An apparatus comprises an end effector, an elongate shaft, and a handle assembly. The shaft includes an articulation section that is operable to deflect the end effector away from the longitudinal axis of the shaft. The handle assembly includes a rotary member positioned within an intermediate section of the handle assembly. The rotary member is rotatable about an axis that is parallel to the longitudinal axis of the shaft. The rotary member is operable to control the articulation section of the shaft. The rotary member may include opposing thread sections that simultaneously drive lead screws in opposite longitudinal directions, to thereby control the articulation section. The shaft may be rotatable relative to the handle assembly, and the apparatus may selectively lock or resist such rotation based on the articulation state of the articulation section.
