PATENT ABSTRACT
This application is directed to a surgical stapling device for performing circular anastomoses. The surgical stapling device includes a handle portion, an elongated body portion and a head portion including an anvil assembly and a shell assembly. The handle portion includes a rotatable approximation knob for approximating the anvil and shell assemblies and a firing trigger for actuating a firing mechanism for ejecting staples positioned within the shell assembly. The firing trigger forms one link of a two bar linkage provided to actuate the firing mechanism. The anvil assembly includes a tiltable anvil which will tilt automatically after firing of the device and unapproximating the anvil and shell assemblies. The head portion also includes a retractable trocar assembly which is slidably positioned within an anvil retainer and is automatically advanced and retracted upon attachment and detachment of the anvil assembly onto the anvil retainer, and a lockout tube.

PATENT DESCRIPTION
This application is a continuation of U.S. application Ser. No. 11/208,667, now U.S. Pat. No. 7,234,624, which is a division of U.S. application Ser. No. 10/472,402filed Sep. 17, 2003. now U.S. Pat. No. 6,945,444, which claims priority from PCT application Ser. No. PCT/US02/10792 filed Apr. 3, 2002, which claims priority from provisional application Ser. Nos. 60/281,259, filed Apr. 3, 2001, 60/327,653, filed Oct. 5, 2001 and 60/363,715, filed Mar. 11, 2002, all of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates generally to a surgical stapling device for applying surgical staples to body tissue. More particularly, the present disclosure relates to a surgical stapling device for performing circular anastomosis of hollow tissue organs. 
     2. Background to Related Art 
     Anastomosis is the surgical joining of separate hollow organ sections so that the sections intercommunicate with each other. Typically, the anastomosis procedure follows surgery in which a diseased or defective section of hollow tissue is removed and the remaining end sections are to be joined. Depending on the desired anastomosis procedure, the end sections may be joined by either circular, end-to-side or side-to-side organ reconstruction methods. 
     In a circular anastomosis procedure, the two ends of the organ sections are joined by means of a stapling instrument which drives a circular array of staples through the end sections of each organ section and simultaneously cores any overlapping tissue to free the tubular passage. Examples of instruments for performing circular anastomosis of hollow organs are described in U.S. Pat. Nos. 6,053,390, 5,588,579, 5,119,983, 5,005,749, 4,646,745, 4,576,167, and 4,473,077. Typically, these instruments include an elongated shaft having a handle portion at a proximal end to actuate the instrument and a staple holding component disposed at a distal end. An anvil assembly including an anvil rod with attached anvil head is mounted to the distal end. Opposed end portion, of the organs to be stapled are clamped between the anvil head and the staple holding component. The clamped tissue is stapled by driving one or more staples from the staple holding component so that the ends of the staples pass through the tissue and are deformed by the anvil head. 
     Generally, during an anastomosis procedure, the anvil assembly is separated from the stapling device and positioned within the patient in one of the tissue sections and the stapling device is positioned within the other of the tissue sections. Thereafter, the anvil assembly and the stapling device are reattached to clamp the tissue sections therebetween. Typically, placement requires the use of a detachable trocar for one or both of the anvil assembly and stapling instrument. Because of limitations on visibility and accessibility to the surgical site, it may be difficult and time consuming for a surgeon to attach and detach a trocar to the anvil assembly and/or the stapling device. Moreover, it may be difficult to determine whether the anvil assembly has been properly reattached to the stapling device. 
     SUMMARY 
     In accordance with the present disclosure, a surgical stapling device is disclosed for performing circular anastomoses. The surgical stapling device includes a handle portion, an elongated body portion and a head portion including an anvil assembly and a shell assembly. The handle portion includes a rotatable approximation knob for approximating the anvil and shell assemblies and a firing trigger for actuating a firing mechanism for ejecting staples positioned within the shell assembly. The firing trigger forms one link of a two bar linkage provided to actuate the firing mechanism. The two bar linkage provides the device with an improved mechanical advantage to reduce the firing forces required to fire the device. 
     The head portion includes an anvil assembly including a tiltable anvil which will tilt automatically after firing of the device and unapproximating the anvil and shell assemblies. The tiltable anvil provides a reduced anvil profile to simplify removal of the device after the anastomoses procedure has been performed. The head portion also includes a retractable trocar assembly which is slidably positioned within an anvil retainer and is automatically advanced and retracted upon attachment and detachment of the anvil assembly onto the anvil retainer. The retractable trocar assembly simplifies the anastomoses procedure by eliminating the step of attaching and detaching a trocar to the stapling device. A lockout tube is provided and is positioned about an anvil retainer for releasably engaging an anvil assembly. The lockout tube prevents inadvertent detachment of the anvil assembly from the anvil retainer such as during firing of the stapling device after a predetermined degree of approximation. 
     The surgical stapling device also includes a firing lockout assembly which prevents actuation of the firing trigger until an anvil has been attached to the device and the anvil has been approximated. In one preferred embodiment, the firing lockout assembly includes a trigger lock and a safety bracket which prevents movement of the trigger lock from a locked to an unlocked position until an anvil has been attached to the device and approximated. The lockout assembly also includes a lockout sleeve for returning the trigger lock to a locked position after the device has been fired. The lockout assembly prevents a surgeon from inadvertently firing the device without an anvil attached and mistakenly firing a device which has already been fired and has no staples. 
     The surgical stapling device also includes tactile indication mechanism. In one preferred embodiment, the tactile indication mechanism notifies a surgeon that the device has been fired. In another prefired embodiment, the tactile indicator notifies a surgeon that the anvil head has been unapproximated a distance sufficient to permit the anvil head to tilt, and thus, indicating that the device can be removed from the patient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various preferred embodiments of the presently disclosed surgical stapling device are disclosed herein with reference to the drawings, wherein: 
         FIG. 1  is an elevated side perspective view from the proximal end of one embodiment of the presently disclosed surgical stapling device. 
         FIG. 2  is an elevated side perspective view from the distal end of the surgical stapling device shown in  FIG. 1 ; 
         FIG. 3  is an elevated side perspective view from the proximal end of another preferred embodiment of the presently disclosed surgical stapling device; 
         FIG. 4  is an elevated side perspective view from the distal end of the surgical stapling device shown in  FIG. 3 ; 
         FIG. 5  is an elevated side perspective view from the proximal end of another preferred embodiment of the presently disclosed surgical stapling device; 
         FIG. 6  is an elevated side perspective view from the distal end of the surgical stapling device shown in  FIG. 5 ; 
         FIG. 7  is an elevated side perspective view of the proximal end of the surgical stapling device shown in  FIG. 1  with a handle section removed; 
         FIG. 8  is an elevated side perspective view of the proximal end of the surgical stapling device shown in  FIG. 7  with parts separated; 
         FIG. 8A  is an enlarged view of the indicated area of detail shown in  FIG. 8 ; 
         FIG. 8B  is an elevated side perspective view of the tactile indicator of the surgical stapling device shown in  FIG. 8 ; 
         FIG. 9  is an elevated side perspective view of the central and distal portions of the surgical stapling device shown in  FIG. 1  with parts separated; 
         FIG. 9A  is an elevated side perspective view of another preferred embodiment of the central and distal portions of the surgical stapling device shown in  FIG. 1  with parts separated; 
         FIG. 9B  is a side elevational view of the pusher link shown in  FIG. 9A ; 
         FIG. 9C  is a top view of the pusher link shown in  FIG. 9A ; 
         FIG. 9D  is a cross-sectional view of taken along section line  9 D- 9 D of  FIG. 9C ; 
         FIG. 9E  is a cross-sectional view taken along section line  9 E- 9 E of  FIG. 9B ; 
         FIG. 9F  is a cross-sectional view taken along section lines  9 F- 9 F of  FIG. 9B ; 
         FIG. 9G  is a cross-sectional view taken along section lines  9 G- 9 G of  FIG. 9B ; 
         FIG. 9H  is a cross-sectional view taken along section lines  9 H- 9 H of  FIG. 9B ; 
         FIG. 9J  is a cross-sectional view taken along section lines  9 J- 9 J of  FIG. 9B ; 
         FIG. 9K  is a cross-sectional view taken along section lines  9 K- 9 K of  FIG. 9B ; 
         FIG. 9L  is a cross-sectional view of the elongated body of the surgical stapling device shown in  FIG. 1 ; 
         FIG. 9M  is a top perspective view of the spacer of the surgical stapling device shown in  FIG. 1 ; 
         FIG. 9N  is a bottom perspective view of the spacer shown in  FIG. 9M ; 
         FIG. 10  is an enlarged view of the indicated area of detail shown in  FIG. 9 ; 
         FIG. 11  is an elevated side perspective view of the screw and screw stop assembly and cam adjustment mechanism with parts separated of the surgical stapling device shown in  FIG. 1 ; 
         FIG. 11A  is a side elevational partial cutaway view of the screw and screw stop assembly of the surgical stapling device shown in  FIG. 11 ; 
         FIG. 11B  is a side elevational partial cutaway view of the screw and screw stop assembly and cam adjustment mechanism shown in  FIG. 11 ; 
         FIG. 11C  is a side elevational partial cutaway view of the screw and screw stop assembly and cam adjustment mechanism shown in  FIG. 11  with the cam adjustment mechanism being rotated in a counter-clockwise direction; 
         FIG. 11D  is a side elevational partial cutaway view of the screw and screw stop assembly and cam adjustment mechanism shown in  FIG. 11  with the cam adjustment mechanism being rotated in a clockwise direction; 
         FIG. 12  is a top perspective view of the screw and screw stop assembly and cam adjustment mechanism shown in  FIG. 11 ; 
         FIG. 13  is a bottom perspective view of the screw and screw stop assembly and cam adjustment shown in  FIG. 12 ; 
         FIG. 14  is an elevated side perspective view with parts separated of the rotatable sleeve and firing lockout assembly of the surgical stapling device shown in  FIG. 1 ; 
         FIG. 15  is an elevated side perspective view of the anvil assembly of the surgical stapling device shown in  FIG. 1 ; 
         FIG. 15A  is an elevated perspective view from the distal end of the anvil assembly of the surgical stapling device shown in  FIG. 1 ; 
         FIG. 15B  is a cross-sectional view of the proximal end of the anvil center rod of the surgical stapling device shown in  FIG. 15 ; 
         FIG. 15C  is a side cross-sectional view of a trocar positioned in the distal end of the anvil center rod of the anvil assembly shown in  FIG. 15 ; 
         FIG. 16  is an elevated side perspective view with parts separated of the anvil assembly shown in  FIG. 15 ; 
         FIG. 16A  is a side cross-sectional view of the anvil assembly shown in  FIG. 15 ; 
         FIG. 16B  is a side cross-sectional view of the anvil assembly shown in  FIG. 15  with the backup plate and cutting ring advanced distally; 
         FIG. 17  is an elevated side perspective view from the distal end of the rotatable sleeve and firing lookout assembly shown in  FIG. 14 ; 
         FIG. 18  is an elevated side perspective view from the proximal end of the rotatable sleeve and firing lockout assembly shown in  FIG. 14 ; 
         FIG. 19  is a side elevational view with a handle section removed of the surgical stapling device shown in  FIG. 1  prior to attachment of the anvil assembly; 
         FIG. 19A  is a side view with the handle section removed of the proximal end of the surgical stapling device shown in  FIG. 19 ; 
         FIG. 19B  is a side cross-sectional view of the surgical stapling device shown in  FIG. 19 ; 
         FIG. 19C  is an enlarged view of the indicated area of detail shown in  FIG. 19B ; 
         FIG. 19D  is an enlarged view of the indicated area of detail shown in  FIG. 19B ; 
         FIG. 19E  is a side view of the proximal end of the surgical stapling device shown in  FIG. 19  with the handle sections removed; 
         FIG. 19F  is a top perspective view of the proximal end of the surgical stapling device shown in  FIG. 19  with the handle sections removed; 
         FIG. 19G  is a bottom perspective view of a portion of the proximal end of the surgical stapling device shown in  FIG. 19  with the handle sections removed; 
         FIG. 19H  is a cross-sectional view taken along section lines  19 H- 19 H of  FIG. 19D ; 
         FIG. 20  is a side elevational view with a handle section removed of the surgical stapling device shown in  FIG. 1  with the anvil assembly attached; 
         FIG. 20A  is a side view with a handle section removed of the proximal end of the surgical stapling device shown in  FIG. 20 ; 
         FIG. 20B  is an elevated side cross-sectional view of the surgical stapling device shown in  FIG. 20 ; 
         FIG. 20C  is an enlarged view of the indicated area of detail shown in  FIG. 20B ; 
         FIG. 20D  is an enlarged view of the indicted area of detail shown in  FIG. 20B ; 
