The answer to the above question is still in doubt. According to Wong, et al.,1 if clinicians based their decision to use ultrasound on clear demonstration of effectiveness in the scientific literature, then many would not use it based on lack of supporting evidence. How many times have we heard this statement about much of what soft-tissue clinicians do, or for that matter, about what practitioners do in all of the healing professions? Yet ultrasound has been widely used and well-accepted as a physical therapy adjunct modality throughout the world since the '50s.1
What the Research Says
Randomized, controlled trials (RCTs) have been conducted; 10 of 35 RCTs were judged to have acceptable methods. Two of these 10 trials suggested that ultrasound was more effective for calcific tendinitis of the shoulder and carpal tunnel than placebo, but the other eight trials did not recommend its use.2 In the journal Pain,3 a systematic review of 38 studies was performed; the review authors also concluded that there seemed to be little evidence to support the use of ultrasound in the treatment of musculoskeletal disorders.
That said, does this mean we should abandon the use of ultrasound? Not necessarily. Most of these studies do not consider dosage, treatment time and the type of tissue it is used on. Like many things we do that seem to help patients, the final word is not yet in. There are studies that conclude ultrasound works. One paper concluded that the results of high-quality studies indicated there was evidence (albeit weak) in favor of ultrasound for lateral epicondylitis.3 I wonder if insurance decision-makers are aware of this literature. Regardless, at present, you have to make up your own mind.
How to Make Ultrasound More Efficient
Ultrasound is thought to exert both a thermal and non-thermal effect. Early on, many perceived its effect primarily as thermal, but studies have shown that the warmth felt by the patient is mostly in the thermal skin receptors and does not create a significant thermal affect in the deeper tissues, even when continuous ultrasound is administered at a relatively high power.4 Some studies have revealed no advantage between ordinary heat therapy and ultrasound with regard to tissue extensibility and stretching; the effect of ultrasound on extensibility lasted only 3 minutes immediately following treatment.5
Non-thermal effects refer to its effect in relation to soft-tissue injury. Rather than thermal, the physical mechanisms thought to be involved are cavitation and acoustic streaming.6 Before discussing non-thermal effects, it is important to note that the absorption of ultrasound into the tissues depends on the particular tissue's ability to absorb the energy.4
Tissues with a higher protein content absorb ultrasound more than tissues with high water content and low protein content. Therefore, tissues with the high collagen content such as ligaments, tendons, fascia, joint capsule and scar tissue are the best absorbers. Immediately after injury (in the bleeding phase), ultrasound is not recommended since it is thought that it may increase blood flow. After the acute bleeding phase, ultrasound is considered pro-inflammatory by stimulating mast cells, platelets, and white cells, which is necessary in the early phases of the repair process.
Some studies4 have shown the possibility that ultrasound may aid in the remodeling scar-tissue phase by influencing collagen fiber orientation. There are even studies involving techniques similar to friction massage and Graston Technique that suggest ultrasound creates increased fibroblastic proliferation and collagen formation.7
There is still a debate regarding dosage of ultrasound in relation to therapeutic effects. Also, while continuous ultrasound may cause a more rapid delivery of energy, pulsed ultrasound may be more effective in the early inflammatory and proliferative inflammatory stages. In comparison to other modalities, Watson4 states that there is an overlap with laser therapy and some pulsed EM fields (short wave). Ultrasound is best on tissues made of dense collagenous tissues, but less effective than these other modalities in tissues like muscle, nerve and edematous tissue.
So, after at least 50 years of use, ultrasound has not yet reached a high level of evidence-based acceptance. Newer methods are often rejected by insurance companies because they are considered to still be in the "experimental" phase. The question of what is responsible for healing continues.
References
- Wong RA, Schumann B, Townsend R, Phelps CA. A survey of therapeutic ultrasound use by physical therapists who are orthopaedic certified specialists. Physical Therapy, 2007;87(8):986-994.
- Robertson J, Baker KG. A review of therapeutic ultrasound: effectiveness studies. Physical Therapy, 2001;81(7):1339-1350.
- Van der Windt D, Van der Heijden G, Van den Berg S, et al. Ultrasound therapy for musculoskeletal disorders: a systematic review. Pain, 1999;81:257-271
- Watson T. Ultrasound in contemporary physiotherapy practice. Ultrasonics, 2008;48:321-329.
- Draper DO, Ricard MD. Rate of temperature decay in human muscle following 3 MHz ultrasound: the stretching window revealed. J Athlet Train, 1995;30(4):304-307.
- Baker KG, Robertson VJ, Duck FA. A review of therapeutic ultrasound:; biophysical effects. Phys Ther, 2001;81 (7):1351-1358.
- RamirezA, Schwane JA, McFarland C, Starcher BC. The effect of ultrasound oncollagensynthesis and fibroblast rolifertion in vitro. Med Sci Sports Exer, 1997;29:326-332.
