Abstract:
Surgical apparatus and method includes a cannula that houses an endoscope and supports a dilating element near a distal end of the cannula. The dilating element has a dimension which is greater than the diameter of the cannula for enlarging a surgical cavity in tissue as the cannula is advanced through tissue at a surgical site to provide working space adjacent a target vessel within which surgical instruments may be conveniently manipulated. The dilating element of oval sided shape permits surrounding tissue to be pushed away or otherwise displaced away from the target vessel atraumatically. A locking mechanism is disposed on the cannula, which accepts a succession of mating dilating elements of progressively larger dimensions for successive insertion and enlargement of a surgical cavity as required. In one embodiment, the dilating element is made of rigid plastic, and in another embodiment, the dilating element is made of resilient material that may be confined within a retractable sheath which, in the extended position, encases and compresses the dilating element to a smaller dimension and which, in a retracted position, allows the dilating element to resiliently expand and enlarge the surgical cavity.

Description:
This is a continuation of application Ser. No. 09/133,136 filed on Aug. 12, 1998, now abandoned, which is incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of surgical apparatus, and more particularly to endoscopic vessel isolators. 
     BACKGROUND OF THE INVENTION 
     During surgical harvesting of vessels, a target vessel is exposed, tributaries are ligated and transected, and the vessel is harvested. In order to view the vessel, a cannula housing an endoscope is inserted into a surgical cavity to visualize the adventitial layer of a target vessel. The vessel is tracked by advancing the cannula along the path of the vessel while bluntly dissecting the cavity as the cannula is advanced. Upon viewing a side branch or tributary of the vessel, a surgical tool is inserted into the surgical cavity to cauterize and sever the side branch. The endoscope remains in the surgical cavity during this process to allow the surgeon to view the procedure, and the size of the cavity is maintained using insufflating gas. Using different tools simultaneously in a surgical cavity is difficult due to the small size of the surgical cavity. Additionally, within the surgical cavity, the surrounding tissue typically collapses upon the cannula and surgical tools, increasing the difficulty of the operation, if performed without insufflation. However, maintaining the surgical cavity open using insufflation with gas under pressure then also requires sliding gas-tight seals for each endoscopic instrument that is inserted into the surgical cavity. 
     Current systems commonly employ a balloon coupled to the cannula for intermittent inflation and deflation to enlarge the surgical cavity as the cannula is advanced. However, use of a balloon to enlarge surgical cavities has the disadvantage that multiple balloon inflation and deflation tires the surgeon&#39;s hands, and makes it difficult to retain the precise hand control needed to perform the surgical procedure. Also, manufacture of a balloon cannula requires manual mounting of the balloon in a tedious process that adds expense to the device. Additionally, balloons have a potential for rupture during use and thereby disrupt the surgical procedure. Thus, a device is needed which retains the endoscopic vessel tracking ability of current systems, while also enlarging the surgical cavity without the disadvantages of balloon systems. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a tissue dissector is provided in which a cannula houses an endoscope, and a dilating element is coupled near the distal end of the cannula. The dilating element has an outer dimension which is greater than the diameter of the distal end of the cannula. This greater dimension serves to enlarge the surgical cavity as the cannula is advanced through the surgical site, thus allowing the cannula to track along the vessel while forming a working cavity and providing room within which additional surgical tools may operate safely. In one embodiment, the dilating element is in the shape of an oval, allowing compression of the surrounding tissue to occur atraumatically. 
     In an alternate embodiment, a locking mechanism is disposed on the cannula, and the dilating element is coupled to the locking mechanism when enlargement of the surgical cavity is required. In this embodiment, multiple dilating elements of differing outer dimensions may be employed responsive to the enlargement required. Various locking mechanisms may be employed in accordance with the current invention, including using screw threads disposed on the surface of the cannula, and mating internal screw threads in a bore hole through the dilating element to permit the dilating element to couple to the screw threads. Alternatively, the dilating element may include a bayonet-type fitting, with mating knobs on the associated surface portion of the cannula for locking the dilating element into place. Additionally, in one embodiment the tip and dilating element are a single detachable component, and may be coupled and decoupled to the main body of the cannula as desired. This greatly facilitates use of dilating elements of different dimensions. 
