Acoustic drivetrain with external collar at nodal position

Abstract

An ultrasonic surgical instrument includes a body, a shaft, an ultrasonic transducer, a waveguide, and an end effector coupled to a distal end of the shaft. A rotation knob is rotatably coupled to the body and is configured to rotate the shaft, the waveguide, and the end effector together relative to the body. A torque transfer structure is positioned radially outwardly of and in direct contact with the waveguide at an acoustic node thereof. The torque transfer structure is rotationally fixed relative to the waveguide and is configured to rotationally couple the waveguide with the shaft and the rotation knob. The waveguide includes a first axial constraining feature defining a distally facing surface, and the torque transfer structure includes a second axial constraining feature defining a proximally facing surface configured to abut the distally facing surface to constrain the waveguide axially relative to the torque transfer structure and the body.