Abstract:
A retractor and a surgical tool are positioned within a cannula, and a dissection cradle of the retractor is positioned at the distal end of the cannula. The retractor includes a first portion with an axis approximately parallel to the axis of the cannula and a second portion with an axis skewed relative to the axis of the cannula. The dissection cradle is located at the distal end of the second portion of the retractor, and may include two substantially parallel, spaced legs with the retractor shaped in a loop between and in a plane skewed relative to the axes of the legs, and with the loop directed away from the surgical tool. Thus, in operation, when the surgeon locates a vessel and side branch of interest, the surgeon extends the retractor to cradle the vessel in the dissection cradle. Once cradled, the retractor may be fully extended to urge the vessel away from the axis of the cannula to isolate the side branch for exposure to the surgical tool. The dissection cradle may include a forward shoulder for positioning a suture loop. A forwardly-projecting tensioner supports a length of suture from the loop to maintain the loop in tension for transport along the vein. During advancement, the suture loop is safely maintained in place due to the tension provided by the tension mount and the support provided by the shoulder. Upon reaching the surgical site of interest, the retractor is retracted, causing the suture loop to be displaced onto the vein at the desired position. In one embodiment, the loop is tightened by pulling on the length of suture near the proximal end of the cannula to constrict the suture loop about the vein near the distal end of the cannula.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS(S) 
     The present application now U.S. Pat. No. 5,895,353 is a continuation of application Ser. No. 09/200,218 filed on Nov. 25, 1998, now U.S. Pat. No. 6,162,173, which is incorporated herein in its entirety, and a continuation-in-part application of application Ser. No. 09/102,723 filed on Jun. 22, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a cannula used for vessel retraction, and more particularly to a cannula and method that includes an endoscopic retractor for vessel ligation. 
     BACKGROUND OF THE INVENTION 
     Certain cannulas have surgical tools located within the cannula for performing surgical operations on a vessel of interest. The cannula is inserted into a surgical site with the distal end of the cannula positioned near the vessel of interest. An endoscope positioned within the cannula allows the surgeon to view the target area, and allows the surgeon to position the surgical tool correctly. One common procedure is to ligate a vessel or other tissue by tightening a suture loop tied as a slipknot on the vessel before transection to provide hemostasis to the vessel. 
     However, surgeons encounter several difficulties in ligation procedures. In one ligation procedure, a second incision must be made at the opposite end of the vessel of interest to ligate and transect the vessel. Multiple incisions are invasive and should be minimized if possible. In order to avoid this second incision, some conventional methods require tying a suture loop around the vessel, and pushing the loop along the vessel with a knot pusher until the opposite end is reached. Then, the loop is tightened to provide ligation. However, this procedure is difficult because the slipknot often catches on stumps of cut tributaries or other tissue, and then constricts around the vessel at the wrong position. Also, there is no easy method for transecting the vessel after the suture loop is tied to the vessel without potentially prematurely severing the suture. 
     Thus, a device and method is needed to allow remote, one-incision, ligation of a vessel which allows a suture loop to be moved reliably to the site of interest, and ensures that the transection instrument is able to transect the vessel, and cut the suture. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a retractor is positioned within a cannula with a dissection cradle end of the retractor positioned at the distal end of the cannula. The retractor includes a first portion that has an axis approximately parallel to a central axis of the cannula, and a second portion that has an axis which is at an angle with respect to the central axis of the cannula. The dissection cradle is located at the distal end of the second portion of the retractor. In another embodiment, the retractor includes two legs having substantially parallel axes that selectively protrude from the distal end of the cannula. The protruding legs support the dissection cradle formed in the shape or a loop that is positioned in a plane skewed relative to the axes of the legs, with a bottom of the loop directed away from the cannula. Thus, in operation, when the surgeon locates a vein and side branch of interest, the surgeon extends the retractor to cradle the vein in the dissection cradle. Once cradled, the retractor may be fully extended, pulling the vein away from the axis of the cannula causing the side branch to be isolated and exposed to a surgical tool. The surgical tool may then be extended from within the cannula to operate on the isolated and exposed side branch. 
