Therapeutic Ultrasound is a commonly
used modality in physical therapy and has been shown in clinical and scientific
trials to increase collagen extensibility, enhance collagen remodeling, enhance
collagen production, increase heat in deep tissues, increase blood flow,
increase range of motion, reduce pain and muscle spasm, and accelerate wound
healing. Therapeutic ultrasound is produced by applying an electric current
through a piezoelectric crystal causing it to vibrate at its resonance
frequency. These oscillations of the crystal cause pressure waves to be emitted
and these are subsequently absorbed by the tissues. The two most commonly
used Ultrasound frequencies are 1.0 MHz and 3.3 MHz. The 1 MHz penetrates
more deeply and is used for heating tissues from 2–5 cm in depth. The 3.3
MHz head is used to heat tissues to a depth of 1–2 cm. With the 3.3 MHz head
maximum heat is generated at the 2 cm level. In most cases, the amount of
time tissue temperatures remain elevated is short (within 10 minutes).
The thermal effects of Ultrasound include:
1. Increased metabolic rate of tissues.
2. Increased blood and lymphatic flow.
3. Increased extensibility of collagenous tissues (tendons,
scars, muscle sheaths, joint capsules, ligaments).
4. Decreased pain and muscle spasm.
The non-thermal effects of Ultrasound are:
1. Increased cell diffusion and cell membrane permeability.
2. Increased production of collagen and hydroxyproline.
3. Increased fibroblast proliferation and activity increases
The rate at which the Ultrasound energy is delivered per unit area is expressed
Intensities of 1–2 W/cm2 are used in areas that have a lot of muscle (such
as the thigh) and less intensity is used for other areas (0.5–1.0 W/cm2).
Continuous Ultrasound is best used to heat tissues, and if available, the
pulsed delivery is used when the non-thermal effects of Ultrasound are desired.
A coupling agent is needed to connect the Ultrasound head with the skin in
order to maximize transfer of the Ultrasound energy in top the tissues. Water-soluble
gels are advisable.
Treatment time and frequency
It is important that the hair be clipped over the desired treatment
area. Steiss has shown that the presence of hair interferes with the absorption
of the Ultrasound energy and it is possible to burn the skin if this is not
done, furthermore the hair absorbs the Ultrasound energy and little is available
to heating deeper tissues. The time necessary to treat an area depends on
the size of the treatment area and the size of the transducer head. One can
estimate how many transducer heads fit into the treatment area and for every
two heads allow five minutes. We typically do daily or every other day treatments.