Present value of ultrasonic diathermy.

Under therapeutic conditions most biological reactions to ultrasound are due essentially to the heating produced by absorption of ultrasonic energy. 1 Nonthermal effects also have been observed. 2 Their therapeutic significance is, as yet, poorly understood. Other reactions, such as cavitation, have been found to be destructive phenomena. 3 They occur only at higher intensities than those used with proper techniques in therapy. Therefore, it seems justifiable to consider ultrasonic therapy primarily as a form of diathermy. However, ultrasonic diathermy has some distinctive features. A specific distribution of temperature in the tissues is caused by a selective absorption of the energy in some tissues. 4 As a result, certain anatomic structures such as bones, joints, nerves, and tendons are heated selectively. Furthermore, owing to the short wave length of ultrasound it is comparatively easy to direct and limit the treatment to a certain area. Although ultrasound is a very efficient