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.

Description:
FIELD OF THE INVENTION  
       [0001]     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  
       [0002]     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.).  
         [0003]     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.  
         [0004]     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.  
         [0005]     One specific advantage of being able to close upon tissue before firing is that the clinician is able to verify via an endoscope that a desired location for the cut has been achieved, including a sufficient amount of tissue has been captured between the 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.  
         [0006]     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, 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.  
         [0007]     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. However, it is believed that the conversion of the reciprocating motion of the firing trigger directly into a solid rack by a pawl constrains design options for a desired amount of firing motion during each firing stroke. In addition, these known surgical stapling instruments with multiple-stroke firing mechanisms do not have the advantages of a separate closure and firing action.  
         [0008]     Consequently, a significant need exists for a surgical stapling instrument that uses multiple firing strokes to achieve a desired length of severing and stapling with a desired relationship of firing stroke travel to longitudinal firing motion produced for an end effector.  
       BRIEF SUMMARY OF THE INVENTION  
       [0009]     The invention overcomes the above-noted and other deficiencies of the prior art by providing a surgical stapling and severing instrument having a rotary transmission that transfers a sequence of multiple firing strokes while preventing backup of a firing member. Thereby, an end effector of the instrument requiring increased firing forces and/or increased firing travel may be readily fired with a multiple stroke firing trigger. Yet, the instrument has a separate closure capability that allows a surgeon to position tissue without necessarily firing the end effector.  
         [0010]     In one aspect of the invention, a surgical instrument has an end effector that is responsive to a longitudinal firing motion to perform a surgical operation. A user causes movement in a firing actuator to create the firing motion that is selectively transferred by a firing mechanism. Specifically, a cam disk has a plurality of cam lobes about at least a portion of its circumference that are respectively engaged by a drive wedge coupled to the firing actuator when making a firing motion. The cam disk is coupled to a rack by gear engagement to translate this intermittent rotational motion into the longitudinal firing motion.  
         [0011]     In another aspect of the invention, a surgical instrument has an end effector that severs and staples tissue. In particular, a staple applying assembly distal has an anvil having a staple forming surface moveable from an open position spaced away from a plurality of staples to a closed position adjacent to the plurality of staples. A staple applying mechanism has a rotary cam member with at least one cam lobe associated with at least one coupling member such that rotation of the rotary cam member causes the application of at least a portion of the staples from the staple applying assembly. Thereby, a multiple stroke firing may be used to sever and staple tissue.  
         [0012]     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  
       [0013]     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.  
         [0014]      FIG. 1  is a perspective view of a surgical stapling and severing instrument having an open end effector.  
         [0015]      FIG. 2  is a left side elevation view in cross section along lines  2 - 2  of the open end effector of  FIG. 1 .  
         [0016]      FIG. 3  is a perspective view of the open end effector of  FIG. 1 .  
         [0017]      FIG. 4  is an exploded, perspective view of an implement portion of the surgical stapling and severing instrument of  FIG. 1 .  
         [0018]      FIG. 5  is an exploded, perspective view of a handle of the surgical stapling and severing instrument of  FIG. 1 .  
         [0019]      FIG. 6  is a left side view in elevation of the handle of the surgical stapling and severing instrument of  FIG. 1  in an open condition with a left portion of a handle housing removed to expose a firing mechanism including a rotary transmission for multiple firing strokes.  
         [0020]      FIG. 7  is a right side view in elevation of the handle of  FIG. 6  with a right portion of the handle portion removed to expose a closure mechanism and anti-backup features.  
         [0021]      FIG. 8  is a downward perspective view of the handle of  FIG. 7 .  
         [0022]      FIG. 9  is a side elevation view of the handle of  FIG. 6  with the closure trigger closed and the firing trigger omitted to expose a firing drive wedge and cam lobes in a cam disk.  
         [0023]      FIG. 10  is a downward perspective view of the firing drive wedge and cam lobes of  FIG. 9 .  
         [0024]      FIG. 11  is an aft perspective view of a rotary transmission firing mechanism of the handle of  FIG. 1 .  
         [0025]      FIG. 12  is a side elevation view of the handle of  FIG. 6  in a closed and fired condition with a small idler gear of the rotary transmission firing mechanism omitted to expose an anti-backup pendulum contacting a solid rack. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     Turning to the Drawings, wherein like numerals denote like components throughout the several views,  FIGS. 1-4  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.  
