Abstract:
A surgical stapling and severing instrument particularly suited to endoscopic procedures incorporates a handle that produces separate closing and firing motions to actuate an end effector. In particular, the handle produces multiple firing strokes in order to reduce the required amount of force required to fire (i.e., staple and sever) the end effector. A linked transmission reduces the required handle longitudinal length, yet achieves a rigid, strong configuration when straightened for firing. A traction biased firing mechanism avoids binding in driving this straightened linked rack in cooperation with an anti-backup mechanism, with a lockout mechanism that prevents releasing the closure trigger during firing. Furthermore, an external indicator gives feedback to the surgeon as to how far firing has progressed, as well as providing a manual retraction capability.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is related to four co-pending and commonly-owned applications filed on even date herewith, the disclosure of each is hereby incorporated by reference in their entirety, these four applications being respectively entitled: 
        “SURGICAL STAPLING INSTRUMENT HAVING MULTISTROKE FIRING WITH OPENING LOCKOUT, Ser. No. ______, to Frederick E. Shelton, Jeffrey S. Swayze, Douglas B. Hoffman;     “SURGICAL STAPLING INSTRUMENT INCORPORATING A FIRING MECHANISM HAVING A LINKED RACK TRANSMISSION”, Ser. No. ______, to Jeffrey S. Swayze, Frederick E. Shelton IV;     “SURGICAL STAPLING INSTRUMENT HAVING MULTISTROKE FIRING INCORPORATING A TRACTION-BIASED RATCHETING MECHANISM, Ser. No. ______, to Jeffrey S. Swayze, Frederick E. Shelton IV; and     “SURGICAL STAPLING INSTRUMENT INCORPORATING A MULTISTROKE FIRING POSITION INDICATOR AND RETRACTION MECHANISM”, Ser. No. ______, to Jeffrey S. Swayze, Frederick E. Shelton IV.       
 
     
    
     FIELD OF THE INVENTION  
       [0006]     The present invention relates in general to surgical stapler instruments that are capable of applying lines of staples to tissue while cutting the tissue between those staple lines and, more particularly, to improvements relating to stapler instruments and improvements in processes for forming various components of such stapler instruments that accomplish firing with multiple strokes of a trigger.  
       BACKGROUND OF THE INVENTION  
       [0007]     Endoscopic surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. Consequently, significant development has gone into a range of endoscopic surgical instruments that are suitable for precise placement of a distal end effector at a desired surgical site through a cannula of a trocar. These distal end effectors engage the tissue in a number of ways to achieve a diagnostic or therapeutic effect (e.g., endocutter, grasper, cutter, staplers, clip applier, access device, drug/gene therapy delivery device, and energy device using ultrasound, RF, laser, etc.).  
         [0008]     Known surgical staplers include an end effector that simultaneously makes a longitudinal incision in tissue and applies lines of staples on opposing sides of the incision. The end effector includes a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil.  
         [0009]     An example of a surgical stapler suitable for endoscopic applications is described in U.S. Pat. No. 5,465,895, which advantageously provides distinct closing and firing actions. Thereby, a clinician is able to close the jaw members upon tissue to position the tissue prior to firing. Once the clinician has determined that the jaw members are properly gripping tissue, the clinician can then fire the surgical stapler with a single firing stroke, thereby severing and stapling the tissue. The simultaneous severing and stapling avoids complications that may arise when performing such actions sequentially with different surgical tools that respectively only sever or staple.  
         [0010]     One specific advantage of being able to close upon tissue before firing is that the clinician is able to verify via an endoscope that desired location for the cut has been achieved, including a sufficient amount of tissue has been captured between opposing jaws. Otherwise, opposing jaws may be drawn too close together, especially pinching at their distal ends, and thus not effectively forming closed staples in the severed tissue. At the other extreme, an excessive amount of clamped tissue may cause binding and an incomplete firing.  
         [0011]     Generally, a single closing stroke followed by a single firing stroke is a convenient and efficient way to perform severing and stapling. However, in some instances, it would be desirable for multiple firing strokes to be required. For example, surgeons are able to select from a range of jaw sizes with a corresponding length of staple cartridge for the desired length of cut. Longer staple cartridges require a longer firing stroke. Thus, a hand-squeezed trigger to effect the firing is required to exert a larger force for these longer staple cartridges in order to sever more tissue and drive more staples as compared to a shorter staple cartridge. It would be desirable for the amount of force to be lower and comparable to shorter cartridges so as not to exceed the hand strength of some surgeons. In addition, some surgeons not familiar with the larger staple cartridges may become concerned that binding or other malfunction has occurred when an unexpectedly higher force is required.  
         [0012]     One approach to lower the required force for a firing stroke is a ratcheting mechanism that allows a firing trigger to be stroked multiple times, as described in U.S. Pat. Nos. 5,762,256 and 6,330,965. These known surgical stapling instruments with multiple-stroke firing mechanisms do not have the advantages of a separate closure and firing action. Moreover, the ratcheting mechanism relies upon a toothed rack and driving pawl to achieve the ratcheting motion, with the length of a handle encompassing these components thus increased to accommodate the toothed rack.  
         [0013]     This increased length is inconvenient given the close confines and increasing amount of equipment associated with a surgical procedure.  
         [0014]     Furthermore, between each stroke of the multiple-stroke firing mechanism, it is desirable that any inadvertent retraction be prevented. Pressure exerted by tissue in the end effector, for instance, tends to push back against the firing system between strokes. In addition, in some instances, the firing mechanism includes a retraction bias that may tend to draw back the firing mechanism between strokes, reducing the effectiveness of the instrument, such as staple malformation, increased number of firing strokes, or an inability to achieve a full firing sequence altogether.  
         [0015]     Consequently, a significant need exists for a surgical stapling instrument with a multiple stroke firing mechanism that prevents inadvertent retraction of the firing mechanism between firing strokes.  
       BRIEF SUMMARY OF THE INVENTION  
       [0016]     The invention overcomes the above-noted and other deficiencies of the prior art by providing a surgical stapling instrument that affirmatively prevents a firing member from returning during firing even when a firing mechanism is uncoupled between strokes, such as when a firing trigger is released. Thus, surgical instruments used to perform surgical operations that could misfire during to such return motion are rendered more reliable and effective.  
         [0017]     In one aspect of the invention, a surgical instrument has an end effector that responds to a longitudinal firing motion between an unfired position and a fully fired position received from a firing member in a shaft to perform a surgical operation. An anti-backup mechanism prevents the return of the firing member during firing by having a locking plate with an aperture circumferentially encompassing the firing member. The locking plate pivots between a locking position and an unlocking position responsive to a locking device that in turn responds to the instrument being in the process of firing. A retract mechanism causes the locking plate to unlock. Thereby, resistance that could cause inadvertent return of the firing member is prevented.  
         [0018]     In another aspect of the invention, a surgical instrument has the end effector connected to a handle via the shaft. Within the handle, a rack is distally coupled to the firing member. A firing control responds to an operator to move in a firing direction and a return direction. A firing mechanism couples the firing control to the rack to impart the firing motion in response to the firing direction and to uncouple the firing control from the rack in response to the return direction. This firing control works in concert with a locking mechanism that impedes firing member motion in the return direction in response to the firing member having traveled between an initial, unfired position and a fired position. This approach has particular advantages for multiple stroke firing approaches wherein the firing member may be released between strokes. These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0019]     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention.  
