Therapeutic Ultrasound for Injury is Quackery (2024)

The pressure wave therapies are huge in physical therapy: both ultrasound therapy (US) and extracorporeal shockwave therapy (ESWT) are used to treat pain and injuries like plantar fasciitis, stress fractures, muscle strains, or runner’s knee.

Therapeutic ultrasound has been one of the staples of musculoskeletal medicine since the 1950s.12 It is still widely used in physical therapy clinics today, and you can buy your own DIY ultrasound machine at the drugstore.

It’s fancier and more potent cousin, shockwave therapy, has been steadily replacing it in the 21^st Century.

Shockwave therapy is ultrasound… reborn!

Although ultrasound and shockwave therapy are different … are they really? All their variants are used in the much same ways for mostly the same conditions. They are all vibration delivery systems, intended to stimulate or even damage tissue — which might, depending on the details, induce regenerative and anti-inflammatory effects in injured bone, cartilage, and tendon. They belong to a family of vibration therapies with massage guns, jacuzzis, and vibrating exercise platforms, all very similar in spirit.

Most people and professionals assume that all of this is good technology, proven medicine — but that just doesn’t seem to be the case. Although there are some interesting exceptions and tantalizing hopes for some conditions, neither ultrasound nor shockwave therapy are good evidence-based medicine. There is a jarring, bizarre lack of quality research for such mainstream treatment modalities, and the results are not encouraging. At best, it’s complicated and unreliable. At worst, there is just no rational basis for hitting tissues with pressure waves at all, and it’s all just modern snake oil. Shockwave therapy is routinely marketed along with much more blatant kinds of quackery — which reveals its true nature.

Ultrasound and shockwave therapy are probably useful for some patients, some of the time — with just-right settings and variables that have never actually been confirmed by research, and little hope that they will be any time soon. Meanwhile, they enjoy far more credibility than they deserve.

I do not like the principle of using magic machines totreat.

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

Ultrasound versus shockwave

Shockwave therapy is often considered a new kind of ultrasound, but shockwave therapy isn’t “ultra” sound — it’s infra!

Also not actually “sound.”

Ultrasound uses high-frequency sound waves, above the range of human hearing (> 20,000 Hz) — which vibrates tissue so quickly that it warms up from the friction, like a gentle microwave. The point of ordinary therapeutic ultrasound is that it’s like a heating pad with a more penetrating warmth. It’s mostly a “heat ray.” It’s cheap, ubiquitous, harmless … and mostly useless.

Shockwave therapy is, weirdly, much more like a powerful vibrating massage “gun.” Its pressure waves are slow but high-energy, smacking the tissue hard, at frequencies in the infrasound range, well below the range of human hearing (< 20 Hz). And yet shockwaves aren’t technically “sound” waves: they are high-energy pulses of pressure rather than continuous oscillations, like sharp mountains rather than rolling hills. This produces much more potent “stimulation,” strong enough to shatter calcifications, and cause micro-injuries that might “kickstart” healing. This is much more expensive than ultrasound, and often painful.

The differences matter … but it’s all just playing with the parameters of pressure waves.

The lack of science about ultrasound and shockwave therapy

When I started studying for this article — back in the mid-2000s! — I was surprised by how little there was to study. I had not yet learned that there’s not enough evidence about anything to do with injury rehab and chronic pain rehab.

Back then, every scientific paper about ultrasound pointed out there was not enough research on this topic, or at least not enough good research.

That hasn’t changed. We’re still starving for decent evidence as of 2024, and I think that will be a safe summary until at least 2030.

For instance, a 2015 paper about ultrasound for rotator cuff tendinopathy found only six trials, all poor quality. A big 2020 review of ultrasound for back pain found just 10 trials, and was scathingly critical of their quality: all bad! “The certainty of the evidence for all outcomes was very low.” And so on, with no real improvement since. (These and many other citations coming up below.)

That’s not a lot to go on, and it’s saldy typical for the field of pain treatment and injury rehab. But the poverty of evidence for this topic is a bit shocking. We’re talking about ultrasound, here: one of the staples of physical therapy. Hardly a fringe treatment. It practically defines the experience of going to a physiotherapist. Everyone has had that cold gel slapped on an injury, and felt that tingling, penetrating … placebo?

