Patent Publication Number: US-9839471-B2

Title: Surgical instrument

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of U.S. patent application Ser. No. 14/043,322, filed on Oct. 1, 2013, now U.S. Pat. No. 9,265,566, which claims the benefit of and priority to U.S. Provisional Application No. 61/714,591, filed on Oct. 16, 2012, the entire contents of each of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to the field of surgical instruments. In particular, the disclosure relates to an endoscopic electrosurgical forceps that is economical to manufacture and is capable of sealing and cutting relatively large tissue structures. 
     2. Background of Related Art 
     Instruments such as electrosurgical forceps are commonly used in open and endoscopic surgical procedures to coagulate, cauterize and seal tissue. Such forceps typically include a pair of jaws that can be controlled by a surgeon to grasp targeted tissue, such as, e.g., a blood vessel. The jaws may be approximated to apply a mechanical clamping force to the tissue, and are associated with at least one electrode to permit the delivery of electrosurgical energy to the tissue. The combination of the mechanical clamping force and the electrosurgical energy has been demonstrated to join adjacent layers of tissue captured between the jaws. When the adjacent layers of tissue include the walls of a blood vessel, sealing the tissue may result in hemostasis, which may facilitate the transection of the sealed tissue. A detailed discussion of the use of an electrosurgical forceps may be found in U.S. Pat. No. 7,255,697 to Dycus et al. 
     A bipolar electrosurgical forceps typically includes opposed electrodes disposed on clamping faces of the jaws. The electrodes are charged to opposite electrical potentials such that an electrosurgical current may be selectively transferred through tissue grasped between the electrodes. To effect a proper seal, particularly in relatively large vessels, two predominant mechanical parameters must be accurately controlled; the pressure applied to the vessel, and the gap distance established between the electrodes. 
     Both the pressure and gap distance influence the effectiveness of the resultant tissue seal. If an adequate gap distance is not maintained, there is a possibility that the opposed electrodes will contact one another, which may cause a short circuit and prevent energy from being transferred through the tissue. Also, if too low a force is applied the tissue may have a tendency to move before an adequate seal can be generated. The thickness of a typical effective tissue seal is optimally between about 0.001 and about 0.006 inches. Below this range, the seal may shred or tear and above this range the vessel walls may not be effectively joined. Closure pressures for sealing large tissue structures preferably fall within the range of about 3 kg/cm 2  to about 16 kg/cm 2 . 
     As is traditional, the term “distal” refers herein to an end of the apparatus that is farther from an operator, and the term “proximal” refers herein to the end of the electrosurgical forceps that is closer to the operator. 
     SUMMARY 
     The present disclosure relates to an electrosurgical apparatus for electrosurgically sealing tissue. The present disclosure describes a surgical instrument for treating tissue that is economical to manufacture and is capable of sealing and cutting relatively large tissue structures. 
     The surgical instrument includes a housing and an elongated shaft having a distal portion and a proximal portion coupled to the housing. The elongated shaft defines a longitudinal axis and a mandrel at the proximal portion. An inner shaft member extends at least partially through the elongated shaft. An actuating mechanism is operably coupled to the mandrel and is configured to selectively cause movement of the elongated shaft in a longitudinal direction with respect to the inner shaft member. The surgical instrument also includes an end effector adapted for treating tissue. The end effector includes an upper jaw member pivotally coupled to a distal portion of the inner shaft member about a pivot axis and a lower jaw member supported by the distal portion of the elongated shaft. The elongated shaft is configured to pivot the upper jaw member relative to the lower jaw member upon longitudinal movement relative to the inner shaft member. 
     Additionally or alternatively, the elongated shaft may be configured to engage a foot extending from the upper jaw member such that longitudinal motion of the elongated shaft biases the foot to pivot the upper jaw member relative to the lower jaw member. 
     Additionally or alternatively, the elongated shaft may have a generally u-shaped profile including opposing interior sidewalls. 
     Additionally or alternatively, the inner shaft member may have a generally u-shaped profile including opposing interior sidewalls disposed laterally outward from the opposing interior sidewalls of the elongated shaft. 
     Additionally or alternatively, the surgical instrument includes a knife disposed between the opposing interior sidewalls of the elongated shaft and selectively movable in a longitudinal direction with respect to the elongated shaft. 
     Additionally or alternatively, the elongated shaft may be constructed from a single piece of metal. 
     Additionally or alternatively, the inner shaft member may be constructed from a single piece of metal. 
