Therapeutic Modalities: Ultrasound

While best known for its imaging, ultrasound has many applications in medicine. It can diagnose or treat, depending on its parameters (frequency, duty cycle, intensity). In therapy, ultrasound is commonly used to treat soft tissue injuries. It can facilitate the healing process, speed recovery, and decrease pain if utilized correctly.

But first of all, what is ultrasound? How does it work? Ultrasound utilizes acoustic, or sound, energy that creates pressure waves when applied to the skin. In 1880, Pierre and Jacques Curies discovered that certain crystals produce an electrical charge when mechanically compressed. This is called the piezoelectric effect. Since it is not very efficient to crush crystals whenever we want high-frequency sound waves, ultrasound uses the same concept but in reverse (also known as the reverse piezoelectric effect). Electrical voltage is applied to the crystal, which contracts and expands in response. The vibration of the crystal generates the pressure waves that affect soft tissue. Nowadays, the crystal is encased in the transducer or head of an applicator of an ultrasound unit, and lubricant is used to transmit the energy through the skin to the underlying tissues.

Therapeutic ultrasound has two primary purposes: elevate tissue temperature or facilitate the healing process. Continuous ultrasound provides a deep heating effect to underlying tissue; it can reach to a depth of 5 centimeters. Pulsed ultrasound, on the other hand, affects the cell membranes of the targeted tissues and causes increased cellular permeability, diffusion, and many second order effects. It has been clinically shown to facilitate tissue repair (Dyson & Suckling, 1978; Ennis Valdes, Gainer, & Meneses, 2006; Fyfe & Bullock, 1985). Below are general effects of each ultrasound mode.

Therapeutic Effects of Ultrasound

• Continuous (thermal) ultrasound
  • Increases extensibility of soft tissue
  • Decreases pain and chronic inflammation
  • Reduces joint stiffness and muscle spasms

• Pulsed ultrasound
  • Facilitates tissue healing or repair
  • Increases protein synthesis
  • Can help with fracture or bone healing
  • Decreases inflammation of an acute injury or peripheral nerves

As with all therapeutic modalities, ultrasound is best used in conjunction with a supervised therapy plan with either your occupational or physical therapist.

Source

Bracciano, A. G. (2008). Physical Agent Modalities: Theory and Application for the Occupational Therapist (2^nd ed.). Thorofare, NJ: SLACK Incorporated.