Is Ultrasound an Effecitive Treatment for Overuse Running Injuries?

Ultrasound is a treatment method for overuse injuries favored by many physical therapists, athletic trainers, and chiropractors.  By running electricity through a special crystal, ultrasound machines generate sound waves that oscillate thousands of times per second.

Diagnostic ultrasound machines are equipped with detectors, which listen for the “echoes” of the ultrasonic waves and create an image.  Ultrasound imaging is useful for everything from examining a damaged Achilles tendon to viewing a fetus in the womb.

But today, we’re only concerning ourselves with therapeutic ultrasound—machines which create lower-frequency ultrasonic waves but with more energy output, with the goal of using the ultrasonic waves to directly aid healing of overuse injuries in athletes.

When a trainer or therapist uses a therapeutic ultrasound machine, it’s fairly easy to tell that something is going on.  After a sound-conductive gel is applied to your skin, the ultrasound machine’s emitter is placed directly over the injured area and you can sense a warm, tingling feeling when it is switched on.  This is the result of heating in the tissues absorbing the ultrasonic waves.

But is this tingly warmth actually accomplishing anything from an injury rehab perspective?

Direct effect of ultrasound on cells and tissue

Though therapeutic ultrasound has been popular for several decades, good scientific research on it has been lacking until relatively recently.  Early studies looked at the direct effects of ultrasound on tissue and cells under a microscope, and the results were promising.

One study by a group of researchers at the University of Texas at Tyler found that ultrasound increased the rate of healing of injured tendon tissue, while having no effect on healthy tendon tissue, and a 2011 review article by W.C. Tsai, S.T. Tang, and F.C. Liang in Taiwan cited in vitro studies (done with biological tissue, but outside of the body) showing increased cell growth, cell migration, and collagen synthesis as supporting the use of therapeutic ultrasound.

Studies in animals would be the next step towards proving the utility of therapeutic ultrasound.  If ultrasonic waves could aid healing of animal muscles or tendons following injury, there’s a good chance ultrasound would be useful in humans too.  But among animal studies, it is a mixed bag.

Animal test results

Some work has yielded good results:

• A 1989 paper by C.S. Enwemeka found that nine five-minute ultrasound treatments significantly increased healing and improved strength in damaged rat tendons compared to a control group which received no ultrasound.

• And a 2001 paper by Alessandra da Cunha, Nivaldo Antonio Parizotto, and Benedicto de Campos Vidal in Brazil found  better organization and healing of collagen fibers in rat tendons after 14 sessions of daily ultrasound.

But other researchers found no discernible effect of ultrasound in animal models.  S.M. Turner, E.S. Powell, and C.S. Ng at Hope Hospital in the UK studied rooster tendons—significant because they are more biologically similar to human tendons than tissue from rats—and found that ultrasonic treatment did not increase strength or healing, even after six weeks of ultrasound.

Human test results

With conflicting results like this, the only reliable way to test the efficacy of ultrasound on a real overuse injury is to actually try it in humans: gather a group of injured patients, then split them into a control group and an experimental group.

To prevent the placebo effect from marring the results, a good study should provide some type of “sham” treatment.  Fortunately, with ultrasound, this is quite easy—you can just turn off the machine while “applying” the treatment!

Thirty five studies on therapeutic ultrasound for various overuse injuries were analyzed in a review article by Valma Robertson and Kerry Baker in Australia.  Of these, Robertson and Baker found that only 10 met their criteria for experimental design and quality.

Two of these studies found a significant benefit when comparing ultrasound to placebo, but the other eight did not.

Robertson and Baker concluded that there was little evidence to support the use of ultrasound to rehab overuse injuries, and use of it is further hampered by wide variation in ultrasonic wave dosage and power levels.

In another review article, Robertson and Baker also pointed out that many of the effects of ultrasound observed in in vitro studies did not occur when ultrasound was applied to cells actually inside the body.  And most of the cellular effects that do occur appear to be at least partially due to heating of the tissue, something that could probably be accomplished just as easily with a hot pack!

Final notes and recommendations

Subsequent review studies by other authors have not found ultrasound to be particularly useful either.  This doesn’t mean that it is dead in the water, though—there is still ongoing research into modifying the power, intensity, and frequency of ultrasonic waves to hopefully aid recovery from various types of injury.

But the therapeutic ultrasound machines in use today at most physical therapy centers and training rooms are of little use for an injured runner; if there’s any benefit at all, you can probably get it by heating up the injured area with a warm water bath or a hot pack.

Our recommendation is continue to use ultrasound if it is easily available and cost effective (i.e. you’re already going to the PT and ultrasound is covered under your insurance or free). However, at this time, looking at the research, we wouldn’t recommend spending a great deal of time, energy or money seeking out the treatment option on its own.