Surgical instrument with replaceable loading unit

[0001] This application is a continuation application of U.S. patent application Ser. No. 12/793,269, filed Jun. 3, 2010, which is a divisional of U.S. patent application Ser. No. 11/891,441, filed Aug. 10, 2007, now U.S. Pat. No. 7,753,246, which is a continuation in part of U.S. patent application Ser. No. 11/701,116, filed Jan. 31, 2007, now U.S. Pat. No. 7,950,562, the entire contents of which are incorporated herein by reference.

[0002] This application relates to a surgical stapling device for applying staples to tissue having a locking mechanism for securing a loading unit onto the surgical stapling device.

[0003] Surgical devices for applying surgical fasteners to tissue are well known. Endoscopic surgical devices for applying staples, clips or other fasteners include a handle assembly for actuating the device, an endoscopic shaft and a tool assembly at the distal end of the endoscopic shaft. Certain of these devices are designed for use with replaceable loading units housing the staples or fasteners. For example, in using an endoscopic linear stapler, the user may select a loading unit with staples of a selected size and arranged in one or more lines of staples having a selected staple line length. After firing, the user may remove the loading unit, select another loading unit of the same or different size, and fire staples from the instrument again. Endoscopic surgical staplers having four lines of staples, arranged in pairs on either side of a cut line, are known.

[0004] Loading units in the form of replaceable cartridges are known. In addition, loading units having a tool assembly, including a cartridge, anvil, drive assembly and knife are known. Such loading units have the benefit of providing a new knife with each loading of the loading unit.

[0005] Although interfaces between the surgical stapling device endoscopic shaft and the loading unit are known, improvements in the ease of loading and unloading of the loading unit are desired.

[0006] In a first aspect of the present invention, a surgical instrument comprises an elongated housing having a proximal end and a distal end. A loading unit is removably mountable with the distal end of the elongated housing and has a tool assembly. The loading unit has at least one lug thereon. A handle assembly is at the proximal end of the elongated housing. A locking structure has a first position for locking movement of the loading unit and a second position for allowing movement of the loading unit. The locking structure includes a locking shaft that extends through the elongated housing to the handle assembly. The locking shaft has a surface engaging the at least one lug in the first position of the locking structure and disengaging the at least one lug in the second position of the locking structure. The elongated housing desirably defines at least one guiding channel for engagement with the at least one lug.

[0007] The surgical instrument further includes a rod extending through the elongated housing, and a drive assembly. The drive assembly is connected to the rod when the loading unit is mounted on the elongated housing. The locking structure may engage the rod when the locking structure is in the second position.

[0008] The locking structure preferably includes a button assembly including a button and the button is preferably adjacent the proximal end of the elongated housing. The button may be distally biased and moveable between a first position and a second position.

[0009] The locking shaft may define a slot for engaging a protrusion on the button. The locking shaft may have a first distally-facing surface, a second distally-facing surface and a longitudinal surface extending therebetween. The at least one lug is desirably captured between the first distally-facing surface, second distally-facing surface, a longitudinal surface of the locking shaft, and the elongated housing when the locking structure is in the first position. The locking shaft and the elongated housing desirably define a space for capturing the at least one lug therebetween.

[0010] In a further aspect of the present invention, a surgical instrument comprises an elongated housing having a proximal end and a distal end, a loading unit removably mountable with the distal end of the elongated housing and having a tool assembly, and a handle assembly at the proximal end of the elongated housing. A rotation member is at the proximal end of the elongated housing and the surgical instrument has a locking structure for securing the loading unit on the elongated housing, the locking structure including a button accessible at the rotation member.

[0011] The locking structure has a first position for locking movement of the loading unit and a second position for allowing movement of the loading unit. The locking structure includes a locking shaft that extends through the elongated housing to the proximal end of the elongated housing.

[0041] 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.

[0042] In the description that follows, the term “proximal” will refer to the end of the stapling device which is closest to the operator, while the term “distal” will refer to the end of the device which is furthest from the operator.