         FIG. 20E  is a side view of the proximal end of the surgical stapling device shown in  FIG. 20  with the handle sections removed; 
         FIG. 20F  is a top perspective view of the proximal end of the surgical stapling device shown in  FIG. 20  with the handle sections removed; 
         FIG. 20G  is a side cross-sectional view of the distal end of the shell assembly and the anvil assembly as shown in  FIG. 1  prior to attachment of the anvil assembly to the anvil retainer; 
         FIG. 20H  is a side cross-sectional view of the distal end of the shell assembly and the anvil assembly shown in  FIG. 20G  during attachment of the anvil assembly to the anvil retainer; 
         FIG. 20J  is a side cross-sectional view of the distal end of the shell assembly and the anvil assembly shown in  FIG. 20G  with the anvil assembly attached to the anvil retainer; 
         FIG. 20K  is a enlarged view of the indicated area of detail shown in  FIG. 20J ; 
         FIG. 21  is a side elevational view with a handle section removed of the surgical stapling device shown in  FIG. 1  with the anvil assembly in the approximated position; 
         FIG. 21A  is a side view with a handle section removed of the proximal end of the surgical stapling device shown in  FIG. 21 ; 
         FIG. 21B  is a side cross-sectional view of the surgical stapling device shown in  FIG. 21 ; 
         FIG. 21C  is an enlarged view of the indicated area of detail shown in  FIG. 21B ; 
         FIG. 21D  is an enlarged view of the indicated area of detail shown in  FIG. 21B ; 
         FIG. 21E  is a side view of the proximal end of the surgical stapling device shown in  FIG. 20  with the handle sections removed; 
         FIG. 21F  is a top perspective view of the proximal end of the surgical stapling device shown in  FIG. 21  with the handle sections removed; 
         FIG. 21G  is a bottom perspective view of a portion of the proximal end of the surgical stapling device shown in  FIG. 21  with the handle sections removed; 
         FIG. 21H  is a perspective cross-sectional view of the distal end of the surgical stapling device shown in  FIG. 21 ; 
         FIG. 22  is a side elevational view with a handle section removed of the surgical stapling device shown in  FIG. 1  with the anvil assembly attached and the firing trigger actuated; 
         FIG. 22A  is a side view with a handle section removed of the proximal end of the surgical stapling device shown in  FIG. 22 ; 
         FIG. 22B  is a side cross-sectional view of the surgical stapling device shown in  FIG. 22 ; 
         FIG. 22C  is an enlarged view of the indicated area of detail shown in  FIG. 22B ; 
         FIG. 22D  is an enlarged view of the indicated are of detail shown in  FIG. 22B ; 
         FIG. 22E  is a side view of the proximal end of the surgical stapling device shown in  FIG. 22  with the handle sections removed; 
         FIG. 22F  is an enlarged view of the indicated are of detail in  FIG. 22E ; 
         FIG. 23  is a side elevational view with a handle section removed of the surgical stapling device shown in  FIG. 1  with the anvil assembly attached after the device has been fired; 
         FIG. 23A  is a side view with a handle section removed of the proximal end of the surgical stapling device shown in  FIG. 23 ; 
         FIG. 23B  is a side cross-sectional view of the surgical stapling device shown in  FIG. 23 ; 
         FIG. 23C  is an enlarged view of the indicated area of detail shown in  FIG. 23B ; 
         FIG. 23D  is an enlarged view of the indicated area of detail shown in  FIG. 23B ; 
         FIG. 23E  is a side view of the proximal end of the surgical stapling device shown in  FIG. 23E  with the handle sections removed; 
         FIG. 23F  is a top perspective view of the proximal end of the surgical stapling device shown in  FIG. 23  with the handle sections removed; 
         FIG. 23G  is a bottom perspective view of a portion of the proximal end of the surgical stapling device shown in  FIG. 23  with the handle sections removed; 
         FIG. 24  is a side elevational view with a handle section removed of the surgical stapling device shown in  FIG. 1  with the anvil assembly unapproximated and the anvil head tilted; 
         FIG. 24A  is a side view with a handle section removed of the proximal end of the surgical stapling device shown in  FIG. 24 ; 
         FIG. 24B  is a side cross-sectional view of the surgical stapling device shown in  FIG. 24 ; 
         FIG. 24C  is an enlarged view of the indicated area of detail shown in  FIG. 24B ; 
         FIG. 24D  is an enlarged view of the indicated area of detail shown in  FIG. 24B ; 
         FIG. 24E  is a side cross-sectional part phantom view of the distal end of the anvil assembly shown in  FIG. 1  with the anvil head partially tilted; 
         FIG. 24F  is a side cross-sectional part phantom view of the distal end of the anvil assembly shown in  FIG. 24E  with the anvil head in a fully tilted position; 
         FIG. 24G  is a side view of the proximal end of the surgical stapling device shown in  FIG. 24 ; 
         FIG. 24H  is an enlarged view of the tactile indicator and screw stop of the surgical stapling device shown in  FIG. 1  during unapproximation of the anvil assembly at a location where the anvil head is able to fully tilt; 
         FIG. 25  is a front perspective view of one embodiment of the presently disclosed surgical stapling device in the unapproximated position; 
         FIG. 26  is a perspective view of the head portion of the surgical stapling device shown in  FIG. 25  in the approximated position; 
         FIG. 27  is a rear perspective view of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 28  is a top view of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 29  is a side view of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 30  is a side perspective view of the surgical stapling device shown in  FIG. 25  with a section of the stationary handle removed; 
         FIG. 31  is a perspective, partial cutaway view of the surgical stapling device shown in  FIG. 25  excluding the anvil assembly with the parts of the handle portion separated; 
         FIG. 31A  is a perspective view of the rear link of the firing mechanism and the safety link of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 32  is a front, perspective, partial cutaway view of the surgical stapling device shown in  FIG. 25  with the stationary handle, trigger and indicator assemblies removed; 
         FIG. 32A  is a rear, perspective view of the proximal portion of  FIG. 32 ; 
         FIG. 33  is an enlarged view of the proximal portion of  FIG. 32 ; 
         FIG. 34  is a perspective view with parts separated of the elongated body portion and the head portion, excluding the anvil, of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 34A  is an enlarged view of the indicated area of detail shown in  FIG. 34 ; 
         FIG. 34B  is an enlarged view of the indicated area of detail shown in  FIG. 34 ; 
         FIG. 35  is a perspective view with parts separated of the proximal end of the pusher link and the indicator connector assembly; 
         FIG. 36  is a perspective view with parts separated of the distal portion of the approximation mechanism and the retractable trocar assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 37  is a top, perspective view of the indicator assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 38  is a top, perspective view with parts separated of the indicator assembly shown in  FIG. 37 ; 
         FIG. 38A  is a bottom perspective view of the indicator assembly shown in  FIG. 37 ; 
         FIG. 39  is a perspective view of the trigger assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 40  is a perspective view with parts separated of the trigger assembly shown in  FIG. 39 ; 
         FIG. 41  is a rear, perspective view of the anvil assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 42  is a front, perspective view of the anvil assembly shown in  FIG. 41 ; 
         FIG. 43  is a rear, perspective view of the anvil assembly shown in  FIG. 41  with a removable trocar attached to the anvil center rod; 
         FIG. 44  is a perspective view with parts separated of the anvil assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 45  is a side cross-sectional view of the anvil assembly and removable trocar shown in  FIG. 43  prior to attachment; 
         FIG. 46  is a side cross-sectional view of the anvil assembly and removable trocar in the attached configuration; 
         FIG. 47  is a side view of the handle portion of the surgical stapling device shown in  FIG. 25  prior to approximation and firing of the device with a section of the stationary handle removed; 
         FIG. 48  is a side cross-sectional view of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 49  is an enlarged view of the indicated area of detail shown in  FIG. 48 ; 
         FIG. 49A  is an enlarged view of the indicated area of detail shown in  FIG. 49 ; 
         FIG. 50  is an enlarged view of the indicated area of detail shown in  FIG. 48 ; 
         FIG. 51  is a side cross-sectional view of the head portion of the surgical stapling device excluding the anvil assembly, with the trocar assembly in an extended position; 
         FIG. 52  is a side cross-sectional view taken along section lines  52 - 52  in  FIG. 50 ; 
         FIG. 53  is a side cross-sectional view of the distal end of the surgical stapling device shown in  FIG. 25  immediately prior to attachment of the anvil assembly to the anvil retainer; 
         FIG. 53A  is a side cross-sectional view of the distal end of the surgical stapling device shown in  FIG. 25  during attachment of the anvil assembly to the anvil retainer; 
         FIG. 54  is a side cross-sectional view of the distal end of the surgical stapling device shown in  FIG. 25  with the anvil assembly spaced from the shell assembly; 
         FIG. 54A  is an enlarged view of the indicated area of detail shown in  FIG. 54 ; 
         FIG. 54B  is an enlarged view of the indicated area of detail shown in  FIG. 54 ; 
         FIG. 55  is a side cross-sectional view of the surgical stapling device shown in  FIG. 25  with the anvil assembly and the shell assembly in the approximated position; 
         FIG. 56  is an enlarged view of the indicated area of detail shown in  FIG. 55 ; 
         FIG. 57  is an enlarged view of the indicated area of detail shown in  FIG. 55 ; 
         FIG. 57A  is an enlarged view of the indicated area of detail shown in  FIG. 57 ; 
         FIG. 58  is a side cross-sectional view of the handle portion of the surgical stapling device shown in  FIG. 25 , after the device has been approximated and during the beginning of the firing stroke of the firing trigger; 
         FIG. 59  is a side cross-sectional view of the handle portion of the surgical stapling device shown in  FIG. 25  after the device has been approximated and during the end of the firing stroke of the firing trigger; 
         FIG. 60  is a side cross-sectional view of the handle portion of the surgical stapling device shown in  FIG. 25  after the firing stroke of the firing trigger; 
         FIG. 61  is a side cross-sectional view of the handle portion of the surgical stapling device shown in  FIG. 25  after the firing stroke of the firing trigger with the trigger released; 
         FIG. 62  is a side cross-sectional view of the head portion of the surgical stapling device shown in  FIG. 25  in the approximated position; 
         FIG. 63  is a perspective view of the anvil assembly of the stapling device shown in  FIG. 25  with the anvil head and anvil removed; 
         FIG. 64  is a side view of the anvil assembly of the stapling device shown in  FIG. 25  with portions of the anvil head assembly in phantom; 
         FIG. 65  is a side cross-sectional view of the head portion of the surgical stapling device shown in  FIG. 25  during the firing stroke of the device; 
         FIG. 66  is a side view with parts in phantom of the anvil assembly during the firing stroke of the stapling device; 
         FIG. 67  is a side view of the anvil assembly shown in  FIG. 66  with the anvil head assembly in a partially tilted position; 
         FIG. 68  is a side view of the anvil assembly shown in  FIG. 66  in a fully tilted position; 
         FIG. 69  is a bottom perspective view of the indicator of the indicator assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 70  is a bottom view of the indicator of the indicator assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 71  is a top view of the indicator arm of the indicator assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 72  is a bottom view of the indicator plate of the indicator assembly of the surgical stapling device shown in  FIG. 25 ; 
         FIG. 73  is a top view of the indicator assembly of the surgical stapling device shown in  FIG. 25  prior to anvil attachment and approximation of the device; 
         FIG. 74  is a top view of the indicator assembly of the surgical stapling device shown in  FIG. 25  after the anvil assembly has been attached but prior to approximation of the device; and 
         FIG. 75  is a top view of the indicator assembly of the surgical stapling device shown in  FIG. 25  after the anvil assembly has been attached and the device has been approximated. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the presently disclosed surgical stapling device will now be described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views. 
       FIGS. 1-6  illustrate one preferred embodiment of the presently disclosed surgical stapling device shown generally as  10 . Briefly, surgical stapling device  10  includes a proximal handle portion  12 , an elongated central body portion  14  including a curved elongated outer tube  14   a , and a distal head portion  16 . Alternately, in some surgical procedures e.g., the treatment of hemorrhoids, it is desirable to have a substantially straight central body portion. See  FIGS. 3 and 4 . Moreover, the length and or the diameter of body portion  14  and head portion  16  may be varied to suit a particular surgical procedure. See  FIGS. 5 and 6 . Throughout this description, the term “proximal” will refer to the portion of the instrument closest to the operator and the term “distal” will refer to the portion of the instrument furthest from the operator. 