         [0020]      FIG. 1  is a right side elevation view of a surgical stapling and severing instrument in an open (start) condition, with a shaft partially cutaway to expose a closure tube and firing rod.  
         [0021]      FIG. 2  is a left side elevation view taken along line  2 - 2  in longitudinal cross section of an end effector at a distal portion of the surgical stapling instrument of  FIG. 1 .  
         [0022]      FIG. 3  is a front perspective view of the end effector of  FIG. 2 .  
         [0023]      FIG. 4  is a perspective, exploded view of an implement portion of the surgical stapling and severing instrument of  FIG. 1 .  
         [0024]      FIG. 5  depicts a left side elevation view in section of the end effector of  FIG. 3  of the surgical instrument of  FIG. 1 , the section generally taken along lines  5 - 5  of  FIG. 3  to expose portions of a staple cartridge but also depicting the firing bar along the longitudinal centerline.  
         [0025]      FIG. 6  depicts a left side elevation view in section of the end effector of  FIG. 5  after the firing bar has fully fired.  
         [0026]      FIG. 7  is a left side elevation view of the handle of the surgical stapling and severing instrument of  FIG. 1  with a left handle housing removed.  
         [0027]      FIG. 8  is a perspective, exploded view of the handle of  FIG. 7 .  
         [0028]      FIG. 9  is a perspective view from an elevated, aft, left vantage point of the linked transmission firing mechanism of the handle of  FIG. 7 .  
         [0029]      FIG. 10  is a detail left side elevation view of the linked rack of the firing mechanism of  FIG. 9 .  
         [0030]      FIGS. 11-14  are left side elevation views in cross section generally along the longitudinal axis of the ramped central track of the linked rack and the pawl of the firing mechanism, and additionally showing the firing trigger, biasing wheel and ramp of the traction biasing mechanism, depicting a sequence during a firing stroke.  
         [0031]      FIG. 15  is a right-side elevation view partially disassembled to expose a distal portion of an anti-backup mechanism in a locked condition in the surgical stapling and severing instrument of  FIG. 1 .  
         [0032]      FIG. 16  is a perspective view from a top, aft, right vantage point of the anti-backup mechanism of  FIG. 15  with the anti-backup cam tube removed.  
         [0033]      FIG. 17  is a right-side elevation view partially disassembled to expose a distal portion of an anti-backup mechanism in an unlocked condition in the surgical stapling and severing instrument of  FIG. 1 .  
         [0034]      FIG. 18  is a right-side elevation view partially disassembled to expose a distal portion of an anti-backup mechanism in an unlocked condition in the surgical stapling and severing instrument of  FIG. 1 .  
         [0035]      FIG. 19  is a rear elevation view of the surgical stapling and severing instrument of  FIG. 1  with the right half shell of the handle housing removed to expose the anti-backup release lever in phantom in a locking condition and in an unlocked condition.  
         [0036]      FIGS. 20-25  are detail views of the anti-backup release lever of  FIG. 18  depicting respectively a firing sequence of unfired, one firing stroke, two firing strokes, three firing strokes, returning or release button pushed, and fully returned.  
         [0037]      FIGS. 26-27  are perspective view from a top, left, distal vantage point of the surgical stapling and severing instrument with the right half shell of the handle housing removed to expose a closure release lockout mechanism, respectively in an initial position with lockout removed and closure release button depressed, and then a lockout being activated during initial firing.  
         [0038]      FIG. 28  is perspective view of a surgical stapling and severing instrument in an open condition similar to  FIG. 1  but incorporating a top-accessible retraction lever.  
         [0039]      FIG. 29  is a left side elevation view of the surgical stapling and severing instrument of  FIG. 28  with the left half shell of the handle housing removed to expose an intermittently toothed indicator gear presenting a first dwell area to the idler gear.  
         [0040]      FIG. 30  is a left side elevation view of the surgical stapling and severing instrument of  FIG. 28  with the left half shell of the handle housing removed to expose an intermittently toothed indicator gear presenting a second dwell area to the idler gear. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     Turning to the Drawings, wherein like numerals denote like components throughout the several views,  FIGS. 1 and 2  depict a surgical stapling and severing instrument  10  that is capable of practicing the unique benefits of the present invention. The surgical stapling and severing instrument  10  incorporates an end effector  12  having an anvil  14  pivotally attached to an elongate channel  16 , forming opposing jaws for clamping tissue to be severed and stapled. The end effector  12  is coupled by a shaft  18  to a handle  20 . An implement portion  22 , formed by the end effector  12  and shaft  18 , is advantageously sized for insertion through a trocar or small laparoscopic opening to perform an endoscopic surgical procedure while being controlled by a surgeon grasping the handle  20 . The handle  20  advantageously includes features that allow separate closure motion of the end effector  12  from firing, as well as enabling multiple firing strokes to effect firing (i.e., severing and stapling) of the end effector  12  while indicating the degree of firing to the surgeon.  
         [0042]     To these ends, a closure tube  24  of the shaft  18  is coupled between a closure trigger  26  and the anvil  14  to cause closure of the end effector  12 . Within the closure tube  24 , a frame  28  is coupled between the elongate channel  16  and the handle  20  to longitudinally position and support the end effector  12 . A rotation knob  30  is coupled with the frame  28 , and both elements are rotatably coupled to the handle  20  with respect to a rotational movement about a longitudinal axis of the shaft  18 . Thus, the surgeon can rotate the end effector  12  by turning the rotation knob  30 . The closure tube  24  is also rotated by the rotation knob  30  but retains a degree of longitudinal movement relative thereto to cause the closure of the end effector  12 . Within the frame  28 , a firing rod  32  is positioned for longitudinal movement and coupled between the anvil  14  of the end effector  12  and a multiple-stroke firing trigger  34 .  
         [0043]     The closure trigger  26  is distal to a pistol grip  36  of the handle  20  with the firing trigger  34  distal to both the pistol grip  36  and closure trigger  26 .  
         [0044]     In endoscopic operation, once the implement portion  22  is inserted into a patient to access a surgical site, a surgeon refers to an endoscopic or other diagnostic imaging device to position tissue between the anvil  14  and elongate channel  16 . Grasping the closure trigger  26  and pistol grip  36 , the surgeon may repeatedly grasp and position the tissue. Once satisfied as to the location of the tissue relative to the end effector  12  and the amount of tissue therein, the surgeon depresses the closure trigger  26  fully toward the pistol grip  36 , clamping the tissue in the end effector  12  and locking the closure trigger  26  in this clamped (closed) position. If not satisfied with this position, the surgeon may release the closure trigger  26  by depressing a closure release button  38  and thereafter repeat the procedure to clamp tissue.  
         [0045]     If clamping is correct, the surgeon may proceed with firing the surgical stapling and severing instrument  10 . Specifically, the surgeon grasps the firing trigger  34  and pistol grip  36 , depressing the firing trigger  34  a predetermined number of times. The number of firing strokes necessary is ergonomically determined based on a maximum hand size, maximum amount of force to be imparted to the instrument during each firing stroke, and the longitudinal distance and force needed to be transferred through the firing rod  32  to the end effector  12  during firing. As will be appreciated in the discussion below, individual surgeons may choose to cycle the firing trigger  34  a different angular range of motion, and thus increase or decrease the number of firing strokes, yet the handle  20  still effects firing without binding.  
