A surgical instrument includes a housing and an elongated shaft having a distal portion and a proximal portion coupled to the housing. The elongated shaft defines a longitudinal axis and a mandrel at the proximal portion. An inner shaft member extends at least partially through the elongated shaft. An actuating mechanism is operably coupled to the mandrel and is configured to selectively cause movement of the elongated shaft in a longitudinal direction with respect to the inner shaft member. The surgical also includes an end effector that is adapted for treating tissue and includes an upper jaw member pivotally coupled to a distal portion of the inner shaft member about a pivot axis and a lower jaw member supported by the distal portion of the elongated shaft. Longitudinal movement of the elongated shaft is configured to pivot the upper jaw member relative to the lower jaw member.