[0043] FIGS. 1-23 illustrate one preferred embodiment of the presently disclosed surgical stapling device shown generally as 10. Briefly, surgical stapling device 10 includes a handle assembly 12 and an elongated body 14. The length of elongated body 14 may vary to suit a particular surgical procedure. The elongated body 14 defines a longitudinal axis for the device 10. A replaceable loading unit or DLU 16 is releasably secured to a distal end of elongated body 14. Loading unit 16 includes a proximal body portion 18, which forms an extension of elongated body 14, a distal tool assembly 20 including a cartridge assembly 22, and an anvil assembly 24. Tool assembly 20 is pivotably connected to body portion 18 about an axis substantially perpendicular to the longitudinal axis of elongated body 14. Cartridge assembly 22 houses a plurality of staples. Anvil assembly 24 is movable in relation to cartridge assembly 22 between an open position spaced from cartridge assembly 22 and an approximated or clamped position in juxtaposed alignment with cartridge assembly 24. The staples are housed in cartridge assembly 22 to apply rows of staples in body tissue. For example, in the embodiment shown, the rows of staples are linear rows of staples which may have a length measuring from about 30 mm to about 60 mm. Other staple configurations and lengths are envisioned.

[0044] Handle assembly 12 includes a stationary handle member 26, a movable handle or trigger 28 and a barrel portion 30. A rotatable member 32 is preferably rotatably mounted to the forward end of barrel portion 30 and secured to elongated body 14 to facilitate rotation of elongated body 14 in relation to handle assembly 12. An articulation lever 122 is supported on a distal portion of barrel portion 30 and is operable, in a manner to be described hereafter, to effect articulation of tool assembly 20 with respect to body portion 18 of loading unit 16. A pair of return knobs 36 are movably supported along barrel portion 30.

[0045] Referring to FIGS. 4-7, handle assembly 12 includes a housing 38, which is preferably formed from plastic molded housing half-sections 38a and 38b. Alternately, other materials may be used to form the housing including metals, e.g., stainless steel. Housing 38 forms stationary handle 26 and barrel portion 30 of handle assembly 12 (see FIG. 1). Movable handle 28 is rotatably supported between housing half-sections 38a and 38b about a cylindrical member 40 which is received within an opening 41 in movable handle 28. A biasing member 42, which is preferably a torsion spring, urges movable handle 28 away from stationary handle 26 to a non-compressed position. Movable handle 28 includes a pair of throughbores 46 dimensioned to receive a pivot member 47. A pawl 48 is rotatably supported on pivot member 47 and is biased by a spring 50 towards actuation shaft 52.

[0046] Actuation shaft 52 is slidably supported between retracted and advanced positions within barrel portion 30 of housing 38 and includes a distal end defining a recess 54 configured to rotatably receive the proximal end 56 of firing rod 58. A spring biased retract arm 57 is rotatably mounted between housing half-sections 38a and 38b and includes an extension 57a. Extension 57a is positioned within a slot 59 (FIG. 4) formed in actuation shaft 52 to urge actuation shaft 52 to a fully retracted position. Actuation shaft 52 includes a toothed rack 60. Pawl 48 has an engagement finger 62 which is biased by spring 50 towards toothed rack 60 of actuation shaft 52. When movable handle 28 is actuated, i.e., is compressed towards stationary handle 26 against the bias of spring 42, engagement finger 62 of pawl 48 engages toothed rack 60 of actuation shaft 52 to advance actuation shaft 52 and firing rod 58 distally. Distal end of firing rod 58 engages proximal end of drive assembly 212 of the loading unit 16, when proximal end of loading unit 16 is engaged with elongated body 14 of surgical stapling device 10.

[0047] The surgical stapling device includes a disposable loading unit or “DLU.” A loading unit having the desired staple size or sizes, and the desired staple line length, is assembled with the device. The loading units can include a tool assembly that can articulate with respect to the proximal body portion, or loading units that do not provide articulation. The loading units can include tool assemblies having linear rows of staples or other staple configurations. After firing staples from a loading unit, the loading unit can be removed from the device and a new loading unit may be assembled with the device.