     In another embodiment, the top of the loop of the dissection cradle is flat and thin, allowing atraumatic support of the vein, and minimizing contact between the retractor and the surgical tool. In yet a further embodiment, the retractor includes a single leg with the loop formed by the one leg of the retractor, and with a stopper coupled to the distal end of the retractor. In still another embodiment, the cannula comprises a sliding tube which encases the retractor, and in a first position is extended out to encase the second portion of the retractor, and in a second position is extended to encase only the first portion of the retractor. In response to being in the first position, the second and first portions of the retractor are both approximately parallel to the axis of the cannula. In the second position, the second portion of the retractor is skewed relative to the axis of the cannula. 
     In accordance with an alternate embodiment of the present invention, a retractor is positioned within a cannula with a dissection cradle end of the retractor positioned at the distal end of the cannula. The dissection cradle comprises a shoulder part and a curved channel part. Suture forming a suture loop is threaded through a hole in a tension mount that is fixed to the distal end of the cannula and is abutted against the distal end of the shoulder. Upon advancement to the surgical site of interest, the suture loop is safely maintained in place due to the tension provided by the tension mount and the support provided by the shoulder. The curved channel provides a groove in which the vessel of interest may be cradled. Upon retraction of the retractor, the suture loop is displaced onto the vessel at the desired position for ligation. In one embodiment, the loop is tightened by detaching the proximal end of the suture from the cannula and pulling on the suture, constricting the suture loop. In an alternate embodiment, a manual controller for retracting the retractor is attached to the proximal end of the suture. Upon slidable retraction of the manual controller, the retractor is retracted, the loop is displaced onto the vessel, and the loop is tightened. 
     In a further embodiment, a transecting device is positioned within the cannula. The distal end of the tension mount is positioned to allow the distal end to be proximal to the shoulder of the dissection cradle responsive to the shoulder being in an axial position relative to the tension mount. This results in the suture and vessel being reliably positioned within reach of the transecting device for transection of the vessel and cutting of the suture. 
     Finally, in a preferred embodiment, the retractor has a distal end having an axis skewed relative to the central axis of the cannula, thus facilitating accurate positioning of the vessel and suture for transection and cutting and ensuring the proper displacement of the suture loop onto the vessel in response to the retraction of the retractor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of cannula  100  showing retractor  112  in an extended position. 
     FIG. 2 a  is a cut-away side view of retractor  112  and cannula  100 . 
     FIG. 2 b  is a top view of retractor  112 . 
     FIG. 3 a  is a perspective side view of cannula  100  with a saphenous vein positioned within the cradle  116 . 
     FIG. 3 b  is a perspective side view of the distal end  122  of cannula  100  in an embodiment in which an endoscope  126  and a surgical tool  120  are present and partially extended. 
     FIG. 3 c  is a front view of the distal end  122  of cannula  100  in which the surgical tool  120  and the retractor  116  are partially extended, and an endoscope  126  is present. 
     FIG. 4 a  is a cut-away top view of cannula  100 . 
     FIG. 4 b  is a cut-away side view of cannula  100 . 
     FIG. 5 a  is a cut-away view of a sliding tube embodiment of cannula  100  in a first position. 
     FIG. 5 b  is a cut-away view of the sliding tube embodiment of FIG. 5 a  in a second position. 
     FIG. 6 a  is a cut-away view of an embodiment of cannula  100  having an angling device  140 . 
     FIG. 6 b  is a cut-away side view of the apparatus illustrated in FIG. 6 a  in which the retractor  112  is extended and the angling device  140  is actuated. 
     FIG. 6 c  is a cut-away side view of the angling device embodiment in which the angling device  140  is in a separate lumen from the retractor  112 . 
     FIG. 7 a  is a cut-away side view of a twistable retractor  112  in a straight position. 
     FIG. 7 b  is a side view of the retractor  112  of FIG. 7 a.    
     FIG. 7 c  is a cut-away side view or twistable retractor  112  in a crossed position. 
     FIG. 7 d  is a side view of the retractor  112  of FIG. 7 c.    
     FIG. 8 a  is a cut-away side view of the handle  104 . 
     FIG. 8 b  is a cut-away side view of an alternate embodiment of handle  104 . 
     FIG. 9 a  is a side view of cradle  116 . 
     FIG. 9 b  illustrates a first alternate embodiment of cradle  116 . 
     FIG. 9 c  illustrates multiple views of a second alternate embodiment of cradle  116 . 
     FIG. 9 d  illustrates multiple views of a third alternate embodiment of cradle  116 . 
