Patent Publication Number: US-10327768-B2

Title: Double fire stapling

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/927,675, filed Oct. 30, 2015, which claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 62/119,354, filed Feb. 23, 2015, the entire disclosure of which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to surgical stapling apparatus, devices and/or systems for performing endoscopic surgical procedures and methods of use thereof. 
     BACKGROUND 
     Surgical stapling apparatus that clamp, cut and/or staple tissue between opposing jaw structure are well known in the art. Such surgical stapling apparatus can include loading units with a tool assembly having two elongated jaw members used to capture or clamp tissue. One of the two jaw members usually carries a staple cartridge that houses a plurality of staples while the other of the two jaw members has an anvil for forming the staples as the staples are driven from the staple cartridge. Generally, a stapling operation is effectuated by a cam bar, a drive sled or other similar mechanism having a cam member that travels longitudinally through channels defined in the staple cartridge and acts upon staple pushers in the channels to sequentially eject the staples from the staple cartridge. 
     During endoscopic or laparoscopic procedures in which surgery is performed through small incisions or through narrow cannulas inserted through the small incisions in the skin, replacement of the staple cartridge or the loading unit, for example, after firing, requires removal of the surgical stapling device from the incision or cannula, replacement of the staple cartridge and/or loading unit and reinsertion of the surgical stapling device into the incision or cannula. 
     It would be advantageous to provide a staple cartridge or loading unit that is capable of being fired a plurality of times before replacement of the staple cartridge or loading unit is required. 
     SUMMARY 
     Accordingly, the present disclosure is directed to a surgical stapling apparatus for use during laparoscopic and/or endoscopic surgical procedures that can be employed to provide multiple firings of the surgical stapling apparatus without requiring removal of the surgical stapling apparatus from the incision/cannula. In particular, the present disclosure is directed to a tool assembly, loading unit, and/or a surgical stapling apparatus that includes a firing cam assembly with one or more firing cams. The firing cam assembly is positioned to repeatedly move longitudinally through a staple cartridge to effectuate multiple firings with each firing cam during longitudinal translations of the firing cam assembly from a proximal end to a distal end of the staple cartridge. The firing cam assembly may include a knife bar configured to cut tissue as the firing cam assembly longitudinally translates through the staple cartridge. Advantageously, the firing cam assembly can be fired multiple times without removing the surgical stapling apparatus from an in vivo work space before the staple cartridge and/or the loading unit would require changing/reload, greatly reducing time to complete the in vivo surgical procedure. 
     In one aspect, the surgical stapling device of the present disclosure includes a housing, a shaft that extends distally from the housing, and a tool assembly supported on the shaft. The tool assembly may include a cartridge assembly, an anvil assembly, and a first firing cam. 
     The cartridge assembly has a cartridge body that may define a tissue contact surface and a plurality of rows of retention slots. Each retention slot of the plurality of rows of retention slots supports a staple therein and defines an opening on the tissue contact surface. The cartridge body defines a first firing channel and a second firing channel. The first firing channel is associated with a first row of staples and the second firing channel associated with a second row of staples. 
     The anvil assembly is supported adjacent the cartridge assembly. The anvil assembly and the cartridge assembly are movable between open and closed positions in relation to each other. 
     The first firing cam is positioned within the first firing channel of the cartridge body. The first firing cam is configured to translate through the first firing channel during a first axial translation of the first firing cam to fire the first row of staples. The first firing cam is biased to move into the second firing channel of the cartridge body upon retraction of the first firing cam after the first axial translation such that the first firing cam moves to a position to translate through the second firing channel upon a second axial translation of the first firing cam to fire the second row of staples. 
     The first firing cam may be engaged with a first T-bar. The first T-bar may be positioned to maintain the first firing cam in registration with the first firing channel when the first firing cam and the first T-bar are in fully retracted positions. 
     In some embodiments, the tool assembly includes a second firing cam and the cartridge body defines third and fourth firing channels. The second firing cam is configured to translate through the third firing channel during the first axial translation to fire a third row of staples. The second firing cam is biased to move into the fourth firing channel upon retraction of the second firing cam after the first axial translation such that the second firing cam is positioned to translate through the fourth firing channel upon the second axial translation to fire a fourth row of staples. 