         [0046]     During these strokes, the surgeon may reference an indicator, depicted as an indicating retraction knob  40 , that positionally rotates in response to the multiple firing strokes. Additionally, the position of the retraction knob may confirm that full firing has occurred when encountering resistance to further cycling of the firing trigger  34 . It should be appreciated that various indicia and instructions may be added to the handle  20  to enhance the indication provided by the rotation of the indicating retraction knob  40 . Upon full travel of the firing rod  32  and when the firing trigger  34  is released, the handle  20  automatically retracts the firing rod  32 . Alternatively, the surgeon, with knowledge that the instrument  10  has not fully fired as depicted by the indicating retraction knob  40 , may depress an anti-backup release button  42  and release the firing trigger  34 . Both of these actions allow the handle  20  to automatically retract the firing rod  32 .  
         [0047]     It will be appreciated that the terms “proximal” and “distal” are used herein with reference to a clinician gripping a handle of an instrument. Thus, the end effector  12  is distal with respect to the more proximal handle  20 . It will be further appreciated that for convenience and clarity, spatial terms such as “vertical” and “horizontal” are used herein with respect to the drawings. However, surgical instruments are used in many orientations and positions, and these terms are not intended to be limiting and absolute.  
         [0048]     The present invention is being discussed in terms of endoscopic procedures and apparatus. However, use herein of terms such as “endoscopic”, should not be construed to limit the present invention to a surgical stapling and severing instrument for use only in conjunction with an endoscopic tube (i.e., trocar). On the contrary, it is believed that the present invention may find use in any procedure where access is limited to a small incision, including but not limited to laparoscopic procedures, as well as open procedures.  
         [0049]     E-Beam End Effector.  
         [0050]     The advantages of a handle  20  capable of providing multiple-stroke firing motion has application to a number of instruments, with one such end effector  12  being depicted in  FIGS. 2-6 . The end effector  12  responds to the closure motion from the handle  20  (not depicted in  FIGS. 2-6 ) first by including an anvil face  50  ( FIGS. 2, 4 ,  6 ) connecting to an anvil proximal end  52  that includes a pair of laterally projecting anvil pivot pins  54  that are distal to a vertically projecting anvil feature  56  ( FIG. 4 ). The anvil pivot pins  54  translate within kidney shaped openings  58  in the elongate channel  16  to open and close anvil  14  relative to elongate channel  16 . The anvil feature  56  engages a bent tab  59  extending inwardly in tab aperture  60  on a distal end  62  of the closure tube  24 , the latter distally terminating in a distal edge  64  that pushes against the anvil face  50 . Thus, when the closure tube  24  moves proximally from its the open position, the bent tab  59  of the closure tube  24  draws the anvil feature  56  proximally, and the anvil pivot pins  54  follow the kidney shaped openings  58  of the channel  16  causing the anvil  14  to simultaneously translate proximally and rotate upward to the open position. When the closure tube  24  moves distally, the tab aperture  60  releases from the anvil feature  56  and the distal edge  64  pushes on the anvil face  50 , closing the anvil  14 .  
         [0051]     With continued reference to  FIG. 4 , the implement portion  22  also includes components that respond to the firing motion of the firing rod  32 . In particular, the firing rod  32  rotatably engages a firing trough member  66  having a longitudinal recess  68 . Firing trough member  66  moves longitudinally within frame  28  in direct response to longitudinal motion of firing rod  32 . A longitudinal slot  70  in the closure tube  24  operably couples with the rotation knob  30  (not shown in  FIGS. 2-6 ). The length of the longitudinal slot  70  in the closure tube  24  is sufficiently long as to allow relative longitudinal motion with the rotation knob  30  to accomplish firing and closure motions respectively.  
         [0052]     The distal end of the frame trough member  66  is attached to a proximal end of a firing bar  76  that moves with the frame  28 , including a guide  78  therein, to distally project an E-beam  80  into the end effector  12 . The end effector  12  includes a staple cartridge  82  that is actuated by the E-beam  80 . The staple cartridge  82  has a tray  84  that holds a staple cartridge body  86 , a wedge sled driver  88 , staple drivers  90  and staples  92 . It will be appreciated that the wedge sled driver  88  longitudinally moves within a recess  94  located between a cartridge tray  84  and the cartridge body  86 . The wedge sled driver  88  presents camming surfaces that contact and lift the staple drivers  90  upward, driving the staples  92  up from staple apertures  96  into contact with staple forming grooves  98  of the anvil  14 , creating formed “B” shaped staples, such as depicted at  100  of  FIG. 6 . With particular reference to  FIG. 3 , the staple cartridge body  86  further includes a proximally open, vertical slot  102  for passage of the E-beam  80 . Cutting surface  104  is provided along a distal end of E-beam  80  to cut tissue after it is stapled.  
         [0053]     In  FIGS. 2, 5 ,  6 , respectively, the end effector  12  is depicted in a sequence of open (i.e., start) condition, clamped and unfired condition, and fully fired condition. Features of the E-beam  80  that facilitate firing of the end effector  12 , in particular, are depicted. In  FIG. 2 , the wedge sled driver  88  is in its fully proximally position, indicating an unfired staple cartridge  82 . A middle pin  106  is aligned to enter the firing recess  94  in the staple cartridge  82 , for distally driving the wedge sled driver  88 . A bottom pin or cap  108  of the E-beam  82  slides along a bottom surface of the elongate channel  16 , thus the middle and bottom pins  106 ,  108  slidingly engage the elongate channel  16 . In the open and unfired state of  FIG. 2 , a top pin  110  of the E-beam  80  has entered and is residing within an anvil pocket  112  of the anvil  14 , and thus does not impede repeated opening and closing of the anvil  14 .  
         [0054]     In  FIG. 5 , the end effector  12  is depicted as clamped and ready to fire. The top pin  110  of the E-beam  80  is aligned with an anvil slot  114  in the anvil  14  distal to and communicating with the anvil pocket  112 . In  FIG. 6 , the E-beam  80  has been fully fired, with the upper pin  110  translating down the anvil slot  114 , affirmatively spacing the anvil  14  from the elongate channel  16  as the cutting surface  104  severs clamped tissue. Simultaneously, the middle pin  106  has actuated the staple cartridge  82  as previously described. Thereafter, the E-beam  80  is retracted prior to opening the end effector  12  and replacing the staple cartridge  82  for an additional operation.  
