Therapeutic Effects of Low-Intensity Pulsed Ultrasound on Osteoporosis in Ovariectomized Rats: Intensity-Dependent Study

Abstract

This study investigated the effects of low-intensity pulsed ultrasound (LIPUS) of different spatial-average-temporal-average intensity (ISATA) ranging from 15-150 mW/cm2 on the treatment of osteoporosis in ovariectomized rats. Healthy 3-mo-old female Sprague-Dawley rats were randomly divided into nine groups (n = 12 per group): sham-ovariectomy (OVX) control group, OVX control group and OVX groups treated with LIPUS at seven different intensities (ISATA: 15, 30, 50, 75, 100, 125 and 150 mW/cm2, respectively). LIPUS was applied to bilateral femurs 12 wk post-OVX for 20 min/d for 6 wk. Micro-computed tomography, biomechanical tests, serum biochemical analysis and grip strength tests were performed to evaluate the therapeutic effects of LIPUS at different intensities. Results revealed that LIPUS intensity yielded strong correlations with bone mineral density and bone microstructure (R2 = 0.57-0.83) and bone mechanical strength (R2 = 0.80-0.97), and that the intensity of 150 mW/cm2, instead of the 30 mW/cm2 widely used in bone fracture healing, was most effective in maintaining bone mass among all the LIPUS signals between 15 and 150 mW/cm2. This suggests that higher ultrasound intensity (i.e., 150 mW/cm2) may be more effective than lower intensity in mitigation of osteopenia and osteoporosis.