Argedine, Heather

Low-intensity pulsed ultrasound is a commonly prescribed therapy for delayed unions and nonunions after fractures. Several prospective double-blind clinical trials have shown that a 1.5-MHz ultrasound signal at a 200-s tone burst repeating at 1 kHz shortens the time to clinically evaluated healing by 30%. We have shown in vitro that pulsed ultrasound increases aggrecan gene expression and aggrecan production in chondrocytes, a key cell in the fracture healing process. Because the square wave pulsed 1.5-MHz signal produces radiation force vibration at 1 kHz, we tested the hypothesis that dynamic radiation force, not ultrasound, is responsible for the biological effect of the signal. Experiments showed that a 1-kHz acoustic square wave, simulating the radiation force caused by the clinically used signal, induced chondrogenesis similarly to pulsed ultrasound treatment in ATDC5 cells. These results may have implications for remote ultrasound or acoustic stimulation of different types of strain-sensitive cells in addition to those responsible for fracture healing.