Ultrasound is ultra-popular … and ultra-unproven.
Therapeutic Ultrasound
Many concerns about the widespread usage of therapeutic ultrasound, especially extracorporeal shockwave therapy (ESWT)
by Paul Ingraham, Vancouver, Canada MORE
Credentials and qualifications
I am a writer and retired Registered Massage Therapist (unusually well-trained for a massage therapist, a 3000-hour program). I’m almost done with a Bachelor of Health Sciences degree. I am a peer reviewer for The Natural Standard, and a copyeditor for Science-Based Medicine. My most important qualification is more than a decade of workaholic post-graduate study, clinical experience, and constant conversations with readers from around the world, including many experts who have provided countless suggestions and criticisms.
For more information, see: Who Am I to Say? More information about my qualifications, credentials and professional experiences for my readers and customers.
Credentials and qualifications
I am a writer and retired Registered Massage Therapist (unusually well-trained for a massage therapist, a 3000-hour program). I’m almost done with a Bachelor of Health Sciences degree. I am a peer reviewer for The Natural Standard, and a copyeditor for Science-Based Medicine. My most important qualification is more than a decade of workaholic post-graduate study, clinical experience, and constant conversations with readers from around the world, including many experts who have provided countless suggestions and criticisms.
For more information, see: Who Am I to Say? More information about my qualifications, credentials and professional experiences for my readers and customers.
Ultrasound therapy (US) is the use of sound waves above the range of human hearing1 to treat musculoskeletal problems, especially inflammation (tendinitis, bursitis). It is most widely employed by physical therapists, and has been an extremely popular therapy since the 1950s.2 There are many flavours of therapeutic ultrasound, using different intensities and frequencies of sound, but all share the basic principle of “stimulating” tissue with sound waves.
Almost everyone seems to assume that ultrasound is proven — good technological medicine — but that just doesn’t seem to be the case.
Unfortunately — although there are some interesting exceptions and tantalizing hopes for some conditions — ultrasound is not a promising therapy for most musculoskeletal conditions. There is a jarring, bizarre lack of research for such a popular therapy. What little research is available paints an overwhelmingly bland picture. And the principle of US itself is, at best, much more complicated and unpredictable than most therapists believe. At worst, there is no rational basis for US at all. Ultrasound therapy is almost certainly useful for some patients, some of the time — but it is not a reliable or evidence-based therapy.
Flavours of therapeutic ultrasound
The vast majority of patients will encounter US in one of two forms: the ordinary sort familiar to almost anyone who’s had any kind of physical therapy, and it’s more expensive, intense, painful and high-tech cousin, Extracorporeal Shock Wave Therapy (ESWT).
Garden variety therapeutic ultrasound is cheap and available virtually everywhere. The machine is small, almost portable, treatment is brief and painless, and used applied to virtually anything that hurts — essentially every common painful musculoskeletal problem.
ESWT uses much stronger sound waves — shock waves!3 Treatment is be painfully intense and expensive. On the one hand, ESWT is pretty much a “more is better” version of standard US, because it is often used with the same imprecise clinical intention to “stimulate” tissues. On the other hand, because it was originally developed for smashing gall stones, ESWT is strong enough to actual disrupt tissue, such as calcifications in tendons — which is nice, precise clinical intention and an entirely different kettle of fish.
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 $250 per visit, with a typical prescription of three to six treatments. This is not cheap therapy!
Ultrasound is used cleverly in several other ways, such as injecting drugs into tissues (phonophoresis) and used sound waves to violently vibrate the tip of a invasive probe (lithotripsy, usually used for gall stones). These are all interesting cousins of ordinary ultrasound, but are not discussed in this article (for now).
Therapeutic ultrasound ignored by science but sold to millions of patients
When I started researching for this article, I was surprised by how little there was to study. There’s hardly any research about ultrasound at all! Every scientific paper about ultrasound starts by pointing out there is not enough research on this topic. There are practically more reviews of scientific papers than there are scientific papers to review. A major review of US for a common knee problem in 2001 comically found only a single worthwhile test of efficacy to report on!4
That’s not a lot to go on.
I didn’t think it would be like this. For years now, I’ve been looking forward to delving deeper into this topic, assuming that there had to be a pile of science about it. We’re talking about ultrasound, here: one of the staples of physical therapy! It practically defines the experience of going for physical therapy. Everyone has had that cold gel slapped on an injury, and felt that tingling, penetrating … placebo?
The disconnect between the ubiquity of the service and the more or less total lack of (adequate) research is jarring. A handful of studies is a disturbing joke for a therapy that is worth literally billions in the marketplace! How can that much therapy be sold without a satisfactory body of evidence that it works? Bizarre! This is exactly what I mean by “pseudo-quackery” — popular treatments that aren’t necessarily junk, but are nevertheless sold with a confidence that is out of whack with reality.
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. Not cool.
The pathetic state of the art and science of 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 not a difficult therapy to test (it’s easy to fake it), and if it works reasonably well then the results should be pretty blatant: simply compare results in patients who received real ultrasound to patients who get a fake instead. To a shocking degree, these simple tests have simply not been done adequately. There should be hundreds of them in the archives. Instead there are dozens.
