Characterization of LIPUS Parameters Suitable for Hip Bone Fracture

Objective: To investigate the effects of ultrasound treatment on the healing of hip bone fractures using frequencies of 0.5 MHz and 1.5 MHz with constant intensity (30 mW/cm²) at the fractured site. Methods: For the ex vivo experiments, acoustic attenuations of 0.5 MHz and 1.5 MHz ultrasound were measured and compared using different thicknesses of human cadaver and porcine tissues in a hydrophone system. For the in vivo experiments, 20 hip-fractured rabbits were divided into four groups, namely: control, 1.5 MHz with unchangeable intensity (positive control), 0.5 MHz with changeable intensity, and 1.5 MHz with changeable intensity. For the 0.5 and 1.5 MHz groups with changeable intensity, a constant intensity of 30 mW/cm² at the fracture site was achieved using a compensation method for power transmission with reference to the acoustic attenuation. Results: The effective intensity measured using a hydrophone was substantially reduced to 6.16 mW/cm² from 30 mW/cm² in the positive control device after propagating soft tissues with a thickness of 5.0 cm, with an attenuation of approximately 6.0 dB. Meanwhile, for the 0.5 and 1.5 MHz groups, the ultrasound intensity was consistently controlled at 30 mW/cm² after passing through tissues with different thicknesses using the compensation method. In the in vivo study using a newly established hip fracture rabbit model, the best results in bone histomorphometry, mechanical properties, and histological evaluation were consistently found in the 0.5 MHz group, while the 1.5 MHz group exhibited relatively better bone healing than the positive control group. Conclusion: The results suggest a LIPUS frequency of 0.5 MHz together with the consistent intensity of 30 mW/cm² at the fracture site for more effective treatment of hip bone fractures.