Patent Publication Number: US-8523882-B2

Title: Clip advancer mechanism with alignment features

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention is a continuation-in-part of U.S. patent application Ser. No. 10/907,763 filed on Apr. 14, 2005, now U.S. Pat. No. 7,297,149 and entitled “Surgical Clip Applier Methods,” U.S. patent application Ser. No. 10/907,764 filed on Apr. 14, 2005, now U.S. Pat. No. 7,288,098 and entitled “Force Limiting Mechanism For Medical Instrument,” U.S. patent application Ser. No. 10/907,765 filed on Apr. 14, 2005, now U.S. Pat. No. 7,261,724 and entitled “Surgical Clip Advancement Mechanism,” U.S. patent application Ser. No. 10/907,766 filed on Apr. 14, 2005, now U.S. Pat. No. 7,686,820 and entitled “Surgical Clip Applier Ratchet Mechanism,” and U.S. patent application Ser. No. 10/907,768 filed on Apr. 14, 2005, now U.S. Pat. No. 7,731,724 and entitled “Surgical Clip Advancement And Alignment Mechanism.” These references are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates broadly to surgical devices, and in particular to methods and devices for applying surgical clips to ducts, vessels, shunts, etc. 
     BACKGROUND OF THE INVENTION 
     In recent years surgery has markedly advanced through the performance of laparoscopic and endoscopic surgical procedures such as cholecystectomies, gastrostomies, appendectomies, and hernia repair. These procedures are accomplished through a trocar assembly, which is a surgical instrument used to puncture a body cavity. The trocar typically contains a sharpened obturator tip and a trocar tube or cannula. The trocar cannula is inserted into the skin to access the body cavity, by using the obturator tip to penetrate the skin. After penetration, the obturator is removed and the trocar cannula remains in the body. It is through this cannula that surgical instruments are placed. 
     One surgical instrument that is commonly used with a trocar cannula is a surgical clip applier for ligating a blood vessel, a duct, shunt, or a portion of body tissue during surgery. Most clip appliers typically have a handle with an elongate shaft having a pair of movable opposed jaws formed on an end thereof for holding and forming a ligation clip therebetween. The jaws are positioned around the vessel or duct, and the clip is crushed or formed on the vessel by the closing of the jaws. 
     In many of the prior art clip appliers, the feeding and forming mechanisms require precise timing and coordinated movement of components to operate. This need for precise timing and control has resulted in the need for complex mechanical designs, thereby increasing the cost of the clip appliers. Many prior art clip appliers also use a spring-loaded clip advancing assembly to advance one or more clips through the shaft of the device. As a result, the jaws must contain a mechanism for preventing accidental projection of the clip from the device before the clip is formed. Other drawbacks of current clip appliers include the inability to handle an overload applied to the jaws by the trigger under a variety of conditions. Many devices require full closure of the jaws, which can result in overload on the jaws when the vessel or duct positioned therebetween is too large to allow full closure, or when a foreign object is positioned between the jaws. 
     Accordingly, there remains a need for improved methods and devices for applying surgical clips to vessels, ducts, shunts, etc. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides method and devices for applying a surgical clip to a vessel, duct, shunt, etc. In one exemplary embodiment, a surgical clip applier is provided having a housing with a trigger movably coupled thereto and an elongate shaft extending therefrom with opposed jaws formed on a distal end thereof. The trigger is adapted to advance a clip to position the clip between the jaws, and to move the jaws from an open position to a closed position to crimp the clip positioned therebetween. 
     The surgical clip applier can have a variety of configurations, and it can include a variety of features to facilitate advancement and formation of a surgical clip. In one embodiment, the surgical clip applier can include a feeder shoe that is slidably disposed within the elongate shaft and that is adapted to drive at least one surgical clip through the elongate shaft. In an exemplary embodiment, the feeder shoe can be adapted to move only in a distal direction, such that proximal movement of the feeder shoe is substantially prevented. The elongate shaft can also include a clip track disposed therein and adapted to seat at least one surgical clip. The feeder shoe can be slidably disposed within the clip track. 
     A variety of techniques can be used to facilitate distal movement and prevent proximal movement of the feeder shoe. In one exemplary embodiment, the feeder shoe can include a tang adapted to engage the clip track to prevent proximal movement of the feeder shoe within the clip track, yet allow distal movement of the feeder shoe within the clip track. The clip track can include several openings formed therein for receiving the tang to prevent proximal movement of the feeder shoe within the clip track. In another exemplary embodiment, the feeder shoe can include a tang and the feed bar can include several detents formed therein and adapted to engage the tang to move the feeder shoe distally when the feed bar is moved distally. 
     In another embodiment, the elongate shaft can include a feed bar slidably disposed therein and coupled to the trigger such that movement of the trigger toward a closed position is adapted to advance the feed bar distally thereby advancing the feeder shoe distally. By way of non-limiting example, the feed bar can be coupled to the trigger by a trigger insert that is mated to the trigger, and by a link that extends between the trigger insert and the proximal end of the feed bar. The proximal end of the feed bar can include a coupler that is adapted to receive a portion of the link. The feed bar can also include a distal end having an advancer that is adapted to engage a distal-most clip and to drive the distal-most clip into the jaws. In certain exemplary embodiments, the feed bar can be adapted to engage and initiate advancement of a distal-most clip into the jaws prior to initiating advancement of the feeder shoe. 
     In another embodiment, a clip advancing assembly for advancing a clip through a surgical clip applier is provided. The clip advancing assembly can be used with a variety of surgical clip appliers, including those known in the art. In one exemplary embodiment, the clip advancing assembly can include a clip track that is adapted to seat at least one clip, and a feeder shoe that is adapted to slidably mate to the clip track and to move in a distal direction to move at least one clip disposed within the clip track in a distal direction. The feeder shoe can include, in one exemplary embodiment, a tang that is adapted to engage the clip track to prevent proximal movement of the feeder shoe within the clip track, and that is adapted to allow distal movement of the feeder shoe within the clip track. The clip track can include a plurality of openings formed therein for receiving the tang to prevent proximal movement of the feeder shoe within the clip track. 
     The clip advancing assembly can also include a feed bar that is adapted to couple to a movable trigger formed on a housing of a surgical clip applier and that is adapted to slidably move distally when the trigger is closed to advance the feeder shoe and at least one clip disposed within the clip track. The feed bar can have a variety of configurations, and in one exemplary embodiment the distal end of the feed bar can include an advancer that is adapted to engage a distal-most clip to drive the distal-most clip from the clip track into jaws formed on a distal end of a surgical clip applier. In another exemplary embodiment, the feeder shoe can include a tang, and the feed bar can include a plurality of detents formed therein that are adapted to engage the tang to move the feeder shoe distally when the feed bar is moved distally. In use, the proximal end of the feed bar can include a coupler that is adapted to receive a link for coupling the feed bar to a trigger of a surgical clip applier. 
     An exemplary method for advancing a surgical clip through an elongate shaft of a surgical clip applier is also provided. In one embodiment, a feed bar can be distally advanced within an elongate shaft of a surgical clip applier to distally drive a feeder shoe disposed within the elongate shaft and thereby distally advance at least one clip. The feed bar can be distally advanced by, for example, actuating a trigger coupled to a housing that is mated to a proximal end of the elongate shaft. In one exemplary embodiment, when the feed bar is distally advanced, an advancer on the distal end of the feed bar can engage a distal-most clip and advance the clip between opposed jaws formed on a distal end of the elongate shaft. The method can also include proximally retracting the feed bar within the elongate shaft while the feeder shoe is maintained in a substantially fixed position. 
     In another exemplary embodiment, a method for applying a surgical clip is provided and includes moving a trigger coupled to a housing a first distance toward a closed position to actuate a clip advancing assembly disposed within the housing, thereby advancing a clip into a jaw assembly formed on a distal end of the elongate shaft, and further moving the trigger a second distance toward the closed position to actuate a clip forming assembly disposed within the housing, thereby forming the clip disposed within the jaw assembly. The trigger is preferably pliant relative to the clip advancing assembly during actuation of the clip forming assembly. The clip forming assembly can also be pliant relative to the jaw assembly during actuation thereof. 
     In other aspects, an overload mechanism is provided for use with a surgical device. In one exemplary embodiment, the overload mechanism can include a force-receiving member pivotally and slidably disposed in a housing and having a surface with a first end and an opposed second end, and a biasing assembly disposed in the housing and adapted to resist movement of the force-receiving member. In an exemplary embodiment, the resistance increases from the first end to the second end. 
     The force-receiving member can have a variety of configurations, but in one embodiment the force-receiving surface formed thereon is positioned within an opening in the housing. The force-receiving surface can include a first portion that is adapted to receive a force for pivotally moving the force-receiving member within the housing, and a second portion that is adapted to receive a force for slidably moving the force-receiving member within the housing. The biasing assembly can also have a variety of configurations, but in one exemplary embodiment the biasing assembly can include a spring disposed around a spring post, and a plunger slidably disposed relative to the spring post and having a head formed thereon and adapted to compress the spring upon slidable movement of the plunger toward the spring post. 
     In another embodiment, the housing can include a pivoting assembly that is coupled between the force-receiving member and the biasing assembly such that pivoting assembly is adapted to transfer a force applied to the force-receiving member to the biasing assembly to overcome the resistance. In one exemplary embodiment, the pivoting assembly can include a toggle link that is pivotally coupled to the force-receiving member, and a pivot link that is pivotally coupled to the toggle link and that is adapted to apply a force to the biasing assembly upon pivotal movement thereof. 
     In another embodiment, a surgical clip applier is provided having an overload mechanism for preventing overload of a closing force applied to jaws of the clip applier. In one exemplary embodiment, the surgical clip applier can include a housing having a trigger movably coupled thereto, an elongate shaft extending from the housing with opposed jaws formed on a distal end thereof and movable between an open position and a closed position, and a camming assembly disposed within the housing and the elongate shaft and coupled to the trigger. The camming assembly can be adapted to apply a closing force to the jaws upon actuation of the trigger to move the jaws from the open position toward the closed position. The camming assembly can also be adapted to transfer the closing force to an overload mechanism disposed within the housing when the closing force is greater than a resistance of the overload mechanism that is applied to the camming assembly. In an exemplary embodiment, the resistance of the overload mechanism correlates to a force required to move the jaws from the open position toward the closed position. 
     While various techniques can be used to couple the camming assembly to the overload mechanism, in one exemplary embodiment the camming assembly moves relative to a force-receiving surface of the overload mechanism such that the closing force of the camming assembly is applied across the force-receiving surface of the overload mechanism as the trigger is actuated to cause the camming assembly to move the jaws from the open position toward the closed position. The force-receiving surface of the overload mechanism can be adapted to resist movement in a proximal direction and the resistance can increase as the trigger is actuated to cause the camming assembly to move relative to the force-receiving surface and to move the jaws from the open position toward the closed position. 
     In another exemplary embodiment, the overload mechanism can include a housing having a profile link slidably and pivotally disposed therein and having the force-receiving surface formed thereon and positioned adjacent to an opening formed in the housing. The force-receiving surface can include a first portion that is adapted to receive a force for pivotally moving the force-receiving member within the housing, and a second portion that is adapted to receive a force for slidably moving the force-receiving member within the housing. The overload mechanism can also include a biasing assembly that is adapted to apply a resistance to the profile link. In one exemplary embodiment, the biasing assembly can be coupled to the profile link by a pivoting assembly that is adapted to pivot upon pivotal movement of the profile link, and that is adapted to slide upon slidable movement of the profile link to apply a force to the biasing assembly to overcome the resistance. 
     Methods for applying a surgical clip applier having an overload mechanism are also provided. In one exemplary embodiment, a closing force can be applied to a pair of opposed jaws formed on a surgical clip applier. The closing force can be effective to move the opposed jaws from an open position to a closed position. When the closing force is greater than a threshold force of an overload mechanism, the closing force is transferred to the overload mechanism disposed within the surgical clip applier. In an exemplary embodiment, the threshold force of the overload mechanism increases as the jaws are moved from an open position toward the closed position. 
     While the overload mechanism can have a variety of configurations, in one embodiment the overload mechanism can include a force-receiving element that is adapted to receive the closing force, and a biasing assembly that is adapted to resist movement of the force-receiving element in response to the closing force. The surgical clip applier can include a camming assembly that is adapted to apply the closing force to the jaws, and that includes a roller member that rolls across the force-receiving element as the closing force is applied to the jaws. The threshold force of the overload mechanism can increase as the roller member rolls across the force-receiving element. In particular, when the roller member rolls across a first portion of the force-receiving element, the force-receiving elements can pivot if the closing force is greater than the threshold force, and when the roller member rolls across a second portion of the force-receiving element, the force-receiving element can slide if the closing force is greater than the threshold force. In an exemplary embodiment, the threshold force required to pivot the force-receiving element is less than the threshold force required to slide the force-receiving element. 
     In other aspects, a surgical clip applier is provided and it can include a clip advancing assembly coupled to a trigger and adapted to advance at least one surgical clip through an elongate shaft extending from a housing, and a clip forming assembly coupled to a trigger and adapted to actuate a jaw assembly formed on a distal end of the elongate shaft to form a surgical clip. The trigger can be coupled to the housing and adapted to actuate the clip advancing assembly and the clip forming assembly. In an exemplary embodiment, the trigger has two sequential stages of actuation. The trigger can be effective to actuate the clip advancing assembly during the first stage of actuation, and it can be effective to actuate the clip forming assembly during the second stage of actuation while being pliant relative to the clip advancing assembly. 