     According to another aspect of the present disclosure, a surgical instrument is provided. The surgical instrument includes a housing and an elongated shaft having a distal portion and a proximal portion coupled to the housing. The elongated shaft defines a longitudinal axis and a mandrel at the proximal portion. The elongated shaft has a generally u-shaped profile including opposing interior sidewalls. An inner shaft member extends at least partially through the elongated shaft. An actuating mechanism is operably coupled to the mandrel and is configured to selectively cause movement of the elongated shaft in a longitudinal direction with respect to the inner shaft member. The surgical instrument also includes an end effector adapted for treating tissue. The end effector includes an upper jaw member pivotally coupled to a distal portion of the inner shaft member about a pivot axis and a lower jaw member supported by the distal portion of the elongated shaft. The elongated shaft is configured to pivot the upper jaw member relative to the lower jaw member upon longitudinal movement relative to the inner shaft member. The surgical instrument also includes a knife extending at least partially through the elongated shaft between the opposing interior sidewalls. The knife is selectively movable in a longitudinal direction and includes a blade extendable through a tissue contacting portion of the jaw members. 
     Additionally or alternatively, the knife may be stamped from a single piece of metal. 
     Additionally or alternatively, the elongated shaft may be stamped from a single piece of metal. 
     Additionally or alternatively, the inner shaft member may be stamped from a single piece of metal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the detailed description of the embodiments given below, serve to explain the principles of the disclosure. 
         FIG. 1  is a perspective view of an electrosurgical forceps according to an embodiment of the present disclosure including a housing, an elongated shaft, and an end effector; 
         FIG. 2A  is an enlarged perspective view of the end effector of  FIG. 1  depicted with a pair of jaw members in an open configuration; 
         FIG. 2B  is an enlarged perspective view of the end effector of  FIG. 1  depicted with the pair of jaw members in a closed configuration; 
         FIG. 3  is a perspective view of the end effector and elongated shaft of  FIG. 1  with parts separated; 
         FIG. 4  is a proximally-facing perspective view of a rotation knob depicting a cavity for receiving the elongated shaft of  FIG. 1 ; 
         FIG. 5  is a cross-sectional, perspective view of the end effector assembled with the elongated shaft of  FIG. 1 ; 
         FIG. 6  is a perspective view of a lower jaw member of the end effector of  FIG. 1  depicting a double flag at a proximal end thereof; 
         FIG. 7  is a cross-sectional, perspective view of the lower jaw member of  FIG. 6 ; 
         FIG. 8  is a perspective view of a proximal portion of the instrument of  FIG. 1  with a portion of the housing removed revealing internal components; and 
         FIG. 9  is a partial, side view of a proximal portion of the instrument of  FIG. 1  with a portion of the housing removed revealing internal components; 
         FIG. 10A  is a perspective view of a proximal portion of the knife actuation mechanism of the end effector of  FIG. 1 ; 
         FIG. 10B  is a cross-sectional, top view of a knife collar of the knife actuation mechanism of the end effector of  FIG. 1 ; 
         FIG. 11A  is a side view of the proximal portion of the instrument of  FIG. 8  depicting a movable handle in a separated position with respect to a stationary handle, which corresponds to the open configuration of the end effector depicted in  FIG. 2A , and a knife trigger in a separated configuration with respect to the stationary handle, which corresponds to an un-actuated or proximal configuration of a knife with respect to the jaw members; 
         FIG. 11B  is a side view of the proximal portion of the instrument of  FIG. 8  depicting the movable handle in an intermediate position with respect to the stationary handle, which corresponds to a first closed configuration of the end effector wherein the jaw members encounter one another; 
         FIG. 11C  is a side view of the proximal portion of the instrument of  FIG. 8  depicting the movable handle in an approximated configuration with respect to the stationary handle, which corresponds to a second closed configuration of the end effector wherein the jaw members apply an appropriate pressure to generate a tissue seal; and 
         FIG. 11D  is a side view of the proximal portion of the instrument of  FIG. 8  depicting the knife trigger in an actuated configuration, which corresponds to an actuated or distal position of the knife with respect to the jaw members. 
     
    
    
     DETAILED DESCRIPTION 
     Referring initially to  FIG. 1 , an embodiment of an electrosurgical forceps  100  generally includes a housing  112  that supports various actuators thereon for remotely controlling an end effector  114  through an elongated shaft  116 . Although this configuration is typically associated with instruments for use in laparoscopic or endoscopic surgical procedures, various aspects of the present disclosure may be practiced with traditional open instruments and in connection with endoluminal procedures as well. 
