embodiments of the presently disclosed surgical instrument , and loading unit for use therewith , are described in detail with reference to the drawings , wherein like reference numerals designate corresponding elements in each of the several views . as is common in the art , the term “ proximal ” refers to that part or component closer to the user or operator , e . g ., surgeon or physician , while the term “ distal ” refers to that part or component farther away from the user . a surgical stapling instrument having linear jaw members of the present disclosure is indicated as reference numeral 100 a in fig1 a . a surgical stapling instrument having curved jaw members of the present disclosure is indicated as reference numeral 100 b in fig1 b . collectively , surgical stapling instruments 100 a and 100 b are referred to herein as reference numeral 100 . similarly , several features that are common to both surgical stapling instruments 100 a and 100 b are collectively referred to as the same reference number ( e . g ., handle portion 110 , endoscopic portion 120 , and jaw members 230 ). handle portion 110 of surgical stapling instrument 100 is shown in fig2 , and an enlarged view of the distal end of handle portion 110 , including a distal end of firing rod 130 , is shown in fig3 . a single use loading unit (“ sulu ”) or a disposable loading unit (“ dlu ”) ( collectively referred to as “ loading unit 200 ”), which is mechanically engageable with handle portion 100 is shown in fig4 . loading unit 200 is attachable to endoscopic portion 120 of surgical stapling instrument 100 , e . g ., to allow surgical stapling instrument 100 to have greater versatility . loading unit 200 may be configured for a single use , and / or may be configured to be used more than once . examples of loading units for use with a surgical stapling instrument are disclosed in commonly - owned u . s . pat . no . 5 , 752 , 644 to bolanos et al ., the entire contents of which are hereby incorporated by reference herein . further details of an endoscopic surgical stapling instrument are described in detail in commonly - owned u . s . pat . no . 6 , 953 , 139 to milliman et al ., the entire contents of which are hereby incorporated by reference herein . generally , jaw members 230 of loading unit 200 include a cartridge assembly 222 and an anvil assembly 224 . cartridge assembly 222 houses a plurality of staples or fasteners ( not explicitly shown in the illustrated embodiments ). cartridge assembly 222 includes a plurality of staple pushers for ejecting the staples therefrom . anvil assembly 224 includes staple pockets ( not explicitly shown in the illustrated embodiments ) that are configured to form the staples as they are driven from cartridge assembly 222 . loading unit 200 may include a plurality of cam bars for interacting with the pushers to deploy the surgical fasteners . for example , the apparatus disclosed in u . s . pat . no . 5 , 318 , 221 , the disclosure of which is hereby incorporated by reference herein , in its entirety , has a cam bar adapter that holds a plurality of cam bars and a knife . in this example , a firing rod is advanced through operation of the handle of the apparatus , which drives the cam bars and knife forward . a clamp tube that surrounds the proximal end of the anvil is advanced to clamp the anvil and cartridge together . in another example , the apparatus disclosed in u . s . pat . no . 5 , 782 , 396 , the disclosure of which is hereby incorporated by reference herein , in its entirety , has an actuation sled . in this example , an elongated drive beam is advanced distally through operation of the handle of the apparatus , driving the actuation sled forward . the distal end of the drive beam engages the anvil and the channel that supports the cartridge as the drive beam travels distally , to deploy the staples and clamp the anvil and cartridge together . in a surgical stapling instrument 100 in accordance with the present disclosure , a firing rod 130 is moved distally through actuation of a movable handle 132 to deploy the staples . for example , referring back to fig1 a and 1b , at least a partial actuation of movable handle 132 with respect a stationary handle 134 translates firing rod 130 longitudinally , such that a knife assembly 240 ( fig5 ) translates longitudinally , to approximate at least one jaw member with respect to the other and to eject surgical fasteners ( e . g ., staples ) from cartridge assembly 222 and / or to advance a cutting blade to cut tissue . it is also envisioned that other types of handles can be used such as , for example , motor - driven , hydraulic , ratcheting , etc . with reference to fig4 , loading unit 200 of the present disclosure is shown . loading unit 200 includes a proximal body portion 210 defining a longitudinal axis “ a - a ,” and a tool assembly 220 including a pair of jaw members 230 . proximal body portion 210 is configured to removably attach to endoscopic