Patent Publication Number: US-2018049739-A1

Title: Pin locking mechanism for a surgical instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 14/922,567 filed Oct. 26, 2015, which is a Continuation of U.S. patent application Ser. No. 13/721,626 filed Dec. 20, 2012, now U.S. Pat. No. 9,198,658, which is a Divisional of U.S. patent application Ser. No. 12/754,022 filed Apr. 5, 2010, now U.S. Pat. No. 8,353,436, which claims benefit of and priority to U.S. Provisional Application No. 61/175,820 filed May 6, 2009, and the disclosures of each of the above-identified applications are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to a surgical instrument and, more specifically, to a surgical instrument for clamping and joining tissue. 
     2. Background of Related Art 
     Certain surgical stapling instruments are used for applying rows of staples through compressed living tissue. These surgical stapling instruments are employed, for example, for fastening tissue or organs prior to transection or resection or during anastomoses. In some cases, these surgical stapling instruments are utilized for occluding organs in thoracic and abdominal procedures. 
     Typically, such surgical stapling instruments include an anvil assembly, a cartridge assembly for supporting an array of surgical staples, an approximation mechanism for approximating the cartridge and anvil assemblies, an alignment or guide pin assembly for capturing tissue between the cartridge and anvil assemblies and for maintaining alignment between the cartridge and anvil assemblies during approximation and firing, and a firing mechanism for ejecting the surgical staples from the cartridge assembly. 
     In use, the alignment pin assembly is advanced and the anvil and cartridge assemblies are approximated. Next, the surgeon fires the instrument to place staples in tissue. Optionally, the surgeon may use the same instrument or a separate device to cut the tissue adjacent or between the row(s) of staples. The alignment pin in some instances is advanced automatically with approximation of the cartridge; in other instances it is advanced by a separate mechanism. 
     It would be advantageous to provide an alignment pin arrangement to enhance engagement between the cartridge and anvil assemblies. 
     SUMMARY 
     The present disclosure relates to a surgical instrument having a locking mechanism for securing an alignment pin. The surgical instrument generally includes a handle portion, an elongated portion defining a longitudinal axis therethrough, an end effector, and an alignment pin. The elongated portion extends distally from the handle portion. The end effector is disposed adjacent the distal portion of the elongated portion and includes a first jaw member and a second jaw member. The pin is disposed in mechanical cooperation with the first jaw member and includes an engagement section. In operation, the pin moves between a first position and a second position. While in the first position, the engagement section of the pin is spaced from the second jaw member. In the second position, the engagement section of the pin engages the second jaw member. The second jaw member includes a locking structure configured to maintain the pin in the second position to maintain the position of the second jaw member with respect to the first jaw member during actuation of the end effector. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Various embodiments of the presently disclosed surgical stapling instrument are disclosed herein with reference to the drawings, wherein: 
         FIG. 1  is a perspective view of a prior art surgical stapling instrument; 
         FIG. 2  is a perspective view of an end effector of the surgical stapling instrument shown in  FIG. 1 ; 
         FIG. 3  is side cross-sectional view of the end effector shown in  FIG. 2  with the jaw members in the open position; 
         FIG. 4  is a side cross-sectional view of the end effector shown in  FIG. 2  with the jaw members in the closed position; 
         FIG. 5  is a perspective view of a first embodiment of an end effector of the present disclosure; 
         FIG. 6  is a perspective view of a pin for use with the end effector shown in  FIG. 5 ; 
         FIG. 6A  is a perspective view of an alternate embodiment of a pin for use with the end effector shown in  FIG. 5 : 
         FIG. 7  is perspective view of the end effector shown in  FIG. 5  with the pin depicted in  FIG. 6  positioned therein, and showing the pin located in a first or disengaged position; 
         FIG. 8  is a perspective view of the end effector shown in  FIG. 5  with the pin depicted in  FIG. 6  positioned therein, and showing the pin located in a second or engaged position. 
         FIG. 9  is a top cross-sectional view of a locking structure within the end effector illustrated in  FIG. 5  and the pin shown in  FIG. 6 , depicting the pin in a disengaged position; 
         FIG. 10  is a top cross-sectional view of a locking structure within the end effector shown in  FIG. 5  and the pin illustrated in  FIG. 6  taken along line  10 - 10  of  FIG. 8 , depicting the pin in the engaged position; 
         FIG. 11  is a perspective view of another embodiment of an end effector; 
         FIG. 12  is a perspective view of another embodiment of a pin for use with the end effector shown in  FIG. 11 ; 
         FIG. 13  is a perspective view of the portion of the end effector shown in  FIG. 11  with the pin depicted in  FIG. 12  positioned therein; 
         FIG. 14  is a top cross-sectional view of the locking structure within the end effector illustrated in  FIG. 13 , showing the pin located in a disengaged position; 
         FIG. 15  is a top cross-sectional view of the locking structure within the end effector shown in  FIG. 13 , taken along line  15 - 15  of  FIG. 13 , illustrating the pin located in an engaged position; 
         FIG. 16  is a perspective view of another embodiment of an end effector; 
         FIG. 17  is a perspective view of another embodiment of a pin for use with the end effector illustrated in  FIG. 16 ; 
         FIG. 18  is a perspective view of a further embodiment of an end effector; 
         FIGS. 19-21  are side views of the pin and a portion of the end effector depicted in  FIG. 18  at different stages of operation to illustrate movement of the pin from a disengaged to an engaged position; 
         FIG. 22  is a perspective view of another embodiment of an end effector; 
         FIG. 23  is a perspective view of another embodiment of a pin for use with the end effector shown in  FIG. 22 ; 
         FIG. 24  is a perspective view of the end effector illustrated in  FIG. 22  with the pin depicted in  FIG. 23  positioned therein in the engaged position; 
         FIG. 25  is a perspective view of yet another embodiment of a pin; 
         FIG. 26  is a perspective view of an embodiment of an end effector with the pin shown in  FIG. 25  positioned in the engaged position; 
         FIG. 27  is a perspective view of another alternate embodiment of a pin; 
         FIG. 28  is a front cross-sectional view of the pin illustrated in  FIG. 27  positioned in an end effector; 
         FIG. 29  is a perspective view of another embodiment of an end effector with a pin positioned therein; 
         FIGS. 30-32  are side views of the pin and engagement structure of the end effector of  FIG. 29  at different stages of operation to illustrate movement of the pin from a disengaged to an engaged position; 
         FIG. 33  is a perspective view of a sheet of an end effector and an alternate embodiment of a pin; 
         FIGS. 34-36  are side cross-sectional views of the pin and the sheet of  FIG. 33  at different stages of operation to illustrate movement of the pin from a disengaged to an engaged position; 
         FIG. 37  is a side cross-sectional view of the sheet shown in  FIG. 33  and an alternate embodiment of the pin; 
         FIGS. 38-40  are side views of another alternate embodiment of a pin and an end effector at different stages of operation; 
         FIGS. 41 and 42  are side views of an alternate embodiment of a pin and an end effector at different stages of operation; 
         FIGS. 43 and 44  are side views of another alternate embodiment of a pin and an end effector at different stages of operation; 
         FIGS. 45 and 46  are side views of yet another alternate embodiment of a pin and an end effector at different stages of operation; 
         FIGS. 47 and 48  are side views of another alternate embodiment of a pin and an end effector at different stages of operation; 
         FIG. 49  is a side view of an embodiment of a pin with a slot formed therein; 
         FIG. 50  is a side view of an alternate embodiment of a pin with a notch formed thereon; 
         FIGS. 51 and 52  are perspective views of an alternate embodiment of a pin and a hook adapted to pivot toward and away from the pin; 
         FIG. 53  is a perspective view of an alternate embodiment of a locking mechanism for securing a pin, the locking mechanism including first and second arm members; 
         FIGS. 54-57  are a side views of the locking mechanism shown in  FIG. 53  engaging a pin at different stages of operation; 
         FIGS. 58 and 59  are side views of an alternate embodiment of a pin and an end effector including a cam mechanism for securing the pin, showing the cam mechanism at different stages of operation; and 
         FIGS. 60 and 61  are side views of an alternate embodiment of a pin and an end effector including a sliding cam member for locking the pin to the end effector, illustrating the sliding cam member at different stages of operation. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the presently disclosed surgical stapling instrument are described in detail with reference to the drawings, wherein like reference numerals designate corresponding elements in each of the several views. In the description that follows, the term “proximal” refers to the end or portion of the surgical stapling instrument closer to the user, whereas the term “distal” refers to the end or portion of the surgical stapling instrument further away from the user. 
     In the interest of brevity, the present disclosure focuses on pin locking mechanisms for a surgical stapling instrument designated in the drawings by reference numeral  100 . U.S. Pat. No. 7,407,076, the entire contents of which are hereby incorporated by reference, describes in detail the structure and operation of an embodiment of surgical stapling instrument  100 . 