Ultrasound and shockwave therapy are pseudo-quackery

There's a very troubling disconnect between the popularity of these therapies and the more or less total lack of informative research. A handful of decent studies is a joke for therapies that are worth billions in the marketplace, something sold to countless pro athletes over the decades. How can that much therapy be sold without a satisfactory body of evidence that it works? Bizarre!

It is bizarre, but it’s also almost standard! Ultrasound and shockwave are just among the best of many more examples of pseudo-quackery: popular treatments that aren’t obvious quackery, but still fall well short of validated, evidence-based medicine, and are sold with excessive confidence and usually considered mainstream rather than alternative.

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, often with the mistaken belief that there is much more evidence than there is. And that is not cool.

Therapeutic ultrasound

• Garden-variety therapeutic US is cheap and available everywhere. There are many consumer ultrasound products, some of them quite cheap and small.
• Treatment is brief and painless, even at high intensities, and is applied to almost all common musculoskeletal problem — almost indiscriminately, really.
• Healthy young adults can hear sounds up to about 20,000 hertz. Ultrasound machines produce sound waves at even higher frequencies. The slowest ultrasound might be just audible as a faint mosquito whine to a young patient with exceptional hearing.
• Those sounds waves can be low or high intensity, but all of it is low intensity compared to shockwave therapy.
• Deep heating is the main point of ultrasound. Vibrating the molecules of tissue causes diffuse friction and therefore warmth, and sound waves can vibrate deep tissues — as opposed to the superficial heat provided by a heating pad.
• At high enough frequencies and energies, ultrasound can actually burn you! Fortunately, this is quite rare in a physical therapy context.
• Ultrasound also has "mechanical" effects, which can be thought of as "micro massage" — basically just moving tissue fluids and gasses. But not far!
• Ultrasound can be pulsed to minimize warming. This is almost literally just turning the thing off and on again, which prevents heat from building up.
• Low-intensity pulsed ultrasound (LIPUS) is a significant variant of ultrasound, mostly used (rather speculatively) to promote bone healing.

The dubious rationale for ultrasound

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 earlier, 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.”3 They also point out — it’s the point of their whole paper — that the situation had not improved in the 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 …

So this was already an old problem in 2001.

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, Tsaietal. declared that “There is strong supporting evidence from animal studies about the positive effects of ultrasound on tendon healing”4 — but animal studies are notoriously misleading, and they certainly can’t justify the use of ultrasound (especially when US has already been tested on human tendinopathy with underwhelming results).

Another great example: the persistent hope that rattling cells might speed the healing of bone fractures, particularly low intensity pulsed ultrasound (LIPUS). Such an effect, if proven, would certainly be a fascinating bit of weird good news. Unfortunately, it is probably dis-proven. In 2017, the British Medical Journal published an excellent review with a very negative conclusion for fresh fractures.5 However, the authors have to concede that “the applicability to other types of fracture or osteotomy is open to debate … ” because it’s impossible to know for sure that there are no black swans anywhere — one could be right around the corner!

But the negative conclusion was echoed in another review in 2023.6 The report that “few studies” even reported on patient outcomes. “It is probable that LIPUS makes little or no difference to delayed union or non‐union.” It’s also noteworthy that they only found a single test of shockwave therapy, and none at all of high-intensity ultrasound.

Meanwhile, there is still just no basis for thinking that ultrasound has a basis. The entire empire of ultrasound rests on the single, oversimplified idea that “stimulation is good” and the hope that we might someday figure out exactly why.

The state of the evidence for 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

Ultrasound is an easy treatment to test scientifically.7 Just compare results in patients who received real ultrasound to patients who get a fake instead! And yet there are just a few dozen such experiments (controlled by a sham) in the scientific literature, and even most of them are still rather flawed. Conclusions from evidence reviews like this one from van der Windtetal. 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 Windtetal., 1999, Pain

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 Windtetal., 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.8 The science is mostly a discouraging, unimpressive mess — a classic case (yet another one) of a damning failure to impress.

The bottom line on standard therapeutic ultrasound

Standard therapeutic ultrasound probably does little or nothing for most people and conditions. A sliver of hope remains that some specific conditions will respond to ultrasound with just the right settings.

