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Ultrasound: Why is it used in physical therapy?

Therapeutic ultrasound is a treatment modality occasionally used at MAXX Physical Therapy. It provides deep heating to soft tissues in the body such as muscles, tendons, ligaments, and joints. Ultrasound in physical therapy is not to be confused with diagnostic ultrasound, which is an ultrasound that is used to see the inside of the body, such as checking on a fetus during pregnancy.

What Does Ultrasound Do?

Therapeutic ultrasound is used primarily for two different effects: the deep heating treatment and non-thermal uses.

Deep Heating Effects

Ultrasound is often used to provide deep heating to soft tissue structures in the body. Deep heating tendons, muscles, or ligaments increases circulation to those tissues, which is thought to help the healing process. Increasing tissue temperature with ultrasound is also used to help decrease pain. Deep heating can be used to increase the "stretchiness" of tight muscles and tendons. If you have shoulder pain and have been diagnosed with a frozen shoulder, your physical therapist may use ultrasound to help improve the extensibility of the tissues around your shoulder prior to performing range of motion exercises. This may help improve the ability of your shoulder to stretch.

Non-Thermal Effects (Cavitation)

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 improves the healing of injured tissue. Two types of cavitation include stable and unstable cavitation. Stable cavitation is desired when your physical therapist is applying ultrasound to your body. Unstable cavitation can be dangerous to your body's tissues, and your physical therapist will ensure that this does not occur during the application of ultrasound.

How Does Ultrasound Work?

Inside your MAXX physical therapist's ultrasound unit is a small crystal. When an electrical charge is applied to this crystal, it vibrates rapidly, creating piezoelectric waves. These waves are emitted from the ultrasound sound head as ultrasound waves. The ultrasound wave then enters into your injured tissues during application of the modality. This increases blood flow and cavitation, leading to the theorized benefits of the treatment.

How Is Ultrasound Applied?

Ultrasound is performed with a machine that has an ultrasound transducer (sound head). A small amount of gel is applied to the particular body part; then your physical therapist slowly moves the sound head in a small circular direction on your body. The therapist may change various settings of the ultrasound unit to control the depth of penetration of the ultrasound waves or change the intensity of the ultrasound. Different settings are used in various stages of healing.

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.) Your physical therapist may use ultrasound gel combined with a topical medication to help treat inflammation around soft tissue in the body. This process is called phonophoresis. While there is some evidence that ultrasound waves help deliver the medicated gel to the injured tissues, most published studies indicate that this treatment may be ineffective.

What Ultrasound Feels Like While you are receiving an ultrasound treatment, you will most likely not feel anything happening, except perhaps a slight warming sensation or tingling around the area being treated. 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.


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

  • Over open wounds

  • Over metastatic lesions or any active area of cancer

  • Over areas of decreased sensation

  • Over parts of the body with metal implants, like in a total knee replacement of 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

  • Over active epiphyses in children

  • Over an area of acute infection

Common Injuries Treated

Usually, orthopedic injuries are treated with ultrasound. These may include:

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

Ultrasound for Chronic Pain

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

Ultrasound may not work for everyone, but it is worth a try if you have chronic, unremitting pain. Some people may argue that the benefit of ultrasound for chronic pain is due to the placebo effect. But, if it gives you relief then it is the right treatment for you.

If you are experiencing any of these commonly treated injuries, contact MAXX Physical Therapy today. Our team of professionals have many treatment methods to best assist you with reducing pain, increasing your range of motion, making you stronger, and promoting the overall health of your joints and soft tissue.

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