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 that can be 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, a surgeon locates a vessel and side branch of interest and extends the retractor to cradle the vessel in the dissection cradle. Once cradled, the retractor may be deflected to urge the vessel away from the axis of the cannula to isolate the side branch for exposure to the surgical tool. Removable, transparent tips are selectively positioned at the distal end of the cannula for performing dissection and transection via a single cannula. Additionally, the tips are configured to align the apices of the tips with the central axis of the endoscope to maximize the visual field through the tips via the endoscope. Wing-like protrusions on an alternate tip for the cannula facilitate tissue dissection in forming a tunnel in tissue along a target vessel. Swept back forward edges on the wing-like protrusions promote easy dissection using reduced force to advance the cannula and alternate tip tough tissue surrounding the target vessel.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is a continuation of application Ser. No. 10/807,368, filed on Mar. 22, 2004, which is a continuation of application Ser. No. 10/218,475, filed on Aug. 12, 2002, now issued as U.S. Pat. No. 6,752,756, which is a continuation of application Ser. No. 09/490,552, filed Jan. 25, 2000, and now issued as U.S. Pat. No. 6,432,044, which is a continuation of Ser. No. 09/227,393, filed Jan. 8, 1999, now abandoned, which is a continuation-in-part application of application Ser. No. 09/102,723 filed on Jun. 22, 1998, now issued as U.S. Pat. No. 5,895,353 and the subject matter hereof is related to the subject matter of application Ser. No. 08/593,533 entitled “Tissue Separation Cannula” filed on Jan. 24, 1996 by Albert K. Chin, now abandoned, which is a continuation-in-part application of application Ser. No. 08/502,494, entitled “Tissue Separation Cannula And Method,” filed on Jul. 13, 1995, now abandoned, which prior applications are assigned to the same assignee as the present application and are incorporated herein in their entireties by this reference thereto.  
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to a cannula used for vessel retraction, and more particularly to a cannula and method for retracting a vessel during dissection and transection.  
       BACKGROUND OF THE INVENTION  
       [0003]     One important component of a surgical cannula is the tip, disposed on the distal end of the cannula. A properly configured tip can provide important functionality to a cannula. For example, the functions of vessel dissection and transection are commonly performed by two separate instruments. The device described in the pending application Ser. No. 08/907,691, entitled “Tissue Separation Cannula with Dissection Probe and Method,” filed on Aug. 8, 1997, discloses a device for separating surrounding connective tissue from a vessel (dissection). The device described in the pending application Ser. No. 09/102,723, entitled Vessel Isolating Retractor Cannula and Method,” filed on Jun. 22, 1998, discloses a device for retracting the vessel, ligating side branches, and transecting the branches to allow removal of the vessel. It is desirable to use a single device for performing the above functions.  
         [0004]     The construction of a cannula tip also affects the visual field provided to a surgeon through an endoscope. When an endoscope is situated in a lumen of the cannula, the surgeon looks through the endoscope and through the transparent tip to view the surgical site. It is desirable to have a tip which maximizes the visual field of the endoscope.  
         [0005]     The cannula tip may also be used to dilate a tunnel or anatomical space through tissue planes. In pending application Ser. No. 09/133,136, entitled “TISSUE DISSECTOR APPARATUS AND METHOD,” filed Aug. 12, 1998, assigned to the same assignee as the present application, and which is hereby incorporated by reference, a cannula is constructed with a bulbous element near the tip of the cannula for performing tissue dilation as the cannula is advanced. Cannula tips for dilating tunnels through tissue require force in order to advance the cannula and dilate the tissue. It is desirable to have a tip which can perform tissue dilation or dissection using a minimal amount of force and causing minimal trauma.  
       SUMMARY OF THE INVENTION  
       [0006]     In accordance with the present invention, a tissue 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 of 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 to urge 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.  
         [0007]     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 the sliding tube being in the first position, the second and first portions of the retractor are both approximately parallel to the axis of the cannula. In response to the sliding tube being in the second position, the second portion of the retractor is skewed relative to the axis of the cannula.  
