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Does Therapeutic Ultrasound Work?

Many concerns about the widespread usage of therapeutic ultrasound, especially extracorporeal shockwave therapy (ESWT)

updated (first published 2009)
by Paul Ingraham, Vancouver, Canadabio
I am a science writer and a former Registered Massage Therapist with a decade of experience treating tough pain cases. I was the Assistant Editor of ScienceBasedMedicine.org for several years. I’ve written hundreds of articles and several books, and I’m known for readable but heavily referenced analysis, with a touch of sass. I am a runner and ultimate player. • more about memore about PainScience.com
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Photograph of ultrasound applied to the back of an elderly man’s shoulder.

Ultrasound is ultra-popular … and ultra-unproven.

SUMMARY

Ultrasound therapy is the use of sound waves to treat medical problems, especially musculoskeletal problems like inflammation from injuries (sprains, tendinitis, bursitis). It has been a popular therapy for decades, its use so widespread that it almost defines physical therapy. Unfortunately, although mainstream, it is not as scientific a treatment as most people assume. It has been condemned or, at best, damned with faint praise by one scientific review after another for a quarter century. Authors had almost nothing good to say about ultrasound. Conclusions like this one (from van der Windt et al) are the rule: “As yet, there seems to be little evidence to support the use of ultrasound therapy in the treatment of musculoskeletal disorders.” Some modern variants of ultrasound are expensive, hyped, and totally unproven for any or many conditions.

full article 3500 words

Ultrasound therapy (US) is the use of sound waves above the range of human hearing12 to treat injuries like muscle strains or runner’s knee. It is mostly used by physical therapists, and has been one of the Greatest Hits of musculoskeletal medicine since the 1950s.34 There are many flavours of therapeutic ultrasound, using different intensities and frequencies of sound, but all share the basic principle of “stimulating” or even provoking tissue with sound waves.5

Almost everyone seems to assume that ultrasound is proven — good technological medicine — but that just doesn’t seem to be the case.

There is a jarring, bizarre lack of research for such a popular therapy.Unfortunately — although there are some interesting exceptions and tantalizing hopes for some conditions — ultrasound is not a promising therapy for most of the painful problems it is used for. There is a jarring, bizarre lack of quality research for such a popular, mainstream therapy. What little research is available paints a bland picture. Ultrasound therapy isn’t even on good theoretical foundations. At best, it’s more complicated and unpredictable than most therapists believe. At worst, there is no rational basis for US at all.

Although ultrasound is almost certainly useful for some patients, some of the time, it is not a reliable or evidence-based therapy, and enjoys far more credibility than it deserves.

I do not like the principle of using magic machines to treat.

“Nari,” physical therapist, in an internet forum discussion

Flavours of therapeutic ultrasound

The vast majority of patients will encounter ultrasound in one of two forms:

  1. the ordinary sort familiar to almost anyone who’s had any kind of physical therapy,
  2. or its more expensive, intense, painful, and high-tech and over-hyped cousin,6 Extracorporeal Shock Wave Therapy (ESWT)

Garden-variety therapeutic US is cheap and available everywhere. The machines are small, even portable (you can buy small handheld ones). Treatment is brief and painless, and applied (indiscriminately?) to virtually anything that hurts — almost any common painful musculoskeletal problem.

ESWT uses much stronger sound waves — shock waves!7 (Radial “shock” wave therapy is a bit different.8) Treatment is painfully intense and painfully pricey.9

On the one hand, ESWT is just a “more is better” version of standard US, because it is often used with the same imprecise clinical intention to stimulate/provoke tissues. On the other hand, because it was originally developed for smashing gall stones, ESWT is strong enough to actually disrupt tissue, such as calcifications in tendons — which is a nice precise clinical goal and a whole different kettle of fish.

Therapeutic ultrasound: the lack of science

When I started studying for this article way back in the mid-2000s, I was quite surprised by how little there was to study. Every scientific paper about US points out there is not enough research on this topic, or at least not enough good research. For instance, a 2015 review of ultrasound for rotator cuff tendinopathy (cited below) found only six trials — all poor quality.