     In other embodiments, a surgical clip applier is provided having features to prevent unintentional clip migration, for example during shipping of the device. In one exemplary embodiment, a surgical clip applier is provided having a clip advancing assembly with a pusher mechanism that is disposed within a clip track and movable toward the jaws to advance a plurality of clips sequentially into the jaws. The pusher mechanism can be adapted to generate friction with the clip track to prevent unintentional movement of the pusher mechanism within the clip track, but it can be adapted to move when the clip advancing assembly is actuated to advance the pusher mechanism distally. 
     While various techniques can be used to generate friction between a pusher mechanism and a clip track, in one embodiment the clip track can include one or more protrusions formed thereon and in contact with the pusher mechanism to generate friction with the clip track. In another embodiment, the pusher mechanism can include a deflectable tang formed thereon and biased against the feed bar to generate friction with the feed bar. The deflectable tang can include a lip formed thereon and adapted to engage a corresponding ridge formed in the feed bar. In yet another embodiment, the pusher mechanism can have a cantilevered configuration to generate friction with the clip track. In one embodiment, opposed sidewalls extending along a length of the clip track can bias the pusher mechanism from a substantially V-shaped cross-section into a substantially straight cross-section, thereby generating friction. 
     In yet another embodiment, a surgical clip applier is provided having a housing with a trigger movably coupled thereto and a shaft extending therefrom with opposed jaws formed on a distal end thereof. A clip track extends through the shaft and is adapted to retain a plurality of clips. The surgical clip applier can also include a feeder shoe slidably disposed within the clip track and adapted to advance the plurality of clips through the clip track. The feeder shoe can be configured to generate friction with the clip track to resist unintentional movement of the feeder shoe. For example, the feeder shoe and/or the clip track can include at least one of a protrusion, a deflectable tang, or other surface feature adapted to generate friction with the clip track. In other embodiments, the pusher can include a deflectable tang with a lip formed thereon and adapted to engage a corresponding ridge formed in the clip track. Alternatively, or in addition, the feeder shoe can have a cantilevered configuration to generate friction with the clip track. The clip track can include a support surface with opposed side walls extending therealong, and the feeder shoe can be slidably disposed between the opposed sidewalls. The opposed sidewalls can bias the feeder shoe from a substantially V-shaped cross-section into a substantially straight cross-section, thereby generating friction. 
     In yet another embodiment, a surgical clip applier is provided having a housing, a shaft extending from the housing, first and second jaws formed on a distal end of the shaft and adapted to receive tissue therebetween, a clip track extending through the shaft and adapted to retain a plurality of clips, and a clip pusher disposed within the clip track and adapted to advance the plurality of clips through the clip track and into the first and second jaws. The clip pusher can be biased within the clip track such that movement of the clip pusher is prevented unless a force is applied to the clip pusher that is greater than a biasing force created between the clip pusher and the clip track. 
     In one exemplary embodiment, the clip pusher can include a biasing mechanism formed thereon and adapted to bias the clip pusher within the clip track. The biasing mechanism can be, for example, a protrusion formed on the clip pusher, or a deflectable tang formed on the clip pusher. In other embodiments, the clip pusher can have a width that is greater than a width of the clip track such that the clip pusher is biased within the clip track. The clip track can optionally be sized to deform the clip pusher to create a biasing force between the clip track and the clip pusher. In an exemplary embodiment, the clip pusher is deflected by the clip track such that the clip pusher is compressed from a substantially V-shaped profile to a planar or flattened profile, thereby generating friction. 
     In yet another embodiment, a surgical clip applier is provided having features to prevent a clip from falling out during formation. In one exemplary embodiment, an improved endoscopic surgical clip applier is provided having jaws which close together to approximate tissues to be clipped, a push rod adapted to close the jaws, a trigger adapted to actuate the push rod, and a ratchet mechanism adapted to prevent the trigger from opening during at least a portion of a closing stroke. A preloaded joint is formed between the push rod and a linkage coupling the push rod to the trigger. The preloaded joint is effective to maintain the jaws in a substantially fixed partially closed position when the trigger is partially opened during a closing stroke to retain a partially formed clip between the jaws. The preloaded joint can also be adapted to maintain the push rod in a substantially fixed position while allowing the linkage to move proximally. 
     The preloaded joint can have a variety of configurations, but in one embodiment the preloaded joint is a biasing element that is adapted to be compressed by the push rod during a closing stroke, and that is adapted to apply a biasing force to the push rod when the trigger is partially opened. The biasing element can be, for example, a cantilevered beam or a spring. In an exemplary embodiment, a proximal end of the push rod and the biasing element are disposed within a recess formed in a coupling mechanism, and the cantilevered beam or spring biases the proximal end of the push rod distally. The recess can also optionally include ridges formed therein and adapted to maintain the spring at a substantially constant load as the spring is compressed during a closing stroke. The ridges can also be adapted to prevent the spring from fully compressing. 
     In yet another embodiment, a surgical clip applier is provided having a handle with a shaft extending therefrom, jaws formed on a distal end of the shaft, a jaw closing mechanism extending through the shaft and coupled to the jaws, and a trigger adapted to actuate the jaw closing mechanism to close the jaws. A preloaded joint is formed between the jaw closing mechanism and the trigger, and it is configured to prevent a clip from falling out of the jaws when the trigger is partially opened during a closing stroke. In one embodiment, the preloaded joint can be a spring adapted to be compressed by a portion of the jaw closing mechanism during a closing stroke. The spring can be formed from, for example, Nitinol. In another embodiment, the preloaded joint can be disposed within a recess formed in a coupling mechanism extending between a push rod and the trigger. The preloaded joint can be adapted to be compressed by the push rod during a closing stroke. 
     In other aspects, a surgical clip applier is provided having a housing, a shaft extending distally from the housing, first and second jaws formed on a distal end of the shaft, a trigger movably coupled to the housing, and an anti-backup mechanism adapted to engage the trigger when the trigger is released during at least a partial closing stroke. An assembly is coupled between the trigger and the jaws and it can be adapted to maintain the jaws in a substantially fixed position to prevent clip fallout when the trigger is released during at least a partial closing stroke. 
     In an exemplary embodiment, the assembly can include a preloaded joint formed therein for maintaining a portion of the assembly in a fixed position and allowing a portion of the assembly to move proximally when the trigger is released during at least a partial closing stroke. In certain aspects, the preloaded joint can be formed between a push rod adapted to advance a cam over the jaws to close the jaws, and a coupling mechanism for coupling the push rod to the trigger. The preloaded joint can maintain the push rod in a fixed position while allowing the coupling mechanism to move proximally when the trigger is released during at least a partial closing stroke. In certain exemplary embodiments, the preloaded joint is a spring disposed between the push rod and the coupling mechanism. 
     The present invention also provides exemplary techniques for aligning a clip with opposed jaws formed on a distal end of a surgical clip applier, and preferably for maintaining the clip in alignment with the jaws during clip formation. In one exemplary embodiment, a surgical clip applier is provided having a shaft with proximal and distal ends, opposed jaws formed on the distal end of the shaft, and a guide member coupled to the jaws and having an alignment mechanism formed thereon and adapted to guide a clip into the opposed jaws and to maintain the clip in alignment with the opposed jaws as opposed legs of the clip are closed. The alignment mechanism can also be adapted to abut against an inferior surface of at least a portion of a clip being formed between the opposed jaws to limit or prevent vertical movement of the clip, i.e., pivoting of the apex and legs in a superior-inferior direction. 
     The alignment mechanism can be formed on various portions of the clip applier, but in one exemplary embodiment, the guide member is a tissue stop having a distal end with a recess formed therein for seating a vessel. The alignment mechanism can be a ramped member protruding from a superior surface of the tissue stop. In an exemplary embodiment, the ramped member increases in height from a proximal end to a distal end of the tissue stop. 
     In another embodiment, a surgical clip applier is provided having a shaft, opposed jaws formed on a distal end of the shaft and adapted to close together to approximate tissues to be clipped, and a clip advancing assembly movably coupled to the shaft and adapted to advance a clip into the opposed jaws. An advancer guide is disposed just proximal to the opposed jaws and is adapted to guide a clip being advanced by the clip advancing assembly into the opposed jaws. The advancer guide can be adapted to align the clip with the opposed jaws. The advancer guide can also be adapted to limit or prevent vertical movement of a clip being formed between the opposed jaws. 
     In certain exemplary embodiments, the advancer guide can be formed on a tissue stop coupled to the opposed jaws, and having a recess formed in a distal tip thereof and adapted to receive tissue therein. The advancer guide can be in the form of a ramped member protruding above a superior surface of the tissue stop. 
     In other aspects, an improved endoscopic surgical clip applier is provided having jaws which close together to approximate tissues to be clipped and a clip advancing assembly adapted to sequentially advance a plurality of clips into the jaws. A ramped guide member is positioned just proximal to the opposed jaws and is adapted to align and guide a clip being advanced by the clip advancing assembly into the opposed jaws, and to limit or prevent vertical movement of the clip as the clip is being formed between the opposed jaws. In one embodiment, the ramped guide member can be formed on a tissue stop coupled to the opposed jaws, and the tissue stop can include a distal tip adapted to receive tissue therein to align the jaws with tissue to be clipped. In certain exemplary embodiments, the ramped guide member increases in height from a proximal end to a distal end thereof. The ramped guide member can be adapted to abut against an inferior surface of at least a portion of a clip being formed between the opposed jaws to limit or prevent vertical movement of the clip, i.e., pivoting of the apex and legs in a superior-inferior direction. In an exemplary embodiment, the ramped guide member has a maximum height of about 0.025″, and/or it is inclined at an angle in the range of about 5° to 45°. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a side view of one exemplary embodiment of a surgical clip applier; 
         FIG. 1B  is an exploded view of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 2A  is a top view of a jaw retainer assembly of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 2B  is a bottom view of the jaw retainer assembly shown in  FIG. 2A ; 
         FIG. 2C  is a side view of the jaw retainer assembly shown in  FIG. 2B ; 
         FIG. 2D  is a cross-sectional view of the jaw retainer assembly shown in  FIG. 2C  taken across line D-D; 
         FIG. 3A  is a top view of a feeder shoe for use with the jaw retainer assembly shown in  FIGS. 2A-2D ; 
         FIG. 3B  is a bottom view of the feeder shoe shown in  FIG. 3A ; 
         FIG. 4A  is a side perspective view of a feed bar that is configured to advance the feeder shoe of  FIGS. 3A and 3B  through the jaw retainer assembly shown in  FIGS. 2A-2D ; 
         FIG. 4B  is a side view of the proximal end of the feed bar shown in  FIG. 4A  and the proximal end of the jaw retainer shaft shown in  FIGS. 2A and 2B , showing the feed bar in a proximal-most position; 
         FIG. 4C  is a side view of the feed bar and jaw retainer shaft shown in  FIG. 4B , showing the feed bar in a distal-most position; 
         FIG. 4D  is a side view of another embodiment of a proximal end of a feed bar shown in connection with the proximal end of the jaw retainer shaft shown in  FIGS. 2A and 2B , showing the feed bar in the proximal-most position; 
         FIG. 4E  is a side view of the feed bar and jaw retainer shaft shown in  FIG. 4D , showing the feed bar in a distal-most position; 
         FIG. 4F  is a side view of yet another embodiment of a proximal end of a feed bar shown in connection with the proximal end of the jaw retainer shaft shown in  FIGS. 2A and 2B , showing the feed bar in the proximal-most position; 
         FIG. 4G  is a side view of the feed bar and jaw retainer shaft shown in  FIG. 4F , showing the feed bar in an intermediate position; 
         FIG. 4H  is a side view of the feed bar and jaw retainer shaft shown in  FIG. 4F , showing the feed bar in a distal-most position; 
         FIG. 5A  is a side perspective view of an advancer that is configured to couple to a distal end of the feed bar shown in  FIG. 4A ; 
         FIG. 5B  is a side perspective view of another embodiment of an advancer that is configured to couple to a distal end of the feed bar shown in  FIG. 4A ; 
         FIG. 6A  is a cross-sectional view of a clip advancing assembly, which includes the jaw retainer assembly shown in  FIGS. 2A-2D , the feeder shoe shown in  FIGS. 3A-3B , and the feed bar shown in  FIG. 4A , showing the feed bar in an initial, proximal position relative to the clip track of the jaw retainer assembly; 
         FIG. 6B  is a cross-sectional view of the clip advancing assembly shown in  FIG. 6A , showing the feed bar moved in a distal direction; 
         FIG. 6C  is a cross-sectional view of the clip advancing assembly shown in  FIG. 6B , showing the feed bar moved further distally, thereby moving the feeder shoe and a clip supply disposed distally of the feeder shoe in a distal direction; 
         FIG. 6D  is a cross-sectional view of the clip advancing assembly shown in  FIG. 6C , showing the feed bar returned to the initial, proximal position, shown in  FIG. 6A , while the feeder shoe and clip supply remain in the advanced position shown in  FIG. 6C ; 
         FIG. 6E  is a bottom perspective view of the advancer shown in  FIG. 5A  disposed within the clip track of the jaw retainer assembly shown in  FIGS. 2A-2D , showing the advancer in a proximal-most position; 
         FIG. 6F  is a bottom perspective view of the advancer shown in  FIG. 6E , showing the advancer in a distal-most position after advancing a clip into the jaws of the surgical clip applier; 