       FIG. 1  illustrates a surgical stapling instrument  100  designed for applying fasteners, cutting tissue, or both. In brief, surgical stapling instrument  100  includes a handle portion  110 , an elongate portion  120 , and an end effector  130  extending from the distal portion of the elongate portion  120 . Handle portion  110  contains a trigger  140  for actuating end effector  130 . Elongate portion  120  extends distally from handle portion  110  and defines a longitudinal axis A-A therealong. End effector  130  is disposed adjacent to the distal portion of elongate portion  120  and includes a first jaw member or cartridge assembly  150  and a second jaw member or anvil assembly  160 . In this embodiment, cartridge assembly  150  is adapted to move longitudinally with respect to anvil assembly  160  upon actuation of trigger  140  to clamp tissue between the jaw members  150 ,  160 . It is also contemplated that the anvil assembly can be moved toward the cartridge or that the cartridge and anvil assemblies can both be moved toward each other to approximate the assemblies and clamp tissue therebetween. 
     With reference to  FIGS. 2-3 , cartridge assembly  150  and anvil assembly  160  of end effector  130  can collectively join tissue. Cartridge assembly  150  includes a plurality of slots  152  each capable of holding a staple or any other suitable fastener. Each slot  152  is operatively associated with a pusher thrust bar or plunger  122 . Pusher  122  extends along elongate portion  120  and partially into cartridge assembly  150 . Cartridge assembly  150  can optionally include a knife advanceable to cut tissue clamped between the cartridge and anvil assemblies  150 ,  160 , respectively. In use, pusher  122  moves distally upon actuation of trigger  140  (see  FIG. 1 ) and causes the ejection of the staples disposed in slots  152 . In addition to slots  152 , cartridge assembly  150  includes a pin  154  operatively connected to pusher  122  and a bore  156  dimensioned to slidably receive pin  154 . Pin  154  is adapted to move longitudinally along bore  156  in response to a translation of pusher  122 . The pin  154  can alternatively be moved by a sliding knob  155  in the handle portion  110 . In the embodiment depicted in  FIG. 2 , anvil assembly  160  has a hole  162  designed to receive at least a portion of pin  154 . Anvil assembly  160  has staple-deforming pockets  164  for deforming the fasteners ejected from cartridge assembly  150 . An elongated slot can be provided between the rows of pockets  164  in the anvil assembly to accommodate a knife if provided. 
     While anvil assembly  160  remains stationary with respect to cartridge assembly  150  during operation, cartridge assembly  150  is movable longitudinally between a proximal position and a distal position upon actuation of trigger  140  (see  FIG. 1 ). In the proximal position, cartridge assembly  150  is spaced apart from anvil assembly  160  as seen in  FIG. 3 . The actuation of trigger  140  causes clamp slides  170  to move distally which in turn causes thrust bar  122  to move distally due to pins  174 . In turn, the distal translation of thrust bar  122  causes the distal movement of cartridge assembly  150  toward anvil assembly  160  to an approximated position. While cartridge assembly  150  moves from the proximal position toward the distal position, end effector  130  clamps any tissue “T” placed between cartridge assembly  150  and anvil assembly  160  as shown in  FIG. 4 . In the distal position, cartridge assembly  150  is located closer to anvil assembly  160  and presses tissue “T” against anvil assembly  160 . 
     Further actuation of trigger  140 , i.e. a second squeeze of the trigger  140 , once cartridge assembly  150  is located in the distal (approximated) position, causes ejection of the fasteners positioned in slots  152 . That is, the continued distal translation of pusher  122 , once cartridge assembly  150  is located in the distal position, causes the deployment of the fasteners positioned in slots  152 . During deployment, these fasteners exit slots  152  and advance through tissue and into contact with staple-deforming pockets  164  of anvil assembly  160  for formation thereof into, e.g. a B-shaped configuration. If a knife is provided, actuation of trigger  140  could also advance the knife. 
     Note the distal motion of clamp slides  170  causes pin  154  to move distally along bore  156  due to the operative connection of the alignment pin pusher  172  to the clamps slides  170  via pins extending through elongated slots in pin pusher  172  as described in the U.S. Pat. No. 7,407,076. Pin pusher  172  includes a vertical portion having an abutment member configured to engage the proximal end of the pin  154 . Upon sufficient distal movement, hole  162  of anvil assembly  160  receives a portion of pin  154 . The structural interaction between pin  154  and hole  162  (when cartridge assembly  150  is located in the distal position) assists in the alignment of slots  152  with staple-deforming pockets  164 . Pin  154  is shown having a substantially cylindrical shape. It should be appreciated that alignment pin  154  can alternatively be moved manually as pin pusher  172  is moved manually, e.g. by sliding knob  115 . 
     Turning now to embodiments of the present disclosure,  FIGS. 5-61  illustrate various pin/hole structures to enhance pin retention. These structures can be used with the stapler of  FIG. 1  described above or with other suitable surgical staplers. They can be configured to move automatically with approximation of the cartridge and/or moved by the user separate from approximation. Note that for brevity, movement of the pins disclosed herein is generally discussed in some embodiments as occurring in response to actuation of the trigger and in other embodiments as being moved selectively movable, e.g. by an independent slidable or other knob. It should be understood, however, that it is contemplated that the pins disclosed herein can be moved in either way or in both ways. 
     Turning first to  FIGS. 5 and 6  illustrating a first embodiment of the locking pin structure of the present disclosure, end effector  230  includes cartridge assembly  250  and anvil assembly  260 . Cartridge assembly  250  includes a bore  256  adapted to receive alignment pin  254 . Pin  254  includes a proximal portion  270  and a distal portion  272  and defines a longitudinal axis B-B therealong. The proximal portion  270  of pin  254  includes a substantially cylindrical body  274  and a pair of protrusions  276  extending radially from body  274 . Pin  254  additionally includes an elongate plate  278  extending distally from body  274 . Elongate plate  278  preferably has a substantially planar configuration and extends between proximal portion  270  and distal portion  272  of pin  274 . Distal portion  272  of pin  254  includes flat engagement section or head section  280  having a substantially triangular shape in the form of an arrowhead. As discussed in detail below, pin  254  is adapted to advance longitudinally through bore  256  of cartridge assembly  250  upon actuation of trigger  140  (see  FIG. 1 ) or by movement of knob  115 . 
     Pin  278 ′ of  FIG. 6A  has a spade shaped distal portion  280 ′. In all other respects, pin  278 ′ is identical to pin  278  of  FIG. 6  and for convenience like parts have been labeled with “prime” designations in  FIG. 6A . 
     Cartridge assembly  250  further includes at least one groove  282  formed therein along bore  256  to aid in the longitudinal motion of pin  254 . In the embodiment shown in  FIG. 5 , cartridge assembly  250  features two grooves  282 . Each groove  282  is configured to slidably receive a protrusion  276  of pin  272 . The geometry of each groove  282  allows pin  254  to slide initially through bore  256  and then rotate to change the orientation or position of engaging section  280  with respect to anvil assembly  260  and cartridge assembly  250 . More specifically, each groove  282  includes a longitudinal or straight portion  284  and an arcuate or curved portion  286  located at a distal end  288  thereof. The straight portion  284  of grooves  282  directs the initial longitudinal translation of pin  254  through bore  256 , whereas the curved portion  286  guides the rotation of pin  254 . As pin  254  moves distally, protrusions  276  slide first along the straight portion  284  of grooves  282 . Upon sufficient distal advancement of pin  254 , the protrusions  276  eventually slidably engage the curved portion  286  of grooves  282 . When protrusions  276  move within the curved portion  286  of grooves  282 , pin  254  rotates about longitudinal axis B-B. As pin  254  rotates about longitudinal axis B-B, engagement section  280  changes its position or orientation, thereby securing pin  254  to anvil assembly  260  as discussed in detail below. 
       FIGS. 7-10  illustrates the operational stages of pin  254  during actuation of the surgical stapling instrument such as instrument  100  of  FIG. 1 . Pin  254  works along with a locking structure  290  disposed in anvil assembly  260  to minimize or prevent anvil assembly  260  from cantilevering away from cartridge assembly  250  during firing. Hole  262  of anvil assembly  260  leads to locking structure  290 . Locking structure  290  includes a slot  292  positioned at a proximal end  294  thereof and a cavity  296  located at distal end  298  thereof. Cavity  296  is disposed in communication with slot  292 . Slot  292  is configured to receive engagement section  280  and at least a portion of elongate plate  278  while pin  254  is oriented in a first position as shown in  FIG. 9 . Cavity  296  can receive engagement section  280  when pin  254  is oriented in either the first position (as seen in  FIG. 7 ) or the second position (as depicted in  FIG. 8 ). When engagement section  280  of pin  254  is positioned inside cavity  296 , the geometry of cavity  296  and slot  292  precludes or at least hinders engagement section  280  from escaping anvil assembly  260  if pin  254  is oriented in the second position as shown in  FIG. 10 . 