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.

Bakeretal., 2001, Physical Therapy

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.

Shockwave therapy: ultrasound reborn!

Extracorporeal Shock Wave Therapy (ESWT) is often shortened to just “shockwave therapy, because “extracorporeal” just means “generated outside the body,” which seems obvious — you don’t swallow it, and it’s not a surgical implant.21 It looks almost exactly like ultrasound: a gadget that you pass over an injury like a magic wand. But it’s the more-is-better cousin of therapeutic ultrasound, so it’s more intense, more technologically impressive, and more expensive.22 Radial “shock” wave therapy is a common variant with lower-energy waves.23

Shockwave therapy generates much lower frequency, faster pressure waves than ultrasound. Those waves slap tissues with much higher energy than ultrasound: the travel much faster than the speed of sound (in flesh), about 1500 meters per second.

They also come at a leisurely tempo that you could almost dance to — mostly under 10 Hz, thousands of times lower than ultrasound. In fact, five shockwaves per second (5 Hz) is quite a bit slower than tap dancing, which can get up to about 18 Hz! But that is way below the range of human hearing, which starts around 20 Hz. So shockwave therapy is closer to infrasound than ultrasound.24

The point of shockwave therapy is mostly microtraumatizing yourself back to health

It’s not clear why kidney-stone smashing tech was adopted by physical therapy. Why “slap tissues with much higher energy than ultrasound”? What’s the point? The goals of ultrasound and shockwave therapy mostly overlap: to “stimulate” tissue, which is the same vague rationale for nearly all gadget-powered treatments. But there are at least two significant differences:

• Shockwaves are too slow for thermal effects.
• But the pressure waves do have enough energy to cause damage. They can also break up some calcifications (which sounds so much more important than it is).

And shockwave therapy’s Big Idea is… maybe damage is healing. 🤯

Maybe, but it sounds a bit ridiculous dumbed down that much. Would you be more impressed if I said that the core hypothesis of shockwave therapy is that microtrauma hormetically stimulates cellular regenerative processes? Oooh, that's more like it! Now shut up and take my money!

Shockwave therapy attacks injured tissues with pressure waves strong enough to do fresh damage: minor, diffuse trauma, sometimes obvious from the minor bruising, sometimes visible only in a microscope (“microtrauma”). This can be painfully intense, so you can think of shockwave therapy as fancy ultrasound with a no-pain-no-gain twist. But does this kind of pain really deliver any gain?

Damaging tissue seems like the wrong idea for something that’s supposed to be treating injuries, but there’s a specific hypothesis that this will stimulate healing processes that weren’t already working well enough. And failed healing probably is a thing: we don’t know why, but sometimes tissues just don’t recover well. The most obvious example is the terrifying phenomenon of fracture non-union, where the bones just do not knit, and presumably it’s likely that something similar but subtler can happen with lesser injuries to soft tissues as well.

Doing a little damage is supposedly a “kickstart” for healing, a signal to the body: Hey, do your job! Clean up this mess! This idea is why shockwave therapy is called a “regenerative” therapy surprisingly often — which is really reaching. There are a lot of problems with this.

“Hormesis” is a biological benefit from a small dose of something that would be dangerous at a higher dose, and it is a familiar pattern in biology. It describes how exercise works, for instance. But exercise leverages adaptive responses tuned by evolution, and it’s a completely different deal to do damage with an artificial passive stimulus … and then it’s another big leap to the hope that this will help tissues that are already in trouble. The strong sensations of such treatments are probably rocket fuel for placebo (potency bias25), so it’s not surprising that there are a bunch of sketchy no-pain-no-gain therapies based on the idea, a rogues gallery of “provocation therapies”: prolotherapy, dry needling, cupping, fascial therapy, “scraping massage” (e.g. Graston), and so on.

Even if it works, shockwave therapy is not exactly from a good neighbourhood.

And consider this weird contradiction: ultrasound’s thermal effects are definitely capable of causing internal burns, but no one ever acts like that’s a good idea. Why not? Other than the fact that “internal burns” sounds nightmarish, what’s the difference between tuning infrasound to cause slight mechanical damage versus tuning ultrasound to cause slight thermal damage? Damage is damage — you clearly don’t want too much of it, even if you do accept that just the right amount is “regenerative.”

