An apparatus comprises a body, a shaft assembly, an end effector, and an articulation joint. The end effector is operable to manipulate (e.g., staple) tissue. The articulation joint couples the end effector with the shaft assembly and permits the end effector to deflect away from the longitudinal axis of the shaft assembly. The articulation joint comprises a locking assembly, which is operable to selectively lock the angular position of the end effector relative to the longitudinal axis of the shaft assembly； and an unlocking feature. The unlocking feature is operable to selectively unlock the locking assembly. The shaft assembly further comprises a first movable member, which is operable to selectively drive articulation of the end effector at the articulation joint； and a second movable member, which is operable to selectively drive the unlocking feature. The second movable member is movable independently relative to the first movable member.
