Ultrasonic therapy: physiological basis and clinical application.

Ultrasound is a relatively new but fairly well accepted physical modality. Therapeutically, ultrasonic energy is employed empirically, but the present trend is to utilize low and medium intensities, 0.5 to 2.0 watts per square centimeter, rather than high intensities, over 2.0 watts per square centimeter, for medical purposes. The important physiological effects of ultrasonic energy on living tissue are thermal, mechanical, chemical and biological. Which one of these effects is dominant is not clearly understood. However, the intensity of the ultrasound field and the duration of application determines the extent to which the thermal or the mechanical effect prevails. From a clinical point of view ultrasonic energy has been most effective in the treatment of painful conditions involving the musculoskeletal and neuromuscular structures. More recently, studies have been directed toward the use of ultrasound as a neurosurgical tool.