Ultrasound Therapy

Ultrasound therapy is the most commonly used deep therapeutic heating modality in sports medicine.  Ultrasound uses high frequency sound waves to heat the tissues.  The energy is derived from acoustic energy rather than the electromagnetic spectrum.  Sound (acoustic) energy causes molecules in the tissue to vibrate producing heat and mechanical energy.

Ultrasound provides the best compromise between therapeutic heating and deep penetration. In general there are three types of the facts that occur from the application of ultrasound: thermal, mechanical, and chemical.

Thermal Effect -- Skin, fat, and muscle are similar in their response to ultrasound properties.  The greatest differences lie at the bone muscle interfaces were temperatures could increase to as high as 106.7°F.  Joint capsules have been heated to as high as 117.5°F!  Nerve tissue is twice as sensitive to ultrasound as muscle.  Heat developed by ultrasound increases collagen tissue elasticity, alters blood flow, changes nerve conduction velocity, elevates the pain threshold, raises enzymatic activity, and changes muscle contractibility.

Mechanical Effect -- the mechanical effect results from mechanical vibration.  Dispersion and agitation of the molecules commonly called "micro-massage" occurs.  This action packs on the cement some that holds collagen fibers together causing a fiber separation.

Chemical Effect -- ultrasound accelerates enzyme activity, increases capillary permeability, and increases ATP activity in skeletal muscle.

Ultrasound should be a treatment of choice for joint contractions, scar tissue, tendonitis, bursitis, skeletal muscle spasm, and pain.

Conditions that develop an undesirable calcification are often also treated with ultrasound.  There are number of approaches in the use of ultrasound therapy.  The use of ultrasound therapy to introduce a medication (hydrocortisone for example) into the patient is called phonophoresis.  Because acoustic energy cannot travel through air, a coupling media must be used between the applicator and the patient skin.  Coupling mediums can include a variety of materials including mineral oil or water-soluble creams or gels.

Ultrasound can be used in combination with electrical stimulation.  This leads to an enhanced benefit. Electrical stimulation is the application of electrical currents to specific muscles through strategic placement of electrodes. It is often used for neuro-muscular reeducation and decreasing pain through nerve blocks, atrophy and muscle spasms while increasing range of motion. It also reduces edema through sensory stimulation.  Combo therapy is efficient in managing contractures, increasing range of motion, managing pain, increasing strength and training muscles to increase continence.

Both ultrasound and electrical stimulation can be used to decrease pain. Ultrasound can increase circulation and blood flow to effected areas, decrease pain, as well as edema and muscle tightness. Electrical stimulation can be used for similar symptoms and for completing a nerve block. This reeducates the sensory system.

Bonus: For those of you who are engineer or physics minded (or for inquiring minds who just want to know) -

The number of movements or oscillations in one sack and is referred to the frequency of the sound wave.  The number of oscillations within one second is known as a Hertz unit.  One Hertz equals one cycle per second; 1kHz equals 1000 cycles per second.  When the sound scatters and is absorbed as it penetrates through the tissue the energy is decreased this is called attenuation.  Absorption of sound increases with an increase in frequency.

1MHz is a frequency most commonly used in ultrasound therapy.  Tissue penetration depends on impedance or physical properties of the tissue that you are treating.  Sound reflection occurs when the adjacent tissues have different impedance.  The greater the impedance, the greater the reflection, and more heat is produced.  The greatest heat is developed between bone and adjacent soft tissue interfaces.

The main piece of equipment for delivering ultrasound is the high frequency generator.  This produces an electrical current, which is transmitted through a coaxial cable to a transducer contained within an applicator.  In the applicator there are crystals, like quartz, that produce piezoelectric affect which causes expansion and contraction of the crystals to produce the oscillation voltage.  The intensity of the ultrasound beam is determined by the amount of energy delivered to the sound head.  Is expressed in the number of watts per square centimeter.  A therapeutic modality in ranges from 0.5 - 3.0 W/cm2.  .

*Referenced by DCOnline and Dr. Bill Moreau, DACBSP(TM)