     FIG. 9 e  illustrates multiple views of a fourth alternate embodiment of cradle  116 . 
     FIG. 9 f  illustrates multiple views of a fifth alternate embodiment of cradle  116 . 
     FIG. 9 g  illustrates multiple views of an embodiment of cradle  116  having a spur. 
     FIG. 10 a  illustrates a top view of an embodiment of the cradle  116  of FIG. 9 c  without a “C” ring. 
     FIG. 10 b  illustrates a side view of the cradle  116  of FIG. 10 a  . 
     FIG. 10 c  illustrates a top view of the cradle  116  of FIG. 9 c  with the “C” ring attached. 
     FIG. 10 d  illustrates a side view of the cradle  116  of FIG. 10 c . 
     FIG. 11 illustrates a perspective side view of cradle  312  for remotely ligating vessel. 
     FIG. 12 illustrates a perspective side view of cradle  312  in operation. 
     FIG. 13 illustrates a perspective side view of cannula  100  having a dissection cradle  312 . 
     FIG. 14 a  illustrates a perspective side view of cannula  100  with retractor  112  extended. 
     FIG. 14 b  illustrates a perspective side view of cannula  100  with retractor  112  retracted. 
     FIG. 15 illustrates a perspective side view of cannula  100  with transection device  316 . 
     FIGS. 16 a-c  illustrates multiple views of tension mount  308 . 
     FIG. 17 is a flowchart illustrating the process of remote ligation of a vessel in accordance with the present invention. 
     FIG. 18 is a flowchart illustrating the process of remote ligation and vessel harvestation under gas insufflation. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a perspective view of a preferred embodiment of cannula  100  showing retractor  112  in an extended position. Cannula  100  includes an outer housing  102  of bioinert material such as polymed UD that may be approximately 12″ to 18″ in length. The proximal end of the cannula  100  is disposed in handle  104  that includes a button  106  which is coupled to retractor  112  for controlling the translational movement of retractor  112 , as described in more detail below. 
     The distal end of the cannula houses a retractor  112 , and optionally an endoscope  126  and a surgical tool  120 , described below. FIG. 2 a  illustrates the retractor  112  in more detail. In one embodiment, retractor  112  is formed of resilient wire which has a smooth bend intermediate to a first portion  110  and a second portion  114  of the retractor. The retractor  112  is described as having two portions for ease of description, although the retractor  112  may be formed as an integrated structure. However, retractor  112  may also be manufactured from two separate portions  110 ,  114  that are coupled together. The first portion  110  of the retractor  112  is positioned within the cannula  100  with the axis  111  of the first portion  110  approximately parallel to the axis  101  of the cannula  100 . The second portion  114  is positioned to bend away from the central axis  101  of the cannula. The angle  117  of displacement between the axis  115  of the second portion and the central axis  101  of cannula  100  may be any angle from zero to 180 degrees. The second portion  114  includes a dissection cradle  116  at the distal end of the second portion  114 . The retractor  112  may be formed of bioinert material such as stainless steel, or a polymer such as nylon or polyetherimide, or other appropriately strong and springy plastic. In one embodiment, the reactor  112  includes a coating for lubrication, insulation, and low visual glare using, for example, parylene or nylon  11 . 
     FIG. 2 b  illustrates the retractor  112  formed with two legs. The legs  141 ,  142  of the retractor  112  at the distal end form the dissection cradle  116  in a loop or “U” shape, as shown in FIG. 2 a . The top portion  144  of the U-shaped bend is preferably flattened to provide additional surface area for atraumatically supporting a vein  118  or vessel of interest. The side arches  128  of the dissection cradle  116  are used for skeletonizing or dissecting the vein from the surrounding tissues, as well as acting as walls to keep the vessel captured within the arch. The several embodiments of dissection cradle  116  are described in more detail below. 
     FIG. 3 a  illustrates a perspective view of the cannula  100  in accordance with the present invention with the retractor fully extended, holding a saphenous vein  118 , and also illustrates an external surgical tool  120  disposed adjacent the cannula  100  for performing a surgical operation, for example, severing a tributary or side branch of the vein  118 . The vein is positioned within the side arches  128  of the cradle  116 . The dissection cradle  116  may be used to cradle a vein. vessel, tissue or organ of interest, and surgical tool  120  may be any surgical tool suitable for performing a surgical procedure near the dissection cradle  116 . 