         [0027]     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 . 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 .  
         [0028]     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 release button  38  ( FIG. 4 ), whose operation is described more fully below, and thereafter repeat the procedure to clamp tissue.  
         [0029]     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.  
         [0030]     In  FIG. 1 , after firing the surgical stapling and severing instrument  10 , a closure release lever  40  is activated to retract the firing mechanism. Depressing the closure release lever  40  disengages a rotary transmission firing mechanism  42  within the handle  20 , enabling a spring  172  to retract the firing rod  32  from the end effector  12 .  
         [0031]     Implement Portion Including an E-Beam End Effector.  
         [0032]     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. 1-4 . The anvil  14  of end effector  12  responds to the closure motion from the handle  20  that is transferred longitudinally and distally by the closure tube  24 . The elongate channel  16  slidingly engages the translating and closing anvil  14  to form opposing jaws, and the frame  28  fixedly engages the stationary channel  16  to form a rigid attachment to the handle  20 . The closure tube  24  engages the anvil  14  distal to the pin in slot connection between the anvil  14  and elongate channel  16 . Thus, a distal movement of the closure tube  24  relative to the frame  28  effects closure and a proximal movement relative to the frame  28  effects opening of the end effector  12 .  
         [0033]     With particular reference to  FIG. 4 , the implement portion  22  also includes components that respond to a firing motion from the handle  20 , specifically of the firing rod  32  (not shown in  FIG. 4 ) that couples a longitudinal motion between the firing mechanism  42  in the handle  20  and the implement portion  22 . In particular, the firing rod  32  (shown disassembled in  FIG. 5 ) rotatably engages a firing trough member  46  slidably located within a longitudinal recess  48  in frame  28 . Firing trough member  46  moves longitudinally within frame  28  in direct response to longitudinal motion of firing rod  32 . A longitudinal slot  50  in the closure tube  24  operably couples with the rotation knob  30  (not shown), the longitudinal slot  50  further allowing the rotation knob  30  to engage the frame  28  at a small longitudinal slot  52  therein to effect rotation. A tab is located in front of slot  50  on the closure tube  24  and the tab is bent down into slot  52  in the frame  28  to couple the closure tube  24  to the frame  28 . The length of the longitudinal slot  50  in the closure tube  24  is sufficiently long as to allow relative longitudinal motion with the rotation knob  30  to accomplish closure motions respectively.  
         [0034]     The distal end of the frame trough member  46  is attached to a proximal end of a firing bar  56  that moves with the frame  28 , to distally project an E-beam  60  into the end effector  12 . The end effector  12  includes a staple cartridge  62  that is actuated by the E-beam  60  that causes staples to be drive up from staple apertures  64  of the cartridge  62  into contact with staple forming grooves  68  of the anvil  14 , creating formed “B” shaped staples. With particular reference to  FIG. 3 , the staple cartridge body  86  further includes a proximally open, vertical slot  70  for passage of a vertically oriented cutting surface provided along a distal end of E-beam  60  to cut tissue while being stapled.  
         [0035]     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.  
         [0036]     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.  
         [0037]     Multi-Stroke Firing Handle.  
         [0038]     In  FIGS. 5-8 , the handle  20  responds to actuation of the closure trigger  26  and firing trigger  34  to generate respectively the closure and firing motions to the implement portion  22 . With regard to the closure motion, the closure trigger  26  includes an upper portion  76  that includes three lateral apertures, a forwardly positioned pin hole  78 , a lower, aft pivot hole  80 , and a center cutout  82 . Three rods laterally oriented between and engaged to right and left half shells  84 ,  86  of a handle housing  88  (with the right half shell  84  shown in  FIGS. 5-6  and the left half shell  86  shown in  FIG. 7 ). In particular, an aft rod  90  passes through the aft pivot hole  84  of the upper portion  80  of the closure trigger  26 , and thus the closure trigger  26  pivots about the aft rod  90 . A front rod  92 , which is distally positioned to the aft rod  90 , and a top rod  94 , which is above the front rod  92 , pass through the center cutout  86 , which is shaped to constrain movement of the closure trigger  26  by contacting the front and top rods  92 ,  94  at each extreme of trigger travel. Thus, the center cutout  86  includes a vertical portion, whose bottom surface contacts the front rod  92  when the closure trigger  26  is forward (distal), and includes an upper, proximally sloped portion, whose top and forward surfaces contact the top rod  94  respectively when the closure trigger  26  is at its forward, relaxed position and its proximal, actuated position.  
