What Is Ultrasound Therapy?
Ultrasound therapy uses sound waves that are above the range of human hearing to treat musculoskeletal problems.
Normal human audible range is from 16Hz to around 15-20,000 Hz beyond this upper limit, the mechanical vibration generated by a therapeutic ultrasound machine is called ultrasound. Frequencies used in my physiotherapy clinic are are between 1.0 and 3.0 MHz (this being 1-3 million cycles per second). The basic principle of ultrasound therapy is about “stimulating” tissue by the use of sound waves. These ultrasonic waves are produced by means of mechanical vibration in the metal treatment head of the machine, this treatment head is then moved over the treatment area transmitting the energy into the tissues.
Typically an ultrasound coupling gel is used because when ultrasound waves come into contact with air it causes a dissipation of these waves and the coupling gel helps ensure maximal contact between the treatment head and the surface of the skin, providing a medium through which the sound waves can travel.
Ultrasound can also be applied under water, water also being a medium for ultrasound waves to travel through.
What Conditions Is Ultrasound Therapy Used To Treat?
Therapeutic ultrasound is used to treat a variety of musculoskeletal conditions and research has shown the modality to cause increases in tissue healing rates and scar tissue breakdown.
Due to the increase in tissue activity ultrasound causes using ultrasound therapy on local malignancy, metal implants, local acute infection, vascular abnormalities, and directly on the abdomen of pregnant women is contraindicated. It is also contraindicated to apply ultrasound directly over active growth plates in children or over the eyes, skull, or testes.
However when used by highly trained professionals, therapeutic ultrasound is very unlikely to cause any adverse effects.
How Does Ultrasound Therapy Work?
The therapeutic effects of ultrasound therapy are generally divided into thermal and non thermal effects.
Thermal Effects Of Ultrasound Therapy:
Sound waves are longitudinal waves consisting of areas of compression and rarefaction, tissues exposed to a sound wave will oscillate as the energy within the sound wave is passed into the tissue. As the an ultrasound wave passes through the tissues, the energy levels within the wave will diminish as energy is transferred to the material meaning tissues sitting deeper from the surface will be exposed to less energy than the more superficial tissues. Hence the appropriate selection of correct treatment frequency relative to the tissue being targeted is vital because as mentioned earlier different frequencies of ultrasound have a different depths of penetration.
An increase in the molecular vibration in tissue due to ultrasound therapy can result in the production of heat in the tissue, thus ultrasound can be used to produce thermal changes in tissues.
Tissues most effectively heated via ultrasound include:
- Collagenous tissues (ligament, tendon & fascia)
- Fibrotic muscle tissue
Non Thermal Effects Of Ultrasound
As well as the above thermal effects, ultrasound therapy is considered to have non thermal effects too.
Ultrasound is thought to accelerate the normal resolution time of the inflammatory process by attracting more mast cells to the site of injury and may cause an increase in blood flow which can be beneficial in the sub-acute phase of tissue injury.
Ultrasound may also stimulate the production of more collagen (the main component in tendons and ligaments) hence accelerating the proliferative phase of tissue healing. Ultrasound is also thought to improve the extensibility of mature collagen thus can have a positive effect to on fibrous scar tissue which forms after injury. It is generally considered that any positive healing effects of ultrasound therapy are attributed to the non‑thermal effects of ultrasound more so than the thermal effects.
Disclaimer: Sydney Physio Clinic does not endorse any treatments, procedures, products mentioned. This information is provided as an educational service and is not intended to serve as medical advice. Anyone seeking specific orthopaedic advice or assistance on What Exactly Is Ultrasound Therapy? should consult his or her general practitioner or physiotherapist or otherwise appropriately skilled practitioner.