         FIG. 7  is a side perspective view of a pair of jaws of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 8  is a side perspective view of a cam for use with the jaws shown in  FIG. 7 ; 
         FIG. 9  is a top perspective view of a push rod that is adapted to couple to the cam shown in  FIG. 8  for moving the cam relative to the jaws shown in  FIG. 7 ; 
         FIG. 10A  is a top view of the cam shown in  FIG. 8  coupled to the jaws shown in  FIG. 7 , showing the cam in an initial position and the jaws open; 
         FIG. 10B  is a top view of the cam shown in  FIG. 8  coupled to the jaws shown in  FIG. 7 , showing the cam advanced over the jaws and the jaws in a closed position; 
         FIG. 11A  is a top perspective view of a tissue stop that is adapted to couple to a distal end of the clip track of the jaw retainer assembly shown in  FIGS. 2A-2D ; 
         FIG. 11B  is a top perspective view of another embodiment of a tissue stop having a ramp formed thereon for guiding a clip into the jaws and stabilizing the clip during clip formation; 
         FIG. 11C  is a side view of the tissue stop shown in  FIG. 11B ; 
         FIG. 11D  is an enlarged view of the tissue stop shown in  FIGS. 11B and 11C ; 
         FIG. 12  is a top view of a distal end of the surgical clip applier shown in  FIG. 1A  showing the tissue stop shown in  FIG. 11A  positioned between the jaws shown in  FIG. 7 ; 
         FIG. 13  is a side, partially cross-sectional view of the handle portion of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 14  is a side perspective view of a trigger insert of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 15A  is a side perspective view of one half of a feed bar coupler of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 15B  is a side perspective view of the other half of the feed bar coupler shown in  FIG. 15A ; 
         FIG. 16  is a top perspective view of a flexible link that forms part of a clip advancing assembly of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 17A  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 1A , showing a clip advancing assembly in an initial position; 
         FIG. 17B  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 17A , showing the clip advancing assembly partially actuated; 
         FIG. 17C  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 17B , showing the clip advancing assembly fully actuated; 
         FIG. 17D  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 17A , showing a clip forming assembly actuated; 
         FIG. 18  is a side view of a closure link roller that forms part of a clip forming assembly of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 19  is a top perspective view of a closure link that couples to the closure link roller shown in  FIG. 18  to form part of a clip forming assembly of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 20A  is a top perspective view of a closure link coupler that couples to the closure link shown in  FIG. 19  and that also forms part of the clip forming assembly of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 20B  is a bottom view of the closure link coupler shown in  FIG. 20A  coupled to the push rod of  FIG. 9  and having one embodiment of a biasing element disposed therein; 
         FIG. 20C  is a bottom view of the closure link shown in  FIG. 20A  coupled to the push rod of  FIG. 9  and having another embodiment of a biasing element disposed therein; 
         FIG. 20D  is a chart showing the amount of force required to displace the biasing element shown in  FIG. 20B ; 
         FIG. 20E  is a side view of another embodiment of a portion of a closure link coupler having ridges formed therein; 
         FIG. 21A  is an enlarged side perspective view of an anti-backup mechanism of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 21B  is a perspective view of a pawl mechanism of the anti-backup mechanism shown in  FIG. 21A ; 
         FIG. 22A  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 1A , showing the anti-backup mechanism in an initial position; 
         FIG. 22B  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 22A , showing the anti-backup mechanism in a partially actuated position; 
         FIG. 22C  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 22B , showing the anti-backup mechanism in a fully actuated position; 
         FIG. 22D  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 22C , showing the anti-backup mechanism returning to an initial position; 
         FIG. 22E  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 22D , showing the anti-backup mechanism returned to the initial position; 
         FIG. 23A  is an exploded view of an overload mechanism of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 23B  is a partially cross-sectional view of the overload mechanism shown in  FIG. 23A , showing the closure link roller first coming into contact with the profile link; 
         FIG. 23C  is a partially cross-sectional view of the overload mechanism shown in  FIG. 23B , showing the closure link roller applying a force to the profile link causing the profile link to pivot; 
         FIG. 23D  is a perspective view of another embodiment of an overload mechanism for use with a surgical clip applier; 
         FIG. 24A  is a side perspective view of a clip quantity indicator wheel of the surgical clip applier shown in  FIG. 1A ; 
         FIG. 24B  is a side view of a clip quantity indicator wheel shown in  FIG. 24A ; 
         FIG. 25  is a top perspective view of a clip quantity actuator for use with the clip quantity indicator wheel shown in  FIG. 24 ; 
         FIG. 26A  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 1A , showing movement of the clip quantity actuator of  FIG. 25  and the clip quantity indicator wheel of  FIG. 24 ; 
         FIG. 26B  is a side, partially cross-sectional view of a portion of the handle of the surgical clip applier shown in  FIG. 26A , showing further movement of the clip quantity actuator of  FIG. 25  and the clip quantity indicator wheel of  FIG. 24 ; and 
         FIG. 27A  is a side view illustration showing another embodiment of a feeder shoe having a pre-formed A-shaped bend formed therein and configured to create friction between the feeder shoe and the clip track; 
         FIG. 27B  is a side view illustration of another embodiment of a feeder shoe having a pre-formed V-shaped bend formed therein and configured to create friction between the feeder shoe and the clip track; 
         FIG. 28A  is a perspective top view of a portion of a clip track having surface protrusions formed therein and configured to create friction between with the feeder shoe according to another embodiment of the invention; 
         FIG. 28B  is perspective end view of another embodiment of a feeder shoe having a tang formed thereon and adapted to engage the surface protrusions formed in the clip track shown in  FIG. 28A ; 
         FIG. 29A  is a bottom perspective view of another embodiment of a feeder shoe having a holdback lip formed on a tang that is adapted to engage a corresponding groove formed in a feed bar; 
         FIG. 29B  is a top perspective view of another embodiment of a feed bar having a catch groove formed therein and adapted to be engaged by the holdback lip formed on the tang of the feeder shoe shown in  FIG. 29A ; and 
         FIG. 29C  is a side cross-sectional view of the feeder shoe of  FIG. 29A  disposed within and engaging the feed bar of  FIG. 29B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention generally provides a surgical clip applier and methods for using a surgical clip applier to apply surgical clips to a vessel, duct, shunt, etc., during a surgical procedure. An exemplary surgical clip applier can include a variety of features to facilitate application of a surgical clip, as described herein and illustrated in the drawings. However, a person skilled in the art will appreciate that the surgical clip applier can include only some of these features and/or it can include a variety of other features known in the art. The surgical clip applier described herein is merely intended to represent certain exemplary embodiments. 
       FIG. 1A  illustrates one exemplary surgical clip applier  10 . As shown, the clip applier  10  generally includes a housing  12  having a stationary handle  14  and a movable handle or trigger  16  that is pivotally coupled to the housing  12 . An elongate shaft  18  extends from the housing  12  and it includes a pair of opposed jaws  20  formed on a distal end thereof for crimping a surgical clip. The elongate shaft  18  can be rotatably coupled to the housing  12 , and it can include a rotation knob  22  for rotating the shaft  18  relative to the housing  12 .  FIG. 1B  illustrates an exploded view of the surgical clip applier  10  shown in  FIG. 1A , and the various components will be described in more detail below. 
       FIGS. 2A-12  illustrate exemplary embodiments of the various components of the shaft  18  of the surgical clip applier  10 . In general, referring to  FIG. 1B , the shaft  18  includes an outer tube  24  that houses the shaft components, which can include a jaw retaining assembly  26  having a jaw retainer shaft  28  with a clip track  30  and a push rod channel  32  formed thereon. The jaws  20  can be configured to mate to a distal end of the clip track  30 . The shaft assembly  18  can also include a clip advancing assembly, which in one exemplary embodiment can include a feeder shoe  34  that is adapted to be slidably disposed within the clip track  30  to advance a series of clips  36  positioned therein, and a feed bar  38  that is adapted to drive the feeder shoe  34  through the clip track  30 . The feed bar  38  can include an advancer assembly  40  that is adapted to mate to a distal end thereof for advancing a distal-most clip into the jaws  20 . The shaft assembly  18  can also include a clip forming or camming assembly, which in one exemplary embodiment can include a cam  42  that is adapted to slidably mate to the jaws  20 , and a push rod  44  that can couple to the cam  42  to move the cam  42  relative to the jaws  20 . The shaft assembly can also include a tissue stop  46  that can mate to a distal end of the clip track  30  for facilitating positioning of the jaws  20  relative to a surgical site. 
     The various components of one exemplary clip advancing assembly are shown in more detail in  FIGS. 2A-5 . Referring first to  FIGS. 2A-2D , the jaw retaining assembly  26  is shown and it includes an elongate, substantially planar jaw retainer shaft  28  having a proximal end  28   a  that mates to the outer tube  24 , and a distal end  28   b  that is adapted to mate to the jaws  20 . While a variety of techniques can be used to mate the proximal end  28   a  of the jaw retainer shaft  28  to the outer tube  24 , in the illustrated embodiment the proximal end  28   a  includes teeth  31  formed on opposed sides thereof that are adapted to be received within corresponding holes or openings (not shown) formed in the outer tube  24 , and a cut-out  29  formed therein that allows the opposed sides of the proximal end  28   a  to deflect or to form a spring. In particular, the cut-out  29  allows the opposed sides of the proximal end  28   a  of the jaw retainer shaft  28  to be compressed toward one another when the jaw retainer shaft  28  is inserted in the outer tube  24 . Once the teeth  31  are aligned with the corresponding openings in the outer tube  24 , the proximal end  28   a  of the jaw retainer shaft  28  will return to its original, uncompressed configuration thereby causing the teeth  31  to extend into the corresponding openings to engage the outer  24 . As will be discussed in more detail below with respect to  FIG. 4A , the device can also include a feature to prevent compression of the opposed sides of the proximal end  28   a  of the jaw retainer shaft  28  during use of the device to prevent accidental disengagement of the teeth  31  from the outer tube  24 . 
     A variety of techniques can also be used to mate the distal end  28   b  of the jaw retainer shaft  28  to the jaws  20 , however in the illustrated embodiment the distal end  28   b  of the jaw retainer shaft  28  includes several cut-outs or teeth  78  formed therein for mating with corresponding protrusions or teeth  94  formed on the jaws  20 , which will be discussed in more detail below with respect to  FIG. 7 . The teeth  78  allow a proximal portion of the jaws  20  to be substantially co-planar with the jaw retainer shaft  28 . 
     The jaw retaining assembly  26  can also include a push rod channel  32  formed thereon for slidably receiving the push rod  44 , which is used to advanced the cam  42  over the jaws  20 , as will be discussed in more detail below. The push rod channel  32  can be formed using a variety of techniques, and it can have any shape and size depending on the shape and size of the push rod  44 . As shown in  FIG. 2D , the push rod channel  32  is fixedly attached, e.g., by welding, to a superior surface of the retainer shaft  28 , and it has a substantially rectangular shape and defines a pathway  32   a  extending therethrough. The push rod channel  32  can also extend along all or only a portion of the retainer shaft  28 . A person skilled in the art will appreciate that the jaw retaining assembly  26  does not need to include a push rod channel  32  for facilitating movement of the push rod  44  within the elongate shaft  18  of the surgical clip applier  10 . 
     As is further shown in  FIGS. 2A-2D , the jaw retaining assembly  26  can also include a clip track  30  mated thereto or formed thereon. The clip track  30  is shown mated to an inferior surface of the jaw retainer shaft  28 , and it extends distally beyond the distal end  28   b  of the jaw retainer shaft  28  to allow a distal end  30   b  of the clip track  30  to be substantially aligned with the jaws  20 . In use, the clip track  30  is configured to seat at least one, and preferably a series, of clips therein. Accordingly, the clip track  30  can include opposed side rails  80   a ,  80   b  that are adapted to seat opposed legs of one or more clips therein, such that the legs of the clips are axially aligned with one another. In an exemplary embodiment, the clip track  30  can be configured to seat about twenty clips that are pre-disposed within the clip track  30  during manufacturing. A person skilled in the art will appreciate that the shape, size, and configuration of the clip track  30  can vary depending on the shape, size, and configuration of clips, or other closure devices such as staples, adapted to be received therein. Moreover, a variety of other techniques can be used, instead of a clip track  30 , to retain a clip supply with the elongate shaft  18 . 
     The clip track  30  can also include several openings  30   c  formed therein for receiving a tang  82   a  formed on a feeder shoe  34  adapted to be disposed within the clip track  30 , as will be discussed in more detail below. In an exemplary embodiment, the clip track  30  includes a quantity of openings  30   c  that corresponds to at least the number of clips adapted to be pre-disposed within the device  10  and applied during use. The openings  30   c  are preferably equidistant from one another to ensure that the tang  82   a  on the feeder shoe  34  engages an opening  30   c  each time the feeder shoe  34  is advanced. While not shown, the clip track  30  can include detents, rather than openings  30   c , or it can include other features that allow the clip track  30  to engage the feeder shoe  34  and prevent distal movement, yet allow proximal movement, of the feeder shoe  34 . The clip track  30  can also include a stop tang  118  formed thereon, as shown in  FIG. 2B , that is effective to be engaged by a corresponding stop tang formed on the feeder shoe  34  to prevent movement of the feeder shoe  34  beyond a distal-most position, as will be discussed below. The stop tang  118  can have a variety of configurations, but in one exemplary embodiment it is in the form of two adjacent tabs that extend toward one another to enclose a portion of the clip track, thus allowing clips to pass therethrough. 