         [0039]     A closure yoke  96 , which engages the closure tube  24 , is longitudinally slidingly received within the handle housing  92  and is engaged at its distal end to a proximal end of the closure tube  24 , thus transferring longitudinal closure motion to the closure tube  24  and hence to the anvil  14  for closing the end effector  12 . This engagement allows rotation of the closure tube  24  while the closure yoke  96  does not rotate. Above this engagement, a lateral pin hole  100  is coupled to a closure link  102  by a front pin  104 , with the other end of the closure link  102  coupled to the pin hole  82  of the closure trigger  26  via an aft pin  106 .  
         [0040]     A triangular spacer  120  includes holes  122 ,  124 ,  126  to receive the rods  90 ,  92 ,  94  respectively and is sandwiched between a cam disk  130  and the upper portion  80  of the closure trigger  26 . Cam disk  130  rotates about the front rod  92  and includes a semi-circular slot  132  that receives the aft and top rods  90 ,  94 . A central hole  134  receives front rod  92 . To the left of the cam disk  130 , a rod hole  136  at an upper end  138  of the firing trigger  34  receives the top rod  94 . Firing trigger  34  rotatably mounts onto rod  94  to sandwich cam disk  130  between the triangular spacer  120  and firing trigger  34 . A distally opened recess  140  in the firing trigger  34  below the rod hole  136  is registered to receive the front rod  92 , allowing the firing trigger  34  to be drawn distally during firing. Actuation of the closure trigger  26  swings the cam link  102  downward into contact with drive wedge pin  184  extending inwardly from firing trigger  34  causing the firing trigger  34  to be partially drawn distally and staging the firing trigger  34  for grasping.  
         [0041]     With particular reference to  FIGS. 5, 9 , and  10 , the cam disk  130  presents a series of cam lobes  142 - 144  ( FIG. 9 ) about the forward portion (when in its unfired state as depicted), specifically along its left side, that are respectively engaged by the firing trigger  34  to impart a top-to-front (counter-clockwise as viewed from the left) rotation to the cam disk  130 . This rotation is transferred through a gear train  150  ( FIGS. 5 and 11 ) of the rotary transmission firing mechanism  42 , beginning with a gear portion  152  about a lower portion of the right side of the cam disk  120  that engages a small idler gear  154 , which thus rotates top to the rear (clockwise) at an increased rate relative to the cam disk  130 . A large idler gear  156  is connected by an idler axle  158  to the small idler gear  154  and thus rotates in the same direction and rate. A second small gear  160  is enmeshed to the larger idler gear  156 , and is thus rotated top to the front (counter-clockwise as viewed from the left) at a greater rate. A fine-toothed large gear  162  is connected by a second axle  164  to the second small gear  160  and thus rotates in the same direction and rate as the second small gear  160 . The gear train  150  thus amplifies the motion of the cam disk  120  by including a double gear reduction feature to provide additional longitudinal firing motion. The fine-toothed large gear  162  engages a gear segment  168  on an underside of a solid rack  170  whose distal end engages the proximal end of the firing rod  32 . The rack  170  has its distal portion longitudinally slidingly received within the closure yoke  96  and its proximal portion longitudinally slidingly received between right and left shell halves  84 ,  86  of the handle housing  88 .  
         [0042]     The selective engagement of the firing trigger  34  to the cam lobes  142 - 144  provides further longitudinal travel by enabling multiple firing strokes of the firing trigger  34 . To prepare the gear train  150  for firing, the cam disk  130  is urged clockwise toward its unfired position by a gear train retraction spring  172  attached to a leftward projecting integral pin  174  formed within an annular recess  176  at a lower proximal edge of the cam disk  120  ( FIGS. 9-10 ). The gear train retraction spring  172  has its other end attached to a pin  178  integral to the handle housing  88 . Activation of the firing trigger  34  rotates cam disk  130  counter-clockwise to elongate the retraction spring  172 . Continued actuation of the firing trigger  34  wraps the elongated retraction spring  172  about the outer diameter of the cam disk  130  as it rotates and into the annular recess  176  (not shown).  
