Pulsed sine wave ultrasound accelerates bone fracture repair

Low-intensity pulsed ultrasound (US) is shown to have a profound effect on the rate of fresh-fracture repair in a rabbit model; its mechanism of action may be via an electrokinetic effect on the cell membrane´s interfaces. The treated osteotomy received US consisting of a 200-μs burst of 1.5-MHz sine waves repeating at 1 kHz and delivering 20 mW/cm² SATA for 20 min daily. The opposite limb served as the contralateral control. Animals were sacrificed at intervals from day 14 to 28. Destructive torsional testing showed that, from day 17 through to day 28, all US treated fractures were as strong as intact fibulae ( p<0.005) whereas control osteotomies attained intact values only by day 28. These results indicate that US nearly doubles the rate of fracture repair vs. contralateral controls. To examine the possible mechanism of action, the effects of US on osteoblast cell membrane impedance were studied. Results indicate that membrane capacitance and ion-binding kinetics are possible targets. Both parameters could be modified by ionic displacement due to the local interfacial pressure wave (microstreaming)