portion 120 of surgical instrument 100 . more particularly , an insertion tip 202 of loading unit 200 is linearly inserted into the distal end of endoscopic portion 120 ( fig2 and 3 ) of surgical stapling instrument 100 . nubs 204 of insertion tip 202 ( fig4 ) move linearly through slots ( not shown ) formed in the distal end of endoscopic portion 120 . subsequently , loading unit 200 is rotated about the longitudinal axis “ a - a ” such that nubs 204 move transversely through slots ( not shown ) within endoscopic portion 120 . additionally , during engagement of loading unit 200 and endoscopic portion 120 , firing rod 130 of handle portion 110 engages knife assembly 240 of loading unit 200 . an example of a proximal portion 250 ′ of a comparative knife assembly 240 ′ is illustrated in fig5 . as shown , proximal portion 250 ′ includes a first arm 260 ′ and a second arm 270 ′. each of first arm 260 ′ and second arm 270 ′ includes a proximal inwardly extending protrusion 262 ′ and 272 ′, respectively , and a distal inwardly extending protrusion 264 ′ and 274 ′, respectively . fig6 - 7b illustrate the engagement between comparative knife assembly 240 ′ and a comparative firing rod 130 ′. as shown in fig6 , comparative firing rod 130 ′ includes a recess 132 ′ therein and a distal lip 134 ′. lip 134 ′ of comparative firing rod 130 ′ is configured to fit between proximal inwardly extending protrusions 262 ′, 272 ′ and distal inwardly extending protrusions 264 ′, 274 ′ of comparative knife assembly 240 ′. with particular reference to fig7 a and 7b , where transverse cross - sectional views are shown , firing rod 130 ′ includes an inner portion 136 ′ and a pair of outer portions 138 ′. as shown , the height h 1 of inner portion 136 ′ is smaller than the height h 2 of outer portions 138 ′. with continued reference to fig7 a and 7b , the translation of loading unit 200 ( including knife assembly 240 ′) with respect to firing rod 130 ′, as discussed above , is configured to allow distal lip 134 ′ of firing rod 130 ′ to pass through an opening 280 ′ disposed between proximal inwardly extending protrusions 262 ′, 272 ′. additionally , the rotation of loading unit 200 ( including knife assembly 240 ′) with respect to firing rod 130 ′ is configured to position distal lip 134 ′ between proximal inwardly extending protrusions 262 ′, 272 ′ and distal inwardly extending protrusions 264 ′, 274 ′. thus , as can be appreciated , firing rod 130 ′ must be rotated to allow distal lip 134 ′ thereof to be able to physically fit through opening 280 ′ disposed between proximal inwardly extending protrusions 262 ′, 272 ′. as such , when firing rod 130 ′ and knife assembly 240 ′ are properly engaged , proximal and distal translation of firing rod 130 ′ results in corresponding proximal and distal translation of knife assembly 240 ′. with reference to fig8 - 11b , firing rod 130 and proximal portion 250 of knife assembly 240 of the present disclosure are illustrated . similarly to comparative knife assembly 240 ′, knife assembly includes a first arm 260 and a second arm 270 , with each of first arm 260 and second arm 270 including distal inwardly extending protrusions 264 and 274 , respectively . additionally , knife assembly 240 includes a locking mechanism . in the embodiments illustrated in fig8 - 11b , locking mechanism includes a pair of wing elements 300 . wing elements 300 are disposed adjacent a proximal end 252 of proximal portion 250 of knife assembly 240 and are pivotal therewith . in the illustrated embodiments , wing elements 300 are pivotal about a pivot structure 310 ( e . g ., a pin or rivet ; see fig1 a and 11b ). it is envisioned that pivot structure 310 for each wing element 300 extends through its respective first arm 260 or second arm 270 . moreover , with reference to fig1 a and 11b , wing elements 300 are shown having a first side wall 302 and a second side wall 304 , which define a channel 306 therebetween . as shown , channel 306 defines a thickness t c , which is wider than a thickness t a of its associated arm , e . g ., first arm 260 . thus , each side wall 302 , 304 of wing element 300 can move along sidewalls 269 a , 269 b of first arm 260 . additionally , in the embodiments illustrated in fig1 a and 11b , wing elements 300 are biased via a biasing element 312 ( e . g ., a torsion spring ( fig1 a ) or a leaf spring ( fig1 b )) towards an initial position ( fig8 ), where wing element 300 is spaced from first arm 260 , from a second position ( fig9 ), wherein wing element 300 pivoted against first arm 260 . with particular reference to fig1 b , first arm 260 includes a pin 261 extending transversely therethrough , and wing element 300 includes an arcuate slot 301 disposed thereon . ( it is also envisioned that pin 261 extends from first arm 260 .) pin 261 and slot 301 are configured to mechanically engage one another . it is envisioned that the engagement between pin 261 and slot 301 provides guidance for