That’s not a lot to go on, and it’s typical. As you’ll see in the overview of reviews below, ultrasound is still shockingly under-studied. We’re talking about ultrasound, here: one of the staples of physical therapy! It practically defines the experience of going to a physiotherapists. Everyone has had that cold gel slapped on an injury, and felt that tingling, penetrating … placebo?

Ultrasound is pseudo-quackery

The disconnect between the popularity of US and the more or less total lack of informative research is troubling. A handful of good studies is a joke for a therapy that is worth literally billions of dollars in the marketplace. How can that much therapy be sold without a satisfactory body of evidence that it works? Bizarre! This is the ultimate example of pseudo-quackery: popular treatments that aren’t overt quackery (they are plausible, not obviously at odds with established science) but fall well short of validated, scientific medicine and are sold with excessive confidence and usually considered mainstream.

This does not mean that US never works for anyone. It does mean that it has been prescribed and sold to patients for decades with unjustified confidence. And that is not cool.

The discouraging state of what little evidence there is about ultrasound

In most cases I consider ultrasound less than useless — that's 8-10 minutes wasted that could be used doing something that might actually help.

Jason Silvernail, DPT, Board-Certified in Orthopedic Physical Therapy, in an internet forum discussion

It’s not rocket science: ultrasound is an unusually easy treatment to test.10 If it works reasonably well, then the results should be pretty clear. Just compare results in patients who received real ultrasound to patients who get a fake instead! And yet, to a shocking degree, these simple tests have simply not been done adequately. There are just a few dozen such experiments in the scientific literature, and most of them are seriously flawed. Conclusions from evidence reviews like this one from van der Windt et al are typical:

As yet, there seems to be little evidence to support the use of ultrasound therapy in the treatment of musculoskeletal disorders. The large majority of 13 randomized placebo-controlled trials with adequate methods did not support the existence of clinically important or statistically significant differences in favour of ultrasound therapy.

van der Windt et al, “Ultrasound therapy for musculoskeletal disorders: a systematic review,” Pain, 1999

Did not support the “existence of”? Ouch! Ultrasound’s therapeutic effect has an existential crisis.

Several reviews give a nod towards some ray of hope. For instance, van der Windt et al, despite their overwhelmingly negative conclusion, also noted that “findings for lateral epicondylitis [tennis elbow] may warrant further investigation.” But, naturally, that optimism about tennis elbow is contradicted by other studies.Staples The science is mostly a discouraging, unimpressive mess — a classic case (yet another one) of failure to impress.

An overview of ultrasound reviews: lots of “garbage in, garbage out”!
van der Windt 199911 musculoskeletal disorders strongly negative review of 13 “adequate” trials did not support “the existence” of therapeutic effects
Robertson 200112 pain and injury “little evidence” of therapeutic benefit in 10 “acceptable” trials out of 35 candidates; 2 positive trials, 8 negative
Baker 200113 biological effects “insufficient biophysical evidence” to justify therapeutic use for pain and injury
Buchbinder 200614 tennis elbow nine studies produced “platinum” level (better than gold!) evidence of “little or no benefit” (for ESWT)
Ho 200715 tennis elbow conflicting, “unconvincing” evidence of efficacy from a few trials (of ESWT again)
Ho 200716 rotator cuff tendinopathy limited evidence “supports … ESWT for chronic calcific rotator cuff tendonitis,” but no non non-calcific
Rutjes 201017 osteoarthritis of knee a positive update to a previously negative review, which is strange because it’s based on just 5 small, poor quality trials with trivial “positive” results
Shanks 201018 lower limb conditions inconclusive review of 10 of 15 candidates: “no high quality evidence available”
van den Bekerom 201119 ankle sprains inconclusive but discouraging review of “five small placebo-controlled trials”; the “potential treatment effects of ultrasound appear to be generally small”
Page 201320 carpal tunnel syndrome inconclusive but slightly encouraging review of “only poor quality evidence from very limited data” from 11 trials
Ebadi 201421 chronic low back pain inconclusive and underwhelming review of 7 small trials, none of them good quality
Desmeules 201522 rotator cuff tendinopathy negative review “does not provide any benefit…based on low to moderate level evidence” from 11 weak trials

Ultrasound reborn as shockwave therapy

Therapeutic ultrasound … has fallen out of favor as research has shown a lack of efficacy and a lack of scientific basis for proposed biophysical effects.