     The housing  112  is constructed of a left housing half  112   a  and a right housing half  112   b . The left and right designation of the housing halves  112   a ,  112   b  refer to the respective directions as perceived by an operator using the forceps  100 . The housing halves  112   a ,  112   b  may be constructed of sturdy plastic, and may be joined to one another by adhesives, ultrasonic welding or other suitable assembly methods. 
     To mechanically control the end effector  114 , the housing  112  supports a stationary handle  120 , a movable handle  122 , a trigger  126  and a rotation knob  128 . The movable handle  122  is operable to move the end effector  114  between an open configuration ( FIG. 2A ) wherein a pair of opposed jaw members  130 ,  132  are disposed in spaced relation relative to one another, and a closed or clamping configuration ( FIG. 2B ) wherein the jaw members  130 ,  132  are closer together. Approximation of the movable handle  122  with the stationary handle  120  serves to move the end effector  114  to the closed configuration and separation of the movable handle  122  from the stationary handle  120  serves to move the end effector  114  to the open configuration. The trigger  126  is operable to extend and retract a knife blade  156  ( FIG. 2A ) through the end effector  114  when the end effector  114  is in the closed configuration. The rotation knob  128  serves to rotate the elongated shaft  116  and the end effector  114  about a longitudinal axis A-A extending through the forceps. 
     To electrically control the end effector  114 , the housing  112  supports a switch  136  thereon, which is operable by the user to initiate and terminate the delivery of electrosurgical energy to the end effector  114 . The switch  136  is in electrical communication with a source of electrosurgical energy such as electrosurgical generator  141  or a battery (not shown) supported within the housing  112 . The generator  141  may include devices such as the LIGASURE® Vessel Sealing Generator and the Force Triad® Generator as sold by Covidien Energy-based Devices of Boulder, Colo. A cable  143  extends between the housing  112  and the generator  141  and may include a connector (not shown) thereon such that the forceps  100  may be selectively coupled and decoupled electrically from the generator  141 . 
     Referring now to  FIGS. 2A-3 , the end effector  114  may be moved from the open configuration ( FIG. 2A ) wherein tissue (not shown) is received between the jaw members  130 ,  132 , and the closed configuration ( FIG. 2B ), wherein the tissue is clamped and sealed. The upper and lower jaw members  130 ,  132  are electrically coupled to cable  143 , and thus to the generator  141  (e.g., via a respective wire extending through the elongated shaft  116 ) to provide an electrical pathway to a pair of electrically conductive, tissue-engaging sealing plates  148 ,  150  disposed on the lower and upper jaw members  132 ,  130 , respectively. The sealing plate  148  of the lower jaw member  132  opposes the sealing plate  150  of the upper jaw member  130 , and, in some embodiments, the sealing plates  148  and  150  are electrically coupled to opposite terminals, e.g., positive or active (+) and negative or return (−) terminals associated with the generator  141 . Thus, bipolar energy may be provided through the sealing plates  148  and  150 . Alternatively, the sealing plates  148  and  150  and/or the end effector  114  may be configured for delivering monopolar energy to the tissue. In a monopolar configuration, the one or both sealing plates  148  and  150  deliver electrosurgical energy from an active terminal, e.g. (+), while a return pad (not shown) is placed generally on a patient and provides a return path to the opposite terminal, e.g. (−), of the generator  141 . 
     Referring now to  FIG. 3 , the elongated shaft  116  includes various longitudinal components that operatively couple the end effector  114  to the various actuators supported by the housing  112  ( FIG. 1 ). An outer shaft member  160  defines an exterior surface of the elongated shaft  116  and includes a mandrel  169  formed on a proximal portion thereof. As described in further detail below, mandrel  169  supports various components disposed within housing  112  that cooperate with the movable handle  122  to effect longitudinal movement of the outer shaft member  160  along the longitudinal axis A-A. The outer shaft member  160  generally exhibits a U-shaped profile including interior sidewalls  162   a ,  162   b  ( FIG. 5 ). An inner shaft member  180  is received within the outer shaft member  160 . Upper jaw member  130  is mechanically coupled to the inner shaft member  180  about a pivot pin  144 . The pivot pin  144  extends through a throughbore  130   a  disposed through a proximal portion of jaw member  130  to pivotally support jaw member  130  at the distal end of the inner shaft member  180 . Outer shaft member  160  is configured for longitudinal motion with respect to the inner shaft member  180 . 
