Effects of Different Therapeutic Ultrasound Intensities on Fracture Healing in Rats

Low-intensity pulsed ultrasound (LIPUS) with ISATA= 30 mW/cm2 has been proven in facilitating fracture healing, which the spatial average intensity over the on period (ISATP) equals 150 mW/cm2. As active ultrasound wave is only delivered during the on period, we postulate 150 mW/cm2 is responsible for the beneficial effect of LIPUS. In this study, we compare the biologic effects of 30 mW/cm2 and 150 mW/cm2. We propose ISATA = 150 mW/cm2 could further enhance fracture healing process. Closed femoral fractured Sprague-Dawley rats were randomized into control, LIPUS-30 (30 mW/cm2) and LIPUS-150 (150 mW/cm2) 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 ISATA= 150 mW/cm2 did not further enhance fracture healing.