Ultrasonic tissue dissector

A surgical tool comprising:

• an elongate waveguide configured for being operatively connected at a proximal end to an ultrasonic generator means for generating ultrasonic vibrations, wherein the waveguide has a first diameter, and
• an operative element provided adjacent a distal end of the waveguide, wherein the operative element comprises an elongate effector element having a second diameter, less than the first diameter, and an elongate intermediate portion extending between the waveguide and the effector element and having a third diameter intermediate between said first and second diameters, and wherein
• a first step junction with the effector element is defined at a distal end of the intermediate portion and a second step junction with the waveguide is defined at a proximal end of the intermediate portion,
• said first step junction being located substantially in a nodal plane of ultrasonic vibrations generated in the waveguide, and said second step junction being located substantially at an anti-nodal plane of ultrasonic vibrations generated in the waveguide;
• wherein the intermediate portion has a length substantially corresponding to a quarter of the wavelength of the ultrasonic vibrations therein.