     Handle portion  12  includes a stationary handle  18 , a firing trigger  20 , a rotatable approximation knob  22  and an indicator opening  24 . Stationary handle  18  is preferably formed from thermoplastic handle sections  18   a  and  18   b , e.g., polycarbonate, which together define a housing for the internal components of handle portion  12 . Handle sections  18   a  and  18   b  are preferably secured together by sonic welding. Alternately, other known securement techniques may be employed including screws, adhesives, snap-fit connectors, etc. The internal components of handle portion  12  will be discussed in detail below. A cushioned and/or resilient slip resistant grip  19  is fastened to or included as part of handle sections  18   a  and  18   b  and firing trigger  20 , preferably using an overmolding procedure. Grip  19  may be formed from neoprene or rubber. Alternately, other suitable materials and joining techniques may be employed. A pivotally mounted trigger lock  26  is fastened to handle portion  12  and is manually positioned to prevent inadvertent firing of stapling device  10 . Indicator opening  24  defines an opening or translucent surface which facilitates viewing of an internally positioned indicator which identifies whether stapling device  10  is in a fire ready position or not. 
     Head portion  16  includes an anvil assembly  30  and a shell assembly  31 . Each of these assemblies will be discussed in detail below. Except where otherwise noted, the components of surgical device  10  are formed from thermoplastics including polycarbonates and metals including stainless steel and aluminum. The particular material selected to form a particular component will depend upon the strength requirements of the particular component. For example, the anvil will be formed from a metal, such as stainless steel, and the stationary handle will be formed from a thermoplastic such as polycarbonate. Alternately, other materials not listed above, which preferably can withstand sterilization procedures, may be used to form components of stapling device  10  provided the materials are suitable for surgical use and meet the strength requirements of the particular component. 
       FIGS. 7 and 8  illustrate the internal components of handle portion  12  of surgical stapling device  10 . Handle portion  12  houses an indicator mechanism, a lockout mechanism, the proximal components of an approximation mechanism and a firing mechanism and other mechanisms for obtaining safe and effective operation of the surgical stapling device. Each of these mechanisms will be described in detail hereinbelow. 
     Approximation Mechanism 
     Referring to  FIGS. 7-14 , the approximation mechanism includes approximation knob  22 , a rotatable sleeve  33  ( FIG. 14 ), a screw  32 , first and second screw extensions  34  and  36  ( FIG. 9 ), respectively, and anvil retainer assembly  38  ( FIG. 10 ). Rotatable sleeve  33  includes a small diameter cylindrical hollow body portion  40  and a large diameter hollow body portion  42 . Body portions  40  and  42  define a central bore  33   a . Body portion  42  includes an annular groove  44  dimensioned to receive an inwardly extending annular flange  46  ( FIG. 7 ) formed on an internal wall of stationary handle  18 . Engagement between groove  44  and flange  46  axially fixes sleeve  30  within stationary handle  18  while permitting relative rotation. The proximal end of hollow body portion  40  of rotatable sleeve  33  extends through an opening formed in the proximal end of stationary handle  18  and includes diametrically opposed elongated ribs  48 . Approximation knob  22  includes a cap  22   a  and a body  22   b  defining a bore  49  having diametrically opposed elongated slots  49   a  configured to receive ribs  48  of sleeve  30  such that rotation of knob  22  effects concurrent rotation of sleeve  30 . 
     The proximal end of screw  32  includes a helical channel  50  and is dimensioned to be slidably positioned within central bore  33   a  of rotatable sleeve  33 . A pin  52  ( FIG. 14 ) extends radially through body portion  42  of sleeve  33  into helical channel  50 . Since sleeve  33  is axially fixed with respect to stationary handle  18 , rotation of sleeve  33  about screw  32  causes pin  52  to move along channel  50  of screw  32  to effect axial movement of screw  32  within stationary handle  18 . An axially extending groove  32   a  is formed along the distal portion of screw  32 . Groove  32   a  is dimensioned to receive an indicator link or wire as will be described below. 
     The distal end of screw  32  includes a transverse slot  54 . Top and bottom screw extensions  34  and  36  ( FIG. 9 ) each include a proximally located flexible flat band portion  58  and a distally located flat band portion  60 . The flexibility of top and bottom screw extensions  34  and  36  permits movement of screw extensions  34  and  36  through curved elongated body portion  14 . The proximal end of each band portion  58  includes a hole  62  dimensioned to receive a pin  64  for securing the proximal end of screw extensions  34  and  36  within transverse slot  54  of screw  32 . Alternately, other fastening techniques may be used to secure each band portion  58  to screw  32 , e.g., welding, crimping, etc. Distally located band portion  60  of each screw extension  34  and  36  is dimensioned to be received within a transverse slot  66  formed in a proximal end of anvil retainer  38  ( FIG. 10 ) to fasten anvil retainer  38  to the distal end of screw extensions  34  and  36 . Preferably, band portion  60  is brazed or welded within slot  66 . Alternately, other fastening techniques may be used including screws, crimping, etc. The distal end of anvil retainer  38  includes a plurality of flexible legs  70  which are configured to flex outwardly to receive and engage the anvil assembly as will be discussed in further detail below. 
     In operation, when approximation knob  22  is manually rotated, rotatable sleeve  33  is rotated about the proximal end of screw  32  to move pin  52  along helical channel  50  of screw  32 . Since sleeve  33  is axially fixed to stationary handle  18 , as pin  52  is moved through channel  50 , screw  32  is advanced or retracted within stationary handle  18 . As a result, top and bottom screw extensions  34  and  36 , which are fastened to the distal end of screw  32 , and anvil retainer  38 , which is fastened to the distal end of screw extensions  34  and  36 , are moved axially within elongated body portion  14 . Since anvil assembly  30  is secured to the distal end of anvil retainer  38 , rotation of approximation knob  22  will effect movement of anvil assembly  30  in relation to shell assembly  31  between spaced and approximated positions. 
     Firing Mechanism 
     Referring to  FIGS. 7-9 , the firing mechanism includes firing trigger  20 , a firing link  72  and an elongated pusher link  74 . Firing trigger  20  includes a body portion  76  and a trigger cover  80 . A cushioned gripping surface  82  preferably formed of neoprene or rubber is provided on trigger cover  80 . Cushioned gripping surface  19  provides a non-slip cushioned surface to make actuation of device  10  more comfortable to a surgeon. Body portion  76  of trigger  20  is pivotally connected to a coupling member  86  secured to the proximal end of pusher link  74  by a pivot member  84 . Coupling member  86  may be formed integrally with pusher link  74  or as a separate element fastened thereto. Firing link  72  has a first end pivotally secured to body portion  76  of trigger  20  by a pivot member  87  and a second end pivotally secured within a vertical slot  82  formed between stationary handle half-sections  18   a  and  18   b  of stationary handle  18  by pivot member  79 . Pivot member  79  is free to move vertically within slot  82 . A spring  82   a  is supported within handle  18  to urge pivot member  79  downwardly towards the bottom of slot  82 . Body portion  76  further includes a pair of abutments including an abutment  89  and an abutment  91  which are positioned to engage the distal end of trigger lock  26  in a manner to be described in greater detail below to prevent actuation of trigger  20  prior to approximation of device  10  and after device  10  has been fired. A projection  93  is also formed on body portion  76  of firing trigger  20  and is configured to activate a trigger lock return mechanism of a firing lockout mechanism of surgical stapling device  10  as will be described below. 
     Coupling member  86  which is supported on the proximal end of elongated pusher link  74  includes a flange  104  ( FIG. 9 ). A spring  106 , positioned between an inner wall or abutment within stationary handle  18  and flange  104 , biases pusher link  74  proximally to a retracted, non-fired position. A pair of wings  108  extend radially outwardly from coupling member  86 . Wings  108  are dimensioned to slide along slots  111  ( FIG. 8 ) formed along the internal walls of stationary handle  18  to maintain proper alignment of pusher link  74  within stationary handle  18  during firing of device  10 . 
     The distal end of pusher link  74  includes a pair of engagement fingers  110  which are dimensioned to lockingly engage with members  220  formed in the proximal end of pusher back  186 . Pusher back  186  forms part of shell assembly  31  and will be discussed in greater detail below. Pusher link  74  is preferably formed from a flexible plastic material and can include a plurality of notches  187  which allow the pusher link to bend more easily as it moves through body  14 . Pusher link  74  defines a hollow channel  75  for slidably receiving the approximation mechanism. A flat surface or cutout  74   a  slidably supports screw extensions  34  and  36 . A spacer  77  is positioned within outer tube  14   a  adjacent cutout  74   a  to provide additional support for screw extensions  34  and  36  and pusher link  74  to prevent each component from buckling during actuation. An annular channel  74   b  is formed about pusher link  74  to receive an O-ring seal  74   c . Pusher link  74  is slidably positioned within body portion  14  such that O-ring  74   c  seals the space between pusher link  74  and an internal wall of body portion  14 . Operation of the firing mechanism of the device will be described in detail below. 
       FIG. 9A  illustrates a preferred embodiment of the firing mechanism of the presently disclosed surgical stapling device. In  FIG. 9A , pusher link  74 ′ is modified to reduce the amount of material from which the pusher link is made and yet reduce the bending moment of the pusher link and, accordingly the force required to actuate the firing mechanism. Referring also to  FIGS. 9B-9E , pusher link  74 ′ includes a curved body portion having upper and lower flats  74   a ′ and  74   b ′ and distal and proximal annular end sections  74   f  and  74   e ′. A slot  74   c ′ is formed in upper flat  74   a ′ and is dimensioned to receive an indicator link or wire as will be described in further detail below. Upper flat  74   a ′ is dimensioned to slidably support screw extensions  34  and  36 . Spacer  77 , as discussed above, is positioned adjacent upper flat  74   a ′ to abut screw extensions  34  and  36  ( FIG. 9L ). Pusher link  74 ′ includes a pair of sidewalls  74   d ′ which confine screw extensions  34  and  36 . As shown in  FIG. 9D , preferably sidewalls  74   d ′ extend the length of upper flat  74   a ′ and communicates with annular end sections  74   e ′ and  74   f ′ of pusher link  74 ′. Sidewalls  74   d ′ convey compressive force in order to balance or equalize the compressive force exerted along pusher link  74 ′ in the portions of the pusher link relative to the portions thereof above and below the centerline of outer tube  14   a.    
     When firing trigger  20  is actuated, i.e., pivoted about pivot member  84 , firing link  72  is moved proximally until pivot member  79  engages an abutment surface  307  ( FIG. 11A-D ) formed on screw stop  306 . Thereafter, firing trigger  20  is pushed distally to advance pusher link  74  or  74 ′ distally against the bias of spring  106 . Since the distal end of pusher link  74  or  74 ′ is connected to pusher back  186 , actuation of firing trigger  20  effects advancement of pusher back  186  within shell assembly  31  to eject staples from shell assembly  31  in a manner to be described below. 
     Anvil Assembly 
     Referring to  FIGS. 15-16A , anvil assembly  30  includes an anvil head assembly  120  and an anvil center rod assembly  152 . Anvil head assembly  120  includes a post  122 , an anvil head  124 , a backup plate  126 , a cutting ring  128  and an anvil  129 . Anvil head  124  includes an inner annular recess  134  and an outer annular recess  136 . Post  122  is centrally located within inner annular recess  134  of anvil head  124 . Anvil  129  is supported on anvil head  124  in annular recess  136  and includes a plurality of pockets  140  for receiving and deforming staples. Backup plate  126  includes a central opening  126   b  which is positioned about post  122  within recess  134  defined between post  122  and annular recess  136 . Backup ring  126  includes a raised platform  126   a . Cutting ring  128  includes an opening  128   a  having a configuration substantially the same as platform  126   a . Opening  128   a  is positioned about platform to rotatably fix cutting ring  128   a  on backup ring  126 . Preferably, cutting ring  128  is formed from polyethylene and is fixedly secured to backup plate  126  using, for example, an adhesive. Backup ring  126  is preferably formed from metal. Alternately other materials of construction may be used to construct plate  126  and ring  128 . Cutting ring  126  and backup plate  148  are slidably mounted about post  122 . Backup plate  126  includes a pair of inwardly extending tabs  150  which will be described in further detail below. 
