What is Therapeutic Ultrasound? Effect, Indication, Contraindication

What is therapeutic ultrasound? Therapeutic ultrasound is a treatment modality in physiotherapy that provides deep heating to injured internal tissues like ligaments, tendons, muscles, and joints.

A person who first encounters therapeutic ultrasound in our clinic often asks me out of curiosity, “What can you see about me on your machine”? The ultrasonic therapy device a physiotherapist uses is not for diagnostic purposes but for therapy/treatment purposes.

And this is why we call it an Ultrasonic THERAPY machine. In this article, we will discuss ultrasonic therapy used by physiotherapists in treating many painful conditions.  

What is therapeutic ultrasound/ UST physiotherapy?

Therapeutic ultrasound is one of the most widely used physical modalities in physiotherapy rehabilitation¹. It is a mode of treatment that uses ultrasonic rays produced by ultrasound therapy machines to relieve musculoskeletal pain, inflammation, swelling, muscle spasms and joint contractures. It is often termed ultrasonic therapy or UST therapy. UST in physiotherapy stands for UltraSonic Therapy, or sometimes it is also called UltraSound Therapy.

There are many technicalities, frequency settings, and intensity adjustments that we need to take care of during the treatment. These technicalities are beyond the scope of discussion here. But you will get the overall picture of what ultrasonic therapy is.  

Ultrasound is a sound wave whose frequency is higher than the frequency of the audible sound wave. It means that there is a certain range of sound wave frequency that the human ear can hear. When the frequency exceeds this audible range, we call it an ultrasound wave.

But, generally, therapeutic ultrasound has a frequency between 0.7 and 3.3 megahertz (MHz) produced by an ultrasonic therapy machine.

What’s the difference between 1 MHz & 3 MHz ultrasound machine

There are two different forms of ultrasound frequency used for therapy purposes. One is 1 MHz frequency, and the other is 3 MHz. Two different ultrasound heads generate these two different frequencies. Depending on the site of the body illness, the types of frequency are selected: 1 MHz is used for treating deeper tissues, and 3 MHz is used to treat superficial tissues².

Both frequencies can be used in continuous and pulsed modes termed Continous Ultrasonic Therapy and Pulsed Ultrasonic Therapy, respectively.

1 MHz vs 3 MHz Ultrasound

How does ultrasound work in physiotherapy

A typical ultrasound therapy machine comprises a device with all its control switches. It is connected to a transducer head through a thick wire. From the device, we can control the intensity and frequency of the ultrasound generated.

We can adjust it according to the needs of the patient. But, it is the transducer head that comes in direct contact with the patient’s body. This transducer head produces the wave.

The transducer head consists of a special material that has piezoelectric properties. It means when a high-frequency electric current passes through this material, it compresses and expands with the alternating current wave.

When this material expands, it pushes the substance in front of it, which produces a compression phase. When it contracts, it rarefies the substance before it, producing a rarefaction phase.

So, there is a continuous production of the wave with alternate compression and a rarefaction phase. The following animation makes this point clearer.

Physiological effects of ultrasound therapy

Two types of mechanisms are commonly invoked to explain the physiological effects produced by ultrasound therapy. These are classed as thermal and non-thermal effects.

Thermal effect of ultrasonic therapy

The thermal or heating effect in the deep tissues is its most important physiological effect. It helps heal tissue injuries that lie deeper by improving the blood supply around the region.

Let us try to understand how ultrasound therapy produces heat in deeper-lying tissues.

During the application of therapeutic ultrasound using an ultrasonic therapy machine, the energy transported by an ultrasonic beam is attenuated (loss of energy) as it passes through tissue. The energy loss is due to scattering out of the beam and absorption. Energy scattered out of the beam may be absorbed elsewhere in the tissue.

We can calculate the loss of energy with this formula³:

I(x) = I0e^-qx

If the intensity in the beam is I0 at a point in the tissue, it will be reduced to I(x) at a distance x from this point. Here, q is the intensity attenuation coefficient.

Acoustic absorption results in tissue healing. In reality, absorption accounts for 60–80% of total attenuation.

Beneficial effects thought to arise from ultrasonically induced heating include:

1. Increase in extensibility of collagenous structures such as tendons and scar tissue.
2. Decrease in joint stiffness.
3. Pain relief.
4. Changes in blood flow.
5. A decrease in muscle spasm and,
6. At high intensities, selective tissue ablation is achieved in focused ultrasound.

Non-thermal effects of ultrasound

Non-thermal mechanisms that can produce beneficial (therapeutic) changes in tissue may be cyclic or non-cyclic.

• ‘Micro-massage’ effect: This is thought to be due to the periodic nature of the sound pressure field.
• Acoustic streaming: Ultrasound waves produce a cavity that oscillates inside the intra- or extracellular fluid called acoustic streaming. Streaming may act to modify the local environment of a cell, leading, for example, to altered concentration gradients in the vicinity of an extracellular membrane. Streaming may account for the reported changes in the potassium and calcium content of cells following ultrasonic exposure.

Therapeutic ultrasound indications

There are many painful conditions where ultrasound therapy is very effective. Its deep micro-massage effect and internal warmth effect can cure many chronic musculoskeletal pain cases.

In my 12 years of physiotherapy career, I have listed these points where I have found them to be very useful.

1.  Muscle pain.
2. Myofascial trigger points.
3. Soften the surgical scar.
4. Softening the tendon after tendon transplant.
5. Plantar fascitis.
6. Carpal tunnel syndrome.
7. Osteoarthritis knee
8. Piriformis syndrome

Contraindications of ultrasound physical therapy

Although it is beneficial in lots of cases, after all, it’s an electromagnetic ray. There are a few conditions where exposure to these rays can trigger internal derangement.

1. Tumor.
2. Pregnancy.
3. Over the metal implants.
4. Knee replacement.
5. Hip replacement.
6. Pacemaker.
7. Eyes.

FAQs on Ultrasonic Therapy in Physiotherapy:

Sunit. S. Ekka

Dr Sunit Sanjay Ekka is a physiotherapist in practice for the last 15 years. He has done his BPT from one of the premium Central Government physiotherapy colleges, ie, SVNIRTAR. The patient is his best teacher and whatever he gets to learn he loves to share it on his Youtube channel and blog.