         [0055]     The illustrative end effector  12  is described in greater detail in five co-pending and commonly-owned U.S. patent applications, the disclosure of each being hereby incorporated by reference in their entirety: (1) “SURGICAL STAPLING INSTRUMENT HAVING A SINGLE LOCKOUT MECHANISM FOR PREVENTION OF FIRING”, Ser. No. 10/441,424, to Frederick E. Shelton, Mike Setser, Bruce Weisenburgh, filed 20 Jun. 2003; (2) “SURGICAL STAPLING INSTRUMENT HAVING SEPARATE DISTINCT CLOSING AND FIRING SYSTEMS”, Ser. No. 10/441,632, to Frederick E. Shelton, Mike Setser, Brian J. Hemmelgarn, filed 20 Jun. 2003; (3) “SURGICAL STAPLING INSTRUMENT HAVING A SPENT CARTRIDGE LOCKOUT”, Ser. No. 10/441,565, to Frederick E. Shelton, Mike Setser, Bruce Weisenburgh, filed 20 Jun. 2003; (4) “SURGICAL STAPLING INSTRUMENT HAVING A FIRING LOCKOUT FOR AN UNCLOSED ANVIL”, Ser. No. 10/441,580, to Frederick E. Shelton, Mike Setser, Bruce Weisenburgh, filed 20 Jun. 2003; and (5) “SURGICAL STAPLING INSTRUMENT INCORPORATING AN E-BEAM FIRING MECHANISM”, Ser. No. 10/443,617, to Frederick E. Shelton, Mike Setser, Bruce Weisenburgh, filed 20 Jun. 2003.  
         [0056]     It should be appreciated that although a nonarticulating shaft  18  is illustrated herein, applications of the present invention may include instruments capable of articulation, such as described in five co-pending and commonly owned U.S. patent applications, the disclosure of each being hereby incorporated by reference in their entirety: (1) “SURGICAL INSTRUMENT INCORPORATING AN ARTICULATION MECHANISM HAVING ROTATION ABOUT THE LONGITUDINAL AXIS”, Ser. No. 10/615,973, to Frederick E. Shelton, Brian J. Hemmelgarn, Jeff Swayze, Kenneth S. Wales, filed 9 Jul. 2003; (2) “SURGICAL STAPLING INSTRUMENT INCORPORATING AN ARTICULATION JOINT FOR A FIRING BAR TRACK”, Ser. No. 10/615,962, to Brian J. Hemmelgarn, filed 9 Jul. 2003; (3) “A SURGICAL INSTRUMENT WITH A LATERAL-MOVING ARTICULATION CONTROL”, Ser. No. 10/615,972, to Jeff Swayze, filed 9 Jul. 2003; (4) “SURGICAL STAPLING INSTRUMENT INCORPORATING A TAPERED FIRING BAR FOR INCREASED FLEXIBILITY AROUND THE ARTICULATION JOINT”, Ser. No. 10/615,974, to Frederick E. Shelton, Mike Setser, Bruce Weisenburgh, filed 9 Jul. 2003; and (5) “SURGICAL STAPLING INSTRUMENT HAVING ARTICULATION JOINT SUPPORT PLATES FOR SUPPORTING A FIRING BAR”, Ser. No. 10/615,971, to Jeff Swayze, Joseph Charles Hueil, filed 9 Jul. 2003.  
         [0057]     It should further be appreciated that the linked rack  200  further may enhance a compact design for the handle  20  by progressing at least partially into the shaft  18  of the implement portion  22  as well as around a corner and into a pistol grip  36  of the handle. Moreover, instead of communicating the firing force to a firing rod  32 , a linked rack consistent with aspects of the invention may travel farther toward the end effector  12  to include an articulation mechanism. A pivotal connection between links may thus enhance the ability of the instrument to articulate.  
         [0058]     Multi-Stroke Firing Handle.  
         [0059]     In  FIGS. 7-8 , the handle  20  of the surgical stapling and severing instrument  10  is shown in greater detail, illustrating a linked transmission firing mechanism  150  that provides features such as increased strength, reduced handle size, minimized binding, etc.  
         [0060]     Closure of the end effector  12  (not shown in  FIGS. 7-8 ) is caused by depressing the closure trigger  26  toward the pistol grip  36  of handle  20 . The closure trigger  26  pivots about a closure trigger pin  152  that is coupled to a handle housing  154  composed of right and left half shells  156 ,  158 , causing an upper portion  160  of the closure trigger  26  to move forward. The closure tube  24  receives this closure movement via a closure yoke  162  that is pinned to a closure link  164  and to the upper portion  160  of the closure trigger  26  respectively by a closure yoke pin  166  and a closure link pin  168 .  
         [0061]     In the fully open position of  FIG. 7 , the upper portion  160  of the closure trigger  26  contacts and holds a locking arm  172  of the pivoting closure release button  38  in the position shown. When the closure trigger  26  reaches its fully depressed position, the closure trigger  26  releases the locking arm  172  and an abutting surface  170  rotates into engagement with a distal rightward notch  171  of the pivoting locking arm  172 , holding the closure trigger  26  in this clamped or closed position. A proximal end of the locking arm  172  pivots about a lateral pivotal connection  174  with the housing  154  to expose the closure release button  38 . An intermediate, distal side  178  of the closure release button  38  is urged proximally by a compression spring  180 , which is compressed between a housing structure  182  and closure release button  38 . The result is that the closure release button  38  urges the locking arm  172  counterclockwise (when viewed from the left) into locking contact with the abutting surface  170  of closure trigger  26 , which prevents unclamping of closure trigger  26  when the linked transmission firing system  150  is in an unretracted condition, as described in greater detail below.  
         [0062]     With the closure trigger  26  retracted fully depressed, the firing trigger  34  is unlocked and may be depressed toward the pistol grip  36  multiple times to effect firing of the end effector  12 . As depicted, the linked transmission firing mechanism  150 , is initially retracted, urged to remain in this position by a combination tension/compression spring  184  that is constrained within the pistol grip  36  of the handle  20 , with its nonmoving end  186  connected to the housing  154  and a moving end  188  connected to a downwardly flexed and proximal, retracted end  190  of a steel band  192 .  
         [0063]     A distally-disposed end  194  of the steel band  192  is attached to a link coupling  195  for structural loading and front link  196   a  of a plurality of links  196   a - 196   d  that form a linked rack  200 . Linked rack  200  is flexible yet has distal links that form a straight rigid rack assembly that may transfer a significant firing force through the firing rod  32  in the implement portion  22 , yet readily retract into the pistol grip  36  to minimize the longitudinal length of the handle  20 .  
         [0064]     It should be appreciated that a dual tension/compression spring  184  increases the amount of firing travel available while essentially reducing the minimum length by half over a single spring.  
         [0065]     The firing trigger  34  pivots about a firing trigger pin  202  that is connected to the housing  154 . An upper portion  204  of the firing trigger  34  moves distally about the firing trigger pin  202  as the firing trigger  34  is depressed towards pistol grip  36 , stretching a proximally placed firing trigger tension spring  206  proximally connected between the upper portion  204  of the firing trigger  34  and the housing  154 . The upper portion  204  of the firing trigger  34  engages the linked rack  200  during each firing trigger depression by a traction biasing mechanism  210  that also disengages when the firing trigger  34  is released. Firing trigger tension spring  206  urges the firing trigger  34  distally when released and disengages the traction biasing mechanism  210 .  