     As illustrated in  FIGS. 9 and 10 , cavity  296  has a width “W 2 ” greater that the width “W 1 ” of slot  292 . Engagement section  280  and elongate plate  278  have substantially similar widths. Width “E 1 ” of engagement section  280  is smaller than width “W 1 ” of slot  292  and “W 2 ” of cavity  296 . Engagement section  280  of pin  254  has a dimension “E 2 ” that is larger than width “W 1 ” of slot  292  but smaller than width “W 2 ” of cavity  296 . The geometries of cavity  296 , slot  292 , and engagement section  280  of pin  254  permit engagement section  280  of pin  254  to pass through slot  292  and cavity  296  when pin is positioned in the first position (see  FIG. 9 ), while preventing or at least inhibiting engagement section  280  from escaping anvil assembly  260  when pin  254  is oriented in the second position and engagement section  280  is located inside cavity  296 . When pin  254  is oriented in the second position and its engagement section  280  is located within cavity  296 , locking structure  290  maintains the position of anvil assembly  260  with respect to cartridge assembly  250  during actuation of end effector  230  (see  FIG. 5 ), thereby impeding or hindering anvil assembly  260  from cantilevering away from cartridge assembly  250 . 
     In operation, when a user actuates trigger  140  (see  FIG. 1 ) to advance the cartridge assembly toward the anvil assembly, pin  254  is advanced distally. As pin  254  moves distally, protrusions  276  initially slide along the straight portion  284  of grooves  282 . At this moment, pin  254  translates longitudinally through bore  256 . While pin  254  advances in a distal direction, engagement section  280  is oriented in the first position (as seen in  FIG. 9 ) and is therefore capable of passing through slot  292 . The continued longitudinal motion of pin  254  through bore  256  drives protrusions  276  toward the curved portion  286  of grooves  282 . The length of straight portion  284  allows protrusions  276  to reach the curved portion  386  of grooves  282  just as engagement section  280  enters cavity  296 . At this point, pin  254  begins to rotate about longitudinal axis B-B, reorienting engagement section  280  from the first position (as shown in  FIG. 9 ) to the second position (as illustrated in  FIG. 10 ). By the time protrusions  276  slide along the curved portion  286  of grooves  282 , engagement portion  280  is already positioned inside cavity  296 . Once engagement portion  280  rotates to its second position (illustratively about 180 degree rotation although other rotations are also contemplated), the geometry of cavity  296  and slot  292  blocks engagement portion  280  from exiting anvil assembly  260  (the slot opening being less than the height of portion  280  so engagement section contacts the wall of the slot if retracted), thereby maintaining the position of the anvil assembly  260  with respect to the cartridge assembly  250  during actuation of end effector  230  (see  FIG. 5 ). A release mechanism (not shown) could be provided to reverse rotate the pin  278  to reorient it for release through slot  292  to unapproximate the cartridge and anvil assemblies. 
       FIGS. 11 and 12  illustrate another embodiment of cartridge assembly  350  and anvil assembly  360  of a surgical stapling instrument such as instrument  100  of  FIG. 1 . In this embodiment, cartridge assembly  350  includes a bore  356  adapted to receive pin  354 . Pin  354  includes a proximal portion  370  and a distal portion  372  and defines a longitudinal axis C-C therealong. A body  374  extends from proximal portion  370  of pin  354  to a location proximal to distal portion  372  of pin  354 . Moreover, body  374  features a substantially cylindrical shape and has a proximal end  375  and a distal end  377 . A pair of protrusions juts out radially from the distal end  377  of body  374 . Pin  354  further includes an elongate plate  378  extending distally from distal end  377  of body  374 . Elongate plate  378  has a substantially planar profile and extends between body  374  and engagement section  380 . Distal portion  372  of pin  354  includes substantially flat engagement section  380  having a substantially triangular shape in the form of an arrowhead. As discussed in detail below, pin  354  is adapted to move longitudinally through bore  356  of cartridge assembly  350  and hole  362  of anvil assembly  350  in response to actuation of trigger  140  (see  FIG. 1 ). 
     Anvil assembly  360  further includes at least one groove  382  formed along hole  362  for facilitating the reorientation of engagement section  380  during the firing process. In the embodiment shown in  FIG. 11 , anvil assembly  360  includes two grooves  382  arranged in diametrically opposed relation with respect to each other. Each groove  382  is configured to slidably receive a protrusion  376  and extends from a tissue-engaging surface  366  of anvil assembly  360  to an inner portion of anvil assembly  360 . The geometry of each groove  382  allows pin  354  to slide initially longitudinally through bore  356  in a linear path and then rotate to change the orientation or position of engaging or head section  380  with respect to anvil assembly  360  and cartridge assembly  350 . In some embodiments, each groove  382  includes a longitudinal or straight portion  384  and an arcuate or curved portion  386  located at a distal end  388  thereof which is directed slightly back in a proximal direction. The straight portion  384  of grooves  382  directs the initial longitudinal translation of pin  354  through hole  362 , whereas the curved portion  386  guides the rotation of pin  254  about longitudinal axis C-C. The proximally extending portion helps define a lockout position so the pin needs to move distally first to disengage it from the grooves  382 . This helps to prevent inadvertent rotation and backing out of the pin  354 . 
     It should be appreciated that the other embodiments of pin receiving grooves disclosed herein could also be provided with a proximally directed groove portion as in  FIG. 11  to require distal movement of the pin, followed by proximal movement, to disengage it from the groove in the anvil assembly. 
     As pin  354  moves distally as a result of the distal motion of pusher  122  (see  FIGS. 3 and 4 ), protrusions  376  first slide along the straight portion  384  of grooves  382 . Protrusions  376  eventually slide along the curved portion  386  of grooves  382  as a result of the continued distal advancement of pusher  122  and pin  354 . When protrusions  376  move within the curved portion  386  of grooves  386 , pin  354  rotates about longitudinal axis C-C. As pin  254  rotates about longitudinal axis C-C, engagement section  380  adjusts its position or orientation, thereby securing pin  354  to anvil assembly  360 . If the proximally directed straight portion is provided at the end of the curve as described above, after rotation, the protrusions  354  will move slightly proximally as they move within this straight portion. As shown, the pin  384  rotates about 180 degrees, however it should be appreciated that other degree rotation for pin  384  as well as for the other pins disclosed herein are also contemplated to lock the pin with respect to the anvil assembly. 
       FIGS. 13-15  illustrate the operational stages of pin  354  during actuation of a surgical stapling instrument such as instrument  100  of  FIG. 1 . Pin  354  works along with a locking structure  390  disposed in anvil assembly  360  to minimize or prevent anvil assembly  360  from cantilevering away from cartridge assembly  350  during firing. Hole  362  of anvil assembly  360  leads to locking structure  390 . The structure and operation of locking structure  390  is substantially similar to the structure and operation of locking structure  290  of  FIGS. 9 and 10 . Locking structure  390  includes a slot  392  positioned at a proximal end  394  thereof and a cavity  396  located at distal end  398  thereof. Cavity  396  is disposed in communication with slot  392 . Slot  392  is configured to receive engagement section  380  and at least a portion of elongate plate  378  while pin  354  is oriented in a first position as shown in  FIG. 14 . Cavity  396  can receive engagement section  380  when pin  354  is oriented in either the first position (as seen in  FIG. 14 ) or the second position (as depicted in  FIG. 15 ). When engagement section  380  is positioned inside cavity  396 , the geometry of cavity  396  and slot  392  precludes or at least inhibits engagement section  380  from exiting anvil assembly  360  if pin  354  is oriented in the second position as shown in  FIG. 15 . The secure engagement between engagement section  380  and cavity  396  maintains the position of anvil assembly  360  with respect to cartridge assembly  350  during actuation of end effector  130  (see  FIG. 1 ), thereby impeding or hindering anvil assembly  360  from cantilevering away from cartridge assembly  350 . 