     The outer shaft member  160 , including the mandrel  169 , may be constructed from a single flat stock piece of metal. In constructing the outer shaft member  160 , a stamping, punching or similar metal-working process may be employed to initially generate a flat blank that includes an appropriate outer profile and any interior openings or features. Thereafter, the necessary bends and curves may be formed by bending the flat blank with a press brake, or other suitable metal-working equipment. The outer shaft member  160  may be formed by folding the flat blank into a generally rectangular profile (or generally circular profile) such that two opposing longitudinal edges of the flat blank meet at a longitudinal seam  161  ( FIG. 3 ). Although the longitudinal seam does not necessarily require joining by a mechanical interlock or any other suitable process, the seam may, in some embodiments, be joined by laser welding (or other suitable process) to form a continuous circular or other geometric (e.g., rectangular) profile. The seam may be generally straight, or alternatively, a box joint, a dovetail joint, or any other suitable interface known in the metal-working arts. Inner shaft member  180  may also be constructed and/or formed from a flat stock piece of metal substantially as described above with respect to outer shaft member  160 . 
     At least a portion of the inner shaft member  180  extends distally from a distal end of the outer shaft member  160 . An opening  164  at a distal end of the inner shaft member  180  is defined by opposing vertical sidewalls  164   a  and  164   b . Sidewalls  164   a ,  164   b  include respective bores  166   a ,  166   b  extending therethrough to support the pivot pin  144  and maintain an orientation of the pivot pin  144  with respect to the outer shaft member  160 . The pivot pin  144  may be frictionally supported by the bores  166   a ,  166   b  or fastened to the inner shaft member  180  by a laser or heat-based welding, adhesives, chemical bonding, or other suitable manufacturing processes. 
     A proximal portion of the upper jaw member  130  includes a foot member  117  that extends from the upper jaw member  130  to slide-fit through a window  113  disposed through a distal end of the outer shaft member  160  and a window  123  disposed through a distal end of the inner shaft member  180 . Proximal longitudinal motion of the outer shaft member  160  causes the window  113  of the outer shaft member  160  to bias the foot member  117  proximally, thereby rotating the upper jaw member  130  about pivot pin  144  toward the lower jaw member  132  to the closed configuration ( FIG. 2B ). During rotation of the upper jaw member  130 , the foot member  117  is free to move through the window  123  of the inner shaft member  180 . The outer shaft member  160  may be drawn proximally relative to the pivot pin  144  to move the end effector  114  to the closed configuration (see  FIG. 2B ). Since the longitudinal position of the pivot pin  144  is fixed (by the inner shaft member  180 ), proximal retraction of the outer shaft member  160  causes the window  113  to bias the foot member  117  proximally, thereby pivoting the upper jaw member  130  about pivot pin  144  toward the lower jaw member  132  to the closed configuration ( FIG. 2B ). Conversely, when the end effector  114  is in the closed configuration, longitudinal translation of the outer shaft member  160  in a distal direction causes the window  113  to bias the foot member  117  proximally, thereby pivoting the upper jaw member  130  about pivot pin  144  away from jaw member  132  toward the open configuration ( FIG. 2A ). 
     The jaw members  130 ,  132  may be pivoted about the pivot pin  144  to move the end effector  114  to the closed configuration of  FIG. 2B  wherein the sealing plates  148 ,  150  provide a pressure to tissue grasped therebetween. In some embodiments, to provide an effective seal, a pressure within a range between about 3 kg/cm 2  to about 16 kg/cm 2  and, desirably, within a working range of 7 kg/cm 2  to 13 kg/cm 2  is applied to the tissue. Also, in the closed configuration, a separation or gap distance “G” may be maintained between the sealing plates  148 ,  150  by an array of stop members  154  ( FIG. 2A ) disposed on or adjacent the sealing plates  148 ,  150 . The stop members  154  contact opposing surfaces on the opposing jaw member  130 ,  132  and prohibit further approximation of the sealing plates  148 ,  150 . In some embodiments, to provide an effective tissue seal, an appropriate gap distance of about 0.001 inches to about 0.010 inches and, desirably, between about 0.002 and about 0.005 inches may be provided. In some embodiments, the stop members  154  are constructed of an electrically non-conductive plastic or other material molded onto the jaw members  130 ,  132 , e.g., by a process such as overmolding or injection molding. In other embodiments, the stop members  154  are constructed of a heat-resistant ceramic deposited onto the jaw members  130 ,  132 . 