     An exemplary feeder shoe  34  is shown in more detail in  FIGS. 3A and 3B , and it can be adapted to directly driving clips through the clip track  30 . While the feeder shoe  34  can have a variety of configurations, and a variety of other techniques can be used to drive clips through the clip track  30 , in an exemplary embodiment the feeder shoe  34  has a generally elongate shape with proximal and distal ends  34   a ,  34   b . The distal end  34   b  can be adapted to cradle the proximal-most clip in the clip track  30  to push the clip(s) through the clip track  30 . In the illustrated exemplary embodiment, the distal end  34   b  is substantially v-shaped for seating a v-shaped bight portion of a clip. The distal end  34   b  also includes a rectangular-shaped notch  34   c  formed therein for allowing the advancer  40  to engage a distal-most clip and advance it into the jaws  20 , as will be discussed in more detail below. The distal end  34   b  can, of course, vary depending on the configuration of the clip, or other closure mechanism, being used with the device  10 . 
     In another exemplary embodiment, the feeder shoe  34  can also include features to facilitate distal movement of the feeder shoe  34  within the clip track  30 , and to substantially prevent proximal movement of the feeder shoe  34  within the clip track  30 . Such a configuration will ensure advancement and proper positioning of the clips within the clip track  30 , thus allowing a distal-most clip to be advanced between the jaws  20  with each actuation of the trigger  16 , as will be discussed in more detail below. In the illustrated exemplary embodiment, the feeder shoe  34  includes a tang  82   a  formed on a superior surface  34   s  thereof and angled proximally for engaging one of the openings  30   c  formed in the clip track  30 . In use, the angle of the tang  82   a  allows the feeder shoe  34  to slide distally within the clip track  30 . Each time the feeder shoe  34  is advanced, the tang  82   a  will move in a distal direction from one opening  30   c  to the next opening  30   c  in the clip track  30 . The engagement of the tang  82   a  with the opening  30   c  in the clip track  30  will prevent the feeder shoe  34  from moving proximally to return to the previous position, as will be described in more detail below. 
     In order to facilitate proximal movement of the feeder shoe  34  within the clip track  30 , the feeder shoe  34  can also include a tang  82   b  formed on the inferior surface  34   i  thereof, as shown in  FIG. 3B , for allowing the feeder shoe  34  to be engaged by the feed bar  38  ( FIG. 4A ) as the feed bar  38  is moved distally. The inferior tang  82   b  is similar to the superior tang  82   a  in that it can be angled proximally. In use, each time the feed bar  38  is moved distally, a detent  84  formed in the feed bar  38  can engage the inferior tang  82   b  and move the feeder shoe  34  distally a predetermined distance within the clip track  30 . The feed bar  38  can then be moved proximally to return to its initial position, and the angle of the inferior tang  82   b  will allow the tang  82   b  to slide into the next detent  84  formed in the feed bar  38 . As previously noted, a variety of other features rather than tangs  82   a ,  82   b  and openings  30   c  or detents  84  can be used to control movement of the feeder shoe  34  within the clip track  30 . 
     As previously mentioned, the feeder shoe  34  can also include a stop formed thereon that is adapted to stop movement of the feeder shoe  34  when the feeder shoe  34  is in the distal-most position and there are no clips remaining in the device  10 . While the stop can have a variety of configurations,  FIGS. 3A and 3B  illustrate a third tang  82   c  formed on the feeder shoe  34  and extending in an inferior direction for engaging the stop tang  118  ( FIG. 2B ) formed on the clip track  30 . The third tang  82   c  is positioned such that it will engage the stop tang  118  on the clip track  30  when the feeder shoe  34  is in a distal-most position, thereby preventing movement of the feeder shoe  34  and the feed bar  38  when the clip supply is depleted. 
       FIG. 4A  illustrates an exemplary feed bar  38  for driving the feeder shoe  34  through the clip track  30  of the jaw retaining assembly  26 . As shown, the feed bar  38  has a generally elongate shape with proximal and distal ends  38   a ,  38   b . The proximal end  38   a  of the feed bar  38   a  can be adapted to mate to a feed bar coupler  50  ( FIG. 1B ), which will be discussed in more detail below. The feed bar coupler  50  can mate to a feed link  52  that is effective, upon actuation of the trigger  16 , to slidably move the feed bar  38  in a distal direction within the elongate shaft  18 . The distal end  38   b  of the feed bar  38   b  can be adapted to mate to an advancer  40 ,  40 ′, exemplary embodiments of which are shown in  FIGS. 5A and 5B , that is effective to drive a distal-most clip disposed within the clip track  30  into the jaws  20 , which will be discussed in more detail below. 
     As previously mentioned, the proximal end  38   a  of the feed bar  38  can include a feature to prevent compression of the opposed sides of the proximal end  28   a  of the jaw retainer shaft  28  ( FIGS. 2A and 2B ) during use of the device to prevent accidental disengagement of the teeth  31  from the outer tube  24 . In one exemplary embodiment, shown  FIGS. 4A-4C , the proximal end  38   a  of the feed bar  38  can include a protrusion  39  formed thereon that is adapted to extend into the opening  29  formed in the proximal end  28   a  of the jaw retainer shaft  28 . When the feed bar  38  is in a proximal-most position (i.e., when the trigger  16  is in an open position), the protrusion  39  will be positioned at the proximal end of the opening  29 , as shown in  FIG. 4B , allowing the proximal end  28   a  of the jaw retainer shaft  28  to compress to allow the shaft  28  to slide into the outer tube  24 . When the feed bar  38  is in a distal-most position (i.e., when the trigger  16  is in at least a partially closed position), the protrusion  39  will be positioned at an intermediate location adjacent to the teeth  31  as shown in  FIG. 4C , to prevent compression of the proximal end  28   a  of the jaw retainer shaft  28 . This is particularly advantageous during use of the device, as the protrusion  39  will prevent accidental disengagement of the jaw retainer shaft  28  from the outer tube  24  during use of the device. While  FIGS. 4A-4C  illustrate a protrusion  39  having a rectangular cross-sectional shape with rounded edges, the protrusion  39  can have a variety of other shapes and sizes. For example, as shown in  FIGS. 4D and 4E , the protrusion  39 ′ has a cross-sectional shape that is somewhat triangular with a tapering end that is adapted to extend between the teeth  31  to further ensure that the proximal end  28   a  of the jaw retainer shaft  28  can not be compressed during use of the device. More than one protrusion can also be used. For example,  FIGS. 4F-4H  illustrate another embodiment in which the proximal end  38   a ′ of the feed bar  38  includes two protrusions  39   a ,  39   b  formed thereon and spaced a distance apart from one another. The two protrusions  39   a ,  39   b  will prevent compression of the proximal end  28   a  of the jaw retainer shaft  28  when the feed bar  38  is in a proximal-most position, as shown in  FIG. 4F , and when the feed bar  38  is in a distal-most position, as shown in  FIG. 4H . Compression of the proximal end  28   a  of the jaw retainer shaft  28  can only occur when the feed bar  38  is at an intermediate position such that the teeth  31  are positioned between the protrusions  39   a ,  39   b , as shown in  FIG. 4G . 
     As was also previously mentioned, the feed bar  38  can include one or more detents  84  formed therein for engaging the inferior tang  82   b  formed on the feeder shoe  34 . The quantity of detents  84  can vary, but in an exemplary embodiment the feed bar  38  has a quantity of detents  84  that corresponds to or is greater than a quantity of clips adapted to be delivered by the device  10 , and more preferably it has one more detent  84  than the quantity of clips adapted to be delivered by the device  10 . By way of non-limiting example, the feed bar  38  can include eighteen detents  84  formed therein for delivering seventeen clips that are pre-disposed within the clip track  30 . Such a configuration allows the feed bar  38  to advance the feeder shoe  34  seventeen times, thereby advancing seventeen clips into the jaws  20  for application. The detents  84  are also preferably equidistant from one another to ensure that the feeder shoe  34  is engaged and advanced by the feed bar  38  each time the feed bar  38  is advanced. 
     The feed bar  38  can also include a feature to control the amount of movement of the feed bar  38  relative to the clip track  30 . Such a configuration will ensure that the feeder shoe  34  is advanced a predetermined distance each time the trigger  16  is actuated, thereby advancing only a single clip into the jaws  20 . While a variety of techniques can be used to control the distal of movement of the feed bar  38 , in an exemplary embodiment the feed bar  38  can include a protrusion  86  formed thereon that is adapted to be slidably received within a corresponding slot  88  ( FIG. 2B ) formed in the jaw retainer shaft  28 . The length of the slot  88  is effective to limit movement of the protrusion  86  therein, thus limiting movement of the feed bar  38 . Accordingly, in use the feed bar  38  can slide between a fixed proximal position and a fixed distal position with respect to the clip track  30 , thereby allowing the feed bar  38  to advance the feeder shoe  34  by a predetermined distance with each advancement of the feed bar  38 . 
       FIG. 5A  illustrates one exemplary embodiment of an advancer  40  that is adapted to mate to the distal end  38   b  of the feed bar  38  and which is effective to drive a distal-most clip from the clip track  30  into the jaws  20 . A variety of techniques can be used to mate the advancer  40  to the feed bar  38 , but in the illustrated embodiment the proximal end  40   a  of the advancer  40  is in the form of a female connector that is adapted to receive the male connector formed on the distal end  38   b  of the feed bar  38 . The advancer  40  preferably fixedly mates to the feed bar  38 , however it can optionally be integrally formed with the feed bar  38 . The distal end  40   b  of the feed bar  38  is preferably adapted to advance a clip into the jaws  20  and thus the distal end  40   b  of the advancer  40  can include, for example, a clip-pusher member  90  formed thereon. The clip-pusher member  90  can have a variety of shapes and sizes, but in one exemplary embodiment it has an elongate shape with a recess  92  formed in the distal end thereof for seating the bight portion of a clip. The shape of the recess  92  can vary depending on the particular configuration of the clip. The clip-pusher member  90  can also extend at an angle in a superior direction with respect to a longitudinal axis A of the advancer  40 . Such a configuration allows the clip-pusher member  90  to extend into the clip track  30  to engage a clip, while the remainder of the advancer  40  extends substantially parallel to the clip track  30 .  FIG. 5B  illustrates another exemplary embodiment of a clip-pusher member  90 ′ of an advancer  40 ′. In this embodiment, the clip-pusher member  90 ′ is slightly more narrow and it has a small recess  92 ′ formed in the distal-most end thereof. In use, the advancer  40  can engage and advance only the distal-most clip disposed within the clip track  30  into the jaws  20 . This is due to the positioning of the feed bar  38 , which is slidably movable between a fixed proximal and distal positions, as previously discussed. 
       FIGS. 6A-6G  illustrate the clip advancing assembly in use, and in particular  FIGS. 6A-6D  illustrate movement of the feed bar  38  within the clip track  30  to advance the feeder shoe  34  and clip supply  36 , and  FIGS. 6E-6F  illustrate movement of the advancer  40  to advance a distal-most clip into the jaws  20 . The components in the housing  12  that are used to actuate the clip advancing assembly will be discussed in more detail below. 
     As shown in  FIG. 6A , in the resting position the feed bar  38  is in a proximal-most position such that the protrusion  86  is positioned proximally within the elongate slot  88  in the jaw retainer shaft  28 . The feeder shoe  34  is disposed within the clip track  30  and, assuming the device  10  has not yet been used, the feeder shoe  34  is in a proximal-most position such that the superior tang  82   a  on the feeder shoe  34  is engaged with the proximal-most or first opening  30   c   1  formed in the clip track  30  to prevent proximal movement of the feeder shoe  34 , and the inferior tang  82   b  on the feeder shoe  34  is positioned between the first detent  84   1  and the second detent  84   2  in the feed bar  38 , such that the inferior tang  82   b  is biased in a superior direction by the feed bar  38 . The detents  84  in the feed bar are labeled sequentially as  84   1 ,  84   2 , etc., and the openings  30   c  in the clip track  30  are labeled sequentially as  30   c   1 ,  30   c   2 , etc. As is further shown in  FIG. 6A , a series of clips  36 , labeled sequentially as  36   1 ,  36   2 , . . .  36   x  with  36   x  being the distal-most clip, are positioned within the clip track  30  distal of the feeder shoe  34 . 
     Upon actuation of the trigger  16 , the feed bar  38  is advanced distally, causing the protrusion  86  to slide distally within the slot  88 . As the feed bar  38  moves distally, the inferior tang  82   b  on the feeder shoe  34  will slide into the first detent  84   1  in the feed bar  38 . Further distal movement of the feed bar  38  will cause the first detent  84   1  to engage the inferior tang  82   b , as shown in  FIG. 6B , and to move the feeder shoe  34  and clip supply  36   1 ,  36   2 , etc. in a distal direction. As shown in  FIG. 6C , when the protrusion  86  abuts the distal end of the elongate slot  88  in the jaw retainer shaft  28 , the feed bar  38  is prevented from further distal movement. In this position, the feeder shoe  34  has advanced a predetermined distance to advance the clip supply  36   1 ,  36   2 , . . .  36   x  within the clip track  30  by a predetermined distance. The superior tang  82   a  of the feeder shoe  34  has been advanced into the second opening  30   c   2  in the clip track  30  to prevent proximal movement of the feeder shoe  34 , and the inferior tang  82   b  on the feeder shoe  34  is still engaged by the first detent  84   1  in the feed bar  38 . 
     Movement of the feed bar  38  from the initial, proximal-most position, shown in  FIG. 6A , to the final, distal-most position, shown in  FIG. 6C , will also advance the distal-most clip  36   x  into the jaws  20 . In particular, as shown in  FIG. 6E , distal movement of the feed bar  38  will cause the clip-pusher member  90  of the advancer  40 , which is attached to the distal end of the feed bar  38 , to engage the distal-most clip  36   x  disposed within the clip track  30  and to advance the clip  36   x  into the jaws  20 , as shown in  FIG. 6F . In an exemplary embodiment, the advancer  40  will engage and initiate advancement of the distal-most clip  36   x  prior to engaging and initiating advancement of the feeder shoe  34 . As a result the distal-most clip  36   x  will advance a distance that is greater than a distance traveled by the feeder shoe  34 . Such a configuration allows only the distal-most clip  36   x  to be advanced into the jaws  20  without accidentally advancing an additional clip into the jaws  20 . 