[0048] Referring to FIGS. 1 and 7-9, a loading unit with an articulating tool assembly is shown. Loading unit 16 includes a tool assembly 20, a proximal body portion 18 and a mounting assembly 202 (FIG. 9). Body portion 18 has a proximal end adapted to releasably engage the distal end of the elongated body 14 in the manner to be discussed in detail below. Mounting assembly 202 is pivotally secured to a distal end of body portion 18 and is fixedly secured to a proximal end of tool assembly 20. Pivotal movement of mounting assembly 202 pivots the tool assembly 20 so that a longitudinal axis of the tool assembly 20 is angled with respect to the longitudinal axis of the elongated body 14. Pivotal movement of mounting assembly 202 about an axis substantially perpendicular to the longitudinal axis of the elongated body 14 effects articulation of tool assembly 20 between a non-articulated position in which the longitudinal axis of tool assembly 20 is aligned with the longitudinal axis of elongated body 14 and an articulated position in which the longitudinal axis of tool assembly 20 is disposed at an angle to the longitudinal axis of elongated body 14.

[0049] Referring to FIGS. 7-9, tool assembly 20 includes a cartridge assembly 22 and an anvil assembly 24. Anvil assembly 20 includes an anvil portion 28 having a plurality of staple deforming concavities 30 (FIG. 8) and a cover plate 32 secured to a top surface of anvil portion 28. Cover plate 32 and anvil portion 28 define a cavity 34 therebetween. Cover plate 32 prevents pinching of tissue during actuation of loading unit 16 and advancement of the drive assembly 212 through the loading unit 16. A longitudinal slot 38 extends through anvil portion 28 to facilitate passage of a retention flange 40 of drive assembly 212. A camming surface 42 formed on anvil portion 28 is positioned to be engaged by a pair of cam members 40a supported on retention flange 40 of drive assembly 212 to effect approximation of the anvil and cartridge assemblies. A pair of pivot members 211 and a pair of stabilization members 215 are formed on the anvil portion 28.

[0050] Cartridge assembly 22 includes carrier 216 which defines an elongated support channel 218 which is dimensioned and configured to receive staple cartridge 220. Carrier 216 has a pair of shoulders 217 and a pair of slots 213 defined in the carrier 216. The pair of slots 213 receives the pair of pivot members 211 to allow the anvil portion 28 to pivot with respect to the cartridge assembly 22. Each of the pair of stabilization members 215 engages a respective shoulder 217 to prevent the anvil portion 28 from sliding axially in relation to the staple cartridge 220 as the anvil portion 28 is pivoted about the pivot members 211. Corresponding tabs 222 and slots 224 formed along staple cartridge 220 and elongated support channel 218, respectively, function to retain staple cartridge 220 at a fixed location within support channel 218. A pair of support struts 223 formed on staple cartridge 220 are positioned to rest on side walls of carrier 216 to further stabilize staple cartridge 220 within support channel 218.

[0051] Staple cartridge 220 includes retention slots 225 (FIG. 7) for receiving a plurality of staples or fasteners 226 and pushers 228. A plurality of laterally spaced apart longitudinal slots 230 extend through staple cartridge 220 to accommodate upstanding cam wedges 232 of an actuation sled 234 (FIG. 7). A central longitudinal slot 282 extends along substantially the length of staple cartridge 220 to facilitate passage of the drive assembly 212 (FIG. 9). During operation of surgical stapling device 10, drive assembly 212 is advanced by the firing rod 58. The drive assembly 212 abuts actuation sled 234 and pushes actuation sled 234 through longitudinal slots 230 of staple cartridge 220 to advance cam wedges 232 into sequential contact with pushers 228. Pushers 228 translate vertically along cam wedges 232 within fastener retention slots 225 and urge fasteners 226 from retention slots 225 into staple deforming cavities 30 (FIG. 8) of anvil assembly 24.

