Deep heat: Ultrasound

1. What is ultrasound?
2. What are the thermal and nonthermal effects of ultrasound?
3. What are the indications for ultrasound?
4. What are contraindications and precautions to using ultrasound?
5. How is ultrasound usually administered? What are the direct and indirect techniques?
6. What is phonophoresis?

Answers:
1. Ultrasound is acoustic vibrations with frequencies above the audible range, which can produce thermal and nonthermal effects.
2. Thermal effects include heating of skin, fat, and muscle, increased distensibility of collagen fibers, and absorption by bone and tendon. The highest temperture is produce in cancellous bone and absorption is greatest at the bone-muscle soft tissue interface. Nonthermal effects include cavitation (gas bubbles in a sound field) and acoustic streaming, both of which are associated with wound contraction and protein synthesis.
3. Indications include bursitis, tendinitis, msk pain, degenerative arthritis and contracture (helps to maintain stretch and increases ROM), and subacute trauma. There is less evidence to show efficacy in scar tissue, postherpetic neuralgia pain, and plantar warts.
4. Contraindications include general heat contraindications, near brain, cervical ganglia, spine, and laminectomy sites, near heart or reproductive organs, near pacemakers, near tumors, gravid or menstruating uterus, infection site, skeletal immaturity, THA with methylmethacrylate or high density polyethylene. Precautions include avoiding intensities over 3W/cm2, use stroking technique, use multiple ports over large joints, and only use over water if water is degassed (allowed to sit overnight).
5. Ultrasound is given at a frequency of 0.8-1.1 MHz with intensity of 0.5-2 W/cm2 for 5-10 mins per site, delivered either continuous (greater thermal effects) or pulsed. The direct technique is most common, in which the applicator is moved slowly over an area of 4 sq in in a circular pattern with gel. The indirect technique is for uneven surfaces and involves immersing applicator and body part in degassed water.
6. Phonophoresis is a technique that utilizes US to drive medications through the skin, but increasing cell permeability.