     Once the clip  36   x  has been partially or fully formed, the trigger  16  can be released to release the formed clip  36   x . Release of the trigger  16  will also retract the feed bar  38  in a proximal direction until the protrusion  86  returns to the initial proximal-most position within the elongate slot  88 , as shown in  FIG. 6D . As the feed bar  38  is retracted proximally, the feeder shoe  34  will not move proximally since the superior tang  82   a  will engage the second opening  30   c   2  in the clip track  30 . The inferior tang  82   b  will not interfere with proximal movement of the feed bar  38 , and once the feed bar  38  is in the initial, proximal-most position, as shown, the inferior tang  82   b  will be positioned between the second detent  84   2  and the third detent  84   3  in the feed bar  38 . 
     The process can be repeated to advance another clip into the jaws  20 . With each actuation of the trigger  16 , the inferior tang  82   b  will be engaged by the next detent, i.e., detent  84   2  formed in the feed bar  38 , the superior tang  82   a  on the feeder shoe  34  will be moved distally into the next opening, i.e., opening  30   c   3  on the clip track  30 , and the distal-most clip will be advanced into the jaws  20  and released. Where the device  10  includes a predetermined amount of clips, e.g., seventeen clips, the trigger  16  can be actuated seventeen times. Once the last clip has been applied, the stop, e.g., the third tang  82   c , on the feeder shoe  34  can engage the stop tang  118  on the clip track  30  to prevent further distal movement of the feeder shoe  34 . 
     The feeder shoe  34 , feed bar  38 , and/or the clip track  30  can also optionally include features to prevent accidental or unintentional movement of the feeder shoe  34 , for example during shipment of the device. This is particularly advantageous as migration of the feeder shoe  34 , particularly prior to first use of the device, can cause the device to malfunction. For example, if the feeder shoe  34  migrates distally, the feeder shoe  34  will advance two clips into the jaws simultaneously, thereby resulting in delivery of two misformed clips. Accordingly, in an exemplary embodiment the feeder shoe  34 , feed bar  38 , and/or the clip track  30  can include an engagement mechanism and/or can be configured to generate a frictional force therebetween that is sufficient to resist movement, but that can be overcome by actuation of the trigger  16  to allow the feed bar to advance the feeder shoe  34  through the clip track  30 . 
     While various techniques can be used to prevent undesirable migration of the feeder shoe  34  within the clip track  30 ,  FIGS. 27A-29C  illustrate various exemplary embodiments of techniques for creating friction or an engagement mechanism between the feeder shoe  34 , feed bar  38 , and/or the clip track  30 . Referring first to  FIG. 27A , one exemplary embodiment of a feeder shoe  34 ′ is shown having a pre-formed cantilevered or bowed configuration in a free state (i.e., when the feeder shoe  34 ′ is removed from the clip track  30 ) such that the feeder shoe  34 ′ forms a cantilevered spring when disposed within the clip track  30 . In particular, a portion of the feeder shoe  34 ′ can include a bend  35 ′ formed therein such that the opposed ends  34   a ′,  34   b ′ of the feeder shoe  34 ′ are angled relative to one another. The bend  35 ′ can cause the height h b  of the feeder shoe  34 ′ to be greater than the height of the clip track  30 . While the height h b  can vary, in an exemplary embodiment the bend  35 ′ is configured to increase a height of the feeder shoe  34 ′ by an amount that is sufficient to create a frictional drag force between the feeder shoe  34 ′ and the clip track  30 , but that still allows the feeder shoe  34 ′ to slide within the clip track  30  when the trigger  16  is actuated. In an exemplary embodiment, the height of the feeder shoe  34 ′ is increased at least about 30%, or more preferably about 40%. In use, the clip track  30  will force the feeder shoe  34 ′ into a substantially planar configuration such that the feeder shoe  34 ′ is biased against the clip track  30  when disposed therein. The bend  35 ′ of the feeder shoe  34 ′, as well as the terminal ends  34   a ′,  34   b ′ of the feeder shoe  34 ′, will therefore apply a force to the clip track  30 , thereby creating a frictional drag force between the feeder shoe  34 ′ and the clip track  30 . The frictional force will prevent the feeder shoe  34 ′ from migrating relative to the clip track  30  unless the trigger  16  is actuated, in which case the force applied by the trigger  16  will overcome the frictional forces. 
     A person skilled in the art will appreciate that the bend  35 ′ can have a variety of configurations, and it can be formed anywhere along the length of the feeder shoe  34 ′. In  FIG. 27A  the bend  35 ′ is formed at or near the mid-portion of the feeder shoe  34 ′. The bend  35 ′ can also extend in various directions. While  FIG. 27A  illustrates the bend  35 ′ extending in a direction perpendicular to the axis such that the bend  35 ′ and the ends  34   a ′,  34   b ′ apply a force to the clip track  30 , the bend  35 ′ can alternatively extend along a longitudinal axis of the feeder shoe  34 ′ such that the feeder shoe  34 ′ applies a force to the opposed side rails  80   a ,  80   b  ( FIG. 2D ) of the clip track  30 . The bend  35 ′ can also angle the opposed ends  34   a ′,  34   b ′ in a downward direction, as shown in  FIG. 27A , such that the feeder shoe  34 ′ is substantially A-shaped, or alternatively the bend  35 ″ can angle the opposed ends  34   a ″,  34   b ″ in an upward direction, as shown in  FIG. 27B , such that the feeder shoe  34 ″ is substantially V-shaped. The feeder shoe  34 ′ can also include any number of bends formed therein. A person skilled in the art will appreciate that the particular configuration of the bend(s) can be modified based on the properties of the feeder shoe  34 ′ and the clip track  30  to obtain a desired amount of frictional force therebetween. 
       FIGS. 28A and 28B  illustrate another embodiment of a technique for creating frictional forces between the feeder shoe and clip track. In this embodiment, the clip track  30 ′ and/or the feeder shoe  34   x  can include one or more surface protrusions formed thereon. As shown in  FIG. 28A , two surface protrusions  82   d   1 ,  82   d   2  are formed on the clip track  30 ′. While the surface protrusions  82   d   1 ,  82   d   2  can be formed at various locations on the clip track  30 ′, including inside the opposed side rails or along the entire length of the clip track  30 ′, or at various locations on the feeder shoe  34   x , in the illustrated embodiment two protrusions  82   d   1 ,  82   d   2  are formed adjacent to the proximal end of the clip track  30 ′ and they are positioned to prevent initial migration of the feeder shoe prior to use, e.g., during shipping. The size of the protrusions  82   d   1 ,  82   d   2  can vary depending upon the amount of frictional force necessary to prevent unintentional migration of the feeder shoe  34   x . 
     While the protrusions  82   d   1 ,  82   d   2  can be configured to provide a sufficient amount of friction to prevent unintentional migration of the feeder shoe  34   x , the feeder shoe  34   x  and/or clip track  30 ′ can optionally include a feature that is adapted to engage corresponding surface protrusions.  FIG. 28B  illustrates opposed tangs  82   e   1 ,  82   e   2  formed on a distal portion of the feeder shoe  34   x  for engaging the protrusions  82   d   1 ,  82   d   2  on the clip track  30 ′. The tangs  82   e   1 ,  82   e   2  can vary in shape and size, and they can include a lip or other protrusion configured to engage or “catch” the protrusions  82   d   1 ,  82   d   2 . As shown in  FIG. 28B , the tangs  82   e   1 ,  82   e   2  extend toward one another from opposed sidewalls of the feeder show  34   x . 
       FIGS. 29A-29C  illustrate another embodiment of a technique for preventing unintentional migration of the feeder shoe. In this embodiment, friction is generated between the feeder shoe and the feed bar. In particular, the feeder shoe  34   y  includes a tang  82   f  with a lip  82   g  formed thereon, as shown in  FIG. 29A , and the feed bar  38   y  includes a corresponding groove  84   y  formed therein. In use, as shown in  FIG. 29C , the lip  82   g  is configured to engage the groove  84   y  to prevent unintentional migration of the feeder shoe  34   y . The lip  82   g  and groove  84   y , however, are configured to allow movement of the feeder shoe  34   y  when a sufficient force is applied to the feeder shoe  34   y  by actuation of the trigger  16 . 
     A person skilled in the art will appreciate that a variety of other techniques can be used to prevent unintentional migration of a feeder shoe or other clip advancement mechanism within a clip track, and that any combination of features can be used and positioned at various locations on one or both components. 
       FIGS. 7-9  illustrate various exemplary components of a clip forming assembly. Referring first to  FIG. 7 , an exemplary embodiment of the jaws  20  are shown. As previously mentioned, the jaws  20  can include a proximal portion  20   a  having teeth  94  for mating with corresponding teeth  78  formed on the jaw retaining shaft  28 . Other techniques can, however, be used to mate the jaws  20  to the jaw retaining shaft  28 . For example, a dovetail connection, a male-female connection, etc., can be used. Alternatively, the jaws  20  can be integrally formed with the retaining shaft  28 . The distal portion  20   b  of the jaws  20  can be adapted to receive a clip therebetween, and thus the distal portion  20   b  can include first and second opposed jaw members  96   a ,  96   b  that are movable relative to one another. In an exemplary embodiment, the jaw members  96   a ,  96   b  are biased to an open position, and a force is required to move the jaw members  96   a ,  96   b  toward one another. The jaw members  96   a ,  96   b  can each include a groove (only one groove  97  is shown) formed therein on opposed inner surfaces thereof for receiving the legs of a clip in alignment with the jaw members  96   a ,  96   b . The jaws members  96   a ,  96   b  can also each include a cam track  98   a ,  98   b  formed therein for allowing the cam  42  to engage the jaw members  96   a ,  96   b  and move the jaw members  96   a ,  96   b  toward one another. In an exemplary embodiment, the cam track  98   a ,  98   b  is formed on a superior surface of the jaw members  96   a ,  96   b.    
       FIG. 8  illustrates an exemplary cam  42  for slidably mating to and engaging the jaw members  96 ,  96   b . The cam  42  can have a variety of configurations, but in the illustrated embodiment it includes a proximal end  42   a  that is adapted to mate to a push rod  44 , discussed in more detail below, and a distal end  42   b  that is adapted to engage the jaw members  96   a ,  96   b . A variety of techniques can be used to mate the cam  42  to the push rod  44 , but in the illustrated exemplary embodiment the cam  42  includes a female or keyed cut-out  100  formed therein and adapted to receive a male or key member  102  formed on the distal end  44   b  of the push rod  44 . The male member  102  is shown in more detail in  FIG. 9 , which illustrates the push rod  44 . As shown, the male member  102  has a shape that corresponds to the shape of the cut-out  100  to allow the two members  42 ,  44  to mate. A person skilled in the art will appreciate that the cam  42  and the push rod  44  can optionally be integrally formed with one another. The proximal end  44   a  of the push rod  44  can be adapted to mate to a closure link assembly, discussed in more detail below, for moving the push rod  44  and the cam  42  relative to the jaws  20 . 
     As is further shown in  FIG. 8 , the cam  42  can also include a protrusion  42   c  formed thereon that is adapted to be slidably received within an elongate slot  20   c  formed in the jaws  20 . In use, the protrusion  42   c  and the slot  20   c  can function to form a proximal stop for the clip forming assembly. 
     Referring back to  FIG. 8 , the distal end  42   b  of the cam  42  can be adapted to engage the jaw members  96   a ,  96   b . While a variety of techniques can be used, in the illustrated exemplary embodiment the distal end  42   b  includes a camming channel or tapering recess  104  formed therein for slidably receiving the cam tracks  98   a ,  98   b  on the jaw members  96   a ,  96   b . In use, as shown in  FIGS. 10A and 10B , the cam  42  can be advanced from a proximal position, in which the jaw members  96   a ,  96   b  are spaced a distance apart from one another, to a distal position, in which the jaw members  96   a ,  96   b  are positioned adjacent to one another and in a closed position. As the cam  42  is advanced over the jaw members  96   a ,  96   b , the tapering recess  104  will push the jaw members  96   a ,  96   b  toward one another, thereby crimping a clip disposed therebetween. 
     As previously mentioned, the surgical clip applier  10  can also include a tissue stop  46  for facilitating positioning of the tissue at the surgical site within jaws  20 .  FIG. 11A  shows one exemplary embodiment of a tissue stop  46  having proximal end and distal ends  46   a ,  46   b . The proximal end  46   a  can be adapted to mate to a distal end of the clip track  30  for positioning the tissue stop  46  adjacent to the jaws  20 . However, the tissue stop  46  can be integrally formed with the clip track  30 , or it can be adapted to mate to or be integrally formed with a variety of other components of the shaft  18 . The distal end  46   b  of the tissue stop  46  can have a shape that is adapted to seat a vessel, duct, shunt, etc. therebetween to position and aligned the jaws  20  relative to the target site. As shown in  FIG. 11A  the distal end  46   b  of the tissue stop  46  is substantially v-shaped. The distal end  46   b  can also have a curved configuration to facilitate placement of the device through a trocar or other access tube. 