     When a user actuates trigger  140  (see  FIG. 1 ), pin  354  is moved distally and eventually reorients engagement section  380  from the first position toward the second position. While pin  354  moves distally, protrusions  376  initially slide along the straight portion  384  of grooves  382 . At this moment, pin  354  translates longitudinally through hole  362 . While pin  354  translates in a distal direction, engagement section  380  is oriented in the first position (as seen in  FIGS. 13 and 14 ) and is therefore capable of passing through slot  392  of locking structure  390 . The continued longitudinal motion of pin  354  through hole  362  drives protrusions  376  toward the curved portion  386  of grooves  382 . The length of straight portion  384  allows protrusions  376  to reach the curved portion  386  of grooves  382  just as engagement section  380  enters cavity  396 . At this point, pin  354  begins to rotate about longitudinal axis C-C, reorienting engagement section  380  from the first position (as shown in  FIG. 14 ) to the second position (as illustrated in  FIG. 15 ). Engagement portion  380  is already positioned inside cavity  396  when protrusions  376  slide along the curved portion  386  of groove  282 . Once engagement portion  380  rotates to its second position, the geometry of cavity  396  blocks engagement portion  380  from exiting anvil assembly  360 , (by the wall of cavity  396 ) thereby maintaining the position of the anvil assembly  360  with respect to the cartridge assembly  350  during actuation of end effector  130  (see  FIG. 1 ). 
       FIGS. 16 and 17  show a cartridge assembly  450 , an anvil assembly  450 , and a pin  454  for use in conjunction with a surgical instrument such as instrument  100  of  FIG. 1 . Anvil assembly  460  is substantially identical to anvil assembly  260  (see  FIG. 5 ). Cartridge assembly  450  includes a bore  456  adapted to slidably receive pin  454 . Pin  454  includes a proximal portion  470  and a distal portion  472  and defines a longitudinal axis D-D therealong. The proximal portion  470  of pin  454  includes a substantially cylindrical body  474 . Cylindrical body  474  has one or more grooves  476  formed thereon. Grooves  476  are arranged in a diametrically opposed relation with respect to each other and each is adapted to slidably receive a protrusion  482  disposed in cartridge  450  as discussed in detail below. In addition to grooves  476 , pin  454  includes an elongate plate  478  extending from body  474  to an engagement section  480  positioned in distal portion  472 . Elongate plate  478  has a substantially planar configuration. Engagement section  480  has a substantially triangular shape. During operation, engagement section  480  secures pin  454  to anvil assembly  460  after pin  454  has been advanced distally through bore  456  of cartridge assembly  450 . 
     Cartridge assembly  450  incorporates one or more protrusions  482  extending inwardly toward bore  456 . Each protrusion  482  has a straight portion  484  spanning alongside a partial length of bore  456  and an arcuate or curved portion  486  located at a distal end  488  thereof. The curl of curved portions  486  of each protrusion  482  follows the circumference of bore  456 . Each protrusion  482  is adapted to be slidably received by a groove  476  of pin  456 . The geometry of each protrusion  482  enables pin  454  to initially slide through bore  456  upon a distal advancement of pusher  122  (see e.g.  FIGS. 3 and 4 ) and subsequently rotate about longitudinal axis D-D, reorienting engagement section  480  from a first position to a second position. When engagement portion  480  is oriented in the first position, elongate plate  478  and engagement portion  480  are able to enter inside a locking structure (not shown) of anvil assembly  460 . The structure and operation of locking structure of anvil assembly  460  is substantially identical to locking structure  290  shown in  FIGS. 9 and 10 . Like locking structure  290 , the locking structure of anvil assembly  460  traps engagement section  480  of pin  454  inside anvil assembly  460  after engagement section  480  has been distally moved into anvil assembly  460  and reoriented to the second position. 
     In operation, pin  454  moves distally toward anvil assembly  460  upon actuation of trigger  140  (see  FIG. 1 ). Initially, pin  454  translates distally through bore  456 . The sliding engagement between grooves  476  of pin  454  and the straight portion  484  of protrusions  482  guide the distal translation of pin  454 . Due to the continued distal advancement of pin  454 , grooves  476  of pin  454  eventually engage the curved portion  486  of protrusions  482 . As grooves  476  slide along the curved portion  486  of protrusions  482 , pin  454  rotates about longitudinal axis D-D and reorients engagement portion  480  from a first position to a second position. The geometry of protrusions  482  allows pin  454  to rotate about longitudinal axis D-D once engagement portion  480  is located within a cavity (not show) of the locking structure. At this point, pin  454  is secured to anvil assembly  460 . A release can be provided as in the other embodiments herein to rotate the pin to reorient it for removal. 
       FIGS. 18-21  illustrate an alternate embodiment of a cartridge assembly  550 , an anvil assembly  560 , and a pin  554  for use with a surgical instrument such as instrument  100  of  FIG. 1 . Cartridge assembly  550  includes a bore for slidably receiving pin  554 . Pin  554  has a proximal portion  570  and a distal portion  572  and defines longitudinal axis E-E therealong. Distal portion  572  of pin  554  incorporates an engagement section or hook  580 . Hook  580  has a first securing surface  582  defining a substantially right angle relative to longitudinal axis E-E and a first camming surface  584  defining an oblique angle with respect to longitudinal axis E-E. In use, hook  580  secures pin  554  to anvil assembly  560  to maintain the position of anvil assembly  560  with respect to cartridge assembly  550  during firing of the surgical stapling instrument. 
     Anvil assembly  560  has a slot  562  configured to receive pin  554 . Slot  562  extends from tissue-engaging surface  566  to an inner portion of anvil assembly  560 . Further, slot  562  has a lower surface  590  defining a plane F. Lower surface  590  extends from tissue-engage surface  566  to locking structure or catch  594 . Locking structure  594  includes a second camming surface  592  defining an oblique angle relative to plane F and a second securing surface  596  defining a substantially right angle with respect to plane F and formed distal of camming surface  592 . Second camming surface  592  is configured to slidably engage first camming surface  584  of pin  554 . In one embodiment, the oblique angle defined by second camming surface  592  is complementary to the oblique angle defined by first camming surface  584 . In use, pin  554  securely engages locking structure  594  when first securing surface  582  of pin  554  abuts second securing surface  596  of locking structure  594 . 
     As shown in  FIGS. 19-21 , hook  580  reaches locking structure  594  when pin  554  is moved distally by any suitable means. In one embodiment, an actuation of trigger  140  (see  FIG. 1 ) prompts the distal translation of pin  554  as seen in  FIG. 19 . As pin  554  moves continuously in a distal direction, first camming surface  584  of hook  580  slides on second camming surface  592  of locking structure  594 , causing pin  554  to move away from lower surface  590 , as seen in  FIG. 20 . Due to the continued distal advancement of pin  554 , first camming surface  584  ultimately passes second camming surface  592  to allow first securing surface  582  to engage second securing surface  596 . 
     Once first securing surface  582  contacts second securing surface  596 , locking structure  594  secures pin  554  in anvil assembly  560 , thereby maintaining the position of anvil assembly  560  relative to cartridge assembly  550 . A mechanism can be provided to move the pin vertically over the second securing surface  596  to disengage the pin  554  from the surface  596  to allow retraction of the pin  554  and unapproximation of the cartridge and anvil assemblies. 
       FIGS. 22 and 23  show a pin  654 , a cartridge assembly  650 , and an anvil assembly  660  for use with a surgical stapling instrument such as instrument  100  of  FIG. 1 . Cartridge assembly  650  includes a bore  656  adapted to receive pin  654 . Pin  654  has a proximal portion  670  and a distal portion  672  and defines a longitudinal axis G-G therealong. Proximal portion  670  of pin  654  includes a body  674  and two protrusions  676  extending radially from body  674 . Although  FIG. 23  shows body  674  with a substantially cylindrical shape, body  674  may have any suitable shape or configuration. An elongate member  678  extends between proximal and distal portions  670 ,  672 . Distal portion  672  of pin  654  has an external thread  680  formed thereabout. External thread  680  is configured for threadedly engaging an inner thread  692  of anvil assembly  660 . As a consequence, pin  654  secures cartridge assembly  650  to anvil assembly  660 . 
     Cartridge assembly  650  includes a bore  656  for receiving pin  654 , as discussed above, and a pair of grooves  682  each adapted to slidably receive a protrusion  676  of pin  654 . Grooves  682  are disposed alongside bore  656  and include a straight portion  684  and spiral portion  686  located at a distal end  688  thereof. In the depicted embodiment, spiral portion  686  includes multiple loops. When pin  654  moves through bore  656  in a distal direction, the geometry of grooves  682  allows pin  654  to initially advance longitudinally and later translate longitudinally and rotate about longitudinal axis G-G. While pin  654  rotates about longitudinal axis G-G, external thread  680  threadedly engages a locking structure  690  of anvil assembly  660 . 
     Anvil assembly  660  includes hole  662  extending from a tissue-engaging surface  666  to locking structure  690 . Locking structure  690  is disposed within anvil assembly  660  and includes an inner thread  692  formed around hole  662 . Inner thread  692  is adapted to securely engage external thread  680  of pin  654 . 