the travel of wing element 300 . additionally , in the illustrated position , pin 261 acts to limit movement of wing element 300 in the direction provided by biasing element 312 . as can be appreciated with respect to fig9 and 10 , the configuration of knife assembly 240 ( including wing elements 300 ) and firing rod 130 allows distal lip 134 of firing rod 130 to enter the space between wing elements 300 and distal inwardly extending protrusions 264 , 274 upon relative longitudinal translation therebetween , and without the need for rotational movement of knife assembly 240 or firing rod 130 . more particularly , distal translation of firing rod 130 , for example , causes distal lip 134 of firing rod 130 to contact wing elements 300 , and to thus cause wing elements 300 to pivot from their initial position ( fig8 ) against the bias of biasing element 312 to their second position ( fig9 ). after distal lip 134 of firing rod 130 translates distally beyond wing elements 300 , wing elements 300 are biased back towards their initial position ( fig1 ). accordingly , wing elements 300 generally serve the same function as proximal inwardly extending protrusions 262 ′, 272 ′ of comparative knife assembly 240 ′. however , wing elements 300 are configured to allow knife assembly 240 of loading unit 200 to engage firing rod 130 of endoscopic portion 120 as surgical stapling instrument 100 is being fired . that is , for example , if knife assembly 240 is prematurely advanced and subsequently is not engaged by firing rod 130 , distal translation of firing rod 130 would automatically cause firing rod 130 to pivot wing elements 300 , and to thus engage with knife assembly 240 . as can be appreciated , if a firing rod only pushes a knife assembly without engaging the knife assembly , retraction of the firing rod would not cause retraction of the knife assembly , thus hindering the unlocking or unclamping of the jaw members . separation of firing rod 130 from knife assembly 240 ( e . g ., to remove loading unit 200 ) is accomplished similarly to comparative firing rod 130 ′ and knife assembly 240 ′, i . e ., by rotating loading unit 200 about longitudinal axis “ a - a ” and longitudinally translating loading unit 200 away from endoscopic portion 120 . with reference to fig1 a - 12c , another embodiment of a knife assembly 240 a is illustrated . here , the locking mechanism includes first arm 260 a and second arm 270 a . each arm 260 a , 270 a is configured to flex in the respective directions of arrows “ a ” and “ b ” ( fig1 b ). additionally , each arm 260 a , 270 a is biased towards the longitudinal axis “ a - a .” it is envisioned that only a single arm 260 a or 270 a is biased towards the longitudinal axis “ a - a .” the flexing and biasing of first arm 260 a and / or second arm 270 a is accomplished via suitable means . for example , it is envisioned that first arm 260 a and / or second arm 270 a is made from stainless steel or another suitable biocompatible metal or polymer . in use , distal translation of firing rod 130 such that distal lip 134 contacts first arm 260 a and second arm 270 a , causes arms 260 a , 270 a to flex in the direction of arrows “ a ” and “ b ,” respectively . after distal lip 134 is translated beyond proximal inwardly extending protrusions 262 a , 272 a , first and second arms 260 a , 270 a move in the direction they are biased , i . e ., towards the longitudinal axis “ a - a ,” such that proximal inwardly extending protrusions 262 a , 272 a are within recess 132 of firing rod 130 ( fig1 c ). accordingly , the flexible , biased arms 260 a and / or 270 a of knife assembly 240 a function similarly to arms 260 , 270 including wing elements 300 . that is , arms 260 a , 270 a are configured to allow knife assembly 240 a of loading unit 200 to engage firing rod 130 of endoscopic portion 120 as surgical stapling instrument 100 is being fired . accordingly , the flexible , biased arms 260 a and / or 270 a of knife assembly 240 a function similarly to arms 260 , 270 including wing elements 300 . that is , arms 260 a , 270 a are configured to allow knife assembly 240 a of loading unit 200 to engage firing rod 130 of endoscopic portion 120 as surgical stapling instrument 100 is being fired . with reference to fig1 a - 13c , another embodiment of a knife assembly 240 b is illustrated . here , the locking mechanism includes a proximal portion 250 b having a first arm 260 b , a second arm 270 b , and a spring 275 b therebetween . proximal portion 250 b is pivotally connected to a distal portion 252 b of knife assembly 240 b . in particular , at least one of first arm 260 b and second arm 270 b is pivotally engaged with distal portion 252 b . in the illustrated embodiment , first arm 260 b is pivotally engaged with distal portion 252 b at a first pivot point 280 b , and second arm 270 b is pivotally engaged with distal portion 252 b at a second pivot point 282 b . additionally , proximal portion 250 b and