         [0008]     In accordance with an alternate embodiment of the present invention, a removable, transparent tip is positioned at the distal end of the cannula to provide a single cannula for performing dissection and transection. When attached, the tip seals the distal end of the cannula in a fluid resistant manner. The tip is conical and ends in a sharp interior point and a slightly rounded exterior point which allows the surgeon to bluntly dissect tissue in the area of interest under endoscopic visualization. When tissue dissection is complete, the surgeon can remove the tip from the cannula, and the surgeon is now able to use the cannula to transect side branches and vessel ends. In order to maximize the visual field provided by the endoscope, the tip is configured to allow the apex of the tip to be aligned with the central axis of the endoscope. In one embodiment, a distal end of the tip is tilted in an oblique fashion to allow the apex of the tip to align with or near to the central axis of the endoscope. In an alternate embodiment, the conical end of the tip has unequal taper angles relative to a plane of transition between the cylindrical and conical portions of the tip, thus skewing the position of the apex of the tip into alignment with or near to the central axis of the endoscope.  
         [0009]     In another embodiment, wing-like protrusions are provided about the cannula near the tip to dilate tissue surrounding the vessel of interest. In one embodiment, the wing-like protrusions are diametrically aligned in a planar configuration with tapered forward edges extending rearward from near the apex of the tip. The planar configuration of the wing-like dilating protrusions near the tip substantially reduces the resistive force encountered during advancement of the cannula through tissue. The wing-like protrusions are positioned on opposite sides of the tip to dissect tissue to form a cavity that may attain a round cross-section under insufflation, thus providing the same resultant tissue dilation as provided by a solid oval dilator, but with less force required to accomplish the tissue dilation. In an alternate embodiment, the leading edges of the wing-like protrusions are curved in a parabolic configuration away from the distal end of the cannula to provide the necessary dilation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of a preferred embodiment of cannula  100  showing retractor  112  in an extended position.  
         [0011]      FIG. 2   a  is a cut-away side view of retractor  112  and cannula  100 .  
         [0012]      FIG. 2   b  is a top view of retractor  112 .  
         [0013]      FIG. 3   a  is a perspective side view of cannula  100  with a sapphenous vein positioned within the cradle  116 .  
         [0014]      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.  
         [0015]      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.  
         [0016]      FIG. 4   a  is a cut-away top view of cannula  100 .  
         [0017]      FIG. 4   b  is a cut-away side view of cannula  100 .  
         [0018]      FIG. 5   a  is a cut-away view of a sliding tube embodiment of cannula  100  in a first position.  
         [0019]      FIG. 5   b  is a cut-away view of the sliding tube embodiment of  FIG. 5   a  in a second position.  
         [0020]      FIG. 6   a  is a cut-away view of an embodiment of cannula  100  having an angling device  140 .  
         [0021]      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.  
         [0022]      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 .  
         [0023]      FIG. 7   a  is a cut-away side view of a twistable retractor  112  in a straight position.  
         [0024]      FIG. 7   b  is a side view of the retractor  112  of  FIG. 7   a.    
         [0025]      FIG. 7   c  is a cut-away side view of twistable retractor  112  in a crossed position.  
         [0026]      FIG. 7   d  is a side view of the retractor  112  of  FIG. 7   c.    
         [0027]      FIG. 8   a  is a cut-away side view of the handle  104 .  
         [0028]      FIG. 8   b  is a cut-away side view of an alternate embodiment of handle  104 .  
         [0029]      FIG. 9   a  is a side view of cradle  116 .  
         [0030]      FIG. 9   b  illustrates a first alternate embodiment of cradle  116 .  
         [0031]      FIG. 9   c  illustrates multiple views of a second alternate embodiment of cradle  116 .  
         [0032]      FIG. 9   d  illustrates multiple views of a third alternate embodiment of cradle  116 .  
         [0033]      FIG. 9   e  illustrates multiple views of a fourth alternate embodiment of cradle  116 .  
         [0034]      FIG. 9   f  illustrates multiple views of a fifth alternate embodiment of cradle  116 .  
         [0035]      FIG. 9   g  illustrates multiple views of an embodiment of cradle  116  having a spur.  
         [0036]      FIG. 10   a  illustrates a top view of an embodiment of the cradle  116  of  FIG. 9   c  without a “C” ring.  
         [0037]      FIG. 10   b  illustrates a side view of the cradle  116  of  FIG. 10   a.    
         [0038]      FIG. 10   c  illustrates a top view of the cradle  116  of  FIG. 9   c  with the “C” ring attached.  
         [0039]      FIG. 10   d  illustrates a side view of the cradle  116  of  FIG. 10   c.    