For some perverse reason, ultrasound damage would only ever be considered a serious error, something you could get sued for. But we pay for shockwave’s minor, diffuse, microtraumatizing powers? What a weird world.

And here’s another major conceptual glitch with shockwave therapy: the reason most overuse injuries don’t heal is probably not because healing has “failed,” but rather because it simply cannot keep up with the mechanical strain on the tissue. The healing is most assuredly happening, but it’s like Lucy trying to keep up with the chocolates on the conveyor belt. Do you want to add more strain to that equation? And yet shockwave therapy is probably applied to overuse injuries more than any other kind of condition!

You can’t kickstart a motorcycle that’s already running. And it probably is in many cases, if not most.

Peculiar, isn’t it? It’s almost like no one has really thought this through.

Break it up: shattering calcifications with pressure waves

Breaking up calcifications is a more specific goal of shockwave therapy, and there’s no question that it can be done. Whether it is therapeutically valuable or not is another question, since calcifications are probably mostly just another symptom, and not the cause of a problem. They aren't even particularly hard. Quoting from my own book about plantar fasciitis, a condition that is often blamed on bone spurts:

Unfortunately for common sense, bone spurs aren’t very bone-y, and it’s not like having a rock in your shoe. Spurs are a slight calcification of the plantar fascia, brittle and thin. It’s as much like bone as tinfoil is like sheet metal. They make the back part of the plantar fascia a bit crispy.26 Stepping on them is more like stepping on a cracker than a nail. A thin cracker.

See Also

LUNG ULTRASOUND AS AN ASSESSMENT TOOL FOR THE INDICATION OF NONINVASIVE MECHANICAL VENTILATION AFTER CARDIAC SURGERY. – ISSN 1678-0817 Qualis B2

So it isn’t too surprising that lots of people have painless spurs. Even when there is pain, it’s not the spur that hurts but the plantar fascia itself or other soft-tissue structures.2728 And surgically removing a bone spur does not necessarily relieve pain, so was it likely to be causing it in the first place?2930 Spurs also tend to just grow back, because they are probably a by-product by the same chronic inflammation that causes the pain.

All this casts shade on the goal of breaking of calcifications. It may just be missing the point: a seemingly obvious target for therapy that actually just doesn't matter. Shockwave therapy could work for other reasons. But does it? Let's get into the evidence.

Hype about the shockwave therapy: profitably misrepresenting the strength of the evidence

Enthusiasm about shockwave therapy has raced ahead of the evidence. Consider this marketing language from a Canadian company, Shockwave Institute, specializing in 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 (and still a good representative example today)

Shockwave Alberta certainly doesn’t think ultrasound has fallen out of favour! 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 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 over whatever ails you? Where is the data to support such a specific promise of therapeutic success? You sure couldn’t find them in 2009. Many years later, it’s still not much clearer.

Shockwave evidence

Things seem to have changed for the better, though “80-85% effective” would still be a hard claim to defend.

Bizarrely, ESWT is being used to treat conditions as unexpected as erectile dysfunction, stroke, and venous leg ulcers. There’s even some preliminary evidence for such uses… though not all.

But there are now some positive reviews of ESWT for its more common uses, like stubborn cases of plantar fasciitis, a painful irritation of the arch of the foot. A good 2016 example is Louetal., who concluded that “ESWT seems to be particularly effective in relieving pain associated with recalcitrant plantar fasciitis.”31 Plantar fasciitis is by far the most widely ESWT-treated condition for some reason: other conditions may be a completely different matter, but certainly the evidence for plantar fasciitis is surprisingly good, almost amazingly so (it’s a stark contrast with the vast majority of treatments for musculoskeletal conditions).

A 2009 test of shockwave therapy for hip pain (greater trochanteric pain syndrome) was clearly positive on its face.32

In a similar 2010 test for proximal hamstring tendinopathy, shockwave therapy seemed to handily “win.”33

But a few positive trials doesn’t mean much these days — musculoskeletal medicine is badly polluted with underpowered studies with untrustworthy “promising” results that are mostly good for the CV’s of the researchers who produce them. Cynincism is justified. There’s never been any replication of those hip and hamstring results.