[0052] The drive assembly 212 includes a drive beam 266 with a working head 268. The distal end of working head 268 of drive beam 266 is defined by a vertical support strut 278 (FIG. 9) which supports a knife blade 280, and an abutment surface 283 which engages a portion of actuation sled 234 during a stapling procedure. Knife blade 280 is positioned to translate slightly behind the actuation sled 234 through a central longitudinal slot 282 in staple cartridge 220 to form an incision between rows of stapled body tissue. A retention flange 40 projects distally from vertical strut 278 and supports a cylindrical cam roller 40a at its distal end. Cam roller 40a is dimensioned and configured to engage cam surface 42 on anvil portion 28 to clamp anvil portion 28 against body tissue.

[0053] In use, the user manipulates handle assembly 12 to clamp tissue and fire staples. To approximate the cartridge and anvil assemblies 22 and 24 and clamp tissue, movable handle 28 is moved in the direction toward stationary handle member 26. Movable handle 28 is compressed towards stationary handle 26 against the bias of torsion spring 42 to engage actuation shaft 52. The engagement finger 62 of pawl 48 engages the toothed rack 60 of actuation shaft 52 to advance actuation shaft 52 and firing rod 58 distally.

[0054] Firing rod 58 is connected at its distal end to axial drive assembly 212 including drive beam 266, such that advancement of firing rod 58 effects advancement of drive beam 266. As drive beam 266 is advanced, cam roller 40a moves into engagement with cam surface 42 of anvil portion 28 to urge anvil portion 28 in the direction of the cartridge 220 to approximate cartridge and anvil assemblies 22 and 24 and clamp tissue therebetween.

[0055] After movable handle 28 is actuated to approximate cartridge and anvil assemblies 22 and 24, biasing member 42 returns handle to its non-compressed position spaced from stationary handle 26.

[0056] To fire stapling device 10 once tissue is clamped, the movable handle 28 is moved toward stationary handle member 26 through an actuation stroke during which, engagement finger 62 of pawl 48 engages toothed rack 60 of actuation shaft 52 to further advance actuation shaft 52 and firing rod 58 distally. More than one actuation stroke may be required to fire all the staples from the loading unit 16. As firing rod 58 is advanced in the manner discussed above, drive beam 266 is advanced distally and engages actuation sled 234 through staple cartridge 22 to simultaneously sever tissue with knife 280 and drive pushers 228 to sequentially eject staples 226 from the cartridge. Loading units having staple lines of different lengths may be used and the number of actuating strokes will vary accordingly. The structure and operation of the tool assembly may be in accordance with certain embodiments disclosed in U.S. Pat. No. 5,865,361, the disclosure of which is hereby incorporated by reference herein.

[0057] The elongated body 14 is mounted in a rotatable member 32 as shown in FIG. 5 and the rotatable member 32 is attached to the handle assembly 12 so as to allow the elongated body 14 and loading unit 16, including the tool assembly 20, to rotate around the longitudinal axis. The rotatable member 32 is formed from one or more tubular or conical members and houses an articulation actuation mechanism for articulating the tool assembly 20 with respect to the longitudinal axis of the device 10. The articulation actuation mechanism includes an articulation lever 122 (FIG. 6). The articulation lever 122 is operably connected to an articulation arm extending through the elongated body 14. The articulation lever 122 may be connected to a mechanism for defining predetermined degrees of articulation of the tool assembly 20. The operation and structure of the articulation lever 122 may be as described in U.S. Published Patent Application No. 2004/0232201, the disclosure of which is hereby incorporated by reference herein. The articulation lever 122 is mounted on the rotatable member 32 about a pivot pin and is attached to an articulation arm so that rotation of the lever 122 about the pivot pin effects longitudinal motion of the articulation arm. The articulation arm extends through the elongated body 14 and is attached to an articulation link 256 of the loading unit 16 (FIG. 9) when the loading unit 16 is mounted on the elongated body 14. The articulation lever 122 can be rotated by the user of the surgical stapling device 10 to articulate the tool assembly 20. As the articulation lever 122 is rotated in a first direction, the articulation arm attached to the lever is advanced in the distal direction. The articulation arm advances the articulation link 256 of the loading unit 16 and pivots the mounting assembly 202 about pivot 244 to articulate the tool assembly 20 in the first direction. As the articulation lever 122 is rotated in a second direction, the articulation arm attached to the lever is retracted in the proximal direction. The articulation arm retracts the articulation link 256 of the loading unit 16 and pivots the mounting assembly 202 about pivot 244 to articulate the tool assembly 20 in the second direction.