       FIG. 24  illustrates the operation of pin  654 . During operation, pin  654  fixes the position of anvil assembly  660  with respect to cartridge assembly  650 , preventing or at least hindering anvil assembly  660  from cantilevering away from cartridge assembly  650  during firing of the surgical stapling instrument. Pin  654  moves distally in response to actuation of trigger  140  which approximates the cartridge and anvil assemblies as discussed above. During this distal motion of pin  654 , grooves  682  (in conjunction with protrusions  676 ) guide the movement of pin  654  through bore  656 . In particular, protrusions  676  first slide along the straight portion  684  of grooves  682  during the distal advancement of pin  654 . While protrusions  676  slide along straight portions  684 , pin  654  does not rotate and merely translates distally toward anvil assembly  660 . Then, pin  654  moves into anvil assembly  660  through hole  662  and external thread  480  engages inner thread  692  when protrusions  676  slide along the spiral portion  686  of grooves  686 . While protrusions  676  slide along the spiral portion  686  of grooves  686 , pin  654  rotates about longitudinal axis G-G (see  FIG. 23 ) and also moves distally toward anvil assembly  660 , causing external thread  680  of pin  654  to threadedly engage inner thread  692  of locking structure  690  to secure pin  654  to anvil assembly  660 . A mechanism for reverse rotation of pin  654  can be provided to retract the pin to unapproximate the cartridge and anvil assemblies. 
     With reference to  FIGS. 25 and 26 , a cartridge assembly  750 , an anvil assembly  760 , and pin  754  work similar to cartridge assembly  650 , anvil assembly  660 , and pin  654  in that there is threaded engagement. Pin  754 , however, is manually secured to anvil assembly  760  and the cartridge does not have a spiral groove. As shown in  FIG. 25 , pin  754  has a proximal portion  770  and distal portion  772  and defines a longitudinal axis H-H. Proximal portion  770  of pin  754  includes a knob or handle  774  rotatable about longitudinal axis H-H. Knob  774  is adapted to be manually rotated. An elongate member  778  extends between knob  774  and distal portion  772 . In operation, rotating knob  774  causes the rotation of elongate member  778  and distal portion  772 . Distal portion  772  includes an external thread  780  formed thereabout. External thread  780  of pin  754  facilitates secure engagement between cartridge assembly  750  and anvil assembly  760 . 
     Cartridge assembly  750  includes a bore adapted to receive pin  754 . Knob  774  is positioned outside of cartridge assembly  750 . The position of knob  774  relative to cartridge assembly  750  allows users to manipulate knob  774  manually. As pin  754  rotates about longitudinal axis H-H, external thread  780  threadedly engages a locking structure  790  of anvil assembly  760 . 
     Anvil assembly  760  has a hole  762  and a locking structure  790  for securing pin  754  to anvil assembly  760 . Locking structure  790  includes an inner thread  792  formed about hole  762 . Inner thread  792  is configured to threadedly engage external thread  780  of pin  754 . 
     In operation, a user actuates trigger  140  (such as in  FIG. 1 ) to advance cartridge assembly  750  toward anvil assembly  760 . After actuating trigger  140 , the user rotates pin  754  through knob  774  to thread pin  754  into hole  762 . As the user rotates knob  774 , external thread  780  rotates about longitudinal axis H-H and securely engages inner thread  792  of locking structure  790 , thereby securing pin  754  to anvil assembly  760 . Reverse rotation of knob  774  unthreads pin  754  from thread  792  to withdraw the pin  754  for unapproximation of the cartridge and anvil assemblies. 
       FIGS. 27 and 28  depict an alternative embodiment of pin  854  and cartridge assembly  850 . The structure and operation of pin  854  and cartridge assembly  850  is substantially similar to the structure and operation of pin  654  and cartridge assembly  650  of  FIG. 23 . In this embodiment, cartridge assembly  850  has protrusions  882  instead of grooves  682  and pin  854  includes grooves  876  in lieu of protrusions  676 . Protrusions  882  extend longitudinally along cartridge assembly  850 , whereas grooves  876  swirl around pin  854  in a helical fashion. 
     The sliding engagement between grooves  876  and protrusions  882  guide the movement of pin  854  through cartridge assembly  850 . In use, as pin  854  is pushed distally, grooves  876  cause pin  854  to rotate while moving in a distal direction. Pin  854  may include an external thread at a distal end thereof for engaging an anvil assembly (not shown), thereby forming a locking structure in a similar manner as the external thread  680  of pin  654  and the inner thread  690  of anvil assembly  660  of  FIGS. 22 and 23 . 
       FIGS. 29-32  show another embodiment of cartridge assembly  950 , anvil assembly  960 , and pin  954 . Cartridge assembly  950  includes a bore (not shown) adapted to receive pin  954 . Anvil assembly  960  includes a locking structure  990  for securing pin  954  inside anvil assembly  960 . Pin  954  has a proximal portion  970  and a distal portion  972  and defines a longitudinal axis I-I. Distal portion  972  of pin  954  includes an engagement section or hook  980 . Hook  980  has a first securing surface  982  defining a substantially right angle relative to longitudinal axis I-I and a first camming surface  984  defining an oblique angle with respect to longitudinal axis I-I. In use, hook  980  fixes pin  954  to anvil assembly  960  to maintain the position of anvil assembly  960  with respect to cartridge assembly  950  during firing of a surgical stapling instrument such as instrument  100  of  FIG. 1 . 
     Anvil assembly  960  has a slot  962  adapted to receive pin  954 . Slot  962  leads to a locking structure  990  disposed in anvil assembly  960 . Locking structure  990  includes a hook or catch  992  pivotally coupled to anvil assembly  960  and a biasing member  994  configured to bias catch  992 . In one embodiment, a pivot pin  996  pivotally connects catch  992  to anvil assembly  992 . Catch  992  has a second camming surface  998  adapted to slidably engage first camming surface  984  and a second securing surface  999  configured to abut first securing surface  982 . 
     In use, locking structure  990  fixes the position of anvil assembly  960  with respect to cartridge assembly  950  through pin  954 . First, when a user actuates trigger  140  (such as in  FIG. 1 ) to approximate the cartridge and anvil assemblies and move pin  954  in a distal direction, pin  954  enters anvil assembly  960  through slot  962  and engages locking structure  990 . Specifically, first camming surface  984  slides on second camming surface  998 , displacing catch  992  away from pin  954  against the influence of biasing member  994  as seen in  FIGS. 30 and 31 . After first camming surface  984  slides distally beyond second camming surface  998 , biasing member  994  biases catch  992  toward pin  954  and, as a result, first securing surface  982  fixedly engages second securing surface  999 , thereby locking pin  954  to anvil assembly  960 . That is, abutment of the securing surface  982  with the securing surface  999  prevents proximal movement of pin  954 . A release mechanism can be provided to separate the surfaces  982  and  999  (e.g. by lifting hook  980  upwardly or forcing catch  992  downwardly as viewed in the orientation of  FIG. 32 ) to allow the pin  954  to pass proximally over the securing surface  999  to enable retraction (unapproximation) of the cartridge and anvil assemblies. 
       FIG. 33  shows an alternate embodiment of pin  1054  attached to a cartridge assembly (not shown) and an anvil assembly (not shown) with a locking structure  1090 . Pin  1054  has a proximal portion (not shown) and a distal portion  1072 . An elongate body  1086  extends between the proximal portion and distal portion  1072 . Distal portion  1072  of pin  1054  includes an engagement section  1080  configured to be attached to locking structure  1090 . Engagement section  1080  incorporates an annular recess  1082  formed thereabout and tip  1084  having a tapered configuration. In an alternate embodiment, tip  1084  has rounded shape as seen in  FIG. 37 . Tip  1084  is adapted to securely engage locking structure  1090 . 
     Locking structure  1090  includes one or more pieces of sheet metal  1092  fixed to the anvil assembly (not shown). Alternatively, sheet metal  1092  is an integral part of the anvil assembly. Sheet metal  1092  has a hole  1094  with a diameter smaller than the diameter of pin  1054 . Hole  1094  can contract and expand when sheet metal  1092  deforms. Sheet metal  1092  deforms when subject to stress and it returns to its original configuration when the stress is removed or decreased. In one embodiment, sheet metal  1092  is made of a shape memory material capable of transitioning between an original configuration and a stressed configuration upon imposition or removal of stress. Other materials are also contemplated. 
     With reference to  FIGS. 34-35 , pin  1054  secures anvil assembly (not shown) to cartridge assembly (not shown) during actuation of a surgical stapling instrument such as instrument  100  of  FIG. 1 . In operation, a user fires surgical stapling instrument  100  by actuating trigger  140  (see  FIG. 1 ). In response to such actuation, the cartridge and anvil assemblies are approximated and pin  1054  advances distally toward locking structure  1090 . As with the other embodiments of the pins disclosed herein, in alternate embodiments the user can optionally move pin  1054  manually. Pin  1054  moves distally toward sheet metal  1092  and then tip  1084  forces its way into hole  1094 . As tip  1084  passes through hole  1094 , sheet metal  1092  deforms and consequently expands hole  1094  to allow the passage of tip  1084 . After tip  1084  passes through hole  1094 , hole  1094  contracts around annular recess  1082 , thereby locking pin  1054  to sheet metal  1092 , as the diameter of the pin adjacent the recess  1082  exceeds the diameter of the hole  1094 . 