         [0066]     As the firing mechanism  150  actuates, an idler gear  220  is rotated counterclockwise (as viewed from the left side) by engagement with a toothed upper surface  222  of the linked rack  200 . This rotation is coupled to an indicator gear  230 , which thus rotates clockwise in response to the idler gear  220 . Both the idler gear  220  and indicator gear  230  are rotatably connected to the housing  154 . The gear relationship between the linked rack  200 , idler gear  220  and indicator gear  230  may be advantageously selected so that the toothed upper surface  222  has tooth dimensions that are suitably strong and that the indicator gear  230  makes no more than one revolution during the full firing travel of the firing mechanism  150 .  
         [0067]     As described in greater detail below, the indicator gear  230  performs at least four functions. First, when the linked rack  200  is fully retracted and both triggers  26 ,  34  are open as shown in  FIG. 7 , an opening  240  in a circular ridge  242  on the left side of the indicator gear  230  is presented to an upper surface  244  of the locking arm  172 . Locking arm  172  is biased into the opening  240  by contact with the closure trigger  26 , which in turn is urged to the open position by a closure tension spring  246 . Closure trigger tension spring  246  is connected proximally to the upper portion  160  of the closure trigger  26  and the handle housing  154 , and thus has energy stored during closing of the closure trigger  26  that urges the closure trigger  26  distally to its unclosed position.  
         [0068]     A second function of the indicator gear  230  is that it is connected to the indicating retraction knob  40  externally disposed on the handle  20 . Thus, the indicator gear  230  communicates the relative position of the firing mechanism  150  to the indicating retraction knob  40  so that the surgeon has a visual indication of how many strokes of the firing trigger  34  are required to complete firing.  
         [0069]     A third function of the indicator gear  230  is to longitudinally and to angularly move an anti-backup release lever  248  of an anti-backup mechanism  250  as the surgical stapling and severing instrument  10  is operated. During the firing strokes, proximal movement of anti-backup release lever  248  by indicator gear  230  activates a one-way clutch mechanism or anti-backup  250  ( FIGS. 15-16 ) that allows distal movement of firing bar  32  and prevents proximal motion of firing bar  32 . This movement also extends the anti-backup release button  42  from the proximal end of the housing  154  for the operator to actuate should the need arise for the firing mechanism to be retracted during the firing strokes. After completion of the firing strokes, the indicator gear  230  reverses direction of rotation as the firing mechanism  150  retracts. The reversed rotation deactivates the anti-backup  250 , withdraws the anti-backup release button  42  into the handle  20 , and rotates the anti-backup release lever  248  laterally ( FIG. 19 ) to allow continued reverse rotation of the indicator gear  230 .  
         [0070]     A fourth function of the indicator gear  230  is to receive a manual rotation from the indicating retraction knob  40  (clockwise in the depiction of  FIG. 7 ) to retract the firing mechanism  150  with anti-backup mechanism  250  is unlocked, thereby overcoming any binding in the firing mechanism  150  that is not readily overcome by the combination tension/compression spring  184 . This manual retraction may be employed after a partial firing of the firing mechanism  150  that would otherwise be prevented by the anti-backup mechanism  250  by depression of the anti-backup release button  42 , which laterally moves the anti-backup release lever  248 .  
         [0071]     Anti-backup mechanism  250  consists of an operator accessible anti-backup release lever  248  operably coupled at the proximal end to anti-backup release lever  42  and at the distal end to an anti-backup yoke  256 . In particular, a distal end  254  of the anti-backup release lever  248  is engaged to the anti-backup yoke  256  by an anti-backup yoke pin  258 . The anti-backup yoke  256  moves longitudinally to impart a rotation to an anti-backup cam slot tube  252  that is longitudinally constrained by the housing  154  and that encompasses the firing rod  32  distally to the connection of the firing rod  32  to the front link  196   a  of the linked rack  200 . The anti-backup yoke  256  communicates the longitudinal movement from the anti-backup release lever  248  via a cam slot tube pin  260  to the anti-backup cam slot tube  252 . That is, longitudinal movement of cam slot tube pin  260  in an angled slot in the anti-backup cam slot tube  252  rotates the tube  252 .  
         [0072]     Trapped between a proximal end of the frame  28  and the anti-backup cam slot tube  252  respectively are an anti-backup compression spring  264 , an anti-backup plate  266 , and an anti-backup cam tube  268 . As depicted, distal movement of the firing rod  32  causes the anti-backup plate  266  to pivot top to the rear, presenting an increased frictional contact to the firing rod  32  that resists proximal movement of the firing rod  32 .  
         [0073]     This anti-backup plate  266  pivots in a manner similar to that of a screen door lock that holds open a screen door when the anti-backup cam slot tube  252  is spaced away from the anti-backup cam tube  268 . Specifically, the anti-backup compression spring  264  is able to act upon a top surface of the plate  266  to tip the plate  266  to its locked position. Rotation of the anti-backup cam slot tube  252  causes a distal camming movement of the anti-backup cam tube  268  forcing the top of the plate  266  distally, overcoming the force from the anti-backup compression spring  264 , thus positioning the anti-backup plate  266  in an unlocked position that allows proximal retraction of the firing rod  32 .  
         [0074]     With particular reference to  FIGS. 8-10 , the traction biasing mechanism  210  is depicted as being composed of a pawl  270  that has a distally projecting narrow tip  272  and a rightwardly projecting lateral pin  274  at its proximal end that is rotatably inserted through a hole  276  in the upper portion  204  of the firing trigger  34 . On the right side of the firing trigger  34 , the lateral pin  274  receives a biasing member, depicted as biasing wheel  278 . As the firing trigger  34  translates fore and aft, the biasing wheel  278  traverses an arc proximate to the right half shell  156  of the handle housing  154 , overruning at its distal portion of travel a biasing ramp  280  integrally formed in the right half shell  156 . The biasing wheel  278  may advantageously be formed from a resilient, frictional material that induces a counterclockwise rotation (when viewed from the left) into the lateral pin  274  of the pawl  270 , thus traction biasing the distally projecting narrow tip  272  downward into a ramped central track  282  of the nearest link  196   a - d  to engage the linked rack  200 . As the firing trigger  34  is released, the biasing wheel  278  thus tractionally biases the pawl  270  in the opposite direction, raising the narrow tip  272  from the ramped central track  282  of the linked rack  200 . To ensure disengagement of the tip  272  under high load conditions and at nearly full distal travel of the pawl  270 , the narrow tip  272  ramps up onto a proximally and upwardly facing beveled surface  284  on the closure yoke  162  to disengage the narrow tip  272  from the ramped central track  282 . If the firing trigger  34  is released at any point other than full closure, the biasing wheel  278  is used to lift the narrow tip  272  from the ramped central track  282 . Whereas a biasing wheel  278  is depicted, it should be appreciated that the shape of the biasing member or wheel  278  is illustrative and may be varied to accommodate a variety of shapes that use friction or traction to engage or disengage the firing of the end effector.  
         [0075]     Linked Rack.  
         [0076]     With particular reference to  FIG. 10 , the linked rack  200  is depicted in greater detail to illustrate a number of advantages. Each link  196   a - d  is pinned to adjacent links  196   a - d  for downward, proximal rotation into the pistol grip  36 . Although bendable in this direction, the linked rack  200  forms a rigid configuration when against a columnar loading, especially a loading that would other urge the distal links  196   a - d  to bend upwardly. In particular, each link  196   a - d  proximally terminates in a male extension  300  having lateral through hole  302  on a lower portion thereof. A left side  304  of each link  196   a - d  includes the toothed upper surface  222  and a right side  306  parallels the left side  304  defining between them the ramped central track  282  that terminates in the male extension  300 .  