         [0043]     With particular reference to  FIGS. 5, 9 ,  11 , below and distal to the upper end  128  of the firing trigger  34  is a drive wedge pin hole  180  and a proximal pin hole  190 . Drive wedge pin  184  and pin  196  extend inwardly from holes  180  and  190  (respectively) in firing trigger  34 . Drive wedge  182  and a standoff finger  186  are pivotally mounted on drive wedge pin  184  and operably connected by a mousetrap-style spring  188 . An opposing tension spring  194  between drive wedge  182  and pin  196  urge the drive wedge  182 , standoff finger  186 , and spring  188  clockwise ( FIG. 10 ). When firing trigger  34  is actuated ( FIG. 9 ), standoff finger  186  is brought into contact with a center, uncammed circumferential surface of the cam disk  120 , rotating the standoff finger  186 , spring  188  and drive wedge  182  counterclockwise. The counterclockwise motion of standoff finger  186  biases drive wedge  182  into firing engagement with the cam lobes  142 - 144  ( FIG. 9 ).  
         [0044]     With particular reference to  FIG. 12 , when the drive wedge  182  is drawn away from one of the cam lobes  142 - 144  between firing strokes, the cam disk  130  would tend to rotate top to the rear by the action of the gear train retraction spring  172  but for the action of an anti-backup lever  200 . Lateral pins  202 ,  204  of the anti-backup pendulum  200  engage respective right and left shell halves  84 ,  86  of the handle housing  88 . Above the pins  202 ,  204 , an anti-backup tension spring  206  is attached to an integral pin  208  of the right half shell  88  distal to the anti-backup pendulum  200 . With particular reference to  FIG. 5 , a lower foot  210  of the anti-backup pendulum  200  makes frictional contact with an upper surface  212  of the solid rack  170 . When the lower foot  210  of the anti-backup pendulum  200  is drawn proximally by a retracting solid rack  170 , the anti-backup lever  20  approaches a perpendicular engagement to the solid rack  170  that increases the frictional force, locking the solid rack  170 , which is sufficient to overcome the backdriving force provided by the gear train retraction spring  172 . When the solid rack  170  is driven distally by the firing trigger  34 , the lower foot  210  is pushed distally, reducing the friction and allowing firing. Excessive forward movement of the lower foot  210  is prevented by the idler axle  158  and by the urging from the anti-backup tension spring  206 .  
         [0045]     In  FIG. 12 , the release button  38  is pivoted upward about its aft pivot pins  220 ,  222 , raising its distal arm  224  above a proximally directed arm  226  of the anti-backup pendulum  200  allowing distal movement of the lower foot  210  for locking the rack  170  between firing strokes. A clamp locking lever  230  rocks about its lateral pivot pins  232 ,  234  to effect this raising of the release button  38 . In particular, a proximally and upwardly projecting arm  236  of the clamp locking lever  230  slidingly abuts an undersurface of the distal arm  224  of the release button  38 . A distally projecting locking arm  238  of the clamp locking lever  230  locks the closure yoke  96  in its clamped condition. In particular, a tab  240  extending down between the proximally and upwardly projecting arm  236  and the distally projecting locking arm  238  is urged proximally by a tension spring  242  that is also attached to the right half shell  84  of the handle housing  88  at a pin  244 . With reference to  FIGS. 6-7 , the distally projecting locking arm  238  rests upon a step  246  presented on a top, proximal portion of the closure yoke  96 , allowing the closure yoke  96  to be distally moved to transfer the closure motion. A clamp locking notch  248 , which is a distally and upwardly open recess of the step  246 , receives the distally projecting locking arm  238  when the closure yoke  96  reaches its distal actuated position ( FIG. 8, 9 ). Thus, the surgeon may release the closure trigger  26  with the end effector  12  remaining clamped.  
         [0046]     With reference to  FIGS. 5-8 ,  12 , in addition to the afore-described anti-backup feature and closure clamping feature, a firing lockout feature is provided by a firing lockout lever  250 . With the surgical stapling and severing instrument  10  in its initial open and unfired state, the firing lockout lever  250  responds to the closure yoke  96  being retracted by blocking distal, firing movement of the solid rack  170 , as shown particularly in  FIGS. 7 and 8 . The firing lockout lever  250  includes a distally extending arm  252  having a distally ramped upper surface  254  that is aligned with a right edge  256  along the proximal portion of the solid rack  170 . A recessed right edge  258  along the remaining distal portion of the solid rack  170  allows the distally ramped upper surface  254  of the firing lockout lever  250  to rotate upward, pivoting about its proximal lateral pins  260 ,  262  urged by a tension spring  264  connected to a vertical tab  266  that is perpendicularly and proximally attached to the distally extending arm  252 . The other end of the tension spring  264  is connected to an integral pin  268  formed in the right half shell  84  of the handle housing  88  aft of the vertical tab  266 .  
