An actuation mechanism for actuating an electrosurgical end effector includes a housing and a shaft assembly extending distally from the housing. The shaft assembly includes an elongate collar, a shaft extending through the elongate collar, and a longitudinal bar axially movable relative to the shaft. The elongate collar has an internal threadform extending along a length thereof. The longitudinal bar includes a proximal end having an extension engaged to the internal threadform of the elongate collar and a distal end configured to be coupled to a knife blade of an electrosurgical end effector. Rotation of the elongate collar axially moves the longitudinal bar relative to the elongate collar to move the knife blade.
