the use of common household current converted to an ultrasound wave by the combination of a transformer, transducer head,
and oscillating circuit. The crystal in the transducer head creates the piezoelectric effect of the ultrasound wave, which
allows these waves to penetrate deep into the tissues.
Therapeutic ultrasound in physical therapy produces sound wave frequencies between
0.7 and 3.3 MHz depending on the level of penetration desired. Maximum
energy absorption in soft tissue is 2 to 5 cm. Intensity decreases
as the waves penetrate deeper. They are absorbed primarily by connective
tissue: ligaments, tendons, and fascia (and also by scar tissue). Therapeutic ultrasound has two types of benefit: Thermal effects and non
effects, namely heat, are due to the absorption of the sound waves.
The therapeutic effects of heat include increasing
the extensibility of collagen tissues; decreasing joint stiffness; reducing pain; relieving muscle spasms; reducing inflammation,
edema, and aids in the post acute phase of healing; and increasing
blood flow. The increased blood flow to the affected area provides proteins, nutrients, and oxygen for better healing.
Non thermal effects are from cavitation, resulting in vibration
of the tissue causing microscopic air bubbles to form, which transmit the vibrations in a way that directly stimulates cell
membranes. This physical stimulation appears to enhance the cell-repair effects of the inflammatory response.
Therapeutic ultrasound is usually recommended for muscle as well as joint pain.