     The body of the cannula may be tapered from a smaller diameter near the distal end of the cannula to a larger diameter remote from the distal end of the cannula. The tip of the cannula is transparent to facilitate endoscopic viewing of the surgical cavity. The tapering of the distal end of the cannula may begin at a point forward of the distal end of the dilating element. This allows the tip of the cannula to track along the target vessel without the enlarged diameter of the dilating element preventing the tip from making contact with the target vessel. In one embodiment, the dilating element is made of rigid plastic to facilitate expansion of a working cavity and ease of translation through the surgical site. In another embodiment, the dilating element is made of a flexible material which compresses as the external walls exert force upon the cannula, but retains sufficient structural rigidity to accomplish the required enlargement of a working cavity. In yet another embodiment, the dilating element is made of flexible material and is shrouded within a retractable sheath which, in the extended position, encases the dilating element and thereby compresses the dilating element to a smaller diameter, and in a retracted position, allows the dilating element to expand and enlarge the working cavity. 
     Methods are also disclosed for dissecting an elongated cavity along the course of a vessel using a cannula according to one or other embodiments of the present invention, including incising the skin of a patient, placing the tip of the cannula along the surface of the vessel, advancing the cannula along the vessel under continuous endoscopic visualization through the tip, enlarging the cavity about the outer dimension of the dilating element, removing the cannula upon reaching the desired length of target vessel, and optionally placing a sealing trocar in the incision and maintaining the enlargement by insufflating the subcutaneous tunnel with gas under pressure. The vessel may then be harvested through a separate incision near the remote end of the surgical cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of the cannula in accordance with one embodiment of the present invention. 
         FIG. 2  is a cut-away side sectional view of the cannula in accordance with the present invention. 
         FIG. 3  is a perspective view of the distal end of cannula in accordance with the present invention. 
         FIG. 4  is a flow chart illustrating the application of cannula in accordance with the present invention. 
         FIG. 5   a  illustrates a cannula having a locking mechanism in accordance with one embodiment of the present invention. 
         FIG. 5   b  is a side view of a dilating element for locking attachment to the cannula in  FIG. 5   a.    
         FIG. 5   c  is a cut-away side sectional view of the dilating element for use with the cannula of  FIG. 5   a.    
         FIG. 6   a  is a cannula having an alternate embodiment of a locking mechanism in accordance with the present invention. 
         FIG. 6   b  is a side view of a dilating element for locking attachment to the cannula of  FIG. 6   a.    
         FIG. 6   c  is a cut-away side sectional view of the dilating element for use with the cannula of  FIG. 6   a.    
         FIG. 7  is an exploded view illustrating the removable module of tip and dilating element on a cannula in accordance with another embodiment of the present invention. 
         FIG. 8  is a flow chart illustrating the operation of the interchangeable dilating element embodiment of the cannula in accordance with the present invention. 
         FIG. 9   a  is a cut-away side sectional view of an embodiment of the present invention including a retractable sheath illustrated in extended position. 
         FIG. 9   b  is a cut-away side sectional view of the embodiment of  FIG. 9   a  with the retractable sheath illustrated in retracted position. 
         FIG. 10  is a flow chart illustrating the operation of the retractable sheath embodiment of the cannula in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a tissue dissector  50  in which a cannula  100  is coupled to a dilating element  112 . The proximal end of cannula  100  is coupled to a handle  116  and the distal end of cannula  100  is enclosed by transparent tapered tip  104 . Dilating element  112  is positioned inwardly from the distal end of the cannula  100 . Cannula  100  may be made from a variety or combination of bioinert, substantially inelastic materials, such as stainless steel, polyethylene, polyurethane, polyvinyl chloride, polyimide plastic, and the like that preferably have a tensile strength of at least 10,000 psi. Handle  116  is ergonomically formed to allow a surgeon to easily and comfortably manipulate cannula  100  within a surgical cavity. 
