What is therapeutic Ultrasound and how does it work?

At Physio Care Owen Sound, we use therapeutic ultrasound in conjunction with active exercises and manual therapy in the management of chronic pain and sports injuries. But what is therapeutic ultrasound and how does it work? This article will discuss Therapeutic Ultrasound. 

Therapeutic ultrasound is a treatment commonly used in physical therapy to provide deep heating to soft tissues in the body. These tissues include muscles, tendons, joints, and ligaments.

Ultrasound in physical therapy is different than diagnostic ultrasound. With the latter, healthcare providers use ultrasound to see the inside of the body. For example, diagnostic ultrasound lets healthcare providers check on a fetus during pregnancy.

What Is Therapeutic Ultrasound?

Therapeutic ultrasound is a treatment modality that emits high-frequency sound waves via a treatment probe. The most commonly used wave frequencies are 1 Mhz and 3 Mhz. When the high-frequency sound waves are introduced to the body it brings about a therapeutic effect.  The effects are, 

Deep Heating Effects

Ultrasound can provide deep heating to soft tissue structures in the body. Deep heating tendons, muscles, or ligaments could have the following benefits:

  • Increase circulation to tissues
  • Speed the healing process
  • Decrease pain
  • Increase elasticity

Deep heating can increase the “stretchiness” of muscles and tendons that may be tight.

If you have shoulder pain and have been diagnosed with a frozen shoulder, your physical therapist (PT) may use ultrasound. This therapy is usually done before performing range of motion exercises because it can help improve the ability of your shoulder to stretch.

Non-Thermal Effects (Cavitation)

In addition to heat, ultrasound introduces energy into the body. This energy causes microscopic gas bubbles around your tissues to expand and contract rapidly, a process called cavitation.

It is theorized that the expansion and contraction of these bubbles help speed cellular processes and help injured tissue heal faster.

When cavitation is unstable, it can be dangerous to your body’s tissues. So, your physical therapist will work to ensure that the cavitation during therapy is stable.

“Therapeutic ultrasound uses heat and energy to increase circulation, decrease pain, increase flexibility, and speed healing.”

How Does Ultrasound Work?

Inside your physical therapist’s ultrasound unit is a small crystal. When an electrical charge hits this crystal, it vibrates rapidly, creating piezoelectric waves (an electric charge that accumulates in some solid materials). These waves emit from the ultrasound sound head as ultrasound waves.

During treatment, the ultrasound wave then enters your injured tissues. This exposure to ultrasonic waves increases blood flow and cavitation, leading to the theorized benefits of the treatment.

When Is It Used?

PTs may use therapeutic ultrasound to treat some injuries and chronic pain.


Usually, PTs treat orthopedic (musculoskeletal) injuries with ultrasound. These may include:

  • Bursitis (inflammation in the fluid-filled sacs along joints)
  • Tendonitis
  • Muscle strains and tears
  • Frozen shoulder
  • Sprains and ligament injuries
  • Joint contracture or tightness

Generally speaking, any soft-tissue injury in the body may be a candidate for ultrasound therapy. For example, your physical therapist may use ultrasound for low back pain, neck pain, rotator cuff tears, knee meniscus tears, or ankle sprains.

Chronic Pain

There is also some evidence that you may benefit from ultrasound treatments if you have chronic pain. It is thought that the ultrasound waves help improve tissue extensibility and circulation, leading to increased mobility and, ultimately, decreased pain.

“Physiotherapists use therapeutic ultrasound for specific soft-tissue injuries, including joint pain, muscle strains and tears, and ligament injuries. In addition, they sometimes use it for chronic pain.”

What to Expect

Ultrasound uses a machine that has an ultrasound transducer (sound head). First, a PT applies a small amount of gel to the particular body part; then, your physical therapist slowly moves the sound head in a small circular direction on your body.

What Ultrasound Feels Like

While receiving an ultrasound treatment, you will most likely not feel anything happening, except perhaps a slight warming sensation or tingling around the treatment area. If the ultrasound sound head is left in place on your skin and not moved in a circular direction, you may experience pain. If this occurs, tell your physical therapist right away.


Alternative methods of ultrasound application are available if the body part is bony and bumpy or if there’s an open wound. (The ultrasound gel and sound head may harbor bacteria that can enter the wound.) These include:

  • Direct contact (most commonly used method)
  • Water immersion
  • Bladder technique
  • Ultrasound + Medication

Your PT may use ultrasound gel combined with a topical medication to help treat inflammation around the soft tissue in the body. This process is called phonophoresis. 

While there is evidence that ultrasound waves help deliver the medicated gel to the injured tissues, most published studies indicate that this treatment may be ineffective.

“Therapeutic ultrasound does not result in many bodily sensations, other than the feeling of the ultrasound wand against your skin. Your PT may use various settings or different application methods depending on your situation.”


There are some instances where you should not use ultrasound at all. These contraindications to ultrasound may include:

  • Over open wounds.
  • Over metastatic lesions (cancer that has spread) or any active areas of cancer.
  • Over areas of decreased sensation
  • Over parts of the body with metal implants, like in a total knee replacement or lumbar fusion
  • Near or over a pacemaker
  • Pregnancy
  • Around the eyes, breasts, or sexual organs
  • Over fractured bones
  • Near or over an implanted electrical stimulation device
  • Overactive epiphyses in children
  • Over an area of acute infection

Is therapeutic ultrasound safe?

Yes, therapeutic ultrasound is a safe, FDA-approved treatment. There are no known harmful side effects from a therapeutic ultrasound performed correctly by a physical therapist.

Is It Right For You?

In a recently completed randomized control trial on the efficacy of therapeutic ultrasound combined with exercises in knee osteoarthritis, the researchers found it to be effective in providing improvements in pain, mobility, and function. Although there is mixed evidence of the benefits of therapeutic ultrasound your physiotherapist would be able to determine if the modality would be useful in your care plan. 


Alfredo PP, Junior WS, Casarotto RA. Efficacy of continuous and pulsed therapeutic ultrasound combined with exercises for knee osteoarthritis: a randomized controlled trial. Clin Rehabil. 2020 Apr;34(4):480-490. doi: 10.1177/0269215520903786. Epub 2020 Feb 17. PMID: 32063035.

Miller DL, Smith NB, Bailey MR, Czarnota GJ, Hynynen K, Makin IR; Bioeffects Committee of the American Institute of Ultrasound in Medicine. Overview of therapeutic ultrasound applications and safety considerations. J Ultrasound Med. 2012 Apr;31(4):623-34. doi: 10.7863/jum.2012.31.4.623. PMID: 22441920; PMCID: PMC3810427.

https://www.verywellhealth.com/therapeutic-ultrasound-in-physical-therapy-2696419, Aug 21, 2022

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