     Anvil center rod assembly  152  includes anvil center rod  154 , a plunger  156  and plunger spring  158 . A first end of center rod  154  includes a transverse throughbore  160  which is spaced radially of a central longitudinal axis of center rod  154 . Post  122  of anvil head assembly  120  also includes a transverse throughbore  162 . A pivot member  164  pivotably secures post  122  to center rod  154  such that anvil head assembly  120  is pivotably mounted to anvil center rod assembly  152 . Plunger  156  is slidably positioned in a bore  154   b  ( FIG. 16A ) formed in the first end of center rod  154 . Plunger  156  includes an engagement finger  168  which is offset from the pivot axis of anvil head assembly  120  and biased into engagement with the base  122   a  of post  122  by plunger spring  158  to urge anvil head assembly  120  to a pivoted position. In a prefired position, tabs  150  formed on backup plate  126  engage a top surface  154   a  ( FIG. 16B ) of center rod  154  to prevent anvil head assembly  120  from pivoting about pivot member  164 . As device  10  is being fired, backup plate  126  and cutting ring  128  are moved deeper into anvil recess  134  of anvil head  124  about post  122  ( FIG. 16B ) by knife  188  ( FIG. 9 ) in a manner to be described in further detail below to move tabs  150  out of engagement with top surface  154   a  of center rod  154  to permit plunger  156  to pivot anvil head assembly  120  about pivot member  164 . 
     A second end of center rod  154  includes a blind bore  170  ( FIG. 15B ) which includes an inwardly tapering opening  170   a  and a spaced annular recess  170   b . Blind bore  170  is dimensioned to receive a removable trocar  157  ( FIG. 15C ). The annular recess is positioned within blind bore  170  and dimensioned to receive an annular rib formed on the trocar (not shown) to secure center rod  154  in engagement with the trocar. Alternately, trocar  157  may be retained within center rod  154  using only a suture  157   a , i.e., no frictional contact is provided between trocar  157  and center rod  154 . This allows for easy removal of trocar  157  from center rod  154  ( FIG. 15C ). The outer surface of center rod  154  includes an annular abutment  175  which defines an annular recess  177 . Annular recess  177  is dimensioned to engage legs  70  of anvil retainer  38  to releasably secure anvil assembly  30  to anvil retainer  38 . A bore  179  extends transversely through center rod  154  and is dimensioned to receive a suture for securing a trocar to the center rod. A collar  181  including a plurality of splines  181   a  is secured about center rod  154 . Splines  181   a  function to align anvil assembly  30  with shell assembly  31  during approximation of the anvil and shell assemblies. 
     Shell Assembly 
     Referring to  FIG. 9 , shell assembly  31  includes a shell  182 , a pusher back  186 , a cylindrical knife  188 , and a staple guide  192 . Shell  182  includes an outer housing portion  194  and an inner guide portion  196 . Outer housing portion  194  defines a throughbore  198  having a distal cylindrical section  200 , a central conical section  202  and a proximal smaller diameter cylindrical section  204 . A plurality of openings  206  are formed in conical section  202 . Openings  206  are dimensioned to permit fluid and tissue passage during operation of the device. A pair of diametrically opposed flexible engagement members  207  are formed on proximal cylindrical section  204  of shell  182 . Engagement members  207  are positioned to be received in openings  209  formed on the distal end of elongated body  14  to secure shell  182  to elongated body  14 . A pair of openings  211  are formed in the proximal end of outer tube  14   a . Openings  211  are dimensioned to receive protrusions (not shown) formed on the internal wall of stationary handle  18  to facilitate attachment of tube  14   a  to handle portion  12 . 
     Pusher back  186  includes a central throughbore  208  which is slidably positioned about inner guide portion  196  of shell  182 . Pusher back  186  includes a distal cylindrical section  210  which is slidably positioned within distal cylindrical section  200  of shell  182 , a central conical section  212  and a proximal smaller diameter cylindrical section  214 . The proximal end of pusher back  186  includes members  220  which are configured to lockingly engage with resilient fingers  110  of pusher link  74  to fasten pusher link  74  to pusher back  186  such that a distal face of pusher link  74  abuts a proximal face of pusher back  186 . 
     The distal end of pusher back  186  defines a pusher  190 . Pusher  190  includes a multiplicity of distally extending fingers  226  dimensioned to be slidably received within slots  228  formed in staple guide  192  to eject staples  230  therefrom. Cylindrical knife  188  is frictionally retained within the central throughbore of pusher back  186  to fixedly secure knife  188  in relation to pusher  190 . Alternately, knife  188  may be retained within pusher back  186  using adhesives, crimping, pins, etc. The distal end of knife  188  includes a circular cutting edge  234 . 
     In operation, when pusher link  74  is advanced distally in response to actuation of firing trigger  20 , as will be described below, pusher back  186  is advanced distally within shell  182 . Advancement of pusher back  186  advances fingers  226  through slots  228  of staple guide  192  to advance staples  230  positioned within slots  228  and eject staples  230  from staple guide  192 . Since knife  188  is secured to pusher back  186 , knife  188  is also advanced distally to core tissue as will be described in more detail below. 
     Cam Adjustment Mechanism 
     Referring to  FIGS. 11-13 , a cam adjustment member  400  is secured by set screw  312  onto a sidewall  306   a  of screw stop  306 , within a recess  306   b  formed in sidewall  306   a . Cam adjustment member  400  includes a circular disc  402  having a throughbore  404 . Throughbore  404  is eccentrically formed through disc  402  and is dimensioned to receive set screw  312 . A smaller notch or hole  406  is also formed in disc  402 . Notch  406  is dimensioned to receive the tip of an adjustment tool (not shown). Recess  306   b  ( FIG. 11A ) includes a forward and a rear shoulder or abutment surface  306   c  and  306   d , respectively, and is dimensioned to receive disc  402  such that the outer edge of disc  402  abuts forward and rear shoulders  306   c  and  306   d.    
     As discussed above, set screw  312  extends through disc  402  and screw stop  306  and engages screw  32  to secure screw stop  306  in an axially fixed position on screw  32 . Cam adjustment member  400  functions to adjust the axial position of screw stop  306  on screw  32 . More specifically, set screw  312  can be loosened to allow disc  402  to rotate within recess  306   b  of screw stop  306  while still remaining axially fixed to screw  32 . Since disc  402  is eccentrically mounted about screw  32  and engages forward and rear shoulders  306   c  and  306   d  of recess  306   b , rotation of disc  402  about fixed set screw  312  will urge screw stop  306  axially along screw  32  to adjust the axial position of screw stop  306  on screw  32 . For example, when disc  402  is rotated in a clockwise direction (as viewed in  FIG. 11D ) identified by arrow “A”, screw stop  306  will be moved axially in relation to screw  32  in the direction indicated by arrow “B” in response to engagement between the outer edge of disc  402  and rear shoulder  306   d  of recess  306   b . Conversely, when disc  402  is rotated in a counter-clockwise direction (as viewed in  FIG. 11C ), identified by arrow “C”, screw stop  306  will be moved axially in relation to screw  32  in the direction indicated by arrow “D” in response to engagement between the outer edge of disc  402  and forward shoulder  306   c  of recess  306   b.    
     When stapling device  10  is in a fully approximated position, i.e., anvil assembly  30  and shell assembly  31  are brought into juxtaposed alignment to define a tissue receiving clearance, screw stop  306  abuts against body portion  42  of the rotatable sleeve  33 . In this position, anvil assembly  30  and shell assembly  31  will be spaced slightly to define the tissue receiving clearance. By providing cam adjustment member  400 , the tissue receiving clearance can be selectively adjusted by adjusting the position of screw stop  306  on screw  32  to be within a desired range. Preferably, cam adjustment member  400  permits adjustment of the tissue receiving clearance of ±0.045 inches, although greater or lesser adjustment capabilities are also envisioned. Typically, adjustments to the tissue receiving clearance will be made by the device manufacturer. A hole or opening (not shown) may be provided in handle portion  12  ( FIG. 1 ) to provide access to cam adjustment member  400 . 
     Retractable Trocar Assembly 
     Referring to  FIGS. 9 and 10 , stapling device  10  includes a retractable trocar assembly slidably positioned within anvil retainer  38 . The retractable trocar assembly includes a trocar assembly  240  and an engagement member  242 . Engagement member  242  may be in the form of a spring clip, as shown. Alternately, other engagement members are envisioned, e.g., spring loaded protrusions, etc. Trocar assembly  240  includes a trocar body  240   a  and trocar tip  240   b . Trocar body  240   a  has a slot  244  which extends through trocar body  240   a  along a portion of its length. Slot  244  is dimensioned to receive engagement member  242 . Trocar tip  240   b  is secured to trocar body  240   a  using, for example screw threads. Alternately, other fastening techniques can be used to secure trocar tip  240   b  to trocar body  240   a . While trocar tip  240   a  is shown rounded or blunt, other tip configurations are envisioned. Trocar tip  240   b  includes a pair of resilient legs  240   c  which deform, i.e., straighten out, as the trocar is pushed through tissue to ramp tissue over anvil retainer  38 . By providing legs  240   c , tissue is less likely to become caught on anvil retainer  38  during use. 
     As shown in  FIG. 10 , engagement member  242  includes a proximal body portion  246  and a pair of distally extending resilient legs  248 . Each leg  248  includes a tapered tip  250  and a proximally facing shoulder  252 . A pin  254  is positioned through openings  256  and  258  formed in body portion  246  of member  242  and trocar  240 , respectively, to secure engagement member  242  within slot  244  of trocar  240 . Pin  254  also extends through an elongated slot  255  formed in anvil retainer  38 , such that the distal and proximal surfaces of slot  255  function as stops to define the fully advanced and fully retracted positions of the retractable trocar assembly. Legs  248  are formed of a resilient material such as spring steel. Alternately, other materials including plastics may be used to form engagement member  242 . In an unbiased position, legs  248  of member  242  extend outwardly of slot  244  of trocar  240  and beyond the outer diameter of anvil retainer  38  such that in the fully advanced position of trocar  240 , shoulders  252  of legs  248  engage a distal end  38   a  of anvil retainer  38  to retain the trocar  240  in the advanced position. See  FIGS. 19H and 20G . 
     Referring to  FIGS. 20G-20K , when the anvil assembly  30  is attached to anvil retainer  38 , anvil center rod  154  of anvil assembly  30  is slid in the direction indicated by arrow “Z” in  FIG. 20G  over tapered tips  250  of legs  248  of engagement member  242  to compress legs  248  inwardly ( FIG. 20H ) into the confines of slot  244  ( FIG. 10 ) such that trocar  240  and member  242  move inside blind bore  170  of center rod  154 . As anvil assembly  30  is forced about trocar  240 , trocar  240  is moved from its extended to its retracted position within anvil retainer  38 . As illustrated, pin  254  moves from a first end  255   a  of slot  255  to a second end  255   b  of slot  255 . 
     When the anvil assembly is disengaged from anvil retainer  38  by pulling the anvil assembly in a direction away from anvil retainer  38 , legs  248  of member  242  flex outwardly to move shoulders  252  of legs  248  of member  242  into annular recess  170   b  of center rod  154  (See  FIG. 20K ). As a result, as anvil assembly  30  is disengaged from anvil retainer  38 , engagement member  242  and thus trocar  240  are pulled distally to move trocar  240  to the advanced position. As discussed above, in the advanced position shoulders  252  of engagement member  242  engage the distal face  38   a  of anvil retainer  38 . 
     The proximal end of trocar  240  includes a transverse slot  241  ( FIG. 10 ). A rigid flexible indicator link or wire  243  has a distal end which is secured within slot  241  of trocar  240  and extends rearwardly through elongated body portion  14  within slot  74   c  ( FIG. 9 ) of pusher link  74  and along slot  32   a  ( FIG. 12 ) in screw  32  into handle portion  12  of stapling device  10 . Wire  243  has a proximal end which is secured to an indicator assembly in handle portion  12  which will be discussed in detail below. 
     Lockout Tube Assembly 
     Referring again to  FIGS. 9 and 10 , a cylindrical lockout tube  270  is slidably positioned about the outer surface of anvil retainer  38  and positioned to extend through inner guide portion  196  of shell  182  and central bore  208  of pusher back  186 . The proximal end of lockout tube  270  includes an annular flange  272 . A cylindrical fitting  273  is secured about the proximal end of lockout tube  270  in the proximal end of bore  208  of pusher back  186 . A biasing member  187  engages flange  272  and urges lockout tube  270  distally to a position in which flange  272  engages fitting  273  ( FIG. 20D ). Biasing member  187  is preferably a torsion spring which is positioned in compression between flange  272  of lockout tube  270  and an abutment formed within pusher link  74 . 