[0058] As depicted in FIG. 6, the loading unit 16 is removably mounted on the distal end of the elongated body 14. The body portion 18 of the loading unit 16 includes a first housing 250 and a second housing 252 that define a channel 253 for allowing the advancement of the axial drive assembly 212. (FIG. 9). The housings 250 and 252 also define a slot for the articulation link 256. The housings 250 and 252 are received in an outer tube 251. The proximal ends of the housings 250 and 252 define an insertion tip 193 on which is formed a pair of lugs 254. The lugs 254 form a releasable connection with the elongated body 14 so that the loading unit 16 may be mounted on and removed from the elongated body 14. A pair of blowout plates 255 are positioned adjacent the distal end of the proximal body portion 18 and adjacent the mounting assembly 202. The blowout plates 255 support the drive assembly 212 during articulation and firing of the tool assembly 20. The structure and operation of the blowout plates 255 are described more fully in U.S. Published Patent Application Number 2004/0232201, the disclosure of which is hereby incorporated by reference herein.

[0059] The distal end of the elongated body 14 defines a tip assembly 301 for mounting the loading unit 16 thereon. FIGS. 10-15 and 18 show a tip assembly 301 according to the present disclosure. The tip assembly includes a ring 300 mounted to the distal end of the elongated body 14 so that it is rotationally fixed and a yoke 400 movably mounted to the ring 300. (See FIGS. 10 and 14). The ring 300 defines a passage 303 in which two helical guiding ramps 302 are formed. Each of the guiding ramps has a distal end 304 and a proximal end 306 and a ledge 310 adjacent the proximal end 306. A groove 312 is defined in the inner surface of the ring 300 for mounting the yoke 400 thereon. (See FIG. 10).

[0060] The moveable yoke 400 has at least one protrusion for interacting with the lugs 254 on the loading unit 16. As shown in FIG. 11, the protrusions include two tabs 402 and two stops 404 arranged in pairs so that each tab 402 and stop 404 define a receiving space 501. The distal end of the yoke 400 also has a ridge 406 which cooperates with the groove 312 of the ring 300 so that the yoke 400 is rotatable with respect to the ring 300 from a first, initial position to a second position. As the yoke 400 rotates, the positions of the tabs and stops with respect to the proximal ends 306 of the guiding ramps 302 change. In the first position of the yoke 400 as shown in FIG. 11, a tab 402 and stop 404 pair are disposed adjacent one of the proximal ends 306 of one of the guiding ramps 302, so that receiving space 501 is positioned for receiving one of the lugs 254 of the loading unit 16. In the second position of the yoke 400 as shown in FIG. 12, the tab 402 and stop 404 pair are positioned so that the receiving space 501, and the lug 254 disposed therein, is disposed beneath the ledge 310.