       FIG. 2  illustrates a cut-away side sectional view of tissue detector  50 . As shown, the distal end of cannula  100  has an outer diameter or dimension  136 , and the dilating element  112  has an outer dimension  132  which is greater than the diameter  136 . The proximal portion of cannula  100  preferably has a smaller dimension than the dilating element  112  to allow more flexibility in maneuvering the cannula  100  in the surgical site. The greater dimension  132  of dilating element  112  enlarges or expands a surgical cavity by pushing away surrounding tissue within a surgical cavity as the cannula  100  is advanced through a surgical site. The surgical cavity may thus be formed adjacent to a target vessel as a result of the blunt tissue dissection caused by the tapered tip  104  as it is advanced along the path of a target vessel, such as the saphenous vein. A preferable diameter  136  of cannula  100  is about 8.5 mm, and preferable outer dimensions  132  of dilating elements  112  are in the range from about 15 mm to about 30 mm. Thus, in application, a surgical cavity is initially formed by the tapered tip  104 , and is initially increased or enlarged to the diameter  136  of the distal end of cannula  100 . Additionally, in accordance with the present invention, the surgical cavity is further enlarged by the dilating element  112  substantially to the dimension  132  of the dilating element  112  and this latter enlargement or expansion of a surgical cavity constitutes two or three times greater enlargement than the enlargement of such a surgical cavity by the diameter  136  of the distal end of the cannula  100 . This enhanced enlargement of a surgical cavity eases further dissection of tissue as the cannula  100  is advanced along a target vessel, and facilitates subsequent manipulation of surgical tools within such surgical cavity. 
     Cannula  100  houses an endoscope  120  for viewing the surgical site and the target vessel through the transparent tip  104 . The proximal end of endoscope  120  is attached to the proximal end of the cannula  100  by mating screw threads  128  at the proximal end of the cannula  100  and the proximal end of the endoscope  120  for fixedly positioning the endoscope  120  within the cannula  100 . The proximal end of the endoscope  120  may include an eyepiece or camera attachment, or the like (not shown), and the distal end of endoscope  120  is positioned near the distal end of the cannula  100  in alignment with the tip  104  for visualization there through of tissue being bluntly dissected thereby as the cannula  100  is advanced along a target vessel. 
     Referring to  FIG. 3 , tip  104  is made of a transparent material, such as polycarbonate plastic. Positioning endoscope  120  near the distal end of cannula  100  and in alignment with the transparent tip  104  therefore allows a surgeon to view objects forward of the cannula  100 . This enables the surgeon to advance the cannula  100  along the path of a target vessel, and to view and thereby avoid avulsing any side branches. Tip  104  is tapered from the distal end thereof (that is blunted with a radius of about 0.045 inches) to the larger diameter of the proximal end of tip  104  that is approximately the diameter  136  of the distal end of the cannula  100 . Tapering of the tip  104  over a taper length of about 0.500 to about 0.800 inches allows advancement of the cannula along the vessel without excessive force and injury to the vessel, as well as better visualization via the endoscope  120  of a target vessel through the tapered walls of the transparent tip  104 . 
     In order to track the path of a target vessel effectively, the tapered wall of tip  104  is placed against the target vessel as the cannula  100  is advanced through connective tissue. The taper angle  116  of the tip  104  allows the target vessel to be seen more clearly and allows a length of vessel equivalent to the length of the taper of the tip  104  to be seen by the surgeon. In order to enable the tapered wall of tip  104  to lay against the target vessel, a spacer length  108  of cannula  100  between the dilating element  112  and the proximal end of tip  104  is provided to set the dilating element  112  back behind the taper angle  116  of the tapered wall of tip  104 . This spacer length  108  of cannula  100  may have a diameter substantially equal to the outer diameter  136  of the distal end of the cannula  100 . The spacer length prevents dilating element  112  from interfering with the contacting of the target vessel by the walls of the tapered tip  104 , at taper angle  116 . Without an intervening spacer length  108 , the dilating element  112  more closely adjacent the tip  104  would prevent the tapered wall of tip  104  from contacting the target vessel within the taper angle  116 , and this would increase the force exerted on the target vessel during cannula advancement. In one embodiment, the distal end of dilating element  112  is 14-28 mm from the proximal end of the tip  104 . Cannula  100  is preferably about 32-47 cm long, and tip  104  is preferably about 10-15 mm long. 