     The second firing cam may be engaged with a second T-bar. The second T-bar may be positioned to maintain the second firing cam in registration with the third firing channel when the second firing cam and the second T-bar are in fully retracted positions. 
     The first and second T-bars are configured to move along the cartridge body in response to movement of the first and second firing cams from a proximal position to a distal position during the first axial translation. The first and second T-bars are retained in the distal position as the first and firing cams are retracted to the proximal position after the first axial translation. In the distal position, the first and second T-bars are positioned to enable movement of the first and second firing cams. The first and second firing cams may be pivotally coupled together and positioned to pivot relative to one another. 
     In certain embodiments, the cartridge body defines a T-bar recess. The first and second T-bars are positioned within the T-bar recess while the first and second T-bars are disposed in the distal position. 
     In some embodiments, the cartridge body includes a first ramp and a second ramp. The first ramp is positioned to align the first firing cam with one of the first and second firing channels. The second ramp is positioned to align the second firing cam with one of the third and fourth firing channels. 
     The tool assembly may further include a knife bar that supports a blade at a distal end of the knife bar. The cartridge body defines a knife channel. The knife bar is distally movable through the knife channel as the first firing cam translates through the first and second firing channels. 
     In some embodiments, the first firing cam includes a cam surface positioned to engage a plurality of pusher members. Each of the plurality of pusher members is disposed within one or more of the retention slots and is configured to support one or more of the staples. The cam surface of the first firing cam may extend distally beyond the blade of the knife bar. 
     In certain embodiments, the cartridge body defines a knife channel therethrough. Two of the first, second, third, and fourth firing channels may be disposed on one side of the knife channel and a remaining two of the first, second, third and fourth firing channels are disposed on another side of the knife channel. 
     Other aspects, features, and advantages will be apparent from the description, the drawings, and the claims that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with a general description of the disclosure given above, and the detailed description of the embodiment(s) given below, serve to explain the principles of the disclosure, wherein: 
         FIG. 1A  is a perspective view of a surgical stapling apparatus in accordance with the principles of the present disclosure; 
         FIG. 1B  is a perspective view, with parts separated, of the surgical stapling apparatus of  FIG. 1A ; 
         FIGS. 2 and 3  are side, perspective views of a loading unit of the surgical stapling apparatus of  FIG. 1A ; 
         FIG. 4  is a perspective view, with parts separated, of the loading unit of  FIGS. 2 and 3 ; 
         FIG. 5  is a perspective view, with parts separated, of a cartridge assembly of the loading unit of  FIGS. 2-4 ; 
         FIG. 6  is a perspective view of a firing cam assembly of the loading unit of  FIGS. 2-4 ; 
         FIG. 7  is an enlarged perspective view of an indicated area of detail shown in  FIG. 6 , 
         FIG. 8  is a top view of the firing cam assembly of  FIG. 6 ; 
         FIG. 9  is an enlarged view of an indicated area of detail shown in  FIG. 8 ; 
         FIG. 10  is a perspective view, with parts separated, of the firing cam assembly of  FIG. 6 ; 
         FIG. 11  is a top, perspective view of a staple pusher of the cartridge assembly of  FIG. 5 ; 
         FIG. 12  is bottom, perspective view of the staple pusher of  FIG. 11 ; 
         FIG. 13  is a top, perspective view of a pair of staple pushers of the cartridge assembly of  FIG. 5  positioned together, each of the pair of staple pushers supporting a pair of staples; 
         FIG. 14  is an enlarged, cross-sectional view of the cartridge assembly taken along section line  14 - 14  illustrated in  FIG. 2 ; 
         FIG. 15  is a bottom view of the cartridge assembly with T-bars of the cartridge assembly shown in a first position; 
         FIG. 16  is a bottom, perspective view of the cartridge assembly shown in  FIG. 15 ; 
         FIG. 17  is an enlarged, bottom, perspective view of portions of the cartridge assembly of  FIGS. 15 and 16 ; 
         FIG. 18  is an enlarged, bottom view of a proximal portion of the cartridge assembly with portions of the cartridge assembly removed and/or shown in phantom for clarity, the firing assembly shown in a first proximal position; 
         FIG. 19  is a side, cross-sectional view of the cartridge assembly with the firing assembly shown in the first proximal position and the T-bars shown in the first position; 
         FIG. 20  is an enlarged, cross-sectional view of a distal portion of the cartridge assembly with the firing assembly shown in a first distal position and with the T-bars shown in a second position; 
         FIG. 21  is a bottom, perspective view of portions of the cartridge assembly with the T-bars shown in the second position; and 
         FIGS. 22 and 23  are bottom views of the proximal portion of the cartridge assembly showing the firing assembly progressing to a second proximal position. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the presently disclosed surgical stapling apparatus are described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. As used herein, the term “distal” refers to that portion of the surgical stapling apparatus, or component(s) thereof, that is farther from the clinician, while the term “proximal” refers to that portion of the surgical stapling apparatus, or component(s) thereof, that is closer to the clinician. 