     Lockout tube  270  is positioned about flexible legs  70  of anvil retainer  38  to provide rigidity to legs  70  during approximation of the anvil and cartridge assemblies. Initially, prior to approximation, legs  70  of anvil retainer  38  project from lockout tube  270 . Accordingly, legs  70  are free to flex outwardly to allow attachment and detachment of anvil assembly  30  to anvil retainer  38 . During approximation, legs  70  are withdrawn into lockout tube  270  to clamp legs  70  about center rod  154  of the anvil and prevent removal of the anvil assembly from the anvil retainer. Anvil retainer  38  is withdrawn into lockout tube  270  during approximation until shoulder  38   b  of anvil retainer  38  engages distal face  270   a  of lockout tube  270 . Thereafter, both anvil retainer  38  and lockout tube  270  are retracted against the bias of spring  187  into bore  208  of pusher back  186 . 
     Indicator Assembly 
     Referring to  FIGS. 7 ,  8  and  11 - 13 , an indicator assembly is mounted within stationary handle  18  and includes an indicator plate  500  having an engagement member  501  and indicia (not shown) formed thereon. The indicia is preferably in the form of colored dots which identify whether the device  10  is in a fire-ready condition or not. For example, a green dot may indicate a fire-ready position and a red dot may indicate a fire not ready position. Alternately, other forms of indicia may be used including graphic, written or numeric indicia. Indicator plate  500  is slidably positioned within stationary handle  18  such that the indicia is visible through indicator opening  24 . A biasing member  502 , preferably a coil spring, is secured at one end to an inner wall of stationary handle  18  and at the other end to indicator plate  500 . Biasing member  502  is positioned in tension to urge indicator plate  500  to its forward-most position within stationary handle  18 . 
     A retainer slide  506  is slidably positioned within a pair of grooves  508  formed in screw stop  306  and includes a first abutment surface  509  and a second abutment surface  510 . A substantially rigid indicator link or wire  243  extends from the proximal end of trocar body  240   a  ( FIG. 10 ) and is connected to retainer slide  506  by a set screw  512 . Alternately, other fastening techniques may be employed. Wire  243  translates linear movement of trocar assembly  240  into linear movement of retainer slide  506  when an anvil assembly is being attached to anvil retainer  38 . Accordingly, when anvil assembly  30  is attached to anvil retainer  38  to move trocar  240  from its advanced position to its retracted position, wire  243  effects movement of retainer slide  506  from its forward-most position on screw stop  306  ( FIG. 12 ) to its rearward-most position. 
     As discussed above, screw stop  306  is secured to screw  32  by set screw  312 . When approximation knob  22  is rotated to retract screw  32  into sleeve  30 , screw stop  306  is retracted towards sleeve  30 . After anvil assembly  30  has been attached to anvil retainer  38  and screw  32  has been retracted a predetermined distance, first abutment surface  509  abuts engagement member  501  of indicator plate  500  such that further approximation moves indicator plate  500  against the urging of biasing member  502  to its rearward-most position. In its rearward-most position, the indicia on plate  500  is visible through opening  24  and identifies that device  10  is in a fire-ready condition. 
     It is noted that if device  10  is approximated without an anvil assembly  30  attached to the anvil retainer  38 , retainer slide  506  will remain in its forward-most position on screw stop  306 , abutment surface  509  of retainer slide  506  will not be in position to contact engagement member  501  of indicator plate  500  during approximation of the device and the indicator assembly will remain in a fire-not ready position and indicated as such through opening  24 . 
     Fire Lockout Assembly 
     Referring to  FIGS. 8 ,  14 ,  17 , and  18 , a firing lockout assembly is provided which includes trigger lock  26  ( FIGS. 1 and 8 ), safety bracket  520 , a lockout sleeve  522  and a compression member  523 . Safety bracket  520  includes a forward collar portion  524 , a body portion  526  having an elongated slot  528  and a rear C-shaped portion  530 . Forward collar portion  524  is positioned about the proximal end of screw  32  adjacent and forward of body portion  42  of rotatable sleeve  30 . Compression member  523  includes a plurality of fins  532  which partially define an annular channel  534 , C-shaped portion  530  is positioned within annular channel  534  of compression member  523 . A biasing member  536 , preferably a coil spring, is positioned in stationary handle  18  behind compression member  523  to urge compression member  523  and safety bracket  520  forwardly within stationary handle  18 . 
     Trigger lock  26  ( FIG. 8 ) is pivotally supported between handle sections  18   a  and  18   b  about pivot member  540  and includes an integrally formed locking portion  542  positioned adjacent pivot member  540 . When device  10  is in the unapproximated position, body portion  526  of safety bracket  520  is positioned adjacent or juxtaposed locking portion  542  of trigger lock  26  to prevent trigger lock  26  from pivoting about pivot member  540  from its locking position ( FIG. 1 ). 
     When device  10  is approximated, retainer slide  506  ( FIG. 11 ) moves with screw stop  306  to a position in which second abutment surface  510  engages forward collar portion  524  of safety bracket  520  to move safety bracket  520  rearwardly. In the rearward position of safety bracket  520 , elongated slot  528  is aligned with locking portion  542  of trigger lock  26  to allow trigger lock  26  to be pivoted away from trigger  20  towards stationary handle  18  and permit actuation of firing trigger  20 . 
     It is noted that if an anvil has not been attached to device  10  and retainer slide  506  is in its forward-most position on screw stop  306 , second abutment surface  510  will not be in position to engage forward collar portion  524  of safety bracket  520 , locking portion  542  will abut body portion  526  of safety bracket  520 , and trigger lock  26  will not be pivotable to an unlocked position. 
     Lockout sleeve  522  includes a cylindrical portion  550 , a semi-cylindrical body portion  552  and a forwardly extending arm  554 . A flexible tab  556  extends downwardly from arm  554  and includes a retaining surface  556   a . A drive member  558  extends downwardly from one end of tab  556 . Lockout sleeve  522  is positioned about rotatable sleeve  33 . A biasing member  560  which is preferably a torsion spring is positioned to urge lockout sleeve  522  rearwardly within stationary handle  18 . Lockout sleeve  522  also includes side fins  563  which are received within grooves within stationary handle  18  to confine lockout sleeve  522  to linear movement. 
     When lockout sleeve  522  is positioned within stationary handle  18 , biasing member  560  is compressed between body portion  42  of rotatable sleeve  33  and cylindrical portion  550  of lockout sleeve  522 . Retaining surface  556   a  of flexible tab  556  is positioned to engage a surface  562  ( FIG. 19C ) within stationary handle  18  such that biasing member  560  is maintained in compression. 
     In operation, when firing trigger  20  is actuated, a projection  93  ( FIG. 1 ) formed on trigger actuator  20  moves into engagement with drive member  558  to disengage retaining surface  556   a  of tab  556  from surface  562  within stationary handle  18 . When this occurs, spring  560  moves lockout sleeve  522  rearwardly such that a portion of sleeve  522  engages locking portion  542  of trigger lock  26  to pivot trigger lock  26  from an unlocked position to a locked position. In this post fire locked position, the distal end of trigger lock  26  returns to a position between abutments  89  and  91  to again prevent the inadvertent firing of device  10 . 
     Tactile Indication 
     Referring to  FIGS. 8 ,  8 A,  8 B, and  11 , a tactile indicator  580  is positioned within stationary handle  18  and is movable within a vertical slot  582  between retracted and extended positions. Tactile indicator  580  includes a protrusion  580   a  which is configured to be received within one of two recesses  582   a  and  582   b  formed in slot  582 . In the extended position, tactile indicator  580  is positioned to engage a wing  584  formed on screw stop  306  at a position of unapproximation sufficient to permit the tilt anvil assembly to have tilted. Prior to firing device  10 , tactile indicator  580  is in the retracted position with protrusion  580   a  positioned within recess  582   a . When device  10  is fired, an abutment surface  588  formed on firing link  72  ( FIG. 8 ) engages indicator  580  to move indicator  580  to the extended position such that protrusion  580   a  is positioned in recess  582   a . When device  10  is unapproximated a distance sufficient to allow the anvil head to pivot, wing  584  of screw stop  306  engages indicator  580  to provide an audible and/or tactile indication that such a point of unapproximation has been reached. Thereafter, a surgeon can remove the device from the patient in order to remove the anvil assembly from the anvil retainer, after it has been removed from the patient the surgeon needs to further unapproximate the device further by providing a force to approximation knob  22  sufficient to urge tactile indicator  580  from the extended to the retracted position. 
     Operation of surgical stapling device  10  will now be described in detail with reference to  FIGS. 19-24F . 
       FIGS. 19-19H  illustrate surgical stapling device  10  in the unapproximated or open position prior to attachment of anvil assembly  30  ( FIG. 1 ) to anvil retainer  38 . In this position, screw stop  306  is positioned adjacent coupling  86  which is secured to the proximal end of pusher link  74  and retainer slide  506  is located in its forward-most position on screw stop  306 . Pusher link  74  is urged by spring  106  to its retracted position. Body portion  526  of safety bracket  520  of the fire lockout assembly is urged by spring  560  to a position to prevent trigger lock  26  from pivoting. See  FIG. 19C . Pivot member  79  secured to firing link  72  is positioned in the base of vertical slot  82  by biasing member  82   a  ( FIG. 19E ). Tactile indicator  580  is in its retracted position with protrusion  580   a  positioned within detent  582   a.    
     Referring to  FIGS. 19D and 19H , as discussed above, prior to attachment of anvil assembly  30  to anvil retainer  38 , trocar assembly  240  is in it extended position with trocar tip  240   b  extending outwardly from anvil retainer  38 . Shoulders  252  of engagement member legs  248  abut against distal face  38   a  of anvil retainer  38  to prevent trocar assembly  240  from being forced to its retracted position. 
       FIGS. 20-20F  illustrate surgical stapling device  10  having anvil assembly  30  secured to anvil retainer  38  and in the unapproximated or open position. Referring to  FIG. 20D , when anvil assembly  30  is attached to anvil retainer  38 , anvil center rod  154  is positioned over trocar tip  240   b  and pushed into anvil retainer  38 . When this occurs, legs  248  of engagement member  242  are compressed inwardly to disengage shoulder  252  of legs  248  from engagement with distal face  38   a  of anvil retainer. This allows center rod  154  to be inserted into anvil retainer  38  until the distal ends of flexible legs  70  of anvil retainer  38  are received within annular recess  177  of anvil center rod  154 . As this happens, trocar assembly  240  is moved to its retracted position with pin  254  positioned at the proximal end of slot  255  in anvil retainer  38 . 
     As the trocar assembly is moved to the retracted position, indicator link or wire  243  ( FIGS. 11 and 12 ) moves retainer  506  from its forward-most position on screw stop  306  to its rearward-most position. In the rearward-most position, upon approximation of device  10 , first abutment surface  509  of retainer slide  506  will engage member  501  of indicator plate  500  and abutment surface  510  will engage forward collar position  524  of safety bracket  520 . The remaining components of device  10  are not affected by attachment of anvil assembly  30  to anvil retainer  38 . 
       FIGS. 21-21G  illustrate surgical stapling device  10  with an anvil assembly  30  attached to anvil retainer  38  in the approximated position. As discussed above, anvil assembly  30  is moved to the approximated position from the unapproximated position shown in  FIG. 20  by rotating rotation knob  22 . Rotation of knob  22  causes rotation of cylindrical sleeve  33  which rotates pin  52  within helical channel  50  of screw  32 . Since sleeve  33  is axially fixed, movement of pin  52  within helical channel  50  effects linear retraction of screw  32  into hollow sleeve  33 . The distal end of screw  32  is connected to screw extensions  34  and  36  which are fastened at their distal ends to anvil retainer  38  such linear movement of screw  32  is translated into linear movement of anvil retainer  38  and anvil assembly  30 . 
     Screw stop  306  is secured to screw  32  by set screw  312 . Thus, during approximation of device  10 , screw stop  306  is moved from a forward position within handle  18  ( FIG. 20 ) to a rearward position within handle  18  ( FIG. 21 ). As screw stop  306  is moved from its forward-most position to its rearward-most position, first abutment member  509  on retainer slide  506  engages member  501  of indicator plate  500  and abutment member  510  on retainer slide  506  engages collar portion  524  of safety bracket  520  to move indicator plate  500 , against the bias of spring  502 , and safety bracket  520 , against the bias of spring  536 , rearwardly within handle  18 . Movement of indicator plate  500  rearwardly positions the fire-ready indicia beneath indicator opening  24 . Movement of safety bracket  520  rearwardly aligns elongated slot  528  in body  526  of safety bracket  520  with locking portion  542  of trigger lock  26  such that trigger lock  26  is free to pivot to the unlocked position. 