Baker et al, “A review of therapeutic ultrasound: biophysical effects,” Physical Therapy, 2001

Except it hasn’t fallen out of favour! It’s still widely used. The only professionals it’s fallen out of favour with, I imagine, are a small minority of scientists and unusually alert clinicians.

Not only that, but ultrasound has found new life in the marketplace as shockwave therapy — faster, stronger waves, and a bigger price tag! Consider this marketing language from a Canadian company, Shockwave Institute, specializing in delivering ESWT:

Provided you are a candidate for this type of treatment, clinical studies suggest there is a 80–85% chance this technology will improve your condition.

from the Shockwave Alberta FAQ, as of Nov 30, 2009

Shockwave Alberta certainly doesn’t think ultrasound has fallen out of favour! Here we have an entire company devoted to delivery of therapeutic US, and selling it with the implication that it is not only proven to be effective, but exactly how effective — to within 5%!

Based on the available evidence, do you think it’s actually possible or meaningful to declare that ESWT is exactly “80–85% effective”? Where are the scientific review papers confirming this marvellous triumph of US? Where is the data to support such a specific promise of therapeutic success?

Photograph of a shockwave therapy applied to the front of a young woman’s shoulder.

Shockwave therapy equipment is generally bigger and more badass.

Patient cynicism about ultrasound

There is nothing a cold slimy prickling ultrasound wand can do that a pair of warm hands can’t do way better.

Diane Jacobs, Canadian physiotherapist and writer

If only I had a buck for every time a patient or reader has told me that they are skeptical about “that ultrasound thing they always do to you at physiotherapy”!

Patients often express irritation with a common physical therapy business model: working with several patients at once, rotating between rooms or beds, often leaving patients with passive therapies (like a moist hot pack from a hydrocollator — nice enough, but worth a steep fee?) Many patients often go a step further and complain specifically about ultrasound and TENS, skeptical that these treatments really do anything.23 To the patient, these treatments seem unremarkable & also obvious ways for a physiotherapist to get paid while not doing much.To the patient, they seem therapeutically unremarkable and also obvious ways for a physiotherapist to get paid while not doing much. This perception really pushes people’s “I don’t want to be a sucker” button.

And so few patients are singing the virtues of standard US. It not only fails to generate testimonials, but actually generates many annoyed antimonials.

Patients do not (yet) feel the same cynicism about shockwave ultrasound. As a more expensive and painful medicine, ESWT is a hope-generating machine. Having spent their hard-earned dollars and endured the discomfort of treatment, patients are more subject to expectation effects (placebo) — and much less willing to entertain the possibility that it was all a waste. At this stage in their quest to feel better, more people will report ambiguous results if they were positive (“Yeah, I think it did some good!”), and even negative reports will often be toned down (“I didn’t seem to get that much out of it, but I guess it works really well for some people.”) This could go on for years.

Photograph of an elderly man lying face down on a therapy table, with a professional applying ultrasound to his back.

Few if any patients are out there singing the virtues of standard ultrasound. It not only fails to generate testimonials, but generates many bitter antimonials.

How ultrasound supposedly works

The big idea is — this will blow your mind! — that cells and tissues respond “well” to being shaken (not stirred). In theory, ultrasound works by vibrating tissues back to health, which sounds like something you’d hear on an infomercial, or the Dr. Oz Show. What, exactly, does vibration do to tissues? Does anyone actually understand it?

No!