[0061] The loading unit 16 is inserted into the tip assembly 301 so that the insertion tip 193 is inserted into passage 303. The lugs 254 are advanced into the passage 303 of the ring 300 and contact the distal ends 304 of the guiding ramps 302. (See FIG. 11). When the loading unit 16 is rotated in Direction A (see FIG. 12), the lugs 254 are guided on the guiding ramps 302 towards the proximal ends 306 of the guiding ramps 302 and drop into the receiving spaces 501 of the yoke 400. FIG. 14 shows the lugs 254 in the receiving spaces 501. The tip assembly 301 is still in the first position and a stop 404 and tab 408 are disposed on either side of a lug 254, and adjacent a proximal end 306 of one of the guiding ramps 302. In this position, the loading unit 16 may be moved distally and removed from the elongated body 14. The user continues to rotate the loading unit 16 in Direction A, so that lugs 254 push against the tabs 402, thereby rotating moveable yoke 400 into the second position, as shown in FIG. 12. The lugs 254 are situated beneath ledges 310. FIG. 15 shows the lugs 254 positioned beneath ledges 310. The stops 404 prevent the loading unit 16 from rotating with respect to the yoke 400. Thus, the loading unit 16 is captured in the tip assembly 301 and cannot be moved without rotating the yoke 400.

[0062] As the loading unit 16 is mounted on to the distal end of the elongated body 14, a distal end of the firing rod 58 is connected to the proximal end of the drive assembly 212. The proximal end of the drive assembly 212 includes a drive member 272 with a porthole for receiving the distal end of the firing rod 58. When the loading unit 16 is rotated during mounting of the loading unit, the articulation link 256 moves into engagement with engagement structure on the distal end of the articulation arm.

[0063] To remove the loading unit 16 from the device, the loading unit 16 is rotated in the direction opposite to Direction A, rotating the yoke 400 with it. The lugs 254 are thereby moved away from the ledges 310. The articulation link 256 and the articulation arm are moved away from engagement with one another as the loading unit is rotated. The loading unit 16 can be removed from the device by continuing to rotate the loading unit 16 so that the lugs 254 follow the guiding ramps 302 toward the distal ends 304 and moving the DLU distally. In removing the DLU from the elongated body 14, the firing rod 58 is disengaged from the drive assembly 212.

[0064] The surgical stapling device 10 according to the present disclosure includes a sensor mechanism 510 and a locking structure 513, as shown in FIGS. 16-23. The sensor mechanism 510 and the locking structure 513 interact with the tip assembly 301 (FIG. 17) to secure the loading unit 16 onto the elongated body 14. The sensor mechanism 510 and locking structure 513 release the loading unit 16 from the elongated body 14. The locking structure 513 locks the firing rod 58 in position until the loading unit 16 is loaded onto the elongated body 14.

[0065] The sensor mechanism 510 includes a sensor tube 502 having a distal end with a groove 504, as shown in FIG. 18. The yoke 400 of the tip assembly 301 has a protrusion 407 that engages the groove 504 and keys movement of the yoke 400 to the sensor tube 502. As the yoke 400 is rotated during the loading of the loading unit 16, the sensor tube 502 is rotated in the same direction. The proximal end of the sensor tube 502 is connected to the locking structure 513. The locking structure 513 includes a button 514 or other manipulatable actuator at the proximal end of the elongated body 14, or on the handle assembly 12, so that it is accessible to the user of the device 10. For example, the button 514 is shown in FIG. 19 on the rotatable member 32. The button 514 has a button tang 512 that extends toward the sensor tube 502. A release flange 508 is attached to the sensor tube 502 and rotates with the sensor tube 502 from a first position away from button tang 512 (FIG. 20) to a second position in which movement of the release flange 508 is blocked by button tang 512 of locking structure 513 (FIG. 19). The button 514 is biased in the distal direction by a spring.

[0066] A plunger 516 interacts with the firing rod 58. The firing rod 58 proximal end 524 has a notch 526 defined therein, as best seen in FIGS. 20-23. The plunger 516 has a first end for engaging the firing rod 58 at the notch 526 and a second end with a beveled surface 522 that is positioned so as to communicate with the button 514 (FIGS. 21 and 23). The plunger 516 is biased in a direction away from the firing rod 58.

