Ultrasound is used for many medical applications, most commonly to produces images of inside of the body. Ultrasound is also used for therapy (such as deep tissue heating) and treatment (such as fracture healing or breaking up kidney stones.)
There is good evidence that ultrasound improves the rate at which bone fractures unite, though the precise mechanism is unknown at the time of writing. There is also evidence that ultrasound devices can help in patients who have poor healing potential including diabetics, smokers, and patients taking oral steroid medications.
[Nelson, FR, et al. "Use of Physical Forces in Bone Healing" J. Am. Acad. Ortho. Surg., September/October 2003; 11: pp344-54]