       FIG. 1A  illustrates one embodiment of the presently disclosed surgical stapling apparatus  10 . Briefly, surgical stapling apparatus  10  includes a handle assembly  12 , an elongated body  14  and a loading unit  100 , which may be disposable and/or include one or more disposable components. Elongated body  14  and loading unit  100  define a longitudinal axis “X 1 -X 1 ” that extends longitudinally along elongated body  14 . With reference also to  FIGS. 1B, 2 , and  3 , loading unit  100  is releasably secured to a distal end of elongated body  14  and includes a tool assembly  110 . Tool assembly  110  includes a cartridge assembly  130  that houses a plurality of staples and an anvil assembly  120  that is pivotally secured to loading unit  100  by a pair of pivot pins  128   a ,  128   b  ( FIG. 4 ) that define a pivot axis “X 2 -X 2 .” Anvil assembly  120  is configured to pivot about pivot axis “X 2 -X 2 ” in relation to cartridge assembly  130 , as indicated by arrow “A,” between spaced and approximated positions. 
     Handle assembly  12  includes a stationary handle  16 , a movable handle  18  and a barrel portion  20 . A rotatable member  22  is rotatably supported on a distal end of barrel position  20 . Rotatable member  22  supports a proximal end of elongated body  14  and is rotatable in relation to barrel portion  20  of handle assembly  12 , as indicated by arrow “B,” to effectuate rotation of elongated body  14  and tool assembly  110  about longitudinal axis “X 1 -X 1 ” in relation to handle assembly  12 . Rotatable member  22  supports an articulation lever  24 , and barrel portion  20  supports a retraction member  26  and a firing release button  28 . Handle assembly  12  is described in detail in, for example, U.S. Pat. No. 8,070,033 to Milliman et al. (“the &#39;033 patent”), the entire contents of which are incorporated herein by reference. 
     Elongated body  14  supports a control rod  15  ( FIG. 1B ) that is coupled to a proximal end of a firing cam assembly  140  ( FIG. 4 ) of loading unit  100  as described in further detail below. A release switch  15   a  ( FIG. 1B ) is provided on rotatable member  22  of handle assembly  12  to facilitate disengagement of loading unit  100  from elongated body  14 . 
     Referring to  FIG. 4 , loading unit  100  includes a proximal body portion  101  having an upper housing half  102  that is adapted to releasably engage a distal end of elongated body  14  ( FIGS. 1A and 1B ) of surgical stapling apparatus  10  and a lower housing half  104  that couples to upper housing half  102  of proximal body portion  101 . A distal end of upper housing half  102  defines a recess  102   a  that receives a first end of a first coupling member  103   a  and distal end of lower housing half  104  defines a recess  104   a  that receives a first end of a second coupling member  103   b . Each coupling member  103   a ,  103   b  defines an opening  1032  therethrough. Upper housing half  102  defines a channel  102   c  and lower housing half  104  defines a channel  104   b . Together, channels  102   c ,  104   b  slidably receive firing cam assembly  140 , as will be described in further detail below. 
     Upper housing half  102  has a proximal end that includes engagement nubs  102   b . Engagement nubs  102   b  are positioned and configured to releasably engage a distal end of elongated body  14  of handle assembly  12  ( FIG. 1 ) in a bayonet-type coupling arrangement to secure loading unit  100  to elongated body  14 . This structure is similar to that described in U.S. Pat. No. 7,780,055 to Scirica et al. (“the&#39;055 patent”) and U.S. Pat. No. 7,143,924 to Scirica et al. (“the&#39;924 patent”), the entire contents of each of which are incorporated by reference herein. 
