An ultrasonic surgical instrument includes a housing, an ultrasonic transducer assembly, and a waveguide. The ultrasonic transducer assembly extends through a proximal opening into the housing and includes a horn disposed within the housing defining a first engagement member (349). The ultrasonic transducer assembly further includes an inner housing extending through the proximal opening and an outer knob (374) disposed externally of the housing and slidably positioned about the inner housing in fixed rotational orientation relative thereto. The outer knob (374) is selectively translatable relative to the inner housing (372) from a proximal, unlocked position and a distal, locked position to rotationally lock the ultrasonic transducer relative to the housing. The waveguide defines a blade at a distal end and a second engagement member at a proximal end. The second engagement member is configured to releasably engage the first engagement member to thereby engage the waveguide with the ultrasonic transducer assembly.
