Ultrasound machines are a fixture of sports medicine and physiotherapy clinics.
A few years ago I suffered a fairly severe ankle sprain. After a physician’s assessment to rule out any broken bones, intensive physiotherapy was recommended and I booked several visits at my local clinic. The recovery process seemed to be relatively straightforward, with lots of assessments and exercises. On a few visits, I was offered ultrasound, which I accepted (I declined the offer of acupuncture). I was told ultrasound would help my ankle heal faster. At the time, it felt a bit like this was a mechanism that allowed the physiotherapist to multi-task multiple patients, but I accepted what was recommended in the hope of getting my ankle back to “normal” or whatever I could expect after this type of injury.
A family member recently suffered a bad ankle sprain and is now seeing a physiotherapist (this time I tried to find one that didn’t offer acupuncture). Digging out my old ankle braces reminded me of my recovery and rehabilitation process, and I thought back to the ultrasound experience. Was that time spent with the machine actually helpful? I did some research to understand just what benefits ultrasound may offer a bad sprain or other acute musculoskeletal injuries. With a shout-out to Paul Ingraham’s detailed, excellent and amazingly comprehensive own resource on ultrasound, what follows is my take on this physiotherapy mainstay:
What is “therapeutic ultrasound”?
Ultrasound when used in the physiotherapy context is different from the imaging modality. Imaging ultrasound sends and receives sound waves with a transducer to generate images of internal body structures. Therapeutic ultrasound, which I’ll just call ultrasound, was invented in the 1940s (apparently by Germans who were killing fish while developing sonar), and these devices are now FDA approved. The proposed mechanism is that ultrasound generates sound waves that stimulate changes in the tissues and cells. A wand generates the sound waves at frequencies of 0.7-3.3 MHz (million cycles per second), which are far above the audible hearing range (15-20,000 Hz). The use of ultrasound gel ensures solid contact with the skin itself. The transmission of the sound wave into the body causes the underlying structures oscillate or vibrate. The vibration is thought to break down scar tissue and potentially even cause gas bubbles to form, which is thought to promote healing. Sound energy, once absorbed, can even cause heat generation, which is the intended effect in some circumstances. Internal heating is thought to improve circulation and consequently promote healing. Beyond the frequency, the power level may be varied, and treatment may be “pulsed” or continuous. Pulsed therapy delivers treatment in intervals, and is typically used when the intent is not to heat tissue. The practitioner may also move the wand continuously around in a small area, which is believed to reduce the risk of unwanted tissue heating in any one area.
There is a variant of ultrasound called shock wave or extracorporeal shock wave therapy (ESWT) which is a more intense form of the treatment that’s also used by physiotherapists and rehabilitation specialists. Originally developed to treat kidney and gall stones, ESWT is much more expensive that regular therapeutic ultrasound, and is purported to provide “more” pain relief that plain vanilla ultrasound. ESWT devices are approved by the FDA for plantar fasciitis and lateral epicondylitis. I will leave ESWT aside for now, because it’s less common and the efficacy of the product for musculoskeletal conditions is unclear.
Ultrasound is used in medicine but more widely in rehabilitative medicine, and particularly by physiotherapists. It is commonly used for soft tissue injuries including sprains and tendinopathies, but also stress fractures and even to promote wound healing. Given how ubiquitous ultrasound machines are, it is reasonable to expect that they are clinically proven to offer benefit. The evidence, however, is not impressive.
What is the evidence for “Therapeutic Ultrasound”?
Despite the potential for ultrasound to heat tissue, it should be reasonably simple to test ultrasound devices for efficacy in blinded studies. Yet despite the ease at which it could potentially be evaluated, and how widely it is used, the number of high-quality, randomized placebo-controlled trials is small. Here are summaries of the systematic and narrative reviews I could find evaluating ultrasound for musculoskeletal injuries:
Robertson (2001), “A Review of Therapeutic Ultrasound: Effectiveness Studies”, 10 of 35 trials met quality criteria.