       FIGS. 38-40  show an alternate embodiment of a pin  1154  and an anvil assembly  1160  with a locking structure  1190 . Pin  1154  is configured to pivot and has a proximal portion (not shown) and a distal portion  1172 . Moreover, pin  1154  defines a longitudinal axis J-J therealong. Distal portion  1172  of pin  1154  includes a hook or engagement section  1180  adapted to interact with locking structure  1190 . Engagement section  1180  includes a first securing surface  1182  defining a substantially right angle relative to longitudinal axis J-J and a first camming surface  1184  oblique with respect to longitudinal axis J-J. In use, engagement section  1180  secures pin  1154  to anvil assembly  1160  to maintain the position of anvil assembly  1160  with respect to a cartridge assembly (not shown) during actuation of a surgical stapling instrument such as instrument  100  of  FIG. 1 . 
     Locking structure  1190  of anvil assembly  1160  includes an aperture  1192  leading to a cavity  1194  located inside of anvil assembly  1160 . Aperture  1192  is configured to receive pin  1154 . Locking structure  1190  further includes a wall  1196  extending upwardly as viewed in the orientation of  FIG. 38 . Wall  1196  has a second securing surface  1198  adapted to engage first securing surface  1182  of pin  1154 . The wall can be integral or can be a separate component attached to the anvil assembly. 
     During operation, a user moves pin  1154  distally (manually or mechanically through trigger  140 ) to insert engagement section  1180  inside cavity  1194 . As pin  1154  translates distally, engagement section  1180  first passes through aperture  1192  until it reaches cavity  1194 . Note the contact of wall  1198  cams the camming surface upwardly to ride over the wall and then downwardly into the position of  FIG. 39 . Once engagement section  1180  of pin  1154  is positioned within cavity  1194 , first securing surface  1182  contacts second securing surface  1198  of wall  1196 , thereby locking pin  1154  to anvil assembly  1160  as the abutting surfaces  1192  and  1198  prevent proximal movement of pin  1154 . To release pin  1154  from anvil assembly  1160  for unapproximation of the cartridge and anvil assemblies, the user pivots pin  1154  upwardly away from wall  1196  as shown in  FIG. 40  by a release mechanism (not shown) operatively connected to pin  1154 . After pin  1154  has been pivoted away from wall  1196  to disengage surface  1198 , the user can move pin  1154  proximally toward its original position. 
       FIGS. 41 and 42  show an alternative embodiment of an anvil assembly  1260  with a locking structure  1260  and a pin  1254 . Pin  1254  is substantially similar to pin  1154 . Like pin  1154 , pin  1254  has an engagement section  1280  and is configured to pivot toward and away from locking structure  1290 . Locking structure  1290  is substantially similar to locking structure  1190 . As in locking structure  1190 , locking structure  1290  includes an aperture  1292 , a cavity  1294 , and wall  1296 . In addition to aperture  1292 , cavity  1294 , and wall  1296 , locking structure  1290  features a cam lever  1258  rotatably connected to anvil assembly  1260 . Cam lever  1258  includes a central portion  1216 , and first and second legs  1218 ,  1220  extending from central portion  1216 . A pin  1212 , or any other suitable member(s), rotatably couples central portion  1216  of cam lever  1258  to anvil assembly  1260 . Cam lever  1258  is adapted to rotate about pin  1212  between a first position, as seen in  FIG. 41 , and a second position, as depicted in  FIG. 42 , upon engagement or disengagement with a knife  1214 . In this embodiment, the surgical stapling instrument such as instrument  100  of  FIG. 1  includes knife  1214  or any other suitable cutting device capable of advancing distally. During operation, advancement of knife  1214  by a trigger, e.g. trigger  140  of  FIG. 1 , pushes first leg  1218  to effect the rotation of cam lever  1258  about pin  1212 . First leg  1218  of cam lever  1258  has an abutting surface  1222  adapted to engage knife  1214 , and second leg  1220  has a camming surface  1224  adapted to engage the camming surface  1284  of engagement section (or hook)  1280 . 
     In operation, actuating  140  ( FIG. 1 ) advances pin  1254  distally to insert pin  1254  inside cavity  1294 . In some embodiments, the user can translate pin  1254  manually. During translation, pin  1254  passes through aperture  1292  into cavity  1294 , cammed upwardly as described above with pin  1154  of  FIG. 38 , and then securing surface  1282  of pin  1254  engages wall  1296 , locking pin  1254  to anvil assembly  1260  due to the abutment of securing surface  1282  and the inner surface of wall  1296 . At this moment, cam lever  1258  is oriented in the first position as shown in  FIG. 41 . After pin  1254  has been fixed to anvil assembly  1260 , the user actuates the firing mechanism to advance fasteners from the approximated cartridge assembly. Such actuation advances knife  1214  in a distal direction to rotate cam lever  1258 . Specifically, knife  1214  pushes abutting surface  1222  of first leg  1218 . As a result, cam lever  1258  rotates about pin  1212  to the second position, as shown in  FIG. 42 . While cam lever  1258  rotates toward the second position, camming surface  1224  of second leg  1220  engages camming surface  1284  of engagement section  1280 , thereby causing pin  1254  to pivot in the direction of the arrow to release engagement section  1280  from locking structure  1290  as surface  1282  is forced out of engagement with wall  1296 . It should be appreciated that other mechanisms can be used to rotate clam lever  1258  to pivot pin  1254 . For example, a tab or other engaging structure can extend from the knife bar, or be actuated by the knife bar, to pivot cam lever  1258 . Tabs or structures operable independent of the knife could also be provided. 
       FIGS. 43 and 44  illustrate another embodiment of a pin  1354  and an anvil assembly  1360  with a locking structure  1390 . Pin  1354  is substantially similar to pin  1154  as pin  1354  contains an engagement section or hook  1380  and is configured to pivot away and toward locking structure  1390 . Locking structure  1390  is substantially similar to locking structure  1160  as locking structure  1390  includes an aperture  1392 , a cavity  1394 , and wall  1396 . Locking structure  1390  also includes a camming member  1358  adapted to push engagement section  1380  of pin  1354 . Camming member  1358  features a triangular shape and includes an abutting surface  1322  facing a knife  1314  and a camming surface  1324  facing pin  1354  when pin  1354  is positioned in cavity  1394 . Moreover, camming member  1358  contains a diagonal slot  1315  configured for slidably receiving a sliding pin  1312 . Sliding pin  1312  slidably couples camming member  1358  to anvil assembly  1360 . In use, camming member  1358  slides with respect to anvil assembly  1360  between a first position, as seen in  FIG. 43 , and a second position, as shown in  FIG. 44 . Locking structure  1390  further includes a biasing member  1316 , such as a spring, for biasing camming member  1358  away from cavity  1394 . In this embodiment, the surgical stapling instrument such as instrument  100  of  FIG. 1  includes knife  1314  configured to translate toward and away from anvil assembly  1360 . 
     In operation, a user moves pin  1354  into cavity  1394  through aperture  1392 , either automatically as the cartridge and anvil assemblies are approximated and/or in some embodiments manually. Once pin  1354  is positioned inside cavity  1394  (after the camming surface rides over the wall  1396 ), engagement section  1380  of pin  1354  engages wall  1396 , thereby locking pin  1354  to anvil assembly  1360  as the abutment of the camming surface of the pin and the wall prevents proximal movement of the pin. The pin  1354  is released from anvil assembly  1360  by advancement of knife  1314  distally. As knife  1314  translates toward anvil assembly  1360 , knife  1314  contacts abutting surface  1322  of camming member  1358  and pushes camming member  1358  toward cavity  1394 , moving camming member  1358  from the first position toward the second position. While camming member  1358  moves from the first position to the second position, slot  1315  and sliding pin  1312  guide the motion of camming member  1358 . During this motion, camming member  1358  pushes pin  1354  away from wall  1396  as shown in  FIG. 44 . As a consequence, engagement section  1380  of pin  1354  releases from wall  1396  of locking structure  1390 , unlocking pin  1354  from anvil assembly  1360  to enable retraction of the pin  1354  and unapproximation of the cartridge and anvil assemblies. It should be appreciated that other mechanisms, e.g. a manual tab, could be utilized to move the camming member  1358  to move and release the pin  1354 . 
