [0036]    The reciprocal motion of the control slide  122  can thus be used to control the deployment of the snare loop  150  from and the retraction of the snare loop into the distal end  133  of the flexible tube  132 . Moving the control slide  122  distally causes the snare loop  150  to be extended from the flexible tube  132 . Moving the control slide  122  proximally causes the withdrawal of the snare loop  150  toward and into the flexible tube  132 .  
         [0037]    To facilitate one hand control of the reciprocal motion of the control slide  122 , finger rings  124 ,  126  may be attached to the central portion  123  of the control slide  122  and a thumb ring  120  may be attached to the proximal portion  118  of the body  112 .  
         [0038]    It will be understood by those having ordinary skill in the art that other mechanisms could be used in the snare control module  110  without departing from the scope and spirit of the present invention. Such mechanisms may include, for example, slide actuators without finger rings and actuators configured for use in electro-cautery.  
         [0039]    The surgical instrument  100  also includes a steering tether  160  that can be used to assist in maneuvering the snare loop  150 . The steering tether  160  has a distal end  164  that is attached to the loop member  152  and a proximal end  162  that is passed out of the patient&#39;s body. The distal end  164  of the steering tether  160  may be attached to the loop member  152  anywhere around the circumference of the loop formed by the loop member  152 . In the embodiment illustrated in FIGS. 1 and 2, the distal end  164  of the steering tether  160  is attached at the distal-most point on the loop member  152 . As will be discussed, hereinafter, this positioning of the tether attachment is particularly useful in assisting the surgeon in maneuvering the snare loop  150  over an object such as a polyp.  
         [0040]    The steering tether  160  may be formed from any thread-like structure including but not limited to thread, wire, cable and chain. The steering tether  160  may be formed from any suitable material including but not limited to steel or other metal, polymeric materials such as nylon, and twisted cotton or other textile materials.  
         [0041]    The proximal end  162  of the steering tether  160  may be placed and/or attached to any arrangement that facilitates the grasping of the steering tether  160  at or near the proximal end  162  to apply tension to the tether  162 . For example, the proximal end  162  may be attached to a ring or other type of handle, tied to a structure external to the patient, or attached to the snare control module  110  in any conventional manner. The proximal end  162  may also be left as a free end for a surgeon to tie off when and if desired.  
         [0042]    Turning now to FIGS. 3 and 4, the flexible tube  132  and the snare loop  150  may be introduced into a body cavity  14  through the lumen  52  of a cannula  50 . The body cavity  14  is defined by first and second tissue walls  10  and  16 . The cannula  50  has been inserted through an opening  12  in the first tissue layer  10 . The distal end  133  of the flexible tube  132  may be passed through the cannula  50  into the cavity  14  with the snare loop  150  retracted within the tube  132  as shown in FIG. 3. In this configuration, the distal end  164  of the steering tether  160 , which is attached to the snare loop  150  is also withdrawn within the tube  132 . When the tube  132  is inserted through the lumen  52 , the proximal end  162  of the steering tether  160  is held so that the distal portion of the steering tether  160  is passed through the lumen  52  along with the tube  132 . The proximal end  160  remains outside of the body cavity  14  and the cannula  50 .  
         [0043]    Under certain circumstances, it may be advantageous or necessary to allow the full length of the steering tether  160  to be inserted into the cavity  14 . This leaves the proximal end  162  of the steering tether  160  inside the body cavity  14  where it can be later grasped to apply tension to the steering tether  160 .  
         [0044]    The tube  132  and the cable  134  are formed so as to be sufficiently flexible to pass through any curves in the cavity  14  that may be encountered as the tube  132  is inserted. Once the tube  132  has been inserted and positioned near the area of interest, the control slide  122  of the snare control module  110  can be moved in the distal direction relative to the body  112  to cause the snare loop  150  to be extended as shown in FIG. 4. It will be understood that, depending on the relative sizes of the snare loop  150  and the cannula lumen  52 , it may be possible to insert the tube  132  through the cannula  50  with the snare loop  150  already deployed. In either case, the snare loop  150  and the steering tether  160  may be positioned within the cavity  14  as shown in FIG. 4.  