         [0040]      FIG. 11   a  illustrates a cut-away side view of a tip  1100  in a cannula housing an endoscope  126 .  
         [0041]      FIG. 11   b  illustrates a side view of the tip  1100  isolated from cannula  100 .  
         [0042]      FIG. 12   a  illustrates a side view of an offset tip  1200  in accordance with the present invention.  
         [0043]      FIG. 12   b  illustrates a cut-away side view of the offset tip  1200  in a cannula  100  housing an endoscope  126 .  
         [0044]      FIG. 12   c  illustrates a cut-away side view of an alternate embodiment of offset tip  1200 .  
         [0045]      FIG. 13  illustrates a cut-away side view of an alternate embodiment of the offset tip  1300 .  
         [0046]      FIG. 14   a  illustrates a perspective side view of the offset tip  1200  and mounting rod  1404 .  
         [0047]      FIG. 14   b  illustrates a perspective side view of cannula  100  for housing offset tip  1200  and mounting rod  1404 .  
         [0048]      FIG. 14   c  illustrates a perspective side view of offset tip housing  1424  at the proximal end of the cannula  100 .  
         [0049]      FIG. 14   d  illustrates a perspective side view of cannula  100  with offset tip  1200  and offset tip housing  1424 .  
         [0050]      FIG. 14   e  illustrates a perspective side view of an alternate embodiment of offset tip mount  1424 .  
         [0051]      FIG. 14   f  illustrates a cut-away side view of the offset tip mounting  1424  of  FIG. 14   e.    
         [0052]      FIG. 15   a  illustrates a side view of an alternate embodiment of offset tip  1200 .  
         [0053]      FIG. 15   b  illustrates a side view of a cannula  100  modified for use with the offset tip  1200  of  FIG. 15   a.    
         [0054]      FIG. 16  is a flow chart illustrating a method of dissecting and transecting vessels according to the present invention.  
         [0055]      FIG. 17   a  illustrates a top view of an embodiment of an offset tip dilator  1700  according to the present invention.  
         [0056]      FIG. 17   b  illustrates a side view of the embodiment of offset tip dilator  1716  of  FIG. 17   a.    
         [0057]      FIG. 17   c  illustrates a top view of an alternate embodiment of offset tip dilator  1700 .  
         [0058]      FIG. 18  is a flow chart illustrating a method of dilating tissue in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0059]      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.  
         [0060]     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 resilient plastic. In one embodiment, the retractor  112  includes a coating for lubrication, insulation, and low visual glare using, for example, parylene or nylon 11.  
         [0061]      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.  
         [0062]      FIG. 3   a  illustrates a perspective view of the cannula  100  in accordance with the present invention with the retractor fully extended, holding a sapphenous 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 .  
         [0063]      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 cauterizing scissors, used to sever a tributary or side branch of a sapphenous 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.  
         [0064]      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 retractor  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 .  
         [0065]     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  translationally under manual control. The button  106  preferably includes lateral grooves to prevent finger or thumb slippage during sliding manipulation of the retractor  112 .  
         [0066]     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 sapphenous vein  118 . When retracted into the cannula  100 , the retractor  112  is again resiliently straightened or flattened.  
         [0067]     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 coupled 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 .  
         [0068]     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 spring  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.  
         [0069]     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 .  
         [0070]     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.  
         [0071]      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 .  
         [0072]      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 of the leg  141 , button  106  is released and is retained place by the engaged teeth  148 ,  152 .  
         [0073]      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 for 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.  
         [0074]     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  FIG. 10   c  and  10   d.    
         [0075]     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.  
         [0076]      FIG. 11   a  illustrates a tip  1100  for use with a multi-lumen cannula  100  housing an endoscope  126 . The tapered tip  1100  may be removed from, and reattached to the distal end of a cannula  100 , as desired. Upon attachment, the tip  1100  seals the distal end of a cannula  100  in a fluid-tight manner. The tip  1100  is configured to provide dissection of the tissue surrounding the vessel of interest, and has a distal radius of approximately 0.045″ to reduce the hazard of penetrating the vessel of interest. The inner surface of the tip  1100  tapers to a sharp interior point and a slightly rounded exterior point and the tip  1100  has a uniform wall thickness. The tip  1100  preferably has taper angles of approximately 15° which provides a maximal, undistorted, visual field through an endoscope  126 . The tip  1100  tapers outward to a maximal diameter of about 12¾ mm at its shoulder to cover the cannula  100  body which also has a diameter of about 12¾ mm. All of these features allow the tip  1100  to effectively dissect tissue. The tip  1100  of  FIG. 11   a  has a central axis  1150  aligned with the central axis  1108  of the cannula  100 . The visual field provided by the endoscope  126 , although satisfactory for surgical procedures, is not complete because the endoscope  126  is in a lumen that is offset from the central axis  1108  of the cannula  100 . The endoscope  126  is offset because of the space required inside the cannula  100  for housing retractors and other instruments in adjacent lumens.  FIG. 11   b  illustrates this tip  1100  detached from the cannula  100 .  