     The tissue stop, or other components of the device, can also optionally include features to support and stabilize a clip during clip formation. When a clip is being formed between the jaws, the clip can pivot and become misaligned. In particular, as the jaws are closed, the terminal end of each leg of the clip will be moved toward one another. As a result, the jaws will only engage a bend portion on each leg, thus allowing the terminal ends of the legs and the apex of the clip to swing out of alignment with the jaws, i.e., to pivot vertically relative to the jaws. Further closure of the jaws can thus result in a malformed clip. Accordingly, the device can include features to align and guide the clip into the jaws, and to prevent the clip from pivoting or otherwise becoming misaligned during clip formation. 
     While the alignment feature can have a variety of configurations, and it can be formed on various components of the device,  FIG. 11A  illustrates a central tang  47  formed at a mid-portion of the distal end  46   b  of the tissue stop  46  for maintaining a clip in alignment with the tip of the advancer assembly  40 . In particular, the central tang  47  can allow the apex of a clip to ride therealong thus preventing the clip from becoming misaligned relative to the advancer assembly  40  that is pushing the clip in a distal direction. A person skilled in the art will appreciate that the tissue stop  46  can have a variety of other configurations, and it can include a variety of other features to facilitate advancement of a clip therealong. 
       FIGS. 11B-11D  illustrate another exemplary embodiment of a tissue stop  46 ′ having an alignment feature or guide member formed thereon and adapted to align and guide the clip into the jaws, and more preferably to maintain the clip in alignment with the jaws during clip formation. In this embodiment, the alignment feature is in the form of a ramped member  47 ′ extending longitudinally along a central axis of the tissue stop  46 ′ and protruding above a superior surface of the tissue stop  46 ′. The ramped member  47 ′ is preferably rigid, and increases in height from a proximal end  46   a ′ to a distal end  46   b ′ of the tissue stop  46 ′. The angle can vary, however, depending on the particular angle of the jaws. The ramp member  47 ′ preferably terminates just proximal to the tissue-receiving recess  46   c ′ formed in the distal tip of the tissue stop  46 ′. As a result, the ramped member  47 ′ is positioned just proximal to the jaws  20 , thus allowing the ramped member  47 ′ to guide a clip, as well as the tip of the advancer assembly  40  that is pushing the clip, into the jaws  20  at an appropriate angle. In use, the ramped member  47 ′ can abut against an inferior surface of the apex of a clip disposed between the jaws  20  to prevent the clip from pivoting vertically as the jaws  20  are closed to form the clip. In particular, when the advancer assembly  40  is moved to the distal-most position along the ramped member  47 ′, the apex of the clip will abut against the surface of the ramped member  47 ′. As the clip is compressed between the jaws  20  and the legs of the clip move toward one another, the jaws  20  will only engage a bend portion on each leg. As a result, legs and the apex of the clip are free to pivot vertically. However, since the apex is resting against the superior surface  47   a ′ of the ramped member  47 ′, the ramped member  47 ′ will prevent the apex from moving vertically in a downward or inferior direction, thereby preventing the legs of the clip from moving vertically in an upward or superior direction, i.e., the ramped member  47 ′ will prevent the clip from swinging within the jaws  20 . Thus, the ramped member  47 ′ is effective to prevent or limit harmful rotational forces generated when the jaws  20  are closed to form the clip. The clip is thus maintained in alignment with the jaws  20 . 
     A person skilled in the art will appreciate that the shape, size, and configuration of the ramp member can vary depending on the particular configuration of the jaws and other components of the clip applier. In one exemplary embodiment, the ramped member  47 ′ can have a maximum height h Rmax  of about 0.025″, as measured from a central plane extending through the tissue stop  46 ′. More preferably the height h Rmax  is in the range of about 0.008″″ to 0.020″, and most preferably the height h Rmax  is in the range of about 0.010′ to 0.015″. The incline angle α R  of the ramped member  47 ′ can also vary, but in an exemplary embodiment the ramped member  47 ′ has an incline angle α R  in the range of about 5° to 45°, and more preferably 5° to 30°, and most preferably 10° to 20°. The width w r  of the ramped member  47 ′ can also vary, but in an exemplary embodiment the ramped member  47 ′ preferably has a width w r  that is slightly less than a space between the jaws  20  in the fully closed position. 
       FIG. 12  illustrates the tissue stop  46  in use. As shown, the tissue stop  46  is positioned just inferior to the jaws  20  and at a location that allows a vessel, duct, shunt etc. to be received between the jaws  20 . As is further shown, a surgical clip  36  is positioned between the jaws  20  such that the bight portion  36   a  of the clip  36  is aligned with the tissue stop  46 . This will allow the legs  36   b  of the clip  36  to be fully positioned around the vessel, duct, shunt, or other target site. 
       FIGS. 13-26B  illustrate various exemplary internal components of the housing  12  for controlling clip advancement and forming. As previously discussed, the surgical clip applier  10  can include some or all of the features disclosed herein, and it can include a variety of other features known in the art. In certain exemplary embodiments, the internal components of the clip applier  10  can include a clip advancing assembly, that couples to the clip advancing assembly of the shaft  18 , for advancing at least one clip through the elongate shaft  18  to position the clip between the jaws  20 , and a clip forming assembly, that couples to the clip forming assembly of the shaft  18 , for closing the jaws  20  to form a partially or fully closed clip. Other exemplary features include an anti-backup mechanism for controlling movement of the trigger  16 , an overload mechanism for preventing overload of the force applied to the jaws  20  by the clip forming assembly, and a clip quantity indicator for indicating a quantity of clips remaining in the device  10 . 
       FIGS. 13-16D  illustrate an exemplary embodiment of a clip advancing assembly of the housing  12  for effecting movement of the feed bar  38  within the shaft  18 . In general, the clip advancing assembly can include a trigger insert  48  that is coupled to the trigger  16 , a feed bar coupler  50  that can mate to a proximal end  38   a  of the feed bar  38 , and a feed link  52  that is adapted to extend between the trigger insert  48  and the feed bar coupler  50  for transferring motion from the trigger insert  48  to the feed bar coupler  50 . 
       FIG. 14  illustrates the trigger insert  48  in more detail. The shape of the trigger insert  48  can vary depending on the other components of the housing  12 , but in the illustrated embodiment the trigger insert  48  includes a central portion  48   a  that is adapted to pivotally mate to the housing  12 , and an elongate portion  48   b  that is adapted to extend into and mate to the trigger  16 . The central portion  48   a  can include a bore  106  extending therethrough for receiving a shaft for pivotally mating the trigger insert  48  to the housing  12 . The central portion  48   a  can also include a first recess  108  formed in a superior side edge for receiving a portion of the feed link  52 . The first recess  108  preferably has a size and shape that allows a portion of the feed link  52  to extend therein such that the feed link  52  will be forced to pivot when the trigger insert  48  pivots due to movement of the trigger  16 . As shown in  FIG. 14 , the first recess  108  is substantially elongate and includes a substantially circular portion formed therein for seating a shaft formed on a proximal end of the feed link  52 , as will be discussed in more detail with respect to  FIG. 16 . The trigger insert  48  can also include a second recess  110  formed in a back side edge for receiving a closure link roller  54  that is coupled to the push bar  44  for moving the cam  42  to close the jaws  20 , and ratchet teeth  112  formed on the bottom side edge thereof for mating with a pawl  60  for controlling movement of the trigger  16 , as will be discussed in more detail below. 
     The exemplary feed bar coupler  50  is shown in more detail in  FIGS. 15A and 15B , and it can be adapted to couple the proximal end of the feed bar  38  to the distal end of the feed link  52 . While a variety of techniques can be used to mate the feed bar coupler  50  to the proximal end  38   a  of the feed bar  38 , in an exemplary embodiment the feed bar coupler  50  is formed from two separate halves  50   a ,  50   b  that mate together to maintain the proximal end  38   a  of the feed bar  38  therebetween. When mated, the two halves  50   a ,  50   b  together define a central shaft  50   c  having substantially circular flanges  50   d ,  50   e  formed on opposed ends thereof and defining a recess  50   f  therebetween for seating a distal portion of the feed link  52 . The central shaft  50   c  defines a lumen  50   g  therethrough for receiving the proximal end  38   a  of the feed bar  38  and for locking the feed bar  38  in a substantially fixed position relative to the feed bar coupler  50 . The feed bar coupler  50  can, however, be integrally formed with the feed bar  38 , and it can have a variety of other shapes and sizes to facilitate mating with the feed link  52 . 
       FIG. 16  illustrates an exemplary feed link  52 , which can extend between the trigger insert  48  and the feed bar coupler  52 . In general, the feed link  52  can have a substantially planar elongate shape with proximal and distal ends  52   a ,  52   b . The proximal end  52   a  is adapted to rotatably sit within the first recess  108  of the trigger insert  48  and thus, as previously discussed, it can include a shaft  53  ( FIG. 1B ) extending therethrough. The shaft  53  can be adapted to pivotally rotate within the first recess  108  of the trigger insert  48 , thereby allowing the trigger insert  48  to pivot the feed link  52 . The distal end  52   b  of the feed link  52  can be adapted to couple to feed bar coupler  50  and thus, in an exemplary embodiment, it includes opposed arms  114   a ,  114   b  formed thereon and defining an opening  116  therebetween for seating the central shaft  50   a  of the feed bar coupler  50 . The arms  114   a ,  114   b  are effective to engage and move the coupler  50  as the feed link  52  pivots about a pivot axis X. The pivot axis X can be defined by the location at which the feed link  52  couples to the housing  12 , and it can be positioned anywhere on the feed link  52 , but in the illustrated embodiment it is positioned adjacent to the proximal end  52   a  of the feed link  52 . 
     In an exemplary embodiment, the feed link  52  can be flexible to eliminate the need to calibrate the clip advancing assembly and the clip forming assembly. In particular, the feed link  52  allows the trigger  16  to continue moving toward a closed position even after the feed bar  38  and feed bar coupler  50  are in a distal-most position, and it provides some freedom to the clip forming and clip advancing assemblies. In other words, the trigger  16  is pliant relative to the feed bar  38  during closure of the trigger. 
     The particular stiffness and strength of the feed link  52  can vary depending on the configuration of the clip advancing assembly and the clip forming assembly, but in one exemplary embodiment the feed link  52  has a stiffness that is in the range of 75 to 110 lbs per inch, and more preferably that is about 93 lbs per inch (as measured at the interface between the link  52  and the feed bar coupler  50 ), and it has a strength of that is in the range of 25 lbs and 50 lbs, and more preferably that is about 35 lbs. The feed link  52  can also be formed from a variety of materials, including a variety of polymers, metals, etc. One exemplary material is a glass-reinforced polyetherimide, but a number of reinforced thermoplastics could be used, including glass reinforced liquid-crystal polymers, glass-reinforced nylons, and carbon-fiber reinforced versions of these and similar thermoplastics. Fiber-reinforced thermoset polymers such as thermoset polyesters could also be used. Feed link  52  could also be fabricated from a metal, such as spring steel to achieve the desired combination of limited flexibility and controlled strength. 
       FIGS. 17A-17D  illustrate the exemplary clip advancing assembly in use.  FIG. 17A  shows an initial position, wherein the trigger  16  is resting in an open position, the feed bar coupler  50  and feed bar  38  are in a proximal-most position, and the feed link  52  extends between the trigger insert  48  and the feed bar coupler  50 . As previously discussed, in the initial open position the protrusion  86  on the feed bar  38  in positioned in the proximal end of the elongate slot  88  in the jaw retainer shaft  28 . A first biasing member, e.g., spring  120 , is coupled to the trigger insert  48  and the housing  12  to maintain the trigger insert  48  and trigger  16  in the open position, and a second biasing member, e.g., spring  122 , extends between a shaft coupler  124 , which rotatably mates the shaft  18  to the housing  12 , and the feed bar coupler  50  to maintain the feed bar coupler  50  and feed bar  38  in the proximal-most position. 
     When the trigger  16  is actuated and moved toward the closed position, i.e., toward the stationary handle  14 , to overcome the biasing forces applied by the springs  120 ,  122 , the trigger insert  48  begins to pivot in a counter-clockwise direction, as shown in  FIG. 17B . As a result, the feed link  52  is forced to pivot in a counter-clockwise direction, thereby moving the feed bar coupler  50  and feed bar  38  in a distal direction. The protrusion  86  on the feed bar  38  thus moves distally within the elongate slot  88  in the jaw retainer shaft  28 , thereby advancing the feeder shoe  34  and the clips  36  disposed within the clip track. Spring  120  is extended between the housing and the trigger insert  48 , and spring  122  is compressed between the feed bar coupler  50  and the shaft coupler  124 . 
     As the trigger  16  is further actuated and the trigger insert  48  continues to pivot, the feed bar coupler  50  and feed bar  38  will eventually reach a distal-most position. In this position, the protrusion  86  on the feed bar  38  will be positioned at the distal end of the slot  88  in the jaw retainer shaft  28  and a clip will be positioned between the jaws  20 , as previously discussed. Spring  122  will be fully compressed between the shaft coupler  124  and the feed bar coupler  50 , and the feed link  52  will flex, as shown in  FIGS. 17C and 17D . As the feed link  52  flexes, and more preferably once the feed link  52  fully flexed, the clip forming assembly will be actuated to close the jaws  20 . The feed link  52  will remain flexed during actuation of the clip forming assembly, e.g., the second stage of actuation, such that the trigger insert  48  is pliant relative to the clip advancing assembly, and in particular the feed bar  38 . 
     An exemplary clip forming assembly of the housing  12  is shown in more detail in  FIGS. 18-20 . In general, the clip forming assembly is disposed within the housing  12  and it is effective to move the push rod  44  and cam  42  relative to the jaws  20  to move the jaws  20  to a closed position and thereby crimp a clip positioned therebetween. While the clip forming assembly can have a variety of configurations, the illustrated exemplary clip forming assembly includes a closure link roller  54  that is slidably coupled to the trigger insert  48 , a closure link  56  that is adapted to couple to the closure link roller  54 , and a closure coupler  58  that is adapted to couple to the closure link  56  and to the push rod  44 . 