     A pair of blow out plate assemblies  105   a ,  105   b  is positioned adjacent distal ends of upper and lower housing halves  102 ,  104  to prevent outward buckling and/or bulging of firing cam assembly  140  during articulation and firing of tool assembly  110 . The configuration of the blow out plate assemblies is described in detail, for example, in International Publication No. WO/2003/030743, the entire contents of which are incorporated by reference herein. 
     A locking member  106  is rotatably supported about proximal body portion  101 . Locking member  106  is movable from a first position engaged with firing cam assembly  140  to axially lock firing cam assembly  140  to a second position, unlocking firing cam assembly  140  to enable axial movement of firing cam assembly  140 . Locking member  106  is movable from the first position to the second position in response to attachment of loading unit  100  to surgical stapling apparatus  10 . For a more detailed description of the construction and operation of locking member  106 , reference can be made to the &#39;924 patent, which has been incorporated by reference herein as noted above. 
     A mounting assembly  107  includes upper and lower mounting portions  107   a ,  107   b  pivotally secured to a distal end of proximal body portion  101  and configured to engage and support a proximal end of anvil and cartridge assemblies  120 ,  130  such that pivotal movement of mounting assembly  107  in relation to proximal body portion  101  effectuates articulation of tool assembly  110  in relation to proximal body portion  101 . Upper mounting portion  107   a  includes a central pin  1074   a  that extends upwardly therefrom and lower mounting portion  107   b  includes a central pin  1074   b  ( FIG. 4 ) that extends downwardly therefrom. Central pins  1074   a ,  1074   b  of upper and lower mounting portions  107   a ,  107   b  are received within respective openings  1032  of first and second coupling members  103   a ,  103   b  to pivotably couple mounting assembly  107  to proximal body portion  101 . Upper mounting portion  107   a  further includes a pin  1076  that is offset from the longitudinal axis “X 1 -X 1 ” of loading unit  100  and lower mounting portion  107   b  defines pin channels  1078 . Both will be described in further detail below. 
     An articulation link  108  is slidably positioned between upper and lower housing halves  102 ,  104  and defines an opening  108   a . Opening  108   a  of articulation link  108  receives pin  1076  of upper mounting portion  107   a  to facilitate articulation of tool assembly  110  about pins  1074   a  and  1074   b  in relation to proximal body portion  101  of loading unit  100 . Pivoting movement of articulation lever  24 , as indicated by arrow “CC,” causes axial movement of articulation link  108  along axis “X 1 -X 1 ” to pivot/articulate mounting assembly  107 , as indicated by arrow “C,” about an axis “X 3 -X 3 ” ( FIG. 1A ) of proximal body portion  101  that is transverse to axes “X 1 -X 1 ” and “X 2 -X 2 ” ( FIG. 1A ). For a more detailed description of the construction and operation of articulation link  108  and mounting assembly  107  reference can be made to the &#39;033 patent, which has been incorporated by reference herein as noted above. 
     Pins  109   a ,  109   b  are received through openings  1072  defined in upper and lower mounting portions  107   a ,  107   b , to couple upper and lower mounting portions  107   a ,  107   b  together. 
     With continued reference to  FIG. 4 , as discussed above, tool assembly  110  includes anvil assembly  120  and cartridge assembly  130  that are positioned to move in relation to each other between unapproximated and approximated positions. Anvil assembly  120  is pivotably secured to mounting assembly  107  by pivot pins  128   a ,  128   b  to enable pivotal movement of anvil assembly  120  relative to mounting assembly  107  and cartridge assembly  130 . Lower mounting portion  107   b  includes a distal portion that is secured within support plate  132  of cartridge assembly  130  by pivot pins  128   a ,  128   b  to fixedly secure cartridge assembly  130  to mounting assembly  107 . 
     Anvil assembly  120  includes an anvil body  122  and an anvil plate  124  that is secured to an underside of anvil body  122 . Anvil plate  124  includes a tissue contact surface  124   a  that defines a plurality of staple forming depressions  124   b  ( FIG. 20 ). A proximal end of anvil body  122  includes a bracket  126  that defines apertures  126   a  therethrough. 