         [0077]      FIG. 12   a  illustrates an offset tip  1200  for a cannula  100  in accordance with the present invention. The offset tip  1200  is a transparent, tapered tip as described above for use in endoscopic dissection of a vessel. However, in this embodiment the axis  1250  of the tip  1200  is skewed relative to the central axis  1108  of the cannula  100 . The axis  1250  of the tip  1200  is skewed approximately 8°, an angle that is chosen to align the apex  1232  of the tip  1200  with a central axis  1112  of the endoscope  126 , as shown in more detail in  FIG. 12   b.    
         [0078]      FIG. 12   b  illustrates the offset tip  1200  housed in cannula  100  in more detail. The cannula  100  houses a 5 mm endoscope  126  having a central axis  1112  eccentric to the central axis  1108  of the cannula  100 . In order to bring the distal end or apex  1232  of the axis of the tapered tip  1200  into the center of the visual field along the central axis  1112  of the endoscope  126 , the tapered tip  1200  is tilted or inclined by approximately 8° toward the lumen housing the endoscope  126 . This allows the apex  1232  of the tip  1200  to approximately intersect with the central axis  1112  of the endoscope  126 . As illustrated in  FIG. 12   b , the tip  1200  is inclined toward the central axis  1112  of the endo scope  126  without altering the taper angles  1236  and  1240  of the side walls. This is accomplished by forming a transition  1228  between the proximal or cylindrical portion  1204  of the tip  1200  and the distal or conical portion of the cannula body  1208  of the tip  1200  substantially along a plane  1230  that is skewed from normal to the central axis  1108  of the cannula  100 . The distal portion  1208  of the tip  1200  retains its conical shape and equal taper angles  1228 ,  1236  between the side walls and the transition plane. The slight extension of the cannula body at the transition plane provides sufficient incline to allow the apex  1232  of the tip  1200  to intersect the central axis  1112  of the endoscope  126 . The tip  1200  may be formed of separate conical and cylindrical parts that are attached together, or the tip  1200  may be formed as an integrated structure in the shape thus described.  
         [0079]     Alternatively, as shown in  FIG. 12   c , the tip  1200  is inclined at a lesser angle, for example, 5 degrees, toward the axis  1112  of the endoscope  126 , positioning the axis  1250  of the distal end  1232  of the tip  1200  intermediate between the central axis  1108  of the cannula  100  and the axis  1112  of the endoscope  126 . Positioning the axis  1250  of the tip  1200  to this intermediate point allows the retention of steep conical angles in the tip  1200  which allow for easier advancement of the cannula  100  while using a minimal amount of force. The intermediate positioning also provides a more complete visual field as seen through endoscope  126 .  
         [0080]     An alternate embodiment of an offset tip  1200  is shown in  FIG. 13  in which the taper angles  1320 ,  1324  of the side walls are selected to form the apex  1328  of the tip  1200  aligned with the central axis  1112  of the endoscope  126 . As illustrated, the lower region  1316  of the cylindrical part  1304  extends beyond the upper region  1312  of the cylindrical part at a plane of transition between cylindrical and tapered regions of the tip. However, in this embodiment, the taper angles  1320 ,  1324  are not equal and the thirty degree angled conical configuration of the tapered part  1308  is not maintained. Rather, the lower taper angle  1324  is increased to an obtuse angle and the upper taper angle  1320  is a reduced acute angle relative to the plane of transition between the cylindrical and tapered portions of the tip. In this configuration of the conical portion  1308 , the apex  1328  of the tip  1200  aligns with the central axis  1112  of the endoscope  126 . Thus, in accordance with either embodiment, a tip  1200  is provided which allows a maximal visual field to be viewed by the surgeon via the endoscope  126  that is eccentric the central axis  1108  of the cannula  100 , but that is aligned with or near to the apex  1232  of the tip  1200 .  