         [0045]    FIGS.  5 - 8  illustrate a sequence by which the snare loop  150  can be used to encircle a polyp  18  attached to the lower tissue wall  16 . As initially deployed from the tube  132 , the steering tether  160  is relatively slack and the snare loop  150  is at a level where it cannot be positioned over the top of the polyp  18  (FIG. 5). This problem can occur as a result of the geometry of the cavity  14  and the stiffness of the tube  132 . The steering tether  160 , however, provides a way of deforming the snare loop  150  to overcome the problem. By pulling on the proximal end  162  of the steering tether  160 , a surgeon can place the steering tether  160  in tension. As shown in FIG. 6, the tensile force transmitted through the steering tether  160  causes the snare loop  150  to be deformed so that the distal portion of the snare loop member  152  may be raised above the level of the polyp as shown in FIG. 6. With the snare loop  150  raised, the tube  132  can then be translated further into the cavity  14  to position the snare loop  150  over the polyp  18  as shown in FIG. 7. The surgeon can then release the tension in the steering tether  160  to allow the snare loop  150  to resume its shape and encircle the polyp  18  as shown in FIG. 8. The snare loop  150  can then be cinched around the polyp  18  by moving the control slide  122  proximally relative to the body  112  of the snare control module  110 . The snare loop  150  could be removed from the polyp  18  by reversing the above procedure.  
         [0046]    This procedure and the steering tether  160  provide an extra degree of maneuverability of the snare. However, when the tube  132  is extended a long distance from the distal end of the cannula  50  or when the tube  132  has been passed through a series of bends in the cavity  14 , it may be difficult to establish the necessary tension on the steering tether  160  or to assure that the tensile force is aligned in the desired direction.  
         [0047]    The present invention therefore provides an alternative configuration as illustrated by the surgical instrument  200  shown in FIGS. 9 and 10. The snare control module  110  and the snare loop  150  are substantially unchanged in this configuration. The surgical instrument  200 , however, includes a steering tether  260  that is slidably disposed through the flexible tube  132  along with the cable  134 . The tube  132  and, in particular, the interior diameter of the passage through the tube  132  may be sized so that the cable  134  and the steering tether  260  can be moved substantially independently within the tube  132 . As shown in FIG. 10, the steering tether  260  passes out of the distal end  133  of the tube  132  along side the cable  134 . In a manner similar to that described above, the distal end  264  of the steering tether  260  is attached to the loop member  152  so that tension applied to the steering tether  260  will cause the loop member  152  to be deformed.  
         [0048]    As shown in FIG. 9, the steering tether  260  passes through the proximal end  135  of the tube  132  and through the connector  130  into the opening  117  between the frame members  114 ,  116 . The proximal end  262  of the steering tether  260  can be thus be extended out from the body  112  of the snare control module  110  and may be secured in any of the above-described ways or may be left as a free end for a surgeon to tie off.  
         [0049]    Turning now to FIGS. 11 and 12, the flexible tube  132  and the snare loop  150  of the surgical instrument  200  may be introduced into a body cavity  14  through the lumen  52  of a cannula  50 . The body cavity  14  is again defined by first and second tissue walls  10  and  16  and the cannula  50  is disposed through an opening  12  in the first tissue layer  10 . The distal end  133  of the flexible tube  132  may be passed through the cannula  50  into the cavity  14  with the snare loop  150  retracted within the tube  132  as shown in FIG. 11. In this configuration, the distal end  264  of the steering tether  260 , which is attached to the snare loop  150  is also withdrawn within the tube  132  so that none of the steering tether  260  extends out from the distal end  133  of the tube  132 . The tube  132  can thus be easily inserted through the lumen  52  of the cannula  50  into the cavity  14 .  
         [0050]    Once the tube  132  has been inserted and positioned near the area of interest, the control slide  122  of the snare control module  110  can be moved in the distal direction relative to the body  112  to cause the snare loop  150  to be extended as shown in FIG. 12. It will be understood that, depending on the relative sizes of the snare loop  150  and the cannula lumen  52 , it may be possible to insert the tube  132  through the cannula  50  with the snare loop  150  already deployed. In either case, the snare loop  150  and the steering tether  260  may be positioned within the cavity  14  as shown in FIG. 12.  