     Turning now to  FIG. 5  and  FIG. 14 , cartridge assembly  130  includes a support plate  132 , a cartridge body  134 , a plurality of staple pushers  136  including staple pushers  136   a ,  136   b ,  136   c ,  136   d , a pair of T-bars  138   a ,  138   b , and a plurality of staples “S.” 
     Support plate  132  includes sidewalls  132   a  that define a plurality of windows  132   b  and pin channels  132   c  therethrough. An inner surface  132   d  of support plate  132  defines a channel  132   e  that extends longitudinally along support plate  132  and is adapted to receive cartridge body  134 . 
     Cartridge body  134  includes a tissue contact surface  134   a  that defines a plurality of staple retention pockets  134   b  arranged in a plurality of rows “R 1 ”-“R 8 ” extending longitudinally along tissue contact surface  134   a . Cartridge body  134  further defines a knife slot  134   d  that extends longitudinally along tissue contact surface  134   a . A plurality of clips  134   e  extends from a side surface of cartridge body  134 . Clips  134   e  of cartridge body  134  are received in the plurality of windows  132   b  of support plate  132  to secure cartridge body  134  within channel  132   e  of support plate  132  by, for example, snap-fit connection. Other forms of connection can be used alternatively and/or additionally to clips  134   e  and windows  132   b . A proximal end of cartridge body  134  defines elongated T-bar channels  134   f ,  134   g  that extend through tissue contact surface  134   a  and a pair of spring channels  134   h ,  134   i . Elongated T-bar channels  134   f ,  134   g  slidably receive T-bars  138   a ,  138   b  therein to enable and limit axial movement of T-bars  138   a ,  138   b  in relation to cartridge body  134 . Spring channels  134   h ,  134   i  receive a pair of leaf springs  135   a ,  135   b  therein that are adapted to bias anvil assembly  120  to an unapproximated/open position relative to cartridge assembly  130  when firing cam assembly  140  is in a proximal position as described in greater detail below. 
     Referring also to  FIG. 4 , pins  128   a ,  128   b  are received within apertures  126   a  of anvil body  122 , pin channels  132   c  of support plate  132 , and pin channels  1078  of lower mounting portion  107   b  to couple mounting assembly  107 , anvil assembly  120 , and cartridge assembly  130  together. As described above, pins  128   a ,  128   b  enable anvil assembly  120  to pivot about pivot axis “X 2 -X 2 ” ( FIG. 1A ) relative to cartridge assembly  130  to position anvil and cartridge assemblies  120 ,  130  between unapproximated and approximated positions. 
     Each of the T-bars  138   a ,  138   b  includes an elongated shaft  1384  and a post  1382  that extends upwardly from elongated shaft  1384 . Elongated shaft  1384  defines proximal and distal elongated channels  1384   a ,  1384   b  and supports a distally located cross member  1386 . Cross member  1386  extends outwardly beyond sidewalls of elongated shaft  1384  in a direction transverse to longitudinal axis “X 1 -X 1 ” of elongated body  14  ( FIG. 1A ) to define a pair of abutments  1386   a ,  1386   b.    
     Referring now to  FIGS. 6-10 , firing cam assembly  140  includes a first or right hand firing cam  142 , a second or left hand firing cam  144 , and a knife bar  146  supporting a drive beam  148 . Proximal ends of right and left hand firing cams  142 ,  144  and knife bar  146  are coupled together using any suitable fastening technique such as tack welding ( FIG. 9 ), for example. Right and left hand firing cams  142 ,  144  are elongated, resilient, and can flex outwardly from knife bar  146  as indicated by arrows “D” and “E” in  FIG. 8 . 
     Right and left hand firing cams  142 ,  144  are substantially identical and therefore, in the interest of brevity, only right hand firing cam  142  is described in detail. A proximal end of right hand firing cam  142  includes first and second spaced arms  142   a ,  142   b  that define an opening  142   c . First and second arms  142   a ,  142   b  extend distally from the proximal end and are joined to an elongated shaft portion  142   d . Elongated shaft  142   d  extends distally from first and second arms  142   a ,  142   b  to a driver head  142   e . Right and left hand firing cams  142 ,  144  are configured to have a narrow profile, for example, to enable smooth translation through firing channels  137   a - 137   d  defined in cartridge body  134 . 