     It is also noted that in the rearward-most position of screw stop  306 , abutment surface  307  which is formed on the base of screw stop  306  ( FIG. 11A ) and comprises a substantially concave surface is positioned to receive and engage pivot member  79  of firing link  72 . 
       FIGS. 22-22D  illustrate surgical stapling device  10  during the firing stroke of firing trigger  20 . As trigger  20  is compressed towards stationary handle  18 , pivot member  79  engages abutment surface  307  on screw stop  306  and firing trigger  20  is pushed distally. As discussed above, the distal end of firing trigger  22  is connected through coupling member  86  to the proximal end of pusher link  74 . Accordingly, as firing trigger  20  is moved distally, pusher link  74  is moved distally to effect advancement of pusher back  186  within shell assembly  31 . Fingers  190  of pusher back  186  engage and eject staples  230  from staple guide  192 . 
     Cylindrical knife  188  is moved concurrently with pusher back  186  such that knife  188  moves into engagement with cutting ring  128  and backup plate  126 . As discussed above, cutting ring  128  is preferably formed from polyethylene and backup plate  126  is preferably formed from metal. When knife  188  engages cutting ring  128 , it cuts through cutting ring  128  and pushes backup plate  126  deeper into anvil head  124  to move tabs  150  from engagement with top surface  154   a  of center rod  154  ( FIG. 16B ). Anvil head  124  is now free to pivot about member  164  and is urged to do so by plunger  156  ( FIG. 24F ). It is noted that because the anvil assembly is in juxtaposed alignment with shell assembly  31 , the anvil head  14  will not pivot fully until the anvil and shell assemblies have been unapproximated a distance sufficient to allow the anvil head to fully pivot. 
     As illustrated in  FIG. 22C , projection  93  on firing trigger  20  is aligned with drive member  558  of lockout sleeve  522 . When firing trigger  20  is fully actuated, projection  93  engages drive member  588  to deflect tab  556  upwardly to disengage retaining surface  556   a  from surface  562  of inner wall of stationary handle  18 . When this occurs, spring  560  which is in compression drives lockout sleeve  522  rearwardly within handle  18  such that a portion of sleeve  522  engages locking portion  542  of trigger lock  26  to pivot trigger lock  26  from the unlocked position ( FIG. 22C ) to the locked position ( FIG. 23 ). In the locked position the distal end of trigger lock  26  is positioned between abutments  89  and  91 . 
     During actuation of firing trigger  20 , an extension  589  on firing link  72  engages tactile indicator  580  and moves tactile indicator  580  from a retracted to an extended position. In the extended position, indicator  580  is positioned to engage wing  584  of screw stop  306  during unapproximation of the anvil and shell assemblies ( FIG. 22F ). 
       FIGS. 23-23G  illustrate surgical stapling device  10  after firing trigger  20  has been released. As illustrated, biasing member  106  has urged pusher link  74  proximally to its retracted position and trigger lock  26  has been moved to the locked position in the manner discussed above by lockout sleeve  522 . As shown in  FIG. 23D , pusher back  186  has moved, in response to movement of pusher link  74 , proximally to its retracted position. Anvil head  124  has begun to pivot but is prevented from further pivoting by shell assembly  31 . 
       FIGS. 24-24H  illustrates surgical stapling device  10  after it has been fired and unapproximated. As illustrated, anvil head  124  has been moved to the pivoted position by plunger  156  ( FIGS. 24E and 24F ). Screw stop  306  has been advanced from its rearward-most position adjacent safety bracket  520  to its forward-most position adjacent the proximal end of pusher link  74 . Retainer slide  506 , which is supported on screw stop  306 , has moved with screw stop  306  to a forward position. As retainer slide  506  moves forwardly, spring  502  returns indicator plate  500  to its forward-most position and spring  536  returns safety bracket  520  to its forward-most position. As such, indicator plate  500  once again identifies the device as being in a fire not ready condition and safety bracket  520  moves to a position preventing movement of trigger lock  520 . 
     Referring to  FIGS. 24G and 24H , as screw stop  306  is moved from its rearward-most position ( FIG. 23 ) to its forward-most position within stationary handle  18 , wing  584  of screw stop  306  engages tactile indicator  580  at the point of unapproximation at which anvil head  124  pivots ( FIG. 24F ). This contact between screw stop  306  and tactile indicator  580  provides a tactile and/or audible indication to a surgeon that the anvil head  124  has tilted and the device can be removed from the patient. It is noted that by providing additional force to approximation knob  22 , wing  584  of screw stop  306  will force tactile indicator  580  to return to its retracted position to allow device  10  to be fully unapproximated. 
       FIGS. 25-29  illustrate another preferred embodiment of the presently disclosed surgical stapling device shown generally as  610 . Briefly, surgical stapling device  610  includes aproximal handle portion  612 , an elongated central body portion  614  including a curved elongated outer tube  614   a , and a distal head portion  616 . 
     Handle portion  612  includes a stationary handle  618 , a firing trigger assembly  620 , a rotatable approximation knob  622  and an indicator window  624 . Stationary handle  618  is preferably formed from thermoplastic handle sections, e.g., polycarbonate, which together define a housing for the internal components of handle portion  612 . These internal components will be discussed in detail below. A pivotably mounted trigger lock  626  is fastened to handle portion  612  and is manually positioned to prevent inadvertent firing of stapling device  610 . Indicator window  624  defines an opening or translucent surface  628  which facilitates viewing of an internally positioned indicator which identifies a multiplicity of operational positions of the stapling device. 
     Head portion  616  includes an anvil assembly  630  and a shell assembly  631 . Each of these assemblies will be discussed in detail below. Except where otherwise noted, the components of surgical device  610  are formed from thermoplastics including polycarbonates and metals including stainless steel and aluminum. The particular material selected to form a particular component will depend upon the strength requirements of the particular component. For example, the anvil will be formed from a metal, such as stainless steel, and the stationary handle will be formed from a thermoplastic such as polycarbonate. Alternately, other materials not listed above may be used to form components of stapling device  610  provided the materials are suitable for surgical use and meet the strength requirements of the particular component. 
       FIG. 30  illustrates handle portion  612  of surgical stapling device  610  with a section of stationary handle  618  removed to expose the internal components of handle portion  612 . Handle portion  612  houses an indicator mechanism and the proximal components of an approximation mechanism and a firing mechanism. Each of these mechanisms will be described in detail hereinbelow. A cushion non-slip grip  619  is fastened to stationary handle  612 . Grip  619  may be formed from rubber or neoprene and secured to stationary handle  18  using an overmolding process. Alternately, other materials and attachment methods not mentioned here may be used. 
     Referring to  FIGS. 30-36 , the approximation mechanism includes approximation knob  622 , a rotatable sleeve  633 , a screw  632 , first and second screw extensions  634  and  636 , respectively, and anvil retainer  638  ( FIG. 34 ). Rotatable sleeve  633  includes a small diameter cylindrical hollow body portion  640  and a large diameter hollow body portion  642 . Body portion  642  includes an annular groove  644  dimensioned to receive an inwardly extending annular flange  646  formed on an internal wall of stationary handle  618 . Engagement between groove  644  and flange  646  axially fixes sleeve  633  within stationary handle  618  while permitting relative rotation. The proximal end of body portion  640  of rotatable sleeve  633  extends through an opening formed in the proximal end of stationary handle  618  and includes a flat surface  648 . Approximation knob  622  includes a bore  649  configured to receive the proximal end of sleeve  633  such that rotation of knob  622  effects concurrent rotation of sleeve  633 . 
     Screw  632  is dimensioned to be slidably positioned within rotatable sleeve  633 . A helical channel  650  is formed in the proximal end of screw  632 . A pin  652  extends radially through body portion  642  of sleeve  633  into helical channel  650 . Since sleeve  633  is axially fixed with respect to stationary handle  618 , rotation of sleeve  633  about screw  632  causes pin  652  to move along channel  650  of screw  632  to effect axial movement of screw  632  within stationary handle  618 . 
     The distal end of screw  632  includes an extension  654  having upper and lower flat surfaces and a throughbore  656 . Top and bottom screw extensions  634  and  636  each include a flexible flat band portion  658  and a distal semi-cylindrical portion  660 . The flexibility of top and bottom screw extensions  634  and  636  facilitate movement of screw extensions  634  and  636  through curved elongated body portion  614 . The proximal end of each band portion  658  includes an opening  662  dimensioned to receive a pin  664  for securing the proximal end of screw extensions  634  and  636  to extension  654  of screw  632  via throughbore  656 . Each semi-cylindrical portion  660  of screw extensions  634  and  636  includes an outwardly extending projection  666 . When top and bottom screw extensions  634  and  636  are positioned in juxtaposed alignment, semi-cylindrical portions  660  of screw extensions  634  and  636  together define a cylindrical member which is dimensioned to be received within a proximal end of anvil retainer  638 . Projections  666  are dimensioned to be received in openings  668  formed in the proximal end of anvil retainer  638  to fasten anvil retainer  638  to the distal end of screw extensions  634  and  636 . The distal end of anvil retainer  638  includes a plurality of flexible legs  670  which are configured to flex outwardly to receive and engage the anvil assembly as will be discussed in further detail below. 
     In operation, when approximation knob  622  is manually rotated, rotatable sleeve  633  is rotated about the proximal end of screw  632  to move pin  652  along channel  650  of screw  632 . Since sleeve  630  is axially fixed to stationary handle  618 , as pin  652  is moved through channel  650 , screw  632  is advanced or retracted within stationary handle  618 . As a result, top and bottom screw extensions  634  and  636 , which are fastened to the distal end of screw  632 , and anvil retainer  638 , which is fastened to the distal end of screw extensions  634  and  636 , are moved axially within elongated body portion  614 . Since anvil assembly  630  is secured to the distal end of anvil retainer  638 , rotation of approximation knob  622  will effect movement of anvil assembly  630  in relation to shell assembly  631  between spaced and approximated positions. 
     Referring again to  FIGS. 30-35 , the firing mechanism includes firing trigger  620 , a firing link  672 , and an elongated pusher link  674 . Firing trigger  620  includes a pair of trigger plates  676  and  678 , a trigger cover  680 , and a cushioned gripping member  682 . See also  FIGS. 39 and 40 . Gripping member  682  is preferably formed from rubber or neoprene and overmolded onto trigger cover  680 . Alternately, other cushioned non-slip gripping materials may be used and fastened to trigger cover using any known technique, e.g., adhesives. The distal end of each of trigger plates  676  and  678  includes a hinge portion  676   a  and  678   a , respectively, having a hole for receiving a pivot member  684 . Pivot member  684  is dimensioned to extend between hinge portions  676   a  and  676   b  through a bore  677  formed in a connector  686  secured to the proximal end of pusher link  674  to pivotably secure the distal end of firing trigger  620  to the proximal end of pusher link  674 . Alternately, connector  686  may be formed integrally with pusher link  674 . The top surface of each trigger plate  676  and  678  includes a notch  683  dimensioned to receive a locking pin  693  to prevent inadvertent firing of device  610 . 
     Firing link  672  includes a right-side link portion  672   a  and a left-side link portion  672   b  interconnected by a spacer  672   c  ( FIG. 31A ). Each link portion includes a pivot opening  688  at each end thereof and a centrally positioned elongated slot  690 . The space between link portions  672   a  and  672   b  is dimensioned to receive a safety link  692 . The function and operation of safety link  692  will be described in detail below. One end  694  of firing link  672  is pivotably connected between openings  679  ( FIG. 40 ) in trigger plates  676  and  678  about pivot member  696 . The other end  698  of firing link  672  is pivotably connected to stationary handle  618  about pivot member  700 . Pivot member  700  is supported in a vertically oriented pocket  702  (only one is shown) formed along the internal wall of stationary handle  618 . Pivot members  696  and  700  may be formed as pins, integral nubs formed on firing link  672 , or any other structure which provides the desired function. 