       FIG. 18  illustrates the closure link roller  54  in more detail and, as shown, the closure link roller  54  includes a central shaft  54   a  having substantially circular flanges  54   b ,  54   c  formed adjacent to the opposed terminal ends thereof. The central shaft  54   a  can be adapted to sit within the second recess  110  in the trigger insert  48  such that the flanges  54   b ,  54   c  are received on opposed sides of the trigger insert  48 . The central shaft  54   a  can also be adapted to mate to opposed arms  126   a ,  126   b  of the closure link  56  to position the arms on opposed sides of the trigger insert  48 . 
     An exemplary embodiment of a closure link  56  is shown in more detail in  FIG. 19 , and as shown it has opposed arms  126   a ,  126   b  that are spaced a distance apart from one another. Each arm  126   a ,  126   b  includes a proximal end  128   a ,  128   b  that is adapted to engage the central shaft  54   a  of the closure link roller  54 , and a distal end  130   a ,  130   b  that is adapted to mate to a closure coupler  58  for coupling the closure link roller  54  and closure link  56  to the push rod  44 . In an exemplary embodiment, the proximal end  128   a ,  128   b  of each arm  126   a ,  126   b  is adapted to pivotally mate to the closure link roller  54 , and thus the arms  126   a ,  126   b  can include, for example, hook-shaped members  132   a ,  132   b  formed thereon for engaging the central shaft  54   a . The hook-shaped members  132   a ,  132   b  extend in opposite directions to facilitate engagement between the closure link  56  and the closure link roller  54 . The distal end  130   a ,  130   b  of the arms  126   a ,  126   b  can be mated to one another, and they can include a lumen  134  extending therethrough for receiving a shaft that is adapted to pivotally mate the closure link  56  to the closure coupler  58 . A person skilled in the art will appreciate that a variety of other techniques can be used to mate the closure link  56  to the closure link roller  54  and the closure coupler  58 . 
     An exemplary closure coupler  58  is shown in more detail in  FIG. 20A , and as shown it includes a proximal portion  58   a  having two arms  136   a ,  136   b  with lumens  138   a ,  138   b  extending therethrough and adapted to be aligned with the lumen  134  in the closure link  56  for receiving a shaft to mate the two components. The closure coupler  58  can also include a distal portion  58   b  that is adapted to mate to the proximal end  44   a  of the push rod  44  ( FIG. 9 ). In an exemplary embodiment, the closure coupler  58  includes a cut-out  59  ( FIGS. 20B and 20C ) formed therein and having a shape that is adapted to seat the proximal end  44   a  of the push rod  44 . The distal portion  58   b  of the closure coupler  58  can also be configured to receive a portion of the feed bar coupler  50  when the trigger  16  is in the open position. A person skilled in the art will appreciate that a variety of other mating techniques can be used to mate the closure coupler  58  to the push rod  44 , and that the closure coupler  58  and the push rod  44  can optionally be integrally formed with one another. 
     In other exemplary embodiments, a preloaded joint can be formed between the push rod  44  and the closure coupler  58  to prevent accidental release of a clip from the jaws, particularly during the early stages of closure, if the user eases-up on the trigger  16 . In particular, while the anti-backup mechanism, discussed in more detail below, can be adapted to prevent the trigger  16  from opening until the trigger  16  reaches a predetermined position, the anti-backup mechanism may allow some minor movement of the trigger  16 . Thus, in the event a user eases-up on the trigger  16  and minor opening of the trigger  16  occurs, the preloaded joint will bias the push rod  44  in a distal direction, thereby maintaining the push rod  44  in a substantially fixed position, while allowing the closure coupler  58  to move proximally until the trigger  16  is engaged by the anti-backup mechanism. 
     While the preloaded joint can have a variety of configurations, and it can be positioned at various locations along the clip forming assembly, in one exemplary embodiment the preloaded joint can be in the form of a biasing member disposed within the cut-out  59  to bias the push rod  44  in a distal direction. While a variety of biasing members can be used, in the embodiment shown in  FIG. 20B , the biasing member is a cantilevered beam  61  that is positioned between the proximal end  44   a  of the push rod  44  and the back wall of the recess  59  to bias the push rod  44  distally. The cantilevered beam  61  can be formed from a shape memory material, such as Nitinol, that allows the beam  61  to flex or flatten when a proximally-directed force is applied thereto. The beam  61  can also be formed from a variety of other materials, such as spring steel or reinforced polymers, and more than one beam can be used.  FIG. 20C  illustrates another embodiment of a biasing member which is in the form of a coil or other type of spring  63 . As shown, the spring  63  is disposed between the proximal end  44   a  of the push rod  44  and the back wall of the recess  59  to bias the push rod  44  distally. The spring  63  is adapted to compress when a proximally-directed force is applied thereto. A person skilled in the art will appreciate that a variety of other biasing members can be used, including elastomeric compression members. 
     The preloaded joint can also optionally include features to enhance performance of the cantilevered beam or spring during the clip forming process. In the embodiment shown in  FIG. 20B , the load of the cantilevered beam  61  remains primarily uniform as the cantilevered beam is compressed during closure, however the load increases significantly during the final stages of closure. This is illustrated in  FIG. 20D , which shows a graph of the load/displacement curve of the cantilevered beam  61  shown in  FIG. 20B . The left end of the curve represents the unloaded height of the cantilevered beam  61 , while the right end of the curve represents the point at which the cantilevered beam  61  is fully compressed or flattened. The upper curve represents the force resulting as the cantilevered beam  61  is compressed during a typical closing stroke, with the exception that the force is measured from a free state of the cantilevered beam  61  whereas the cantilevered beam  61  is initially partially compressed when it is disposed within the closure coupler  58 . As shown, the load remains substantially constant (excluding the initial compression stages), increasing only slightly during the closing stroke as the cantilevered beam  61  is being compressed. However, the load increases significantly at the final stages of closure when the cantilevered beam  61  is fully flattened. This is due to deflection of the cantilevered beam  61  which causes the load to be transferred from the terminal ends of the cantilevered beam  61  inward. As the cantilevered beam  61  deflects and the load is transferred inward, the effective length of the cantilevered beam  61  is decreased, thereby increasing the load. In order to prevent this, the preloaded joint can optionally include features to enhance the cantilevered beam or spring performance, and in particular to maintain a substantially constant load during clip formation. 
       FIG. 20E  illustrates one exemplary embodiment of a technique for enhancing the cantilevered beam or spring performance. As shown, the recess  59 ′ in the closure coupler  58 ′ includes two ridges  59   a ′,  59   b ′ formed therein on the back surface thereof such that the ridges  59   a ′,  59   b ′ are positioned underneath or behind the cantilevered beam (not shown). The ridges  59   a ′,  59   b ′ are spaced a distance apart from one another and each ridge  59   a ′,  59   b ′ has a height of at least about 0.005″ to prevent the cantilevered beam from fully flattening against the back surface of the recess. As a result, the ridges  59   a ′,  59   b ′ will prevent the cantilevered beam from deflecting, thereby preventing the load of the spring or cantilevered beam from transferring from the terminal ends inward. A person skilled in the art will appreciate that the particular location, quantity, and size of the ridges  59   a ′,  59   b ′ can vary depending on the configuration of the preloaded joint, as well as the forces necessary to prevent clip fallout during closure. 
     In use, referring back to  FIGS. 17A-17D , as the trigger  16  is initially moved from the open position toward the closed position, the closure link roller  54  will roll within the recess  110  in the trigger insert  48 . Once the feed bar  38  and feed bar coupler  50  are in the distal-most position, as shown in  FIG. 17C , further actuation of the trigger  16  will cause the recess  110  in the trigger insert  48  to engage the closure link roller  54  forcing it to pivot with the trigger insert  48 , as shown in  FIG. 17D . As a result, the closure coupler  58  will move distally, thereby causing the push rod  44  to move distally. As the push rod  44  advances distally, the cam  42  is advanced over the jaws  20  to close the jaws  20  and crimp the clip positioned therebetween. The trigger  16  can optionally be partially closed to only partially close the jaws  20  and thus partially crimp a clip disposed therebetween. Exemplary techniques for facilitating selective full and partial closure of the clip will be discussed in more detail below. Once the clip is applied, the trigger  16  can be released thereby allowing spring  120  to pull the trigger insert  48  back to its initial position, and allowing spring  122  to force the feed bar coupler  50  and feed bar  38  back to the proximal position. As the trigger insert  48  returns to its initial position, the closure link roller  54  is moved back to its initial position as well, thereby pulling the closure link  56 , closure coupler  58 , and push bar  44  proximally. 
     The surgical clip applier  10  can also include a variety of other features to facilitate use of the device  10 . In one exemplary embodiment, the surgical clip applier  10  can include an anti-backup mechanism for controlling movement of the trigger  16 . In particular, the anti-backup mechanism can prevent the trigger  16  from opening during a partial closing stroke. However, once the trigger reaches a predetermined position, at which point the clip positioned between the jaws can be partially crimped, the anti-backup mechanism can release the trigger allowing the trigger to open and release the clip or to close to fully crimp the clip, as may be desired by the user. 
       FIGS. 21A and 21B  illustrate one exemplary embodiment of an anti-backup mechanism in the form of a ratchet. As shown, the ratchet includes a set of teeth  112  formed on the trigger insert  48 , and a pawl  60  that is adapted to be rotatably disposed within the housing  12  and positioned adjacent to the trigger insert  48  such that closure of the trigger  16  and pivotal movement of the trigger insert  48  will cause the pawl  60  to engage the teeth  112 . The teeth  112  can be configured to prevent rotation of the pawl  60  until the pawl  60  reaches a predetermined position, at which point the pawl  60  is free to rotate, thereby allowing the trigger  16  to open or close. The predetermined position preferably corresponds to a position at which the jaws  20  are partially closed. In an exemplary embodiment, as shown, the teeth  112  include a first set of teeth  112   a , e.g., ten teeth, having a size that prevents rotation of the pawl  60  relative thereto, thus preventing the trigger  16  from opening when the pawl  60  is engaged with the first set  112   a  of teeth  112 . The teeth  112  can also include a final or terminal tooth, referred to as a tock tooth  112   b , that has a size that allows the pawl  60  to rotate relative thereto when the pawl  60  is engaged with the tock tooth  112   b . In particular, the tock tooth  112   b  preferably has a size that is substantially greater than the size of the first set of teeth  112   a  such that a relatively large notch  140  is formed between the first set of teeth  112   a  and the tock tooth  112   b . The notch  140  has a size that allows the pawl  60  to pivot therein, thus allowing the pawl  60  to be selectively moved beyond the tock tooth  112   b  or back toward the first set of teeth  112   a . A person skilled in the art will appreciate that the tock tooth  112   b  can have the same size or a smaller size than the first ten teeth  112   a  while still providing a notch  140  formed therebetween that allows the pawl  60  to pivot therein. 
       FIGS. 22A-22D  illustrates the ratchet mechanism in use. When the trigger  16  is initially moved toward a closed position, as shown in  FIG. 22A , the pawl  60  will engage the first set of teeth  112   a  thereby preventing the trigger  16  from opening. Further actuation of the trigger  16  will cause the pawl  60  to advance past the first set of teeth  112   a  until the pawl  60  reaches the notch  140  next to the tock tooth  112   b . Once the pawl  60  reaches the tock tooth  112   b , at which point the jaws  20  are partially closed due the partial distal movement of the cam  42  over the jaws  20 , the pawl  60  is free to rotate thereby allowing the trigger  16  to open or close, as may be desired by the user.  FIG. 22C  illustrates the trigger  16  in a fully-closed position, and  FIGS. 22D and 22E  illustrate the trigger  16  returning to the open position. 
     The ratchet mechanism can also be configured to emit an audible sound that indicates the position of the jaws  20 . For example, a first sound can be emitted when the pawl  60  engages the first set of teeth  112   a , and a second, different sound, e.g., a louder sound, can be emitted when the pawl  60  engages the tock tooth  112   b . As a result, when the trigger  16  reaches the predetermined position at which the pawl  60  is engaged with the tock tooth  112   b , the sound indicates to the user that the jaws  20  are in the partially closed position. The user can thus release the trigger  16  to release a partially closed clip, or they can fully close the trigger  16  to fully close the clip. 
     In another exemplary embodiment, the surgical clip applier  10  can include an overload mechanism that is adapted to prevent overload of a force applied to the jaws  20  by the trigger  16 . Typically, during application of a surgical clip, a certain force is required to close the jaws  20  and crimp the clip around the tissue positioned therebetween. As the forming process proceeds and the clip is at least partially closed, the force required to continue closing the jaws  20  around the clip significantly increases. Accordingly, in an exemplary embodiment, the overload mechanism can have a resistance that correlates to the force required to close the jaws  20 . In other words, the resistance of the overload mechanism can increase as the force required to close the jaws  20  increases. The resistance is, however, preferably slightly greater than the force required to close the jaws  20  to prevent accidental actuation of the overload mechanism. As a result, if the jaws  20  are prevented from closing when the trigger  16  is initially actuated, the force required to overcome the resistance of the overload mechanism is relatively low. This is particularly advantageous as the jaws  20  are more susceptible to being deformed when they are open or only partially closed. The overload mechanism will actuate more readily in the early stages of clip formation to prevent deformation of the jaws. Conversely, when the jaws  20  are substantially closed, the resistance is relatively high such that the overload mechanism can only be actuated upon application of a significant force applied to the jaws  20 . 