     As seen in  FIG. 7 , a bottom surface of driver head  142   e  of each of right and left hand firing cams  142 ,  144 , respectively, includes a rib  142   f  and a top surface of driver head  142   e  defines a cam surface  142   g . A distal end of rib  142   f  defines a shoulder  142   h  that is positioned beneath a tip portion  142   i  of cam surface  142   g.    
     With reference to  FIGS. 9 and 10 , knife bar  146  includes resilient bars  146   a ,  146   b ,  146   c ,  146   d  that are substantially identical. A proximal end of each bar of the plurality of bars  146   a ,  146   b ,  146   c ,  146   d  includes first and second spaced arms  1462 ,  1464  that define an opening  1466  open at its proximal end. Opening  1466  is positioned to receive control rod  15  of surgical stapling apparatus  10  when loading unit  100  is coupled to elongated body  14  of surgical stapling apparatus  10 . First and second arms  1462 ,  1464  are secured together by one or more posts  1468   a ,  1468   b.    
     With reference again to  FIG. 7 , drive beam  148  is secured to a distal end of knife bar  146  and has an I-shaped cross-sectional profile. Drive beam  148  includes a lower retention foot  148   a , an upper retention foot  148   b , and a vertically-oriented support strut  148   c  that couples lower and upper retention feet  148   a ,  148   b  together. Vertically-oriented support strut  148   c  supports a blade  148   d  with a sharpened edge adapted to sever tissue. Drive beam  148  is positioned between right and left hand firing cams  142 ,  144  and disposed proximal of driver heads  142   e  of right and left hand firing cams  142 ,  144 . 
     With reference to  FIGS. 11-14 , staple pushers  136  are substantially similar in that each staple pusher of the plurality of staple pushers  136  includes a first pusher plate  1362 , a second pusher plate  1364 , and a cam member  1366  that connects first and second pusher plates  1362 ,  1364  together. First and second pusher plates  1362 ,  1364  are longitudinally offset and each defines a staple support channel  1363  that is configured to support a backspan of one of the staples “S.” Cam member  1366  includes a pusher ramp  1368  that is adapted to engage cam surface  142   g  of one of right and left hand firing cam members  142 ,  144 . 
     Staple pushers  136  are arranged in cartridge body  134  on each side of knife slot  134   d  such that staple pushers  136  are disposed in registration with corresponding rows of staple retaining pockets  134   b  of cartridge body  134  (e.g., rows “R 1 ”-“R 8 ” seen in  FIG. 5 ) (four rows on either side of knife slot  134   d ). Each staple pusher  136  is associated with two of the four rows on one of the two sides of knife slot  134   d  of cartridge body  134 . 
     Staple pushers from adjacent rows of staple pushers within cartridge body  134  are disposed in a nested relationship to support staples “S” in four adjacent rows (e.g., rows “R 1 ”-“R 4 ”) on each side of knife slot  134   d . In the nested relationship, staple pushers  136   a ,  136   b  ( FIG. 13 ) include cam members  1366   a ,  1366   b  disposed in mirrored relationship such that first pusher plate  1362  of staple pusher  136   a  is longitudinally aligned with second pusher plate  1364  of staple pusher  136   b , and second pusher plate  1364  of staple pusher  136   a  is longitudinally aligned with first pusher plate  1362  of staple pusher  136   b.    
     Referring to  FIGS. 15-18 , cartridge body  134  further defines a plurality of firing channels  137   a - 137   d . Firing channels  137   a  and  137   c  are adapted to receive right hand firing cam  142  and firing channels  137   b ,  137   d  are adapted to receive left hand firing cam  144 . Firing assembly  140  is preloaded within cartridge body  134  in a first proximal position. In the first proximal position, resilient right hand firing cam  142  is disposed in an outwardly deformed orientation against its natural bias with drive head  142   e  of right hand firing cam  142  positioned within firing channel  137   a . Also in the first proximal position, left hand firing cam  144  is disposed in an inwardly deformed orientation against its natural bias with drive head  142   e  of left hand firing cam  144  positioned within firing channel  137   d.    