Between 1995 and 2008, the science that has been done was reviewed in ten papers I considered to be worthwhile.567891011121314 Eight of those were unambiguously negative, some of them strongly so. Authors had almost nothing good to say about ultrasound. Conclusions like this one are the rule:
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.
Windt et al, Pain, 1999
I like that phrasing, “did not support the existence of clinically important differences.” Ouch. Ultrasound’s therapeutic effect has an existential crisis!
Most of these reviews give a nod to some reason for optimism about US used for a particular purpose, or in a particular way. For instance, the review I just quoted, despite its overwhelming negative conclusion, also notes that “findings for lateral epicondylitis [tennis elbow] may warrant further investigation.” Naturally, that optimism about tennis is contradicted by other studies, of course (Ho, Staples).
In short, it’s all just a discouraging mess, and a classic case (yet another one) of failing the impress me test. If ultrasound were generally effective, it certainly should have performed much better in the few studies that have been done.
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.
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.
Consider this marketing language from a Canadian company, Shockwave Alberta, 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
Here we have an entire company devoted to delivery of therapeutic ultrasound, and selling it with the implication that it is not only proven to be effective, but that they know 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 “80–85% effective”? Where are the scientific review papers confirming this marvellous triumph of ultrasound? Where is the data to support such a specific promise of therapeutic success?
Patient cynicism about ultrasoundIf 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 the common physical therapy operating procedure of working with several patients at once, rotating between rooms or beds — this is the standard complaint about physical therapy. Many patients often go a step further and complain to me, specifically, that they are doubtful that ultrasound and TENS do anything. To the patient, these procedures obviously seem therapeutically unremarkable and like fairly obvious ways for the physiotherapist to get paid for doing not much. This perception really pushes people’s “I don’t want to be a sucker” button.
Thus,fFew if any patients are out there singing the virtues of standard ultrasound. Standard ultrasound not only fails to generate testimonials, but actually generates quite a few rather bitter antimonials.
Patients do not feel the same cynicism about ESWT. 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 obviously more subject to placebo effects, and much less willing to entertain the possibility that it was all a waste.
How ultrasound supposedly works
In theory, ultrasound works essentially by vibrating tissues back to health, on the general principle that cells and tissues respond well to being stimulated. But what, exactly, does ultrasound do to tissues? Does anyone actually understand it?
The general answer is, emphatically, no.
In 2001, Physical Therapy published a review of the biological effects of ultrasound. A decade ago, the authors — Baker, Robertson and Duck — pointed out 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.”15 They also point out — it’s the point of their paper — that the situation had not improved in twenty years:
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 a great deal of interesting ultrasound biology to consider, and I have little doubt that there is still potential for scientists to nail down some interesting effects that may someday be the basis for evidence-based therapies. But now? Today? For now, the clinical bottom line is that it is extremely complex and unpredictable, and there is virtually no basis for concluding that ultrasound has a basis. The entire enterprise rests on the single, oversimplified idea that “stimulation is good.”
The gate control mechanism: a particular bogus rationale for ultrasound, especially ESWT
Physical therapists often cite the “gate control” mechanism as a justification for ESWT. This is nonsense, and a great example of why patients should be cautious about buying ESWT.
The “gate control” mechanism is an important idea in pain science, proposed in the sixties by Dr. Ronald Melzack. In a nutshell, the idea is that the brain can only process so much sensory input from one area at a time. If you add a novel stimulus to a painful spot, we are “distracted” from the pain. This is why we tend to rub banged elbows and toes: the rubbing reduces the pain sensation by flooding the brain with additional non-painful stimuli.
This may well occur in ESWT — I’m not saying that ESWT doesn’t leverage the idea. But it’s completely ridiculous as a justification for an expensive therapy, when essentially exactly the same effect can be achieved by rubbing the area yourself!
Gate control theory is often tossed into the mix of reasons for doing ESWT, but it’s clearly padding the list. The reasons for doing ESWT are not at all clear, and adding this one is just a way to pad the list in a way that sounds scientific, but is actually almost completely meaningless.
In the case of standard ultrasound, it’s not such a problem, because standard ultrasound is much less expensive.
Notes
- 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. Return to text.
- Wong et al. Physical Therapy. 2007. Ultrasound is widely used but poorly studied. 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.” Return to text.
- Specifically, strong sonic pulse for a short length of time (approximately 10 milliseconds). Return to text.
- Brosseau et al. Cochrane Database of Systematic Reviews. 2001. Return to text.
- Gam et al. Pain. 1995. Return to text.
- Windt et al. Pain. 1999. Return to text.
- Brosseau et al. Cochrane Database of Systematic Reviews. 2001. Return to text.
- Robertson et al. Physical Therapy. 2001. Return to text.
- Welch et al. Cochrane Database of Systematic Reviews. 2001. Return to text.
- Baker et al. Physical Therapy. 2001. Return to text.
- Buchbinder et al. Journal of Rheumatology. 2006. Return to text.
- Ho. Issues In Emerging Health Technologies. 2007. Return to text.
- Ho. Issues In Emerging Health Technologies. 2007. Return to text.
- Jamtvedt et al. Physical Therapy. 2008. Return to text.
- Baker et al. Physical Therapy. 2001. Return to text.