     FIG. 3 b  illustrates a perspective view of cannula  100  in an embodiment in which the surgical tool  120  is positioned within the cannula  100 , and an endoscope  126  is present. In this embodiment, cradle  116  preferably overlays the endoscope  126  with sufficient clearance to facilitate relative movements thereof. However, the endoscope may also be located adjacent the surgical tool  120 . In one embodiment, endoscope  126  is positioned with cannula  100  to allow a clear field of view upon extension of the retractor  112 . Surgical tool  120  is illustrated as scissors, used to sever a tributary or side branch of a saphenous vein  118 . In this embodiment, surgical tool  120  is maximally displaced from the cradle  116  at the cannula end  122 . More specifically, as shown in FIG. 3 c , the “U”-shaped loop  129  of the cradle  116  is closest to the surgical tool  120 . This ensures that a vein  118  or other tissue of interest is retracted away from the surgical tool  120  to facilitate manipulating the surgical tool  120  relative to the side branch or other tissue. 
     FIG. 4 a  is a cut-away top view of cannula  100 . The retractor  112  is slidably positioned within minor lumens  113  along the length of the cannula  100  within close tolerances in order to position the retactor  112  stably within the cannula  100 . For example, in one embodiment retractor legs  141 ,  142  are approximately 0.045 inches in diameter and the lumens  113  encasing the legs  141 ,  142  are approximately 0.080 inches in diameter, as friction between the legs of the retractor  112  and the lumens  113  holds the retractor stably within the cannula. This configuration restricts rotational movement of the retractor to provide more stable retraction as compared with conventional retractors. The legs  141 ,  142  of the retractor  112  are formed of flexible, resilient material and are retained within the lumen  113  in substantially straight or flat orientation, but may return to a material bend or curve, as illustrated in FIG. 5 a , as the retractor  112  is extended from the distal end of the cannula  100 . 
     The leg  141  of the retractor  112  passes through a sliding gas or fluid seal  130  at the proximal end of the lumen  113 . The leg  141  of the retractor  112  passes out of the cannula  100  and into handle  104  for attachment to a slider button  106  for facilitating translational movement of the retractor  112  from the proximal or handle end of the cannula  100 . However, other types of control devices such as knobs, grips, finger pads, and the like may be linked in conventional ways to the retractor  112  in order to manually control the translational movement of retractor  112 . In one configuration, the proximal end of leg  141  is bent relative to the axis of the cannula, and the button  106  is attached to the bent position of the leg  141  to facilitate moving the button  106  and the retractor  112  traditionally under manual control. The button  106  preferably includes lateral grooves to prevent finger or thumb slippage during sliding manipulation of the retractor  112 . 
     Thus, in the operation of a preferred embodiment, a user actuates the slider button  106  to extend retractor  112  out of the lumen  113  at the distal end of the cannula  100 . In one embodiment, the resilient retractor  112  is formed in a smooth bend, as shown in FIG. 2 a , and gradually deflects away from the central axis  101  of the cannula  100  as the retractor is extended. Upon encountering the target vessel or tissue of interest, the vessel is restrained in the cradle  116 , and a lateral resilient force is exerted on the target vessel in a direction away from the cannula The vessel is thus pushed away from the axis of the cannula  100 , isolating it from surrounding tissue or adjacent vessels such as tributaries or side branches. As a tributary is thus isolated, a surgical tool  120  such as cauterizing scissors may be safely employed to operate on the tributary without harming the saphenous vein  118 . When retracted into the cannula  100 , the retractor  112  is again resiliently straightened or flattened. 
     In an alternate embodiment as illustrated in FIGS. 5 a  and  5   b , a sliding tube  132  is added to provide operational versatility to cannula  100 . In a first position, the sliding tube  132  is retracted and the retractor  112  protrudes from the distal end at an angle with respect to the central axis  101  of the cannula  100 . In a second position, the sliding tube  132  is extended out, temporarily straightening the retractor  112 . As illustrated in FIG. 5 a , a sliding tube  132 , in a first position encases the retractor  112  up to the point at which the retractor  112  curves away from the central axis  101  of the cannula thus allowing the retractor  112  to displace and isolate a target vessel. The proximal end of the sliding tube  132  is linked to button  107  for translationally moving retractor  112  as well as actuating the sliding tube  132 . In one embodiment, as illustrated in FIG. 5 a , the sliding tube  132  is in a first position with the button  107  in an upright position. A spring  134  is coupied between a support structure  135  and the proximal end  137  of the sliding tube  132 . In the first position of sliding tube  132 , the spring  134  is extended fully and exerts little or no force on the sliding tube  132 . Of course, sliding tube  132  may be manually manipulated without linkage to a button  107 . 
