Longitudinal effects of low-intensity pulsed ultrasound on osteoporosis and osteoporotic bone defect in ovariectomized rats

Low-intensity pulsed ultrasound (LIPUS) with an intensity (spatial average temporal average, ISATA) of 30 mW/cm2 has been widely proved to be effective on impaired bone healing, but showing little effectiveness in the treatment of osteoporosis. We hypothesized that the intensity of LIPUS may be a key factor in explaining this difference, thus two intensity levels, the widely used 30 mW/cm2 and a higher 150 mW/cm2, were used to simultaneously treat osteoporosis and osteoporotic bone defect in ovariectomized (OVX) rats with a 1-mm drill hole on their left femurs.Results showed that 150 mW/cm2 LIPUS augmented the healing rate of the drill hole than 30 mW/cm2 after 3-week LIPUS treatment, although did not further enhance the healing rate after 6-week LIPUS treatment. For ameliorating osteoporosis, 150 mW/cm2 LIPUS achieved more advantages over 30 mW/cm2 in improving bone density, microstructure and biomechanics 6 weeks after LIPUS intervention. In conclusion, LIPUS with an intensity of 30 mW/cm2 was sufficient to facilitate bone defect healing, but a higher intensity can be considered as a rapid trigger for osteoporotic bone repair. In addition, improving the intensity of LIPUS may be a potentially effective consideration for alleviation of osteoporosis, and the LIPUS regimen in the treatment of osteoporosis remains to be optimized.