     Safety link  692  includes a body portion  692   a  having a guide member  692   b  formed at one end thereof and a bore  692   c  formed at an opposite end thereof. Bore  692   c  is dimensioned to receive a locking pin  693 . Safety link  692  is positioned between right-side link portion  672   a  and left-side link portion  672   b  of firing link  672 . Locking pin  693  is slidably positioned in slots  690  of firing link  672  and guide member  692   b  is slidably positioned in a horizontal slot  695  formed along the internal wall of stationary handle  618 . A biasing member, e.g., coil spring  697 , is secured between end  694  of firing link  672  and a central portion of safety link  692  to bias safety link  692  towards end  694  of firing link  672 . Body portion  692   a  of firing link includes a weakened portion  699 . The purpose of weakened portion  699  will be discussed in detail below. 
     Elongated pusher link  674  includes a flange  704  positioned about its proximal end distally of connector  686 . A spring  706 , positioned between a forward end of stationary handle  618  and flange  704 , biases pusher link  674  to a retracted, non-fired position. A pair of wings  708  extend radially outwardly from the proximal end of pusher link  674 . Wings  708  are dimensioned to slide along slots  710  formed along the internal walls of stationary handle  618  to maintain proper alignment of pusher link  674  within stationary handle  618  during firing of device  610 . The distal end of pusher link  674  includes a pair of flexible arms  710  which are dimensioned to extend through slots  820  ( FIG. 50 ) formed in the proximal end of pusher back  786 . Pusher back  786  forms part of shell assembly  631  and will be discussed in greater detail below. Pusher link  674  is preferably formed from a flexible plastic material and includes a plurality of notches  787  which allow the pusher link to bend more easily as it moves through body  614 . An annular channel  674   a  is formed about pusher link  674  to receive an o-ring seal  674   b . Operation of the firing mechanism of the device will be described in detail below. 
     As discussed above, head portion  616  includes anvil assembly  630  and shell assembly  631 . Referring to  FIGS. 41-46 , anvil assembly  630  includes an anvil head assembly  720  and an anvil center rod assembly  752 . Anvil head assembly  720  includes a post  722 , an anvil head  724 , a backup plate  726 , a cutting ring  728  and an anvil  729 . Anvil head  724  includes a central hole  732  dimensioned to receive post  722 , an inner annular ring  734 , and an outer annular ring  736 . Anvil  729  is supported on anvil head  724  in an annular channel  738  defined between annular rings  734  and  736 . Anvil  729  includes a plurality of pockets  740  for receiving and deforming staples. A tab  742  formed on anvil  729  is dimensioned to be received in a slot  744  formed in anvil head  724  to maintain proper alignment of anvil  729  and anvil head  724 . Cutting ring  724  and backup plate  726  each include a central opening and are positioned about post  722  in stacked relation in an annular channel  746  defined between central hole  732  and annular ring  734 . Preferably, cutting ring  724  is formed from polyethylene and is fixedly secured to backup plate  726  using, for example, adhesives. Cutting ring  724  includes a pair of diametrically opposed slots  748  dimensioned to receive tabs  750  formed on backup plate  726 . The cutting ring  726  and backup plate  748  assembly is slidably mounted about post  722 . 
     Anvil center rod assembly  752  includes anvil center rod  754 , a plunger  756  and plunger spring  758 . A first end of center rod  754  includes a transverse throughbore  760  ( FIG. 44 ) which is spaced radially of a central longitudinal axis of center rod  754 . Post  722  of anvil head assembly  720  also includes a transverse throughbore  762 . A pivot member  764  pivotably secures post  722  to center rod  754  such that anvil head assembly  720  is pivotably mounted to anvil center rod assembly  752 . As best seen in  FIGS. 45 and 46 , plunger  756  is slidably positioned in a bore  766  formed in the first end of center rod  754 . Plunger  756  includes an engagement finger  768  which is offset from the pivot axis of anvil head assembly  720  and biased into engagement with the base of post  722  by plunger spring  758  to urge anvil head assembly  720  to a pivoted position. In a prefired position, tabs  750  formed on backup plate  726  engage a top surface  754   a  of center rod  754  to prevent anvil head assembly  720  from pivoting (see  FIGS. 63 and 64 ). As device  610  is being fired, backup plate  726  and cutting ring  728  are moved deeper into anvil head  724  about post  722  by knife  788  to move tabs  750  out of engagement with top surface  754   a  of center rod  754  to permit plunger  756  to pivot anvil head assembly  720  about pivot member  764 . See  FIGS. 66-68 . As illustrated in  FIG. 68 , the upper end of  754   b  of center rod  754  is angled to further accommodate a tissue specimen. It is noted that after the device has been fired, the anvil will only move to the tilted position after the anvil assembly and the shell assembly have been unapproximated a predetermined distance. 
     A second end of center rod  754  includes a blind bore  770  ( FIGS. 45 and 46 ). Blind bore  770  includes an inwardly tapering opening  772  and a spaced annular recess  774 . Blind bore  770  is dimensioned to receive a removable trocar  776 . Annular recess  774  is positioned within blind bore  770  and dimensioned to receive annular rib  778  formed on trocar  776  to secure center rod  754  in engagement with trocar  776 . The outer surface of center rod  754  also includes an annular abutment  775 . Annular abutment  775  is dimensioned to be received within an annular recess  777  ( FIG. 50 ) formed in the distal end of anvil retainer  638  to retain anvil assembly  630  within anvil retainer  638 . 
     Referring to  FIGS. 34 and 50 , shell assembly  631  includes a shell  782 , a sleeve  784 , a pusher back  786 , a cylindrical knife  788 , a pusher  790  and a staple guide  792 . Shell  782  includes an outer housing portion  794  and an inner guide portion  796 . Sleeve  784  is fixedly positioned within inner guide portion  796  of shell  782  and defines a stepped bore  785 . A locking member  787  having a detent  789  ( FIG. 34A ) is retained within the stepped bore  785 . Outer housing portion  794  defines a throughbore  798  having a distal cylindrical section  800 , a central conical section  802  and a proximal smaller diameter cylindrical section  804 . A plurality of openings  806  are formed in conical section  802 . Openings  806  are dimensioned to permit fluid and tissue passage during operation of the device. A pair of diametrically opposed flexible engagement members  807  are formed on proximal cylindrical section  804  of shell  782 . Engagement members  807  are positioned to be received in openings  809  formed on the distal end of elongated body  614  to secure shell  782  to elongated body  614 . A pair of openings  811  are formed in the proximal end of outer tube  614   a . Openings  811  are dimensioned to receive protrusions (not shown) formed on the internal wall of stationary handle  618  to facilitate attachment of tube  614   a  to handle portion  612 . 
     Pusher back  786  includes a central throughbore  808  which is slidably positioned about inner guide portion  796  of shell  782 . Pusher back  786  includes a distal cylindrical section  810  which is slidably positioned within distal cylindrical section  800  of shell  782 , a central conical section  812  and a proximal smaller diameter cylindrical section  814 . A distal face of pusher back  786  includes an inner annular shoulder  816  and an outer annular recess  818 . The proximal end of pusher back  786  includes a pair of slots  820  configured to receive flexible arms  710  of pusher link  674  to fasten pusher link  674  to pusher back  786  such that a distal face of pusher link  674  abuts a proximal face of pusher back  786  (see  FIG. 53 ). 
     Pusher  790  includes a body  822  having a proximally extending ring  824  and a multiplicity of distally extending fingers  826  dimensioned to be slidably received within slots  828  formed in staple guide  792  to eject staples  830  therefrom. Ring  824  is dimensioned to be received within annular recess  818  formed in the distal face of pusher back  786  to fasten pusher  790  to pusher back  786 . Cylindrical knife  788  includes a plurality of radially extending tabs  832  formed about its proximal end and is positioned within annular shoulder  816  of backing  786  with tabs  832  positioned between the distal face of pusher back  786  and body  822  of pusher  790  to fixedly secure knife  788  in relation to pusher  790 . The distal end of knife  788  includes a circular cutting edge  834 . 
     In operation, when pusher link  674  is advanced distally in response to actuation of firing trigger  620 , as will be described below, pusher back  786  is advanced distally within shell  782 . Advancement of pusher back  786  effects advancement of pusher  790  and knife  788 . As pusher  790  is advanced, fingers  826  engage staples  830  positioned within slots  828  in staple guide  792  to eject staples  830  from staple guide  192 . 
     Referring to  FIGS. 34 ,  36 ,  51  and  52 , stapling device  610  includes a retractable trocar assembly slidably positioned within anvil retainer  638 . The retractable trocar assembly includes a trocar  840  and a engagement member  842 . Engagement member  842  may be in the form of a spring clip, as shown. Alternately, other engagement members are envisioned, e.g., spring loaded protrusions, etc. Trocar  840  includes a slot  844  which extends through the body of trocar  840  along a portion of its length. Slot  844  is dimensioned to receive engagement member  842 . Engagement member  842  includes a proximal body portion  846  and a pair of distally extending resilient legs  848 . Each leg  848  includes a tapered tip  850  and a proximally facing shoulder  852 . A pin  854  is positioned through openings  856  and  858  formed in body portion  846  of member  842  and trocar  840 , respectively, to secure engagement member  842  within slot  844  of trocar  840 . Pin  854  also extends through an elongated slot  855  formed in anvil retainer  638 , such that the distal and proximal surfaces of slot  855  function as stops to define the fully advanced and fully retracted positions of the retractable anvil assembly. Legs  848  are formed of a resilient material such as spring steel. In an unbiased position, legs  848  of member  842  extend outwardly of trocar  840  and anvil retainer  638  such that in the fully advanced position of trocar  840 , shoulders  852  of legs  848  engage a distal end of anvil retainer  638  to retain the trocar  840  in the advanced position. See  FIG. 51 . 
     Referring to  FIG. 53 , when the anvil assembly  630  is attached to anvil retainer  638 , anvil center rod  754  of anvil assembly  630  is slid over tapered tips  852  of legs  848  to compress legs  848  inwardly in the direction indicated by arrow “A” such that trocar  840  and member  842  move inside blind bore  770  of center rod  754 . When the tip of trocar  840  engages the bottom of bore  770 , further movement of center rod  754  towards anvil retainer  638  in the direction indicated by arrow “B” causes the trocar assembly to move to the retracted position within anvil retainer  638 . 
     Referring to  FIG. 53A , when the anvil assembly is disengaged from anvil retainer  638  by pulling the anvil assembly in the direction indicated by arrow “C”, legs  848  flex outwardly to move shoulders  852  of legs  848  of member  842  into annular recess  774  of center rod  754 . As a result, as anvil assembly  630  is disengaged from anvil retainer  638 , member  842  and thus trocar  840  are pulled distally in the direction indicated by arrow “D” with the anvil assembly to the advanced position as shown in  FIG. 57 . 
     The proximal end of trocar  840  includes a blind bore  841 . A rigid flexible wire  843  has a distal end which is secured within bore  841  of trocar  840  and extends rearwardly through elongated body portion  614  and into handle portion  612  of stapling device  610 . Wire  843  has a proximal end which is secured to an indicator assembly in handle portion  612  which will be discussed in detail below. 
     Referring again to  FIGS. 34 ,  36 ,  51  and  52 , a cylindrical lockout tube  870  is slidably positioned about the outer surface of anvil retainer  638  and positioned to extend through inner guide portion  796  of shell  782 , sleeve  784  and locking member  787  of shell assembly  631 . The proximal end of lockout tube  870  includes an annular protrusion  872  ( FIG. 34B ). Locking member  787 , which is fixedly positioned within sleeve  784  of shell assembly  631 , includes a detent  789  ( FIG. 34A ) dimensioned to frictionally receive annular protrusion  872  to prevent sliding movement of lockout tube  870  about anvil retainer  638  until a predetermined force has been exerted on lockout tube  870 . Lockout tube  870  is positioned about flexible legs  670  of anvil retainer  638  to provide rigidity to legs  670  during approximation of the anvil to prevent anvil assembly  630  from becoming inadvertently detached from anvil retainer  638 . Movement of cylindrical lockout tube  870  about anvil retainer will be discussed in more detail below. 
     Referring to  FIGS. 33 ,  35 ,  37 ,  38 A, and  69 - 72  an indicator assembly is mounted within stationary handle  618  and includes an indicator  900  with indicia  901   a ,  901   b  and  901   c  which provides a visual indication to a surgeon via indicator window  624  that the anvil assembly is not attached ( 901   a ), that the anvil assembly is attached ( 901   b ), or that anvil assembly is attached and approximated  901   c , i.e., the device is ready to fire. The indicia  901   a - c  may include red, yellow, and green coloring, respectively. Alternately, other color coded, graphic, or written indicia may be used to indicate the above described device conditions. 