       FIGS. 45 and 46  show an alternate embodiment of a pin  1454  and an anvil assembly  1460  with a locking structure  1490 . Pin  1454  is substantially similar to pin  1154 . Pin  1454  includes an engagement section or hook  1480  and is adapted to move longitudinally toward and away from anvil assembly  1460 . Locking structure  1490  is substantially similar to locking structure  1190 . Locking structure  1490  includes a cavity  1494 , an aperture  1492  leading to cavity  1494 , and a camming member  1458  configured to retain and displace pin  1454  from anvil assembly  1460 . Camming member  1458  includes an abutting surface  1422  facing knife  1414 , a wall  1496  extending toward cavity  1494 , and a diagonal slot  1415  configured to slidably receive a sliding pin  1412 . Sliding pin  1412  slidably connects camming member  1458  to anvil assembly  1460 . During operation, camming member  1458  slides with respect to anvil assembly  1460  between a first position, as seen in  FIG. 45 , and a second position, as depicted in  FIG. 46 . In the first position, wall  1496  of camming member  1458  is partially located inside cavity  1494 . In the second position, wall  1496  is located outside of cavity  1494 , or at least sufficiently spaced from engagement section  1480  to allow proximal movement of pin  1480 . Locking structure  1490  also includes a biasing member  1416 , such as a spring, for biasing camming member  1458  toward cavity  1494 . As shown in  FIG. 46 , a surgical stapling instrument such as instrument  100  of  FIG. 1  includes a knife  1414  adapted to move longitudinally toward and away from anvil assembly  1460 . 
     During use, a user moves pin  1454  distally into cavity  1494  through aperture  1492  either automatically as the cartridge and anvil assemblies are approximated and/or in some embodiments manually. The pin  1454  rides over the member  1458  and moves to the first position as seen in  FIG. 45 . When pin  1454  is located inside cavity  1494  and camming member  1458  is in the first position, engagement section  1480  engages wall  1496  of camming member  1458 , locking pin  1454  to anvil assembly  1460  as the abutting surfaces prevent proximal movement of pin  1454 . Biasing member  1416  maintains camming member  1458  in the first position. Advancement of knife  1414  distally toward anvil assembly  1460  releases pin  1454  from anvil assembly  1460  as the knife  414  pushes camming member  1458  in a distal direction moving camming member  1458  (along with wall  1496 ) away from cavity  1494 . When wall  1496  moves away from cavity  1494 , wall  1496  disengages from engagement section  1480  of pin  1454  ( FIG. 46 ), releasing pin  1454  from anvil assembly  1460  for subsequent retraction. It should be appreciated that other mechanisms, e.g. a manual tab, could be utilized to move the camming member  1458  to release the pin. 
       FIGS. 47 and 48  show an alternate embodiment of a pin  1554  and an anvil assembly  1560  with a locking structure  1590 . Pin  1554  is substantially similar to pin  1154 . Pin  1554  includes an engagement section  1580  and is configured to move longitudinally toward and away from anvil assembly  1560 . Locking structure  1590  includes a cavity  1594 , an aperture  1592  leading to cavity  1594 , a camming member  1558  adapted to hold and release pin  1554 , and a diagonal opening  1518  configured for slidably receiving at least a portion of camming member  1558 . Camming member  1558  includes a slidable portion  1522  adapted to slide through diagonal opening  1518  and a clasp  1524  configured to hold engagement section  1580  of pin  1554 . Portion  1522  of camming member  1558  includes a diagonal slot  1515  configured for receiving a sliding pin  1512 . Sliding pin  1512  is fixed in anvil assembly  1560  and, along with diagonal slot  1515 , guides the motion of camming member  1558  through anvil assembly  1560 . A biasing member  1516 , such as a spring, is disposed within diagonal slot  1515 , and is adapted to bias camming member  1558  downwardly. 
     In this embodiment, a surgical stapling instrument such as instrument  100  of  FIG. 1  includes a knife  1514  movable longitudinally away and toward anvil assembly  1560 . When knife  1514  is advanced distally by a firing mechanism of the surgical stapling instrument, knife  1514  pushes slidable portion  1522  and exerts a distal force on camming member  1558 . In response to such distal force, camming member  1558  moves from a first position ( FIG. 47 ) toward a second position ( FIG. 48 ). In the first position, clasp  1524  of camming member  1558  engages engagement section  1580  of pin  1554  and maintains pin  1554  secured to anvil assembly  1560 . In the second position, clasp  1524  of camming member  1558  is spaced apart from engagement section  1580  when pin  1554  is located inside cavity  1594  and therefore does not hold pin  1554 . 
     In operation, when pin  1554  is moved distally into cavity  1594  automatically upon approximation of the cartridge and anvil assemblies and/or in some embodiments manually, it forces the camming member  1558  slightly upwardly against the downward bias to slide under the engaging hook portion of clasp  1524 . Once under the hook portion, the camming member  1558  returns to the first position to secure pin  1558  to anvil assembly  1560  due to the abutment of the surfaces. When camming member  1558  is located in the first position, clasp  1524  partially surrounds engagement section  1580  and secures pin  1554  to anvil assembly  1560  as shown in  FIG. 47  by preventing proximal movement of pin  1554 . Thereafter, when knife  1515  is advanced distally toward camming member  1558  by the firing mechanism, knife  1514  engages sliding portion  1522  of camming member  1558 , urging camming member  1558  upwardly (in the orientation of  FIG. 48 ) toward the second position. When camming member  1558  is in the second position, clasp  1524  is moved away from engagement section  1580 , thereby releasing pin  1554  from anvil assembly  1560  as seen in  FIG. 48  to allow retraction. 
       FIGS. 49 and 50  illustrate alternate embodiments of pins for use with the disclosed embodiments. In  FIG. 49 , pin  1654  includes an engagement section  1680  with a transverse slot  1682 . In  FIG. 50 , pin  1754  includes an engagement section  1780  with a notch  1782 . 
     With reference to  FIGS. 51 and 52 , a pin  1854  and a locking structure  1890  for use with a surgical stapling instrument such as instrument  100  of  FIG. 1  are disclosed. Pin  1854  defines a longitudinal axis K-K and has a proximal portion  1870  and a distal portion  1872 . A cylindrical body  1874  extends from proximal portion  1870  to distal portion  1872 . Distal portion  1872  incorporates an engagement section  1880  having a tapered configuration. The tapered configuration of engagement section  1880  extends from a proximal end  1882  of section  1880  to a distal tip  1884 . The diameter of proximal end  1882  is larger than the diameter of cylindrical body  1874 . Pin  1854  is disposed in a cartridge assembly (not shown) and is configured to move longitudinally toward and away from an anvil assembly (not shown). 
     Locking structure  1890  is positioned within the anvil assembly (not shown) and includes a latch  1892  pivotally connected to the anvil assembly. A pivot pin  1894 , or any other suitable apparatus or means, pivotally couples latch  1892  to the anvil assembly. Latch  1892  is adapted to pivot transversely relative to longitudinal axis K-K between a first position (as seen in  FIG. 51 ) and a second position (as shown in  FIG. 52 ). In the first position, latch  1892  is separated from pin  1854  and therefore pin  1854  is free to move away from the anvil assembly. In the second position, latch  1892  engages pin  1854  and secures pin  1854  to anvil assembly. When latch  1892  is located in the second position, at least a portion of latch  1892  abuts proximal end  1882  of engagement section  1860 , thereby fixing pin  1854  within the anvil assembly. 
     In use, a user first moves pin  1854  inside the anvil assembly, automatically upon approximation of the cartridge and anvil assemblies and/or in some embodiments manually, while latch is located in the first position as illustrated in  FIG. 51 . Then, the user pivots latch  1892  toward the second position as depicted in  FIG. 52 . When latch  1892  is located in the second position, latch  1892  engages engagement section  1860  of pin  1854 , securing pin  1854  to the anvil assembly. 
       FIGS. 53 and 54  depict an alternate embodiment of a pin  1954  and a locking structure  1990  for use with surgical stapling instrument such as instrument  100  of  FIG. 1 . Pin  1954  is configured to move longitudinally from a cartridge assembly (not shown) between a proximal position and a distal position. Further, pin  1954  has a proximal portion (not shown) and a distal portion  1972 . Distal portion  1972  of pin  1954  includes an engagement section  1980  adapted to be securely received by locking structure  1990 . Engagement section  1980  has a tapered configuration forming an arrowhead like configuration and is adapted to be retained by locking structure  1990 . 
     Locking structure  1990  is disposed in an anvil assembly (not shown) and includes a first jaw member  1992  and a second jaw member  1994 . First and second jaw members  1992 ,  1994  are operatively connected to each other. A pivot pin  1996 , or any other suitable member(s), pivotally interconnects first jaw member  1992  and second jaw member  1994 . First and second jaw members  1992 ,  1994  are adapted to pivot between a first position, as seen in  FIG. 53 , and a second position, as depicted in  FIG. 54 . First and second jaw members  1992 ,  1994  are closer to each other in the first position than in the second position. Each of the first and second jaw members  1192 ,  1994  includes protrusions  1998  extending transversely therefrom. Locking structure  1990  further includes a biasing member  1982 , such as a torsion spring, for biasing first and second jaw members  1992 ,  1994  toward their first position. 