     To extend the sliding tube  100 , button  107  is pushed down. As illustrated in FIG. 5 b , the button  107  has a cam surface  136  which pushes on the proximal end  137  of the sliding tube  132  as the button  107  is pressed. The sliding tube  132  is pushed forward, overcoming the resilient force of sprint  134 , to encase the retractor  112  and decrease angle  117  between the distal end of the retractor  112  and the central axis  101  of the cannula  100 . Upon releasing the button  107 , the spring force urges the proximal end  137  of the sliding tube  132  back toward the first position against button  107 . The sliding tube  132  is formed of material having sufficient strength to force the retractor  112  to straighten out the angle  117 , and the retractor  112  is formed of resilient material having a sufficient flexibility to straighten out the angle  117  in response to a tube  132  being slid over the retractor  112 , but having sufficient rigidity to cradle and dissect a target vessel. Resiliency of the retractor  112  ensures return to the downwardly-curved shape after being released from tube  132 . Thus, in accordance with this embodiment, a user may employ the curved retractor for certain applications and employ the straightened form for other applications. A manual actuator may be configured in other ways than button  107  to extend the sliding tube  132  in response, for example, to being pulled up instead of pushed down. 
     Another embodiment employs a retractor  112  which has a naturally straight shape. As illustrated in FIGS. 6 a  and  6   b , an angling device  140  is disposed between the distal end of the retractor  112  and the proximal end of the cannula. The angling device  140  may be positioned within the same lumens  113  as the retractor  112  and preferably may comprise two wires coupled to points below the cradle  116  of the retractor  112  substantially in parallel positions on each of the legs  141 ,  142 . 
     Upon extending the retractor  112  using button  106 , the angling device  140  is extended with the retractor  112 . The angling device  140  is coupled to a handle  145  at the proximal end of the cannula  100  to facilitate establishing an angle in the retractor  112  by pulling with a backward force on the angling device  140 . As illustrated in FIG. 6 b , after the retractor  112  is extended. the angling device  140  is actuated and a bend is created in the retractor  112  as the backward force exerted on the distal end of the retractor is exerted against the relatively fixed position of the retractor legs  141 ,  142  disposed within the lumens  113 . As shown in FIG. 6 c , the angling device  140  may also be located in a separate lumen  202  from the retractor  112  with part of the angling device  140  positioned outside of the cannula  100  when the retractor  112  is in the retracted position. 
     FIG. 7 a  illustrates another embodiment of cannula  100  in which the retractor  112  is pre-formed with one leg  141  of the retractor  112  bent at an angle at its proximal end skewed to the axis of the distal end of the other leg  142 . The bent portion of the leg  141  may be linked to a sliding knob  147  for convenient manual manipulation of this embodiment of the invention. Upon sliding the knob  147 , the leg  142  coupled to knob  147  is twisted rotationally. The two legs  141 ,  142  of retractor  112  are coupled together via cradle  116 . The axis of the second portion of the retractor  112  in the first position is at a first angle  117  to the axis of the cannula  100 , as shown in FIG. 7 b . As knob  147  is moved, leg  141  is rotated and crosses under leg  142 , as shown in FIG. 7 c . This causes cradle  116  to flip 180 degrees and bends the retractor  112  at a second angle  119 , as shown in FIG. 7 d . Thus, if a vessel is disposed on one side of cradle  116  or cannula  100  while the retractor  112  is in the first position, then upon rotating the knob  147 . the vessel is transported to the other side of the cannula  100 . This allows the user to isolate the vessel by simply actuating knob  147 . 