     T-bars  138   a ,  138   b  are movable from a proximal or retracted position within cartridge body  134  to a distal or advanced position. In the proximal position, the proximal end of T-bars  138   a  and  138   b  are positioned to retain right and left hand firing cams  142  and  144 , respectively, within firing channels  137   a  and  137   d , respectively. More specifically, side surfaces of T-bars  138   a ,  138   b  engage side surfaces of right and left hand firing cams  142 ,  144  to prevent right and left hand firing cams  142 ,  144  from moving toward their non-deformed orientation when right and left hand firing cams  142 ,  144  and T-bars  138   a ,  138   b  are fully retracted (see  FIGS. 22-23 ). 
     Cartridge body  134  also includes ramps  139  that are positioned to engage right and left hand firing cams  142 ,  144  during first and/or second axial translations of firing cam assembly  140  within cartridge body  134 , as described in greater detail below. The plurality of ramps  139  includes a first ramp  139   a  that is configured to direct drive head  142   e  of right hand firing cam  142  into firing channel  137   c  so that drive head  142   e  of right hand firing cam  142  is positioned to axially translate along firing channel  137   c . A second ramp  139   b  of the plurality of ramps  139  directs drive head  142   e  of left hand firing cam  144  within firing channel  137   b  so that drive head  142   e  of left hand firing cam  144  is positioned to axially translate along firing channel  137   b . First ramp  139   a  is shown with a rounded bump and second ramp  139   b  is shown with a flat, shallow slope, but one or both of these ramps  139   a ,  139   b  may include any suitable shape and/or dimension to facilitate movement of right and left hand firing cams  142 ,  144  into the appropriate firing channels. 
     Cartridge body  134  includes proximal and distal T-bar engagement posts  131   a ,  131   b  and defines a T-bar recess  133  dimensioned to receive a distal portion of T-bars  138   a ,  139   b . Proximal and distal T-bar engagement posts  131   a ,  131   b  are received within proximal and distal elongated channels  1384   a ,  1384   b  of T-bars  138   a ,  138   b , respectively, to maintain alignment of T-bars  138   a ,  138   b  as T-bars  138   a ,  138   b  translate relative to cartridge body  134 , as described in greater detail below. Engagement surfaces  133   a  ( FIG. 15 ) extend from cartridge body  134  into T-bar recess  133 . Engagement surfaces  133   a  are adapted to frictionally engage cross members  1386  of T-bars  138   a ,  138   b  to maintain T-bars  138   a ,  138   b  in an advanced position relative to cartridge body  134  when T-bars  138   a ,  138   b  are received within T-bar recess  133 . The pair of engagement surfaces  133   a  can have any suitable shape/dimension (e.g., rounded, tapered, etc.) and/or may include surface texturing (e.g., bumps knurling, ribs, etc.). 
     In use, as illustrated in  FIGS. 1A and 18-23 , firing cam assembly  140  is actuated (e.g., via pivotal retraction of movable handle  18  of handle assembly  12 , as indicated by arrow “AA”) to advance drive beam  148  and right and left hand firing cams  142 ,  144  distally through cartridge body  134  as indicated by arrow “F.” As drive beam  148  advances distally through cartridge body  134 , upper and lower retention feet  148   a ,  148   b  are received within channels (not shown) defined within anvil and cartridge assemblies  120 ,  130  to approximate anvil and cartridge assemblies  120 ,  130  while blade  148   d  ( FIG. 7 ) advances through knife slot  134   d  to severe tissue grasped between anvil and cartridge assemblies  120 ,  130 . With drive beam  148  advancing through cartridge body  134 , right and left hand firing cams  142 ,  144  simultaneously distally translate through firing channels  137   a ,  137   d , respectively, so that cam surfaces  142   g  of right and left hand firing cams  142 ,  144  engage pusher ramps  1368  of the plurality of staple pushers  136  during a first axial translation of firing cam assembly  140  to fire staples “S” of rows “R 2 ,” “R 4 ,” “R 6 ,” and “R 8 ” and to form the fired staples within corresponding staple forming depressions  124   b  of anvil assembly  120 . 