In 2001, Physical Therapy published a review of the biological effects of ultrasound. More than ten years ago, the authors — Baker, Robertson, and Duck — explained that it had already been at least two decades since it was first pointed out that “physical therapists tended to overlook the tenuous nature of the scientific basis for the use of therapeutic ultrasound.”24 They also point out — it’s the point of their whole paper — that the situation had not improved in twenty years (before 2001):

The frequently described biophysical effects of ultrasound either do not occur in vivo under therapeutic conditions or have not been proven to have a clinical effect under these conditions. This review reveals that there is currently insufficient biophysical evidence to provide a scientific foundation for the clinical use of therapeutic ultrasound …

There is lots of interesting ultrasound biology to consider, and scientists may eventually nail down effects that might be the basis for new evidence-based therapies. For instance, a decade later, Tsai et al declared that “There is strong supporting evidence from animal studies about the positive effects of ultrasound on tendon healing”25 — but animal studies are notoriously misleading, and they certainly can’t justify the use of ultrasound (especially when US has already been tested on tendinopathy with underwhelming results).

The clinical bottom line is complex and unpredictable, and there is no basis for concluding that ultrasound has a basis. The entire enterprise rests on the single, oversimplified idea that “stimulation is good” and the hope that we might someday figure out exactly why. Ultrasound is literally just tissue vibration therapy.

The gate control mechanism: a particularly bogus rationale for ultrasound (especially ESWT)

Physical therapists often cite the “gate control” mechanism as a justification for US and ESWT (and some other popular treatments, especially TENS). This is nonsense and a great example of why patients should be cautious, especially with the expense of ESWT.

The “gate control” mechanism is an important idea in pain science, proposed in 1965 by Dr. Ronald Melzack and Dr. Patrick Wall, and still accepted today as an explanation for a familiar phenomenon: the way we rub injured body parts for a little pain relief. The idea is that pain signals pass through a “gate” in the spinal column. The state of the gate is controlled by many factors. How much pain can get through depends on competing signals and information from other sources, such as touch and pressure, as well as emotional context.

So the idea with US is that the stimulation closes the gate and thus reduces pain. This may well occur, but it’s nothing to write home about. It’s not a “treatment” — it doesn’t fix anything— and it’s simply ridiculous as a justification for an expensive therapy. It’s a minor and temporary effect, and can be achieved just as easily by rubbing the area yourself! There is no reason to think that any kind of ultrasound closes the gate better or longer than any other stimulus.

The reasons for doing ultrasound are not at all clear, and adding this one is just a way to pad the list in a way that sounds scientific — especially handy when you’re trying to sell expensive ESWT — but is actually almost meaningless. It’s disturbingly marketing-savvy, but not at all medically savvy.

A study of ultrasound therapy shows a clear effect on trigger point sensitivity

File this one under “intriguing”: Canadian researchers treated trigger points (muscle knots) in 50 patients with either ultrasound or a sham, and the amount of pressure on the trigger point required to induce pain was measured before and after. Trigger points treated with ultrasound were more tolerant of pressure than those that were not treated, at 1, 3 and 5 minutes after treatment.26 The improvement was no longer significant just 10 and 15 minutes later, however — so the effect in this case was brief. The authors concluded:

…low-dose ultrasound evokes short-term segmental antinociceptive effects on trigger points which may have applications in the management of musculoskeletal pain.

They are not necessarily proposing that ultrasound is a useful treatment for myofascial pain syndrome, but producing evidence of an interesting effect that may prove to be clinically significant in time — an important distinction.

Although it may be surprising in contrast to the generally unimpressive evidence of the effectiveness about therapeutic ultrasound, it nevertheless reinforces that ultrasound does indeed do some interesting things to tissues: it’s just not clear exactly what. An important caveat is that there is significant scientific debate about what “trigger points” really are.27 Some would say it’s hard to study the effect of ultrasound on a phenomenon that may or may not even exist!


About Paul Ingraham

Headshot of Paul Ingraham, short hair, neat beard, suit jacket.

I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.

Related Reading

What’s new in this article?

Big science update — Added a table of summarized recent reviews, including six new citations from the last decade (basically all still about scanty, crappy evidence). Several related editorial changes.

Notes

  1. Healthy young adults can hear sounds up to about 20 kilohertz (20,000 hertz). Ultrasound machines produce sound waves from about that frequency and up. BACK TO TEXT
  2. Below the range of human hearing is “infrasound,” which doesn’t come up much. Some animals, like elephants, use infrasound for communication. Not therapy, as far as we know, but I wouldn’t put it past them! Elephants are clever. Other infrasound communicators: hippos, alligators, whales. Cat purring drops down almost to infrasound range. BACK TO TEXT
  3. Wong RA, Schumann B, Townsend R, Phelps CA. A survey of therapeutic ultrasound use by physical therapists who are orthopaedic certified specialists. Phys Ther. 2007 Aug;87(8):986–94. PubMed #17553923. PainSci #55380.

