A surgical instrument, comprising: a housing; an elongated shaft extending distally from the housing, the elongated shaft having a proximal portion coupled to the housing and a distal portion opposite the proximal portion, the elongated shaft defining a longitudinal axis; a drive rod extending at least partially through the elongated shaft, wherein the drive rod is selectively movable in a longitudinal direction with respect to the elongated shaft; an end effector supported by the distal portion of the elongated shaft and adapted for treating tissue, the end effector including an upper jaw member (30,150,222) pivotally coupled to the distal portion of the elongated shaft about a pivot axis and including a first pair of laterally spaced flanges (30a,30b,150a,150b), the end effector further including a lower jaw member (32,152,224) pivotally coupled to the distal portion of the elongated shaft about the pivot axis and including a second pair of laterally spaced flanges (32a,32b,152a,152b), wherein either: (a) the first and second pairs of flanges of the jaw members are arranged in an offset configuration such that one flange of the upper jaw member is positioned on a laterally exterior side of a corresponding flange of the lower jaw member, and the other flange of the upper jaw member is positioned on a laterally interior side of the other flange of the lower jaw member, or (b) the laterally spaced flanges of the jaw members are arranged in a nestled configuration wherein both of the flanges (30a,30b) of one of the jaw members are arranged within a laterally interior side of the laterally spaced flanges (32a,32b) of the other jaw member; some or all of the flanges being configured to cooperate with the drive rod such that longitudinal movement of the drive rod causes the jaw members to move between open and closed positions; the surgical instrument further comprising a knife selectively movable in a longitudinal direction with respect to the drive rod, wherein the knife has a flat profile and the drive rod has a u-shaped profile that includes opposed sidewalls (82a,82b) disposed on either side of and constraining the knife and a lower side wall connector portion for supporting the knife, the connector portion extending between the sidewalls, whereby the drive rod is shaped to envelope and guide the flat knife from at least three sides from a proximal end of the drive rod to a distal end. a housing; an elongated shaft extending distally from the housing, the elongated shaft having a proximal portion coupled to the housing and a distal portion opposite the proximal portion, the elongated shaft defining a longitudinal axis; a drive rod extending at least partially through the elongated shaft, wherein the drive rod is selectively movable in a longitudinal direction with respect to the elongated shaft; an end effector supported by the distal portion of the elongated shaft and adapted for treating tissue, the end effector including an upper jaw member (30,150,222) pivotally coupled to the distal portion of the elongated shaft about a pivot axis and including a first pair of laterally spaced flanges (30a,30b,150a,150b), the end effector further including a lower jaw member (32,152,224) pivotally coupled to the distal portion of the elongated shaft about the pivot axis and including a second pair of laterally spaced flanges (32a,32b,152a,152b), wherein either: (a) the first and second pairs of flanges of the jaw members are arranged in an offset configuration such that one flange of the upper jaw member is positioned on a laterally exterior side of a corresponding flange of the lower jaw member, and the other flange of the upper jaw member is positioned on a laterally interior side of the other flange of the lower jaw member, or (b) the laterally spaced flanges of the jaw members are arranged in a nestled configuration wherein both of the flanges (30a,30b) of one of the jaw members are arranged within a laterally interior side of the laterally spaced flanges (32a,32b) of the other jaw member; some or all of the flanges being configured to cooperate with the drive rod such that longitudinal movement of the drive rod causes the jaw members to move between open and closed positions; the surgical instrument further comprising a knife selectively movable in a longitudinal direction with respect to the drive rod, wherein the knife has a flat profile and the drive rod has a u-shaped profile that includes opposed sidewalls (82a,82b) disposed on either side of and constraining the knife and a lower side wall connector portion for supporting the knife, the connector portion extending between the sidewalls, whereby the drive rod is shaped to envelope and guide the flat knife from at least three sides from a proximal end of the drive rod to a distal end.