distal portion 252 b include one of a pair of cam slots 290 b and a pair of pins 292 b , not necessarily respectively , adjacent each pivot point 280 b and / or 282 b . as can be appreciated , the inclusion of cam slots 290 b and pins 292 b help limit the pivotal movement of proximal portion 250 b with respect to distal portion 252 b . each arm 260 b , 270 b is configured to flex in the respective directions of arrows “ c ” and “ d ” ( fig1 b ). additionally , each arm 260 b , 270 b is biased towards the longitudinal axis “ a - a ” via spring 275 b . as discussed above , it is also envisioned that only a single arm 260 b or 270 b is pivotal with respect to distal portion 252 b . in use , distal translation of firing rod 130 a such that distal lip 134 a thereof contacts first arm 260 b and second arm 270 b , causes arms 260 b and / or 270 b to flex in the direction of arrows “ c ” and “ d ,” respectively . after distal lip 134 a is translated beyond proximal inwardly extending protrusions 262 b , 272 b , first and / or second arms 260 b , 270 b move in the direction they are biased , i . e ., towards the longitudinal axis “ a - a ,” such that proximal inwardly extending protrusions 262 b , 272 b are within recess 132 a of firing rod 130 a ( fig1 c ). as shown in fig1 a - 13c , distal lip 134 a of firing rod 130 a includes a pair of angled surfaces 136 a , 138 a . as can be appreciated , angled surfaces 136 a , 138 a facilitate the introduction of distal lip 134 a distally beyond protrusions 262 b , 272 b . additionally or alternatively , a proximal face of proximal inwardly extending protrusions 262 b , 272 b may include an angled surface , such as protrusions 262 a , 272 a illustrated in fig1 a - 12c . accordingly , arms 260 b and / or 270 b of knife assembly 240 b function similarly to arms 260 , 270 including wing elements 300 and to arms 260 a and 270 a . that is , arms 260 b , 270 b are configured to allow knife assembly 240 b of loading unit 200 to engage firing rod 130 a of endoscopic portion 120 as surgical stapling instrument 100 is being fired . it is envisioned that knife assembly 240 , 240 a , 240 b of the present disclosure can be used in combination with an articulatable surgical instrument , e . g ., surgical stapling instrument 100 a in fig1 a . in fig1 a , a lever 140 is shown adjacent a rotation dial 142 and may be used to facilitate articulation of jaw members 230 . actuation of lever 140 causes jaw members 230 to move between a first position , where jaw members 230 are substantially aligned with longitudinal axis “ a - a ,” and a second position , where jaw members 230 are disposed at an angle with respect to longitudinal axis “ a - a .” it is envisioned that moving lever 140 causes an articulation link to move longitudinally , which results in a proximal portion of at least one jaw member moving proximally or distally . that is , moving lever 140 in a first direction causes the articulation link to move proximally ( which articulates jaw members 230 in a first direction ) and moving lever 140 in a second , opposite direction causes the articulation link to move distally ( which articulates jaw members 230 in a second direction ). an articulating loading unit for an endoscopic surgical stapler is disclosed in u . s . pat . no . 6 , 953 , 139 to milliman et al ., the entire contents of which have been incorporated by reference herein . while the above description contains many specifics , these specifics should not be construed as limitations on the scope of the present disclosure , but merely as illustrations of various embodiments thereof . for example , knife assembly 240 , 240 a , 240 b may be configured as a unitary unit , may include multiple layers , and / or may be comprised of several portions ( e . g ., as shown in fig5 ). additionally , it is envisioned that wing elements 300 are disposed on firing rod 130 instead of , or in addition to being disposed on knife assembly 240 , 240 a , 240 b . further , the present disclosure includes a method of modifying a knife assembly to include pivotable wing elements 300 . 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 .
a loading unit configured for engagement with a surgical instrument having a firing rod is disclosed . the loading unit comprises a proximal body portion , a tool assembly , and a knife assembly . the tool assembly is disposed in mechanical cooperation with the proximal body portion . the knife assembly is movably disposed at least partially within the proximal body portion and includes a proximal end positioned to engage the firing rod , and includes a first arm and a second arm . the first arm is biased towards the longitudinal axis via a biasing force . the biasing force is selected to allow the first arm to deflect when the firing rod is advanced . the first arm and the second arm of the knife assembly are configured to engage a firing rod of a surgical instrument as the surgical instrument is being actuated .