         [0051]    FIGS.  13 - 16  illustrate a sequence by which the snare loop  150  of the surgical instrument  200  can be used to encircle a polyp  18  attached to the lower tissue wall  16 . As initially deployed from the tube  132 , the steering tether  260  is relatively slack and the snare loop  150  is at a level where it cannot be positioned over the top of the polyp  18  (FIG. 13). By pulling on the proximal end  262  of the steering tether  260 , a surgeon can place the steering tether  260  in tension. As shown in FIG. 14, the tensile force transmitted through the steering tether  260  causes the snare loop  150  to be deformed so that the distal portion of the snare loop member  152  may be raised above the level of the polyp as shown in FIG. 14. Because the steering tether  260  is threaded through the flexible tube  132 , the problems associated with the distance from the cannula  50  and possible bends in the cavity  14  are significantly reduced or eliminated. With the snare loop  150  raised, the tube  132  can then be translated further into the cavity  14  to position the snare loop  150  over the polyp  18  as shown in FIG. 15. The surgeon can then release the tension in the steering tether  260  to allow the snare loop  150  to resume its shape and encircle the polyp  18  as shown in FIG. 16. The snare loop  150  can then be cinched around the polyp  18  by moving the control slide  122  proximally relative to the body  112  of the snare control module  110 . The snare loop  150  could be removed from the polyp  18  by reversing the above procedure.  
         [0052]    As previously noted, the tethers  160 ,  260  of the surgical instruments  100 ,  200  of the present invention may be attached anywhere around the circumference of the loop member  152  of the snare loop  150 . Accordingly, a steering tether  160 ,  260  could be attached to one side of the loop formed by the loop member  152 . Tension applied to such a tether could be used to deform the snare loop  150  so as to steer it to the side. This allows the use of multiple tethers, each attached to a different circumferential point around the loop member  152  to allow steering of the snare loop  152  in a different direction.  
         [0053]    An exemplary surgical instrument  300  having multiple steering tethers  360   a ,  360   b ,  360   c  is illustrated in FIGS. 17 and 18. The snare control module  110  and the snare loop  150  are again substantially similar to those of the previous embodiments. The steering tethers  360   a ,  360   b ,  360   c  are slidably disposed through the flexible tube  132  along with the cable  134 . The tube  132  and, in particular, the interior diameter of the passage through the tube  132  may be sized so that the cable  134  and the steering tethers  360   a ,  360   b ,  360   c  can be moved substantially independently within the tube  132 . As shown in FIG. 10, the steering tethers  360   a ,  360   b ,  360   c  pass out of the distal end  133  of the tube  132  along side the cable  134 . The distal end  364   a  of a first tether  360   a  is attached to one side of the snare loop  150 . The distal end  364   b  of a second tether  360   b  is attached to the opposite side of the snare loop  150 . The distal end  364   c  of a third tether  360   c  is attached to the distal tip of the snare loop  150 .  
         [0054]    As shown in FIG. 17, the steering tethers  360   a ,  360   b ,  360   c  pass through the tube  132  and through the connector  130  into the opening  117  between the frame members  114 ,  116 . The proximal ends  362   a ,  362   b ,  362   c  of the steering tethers  360   a ,  360   b ,  360   c  can be thus be extended out from the body  112  of the snare control module  110  and may be secured in any of the above-described ways or may be left as free ends for a surgeon to tie off as desired.  
         [0055]    The steering tethers  360   a ,  360   b ,  360   c  of the surgical instrument  300  are used in a manner similar to the tethers  160 ,  260  of the previous embodiments. The first and second steering tethers  360   a ,  360   b  may be used to steer the snare loop  150  from side to side and the third tether  360   c  may be used to raise the distal portion of the snare loop  150  as previously described. The steering tethers  360   a ,  360   b ,  360   c  may be used individually or in combination to maneuver the snare loop  150  as desired.  
         [0056]    It will be understood that multiple steering tethers may also be used in an instrument configuration wherein the steering tethers are not disposed through the tube  132  but are instead separately passed out of the body cavity through the cannula in a manner similar to that described for the single steering tether  160  of the surgical instrument  100 .  
         [0057]    It will be understood that the steering tethers of the present invention may be applied to other forms of surgical snare. This includes snares with loops formed by a belt or wire having either or both ends passing out through a cannula. Such snares are typically cinched by applying tension to the free end (or ends) of the belt or wire. The steering tethers of the present invention could easily be attached to the loops of such snares.  
         [0058]    Other embodiments and uses of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The specification and examples should be considered exemplary only. The scope of the invention is limited only by the claims appended hereto.