PHYSICS OF ULTRASONIC SURGERY USING TISSUE FRAGMENTATION .2.

Ultrasonic surgical aspirators typically operate at a frequency betwee n 20 and 60 kHz. A vibrating hollow horn moves against the tissue and suction is applied, The interaction causes tissue to fragment; the fra gmented material is then aspirated, However, the mechanism of interact ion is poorly understood: the most common view relates it to cavitatio n, probably active in concert with other mechanisms, including the dir ect jack-hammer effect, shock-induced stress, acoustic microstreaming and shearing stress, It has also been attributed to chopping, which wi ll produce emulsification. This article reports a study that collected and analyzed ultrasonic, high-speed photographic, visual/optical and electrical data for a 23-kHz unit operating in water and a range of fr esh pig tissues. The primary mechanism for tissue fragmentation is sho wn to be horn-tip impact and other mechanical forces, operating in com bination with hydrodynamic forces applied to the tissue on the forward stroke in each cycle, No evidence of cavitation in tissue was observe d.