Almost 2 decades ago, it was pointed out that physical therapists tended to overlook the tenuous nature of the scientific basis for the use of therapeutic ultrasound. The purpose of this review is to examine the literature regarding the biophysical effects of therapeutic ultrasound to determine whether these effects may be considered sufficient to provide a reason (biological rationale) for the use of insonation for the treatment of people with pain and soft tissue injury. This review does not discuss articles that examined the clinical usefulness of ultrasound (see article by Robertson and Baker titled “A Review of Therapeutic Ultrasound: Effectiveness Studies” in this issue). The frequently described biophysical effects of ultrasound either do not occur in vivo under therapeutic conditions or have not been proven to have a clinical effect under these conditions. This review reveals that there is currently insufficient biophysical evidence to provide a scientific foundation for the clinical use of therapeutic ultrasound for the treatment of people with pain and soft tissue injury.

/pdf/a-review-of-therapeutic-ultrasound-biophysical-effects-38y2gtr660.pdf

A Review of Therapeutic Ultrasound: Biophysical Effects

Ultrasound-mediated transdermal drug delivery: mechanisms, scope, and emerging trends.

Anti-inflammatory activity of nanocrystalline silver in a porcine contact dermatitis model.

https://www.archives-pmr.org/article/0003-9993(92)90132-G/pdf

Low-dose ultrasound effects on wound healing: a controlled study with Yucatan pigs

The effect of ultrasound at a space-averaged intensity of 0.5 W/cm2:administered for 2-5 min at frequencies of 2.9, 1.5 and 0.79 MHz and mark-space ratios of 1:4(2 ms:8 ms) and 1:1(2 ms:2 ms) was investigated on the acute oedema response of rats to intracutaneous injection of silver nitrate. Rats. anaesthetized with ether were given Evans blue intravenously and two intracutaneous injections of silver nitrate (2 × 10-6 mol) into the abdominal skin. Insonation of one skin site and mock-insonation of the other was performed immediately after the injections. Rats were killed 30 min after the injections and oedema response measured by the amount of dye leakage expressed as absorbance. Significant reduction of dye leakage occurred with treatment of injection sites with ultrasound at 0.79 MHz frequency and durations of application of 2 and 4 min for both mark-space ratios,but not with the other frequencies and durations tested. Further studies are necessary to determine the relevance of this finding to the clinical efficacy of ultrasound in certain inflammatory conditions.

The effect of ultrasound on experimental oedema in rats

The effect of "therapeutic" ultrasound upon plasma extravasation during the inflammatory process induced in the rat hindpaw ankle by intra-articular injection of silver nitrate was investigated in two series of experiments. Both series utilised three ultrasonic frequencies, 0.75, 1.5, and 3.0 MHz, and two pulse ratios, mark:space 1:4 and 1:1. Series 1 examined the effect of two durations of ultrasound, 1 or 2 min, administered once only, and series 2 examined the effect of single or repeated insonations of 1 min duration. It was found that ultrasound treatment increased plasma extravasation compared to controls during the first 24 hr, but later reduced it significantly compared to controls. This secondary effect of reduction in plasma extravasation was delayed in animals given three insonations, this number of insonations being found to prolong the plasma extravasation phase.

The effect of single or repeated applications of "therapeutic" ultrasound on plasma extravasation during silver nitrate induced inflammation of the rat hindpaw ankle joint in vivo.

The origin and early clinical use of ‘therapeutic’ ultrasound are reviewed and theories about the mechanism of action of ultrasound are traced and discussed. Changes of emphasis which have taken place in the empirically-based use of ultrasound are described. Some experimental evidence about the effect of ultrasound on tissue healing in vivo is presented, which indicates the need for controlled clinical trials in physiotherapeutic practice.

Therapeutic Ultrasound: Some Historical Background and Development in Knowledge of its Effect on Healing

Seven newly purchased therapeutic ultrasound transducers were tested using a radiation pressure balance and steel baffles in compliance with Australian Standard Specification T40-1969. Total acoustic output at maximum meter settings, and effective transducer radiating areas were measured. Only one transducer demonstrated the output values nominated by the manufacturer. Two had an appropriate relationship between effective area and total output, though these values were not those stated by the manufacturer. The remaining four had effective radiating areas below the Australian Standards Association tolerance. Three of these had an otherwise acceptable power output and one had a very low output. These data substantiate the need for adequate testing facilities to be available for physiotherapists using ultrasound clinically.

A Survey of Output Characteristics of Some New Therapeutic Ultrasound Instruments Manufactured in Australia

This paper describes an investigation, undertaken at the University of Queensland, into the effect of different ultrasonic frequencies in "therapeutic" dosages on experimental oedema in rats, by means of due leakage estimation. Results indicate that ultra-sound is effective in limiting oedema, but further investigation is required to ascertain the means by which this is brought about.

Margaret C. Fyfe

Papers

The effect of ultrasound on experimental oedema in rats

The effect of single or repeated applications of "therapeutic" ultrasound on plasma extravasation during silver nitrate induced inflammation of the rat hindpaw ankle joint in vivo.

Therapeutic Ultrasound: Some Historical Background and Development in Knowledge of its Effect on Healing

A Survey of Output Characteristics of Some New Therapeutic Ultrasound Instruments Manufactured in Australia

A study of the effects of different ultrasonic frequencies on experimental oedema