     FIG. 8 a  illustrates a cut-away side view of button  106  on the handle  104  of cannula  100 , with an endoscope  126  positioned within cannula  100 . As mentioned above, button  106  is coupled to one leg  141  of the proximal end of retractor  112 . Sliding the button  106  in groove  146  translationally moves the retractor  112 . Groove  146  is preferably minimally wider than the shaft of button  106  to minimize excessive horizontal movement of button  106  while still allowing smooth translational movement of button  106 . As illustrated in FIG. 8 b , the button  106  may include locking or ratcheting teeth  152  to give tactile feedback of its location, and to positively retain the button and the associated leg  141  in an extended or retracted position. Several mating teeth  148  are located underneath groove  146 , and a spring member  150  is attached to button  106  to exert pressure against the base of groove  146 , to engage mating teeth  148 ,  152 . When a force is applied on the top of button  106 , the interlocking sets of teeth are disengaged and button  106  can move freely. Upon achieving the desired extension or retraction the leg  141 , button  106  is released and is retained place by the engaged teeth  148 ,  152 . 
     FIG. 9 a  illustrates a top view of cradle  116  in an embodiment in which the cradle  116  is formed by two legs  141 ,  142  of retractor  112 . The distal end of the legs form “U”-shaped side guides. The top  144  of the distal portion of the “U” is preferably flattened. This provides atraumatic support or the target vessel retained within cradle  116 . Additionally, by minimizing the thickness of distal portion  144 , contact with other devices in close proximity with retractor  112  is minimized. 
     The cradle  116  may have other effective shapes, for example, as illustrated in FIG. 9 b  in which a “C” ring element is attached to legs of the cradle  116 . The “C” ring may have a small hole  200  in one side with an axis approximately parallel to the axis of the retractor  112 . This hole  200  is used to hold suture or other ligating materials, and may also be used as a knot pusher. As shown in FIGS. 10 a  and  10   b , in an alternate embodiment of the embodiment of FIG. 9 b , the retractor  112  is formed and flattened and a “C”-shaped ring is coupled to the retractor  112  by, for example, gluing or molding the “C” ring to the distal end of the retractor  112 , as shown in FIGS. 10 c  and  10   d.    
     Referring back to FIGS. 9 c ,  9   d , and  9   e , the side guides of the cradle may include a loop  129  in a “V” shape, an arced “U” shape, or a semi-circular shape. In one embodiment, as illustrated in FIG. 9 f , the retractor  112  has only one leg  141 , and the cradle  116  is formed by the leg  141 . A stopper  160  is coupled to the end of the leg  141  to serve as a guide to retain the target vessel, and add a blunt surface to the end of the wire, for example, for pushing and probing tissue. FIG. 9 g  illustrates a retractor  112  having a spur  204  formed in one or both legs  141 ,  142  for allowing the retractor  112  to be used for dissection. Sinusoidal, half-sinusoidal, and other geometric configurations may be used equally effectively as the shape of loop  129  in accordance with the present invention. 
     FIG. 11 illustrates an alternate dissection cradle  312  for use in remote vessel ligation. Remote vessel ligation as discussed above is necessary to provide hemostasis to a vessel or other tissue after the vessel has been transected. In accordance with the present invention, hemostasis is accomplished by tightening suture formed in a loop adjacent the point of transection of the vessel. However, it is preferable to provide hemostasis to the vessel without incising the body a second time at the point of transection. The cannula  100  and dissection cradle  312  provide this functionality. 
     At the distal end of the retractor  312 , a shoulder part  300  is preferably formed of a rigid plastic encapsulating the distal end of the retractor  112 . A curved channel part  304  is attached to the shoulder  300 . The cured channel  304  is formed in the shape of a “C” as shown. The curve of curved channel  304  exposes a portion of the distal face of the shoulder  300 , upon which a suture loop  328  may be abutted, as shown in FIG.  12 . Other shapes, such as those shown in FIGS. 9 a-e , may also be used as curved channel  304 . 
     FIG. 12 illustrates the manner in which the suture loop  328  is transported safely to the point of transection. The loop  328  is formed as a slipknot, which may be cinched tighter by exerting a backwards force on the free end of the suture  320 . The suture loop  328  is tied around the vessel and the curved channel part  312 , and is abutted against the shoulder  300 . Next, the loop  328  is tightened onto the curved channel  304  by pulling back on the free or proximal end of the suture  320 . The loot  328  is tightened sufficiently to permit safe advancement, but is provided with sufficient slack to allow displacement of the loop  328  onto the vessel adjacent the point of transection upon retraction of the retractor  312  into the cannula  100 . 