     Electrosurgical energy may be delivered to the tissue through the electrically conductive seal plates  148 ,  150  to effect a tissue seal. Once a tissue seal is established, a knife blade  156  may be advanced through a knife channel  158  defined in one or both jaw members  130 ,  132  to transect the sealed tissue. Knife blade  156  is depicted in  FIG. 2A  as extending from the elongated shaft  116  when the end effector  114  is in an open configuration. In some embodiments, a knife lockout is provided to prevent extension of the knife blade  156  into the knife channel  158  when the end effector  114  is in the open configuration. 
     At a proximal portion of the outer shaft member  160 , various features are provided that serve to couple the outer shaft member  160  to various elements of the housing  112 . More specifically, the proximal portion of the outer shaft member  160  includes, in order from distal to proximal, a series of tabs  187  extending therefrom that serve to aid in securing the proximal portion of the outer shaft member  160  within the housing  112 , a pair of opposing longitudinal slots  168   a ,  168   b  defined therethrough to allow longitudinal translation of a dowel pin  193  through the outer shaft member  160 , and the mandrel  169 . The mandrel  169  includes a distal set of through bore pairs  170   a ,  170   b  configured to receive a pair of stop pins  147   a ,  147   b , respectively, and a proximal set of through bores  172   a ,  172   b  configured to receive a pair of stop pins  149   a ,  149   b . The outer shaft member  160  may also include a suitable mechanical interface (not shown) configured to couple the outer shaft member  160  to the rotation knob  128 . One example of a connection established between the outer shaft member  160  and the rotation knob  128  is described in the commonly-assigned patent application entitled SURGICAL INSTRUMENT WITH STAMPED DOUBLE-FLAG JAWS (application Ser. No. 13/461,335 filed May 1, 2012). 
     A proximal portion of the inner shaft member  180  includes a pair of opposing longitudinal knife slots  188   a ,  188   b  extending therethrough and configured to axially align with the pair of opposing longitudinal slots  168   a ,  168   b  defined through the outer shaft member  160  to allow longitudinal translation of the dowel pin  193  therethrough. 
     The knife  102  is a generally flat, metal component defining a profile that may be constructed by a stamping process. The knife  102  supports the sharpened knife blade  156  at a distal-most end thereof. The sharp edge of the knife blade  156  may be applied to the distal end of the knife  102  subsequent to the stamping process that forms the profile. For example, various manufacturing techniques may be employed such as grinding, coining, electrochemical etching, electropolishing, or other suitable manufacturing processes, for forming sharpened edges. A longitudinal slot  106  is defined within the knife  102  to provide clearance for the pivot pin  144 . A proximal through bore  108   a  extends through a proximal portion  108  of the knife  102  and provides a mechanism for operatively coupling the knife  102  to the trigger  126  via the dowel pin  193 . The connection between the knife  102  and the trigger  126  is described in detail below with reference to  FIGS. 8, 9, 10A, and 10B . 
     The knife  102  is centrally disposed within the elongated shaft  116  between the interior sidewalls  162   a ,  162   b  of the outer shaft member  160  to provide lateral support to the knife  102 . Free motion of the knife  102  is permitted only in a longitudinal direction. Thus, the outer shaft member  160  serves as a knife guide by urging the knife  102  into a central position within the elongated shaft  116  and, thus, ensuring proper alignment of the knife  102  as the knife  102  reciprocates within knife channel  158  ( FIG. 2A ). The outer shaft member  160  may also serve to protect the knife  102  and other components from damage throughout the assembly of the elongated shaft  116  and jaw members  130 ,  132 . 
     With reference to  FIG. 4 , the rotation knob  128  includes a passageway  129  defined therethrough for receiving the outer shaft member  160 . The passageway  129  has a generally rectangular profile corresponding to the rectangular profile of the outer shaft member  160 . As shown in  FIG. 9 , the rotation knob  128  is seated within an interior compartment  134  of the housing  112  and, as shown in  FIG. 1 , extends laterally outward from opposing sides of the housing  112  (only shown extending laterally outward from housing half  112   b ). 
     With reference to  FIG. 5 , the pivot pin  144  is coupled to the sidewalls  164   a  and  164   b  of the opening  164  defined at the distal end of the inner shaft member  180 . Thus, the pivot pin  144  represents a longitudinally stationary reference for the longitudinal movements of outer shaft member  160 . Laterally inward of the sidewalls  164   a ,  164   b , the pivot pin  144  extends through the proximal end of the upper jaw member  130 . Jaw member  130  is free to pivot about the pivot pin  144 , and the knife  102  is free to translate longitudinally around the pivot pin  144 . Inner shaft member  180  exhibits a generally U-shaped profile including exterior sidewalls  182   a ,  182   b . Inner shaft member  180  is disposed axially within outer shaft member  160  such that exterior sidewalls  182   a ,  182   b  are disposed laterally outward from the interior sidewalls  162   a ,  162   b  of the outer shaft member  160 . 