         [0047]     As shown in  FIG. 8 , the distally ramped surface  254  blocks distal movement of the solid rack  170  by being wedged upward by a step  270  formed across the proximal end of the closure yoke  96 , open proximally and upwardly to receive the downwardly pivoting distally extending arm  252  of the firing lockout lever  250 . With the closure yoke  96  moved distally to close the end effector  12  as shown in  FIG. 12 , the right edge  256  of the solid rack  170  is allowed to pass over the distally ramped surface  254  that responds thereto by moving the distally extending arm  252  downward to engage a lower step  272  formed in the closure yoke  96  proximal to the higher and more distal step  270 . The engagement of the firing lockout lever  250  to the lower step  272  has a benefit of preventing retraction (proximal movement) of the closure yoke  96  until the solid rack  170  is fully retracted. Thus, initiating retraction of the firing mechanism  42  advantageously occurs prior to unclamping of the end effector  12 , which may otherwise cause binding in the firing mechanism  42 . Moreover, enough frictional contact may exist between the lower step  272  and the firing lockout lever  250  to advantageously require a two-step procedure to return the surgical stapling and severing instrument  10  to its open and retracted condition. In particular, once the firing mechanism  42  has been retracted by depressing the release button  38 , a slight squeeze on the closure trigger  26  would tend to allow the firing lockout lever  250  to raise to its firing lockout position. Thereafter, the release of the closure trigger  26  may proceed with the firing lockout lever  250  aligned for engagement of the higher step  270  when the closure yoke  96  is fully retracted and thus the end effector  12  opened.  
         [0048]     It should further be appreciated that the rack  170  may be advantageously formed of links that allow a portion proximal to the firing mechanism  42  to be curved into the handle, allowing for a more compact design. Such a linked rack is described in greater detail in co-owned “SURGICAL STAPLING INSTRUMENT INCORPORATING A FIRING MECHANISM HAVING A LINKED RACK TRANSMISSION”, Ser. No. 10/673,930, to Jeffrey S. Swayze, Frederick E. Shelton IV, filed 29 Sep. 2003, which is incorporated herein by reference in its entirety.  
         [0049]     In use, the surgeon positions the end effector  12  and shaft  18  through the cannula of a trocar to a surgical site, positions 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 fully depressed toward the pistol grip  36  of the handle  20 , causing a closure link  102  to advance a closure yoke  96  and thus a closure tube  24  to close the end effector  12 . The distally moved closure yoke  96  presents a clamp locking notch  248  that receives a clamp locking lever  230 , clamping the end effector  12 . Stroking the firing trigger  34  multiple times effects firing of the firing rod  32  by sequentially engaging a drive wedge  182  that is coupled to the firing trigger  34  to cam lobes  142 - 144  on the cam disk  130 . This ratcheting rotation is transferred through the rotary transmission firing mechanism  150  to distally advance the solid rack  170 . With the closure yoke  96  advanced, the rack  170  is able to depress a firing lockout lever  250  out of the way. Between firing strokes, the anti-backup pendulum  100  is drawn into a perpendicular locking contact with the rack  170 , opposing a retraction force imparted by the gear train retraction spring  172  connected to the cam gear  130 . Once full firing travel is achieved, depressing the closure release lever  40  first disengages the anti-backup pendulum  100 , allowing the solid rack  170  to retract and secondly disengages the clamp locking lever  230  from the closure yoke  96  to remove one impediment from opening the end effector  12 . The surgeon squeezes the closure yoke  26  to allow the firing lockout lever  250  to release from the closure yoke  96  and releases the closure trigger  26 , allowing the closure yoke  96  to proximally move to where it holds up the firing lockout lever  250  to lock out the sold rock  170  from firing. Thereafter, the implement portion  22  of the surgical stapling and severing instrument  10  may be removed such as for replacing the staple cartridge  62  in preparation for another operation.  
         [0050]     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.  
         [0051]     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.  
         [0052]     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.  
         [0053]     For instance, while a surgical stapling and severing instrument  10  is described herein that advantageously has separate and distinct closing and firing actuations, 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.  
         [0054]     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.