And, despite all that, the evidence is predictably mixed.

Shockwave therapy for adhesive capsulitis (frozen shoulder), for instance, is being sold to patients without adequate evidence. There is scarcely any evidence, just a tiny handful of weak studies — including that one that seems most promising.34 For full analysis, see my frozen shoulder article.

Another good example of a bad result is Heideetal., in which shockwave therapy for plantar fasciitis couldn’t beat a sham in a good quality new test — following the classic pattern of “better studies undermine weaker early ones.” It almost always goes like this. It’s not a good sign.35

And not all reviews have happy endings! A notable general review in the British Medical Journal of Sports Medicine in 2018, of ESWT for “common lower limb conditions,”36 found only a “low level of evidence” that it “may” be effective for some conditions, which is getting pretty wishy-washy. They rejected thirteen studies for a high risk of bias and noted that “a relatively small number of research groups account for the majority of research.” And finally:

There are no occasions where multiple high-quality studies exist for a single pathology, hence for any individual pathology there are low and very low levels of evidence.

More recently, in 2023, Ko et al. concluded that “ the overall confidence in non-surgical treatments from all included trials was very low. No recommendation of the best treatment option can be made.” And the least-lame option they identified was not shockwave but eccentric training.37

Shockwave therapy absolutely cannot be considered evidence-based medicine, despite years of hype to that effect. There’s just not enough (good) evidence — as usual — and what we have is just not that encouraging.

Patient cynicism about therapeutic 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.41 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 therapy. 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.

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

Physical therapists often cite "counterstimulation and 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. It sounds much smarter than it is.

The “gate control” mechanism is an important idea in pain science, proposed in 1965 by Dr. Ronald Melzack and Dr. Patrick Wall,42 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, which can be blocked by other sensations, which are (weirdly) given priority by the nervous system.

So the idea with US is that the stimulation of the sound waves closes the gate to pain. This may well occur, because counterstimulation is a real phenomenon — but it’s also nothing to write home about. It’s just a mechanism for transient, minor pain relief. It can be achieved just as easily by rubbing the area yourself! It certainly doesn’t “fix” anything, which is what ultrasound is supposed to be doing. So bringing it up is just a bit of bafflegab, a scientific-sounding rationalization for an expensive therapy. 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 — especially handy when you’re trying to sell expensive ESWT, which might also exploit the term counter-irritation — 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.43 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.44 Some would say it’s hard to study the effect of ultrasound on a phenomenon that may or may not even exist!

Related Reading

• Zapped! Does TENS work for pain? — The peculiar popularity of being gently zapped with electrical stimulation therapy. TENS is a near sibling to ultrasound: two nearly identical treatment ideas, differing only in the form of stimulation delivered to tissues.
• Tissue Provocation Therapies in Musculoskeletal Medicine — Can healing be forced? The theme of hormesis in pain and injury medicine.
• Cold Laser Therapy Reviewed — A critical analysis of treating pain and injury with frickin’ laser beams.
• Heat for Pain and Rehab — A detailed guide to using heat as therapy for acute and chronic pain and recovery from injury. The discussion of infrared radiation particularly relevant.
• The Chiropractic Controversies — An introduction to chiropractic controversies like aggressive billing, treating kids, and neck manipulation risks.
• Pseudo-Quackery in Physical Therapy — The large, dangerous grey zone between evidence-based care and overt quackery in rehab and pain treatments. Ultrasound is one of the best examples of something in that zone.
• Guide to Repetitive Strain Injuries — Five surprising and important ideas about repetitive strain injuries for patients and professionals.

Notes

1. 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. PubMed17553923❐ PainSci Bibliography55380❐

   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.”

2. 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. PubMed24403700❐ PainSci Bibliography53385❐

   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.”