         [0081]      FIG. 14   a  illustrates a perspective side view of the offset tip  1200  and mounting rod  1404 . The tip  1200  is attached to the cannula  100  via the long rod  1404  which extends through an eccentric lumen of the cannula  100 , as shown in  FIG. 14   b , and the apex of the tip  1200  is tilted away from the rod  1404  and towards the endoscopic lumen (not shown). The elongated rod  1404  may be attached to the tip  1200 , or may be constructed as an integral part of the tip  1200 . The elongated rod  1404  preferably is secured in housing  1424 , shown in  FIG. 14   c , via threads  1408  on the proximal end of rod  1404  and mating threads within nut or knob  1416 . The rod  1404  and housing  1424  abut against the proximal end of the cannula handle  1412 , as illustrated in the perspective side view of the assembled device shown in  FIG. 14   d . Referring back to  FIGS. 14   a - c , the housing  1424  includes a slot  1420  configured to slip over the light cable outlet  1428  on the endoscope  126  as assembled within the cannula  100 . The housing  1424  preferably contains a rotating nut  1416  which accepts the threaded proximal end  1408  of the rod  1404 . When tightened onto the rod  1404 , as shown in  FIG. 14   d , the housing  1424  prevents the cannula  100  from rotating about the endoscope  126  by holding the endoscope  126  fixed with respect to the handle  1412 . This allows the operator to maintain the correct orientation of the endoscope  126  on the vessel. If the endoscope  126  is allowed to rotate freely, the image may turn sideways or upside down without the operator realizing it, and injury may occur to the vessel if the cannula  100  is advanced in the wrong direction.  
         [0082]     In one embodiment, as shown in  FIGS. 14   e  and  14   f , the elongated rod  1404  slips into the housing  1424  via a groove  1450  near its proximal end, and passes through the main hole  1454  in the housing  1424 . The groove  1450  allows for the housing  1424  to cover the proximal end of the mounting rod  1404  without completely clearing the most proximal tip of the mounting rod  1404 . This allows more room for attaching the housing  1424  which lies between the elongated rod  1404  and additional optical components. The rod  1404  may contain an elastic section, or the rod  1404  may be somewhat elastic along its entire length to facilitate stretching the rod  1404  and pulling it into position in the slot  1454  on the housing  1424 , while locking the tip  1200  in place. The elastic force also facilitates sealing the tip  1200  against the distal face of the cannula body.  
         [0083]      FIGS. 15   a  and  15   b  illustrates an alternate embodiment of offset tip  1200  and cannula  100 . In this embodiment, offset tip  1200  is formed with an elongated case  1500  which slides over the cannula body  100  and locks to the proximal end of cannula  100 . In this embodiment, proximal end of cannula  100  is threaded and allows a threaded proximal section of elongated case  1500  to mate securely to the cannula  100 .  
         [0084]     In a surgical procedure using the tissue-dissecting cannula of the present invention, the surgeon first incises  1600  the skin overlying a vessel of interest to expose the vessel as an initial step of the procedure illustrated in the flow chart of  FIG. 16 . A scissor tool is inserted  1602  into the incision to create a path to the vessel by dissecting the overlying tissue. Next, the tip  1200  of the cannula  100  is inserted  1604  into the incision to bluntly dissect tissue to form an initial tunnel along the vessel from the incision. The incision is then sealed  1608  using a blunt tip trocar and a tunnel is insufflated  1612 . The cannula is advanced  1616  along the vessel to dissect tissue adjacent the vessel under endoscopic visualization through the transparent tip. The offset tip  1200  with the apex thereof in alignment with the endoscope  126  provides a full visual field for the surgeon as the cannula  100  is advanced. The conical end of the tip  1200  dissects the tissue as the cannula  100  is advanced along the vessel. The surgeon dissects both on the anterior and posterior sides of the vessel to create a full 360 degree tunnel around the vessel. Once a selected surgical site is reached, the cannula  100  is removed  1620  from the incision seal and the tip  1200  is removed  1624  from the cannula  100 . In one embodiment, as described above, the tip  1200  is removed by unscrewing the threaded portion  1408  of the rod  1404  from the rotating nut  1416 . The tip housing  1424  itself is also removed in this embodiment. Insufflation is maintained and the cannula  100  without tip  1200  is inserted  1628  into the seal into the tunnel adjacent the vessel. Transecting devices are then inserted  1630  into the cannula  100 . Without tip  1200  disposed over the distal end, the cannula  100  can now be used for transecting  1632  side branches and the ends of the vessel of interest using endoscopic instruments that are selectively installed and removed within instrument lumens in the cannula body  100 . After these procedures are completed, the vessel may be removed  1636 .  