There was little evidence that active therapeutic ultrasound is more effective than placebo ultrasound for treating people with pain or a range of musculoskeletal injuries or for promoting soft tissue healing.
Desmeules (2014), “The efficacy of therapeutic ultrasound for rotator cuff tendinopathy: A systematic review and meta-analysis”, 11 RCTs.
Therapeutic US did not provide greater benefits than a placebo intervention or advice in terms of pain reduction and functional improvement. When provided in conjunction with exercise, US therapy is not superior to exercise alone in terms of pain reduction and functional improvement.
Shanks (2010), “The effectiveness of therapeutic ultrasound for musculoskeletal conditions of the lower limb: A literature review”, 10 studies.
This literature review found that there is currently no high quality evidence available to suggest that therapeutic ultrasound is effective for musculoskeletal conditions of the lower limb.
van den Bekerom (2011), “Therapeutic ultrasound for acute ankle sprains” (Cochrane Review), 6 trials, 606 participants.
The evidence from the five small placebo‐controlled trials included in this review does not support the use of ultrasound in the treatment of acute ankle sprains.
Page (2013), “Therapeutic ultrasound for carpal tunnel syndrome” (Cochrane Review), 11 studies including 414 participants.
There is only poor quality evidence from very limited data to suggest that therapeutic ultrasound may be more effective than placebo for either short‐ or long‐term symptom improvement in people with CTS…More methodologically rigorous studies are needed to determine the effectiveness and safety of therapeutic ultrasound for CTS.
Ebadi (2014, updated 2020), “Therapeutic ultrasound for chronic low back pain (Cochrane Review)”, 10 RCTs involving a total of 1,025 participants with chronic LBP.
The current evidence does not support the use of therapeutic ultrasound in the management of chronic LBP.
Peris Moya (2021), “Ultrasound improves motor distal latency on patients with carpal tunnel syndrome: systematic review and meta-analysis”, 8 trials of 2,069 patients.
The use of ultrasound on patients with carpal tunnel syndrome seems to improve motor distal latency.
Qing (2021), “Effect of Therapeutic Ultrasound for Neck Pain: A Systematic Review and Meta-Analysis”, 12 trials, 705 patients.
Therapeutic ultrasound may reduce the intensity of pain more than sham or no treatment, and it is a safe treatment. Whether therapeutic ultrasound in combination with other conventional treatments produced additional benefits on pain intensity, disability, or quality of life is not clear.
Luo (2022), “The effect of ultrasound therapy on lateral epicondylitis: A meta-analysis”, 13 studies, 442 patients.
The ultrasound therapy is helpful to relieve pain for LE patients, but no such benefit could be found for grip strength. However, it has no significant advantage against other conservative treatments like rest and brace.
Smallcomb (2022), narrative review, “Therapeutic Ultrasound and Shockwave Therapy for Tendinopathy”.
Despite mixed outcomes, all three therapies show potential as an alternative therapy with lower-risk adverse effects than more invasive methods like surgery. There is currently insufficient evidence to conclude which ultrasound modality or settings are most effective. More research is needed to understand the healing effects of these different therapeutic ultrasound and shockwave modalities.
The medical resource Up-To-Date only discusses ultrasound therapy in a discussion of tendinopathy:
…evidence supporting its efficacy in treating tendinopathy is lacking, and that there is no convincing evidence ultrasound is beneficial for tendinopathy of the knee, elbow, Achilles, or rotator cuff.
Conclusion: Despite popularity, little evidence to show effectiveness
The rationale for ultrasound therapy is based on the (plausible, but unproven) idea that vibrating injured tissue is better than not vibrating it. Given it has been in use for decades, and given possibly thousands (or tens of thousands) of patients receive ultrasound treatments every day, it seems reasonable to expect that it would be well studied and its use would informed by good evidence. Surprisingly and disappointingly, there is a lack of good information to show the benefits of ultrasound, and consequently its role in the treatment of musculoskeletal injuries remains unclear.