     Dilating element  112  is preferably formed of Teflon or polyurethane, or polycarbonate, or the like, to form a rigid shape which compresses or otherwise displaces tissue on the walls of the surgical cavity to form an enlarged surgical cavity. In an alternate embodiment, dilating element  112  comprises resilient foam which compresses in response to an applied external force. For example, pressure from inserting the dilating element  112  into a small incision may reduce the diameter of the dilating element  112  and prevent the dilating element  112  from causing further rupture or tearing of the incision. Since the tissue typically surrounding a target vessel such as the saphenous vein is soft fatty tissue, a foam dilating element  112  with sufficient resilience and rigidity may push back the fatty tissue and enlarge a surgical cavity adjacent the vessel. Dilating element  112  is preferably of oval shape to facilitate atraumatic expansion of the surrounding tissue following blunt dissection of the fatty tissue by the tapered tip  104 . Of course, other shapes of dilating element  112  may be used that have maximum dimensions  132  greater than the dimension of the proximal end of tip  104 . 
     In application, as shown in  FIG. 4 , the surgeon incises  400  the skin of the patient and dissects  404  to expose the surface of the target vessel. The surgeon next places  408  the tapered wall of the transparent tip  104  on the surface of the vessel and advances  412  the tip  104  and cannula  100  under endoscopic visualization through the tip  104  along the path of the target vessel. Following dissection of the cavity along the vessel, the cannula  100  is removed  416 , and a sealing trocar may be placed  420  in the incision for insufflating  424  the subcutaneous tunnel with gas under pressure to maintain the enlargement of the cavity. The vessel thus isolated is then harvested  428 . A combined endoscopic and dissection instrument may be introduced through the sealing trocar to ligate and remove the target vessel for use, for example, as a coronary artery or peripheral vascular bypass graft. Alternatively, the isolated vessel may be left in place for surgical formation of an in-situ femoropopliteal or femoral-distal graft. Alternatively, following incision of the skin of the patient and dissection to expose the surface of the target vessel, gas insufflation may be initiated through a sealing trocar. The sealing trocar may be loaded onto the shaft of the cannula  100  prior to fixation of the dilating element  112  (if the outer dimension  132  of the dilating element  112  is greater than the inner diameter of the sealing trocar). The advancement  412  of the cannula  100  may then be conducted under gas insufflation, to improve visualization of the previously formed surgical cavity. 
       FIG. 5   a  illustrates an embodiment of cannula  100  with a locking mechanism  150  for a detachable dilating element  112  as shown in  FIG. 5   b . Locking mechanism  150  includes a length of screw threads disposed on the surface or outer housing of the cannula  100  at a position near the distal end of the cannula that allows the locked dilating element  112  to be located in a position on the cannula  100  as described previously herein with reference to  FIGS. 1-3 . 
       FIG. 5   c  illustrates a cross-section of the dilating element  112  having a mating lock or set of screw threads  162  which couples to locking mechanism  150  of  FIG. 5   a . A bore hole  154  is formed along the horizontal axis of the dilating element  112  and the screw threads are disposed along a portion of the bore hole  154  as a mating lock  162 . The dimension  158  of the bore hole  154  is wider than the diameter  136  of the cannula  100  but is small enough to ensure a tight coupling upon inserting the dilating element  112  into the locking mechanism  150 . Thus, in this configuration, the dilating element  112  is locked onto the cannula  100  by rotating the grooved end of the dilating element  112  around the shaft of the cannula  100  until the distal end of the screw threads  150  on the cannula  100  contacts the unthreaded portion of the dilating element  112  in the bore hole  154 . At this point, the dilating element  112  is locked. 
       FIG. 6   a  illustrates an alternate embodiment of locking mechanism  150 . A knob or protuberance is disposed on the surface of cannula  100  for mating with a corresponding groove  162 , as shown in  FIG. 6   c , in the dilating element  112 . The groove  162  is formed to slide over knob  150  and mate therewith through partial rotation on the cannula  100  for locking the dilating element  112  of  FIG. 6   b  in place. In another embodiment, the locking mechanism  150  includes the groove in the surface of the cannula  100 , and the dilating element  112  includes the protuberance disposed in the bore hole of the dilating element  112 . 