     Referring to  FIGS. 6 and 7 , the upper jaw member  130  is constructed of a jaw insert  140 , an insulator  142 , and the sealing plate  150 . The insulator  142  may be constructed of an electrically insulative plastic such as a polyphthalamide (PPA) (e.g., AMODEL®), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), a blend of PC and ABS, nylon, ceramic, etc. The electrically insulative plastic may be overmolded onto the jaw insert  140  in a single-shot injection molding process such that sealing plate  150  is overmolded to the jaw insert  140 . Additionally or alternatively, the electrically insulative plastic may be mechanically coupled to the jaw insert  140 , e.g., pressed, snapped, glued, etc. Various features may be molded into the insulator  142  that facilitate the attachment of the sealing plate  150  to the insert  140 . For example, tabs may be provided that permit a snap-fit attachment of the sealing plate  150 , or ridges may formed that permit ultrasonic welding of the sealing plate  150  onto the insulator  142 . The sealing plate  150  may be constructed of an electrically conductive metal, and may be stamped from a flat sheet stock. Lower jaw member  132  includes the same four major components as upper jaw  130 , including sealing plate  148 , and is constructed in the same manner as upper jaw member  130 . 
     Referring now to  FIG. 8 , the connection of the movable handle  122  and the knife trigger  126  to the longitudinally movable components of the elongated shaft  116  is described. The movable handle  122  may be manipulated to impart longitudinal motion to the outer shaft member  160 , and the knife trigger  126  may be manipulated to impart longitudinal motion to the knife  102 . As discussed above, longitudinal motion of the outer shaft member  160  serves to move the end effector  114  between the open configuration of  FIG. 2A  and the closed configuration of  FIG. 2B , and longitudinal motion of the knife  102  serves to move knife blade  156  through knife channel  158  ( FIG. 2A ). 
     A clevis  178  is defined at an upper end of the movable handle  122  and is pivotally supported on the left housing half  112   b  by a pivot boss  179 . A second complementary pivot boss (not shown) is provided on the right housing half  112   a  to support the clevis  178 . Each of two upper flanges  178   a  and  178   b  of the clevis  178  extend upwardly about opposing sides of a drive collar  184  supported on the mandrel  169  of the outer shaft member  160  and include rounded drive surfaces  197   a  and  197   b  formed thereon. Drive surface  197   a  engages a proximal-facing surface of a distal rim  184   a  of the drive collar  184  and drive surface  197   b  engages a distal facing surface of a proximal rim  184   b  ( FIG. 9 ) of the drive collar  184 . A proximal lock washer  185  is supported on the mandrel  169  proximal of the drive collar  184  and a distal lock washer  186  is coupled to the mandrel  169  proximal to the stop pins  147   a ,  147   b  such that the stop pins  147   a ,  147   b  restrict longitudinal movement in the distal direction of the distal lock washer  186  relative to the outer shaft member  160 . Drive surface  197   a  is arranged along the longitudinal axis A-A such that pivotal motion of the movable handle  122  about the pivot bosses  179  induces corresponding longitudinal motion of the drive collar  184  along the longitudinal axis A-A in the proximal direction. Drive surface  197   b  is arranged along the longitudinal axis A-A such that pivotal motion of the movable handle  122  about the pivot bosses  179  induces corresponding longitudinal motion of the drive collar  184  along the longitudinal axis A-A in the distal direction. 
     Referring now to  FIG. 9 , proximal longitudinal motion may be imparted to the outer shaft member  160  by pushing the proximal collar  184   b  proximally with the movable handle  122  ( FIG. 8 ) as indicated by arrow D 4 . The proximal collar  184   b  engages a spring  189  that is constrained between the proximal collar  184   b  and a proximal lock collar  115 . The proximal lock collar  115  engages the mandrel  169  of the outer shaft member  160  distal to the stop pins  149   a ,  149   b . Thus, the stop pins  149   a ,  149   b  restrict longitudinal movement in the distal direction of the lock collar  115  relative to the outer shaft member  160  such that the lock collar  115  serves as a proximal stop against which spring  189  compresses. 
