Clinically, this overheating of the periosteum is felt as a dull ache in the bone. Damage to the periosteum, as well as to the capillaries, can occur due to overheating. With excessive therapeutic ultrasound application, increased blood flow from the inflammation can cause bone resorption. Therefore, the therapist should use caution when applying therapeutic ultrasound to joints, to the anterior surface of the lower leg, or to other areas of the body where bone is superficial. The ultrasound unit produces ultrasound waves by applying electrical current to a specialized material that is housed in the sound head of the unit.
Electrical voltage is applied to a crystal with piezoelectric qualities located in the sound head.
Piezoelectric materials change shape when voltage is applied across them. The crystal contracts and expands to alternating electrical current. Therefore, when rapidly alternating current is applied to the crystal, vibration occurs. This vibration typically occurs at one million oscillations per second. Transducers are available with diameters of one cm, five cm, and 10 cm to accommodate both large and small treatment areas.