     One embodiment of the present invention for exerting a backward or disengaging force on the loop  328  is shown in FIG.  13 . FIG. 13 illustrates a tension mount  308  attached to cannula  100  for providing secure transport of the suture  320  to the surgical site of interest and for providing a controlling mechanism for tightening the suture loop  328  around the vessel when ligation is desired. The tension mount  308  is also formed of rigid plastic with some flexibility to allow other surgical tools  120  (not shown) to extend beyond the distal end of the tension mount  308 , and to allow atraumatic advancement of the tension mount  308  through the body. The distal end of the tension mount  308  includes a hole  324  through which the suture is threaded to tighten the suture loop  328 . The distal end of the tension mount  308  protrudes toward the central axis of the cannula  100 . This ensures that the vessel and the suture will be in the optimal position for transection or cutting after the loop  328  has been displaced onto the vessel. Additionally, the forward angle of the tension mount  308  also ensures that the loop  328  will be displaced onto the vessel upon retraction of the retractor  312 , as discussed in greater detail below. The length of the tension mount  308  is chosen to allow the cradled vein to remain in endoscopic view upon advancement. Alternatively, a long knot pusher may be used in place of tension mount  308 . The suture  320  is looped around the vessel and the curved channel  304 , previously described. However, the free end of the suture  320  is threaded through a hole in the long knot pusher disposed within the cannula  100 . The cannula  100  and knot pusher are advanced to the point of transection. Displacement of the loop  328  occurs by advancing the knot pusher while maintaining the position of the dissection cradle  312  relative to the vessel. After the loop  328  is displaced onto the vessel, the loop  328  is tightened by pulling backward on the suture  320 . The long knot pusher may contain a lumen which runs the length of the cannula  100  or it may contain a shorter lumen which starts at the tip of the cannula and exits a side of the cannula  100  after a short distance proximally. 
     FIG. 14 a  illustrates the operation of the cannula  100  which has a tension mount  308 . The cradle  312  holds a vessel  330 . The vessel  330  is safely cradled in the curved channel  304  as the cannula  100  is advanced. The suture  320  is threaded through the hole  324  disposed in the distal end of the tension mount  308 . The distal end of the suture  320  is then formed into a suture loop  328  around the vessel  330 , and is abutted against the shoulder  300 . In this embodiment, the proximal end of the suture  320  is wrapped around a cleat  332  on button  106  at the proximal end of the cannula  100 . The loop  328  is tightened around curved channel  304  by winding the proximal end of the suture  320  around the cleat  332  which has the effect of pulling on the suture loop  328  and cinching, the knot tightly around the curved channel  304  against the shoulder  300 . The suture loop  328  may now be safely advanced to the surgical site as excessive slack does not occur in the loop  328 , which would cause the loop  328  to be dislodged from the cradle  302 . In an alternate embodiment, the loop  328  is tightened responsive to the sliding of the button  106 . The button  106  has a lock with a release mechanism which restricts the sliding of the button  106 . When the loop  328  requires tightening after displacement onto the vessel, the lock is released and the button  106  is retracted. This embodiment ensures that the surgeon does not accidentally dislodge the loop  328  from the shoulder  300  by prematurely retracting the retractor  312  into the cannula  100 . 
     Upon reaching the site of interest, the loop  328  is displaced onto the vessel  330  by sliding a manual controller backwards, causing the retractor  112  to retreat to an axial position. In the embodiment of FIGS. 14 a  and  b , the loop  328  is displaced by sliding the button  106  backwards. Upon sliding the button  106  backwards, as shown in FIG. 14 b  the cradle  312  is retracted into cannula  100 , causing the loop  328  to be forcibly displaced from the shoulder  300  of the dissection cradle  312  onto the vein  330  at the desired location. 
     After displacement onto the vessel  330 , a knot tightener  340  is then used to tighten the suture loop  328  onto the vessel  330  to provide hemostasis. In the embodiment of FIGS. 14 a  and  b , the loop  328  is tightened onto the vessel  330  as the proximal end of the suture  320  is wound around the cleat  332 . The proximal end of the suture  320  could also simply be detached from the proximal end of the cannula  100 , and the loop  328  tightened by pulling on the free end of the suture  320 . Alternatively, the loop  328  may be tightened by fixing the proximal end to the button  106 . Sliding the button  106  towards the proximal end of the cannula  100  exerts a backwards force on the loop  328 , tightening the loop  328 . 