     The indicator assembly includes an indicator  900 , an indicator subplate  902 , an indicator arm  904 , a screw stop  906  and a rotatable disk  908 . Screw stop  906  includes a throughbore  910  dimensioned to be positioned about screw  632 . A set screw  912  is used to fixedly secure screw stop  906  to screw  632 . Disk  908  includes a central throughbore  914 , an upwardly extending cam member  916  and a wire connector  918 . Disk  908  is rotatably secured to the top of screw stop  906  by screw  920 . Wire connector  918  includes a post  922  which extends through an opening  924  in disk  908  and is rotatably fixed therein by a D-clip  926  or the like. Wire connector  918  includes a bore  928  for receiving one end of wire  843 . A pin  930  secures wire  843  to wire connector  918 , such that when wire  843  is advanced or retracted in response to attachment or detachment of anvil assembly  630  onto or from anvil retainer  638 , as discussed above, disk  908  will rotate about screw  920  to rotate cam member  916 . 
     Indicator subplate  902  is fixedly secured between internal walls of stationary handle  618  via a notch  934  formed in subplate  902  and channels (not shown) formed in the internal walls of stationary handle  618 . A centrally disposed cutout  932  defining on elongated channel  936  is formed in subplate  902 . Indicator arm  904  also includes a cutout  937  having a first end  937   a  and a second end  937   b . A projection  938  which is slidably and rotatably positioned in elongated channel  936  extends downward from indicator arm  900  in subplate  902 . A projection  940  extends from a top surface of indicator arm  904  into a curved bore  941  formed in the bottom of indicator  900 . A projection  943  extends downwardly from indicator  900  and is positioned in channel  936  of subplate  902  to rotatably secure indicator  900  to subplate  902 . The bottom of indicator  900  also includes a cam slot  942  for receiving cam member  916  of disk  908 . 
     In the assembled condition, indicator subplate  902  is fixedly secured within stationary handle  618 , with indicator arm  904  and indicator  900  slidably and rotatably mounted thereon and curved bore  941  of indicator  900  positioned on projection  940  of indicator arm  904 . The entire assembly is engaged and maintained in an assembled state by indicator window  624 . Cam member  916  extends upwardly from disk  908  through channel  936  in subplate  902  and cutout  937  in indicator arm  904  into cam slot  942  formed in the bottom of indicator  900 . A spring  952  supported between indicator subplate  902  and indicator arm  904  biases indicator arm  904  towards the end of subplate  902  supporting indicator  900 . Referring also to  FIGS. 73-75 , prior to attaching anvil assembly  630  to anvil retainer  638 , indicia  901   a  (e.g., red dot) is positioned beneath opening  628  of indicator window  624  ( FIG. 73 ). When anvil assembly  630  is attached to anvil retainer  638  in the manner described above, trocar  840  is retracted, i.e., pushed proximally, within anvil retainer  638  to move wire  843  proximally. Wire  843  is secured to connector  918  which is secured to the bottom of disk  908 . As wire  843  is moved proximally, disk  908  is rotated in the direction indicated by arrow “E” on screw stop  906  about screw  920  to move cam member  916  which is positioned within the cam slot  942  formed in the bottom of indicator  900  in the same direction. Movement of cam member  916  against cam slot  942  causes indicator  900  to rotate in the direction indicated by arrow “F” about protrusion  943  to move indicia  901   b  (e.g., yellow dot) beneath opening  628  of indicator window  624  ( FIG. 25 ). Cam member  916  also engages cutout  937  of indicator arm  904  near first end  937   a  of cutout  937  to rotate arm  904  in the direction indicated by arrow “G” about protrusion  938  to the position shown in  FIG. 74 . As discussed above, indicia  901   b  indicates to a surgeon that the anvil has been attached to the anvil retainer. 
     Next, when the surgeon approximates the device, screw  632  is moved proximally in the manner described above. Thus, screw stop  906 , which is mounted on screw  632 , and disk  908 , including cam member  916 , are moved proximally. As cam member  916  is moved proximally, cam member  916  moves out of cam slot  942  in indicator  900  and moves from first end  937   a  of cutout  937  formed in indicator arm  904  to second end  937   b  of cutout  937 . When cam member  916  reaches second end  937   b  of cutout  937 , cam member  916  engages a wall  950  of indicator arm  904  and drags indicator arm  904  proximally, against the bias of spring  952 . As indicator arm  904  is moved proximally in the direction indicated by arrow “H”, indicator  900  is also moved proximally to move indicia  901   c  (e.g., green light) beneath opening  628  of indicator window  624 . As discussed above, indicia  901   c  indicates to a surgeon that the anvil assembly has been attached to the anvil retainer  638  and approximated, i.e., the instrument is ready to fire. 
     Operation of surgical stapling device  610  will now be described in detail. 
       FIGS. 47-51  illustrate surgical stapling device  610  with anvil assembly  631  attached to anvil retainer  638  in the unapproximated position. As shown in  FIGS. 47 and 49 , screw  632  is in its distal-most position, with screw stop  906  positioned adjacent the proximal end of pusher link  674 . In this position, locking pin  693 , which is secured to safety link  692  ( FIG. 31 ) is positioned in notches  683  on firing trigger plates  676  and  678  ( FIG. 39 ) to prevent actuation of firing trigger  620 . As shown in  FIG. 50 , legs  670  of anvil retainer  638  are positioned about center rod  754  of anvil assembly  630  such that abutment  775  of center rod  754  is positioned within annular recess  777  of anvil retainer  638 . Annular protrusion  872  of lockout tube  870  is positioned within detent  789  of locking member  787  ( FIG. 54A ) to fix lockout tube  870  about legs  670  of anvil retainer  638  during approximation of the device. As anvil retainer  638  is retracted into lockout tube  870  during approximation, the exposed length of legs  870  of anvil retainer  638  will shorten to increase the force required to remove anvil assembly  630  from anvil retainer  638 . When anvil retainer is retracted into lockout tube  870  a predetermined distance, shoulder  871  on anvil retainer  638  will engage the distal end of lockout tube  870  ( FIG. 54B ) to force annular protrusion  872  from detent  789  and force lockout tube  870  proximally with anvil retainer  638 . 
     Referring to  FIGS. 56 and 57 , anvil assembly  630  and shell assembly  631  are approximated by rotating approximation knob  622  in the direction indicated by arrow “J” in  FIG. 56 . Rotation of knob  622  effects rotation of sleeve  633  to move sleeve pin  652  along channel  650  of screw  632 . Since sleeve  633  is axially fixed to stationary handle  618 , as pin  652  is moved through channel  650 , screw  650  is moved proximally within stationary handle  618 . As screw  650  is moved proximally, it pulls screw extensions  634  and  636 , anvil retainer  638  and anvil assembly  630  proximally. Anvil assembly  630  is approximated into juxtaposed alignment with shell assembly  631 . 
     As illustrated in  FIG. 56 , as screw  632  is moved proximally within stationary handle  618 , screw stop  906 , which is fixedly secured to screw  632 , also moves proximally. Screw top  906  includes a downwardly extending abutment  1000  and a concavity  1002 . During the final stages of approximation, abutment  1000  engages guide member  692   b  of safety link  692  and pulls safety link  692  proximally such that guide member  692   b  moves along slot  695  in internal wall of stationary handle  618  against the bias of spring  697 . As safety link  692  is moved proximally, locking pin  693  moves upwardly in channel  690  of firing link  672  and locking pin  693  is moved out of engagement with notches  683  in firing trigger  620  to activate the firing trigger. 
     As illustrated in  FIG. 57A , shoulder  871  on anvil retainer  638  has moved lockout tube  870  proximally such that annular protrusion  872  on lockout tube  870  is no longer positioned in detent  789  of locking member  787 . 
       FIGS. 58-61  illustrate handle portion  62  of surgical stapler  610  during the firing stroke of trigger  620 . After anvil  630  and shell assembly  631  have been approximated, pivot member  700  on end  698  of firing link  672  is positioned in concavity  1002  of screw stop  906  and locking pin  693  is positioned proximally of notches  683 . Trigger lock  626  has also been released, i.e., manually pivoted to an unlocked position. Surgical stapling device  610  is now in a firing position. 
     To fire stapling device  610 , firing trigger  620  is pivoted in the direction indicated by arrow “K”. Since pivot member  700  is locked in concavity  1002  of screw stop  906 , trigger  620  is forced to move distally. Trigger  620  is secured to the proximal end of pusher link  674  by pivot member  684 . Thus, pusher link  674  is also moved distally within elongated body portion  614 . Concurrently, a top surface of trigger plates  676  and  678  engages locking pin  693  to force guide member  692   b  of safety link  692  further proximally in the direction indicated by arrow “L” along slot  695 . When firing trigger  620  reaches the end of its firing stroke, an engagement member  1010  formed on firing trigger  620  engages weakened portion  699  of safety link  692  ( FIG. 60 ) to break safety link  692  into two parts ( FIG. 61 ). As safety link  692  breaks, an audible and tactile indication is given to the surgeon that firing is complete. When firing trigger  620  is released ( FIG. 61 ), spring  706  returns pusher link  674  to the retracted position. Spring  697  also returns locking pin  693  into engagement with notches  683  in firing trigger  620  to prevent further pivoting of firing trigger  620 . Since safety link  692  is broken, approximation of device  610  will not remove locking member  693  from notches  683 . 
       FIGS. 62 and 65  illustrate head portion  616  of surgical stapling device  610  immediately prior to and immediately after the firing stroke of firing trigger  620 . As discussed above, as pusher link  674  is moved in the direction indicated by arrow “M” in  FIG. 65 , pusher back  786  and pusher  790  are advanced distally such that fingers  826  are pushed through slots  828  to force staples  830  through tissue  1040  into pockets  740  of anvil  729 . Simultaneously, circular knife  788  is advanced to core the tissue. As knife  788  is advanced distally, knife  788  engages and moves cutting ring  728  and backup plate  726  further into anvil head  724  to move tabs  750  of backup plate  726  out of engagement with center rod  754 . See  FIGS. 66-68 . By moving tabs  750  out of engagement with center rod  754 , as discussed above, anvil head assembly  720  is free to pivot about pivot member  764  on center rod  754  after anvil assembly  630  and shell assembly  631  have been unapproximated. 
     Surgical stapling device  610  is used to perform a circular anastomoses. Typically, circular anastomoses are required during procedures for removing a portion of a diseased vessel such as the colon or the intestine. During such a procedure, the diseased portion of the vessel is removed and the remaining vessel section end portions are joined together using a surgical stapling device. 
     During such a procedure using surgical stapling device  610 , prior to removing the diseased vessel portion, anvil assembly  630  with removable trocar  776  attached thereto ( FIG. 46 ) is positioned in a first vessel section on a first side of the diseased vessel portion. Removable trocar  776  includes bore  776   a  for receiving a suture line for manipulating the anvil assembly. After the diseased vessel portion is removed and the open ends of the first and second vessel sections have been sutured, the distal end of device  610  as shown in  FIG. 51  is positioned in the second vessel section on the other side of the diseased (now removed) vessel portion. At this time, trocar  776  is pushed through the suture line in the end of the first vessel section and removed from center rod  754 . Next, trocar  840  is pushed through the suture line in the second vessel section. Center rod  754  is now positioned about trocar  840  and pushed into anvil retainer  638  to secure anvil assembly  630  to anvil retainer  638  ( FIG. 52 ). Surgical stapling device  610  can now be approximated and fired in the manner discussed above, to join the ends of the first and second vessel sections and core out any tissue obstructing the vessel section lumen. After surgical stapling device is fired and unapproximated, head assembly  720  will tilt to the position shown in  FIG. 68  to reduce the profile of the anvil assembly and simplify removal of the instrument from the vessel lumen. It has been contemplated providing an engagement member in handle portion  612  which would engage a component of the approximation mechanism during unapproximation of the anvil assembly to provide a tactile and/or audible indication that the anvil head assembly has been unapproximated a sufficient distance to tilt. It is envisioned that the engagement member may be moved to a position aligned with a component of the approximation mechanism by the firing trigger. 
     It will be understood that various modifications may be made to the embodiments disclosed herein. For example, the materials used to construct the individual components of the device may be chosen from a variety of known materials to achieve the desired result. Moreover, the particular indicia formed on the indicator may be other than that disclosed herein, i.e., other indicia is envisioned. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.