    Ultrasound is widely used. This 2007 survey of the usage of ultrasound, the first such American survey for almost 20 years (see Robinson 1988), “examined the opinions of physical therapists with advanced competency in orthopedics about the use and perceived clinical importance of ultrasound.” They found that “ultrasound continues to be a popular adjunctive modality in orthopedic physical therapy. These findings may help researchers prioritize needs for future research on the clinical effectiveness of US.”

    BACK TO TEXT
  4. Armijo-Olivo S, Fuentes J, Muir I, Gross DP. Usage Patterns and Beliefs about Therapeutic Ultrasound by Canadian Physical Therapists: An Exploratory Population-Based Cross-Sectional Survey. Physiother Can. 2013;65(3):289–99. PubMed #24403700. PainSci #53385.

    This 2013 Canadian survey of the usage of ultrasound found that “despite the questionable effectiveness of therapeutic US, physical therapists still commonly use this treatment modality, largely because of a belief that US is clinically useful. However, US usage has decreased over the past 15 years.”

    BACK TO TEXT
  5. This is also the core principle of numerous other treatment modalities, particularly the gadgets and widgets — your muscle vibrators and lasers and so on — they all stimulate in one way or another, generally with unknown biological and clinical relevance. It would be going a little too far to say that they are all equally dubious (without citations), but after a few years of studying this stuff they do start to seem awfully similar and under-impressive. BACK TO TEXT
  6. If the Wikipedia page for a treatment sports the warning “appears to be written like an advertisement,” that’s a bright red flag about its validity. Same with the “needs additional citations” warning. As of early 2015, the ESWT page has both. BACK TO TEXT
  7. Specifically, a strong (fast) sonic pulse for a short length of time (approximately 10 milliseconds). Shockwave therapies use waves travelling faster than the speed of sound (in flesh), about 1500 meters per second. BACK TO TEXT
  8. There are several different types of extracorporeal shockwave therapy. One of them, radial shockwave therapy, is often called “shockwave” therapy, but probably shouldn’t be, because it uses much lower velocity waves. Radial ultrasound is a couple orders of magnitude slower than other shockwave ultrasound — about 100 meters per second, instead of 1500 — and would be more properly described as a pressure wave therapy. It’s probably not quite fair to lump them all in together when assessing shockwave therapy…but I’m going to do it anyway for now (in my ultrasound article). Until such time as there’s compelling evidence that one flavour has impressively different and better effects than another, it’s all just variations on a theme: stimulating tissues with different sorts of sound waves. Does that seem reasonable? BACK TO TEXT
  9. ESWT requires much more expensive and sophisticated machinery, and it was extravagantly expensive for a long time. It’s come down a lot, but even now it will run you at least $200 per visit, with a typical prescription of three to six treatments. This is not cheap therapy! I last checked prices in early 2014. BACK TO TEXT
  10. In particular, even though there are many “flavours,” it’s easy to standardize it for apples-to-apples comparisons, and it’s really easy to fake treatment for a good controlled and blinded test. It’s basically effortless to create a perfect “sham” version of ultrasound, so that the study subjects can’t tell if they are getting the real thing. Many other popular interventions in manual therapy are difficult or even impossible to standardize and/or fake — so it makes more sense that there’s long-term uncertainty about their effectiveness. Ultrasound has much less excuse in this regard. BACK TO TEXT
