How does Therapeutic Ultrasound work?

Therapeutic Ultrasound Overview

Therapeutic Ultrasound is commonly used in physiotherapy clinics for the purpose of stimulating soft tissue repair and for pain relief.

It uses high frequency sound waves that are inaudible to the human ear.  The mechanical effect of these sounds waves causes vibrations that travels through our tissues.

Although there are many applications, ultrasound treatments are broadly divided into 2 categories:  Thermal or Non Thermal.

Thermal Effects

The goal of this type of ultrasound is to provide a deep heating effect.  Therapeutic ultrasound waves travel well through tissues high in water content and are absorbed by tissues with high in protein content.  The absorption of the energy in protein rich tissues is what causes the heating.  The effects of heating tissues include:

  1. Improving circulation
  2. Decreasing joint stiffness
  3. Reducing muscle spasms
  4. Decreasing pain

Non Thermal Effects

In contrast, non thermal (pulsed) ultrasound can lead to increased permeability of cell membranes to sodium an calcium by biophysical processes called cavitation and microstreaming.  Increased calcium stimulates productions of histamines which attracts leukocytes and monocytes.  These cells are an important part of the inflammatory phase of tissue healing.   They assist with cleaning up debris resulting from the injury and forming new connective tissue.

This is how therapeutic ultrasound is thought to accelerate healing.

Contraindications for therapeutic ultrasound

There are some contraindications to using ultrasound including pregnancy, malignancy, infection, and decreased temperature sensation.

This is why you should discuss with your physiotherapist to see if ultrasound is right for you.


In summary, therapeutic ultrasound can serve as a great complement to a robust active rehabilitation program with your physiotherapist.

However, you should not rely solely on this one passive modality to provide a complete and sustainable recovery.  Therapy protocols need to address the source of the problem and any mechanical impairments.

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