       FIG. 7  illustrates an exploded view of an embodiment of cannula  100  in which the tip  104  and the dilating element  112  are fixably coupled together as a unit, and are detachable from the distal end of cannula  100 . This embodiment allows convenient change of dilating elements  112  by simply removing the dilating element  112  and tip  104  unit for replacement with an alternate dilating element  112  of different dimension and tip  104  unit. Threads  170  positioned at the distal end of the cannula  100  allows a threaded bore hole  154  (not shown) in the dilating element  112  or tip  104  unit to couple to the threaded shaft  170 . This embodiment employing detachable or interchangeable dilating elements  112  allows the surgeon to control the size of the surgical cavity being dissected in tissue. This is accomplished by coupling dilating elements  112  of differing outer dimensions  132  to the cannula  100  which, in turn, enlarge the surgical cavity to sizes corresponding substantially to the dimensions  132  of the dilating elements  112 . Different surgical cavities require different amounts of enlargement and therefore the surgeon may select the amount of enlargement provided by the cannula  100  in a specific surgical cavity in accordance with the multiple dilating elements  112  that may be attached and utilized in succession in accordance with the described embodiments of the present invention. 
     The flow chart of  FIG. 8  illustrates a method for isolating a target vessel using the detachable dilating element  112 . The surgeon incises  800  the skin and dissects  804  to expose the adventitial surface of the target vessel. The surgeon next places  808  the transparent tapered tip  104  on the adventitial surface of the vessel. The cannula  100  is advanced  812  under endoscopic visualization through the tip  104  until the target vessel is sufficiently isolated. The cannula  100  is removed  816  after establishing a subcutaneous tunnel or surgical cavity adjacent the target vessel which is more constricted than desirable, and therefore requires greater enlargement. The dilating element  112  is then removed and replaced  820  with a larger dilating element  112  and the cannula  100  is again advanced  824  through the tunnel until the surgical cavity is sufficiently dissected using interchangeable dilating elements  112  in a succession of progressively larger dimensions as necessary to attain the required amount of enlargement of the surgical cavity. The cannula  100  is removed  828  and a sealing trocar is placed  832  in the incision and the tunnel is insufflated  836  with gas under pressure to facilitate harvesting the vessel  840 . 
     The cut-away side sectional views of  FIGS. 9   a  and  9   b  illustrate an alternate embodiment of cannula  100  in which a slidable sheath  160  is employed to reduce the outer dimension  132  of the dilating element  112 . In this embodiment, the dilating element  112  includes resiliently compressible foam, as described above. The sheath may be formed as a plastic tube which is slidably disposed on the cannula  100  and which has a distal end  168  and a proximal end  172 . 
     Upon sliding or extending the sheath  160  in a distal direction, the distal end  168  of the sheath  160  encases the dilating element  112  and thereby compresses the dilating element  112  to a reduced dimension  132 . Upon retracting the sheath  160  by sliding the sheath  160  in a proximal direction, the distal end  168  of the sheath  160  releases the dilating element  112  which resiliently expands to a larger dimension  132 , as shown in  FIG. 9   b . Thus, by compressing the dilating element  112  upon inserting the cannula  100  into an incision, rupture or tearing of the incision is minimized. When properly placed, the sheath  160  is retracted to enable resilient expansion of the dilating element  112 , thereby to provide enlargement of the surgical cavity. 
     In application, as shown in the flow chart of  FIG. 10 , the surgeon incises  1000  the skin and dissects  1004  to expose the adventitial surface of the target vessel. The surgeon next extends  1006  the sheath and places  1008  the transparent tapered tip  104  of the cannula  100 , with the sheath extended, on the surface of the vessel. The sheath  160  retains the dilating element  112  in compressed configuration as the cannula is advanced  1012  until the ensheathed dilating element  112  is in selected position under the skin. The sheath  160  is retracted  1016  to allow the compressible dilating element  112  to expand. The cannula  100  is advanced  1020  under endoscopic visualization through the tip  104  until the target vessel is sufficiently isolated. The cannula  100  is removed  1024 , and a sealing trocar is placed  1028  in the incision and the tunnel is insufflated  1032  with gas under pressure to facilitate harvesting  1036  the isolated vessel. 
     Therefore the method and apparatus of the present invention facilitate enlargement of a surgical cavity simultaneous with the advancement of the cannula  100  through the surgical cavity, without requiring intermittent manual manipulation of balloons or other similar devices. Additionally, the method and apparatus of the present invention provides for dilating the surgical cavity to different dimensions responsive to interchanging detachable dilating elements  112 . Finally, the method and apparatus of the present invention provides for a dilating element  112  which has a compressible resilient dimension for insertion through an incision in a state of compressed dimension for minimizing rupture or tearing of the incision while still providing for enlargement of the surgical cavity in a state of resilient expansion.