  11. van der Windt DA, van der Heijden GJ, van den Berg SG, et al. Ultrasound therapy for musculoskeletal disorders: a systematic review. Pain. 1999 Jun;81(3):257–71. PubMed #10431713. BACK TO TEXT
  12. Robertson VJ, Baker KG. A review of therapeutic ultrasound: effectiveness studies. Phys Ther. 2001 Jul;81(7):1339–50. PubMed #11444997. PainSci #55377. BACK TO TEXT
  13. Baker KG, Robertson VJ, Duck FA. A review of therapeutic ultrasound: biophysical effects. Phys Ther. 2001 Jul;81(7):1351–8. PubMed #11444998. PainSci #55382. BACK TO TEXT
  14. Buchbinder R, Green SE, Youd JM, et al. Systematic review of the efficacy and safety of shock wave therapy for lateral elbow pain. J Rheumatol. 2006 Jul;33(7):1351–63. PubMed #16821270. BACK TO TEXT
  15. Ho C. Extracorporeal shock wave treatment for chronic lateral epicondylitis (tennis elbow). Issues In Emerging Health Technologies. 2007 Jan;(96 (part 2)):1–4. PubMed #17302021. BACK TO TEXT
  16. Ho C. Extracorporeal shock wave treatment for chronic rotator cuff tendonitis (shoulder pain). Issues In Emerging Health Technologies. 2007 Jan;(96 (part 3)):1–4. PubMed #17302022. BACK TO TEXT
  17. Rutjes AW, Nüesch E, Sterchi R, Jüni P. Therapeutic ultrasound for osteoarthritis of the knee or hip. Cochrane Database Syst Rev. 2010 Jan;(1):CD003132. PubMed #20091539. BACK TO TEXT
  18. Shanks P, Curran M, Fletcher P, Thompson R. The effectiveness of therapeutic ultrasound for musculoskeletal conditions of the lower limb: A literature review. Foot (Edinb). 2010 Dec;20(4):133–9. PubMed #20961748. BACK TO TEXT
  19. van den Bekerom MP, van der Windt DA, Ter Riet G, van der Heijden GJ, Bouter LM. Therapeutic ultrasound for acute ankle sprains. Cochrane Database Syst Rev. 2011 Jun;(6):CD001250. PubMed #21678332. BACK TO TEXT
  20. Page MJ, O'Connor D, Pitt V, Massy-Westropp N. Therapeutic ultrasound for carpal tunnel syndrome. Cochrane Database Syst Rev. 2013 Mar;(3):CD009601. PubMed #23543580. BACK TO TEXT
  21. Ebadi S, Henschke N, Nakhostin Ansari N, Fallah E, van Tulder MW. Therapeutic ultrasound for chronic low-back pain. Cochrane Database Syst Rev. 2014 Mar;(3):CD009169. PubMed #24627326. BACK TO TEXT
  22. Desmeules F, Boudreault J, Roy JS, et al. The efficacy of therapeutic ultrasound for rotator cuff tendinopathy: A systematic review and meta-analysis. Phys Ther Sport. 2015 Aug;16(3):276–84. PubMed #25824429. BACK TO TEXT
  23. TENS may be more evidence-based than ultrasound, particularly for some specific medical situations, but its widespread, indiscriminate use is definitely dubious. Like ultrasound, it is clearly sold to patients for more purposes than the evidence can possibly support. For more information, see Zapped! Does TENS work for pain? BACK TO TEXT
  24. Baker KG, Robertson VJ, Duck FA. A review of therapeutic ultrasound: biophysical effects. Phys Ther. 2001 Jul;81(7):1351–8. PubMed #11444998. PainSci #55382. BACK TO TEXT
  25. Tsai WC, Tang ST, Liang FC. Effect of therapeutic ultrasound on tendons. Am J Phys Med Rehabil. 2011 Dec;90(12):1068–73. PubMed #21552108. BACK TO TEXT
  26. Srbely JZ, Dickey JP, Lowerison M, et al. Stimulation of myofascial trigger points with ultrasound induces segmental antinociceptive effects: A randomized controlled study. Pain. 2008 Oct 15;139(2):260–6. PubMed #18508198. BACK TO TEXT
  27. The dominant theory is that a trigger point is basically an isolated spasm affecting just a small patch of muscle tissue. Unfortunately, it’s still just a theory, and trigger point science is a bit half-baked and somewhat controversial, and it’s not even clear that it’s a “muscle” problem. The pain is certainly real, but it isn’t necessarily coming from the muscle at all. See Trigger Point Doubts. BACK TO TEXT