     Distal longitudinal motion is imparted to the inner shaft member  180  by pushing the distal lock collar  184   a  distally with drive surface  197   a  of movable handle  122  as indicated by arrow D 3  ( FIG. 9 ). Distal longitudinal motion of the distal lock collar  184   a  induces a corresponding distal motion of the outer shaft member  160  by virtue of the coupling of the distal lock collar  184   a  to the mandrel  169  of the outer shaft member  160 . 
     Proximal longitudinal motion of the outer shaft member  160  draws the foot  117  proximally to pivot jaw member  130  toward jaw member  132  to move the end effector  114  to the closed configuration ( FIG. 2B ). Once the jaw members  130  and  132  are closed, further proximal movement of the outer shaft member  160  is prohibited since the jaw members  130 ,  132  contact one another. Further proximal movement of the movable handle  122  ( FIG. 8 ), however, will continue to move the drive collar  184  proximally. This continued proximal movement of the drive collar  184  further compresses the spring  189  to impart additional force to the outer shaft member  160 , which results in additional closure force applied to tissue grasped between the jaw members  130 ,  132 . 
     Referring again to  FIG. 8 , the trigger  126  is pivotally supported in the housing  112  about a pivot boss  103  protruding from the trigger  126 . The trigger  126  is operatively coupled to the knife  102  by a knife connection mechanism  104  such that pivotal motion of the trigger  126  induces longitudinal motion of the knife  102 . The knife connection mechanism  104  includes upper flanges  126   a ,  126   b  of the trigger  126  and a knife collar  110 . 
     Referring now to  FIGS. 9, 10A, and 10B , the knife collar  110  includes a cap member  111  coupled thereto and a pair of integrally formed pin bosses  139   a ,  139   b  extending from opposing sides thereof. The knife collar  110  may include indentations or catches defined therein (not shown) that receive corresponding snap-in features (e.g., arms) of the cap member  111 . The cap  111  may thus be assembled to the knife collar  110  such that the cap  111  and the knife collar  110  translate together. As shown by  FIG. 10B , the coupling of the knife collar  110  to the cap  111  forms an interior circular channel  113  to capture the dowel pin  193  therein such that the dowel pin  193  is supported on opposing ends between the knife collar  110  and the cap  111 . The dowel pin  193  extends through the proximal through bore  108   a  extending through the proximal portion  108  of the knife  102  ( FIG. 3 ) to operably couple the knife  102  to the knife collar  110 . Upon longitudinal motion of the outer shaft member  160 , dowel pin  193  translates longitudinally within slots  188   a ,  188   b  of the inner shaft member  180  and slots  168   a ,  168   b  of the outer shaft member  160  such that the longitudinal motion of outer shaft member  160  is unimpeded by dowel pin  193 . Upon rotation of the elongated shaft  116  and end effector  114  about the longitudinal axis A-A via the rotation knob  128  ( FIG. 1 ), dowel pin  193  freely rotates within the interior circular channel  113  such that the outer and inner shaft members  160  and  180  (removed from view in  FIG. 10B  for clarity), the knife  102 , and the dowel pin  193  rotate within the knife collar  110  about the longitudinal axis A-A. 
     Referring again to  FIG. 8 , the upper flanges  126   a ,  126   b  of the trigger  126  include respective slots  127   a ,  127   b  defined therethrough that are configured to receive the pin bosses  139   a ,  139   b , respectively, of the knife collar  110  such that pivotal motion of the trigger  126  induces longitudinal motion of the knife collar  110  and, thus, the knife  102  by virtue of the coupling of knife  102  to the knife collar  110  via the dowel pin  193  extending through the through bore  108   a . During longitudinal motion of the knife collar  110 , dowel pin  193  translates longitudinally within the opposing slots  168   a ,  168   b  of the outer shaft member  160  and the slots  188   a ,  188   b  of the inner shaft member  180 . 
     Referring now to  FIGS. 9 and 10A , when the trigger  126  is moved to induce motion of the knife collar  110  in order to translate the blade  156  through the knife channel  158 , the knife collar  110  translates along the outer shaft member  160  in the direction of arrow A 9  to abut a spring  119  such that spring  119  compresses against a bobbin  199  disposed within the interior of the housing  112 . The spring  119  biases the knife collar  110  in a proximal direction to a proximal position along the outer shaft member  160 . 