3. Baker 2001, op. cit.
4. Tsai WC, Tang ST, Liang FC. Effect of therapeutic ultrasound on tendons. Am J Phys Med Rehabil. 2011 Dec;90(12):1068–73. PubMed21552108❐
5. Schandelmaier S, Kaushal A, Lytvyn L, etal. Low intensity pulsed ultrasound for bone healing: systematic review of randomized controlled trials. BMJ. 2017 Feb;356:j656. PubMed28348110❐ PainSci Bibliography52780❐ From the abstract: “trials at low risk of bias failed to show a benefit with LIPUS, while trials at high risk of bias suggested a benefit” and “LIPUS does not improve outcomes important to patients and probably has no effect on radiographic bone healing.”
6. Searle HKC, Lewis SR, Coyle C, Welch M, Griffin XL. Ultrasound and shockwave therapy for acute fractures in adults. Cochrane Database Syst Rev. 2023 Mar;3(3):CD008579. PubMed36866917❐ PainSci Bibliography49769❐
7. 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.
8. Staples MP, Forbes A, Ptasznik R, Gordon J, Buchbinder R. A randomized controlled trial of extracorporeal shock wave therapy for lateral epicondylitis (tennis elbow). J Rheumatol. 2008 Oct;35(10):2038–46. PubMed18792997❐
9. van der Windt DA, van der Heijden GJ, van den Berg SG, etal. Ultrasound therapy for musculoskeletal disorders: a systematic review. Pain. 1999 Jun;81(3):257–71. PubMed10431713❐
10. Robertson VJ, Baker KG. A review of therapeutic ultrasound: effectiveness studies. Phys Ther. 2001 Jul;81(7):1339–50. PubMed11444997❐ PainSci Bibliography55377❐
11. Baker KG, Robertson VJ, Duck FA. A review of therapeutic ultrasound: biophysical effects. Phys Ther. 2001 Jul;81(7):1351–8. PubMed11444998❐ PainSci Bibliography55382❐
12. Buchbinder R, Green SE, Youd JM, etal. Systematic review of the efficacy and safety of shock wave therapy for lateral elbow pain. J Rheumatol. 2006 Jul;33(7):1351–63. PubMed16821270❐
13. Ho C. Extracorporeal shock wave treatment for chronic lateral epicondylitis (tennis elbow). Issues In Emerging Health Technologies. 2007 Jan;(96 (part 2)):1–4. PubMed17302021❐
14. 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. PubMed17302022❐
15. 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. PubMed20091539❐
16. 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. PubMed20961748❐
17. 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. PubMed21678332❐
18. Page MJ, O’Connor D, Pitt V, Massy-Westropp N. Therapeutic ultrasound for carpal tunnel syndrome. Cochrane Database Syst Rev. 2013 Mar;(3):CD009601. PubMed23543580❐
19. Desmeules F, Boudreault J, Roy JS, etal. The efficacy of therapeutic ultrasound for rotator cuff tendinopathy: A systematic review and meta-analysis. Phys Ther Sport. 2015 Aug;16(3):276–84. PubMed25824429❐
20. Ebadi S, Henschke N, Forogh B, etal. Therapeutic ultrasound for chronic low back pain. Cochrane Database Syst Rev. 2020 Jul;7(7):CD009169. PubMed32623724❐ PainSci Bibliography49771❐
21. This technology was adapted from a revolutionary method of smashing gall stones and kidney stones with pressure waves, one of the greater victories of modern medicine, back in the 1980s. That technology was known as “extracorporeal” to emphasize the fact that you didn’t have to cut into someone, or insert a probe up the urethra — which, eek, had been routine! In a physical therapy context, we don’t much care about the fact that there’s no cutting, so the term is often dropped.
22. This 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 $100 per visit, often much more, with a typical prescription of three to six treatments. I last checked prices in 2024.
23. There are actually several different types of extracorporeal shockwave therapy. 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 therapies — about 100 meters per second, instead of 1500. It’s might not even be fair to lump them all in together when assessing shockwave therapy … but I’m going to do it anyway for now. Until such time as there’s compelling evidence that one flavour has impressively different and better effects than another, it’s all just trivial variations on a consistent theme.
24. 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.

25. People equate strong sensations in a medical context with therapeutic potency. In short, we really believe that there is no gain without pain, and we assume that pain is justified by gain.

