A surgical instrument adapted for applying a plurality of surgical fasteners to body tissue includes a cartridge module having a cartridge housing containing a plurality of surgical fasteners and a knife. The cartridge module includes a driver disposed to push surgical fasteners out of the cartridge housing. The instrument also includes a firing mechanism associated with the cartridge housing for ejecting the surgical fasteners and the knife from the cartridge housing. The knife includes a detent disposed to contact a mating detent of the cartridge module during longitudinal travel of the knife thereby preventing undesired forward and rearward motion of the knife. The driver includes a detent disposed to contact at least one mating detent formed on the cartridge module.