Low-intensity pulsed ultrasound (LIPUS) is considered as a type of mechanical stimulus (mechanical stress). When the bone fracture part is treated with a low power ultrasonic pulse, various cells present in the fracture part act as a sensor of the mechanism. It has been reported that the acceptance of mechanical stress is mediated through the cell adhesion factor integrin at the cytoskeleton. Bone response to physical stimulus is different from acceptance of extension (compression) stimulus, which is well-known as mechanical stress acceptance. Accepted information is delivered intracellularly via various intracellular transmission systems and regulates the transcriptional regulatory region of the target gene. The reacted cells act on these stimuli to autocrine, paracrine, differentiation promoting action, cell migration action and the like.
At the fracture site, the fracture healing process as wound healing is progressing, and various cell reactions occur simultaneously or overlapping in time and space. It is thought that when the low power ultrasonic pulse is irradiated, reaction by the above-mentioned mechanical stress occurs in each cell, thereby promoting the overall fracture healing process.