[0067] In the initial position, before a loading unit 16 is mounted on the device 10, the locking structure 510 engages the firing rod 58 in the notch 526, preventing the advancement of the firing rod 58. The release flange 508 prevents the button 514 from moving distally so that the button 514 maintains the plunger 516 in engagement with the notch 526. When the loading unit 16 is mounted onto the device, the yoke 400 is turned, thereby turning the sensor tube 502. The release flange 508 moves away from button tang 512, allowing the button 514 to move distally. The button 514 allows the plunger 516 to move away from notch 526, as shown in FIG. 23. The locking structure 510 has been disengaged from firing rod 58, allowing the firing rod 58 to move when the moveable handle 28 is manipulated and the device 10 is actuated to clamp tissue and fire staples. The loading unit 16 is also locked onto the device 10, as the release lever 508 is blocked by the button tang 512, preventing rotation of the sensor tube 502. With the sensor tube 502 prevented from rotation, the yoke 400, which holds the loading unit 16 onto the device 10, is prevented from rotation.

[0068] When the loading unit 16 is to be removed from the device 10, button 514 of locking structure 510 is moved against the bias of the button spring, as shown in FIG. 21, moving button tang 512 away from release flange 508, as shown in FIG. 20. The loading unit 16 can then be rotated and removed from the tip assembly 301 on the elongated body 14. In addition, the locking structure 510 engages the firing rod 58, as the button 514 cams the plunger 516 downwardly into the notch 526, as shown in FIG. 21.

[0069] A locking structure and/or sensor mechanism in accordance with the present disclosure may be used to secure any surgical loading unit, such as a staple cartridge, replaceable tool assembly, or other end effector, while providing for the release of the same from a surgical instrument. Desirably, the manipulatable actuator for releasing and/or locking the surgical loading unit is disposed adjacent the handle assembly. In an endoscopic instrument, the manipulatable actuator is disposed at or adjacent to the proximal end of the endoscopic shaft or elongated body.

[0070] After firing and before removing a loading unit, a retraction mechanism is employed. The retraction mechanism includes return knobs 36 (FIG. 1) which are connected to the proximal end of actuation shaft 52 by a coupling rod 82 (FIG. 4). Coupling rod 82 has right and left engagement portions 82a and 82b which extend through elongated slots 83 (FIG. 1) formed in housing half-sections 38a and 38b and are configured to receive return knobs 36. A central portion 82c of coupling rod 82 is dimensioned to be slidably received within slots 84 formed in the proximal end of actuation shaft 52. A release plate 86 is supported on one side of actuation shaft 52 by a pair of pins 88 (FIG. 4). Pins 88 are positioned within angled cam slots 90 formed through release plate 86. Coupling rod 82 extends through an opening 92 formed in the proximal end of release plate 86.

[0071] In use, when knobs 36 are pulled rearwardly by a surgeon, coupling rod 82 initially moves release plate 86 rearwardly in relation to actuation shaft 52 as rod 82 slides in slots 84 of actuation shaft 52. As this occurs, pins 88 cam release plate 86 downwardly to a position covering toothed rack 60 of actuation shaft 52 to disengage finger 62 of pawl 48 from toothed rack 60. When coupling rod 82 is pulled rearwardly to a position at which it engages the back end 84a of slots 84, additional rearward movement of knobs 36 effect proximal movement of actuation shaft 52 and firing rod 58.

[0072] A hook 96 is supported in a slot 98 formed in a top surface of actuation shaft 52. Hook 96 includes a throughbore 96a dimensioned to receive coupling rod 82. A forward end of hook 96 includes an upturned portion 98 configured to receive one looped end 100a of spring 100. The opposite end of spring 100 includes a loop 100b dimensioned to receive a post 102 formed on actuation shaft 52. Spring 100 is maintained in tension to urge coupling rod 82 towards the forward end of slots 84 in actuation shaft 52. When coupling rod 82 is positioned at the forward end of slots 84 of actuation shaft 52, release plate 86 is held or cammed in a raised position above toothed rack 60 of actuation shaft 52.