         [0077]     The proximal portion of the central track  282  terminates before the right and left sides  304 ,  306 , forming a device  308  for receiving a male extension  300  from a leading link  196   a - d , which is hingedly attached by a pivot pin  310 . Each leading link  196   a - d  has a flat  312  at the proximal end that is generally perpendicular to the direction of columnar loading from the firing rod  32 . Each trailing link  196   a - d  has a contact surface  314  at the distal end that is also generally perpendicular to the direction of columnar loading. The lateral through hole  302  is spaced away sufficient so that a notch  316  is formed between lower portions of adjacent flat  312  and contact surface  314  to provide clearance for downward pivoting of the trailing link  196   a - d  relative to the leading link  196   a - d . Yet, the upper portions of the adjacent flat  312  and contact surface  314  are registered for abutment as the leading and trailing links  196   a - d  are longitudinally aligned, thereby resisting further upward deflection. As shown, when adjacent links  196   a - d  are horizontal, the holes  302  and pins  310  are located below the line of action of the firing rod  32 . When loads are applied to the firing trigger  34 , the traction biasing mechanism  210  applies a pushing load along the line of action and biases consecutive horizontal links  196   a - d  together. Thus, imparting a line of action of a firing force above the pivot pins  310  maintains any leading links  196   a - d  in a rigid, straight configuration. The ramped central track  282  of a trailing link  196   b - d  directs the distally projecting narrow tip  272  of the pawl  270  into engagement with the male extension  300  of the leading link  196   a - c.    
         [0078]     The front link  196   a  is distally attached to the link coupling  195  that includes features that couple to the proximal end of the firing rod  32  as well as including a male extension  300  and flat  312  similar to the links  196   a - d , with sufficient spacing to receive therebetween tabs  320 ,  322  ( FIG. 8 ) of the distally-disposed end  194  of the steel band  192 , the tabs  320 ,  322  attached by the same pivot pin  310  that attaches the front link  196   a  to the link coupling  195 . Application of the retraction force at this force advantageously reduces frictional forces by applying the force along the longitudinal axis of the firing rod  32  and straight portion of the linked rack  200 .  
         [0079]     Having a toothed upper surface  222  on the left side  304  that is distinct from the ramped central track  282  advantageously allows a nonbinding, strong engagement between the pawl  270  and the linked rack  200 , even if the firing trigger  34  has been stroked with varying ranges of motion. Meanwhile the toothed upper surface  222  provides a continuous engagement with the idler gear  220  for the advantages described above.  
         [0080]     It should be appreciated that although a pinned clevis connection between links  196   a - d  has been advantageously depicted, a resilient or flexible connection may be used. In addition, four links  196   a - d  are depicted, but various numbers and lengths of links may be selected depending on firing travel, radius of curvature, etc.  
         [0081]     Traction-Biasing Mechanism.  
         [0082]     In  FIGS. 11-14 , the linked transmission firing mechanism  150  is depicted in a sequence that illustrates how the traction biasing mechanism  210  (i.e., pawl  270 , biasing wheel  278 , and biasing ramp  280 ) affirmatively respond to the direction of travel of the firing trigger  34 . Moreover, since the biasing wheel  278  makes a frictional contact with the biasing ramp  280 , the biasing wheel  278  slides when full disengagement or engagement movement of the pawl  270  is achieved.  
         [0083]     In  FIG. 11 , the firing trigger  34  has been partially depressed to where the traction biasing mechanism  210  begins to initiate engagement of the firing trigger  34  movement to the linked rack  200 . In particular, the biasing wheel  278  has contacted the proximal end of the biasing ramp  280 , and thus begins to rotate counterclockwise, as viewed from the left, imparting this rotation to the pawl  270 , which is initially disengaged from the linked rack  200 . In  FIG. 12 , the firing mechanism  150  has advanced a distance sufficient for the pawl  270  to have fully rotated into engagement with the ramped central track  282  of the first link  196   a , abutting the link coupling  195  and thereby transferring a firing motion into the firing rod  32 . In  FIG. 13 , the firing trigger  34  and overall firing mechanism  150  has continued to a nearly full travel position, during which movement the biasing wheel  278  has slid along the biasing ramp  280 . At the end of the firing stroke, the farside lower edge of the pawl  270  ( FIG. 8 ) contacts the proximally and upwardly facing beveled surface  284  of the closure yoke  162  and lifts the pawl  270  from engagement with a link  196 , allowing the linked rack  200  to retract.  
         [0084]     In  FIG. 14 , the firing trigger  34  has been released sufficient for the biasing wheel  278  to gain traction proximally on the biasing ramp  280 , causing a clockwise rotation, when viewed from the left, and raising the pawl  270 . Given the proximally directed slope of the ramped central track  282  of the linked rack  200 , the firing mechanism  150  is not obstructed in being moved proximally in preparation for either another firing stroke or for a retraction cycle.  
         [0085]     It should be appreciated that the traction biasing mechanism  210  may be implemented in an instrument that performs at least a single stroke.  
         [0086]     Anti-Backup Mechanism.  
         [0087]     As described above, the anti-backup mechanism  250  locks during the firing strokes to prevent the firing rod  32  and thus the firing mechanism  150  from retracting until full firing travel is achieved or the user selects to retract. In  FIG. 15 , the anti-backup mechanism  250  is depicted in a locked condition. The anti-backup release lever  248  is in the proximal-most position and has rotated anti-backup cam slot tube  252  to engage the anti-backup cam tube  268  to form a minimum longitudinal length, creating an increased space for the locking plate  266 . Locking plate  266  is tipped to the angle shown by the anti-backup compression spring  264  and grips on the firing rod  32 , as shown in  FIG. 16 .  
         [0088]     In  FIG. 16 , a proximal end  400  of the frame  28  include a half spool portion  402  that receives the anti-backup compression spring  264  against its distal annular ring  404 . Proximal to the spring  264 , the frame  28  has a top and proximally open trough  406  that communicates with the interior of the frame  28 . The anti-backup plate  266  is a generally flat plate shaped to fit into the open trough  406  adjacent to the spring  264 . Central orifice  408  extends through plate  266 . In particular, the top portion of the anti-backup plate  266  that is exposed from the open trough  406  projects upwardly to receive a force from the spring  264 . The lower portion of the anti-backup plate  266  is longitudinally constrained and not in contact with the spring  264 . Thus, unless restrained by the anti-backup cam tube  268 , the top of the anti-backup plate  266  is urged to tip proximally, causing the central orifice  408  in the anti-backup plate  266  to bind against the firing rod  32 .  
         [0089]     In  FIG. 17 , the anti-backup mechanism  250  is depicted as unlocked. The anti-lock release lever  248  has laterally moved to the right, impart a movement to the right of the anti-backup yoke  256 , thereby imparting a clockwise rotation of the anti-backup cam slot tube  252 , when viewed from a proximal position. A camming surface  410  of the anti-backup cam slot tube  252  departs from a proximal cutout  412  in the anti-backup cam tube  268 , forcing the latter to move distally against the anti-backup plate  266 , which in turn moves to a perpendicular, unlocked position and further compresses anti-backup compression spring  264 .  
