A stapler cartridge comprising: a cartridge body elongated between a distal end and a proximal end, the cartridge body comprising a plurality of openings at an upper surface for ejecting staples, the cartridge body comprising an upward sloping distal cam surface, a longitudinal slot, and a central cavity ceiling; a drive member slidingly coupled to the cartridge body, the drive member comprising a receptacle and one or more distally-facing ramps configured to deploy staples as the drive member is advanced distally; and a knife member comprising a body portion disposed within the longitudinal slot, a cutting blade, a first protrusion extending from the body portion transverse to the longitudinal slot, and a second protrusion extending from the body portion transverse to the longitudinal slot wherein the first protrusion is configured to be contacted by the drive member during a distal advancement of the drive member so that the knife member is advanced distally with the drive member during a first portion of the distal advancement of the drive member, the knife member being configured to be constrained by both the drive member and the central cavity ceiling during the first portion of the distal advancement of the drive member, and wherein, the second protrusion is configured to be disposed within the receptacle during the distal advancement of the drive member, a distal end portion of the knife member being configured to be driven along the upward sloping distal cam surface during a second portion of the distal advancement of the drive member so as to rotate the knife member relative to the drive member around the second protrusion, thereby lowering the cutting blade into the cartridge body. a cartridge body elongated between a distal end and a proximal end, the cartridge body comprising a plurality of openings at an upper surface for ejecting staples, the cartridge body comprising an upward sloping distal cam surface, a longitudinal slot, and a central cavity ceiling; a drive member slidingly coupled to the cartridge body, the drive member comprising a receptacle and one or more distally-facing ramps configured to deploy staples as the drive member is advanced distally; and a knife member comprising a body portion disposed within the longitudinal slot, a cutting blade, a first protrusion extending from the body portion transverse to the longitudinal slot, and a second protrusion extending from the body portion transverse to the longitudinal slot wherein the first protrusion is configured to be contacted by the drive member during a distal advancement of the drive member so that the knife member is advanced distally with the drive member during a first portion of the distal advancement of the drive member, the knife member being configured to be constrained by both the drive member and the central cavity ceiling during the first portion of the distal advancement of the drive member, and wherein, the second protrusion is configured to be disposed within the receptacle during the distal advancement of the drive member, a distal end portion of the knife member being configured to be driven along the upward sloping distal cam surface during a second portion of the distal advancement of the drive member so as to rotate the knife member relative to the drive member around the second protrusion, thereby lowering the cutting blade into the cartridge body.