       FIG. 23A  illustrates one exemplary embodiment of an overload mechanism  62 , showing an exploded view. In general, the overload mechanism can include an overload housing  64  formed from two halves  64   a ,  64   b  and containing a profile link  66 , a toggle link  68 , a pivot link  70 , and a biasing assembly  72 . The biasing assembly  72  can include a spring post  150  that is coupled to the housing  64  and that includes a bore extending therethrough for receiving a plunger  154 . A spring  152  is disposed around the spring post  150 , and the plunger  154  extends through the spring post  150  and includes a head  154   a  formed thereon that is adapted to abut against the spring  152 . The pivot link  70  can be generally L-shaped and it can be coupled to the housing  64  by a pivot pin  156  extending therethrough. A proximal end  70   a  of the pivot link  70  can contact the head  154   a  of the plunger  154 , and a distal end  70   b  of the pivot link  70  can be pivotally coupled to the toggle link  68  by a pivot pin  166 . The toggle link  68 , in turn, can be coupled to the profile link  66 , which can be slidably and pivotally positioned within the housing  64  adjacent to an opening  64   d  formed in the housing. Pivotal movement of the profile link  66  within the housing  64  can be achieved by, for example, a pivot pin  158  that extends through the profile link  66  and is that disposed within a first slot  160   a  (only one slot is shown) formed in each half  64   a ,  64   b  of the housing  64 , and slidable movement of the profile link  66  within the housing  64  can be achieved by, for example, opposed protrusions  168   a ,  168   b  formed on the profile link  66  that are received within a second slot  160   b  (only one slot is shown) formed in each half  64   a ,  64   b  of the housing  64 . 
     In use, the profile link  66  can be adapted to receive a force from the clip forming assembly and to counter the force with the resistance of the biasing assembly  72 . In particular, the overload mechanism  62  uses the spring  152  along with the toggle link  68  and pivot link  70  to bias the profile link  66  from either rotating about the pivot pin  158  or sliding against the housing  64 . For the rotational aspect, the force exerted by the compressed spring  152  is transferred through the toggle link  68  and pivot link  70 , such that a rotational moment is applied to the profile link  66  against the housing  64 . Thus this assembly causes the profile link  66  to resist rotation with respect to the housing  64 . If the moment generated by a radial load from the closure link roller  54  against the profile link  66  exceeds the moment of the pivot link  70  and toggle link  68 , the profile link  66  begins to rotate, buckling the toggle link  68  and causing the pivot link  70  to further compress the spring  152 . For the sliding aspect, the pivot link  70 , toggle link  68 , and profile link  66  are aligned such that the sliding force (resistance to slide) is the force required to buckle the toggle link  68  and pivot link  70 . If the radial load from the closure link roller  54  against the profile link  66  exceeds the buckling force of the linkages, then the pivot link  70  further compresses the spring  152  as the profile link  66  slides proximally. 
     This is shown in more detail in  FIGS. 23B-23C , and as shown the opening  64   d  in the housing  64  allows the closure link roller  54  of the clip forming assembly to roll against the profile link  66 . As a result, when the trigger  16  is actuated and moved toward the closed position, the closure link roller  54  applies a force to the profile link  66 . The resistance of the overload spring  152  will, however, maintain the profile link  66  in a substantially fixed position unless the force applied by the closure link roller  54  increases to a force that is greater than the resistance, e.g., a threshold force. This can be caused by, for example, a foreign object positioned between the jaws  20  or when the jaws  20  are fully closed with the clip and vessel, duct, shunt, etc. therebetween. When the jaws  20  cannot be further closed, the force applied to the closure link roller  54  from the closing motion of the trigger  16  will be transferred to the profile link  66 , which will then pivot and slide within the housing  64 , thereby causing the pivot link  70  to pivot, which forces the plunger  154  to compress the overload spring  152 . 
     As previously noted, the force required to actuate the overload mechanism can correlate to the force required to close the jaws  20 , which increases as the trigger  16  is moved to the closed position. This can be achieved due to the configuration of the profile link  66 . In particular, when the closure link roller  54  first comes into contact with the profile link  66  and is thus in a lower position, the profile link  66  can pivot within the housing  64 , as shown in  FIG. 23B . As the closure link roller  54  moves upward along the profile link  66 , the force required to overcome the resistance of the overload mechanism increases because the profile link  66  must slide within the housing  64 , as shown in  FIG. 23C . The force required to pivot the profile link  66  can be less than the force required to slide the profile link  66 . Accordingly, if the jaws  20  are prevented from being closed, e.g., by a foreign object, as the trigger is initially actuated, a minimal force will be required to cause the closure link roller  54  to transfer the force to the lower portion of the profile link  66  causing the profile link  66  to pivot. When the jaws  20  are substantially closed and the trigger  16  is almost fully actuated, a significant amount of force is required to cause the closure link roller  54  to transfer the force to the upper portion of the profile link  66  causing the profile link  66  to slide within the housing  64  to overcome the resistance of the overload spring  152 . While the amount of force required to actuate the overload mechanism can be greater than and can increase relative to the amount of force required to close the jaws  20 , the force is preferably only slightly greater than the force required to close the jaws  20  to prevent deformation or other damage to the jaws  20 . A person skilled in the art will appreciate that the resistance can be adjusted based on the force necessary to close the jaws  20 . 
     The profile link  66 , and in particular the distal-facing surface  66   s  of the profile link  66 , can also have a shape that facilitates correlation between the force required to actuate the overload mechanism and the force required to close the jaws  20 . For example, where the force required to close the jaws  20  increases at a linear rate, the distal-facing surface  66   s  of the profile link  66  can be planar to prevent the profile link  66  from interfering with movement of the closure link roller  54  there over, and to allow a linear force to be applied to the trigger  16  to close the jaws  20 . Conversely, where the force required to close the jaws  20  is non-linear as the trigger  16  is moved to the closed position, the profile link  66  can have a non-linear shape that corresponds to the non-linear force. Such a configuration will prevent the forces required to close the cam  42  ( FIG. 8 ) from becoming too high. 
     By way of non-limiting example, the force required to close the jaws  20  can be non-linear due to the shape of the recess  104  in the cam  42  that is adapted to push the jaw members  96   a ,  96   b  toward one another. As shown in  FIG. 8 , the recess  104  can have a curved configuration such that the force will vary as the cam  42  passes over the jaw members  96   a ,  96   b . The profile link  66  can therefore having a corresponding curved distal-facing surface such that the force will also vary as the closure link roller  54  passes there over. As shown in  FIGS. 23A and 23B , the profile link  66  is curved such that the lower portion of the profile link  66  is substantially convex and the upper portion of the profile link  66  is substantially concave. A person skilled in the art will appreciate that the profile link  66  can have a variety of other shapes, and that a variety of other techniques can be used to optimize the force necessary to close the jaws  20  and the force necessary to actuate the overload mechanism. 
     A person skilled in the art will also appreciate that the overload mechanism can have a variety of other configurations. By way of non-limiting example,  FIG. 23D  illustrates an overload mechanism that is in the form of a cantilevered beam  170  for receiving a force applied by the closure link roller  54 . The beam  170  can have a substantially curved member  172  with a bracket  174  coupled to one end thereof. The curved member  172  can have a bending moment that, when loaded with a force greater then the bending moment, buckles to assume a low rigidity condition. The bracket  174  can provide more rigidity to the curved member  172  such that the bending moment increases adjacent to the bracket  174 . In use, the beam  170  can be loaded within the housing  12  of the clip applier  10  such that the closure link roller  54  contacts the concave surface, and the beam  170  can be positioned at an angle such that the closure link roller  54  is farther away from the beam when the trigger  16  is initially actuated, and the closure link roller  54  becomes closer to the beam as the trigger  16  moves to the closed position. As a result, the resistance to buckling will increase as the closure link roller  54  moves thereof and the trigger  16  of the clip applier is moved to the closed position. Although not shown, multiple beams could optionally be used in a stacked fashion and the terminal or free end of the beam(s) could be contoured to tailor the buckling load at a particular point along the length of the beam. 
     In another exemplary embodiment, the surgical clip applier  10  can include a clip quantity indicator for indicating the number of clips remaining in the device  10 . While various techniques can be used to indicate the quantity of clips remaining,  FIGS. 24A-25  illustrate one exemplary embodiment of a clip quantity indicator having an indicator wheel  74  and an indicator actuator  76 . 
     The indicator wheel  74  is shown in detail in  FIGS. 24A and 24B , and as shown it has a generally circular or cylindrical shape that defines a central axis Y about which the wheel  74  is adapted to rotate. The wheel  74  includes teeth  142  formed therearound and adapted to be engaged by the indicator actuator  76 , and an indicator member  144 . The indicator member  144  can have a variety of configurations, but in an exemplary embodiment the indicator member  144  is in the form of a contrasting color pad having a color, e.g., orange, red, etc., that differs from the remainder of the indicator wheel  74 . 
       FIG. 25  illustrates the exemplary indicator actuator  76  in more detail. The actuator  76  is adapted to be slidably disposed within the housing  12  and to couple to the feed link coupler  50  and move as the feed bar coupler  50  and feed bar  38  are moved. Accordingly, the indicator actuator  76  can include a protrusion  146 , only a portion of which is shown, formed on an inferior surface thereof for extending into the recess  50   f  formed between the circular flanges  50   d ,  50   e  on the feed bar coupler  50 . The protrusion  146  allows the indicator actuator  76  to be engaged by the feed bar coupler  50  and moved therewith. The indicator actuator  76  can also include an engagement mechanism  148  formed thereon and adapted to engage the teeth  142  formed on the indicator wheel  74 . As shown in  FIG. 25 , the engagement mechanism  148  on the indicator actuator  76  is in the form of an arm having a tab formed on the end thereof for engaging the teeth  142 . 
     In use, the indicator wheel  74  is rotatably disposed within the housing  12 , as shown in  FIGS. 26A-26B , and the indicator actuator  76  is slidably disposed within the housing  12  such that the engagement mechanism  148  is positioned adjacent to the indicator wheel  74  and the protrusion  146  extends into the feed bar coupler  50 . The housing  12  includes a window  12   a  formed therein for providing visual access to the indicator wheel  144 . As the trigger  16  is moved to the closed position and the feed bar coupler  50  is moved distally, the indicator actuator  76  will move distally with the feed bar  38  and feed bar coupler  50 . As a result, the engagement mechanism  148  on the indicator actuator  76  will engage the teeth  142  on the indicator wheel  74 , thereby causing the wheel  74  to rotate as a clip is advanced into the jaws  20 . Each time the trigger  16  is actuated to advance a clip  20  into the jaws  20 , the indicator actuator  74  rotates the indicator wheel  76 . When the clip supply has two or three clips left, the contrasting color pad  144  on the indicator wheel  74  will begin to appear in the window  12   a  formed in the housing  12 , thereby indicating to the user that only a few clips remain. The contrasting color pad  144  can be adapted to occupy the entire window  12   a  when the clip supply is depleted. 
     In another exemplary embodiment, the indicator wheel  74  can include an anti-backup mechanism that is adapted to prevent the indicator wheel  74  from rotating in a reverse direction, e.g., a counter-clockwise direction, after being advanced. While the anti-backup mechanism can have a variety of configurations, in the embodiment shown in  FIG. 24B  the indicator wheel  74  includes opposed arms  73   a ,  73   b  that extend substantially parallel to the axis Y. Each arm  73   a ,  73   b  has a pawl  75   a ,  75   b  formed on a distal-most end thereof that is adapted to engage corresponding teeth formed on the housing  12 . While not shown, the corresponding teeth can be formed within a circular protrusion formed on an inner portion of the housing  12  adjacent to the window  12   a . When the indicator wheel  74  is disposed within the housing  12 , the arms  73   a ,  73   b  extend into the circular protrusion formed around the inner circumference thereof. As a clip is applied and the indicator wheel  74  is rotated, the arms  73   a ,  73   b  can deflect over the teeth in the housing to move to the next position. When the indicator actuator  76  slides proximally to return to its initial position, the arms  73   a ,  73   b  will engage the teeth in the housing to prevent the indicator wheel  74  from rotating in a reverse direction, i.e., returning to the previous position. A person skilled in the art will appreciate that a variety of other techniques can be used to prevent backup of the indicator wheel  74 . 
     As previously mentioned, the surgical clip applier  10  can be used to apply a partially or fully closed clip to a surgical site, such as a vessel, duct, shunt, etc. In laparoscopic and endoscopic surgery, a small incision is made in the patient&#39;s body to provide access to a surgical site. A cannula or access port is typically used to define a working channel extending from the skin incision to the surgical site. Often during surgical procedures it is necessary to cease blood flow through the vessels or other ducts, and some procedures may require the use of a shunt. A surgical clip can thus be used to crimp the vessel or to secure the shunt to the vessel. Accordingly, a surgical clip applier, such as clip applier  10 , can be introduced through the cannula or otherwise introduced into the surgical site to position the jaws  20  around the vessel, shunt, or other duct. The tissue stop  46  can facilitate positioning of the jaws  20  around the target site. The trigger  16  can then be actuated to cause a clip to be advanced between the jaws and positioned around the target site, and to cause the jaws  20  to close to crimp the clip. Depending on the intended use of the clip, the trigger  16  can be partially actuated, as indicated by the audible sound of the pawl  60  reaching the tock tooth  112   b , or it can be fully actuated. The trigger  16  is then released to release the partially or fully closed clip, and the procedure can be repeated if necessary to apply additional clips. 
     One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.