Effects of different therapeutic ultrasound intensities on fracture healing in rats.

Low-intensity pulsed ultrasound (LIPUS) with I(SATA)= 30 mW/cm(2) has been proven in facilitating fracture healing, which the spatial average intensity over the on period (I(SATP)) equals 150 mW/cm(2). As active ultrasound wave is only delivered during the on period, we postulate 150 mW/cm(2) is responsible for the beneficial effect of LIPUS. In this study, we compare the biologic effects of 30 mW/cm(2) and 150 mW/cm(2). We propose I(SATA) = 150 mW/cm(2) could further enhance fracture healing process. Closed femoral fractured Sprague-Dawley rats were randomized into control, LIPUS-30 (30 mW/cm(2)) and LIPUS-150 (150 mW/cm(2)) groups. Weekly radiographs and endpoint microCT, histomorphometry, and biomechanical tests were performed. The results show that LIPUS-30 had significantly higher low-density bone volume fraction and woven bone percentage than that of control and LIPUS-150 in microCT and histologic measurements, respectively. Mechanically, failure torque of LIPUS-30 was significantly higher than control and LIPUS-150 at week 6. In conclusion, LIPUS at I(SATA)= 150 mW/cm(2) did not further enhance fracture healing.