Ultrasonic surgical instrument with clamp arm deflection feature

An apparatus includes a shaft assembly and an end effector. The shaft assembly includes a first tube, a second tube, and a distally projecting tongue. The second tube is coaxially disposed within the first tube. One of the first tube or the second tube is configured to translate relative to the other of the first tube or the second tube. The tongue is fixed to either the first tube or the second tube. The end effector includes an ultrasonic blade and a clamp arm. The clamp arm is pivotally coupled to the tongue. The clamp arm is configured to pivot toward and away from the ultrasonic blade in response to relative translation between the first and second tubes. The tongue is configured to flex relative to the first tube and the second tube in response to the clamp arm grasping tissue.