If you have ever had to avail yourself of the services of a physical therapist for a musculoskeletal condition/injury, the chances are pretty good that you have experienced a treatment modality known as ultrasound.
Therapeutic ultrasound (TUS) is the application of high-frequency (1-3 million cycles per second – the upper limit of human hearing is 20,000 cycles/sec) sound waves to injured tissues such as muscles, ligaments, tendons, etc., with the goal of accelerating healing time, decreasing pain, and improving function.
TUS was developed about 80 years ago and has been a standard practice in physical therapy for at least 50 years. Ultrasound units convert electrical into acoustic energy in a manner too complicated (and useless) to describe here. The sound waves generated are introduced into the human body via a sound head (about 1/5” in diameter). The characteristics of these sound waves are such that they are able to pass through the skin and underlying fat tissues without being affected. When they reach the denser, deeper tissues (mentioned earlier), the sound waves meet some resistance and this results in those tissues being vibrated.
Early laboratory and animal studies showed that this tissue vibration had several effects. One was an increase in the temperature of the tissue if the ultrasound was applied in a continuous manner, which improved tissue extensibility and increased blood flow.
If the TUS was delivered in a pulsed manner, changes in cellular function and protein development were observed, which theoretically would promote tissue healing.
Because these non-human subject studies were so clear in their results, an assumption was made that actual, live people would benefit from the application of TUS, and some limited studies on the physiological effects in human subjects did show at least an increase in deeper body tissue temperatures, so the use of TUS in PT practice took off like a rocket in the 1950s and 60s and the profession as a whole has not looked back. Surveys show that the large majority of orthopedic physical therapists still routinely use TUS in practice, which is why I stated at the beginning that if you’ve had PT, you’ve likely had that cold gel squirted onto you skin and then sat there for 5 minutes while it was spread around with a metallic wand, with you feeling maybe a slightly warm sensation while the therapist told you this was going to help heal your injury faster.
It all sounds good and logical and based on solid science. But there is one problem: the overwhelming majority of clinical studies on the effectiveness of TUS in the real world, with real people with real injuries, have failed to show any significant benefit in terms of reducing pain long-term or in decreasing healing time (as measured by return to activity or function)! Any improvements in either outcome measure are minimal and can easily be attributed to the placebo effect.
s you can imagine, there have been hundreds of studies conducted over the past 60 years, so if the available evidence to support the use of TUS in the clinical setting is underwhelming, why is it still being used so regularly? I think there are two reasons: one is the line of thinking that absence of “proof of effectiveness” does not indicate proof of “absence of effectiveness.” In other words, some argue that until you can prove to me that it doesn’t work, I’ll still go with it.
The other factor is the “…because we’ve always done it this way” philosophy. Inertia is a powerful force to overcome and unfortunately, many physicians still write “ultrasound” on their referrals to PT so patients come to expect that this is supposed to be done and often demand it to some degree, so the train just keeps rolling down the tracks.
If TUS is applied correctly, there is virtually no risk and no downside to you other than potential cost and wasted time. But why incur those if it is unnecessary? If you are receiving physical therapy and they (or your physician) are recommending TUS as part of your treatment, be sure they have a good reason for doing so, and one that counters the large body of evidence to date that argues against its use.