         [0085]      FIG. 17   a  illustrates another embodiment of an offset tip dilator  1700 . In this embodiment of the present invention, the tip  1700  also includes wing-like protrusions for enlarging or dilating a peri-vascular cavity in the course of separating a vessel from adjacent connective tissue. For example, after tissue dissection with an offset tip  1200  to form a tunnel or working cavity adjacent a target vessel by dissecting along the anterior and posterior sides of the vessel, the cannula  100  is removed from the distal end of the body, the offset tip  1200  is detached, and a second tip  1700  is attached to the distal end of the cannula body  100 . In one embodiment, the second tip  1700  includes a transparent tapered tip with planar wing-like protrusions or extensions disposed proximal to the distal end  1720  of the tip  1700 . The wing-like protrusions  1702 ,  1704  each include a swept back leading edge. As shown in  FIG. 17   b , the tip  1200  is tilted away from the mounting rod  1404  to align with the central axis of an endoscopic lumen (not shown). The wing-like protrusions  1702 ,  1704  may also include curved distal and proximal edges, for example, in a parabolic configuration as shown in  FIG. 17   c , providing a smoother withdrawal of the cannula  100  from the insufflated tunnel. The tip  1700  attaches to the cannula body  100  in the same manner as previously described with reference to the offset tip  1200 , with an elongated rod  1404  extending through a lumen of the cannula  100  and locking at the proximal end of the handle  1412 . The cannula  100  may thus be advanced through tissue under full-field endoscopic visualization through the tapered tip  1720  with the wing-like protrusions  1702 ,  1704  extending substantially diametrically to facilitate tunnel dilation.  
         [0086]     The wing-like protrusions  1702 ,  1704  of the tip  1700  are arranged in substantially planar geometry in contrast to the solid bulbous, oval element described above. The planar configuration of the wing-like protrusions  1702 ,  1704  substantially reduce the frontal profile of the dilator required to penetrate tissue, and thus reduces the resistive force encountered during advancement of the cannula  100  through tissue. Although the tissue-dilating force is exerted on tissue surrounding the cavity in a bilateral, substantially planar orientation by the outer edges of the wing-like protrusions  1702 ,  1704  that dissect tissue forming the cavity walls, the dilated cavity may retain a round cross-section for example, within an insufflated cavity, in the same manner as if tissue dilation was performed using a solid oval dilator that applies dilating force circumferentially.  
         [0087]      FIG. 18  illustrates a method of dilating tissue in accordance with one method embodiment of the present invention. The skin is incised  1800  overlying the vessel of interest, and the scissor tool is inserted into the incision to create a path to the vessel by dissecting the overlying tissue. The incision is then bluntly dissected  1804  using the offset tip  1200  to expose the vessel surface. The incision is sealed  1808  and a tunnel is insufflated  1812 . The cannula  100  is advanced  1816  along the vessel under endoscopic visualization through the transparent tip  1200 . After sufficient length of tunnel is formed adjacent the vessel, the cannula  100  is removed  1820  and the incision seal is removed or slid backwards to the proximal end of the cannula  100 . The offset tip  1200  is then replaced  1824  with the dilating tip  1700 . The seal is reinserted and the incision is sealed  1826 . The cannula  100  is advanced  1828  and the cavity is further dilated responsive to the advancement of the planar wing-like protrusions  1702 ,  1704  through tissue forming the tunnel walls. The cannula  100  is removed  1832  a second time, and the incision seal is again removed or slid backwards to the proximal end of the cannula  100 . The dilating tip is removed  1836  and the incision is sealed  1837 . Transection devices are loaded  1838  through instrument lumens within the cannula body  100  into the cannula  100  and the cannula  100  is then inserted  1839  back into the incision. Without any tip covering the distal end of the cannula  100 , the vessel side branches and ends are transected  1840  using endoscopic instruments, and the vessel is then removed  1844  from the dilated tunnel.