     Referring now to  FIGS. 11A, 11B, 11C and 11D , a sequence of motions may be initiated by moving the movable handle  122  to induce motion of the outer shaft member  160  in order to close the jaw members  130 ,  132 , and by moving the trigger  126  to induce motion of the knife collar  110  in order to translate the blade  156  through the knife channel  158 . Initially, both the moveable handle  122  and the knife trigger  126  are in a distal or un-actuated position as depicted in  FIG. 11A . This arrangement of the moveable handle  122  and trigger  126  sustains the end effector  114  in the open configuration ( FIG. 2A ) wherein the jaw members  130 ,  132  are substantially spaced from one another, and the knife blade  156  is in a retracted or proximal position with respect to the jaw members  130 ,  132 . The initial distal position of the trigger  122  is actively maintained by the influence of the spring  119  on the knife collar  110 . When both the moveable handle  122  and the knife trigger  126  are in the distal, un-actuated position, pivotal motion of the knife trigger  126  in a proximal direction, i.e., toward the stationary handle  120 , is prohibited by interference between the trigger  126  and moveable handle  122 . This interference prohibits advancement of the knife blade  156  through the knife channel  158  when the end effector  114  is in the open configuration. 
     The movable handle  122  may be moved from the distal position of  FIG. 15A  to the intermediate position depicted in  FIG. 15B  to move the jaw members  130 ,  132  to the closed configuration ( FIG. 2B ). As the movable handle  122  pivots about the pivot boss  179  in the direction of arrow M 1  ( FIG. 11B ), the drive surface  197   b  of the movable handle  122  engages the proximal collar  184   b . The drive collar  184  and the spring  189  are both driven proximally against the proximal lock collar  115  and, thus, the outer shaft member  160  is driven proximally in the direction of arrow M 2  ( FIG. 11B ). Proximal movement of the outer shaft member  160  serves to pivot jaw member  130  toward jaw member  132 . 
     The movable handle  122  may be moved from the intermediate position of  FIG. 15B  to the actuated or proximal position of  FIG. 11C  to increase the pressure applied by the jaw members  130 ,  132 . As the movable handle  122  pivots further about the pivot boss  179  in the direction of arrow M 3  ( FIG. 11C ), the drive surface  197   b  presses the proximal collar  184   b  further distally against the spring  189  in the direction of arrow M 4  ( FIG. 11C ). The spring  189  is compressed against the proximal lock collar  115 , and a tensile force is transmitted through the outer shaft member  160  to the jaw members  130 ,  132 . The tensile force supplied by the spring  189  ensures that the jaw members  130 ,  132  apply an appropriate pressure to effect a tissue seal. When the movable handle  122  is in the actuated or proximal position, electrosurgical energy may be selectively supplied to the end effector  114  to generate a tissue seal. 
     When the movable handle  122  is in the actuated or proximal position, a t-shaped latch  122   a  extending proximally from an upper portion of the moveable handle  122  is received in a railway  120   a  supported within the stationary handle  120 . The railway  120   a  serves to temporarily lock the movable handle  122  in the proximal position against the bias of the spring  189 . Thus, the railway  120   a  permits the maintenance of pressure at the end effector  114  without actively maintaining pressure on the movable handle  122 . The latch  122   a  may be released from the railway  121   a  by pivoting the movable handle  122  proximally and releasing the movable handle  122  to move under the influence of the spring  189 . Operation of the railway  120   a  is described in greater detail in U.S. patent application Ser. No. 11/595,194 to Hixson et al., now U.S. Pat. No. 7,766,910. In some embodiments (not shown), the latch  122   a  and the railway  120   a  may be eliminated to provide an instrument without the temporary locking capability provided by these features. 
     When the movable handle  122  is in the actuated or proximal position, the knife trigger  126  may be selectively moved from the distal position of  FIG. 11C  to the proximal position of  FIG. 11D  to advance the knife blade  156  distally through knife channel  158 . The knife trigger  126  may be pivoted in the direction of arrow M 5  ( FIG. 11D ), about pivot boss  103  to advance the flanges  126   a ,  126   b  of the knife trigger  126  distally in the direction of arrow M 6  such that the pin bosses  139   a ,  139   b  translate within slots  127   a ,  127   b , respectively, from the position shown in  FIGS. 11A-11C  to the position shown in  FIG. 11D . Movement of flanges  126   a ,  126   b  draws the knife collar  110  distally, which induces distal longitudinal motion of the knife  102  by virtue of the coupling of knife  102  to the knife collar  110  via the dowel pin  193  extending through the through bore  108   a , as described above with reference to  FIGS. 3 and 10B . 
     While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as examples of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto. 
     Although the foregoing disclosure has been described in some detail by way of illustration and example, for purposes of clarity or understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.