[0073] In another embodiment shown in FIGS. 24-28, a locking structure 600 includes a button assembly 602 and an elongated housing 604. The locking structure 600 has a first position (FIG. 27) for locking loading unit 620 and a second position (FIG. 26) for unlocking and disengaging loading unit 620.

[0074] The elongated housing 604 includes an outer tube 622, tube housing 612, and loading portion 606 at the distal end 604b thereof. The locking shaft 614 extends through elongated housing 604 and is shaped to be received by a recess in the tube housing 612 so that the locking shaft 614 is slideable with respect to the tube housing 612 and rotationally fixed with respect to the tube housing 612. The tube housing 612 and locking shaft 614 also define a notch 613 for receiving spring 618 therebetween. (FIG. 26) The loading portion 606 is configured to receive one or more lugs 610 on the loading unit 620 and guides movement of the loading unit 620 onto device 10.

[0075] The tube housing 612 and locking shaft 614 define a space 611 for receiving and locking a lug 610a of the loading unit 620. The tube housing 612 has a shelf 616 on a proximal side of the space 611, an edge 612a on a distal side of the space 611, and edges 612b and 612c on lateral sides of the space 611. The locking shaft 614 has a distally-facing surface 614a, another distally-facing surface 614c, and a longitudinal surface 614b extending therebetween. As best seen in FIG. 26, the distal end of the locking shaft 614 which is defined by the surfaces 614a, 614b, and 614c, has a stepped shape.

[0076] A seal 624 and end cap 626 is disposed at the proximal end 604a of the elongated housing 604. (FIG. 25) The seal 624 is circular in shape and includes 2 walls, which define separate chambers. In a preferred embodiment, the seal 624 and end cap 626 slide over the tube housing 612, as best seen in FIG. 25. The seal 624 has three chambers. The three chambers receive the locking shaft 614, tube housing 612 and an articulation rod (not shown). End cap 626 is in communication with the seal 624, and, upon assembly, the seal 624 presses against the outer tube 622.

[0077] The locking structure 600 includes a button assembly 602, located at the proximal end of the elongated housing 604, which is moveable between a first locked position and a second unlocked position. Button assembly 602 includes a return spring 633 (FIG. 25) which biases the button 631 distally. The button 631 defines a protrusion 632 which engages a slot 634 on the locking shaft 614. Through the interaction of the slot 634 and protrusion 632 the button 631 and locking shaft 614 are moveable between a first and second position as the button 631 is moved by user.

[0078] As shown in FIGS. 24-26, the elongated housing 604 defines a loading portion 606 dimensioned to receive the lugs 610. The tube housing 612 has a groove forming a guiding channel 608 which guides movement of the loading unit 620. As loading unit 620 is inserted into the loading portion 606, lug 610a abuts the surface 614a of the locking shaft 614, moving the locking shaft 614 proximally. A shelf 616, located on tube housing 612, abuts the lug 610a, thus preventing further movement proximally. The loading unit 620 is rotated in Direction A shown in FIG. 26, toward edge 612c. When the lug 610a is aligned with surface 614c, the locking shaft 614 will move distally under the influence of spring 618. The lug 610a is captured between edges 614b, 614c and surfaces 612a, 612c, as shown in FIG. 26, preventing rotational and longitudinal movement. When the user moves the button assembly 630 proximally, against the bias of the spring 618, locking shaft 614 is moved rearwardly, the locking structure 600 disengages loading unit 620 (FIG. 26) and loading unit 620 can be removed. To remove the loading unit 620, the button assembly 630 is moved rearwardly, sliding locking shaft 614 proximally across tube housing 612. The loading unit 620 is removed from the loading portion 606 by rotating the loading portion 606 in the direction opposite to Direction A.

[0079] It will be understood that various modifications may be made to the embodiments disclosed herein. For example, the above described lock assembly may be incorporated into a variety of surgical instruments which include loading units and is not limited to use on endoscopic staplers. Further, the loading unit may be configured to receive an insertion tip of a surgical instrument in contrast to that disclosed. Therefore, the above description should not be construed as limiting, but merely as exemplifications of various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.