    A funny example: people love to love Buckley’s cough syrup, a notoriously foul-tasting Canadian “medicine” with no conventional active ingredients, just gross ones like lots of camphor and pine needle oil, advertised with the slogan, “It tastes awful. And it works.” That slogan taps directly into the pro-potency bias! It’s practically an explanation for it. People can’t love Buckley's because it’s actually effective, because it cannot possibly be, so they love it simply because the taste is horrifying …and they think intense medicines must be more potent. Surely no one would sell such diabolical swill if it wasn’t good medicine?! Right?

    This phenomenon is also related to the way stronger placebo effects are generated by needles than pills … and even more by red pills than white pills … and why surgery is the ultimate placebo, because it is a very dramatic medical intervention, and the extremity is equated with efficacy to an astonishing degree (see Surgery: The ultimate placebo).

    I see this in the world of manual therapy and rehab constantly, in many forms.

26. Some bones spurs are undoubtedly thicker and harder than others, just like some people have much larger calluses than other people. (I have a callus on one foot that is always far thicker and sturdier than I seem to need.) But regardless, the spur tends to disintegrate the further it gets from the heel.
27. Osborne HR, Breidahl WH, Allison GT. Critical differences in lateral X-rays with and without a diagnosis of plantar fasciitis. J Sci Med Sport. 2006 Jun;9(3):231–7. PubMed16697701❐

    From the abstract: “ ... the key radiological features that differentiate the groups were not spurs but rather changes in the soft tissues.”

28. Tountas AA, Fornasier VL. Operative treatment of subcalcaneal pain. Clin Orthop Relat Res. 1996 Nov:170–8. PubMed2663678❐

    This paper reports on a study of twenty patients in the years after surgical removal of bone spurs. Although most of the patients had “excellent” or “good” results three years later, their spurs had reformed in many cases, and analysis of the soft tissues showed that “changes within the fascia, rather than the spur, are primarily responsible for the pathogenesis of the syndrome.”

29. Onwuanyi ON. Calcaneal spurs and plantar heel pad pain. Foot. 2000;10.

    From the abstract: “Calcaneal spurs cause plantar heel pad pain, but the roles of other co-morbid factors are significant. The excision of these spurs does not necessarily abolish pain.”

30. Fishco WD, Goecker RM, Schwartz RI. The instep plantar fasciotomy for chronic plantar fasciitis. A retrospective review. J Am Podiatr Med Assoc. 2000 Feb;90(2):66–9. PubMed10697969❐ In this study, surgical outcomes were similar — and generally good — with or without heel spur removal.
31. Lou J, Wang S, Liu S, Xing G. Effectiveness of Extracorporeal Shock Wave Therapy Without Local Anesthesia in Patients With Recalcitrant Plantar Fasciitis: A Meta-Analysis of Randomized Controlled Trials. Am J Phys Med Rehabil. 2016 Dec. PubMed27977431❐
32. Furia JP, Rompe JD, Maffulli N. Low-energy extracorporeal shock wave therapy as a treatment for greater trochanteric pain syndrome. Am J Sports Med. 2009 Sep;37(9):1806–13. PubMed19439756❐

    33 patients were given low-energy shockwave therapy for greater trochanteric pain syndrome, while 33 others were treated with other forms of conservative therapy. Those who got shockwave therapy were the lucky ones: the results were clear and positive, both statistically and clinically significant, and sustained as long as a year later. The study is underpowered and cannot be taken too seriously, but it’s certainly positive on its face. Conclusion: “Shock wave therapy can be an effective treatment for greater trochanteric pain syndrome.”

33. Cacchio A, Rompe JD, Furia JP, etal. Shockwave Therapy for the Treatment of Chronic Proximal Hamstring Tendinopathy in Professional Athletes. Am J Sports Med. 2010 Sep. PubMed20855554❐
34. Hussein AZ, Donatelli RA. The efficacy of radial extracorporeal shockwave therapy in shoulder adhesive capsulitis: a prospective, randomised, double-blind, placebo-controlled, clinical study. European Journal of Physiotherapy. 2016 Mar;18(1):63–76.

    This test of shockwave therapy for frozen shoulder hits all the highlights of well-designed experiment. The researchers gave real shockwave therapy to one group of 52 patients weekly for a month, and sham shockwave therapy to the other group, and measured pain and function. The real shockwave group did “significantly” better, with the researchers notably claiming both statistical and clinical significance of the results … but not reporting the actual effect sizes in the abstract, which is always suspicious (if they are impressive, they get featured).