     Just before right and left hand firing cams  142 ,  144  reach a distal-most position, shoulders  142   h  of drive heads  142   e  of right and left hand firing cams  142 ,  144  engage one of the pair of abutments  1386   a ,  1386   b  of cross members  1386  of T-bars  138   a ,  138   b , respectively. With proximal and distal T-bar engagement posts  131   a ,  131   b  of cartridge body  134  maintaining lateral alignment of T-bars  138   a ,  138   b  within cartridge body  134 , posts  1382  of T-bars  138   a ,  138   b  distally translate through T-bar channels  134   f ,  134   g  of cartridge body  134  as right and left hand firing cams  138   a ,  138   b  engage and drive first and second T-bars  138   a ,  138   b  distally to a distal-most position relative to cartridge body  134 . In the distal-most position, the distal portions of T-bars  138   a ,  138   b  are received within T-bar recess  133  of cartridge body  134  and maintained therein via frictional engagement with the pair of engagement surfaces  133   a  of cartridge body  134  (see  FIG. 21 ). 
     Referring to  FIGS. 22-23 , with T-bars  138   a ,  138   b  fixed in the distal-most position, firing cam assembly  140  can then be retracted proximally to a second proximal position, as indicated by arrows “G,” (e.g., via retraction of retraction member  26  of handle assembly  12  in the proximal direction, as indicated by arrow “AAA” in  FIG. 1A ). Retraction of firing cam assembly  140  moves drive beam  138  proximally and unapproximates anvil and cartridge assemblies  120 ,  130 . When firing cam assembly  140  is retracted to its second proximal position, drive heads  142   e  of right and left hand firing cams  142 ,  144  are disposed proximal to proximal ends of T-bars  138   a ,  138   b . Since drive heads  142   e  no longer engage the proximal end of T-bars  138   a ,  138   b , drive heads  142   e  of right and left hand firing cams  142 ,  144  move/pivot toward their natural, unflexed orientation, as indicated by arrows “H” and springs  135   a ,  135   b  ( FIG. 5 ) spring bias anvil assembly  120  open. In the natural, unflexed orientations of right and left hand firing cams  142 ,  144 , drive heads  142   e  of right and left hand firing cams  142 ,  144  are aligned with firing channels  137   b ,  137   c  of cartridge body  134 , respectively. First ramp  139   a  of cartridge body  134  directs right hand firing cam  142  into firing channel  137   c  of cartridge body  134  and second ramp  139   b  directs left hand firing cam  144  into firing channel  137   b . Firing cam assembly  140  can then again be distally advanced, as indicated by arrow “F,” to fire loading unit  100  a second time. Surgical stapling apparatus  10  can be released from tissue after the first firing and re-positioned to clamp tissue at a different location before the second firing. 
     During a second axial translation of firing cam assembly  140 , drive beam  148  again advances distally through cartridge body  134  so that upper and lower retention feet  148   a ,  148   b  of drive beam  148  approximate anvil and cartridge assemblies  120 ,  130 . With drive beam  148  advancing distally through cartridge body  134 , right and left hand firing cams  142 ,  144  simultaneously distally translate through firing channels  137   c ,  137   b , respectively, so that cam surfaces  142   g  of right and left hand firing cams  142 ,  144  engage pusher ramps  1368  of the plurality of staple pushers  136  during a first axial translation of firing cam assembly  140  to fire staples “S” of rows “R 1 ,” “R 3 ,” “R 5 ,” and “R 7 ” and to form the fired staples within corresponding staple forming depressions  124   b  of anvil assembly  120 . 
     Loading unit  100  and/or cartridge assembly  130  can be removed and/or replaced with a new loading unit  100  and/or a new cartridge assembly  130  as desired. 
     Persons skilled in the art will understand that the structures and methods specifically described herein and shown in the accompanying figures are non-limiting exemplary embodiments, and that the description, disclosure, and figures should be construed merely as exemplary of particular embodiments. It is to be understood, therefore, that the present disclosure is not limited to the precise embodiments described, and that various other changes and modifications may be effected by one skilled in the art without departing from the scope or spirit of the disclosure. Additionally, the elements and features shown or described in connection with certain embodiments may be combined with the elements and features of certain other embodiments without departing from the scope of the present disclosure, and that such modifications and variations are also included within the scope of the present disclosure. Accordingly, the subject matter of the present disclosure is not limited by what has been particularly shown and described.