         [0090]     In  FIG. 18 , the interaction between the anti-backup release lever  248  and the right side of the indicator gear  230  are depicted after the firing trigger  34  has been fired twice. A lever opening  420  extends through anti-backup release lever  248  to receive and interact with a curved ramp  434  extending outwardly from the right side of the indicator gear  230 . Rotation of the indicator gear  230  drives the anti-backup release lever  248  distally, which bottoms out the anti-backup release button  42  into a button receptacle  422  and disengages the anti-backup mechanism  250 , and proximally, which exposes the anti-backup release button  42  as depicted, as well as kicking the anti-backup release lever  248  to the right to actuate the anti-backup mechanism  250 . The anti-backup yoke  256  allows this motion with a longitudinal slotted connection with the anti-backup yoke pin  258  (not shown). These movements of the anti-backup release lever  248  are caused by a curved ramp  430  that surrounds almost a quarter of the circumference of an indicator pin  432 , about which the indicator gear  230  turns. The clockwise most portion (when viewed from the right), or peak  434 , of the curved ramp  430  projects the farthest to the right away from the surface of the indicator gear  230 . The counterclockwise most portion or entry  436  of the curved ramp  430  is thus flush with the surface of the indicator gear  230 .  
         [0091]     In  FIGS. 18-25 , the lever opening  420  is shaped with a horizontal slot  440  that defines the proximal and distal movement available to the anti-backup release lever  248 , with the indicator pin  432  residing within this horizontal slot  440 . A top recess  442  and a bottom recess  444  vertically widen and communicate with the horizontal slot  440  and define at what angular position the clockwise most portion  434  of the curved ramp  430  longitudinally translates the anti-backup release lever  248 . The top and bottom recesses  442 ,  444  are sized to allow the curved ramp  430  to enter the respective recess  442 ,  444  without tipping the anti-backup release lever  248  until the end of normal firing. The lever opening  420  is above the longitudinal axis of the anti-backup mechanism  250 , and thus a rightward force creates a rotating force of the anti-backup cam slot tube  252 .  
         [0092]     In  FIG. 20 , the anti-backup release lever  248  and indicator gear  230  are shown in their initial condition that remains through the time in which the closure trigger  26  is being actuated. In particular, the anti-backup release lever  248  is distally positioned, bottoming out the anti-backup release button  42  in its button receptacle  422 . The curved ramp  430  is at its counterclockwise extreme, with its peak  434  at approximately the 6 o&#39;clock position adjacent distally to a proximal vertical surface of the lower recess  444  of the lever recess  420  with the entry  436  of the ramp  430  at about 3 o&#39;clock.  
         [0093]     In  FIG. 21 , the first firing stroke of the firing trigger  34  has occurred, wherein the peak  434  has acted against the proximal vertical surface of the bottom recess  444  and the curved ramp  430  has rotated clockwise to about the 9 o&#39;clock position. Thereby, the anti-backup release lever  248  has translated proximally to exposes the anti-backup release button  42  from the button receptacle  422  and actuated the anti-backup mechanism  250 . The relationship of the rate of clockwise rotation of the indicator gear  230  to the desired number of full firing strokes is selected so that the curved ramp  430  continues unimpeded as subsequent firing strokes are made, as depicted in  FIG. 22  wherein the two firing strokes have been completed moving the peak to approximately the twelve o&#39;clock position. Thus, the peak  434  is proximal to and adjacent to the distal vertical edge of the upper recess  442 , positioned so that a subsequent firing stroke will act upon the anti-backup release lever  248  to cause distal horizontal movement. Note that during these firing strokes that the curved ramp  430  resides proximal to the indicator pin  432 . Depressing the release button  42  would cause the proximal edge of the lever opening  420  to ride up onto the curved ramp  430 , tilting the anti-backup release lever  248  as depicted in  FIG. 19 .  
         [0094]     In  FIG. 23 , the final firing stroke is concluding, during which the peak  434  has moved to approximately 3 o&#39;clock while moving the proximal end of the horizontal slot  440  up against the indicator pin  432 , bottoming out the anti-backup release button  42 , releasing the anti-backup mechanism  250  and initiating the retraction of linked transmission firing mechanism  150 .  
         [0095]     In  FIG. 24 , the unlocked anti-backup mechanism  250  has allowed the spring-powered retraction of the linked rack  200  to occur, which in turn causes a counterclockwise rotation, when viewed from the right, of the indicator gear  230 . As the firing mechanism  150  begins to retract, the counterclockwise rotation of indicator gear  230  slides the angled surface of curved ramp  430  into ramped contact with the proximal edge of the top recess  442 . Continued rotation of indicator gear  230  drives the curved ramp  430  under the upper portion of backup release lever  248  and tilts or deflects lever  248  to the position shown in  FIG. 19 . The tilting motion of the backup release lever  248  is provided to prevent longitudinal motion of lever  248  by the curved ramp  430  during retraction of the linked rack  200 . Should the linked rack  200  not retract at the end of the last stroke after anti-backup mechanism  250  is automatically unlocked at the end of the firing sequence, turning the indicator knob  40  (not shown in  FIGS. 20-25 ) would provide extra force to retract the linked rack  200 . It should further be appreciated that during partial firing of the firing mechanism  150 , such as depicted in  FIG. 22 , depressing the release button  42  would also retract the linked rack  200  by move the backup release lever  248  distally to unlock the anti-backup mechanism  250 . The retraction motion continues until the indicator gear is returned to its initial position, as depicted in  FIG. 25 .  
         [0096]     It should be appreciated that the shape of the lever opening  420  and arcuate size of the arced ramp  430  are illustrative and may be varied to accommodate a handle configured for a different number of firing strokes.  
         [0097]     It should be appreciated that the rotary release mechanism formed by the interaction of the indicator gear  230  and the lever opening  420  may be replaced with other linkages. In addition, one or both of the anti-backup plate  266  and firing rod  32  may advantageously include surface treatments (e.g., coating, knerling, sandblasted texture, ridges, etc.) to enhance the frictional engagement therebetween.  
         [0098]     Opening Lockout.  
         [0099]     In  FIG. 26 , the surgical stapling and severing instrument  10  is in its initial open condition with both closure and firing triggers  26 ,  34  forward and the linked rack  200  retracted. As described above, in this unfired condition, the indicator gear  230  presents its opening  240  in circular ridge  242  to the upper surface  244  of the locking arm  172 , which is ordinarily rotated downward out of the opening  240  by the action of the compression spring  180  between the housing structure  182  and the intermediate distal side  178  of the closure release button  38 . In  FIG. 26 , the closure release button  38  has been depressed, causing the upper surface  244  into the opening  240 . In  FIG. 27 , the closure trigger  26  and the locking arm  172  are in clamping abutment after closing with the closure trigger  26  against the pistol grip  36  and the firing trigger  34  swung into position for firing. The closure release button  38  is not depressed, as noted by the expanded closure spring  180 . The upper surface  244  of the locking arm  172  is swung below circular ridge  242  and indicator gear  230  is unlocked and free to rotate counterclockwise. The downward movement of locking arm  172  unlocks the indicator gear  230  and connected linked transmission firing mechanism  150  and allows the firing trigger  34  to be actuated. Thus, as the indicator gear  230  continues to rotate with further firing, the closure release button  38  is precluded from releasing the clamped closure trigger  26 .  