     With reference to  FIGS. 55-57 , a user can employ locking structure  1990  to secure pin  1954  to the anvil assembly. Upon advancement of pin  1954  distally toward locking structure  1990  either automatically upon approximation of the cartridge and anvil assemblies and/or in some embodiments manually, pin  1954  subsequently forces its way into locking structure  1990 . As pin  1954  advances into locking structure  1990 , engagement section  1980  spreads apart first and second jaw members  1992 ,  1994 , urging first and second jaw members  1992 ,  1994  toward the second position as seen in  FIG. 55 . Once engagement section  1980  is positioned within locking structure  1990 , biasing member  1996  urges first and second jaw members  1992 ,  1994  to their first position, as seen in  FIG. 56 , thereby securing pin  1954  to the anvil assembly. Release of pin  1954  from the anvil assembly occurs as knife  1914  of a surgical stapling instrument such as instrument  100  of  FIG. 1  advances in a distal direction, causing knife  1914  to engage protrusions  1998  and push first and second jaw members  1992 ,  1994  to their second position as seen in  FIG. 57 . After spreading apart first and second jaw members  1992 ,  1994  with knife  1914 , pin  1954  can be moved proximally to disengage engagement section  1980  from locking structure  1990 . 
       FIGS. 58 and 59  show an alternate embodiment of a pin  2054  and an anvil assembly  2060  with a locking structure  2090 . Pin  2054  is substantially similar to pin  1554  of the embodiment of  FIG. 28 . Particularly, pin  2054  includes an engagement section  2080  disposed at a distal portion  2072  thereof. Engagement section  2080  is adapted to securely engage locking structure  2090 . 
     Locking structure  2090  includes a cavity  2094 , an aperture  2092  leading to cavity  2094 , and camming mechanism  2058  adapted to hold and release pin  2054 . Camming mechanism  2058  includes a cam  2012  rotatably connected to anvil assembly  2060  and a clasp  2014  slidably disposed in a longitudinal opening  2062  of anvil assembly  2060 . A pivot pin  2016 , or any other suitable member(s), pivotally connects cam  2012  to anvil assembly  2060 . Clasp  2014  contains a cam follower  2018  at least partially disposed in longitudinal opening  2062  and a clasping section  2022  adapted to surround and hold engagement section  2080  of pin  2054 . Cam follower  2018  is operatively associated with cam  2016  such that cam follower  2018  moves longitudinally in response to a rotation of cam  2016 . Since cam follower  2018  is connected to (or alternatively integral with) clasping section  2022 , the longitudinal motion of cam follower  2018  causes clasping section  2022  to move axially from a first position, as depicted in  FIG. 58 , to a second position, as shown in  FIG. 59 . In the first position, clasping section  2022  engages and partially surrounds engagement section  2080  of pin  2054 , thereby securing pin  2054  to anvil assembly  2060 . In the second position, clasping section  2022  is spaced apart from engagement section  2080  and pin  2054  is free to move away from anvil assembly  2060 . Locking structure  2090  further includes a biasing member  2024 , such as spring, for biasing clasping section  2022  toward the first position. Biasing member  2024  is disposed in a longitudinal slot  2026  formed on cam follower  2018 . Longitudinal slot  2026  is configured to slidably receive a sliding pin  2028 . Sliding pin  2028  is fixed to anvil assembly  2060  and, in conjunction with longitudinal slot  2026 , directs the longitudinal motion of cam follower  218  through longitudinal opening  2062 . 
     In operation, movement of pin  2054  distally toward anvil assembly  2060  forces cam follower  2018  slightly upwardly as engagement section forces its way past clasping section  2022 , facilitated by the angled camming surface  2081  of engagement section  2080 . Pin  2054  is advanced automatically upon approximation of the cartridge and anvil assemblies and/or in some embodiments manually until engagement section  2080  is positioned inside cavity  2094 . Thus, this movement enables pin  2054  to slide under the hook portion of clasping section  2022  of clasp  2014  in a similar manner as described in the embodiment of  FIG. 47 . Clasp  2014  then returns to its first position of  FIG. 58  to secure/retain pin  2054  after the engagement section passes by the clasping section  2022 . While in the first position, clasping section  2022  engages engagement section  2080 , maintaining pin  2054  secured to anvil assembly  2060  due to the abutment of the surfaces preventing proximal movement of pin  2054 . The user can release pin  2054  from anvil assembly  2060  by rotating cam  2012  about pivot pin  2016 . The rotary motion of cam  2012  causes clasping section  2022  to move to the second position (upwardly in the orientation shown) as seen in  FIG. 59 . When clasping section  2022  is located in the second position, the locking structure  2094  unlocks engagement section  2080  from anvil assembly  2060 . Once engagement section  2080  has been unlocked, the pin  2054  can be moved proximally away from anvil assembly  2060  and the cartridge and anvil assemblies unapproximated. It should be appreciated that alternatively, to obtain the first position of clasp  2014 , cam  2012  would be rotated to the position of  FIG. 58 . Various mechanisms can be used to rotate cam  2012 . 
     The cam  2016  can optionally be provided with a series of teeth to engage a rack on cam  2012  to provide stepped (incremental) movement of the cam. 
       FIGS. 60 and 61  show another embodiment of a pin  2154  and a locking structure  2090  for use with a surgical stapling instrument such as instrument  100  of  FIG. 1 . In this embodiment, the surgical instrument includes a knife  2114  adapted to move longitudinally between a proximal position and a distal position. Pin  2154  includes an enlarged head engagement section  2180  disposed at a distal portion  2172  thereof. Engagement section  2180  has a tapered configuration and is configured to be securely received by locking structure  2190 . 
     Locking structure  2190  is disposed in mechanical cooperation with an anvil assembly (not shown) and includes a first camming member  2116  and a second camming member  2118  operatively connected to each other. First camming member  2116  features a right triangular shape and is adapted to move transversely with respect to the anvil assembly (not shown) upon engagement with knife  2114 . In addition, first camming member  2116  includes a diagonal slot  2120  configured to slidably receive a first pin  2122 . First pin  2122  is fixed to the anvil assembly (not shown) and, during operation, guides the motion of first camming member  2116 . In operation, first camming member  2116  moves from a first position, as seen in  FIG. 60 , to a second position, as shown in  FIG. 61 , upon engagement with knife  2114 . While moving to the second position, first camming member  2116  drives second camming member  2118  from a first position, as depicted in  FIG. 60 , to a second position, as illustrated in  FIG. 61 . Second camming member  2118  includes an aperture  2192  for allowing passage of pin  2154 , a catch  2196  configured to secured pin  2154  to the anvil assembly (not shown), and a slot  2198  adapted to slidably receive a second slidable pin  2128 . Second slidable pin  2128  is fixed to the anvil assembly and, in conjunction with slot  2198 , directs the longitudinal motion of second camming member  2118  during operation. Catch  2196  of second camming member  2118  includes cavity  2194  configured to receive engagement section  2180  of pin  2154 . 
     In operation, pin  2154  is moved distally toward catch  2196  automatically upon approximation of the cartridge and anvil assemblies and/or in some embodiments manually while first and second camming members  2116 ,  2118  are in their respective second positions as shown in  FIG. 61 . During its distal translation, pin  2154  passes through aperture  2196  and positions itself inside cavity  2194  forcing camming member  2118  slightly upwardly (in the orientation of  FIG. 60 ) so the pin can slide into the cavity. The angled surface of the engagement section  2180  facilitates such upward movement. First camming member  2116  is in its first position in  FIG. 60 . While first camming member  2116  is in its first position, second camming member  2118  is in its first position and catch  2196  engages engagement section  2180  of pin  2154 , thereby locking pin  2154  to locking structure  2190 . Pin  2154  is released from locking structure  2190  by translating knife  2114  distally toward first camming member  2118  (by actuation of a firing mechanism of the surgical stapler). When knife  2114  engages first camming member  2116 , first camming member  2116  moves toward the second position and drives second camming member  2118  toward the second position as shown in  FIG. 61  (see arrows). After second camming member  2118  has reached its second position, the user may remove pin  2154  from locking structure  2190  as the engagement section  2180  is spaced from the catch  2196 . Retraction of knife  2114  allows the camming members to return to their normal position of  FIG. 60 . 
     While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the present disclosure, but merely as illustrations of various embodiments thereof. Therefore, the above description should not be construed as limiting, but merely as exemplifications of various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.