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Leicester and Northants branch CPD July 2014 therapeutic ultrasound--practical workshop.

On 20th July 2014, Leicester and Northants branch member and MAC representative Barbara Bletsoe, Podiatrist, gave a lecture and directed a practical hands-on workshop on therapeutic ultrasound procedures.

In this well-attended meeting, Barbara explained the historical background to this modality, the type of equipment available, how it is used in her practice and then conducted live treatments on a steady stream of willing volunteers, who vied with each other to be bombarded with ultrasonic waves.

Barbara explained that the history of ultrasound as a therapeutic tool dates back to the development of what was known in the second world war as SONAR (originally an acronym for SOund Navigation And Ranging) that became the underwater navigation and detection equivalent of RADAR (an acronym for RAdio Detection And Ranging). Sound waves are longitudinal in waveform and require the compression and refraction of a medium (be that air, water or many solids) to be transmitted from the point of origin, and the medium affects the speed of transmission. Electromagnetic waveforms, such as those used in radar on the other hand can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields that travel at the speed of light, even across a vacuum without a physical medium being required for their travel.

Sonar (and Radar) 'came of age' in the 1939-45 war, but both had been based on much earlier research. In the case of sonar, the first UK patent for an underwater echo ranging device was filed at the British Patent Office by English meteorologist Lewis Richardson in 1912 and German physicist Alexander Behm obtained a patent for an echo sounder in 1913. When sonar was used in the second world war it was noted that fish and marine life could be killed by active sonar (active is generating sound and listening for its return as opposed to passive sonar which just listens for sound from, for example, submarines). It was speculated, correctly, that the marine life was being killed by the high frequency sound waves heating them up.

Observation of this warming phenomenon led to speculation that the effect could be used as a therapeutic tool, because the idea of warming tissue to provoke healing was already well-established. For example; American engineer and inventor Nikola Tesla in 1891 first noted that heat resulted from irradiation of tissue with high-frequency alternating current (wavelengths somewhat longer than the longest radio waves) and pointed out its possible medical uses whilst K.F. Nagelschmidt, a German physician, in 1909 coined the term medical diathermy, meaning "heating through". Also, in 1927 Wood and Loomis had published research on "the physical and biological effects of high frequency sound waves of great intensity"

Physical therapies using various electrically operated devices were very popular a few decades ago in podiatry (or chiropody as it was then), seemingly more so than now. For example, my own Aunt, a Birmingham chiropodist who was a member of the Institutes forerunner the JCC, and later the Institute, had by my recollection from the 1950's two 'black light' (ultraviolet) therapy lamps for heating tissue in the lower limb which dated from the 1930's. I also remember large water-filled footbaths with conduction plates in the bottom on which clients would place their feet to have electrical currents passed through them to cure pes planus (apparently). Ultrasound however, has until recently only found its way into a few podiatry practices, being mainly used by physiotherapists.

Barbara went on to explain that in the 'sound head' of a medical ultrasound device, a high frequency electric current is applied to a quartz or barium titanate crystal which provokes oscillation in the crystal and plate to which it is attached and thereby an ultrasonic sound wave. Therapeutic frequencies for ultrasound are 1MHz--3MHz (1 MHz = 1 million cycles per second) which is far outside the range of sound that one can hear, which is between 20 to 20,000 Hz, although the range of frequencies individuals hear is greatly influenced by environmental factors. Frequencies below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great enough.

The devices sound head is applied to skin at the required site and a water based contact gel is used to both provide a direct transmission medium and also lubricate the passage of the applicator as it is moved over the skin.

Either continuous or pulsed ultrasound settings can be employed, pulsed over bony prominences or at acute injury stages (2-10 days old) or continuous for chronic (>11days) or deep tissue injuries. The maximum energy absorption is at the 2-5cm depth in connective tissue, ligaments, tendons, fascia and scar tissue.

Barbara described the effects of ultrasound as follows: a) Thermal--due to the sound waves generating heat in the tissue and b) Vibration--in which the ultrasound produces cavitation that occurs when gas-filled bubbles expand and compress because of ultrasonically induced pressure changes in tissue fluids, with a resulting increase in flow in the surrounding fluid. Acoustic microstreaming, the unidirectional movement of fluids along cell membranes, occurs as a result of the mechanical pressure changes within the ultrasound field. Microstreaming may alter cell membrane structure, function and permeability, which has been suggested to stimulate tissue repair. Effects of cavitation and microstreaming that have been demonstrated in vitro include stimulation of fibroblast repair and collagen synthesis, tissue regeneration and bone healing.

The effects of ultrasound thus translate into benefits that can be summarised as follows; speeding up healing and decreasing pain. Many conditions can respond well to ultrasound such as ligament sprains, muscle strains, tendinopathy, metatarsalgia, bursitis, plantar fasciitis and enthesopathies.

As with any therapy or modality there are of course contra-indications; primarily these are vascular pathologies such as thrombosis, acute sepsis, recent radiotherapy (in the past 9 months) and malignancies. Also, it is suggested that therapeutic ultrasound should not be used, especially on the feet, in persons less than 18 years of age as it may retard osseous development.

The equipment used has in recent years become more affordable, and portable hand-held units running off a transformer that plugs into a normal three-pin socket can be obtained for less that 100 [pounds sterling]. Barbara's 1MHz machine is shown in the photograph earlier in this article. The larger semi-portable machines that undergo heavy use in sports injury and physiotherapy clinics are naturally considerably more.

As with any equipment used professionally, the purchaser has the responsibility of ensuring that it is fit for purpose, safe and complies with legislation concerning electrical appliances such as PAT testing. Also of course, suitable training is necessary to use such items responsibly and safely. Barbara can be contacted via the Leicester and Northants branch if any members wish to discuss this further.

Martin Harvey PGDip PGCert BSc(Hons) Leicester & Northants branch. July 2014.

References

(I) Wood RW, Loomis AL. The physical and biological effects of high frequency sound waves of great intensity. London, Edinburgh, Dublin Philosophical Magazine J Sci 1927;4:417-36

(II) Dyson M. Mechanisms involved in therapeutic ultrasound. Physiotherapy 1987;73:116-20

(III) Webster DF, Harvey W, Dyson M, Pond JB. The role of ultrasound-induced cavitation in the 'in vitro' stimulation of collagen synthesis in human fibroblasts. Ultrasonics 1980;18:33-7

(IV) Byl NN, McKenzie AL, West JM et al. Low dose ultrasound effect on wound healing: a controlled study with Yucatan pigs. Arch Phys Med Rehab 1992;73:656-64
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Title Annotation:BRANCH NEWS
Publication:Podiatry Review
Article Type:Conference news
Date:Sep 1, 2014
Words:1228
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