     FIG. 15 illustrates the use of the transection instrument  316  in accordance with the present invention. The transection instrument  316  is preferably endoscopic shears disposed within cannula  100 . The shears  316  are positioned between tension mount  308  and cradle  312 . After the vessel  330  has been ligated as described above, the shears  316  are extended to transect the vessel. As the vessel is tied by the suture  320  which passes into the tension mount  308 , the vessel is thus placed within easy reach of the blades of the shears  316 . The tension mount  308  is formed with a slight bend toward the center of the cannula  100  to facilitate keeping the vessel  330  within the apex of the open blades of the shears  316 . After transecting the vessel  330 , the vessel  330  will fall away as shown in FIG.  15 . The suture  320 , however, is now within the apex of the open blades of the shears  316 . The shears  316  are then extended again and used to cut the suture  320 . The ligated vessel  330  remains in the surgical site, and the graft is able to be removed through the first and only incision. 
     FIGS. 16 a-c  illustrates multiple views of tension mount  308 . FIG. 16 a  illustrates tension mount  308  attached to a collar  336 . The collar  336  allows the cannula  100  to be used without a tension mount  308  for the initial transection operation in which the tributaries of the vessel  330  are transected to allow the main length of the vessel to be extracted from the body. For this initial transection operation, the tension mount  308  may interfere with this procedure, and thus should be removed. 
     The collar  336  of the tension mount  308  has proximal and distal ridges  338 ,  339  disposed on its inner surface. FIG. 16 b  illustrates in greater detail the proximal ridge  338  which mates with ridges disposed on the cannula surface. As shown in FIG. 16 c , the distal end  342  of the cannula  100  is smooth plastic or other bioinert material on which the ridged collar  336  may slide easily. Ridges  346  situated at flat or recessed portions  345  on the surface of the body of cannula  100  form edges  344  for retaining the collar  336 . Upon sliding the collar  336  onto the distal end  342  of the cannula  100 , the collar  336  resiliently expands and ridges  338 ,  339  of the collar  336  align with edges  344  of the cannula  100 . Upon alignment, the collar  336  resiliently contracts and thus forms a secure fitting of collar  336  on cannula  100 . When the surgeon wants to remove the collar  336 , the surgeon simply twists the collar  336  to misalign the ridges  338 ,  339  of the collar with ridges  346  of the cannula  100 , causing the collar  336  to resiliently expand again, thus allowing the collar  336  to be easily removed from the cannula  100 . 
     FIG. 17 illustrates a method of performing remote vessel ligation in accordance with the present invention. The surgeon advances  1700  a suture loop  328  along a vessel to a remote site from incision. The suture loop  328  is displaced  1704  onto the vessel responsive to retraction of the retractor, and, responsive to exerting  1708  a backward force on the suture, the vessel is ligated. 
     In a further embodiment, as shown in FIG. 18, the one-incision ligation and harvesting operation is performed under gas insufflation. First, an incision is made  1800  at the desired beginning point of the graft. For example, for saphenous vein harvesting for coronary artery bypass grafting, the incision is made at the knee. Next, the cannula  100  is inserted  1804  into the incision, and the incision is sealed  1808 . A tunnel is formed along the vessel by insufflating  1812  the area with gas. The suture loop  328  is safely advanced  1816  to the destination. For saphenous vein harvesting, the loop  328  is advanced to its origin at the saphenofemeral junction. The loop  328  is displaced  1820  onto the vessel, and a backwards force is applied  1824  to the suture  320  to ligate the vessel. The vessel is transected  1828  and the suture is cut  1832 . The vessel can now be removed  1836  from the original incision. 
     Thus, in accordance with the present invention, only one incision is required to harvest and ligate vessel in accordance with the present invention. The use of dissection cradle  312  allows the suture loop  328  of suture  320  to be advanced safely to the surgical site without being caught on the main trunk of the vessel or side branches thereof. The tension mount  308  accurately and reliably positions the vessel for transection and the suture  320  for cutting and provides the tension required to tighten the suture loop  328  of suture  320  onto a forward shoulder of the curved channel  304  for safe advancement and tensioning as required to provide hemostasic transection and harvesting of a target vessel.