         [0100]     Position Indicator and Release Mechanism.  
         [0101]     In  FIG. 28 , a surgical stapling and severing instrument  610  has the indicator retraction knob replaced by an alternate indicator device  640  upwardly extended to present a top-accessible retraction lever  642  that functions as a stuck firing retractor that may be readily actuated by either hand. The instrument is shown opened and unfired, as indicated by the distally forward closure and firing triggers  26 ,  34  and the open end effector  12 . When firing has not commenced, the retraction lever  642  is normally distally rotated adjacent to the handle housing  154 . The indicator  640  may be coupled (not shown) to the previously described idler gear  220  and a firing mechanism  150  as described previously in which the retraction lever  642  would rotate proximally as the linked transmission is fired, presenting a visual indication of firing as well as allowing a way of assisting automatic retraction by applying a manual distal force thereto as a rotary position indicator, the direction of rotation must be reversed so it must be attached to the idler gear  220  for this embodiment.  
         [0102]     In  FIG. 29 , another alternate firing mechanism  650  incorporates the afore-described top-accessible retraction lever  642  and indicator device  640  that is coupled to an indicator gear  660  having first and second dwell areas  662 ,  664  within a toothed area  668 . The first dwell area  662  is presented to the idler gear  220  when the retraction lever  642  is at its distal position adjacent to the handle housing  154 . Thereby, the idler gear  220  is allowed free clockwise and counterclockwise rotation as driven by the longitudinally moving linked rack  200 . Should the E-beam  80  (not shown in  FIG. 29 ) become stuck within the end effector  12  for any reason and cannot be withdrawn proximally by the combination tension/compression spring  184 , the retraction lever  642  may be pulled proximally by the surgeon to rotate the indicator gear  660  clockwise, as viewed from the left. This rotational movement of the retraction lever  660  rotates the indicator gear  660  and brings a curved tooth segment  670  that is between the first and second dwell  662 ,  664  into contact with the teeth of the idler gear  220  to operably couple the retraction lever  642  to the firing mechanism  650 .  
         [0103]     Once coupled, the surgeon may apply extra force to the retraction lever  642  to retract the firing mechanism  650 , thereby rotating the idler gear  220  counterclockwise and longitudinally moving the linked rack  200  proximally to retract the E-beam  80 . As the retraction lever  642  is further rotated to the position of  FIG. 30 , the idler gear  220  disengages with the curved tooth segment  670  and is decoupled from the retraction lever  642  by second dwell area  664 . At this point, the application of force has freed the stuck firing mechanism  650  and the combination tension/compression springs  184  will fully retract the linked rack  200 .  
         [0104]     An alternate design (not shown) involves the addition of a one way slip clutch such as a Sprague clutch or an equivalent (not shown) between the retraction lever  642  and the indicator gear  660 . In the previous design, the range of motion of the retraction lever  642  is limited by contact with the handle housing  154  at each end of the range or motion less than a full revolution. This limits the distance that the firing system  650  can be retracted for one movement of the retraction lever  642 . The addition of the one way slip clutch between the retraction lever  642  and indicator gear  660  allows the retraction lever  642  to operably engage with the indicator gear  660  as the retraction lever  642  rotates back (distal to proximal) and disengages as the lever moves forward (proximal to distal). This ensures full retraction of the firing mechanism  650  by allowing multiple pulls on the retraction lever  642 . Second dwell area  664  may be removed from the indicator gear  660  to ensure more tooth to tooth engagement. Additionally, the incorporation of a clutch mechanism allows the retraction lever to be rotated adjacent to the handle after use.  
         [0105]     In use, the surgeon positions the end effector  12  and shaft  18  through the cannula or a trocar to a surgical site, positioned the anvil  14  and elongate channel  16  as opposing jaws to grasp tissue to be stapled and severed. Once satisfied with the position of end effector  12 , the closure trigger  26  is full depressed toward the pistol grip  36  of the handle  20 , causing the upper portion  160  of the closure trigger  26  to lock against a locking arm  172  that is pivotally attached to the closure release button  38 . Then, the firing trigger  34  is depressed and released a predetermined number of times to effect full firing travel to drive a firing rod  32  down the shaft  18  to the E-beam  80  in the end effector  12 . During firing, the anti-backup mechanism  250  is in a locked condition, with an anti-backup plate  266  allowed to tip back, binding any proximal motion of the firing rod  32 . The distal firing motion is imparted to the firing rod  32  by a linked transmission firing mechanism  150  that includes linked rack  200  proximally attached to the firing rod  32 , with each link  196   a - d  pinned to adjacent links  196   a - d  such that bending is allowed down into the pistol grip  36  but not upward, forming a rigid structure when straight with a force imparted above the pivot pins  310  between links  196   a - d . Specifically, a traction biasing mechanism  210  coupled to the firing trigger  34  includes a biasing wheel  278  that is frictionally coupled the handle housing  154  such that a distal firing motion imparts an engaging bias to the pawl  270 , urging the pawl  270  into engagement with the linked rack  200 . At the end of the stroke, the pawl  270  is lifted from firing engagement with link  196  by being brought into contact with angled surface  284  of the closure yoke  162 . A return motion of the firing mechanism  150  causes the biasing wheel  278  to impart a reversing bias to the pawl  270 , holding pawl  270  above the linked rack  200  that is thereby held in place by the anti-backup mechanism  250 . Upon full firing travel, the indicator gear  230  includes the curved ramp  430  that trips the anti-backup release lever  248  that forces the anti-backup plate  266  into an unlocked condition, allowing the linked rack  200 , and thus the firing rod  32 , to be withdrawn by a compressive force stored in a combination tension/compression spring  184 . Thereby, the linked rack  200  is withdrawn into the handle grip  36 . Alternatively, during the firing strokes, the surgeon may depress the anti-backup release button  42  that causes the anti-backup release lever to tip. The indicator knob  40  may advantageously allow the surgeon to know how far firing has progressed and to assist in retracting the E-beam  80  that has encountered binding.  
         [0106]     While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art.  
         [0107]     For instance, while a surgical stapling and severing instrument  10  is described herein that advantageously has separate and distinct closing and firing actuation, providing clinical flexibility. However, it should be appreciated that applications consistent with the present invention may include a handle that converts a single user actuation into a firing motion that closes and fires the instrument.  
         [0108]     In addition, while a manually actuated handle is illustrated, a motorized or otherwise powered handle may benefit from incorporating a linked rack as described herein, allowing reduction of the size of the handle or other benefits. For instance, while partially stowing the linked rack into the pistol grip is convenient, it should be appreciated that the pivot connection between links allows for stowing the link parallel to the straight portion defined by the shaft and the barrel of the handle.  
         [0109]     As another example, while a linked rack  200  is advantageously depicted, a surgical instrument having a nonbendable rack may also benefit from an anti-backup mechanism.  
         [0110]     As yet another example, it should be appreciated that a circular firing rod  32  is illustrative and that many cross sectional shapes may be employed.