    Despite the good design, a major concern here is that sham treatment. Shockwave therapy is high energy, and uncomfortable at best, painful at worst. In the sham group, the shockwaves were simply “blocked.” It seems like many or most patients would certainly know that they weren’t getting the real shockwave therapy … which would spoil the data for sure.

    The results are very promising, but it’s a mystery why shockwave therapy would work, the effect they observed was probably not very large, and there’s probably one huge flaw that would be a deal-breaker.

35. Heide M, Røe C, Mørk M, etal. Is radial extracorporeal shock wave therapy (rESWT), sham-rESWT or a standardised exercise programme in combination with advice plus customised foot orthoses more effective than advice plus customised foot orthoses alone in the treatment of plantar fasciopathy? A double-blind, randomised, sham-controlled trial. Br J Sports Med. 2024 Jul;58(16):910–918. PubMed38904119❐ PainSci Bibliography49858❐

    This trial was designed to test the efficacy of radial extracorporeal shock wave therapy (rESWT) for plantar fasciitis, by comparing it to a sham, an exerciseprogram, and just advice and orthoses). They recruited 200 patients and split them up into four groups, and checked on at the start and then after 3, 6, and 12 months. The shockwave group got three treatments.

    There were “no statistically significant between-group differences,” so it was a wash: not only no measurable difference between real and fake shockwave therapy, but exercise, advice, and orthoses also all failed to be helpful. The authors concluded:

    “In patients with plantar fasciopathy, there was no additional benefit of rESWT, sham-rESWT or a standardised exercise programme over advice plus customised foot orthoses in alleviating heel pain.”

36. Korakakis V, Whiteley R, Tzavara A, Malliaropoulos N. The effectiveness of extracorporeal shockwave therapy in common lower limb conditions: a systematic review including quantification of patient-rated pain reduction. Br J Sports Med. 2018 Mar;52(6):387–407. PubMed28954794❐
37. Ko VMC, Cao M, Qiu J, etal. Comparative short-term effectiveness of non-surgical treatments for insertional Achilles tendinopathy: a systematic review and network meta-analysis. BMC Musculoskelet Disord. 2023 Feb;24(1):102. PubMed36750789❐ PainSci Bibliography49666❐
38. Searle HKC, Lewis SR, Coyle C, Welch M, Griffin XL. Ultrasound and shockwave therapy for acute fractures in adults. Cochrane Database Syst Rev. 2023 Mar;3(3):CD008579. PubMed36866917❐ PainSci Bibliography49769❐
39. Yazdani A, Nasri P, Baradaran Mahdavi S. The Effects of Shock Wave Therapy on the Symptoms and Function of Individuals With Dupuytren Disease: A Systematic Review. Arch Phys Med Rehabil. 2024 Oct;105(10):1985–1992. PubMed38866227❐
40. It may be correct, of course, but this is a small review of dubious quality, looking at a handful of tiny studies that almost certainly had a high risk of bias. Garbage in, garbage out. Similar reviews of shockwave therapy for conditions in this pathological family (e.g. Peyronie’s) are much the same, and some are more negative. For more detailed analysis, see the shockwave section in my Dupuytren’s contracture guide.
41. 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?
42. Melzack R, Wall PD. Pain mechanisms: a new theory. Science. 1965 Nov;150(3699):971–9. PubMed5320816❐

    This is Melzack and Wall’s seminal paper arguing that (emphasis mine) “pain perception and response is triggered after the cutaneous sensory input has been modulated by both sensory feedback mechanisms and the influences of the central nervous system. We propose that the abstraction of information at the first synapse may mark only the beginning of a continuing selection and filtering of the input.” Among other things, this is the paper that described the mechanism of gate control and ultimately gave rise to the highly influential concept of the neuromatrix (Melzack).

43. Srbely JZ, Dickey JP, Lowerison M, etal. Stimulation of myofascial trigger points with ultrasound induces segmental antinociceptive effects: A randomized controlled study. Pain. 2008 Oct 15;139(2):260–6. PubMed18508198❐
44. 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.