Does Ultrasound Enhance Stretching of Soft Tissue Contractures?
abstract & commentary
Synopsis: Ultrasound did not increase tissue stretch with a continuous applied load as compared to sham ultrasound treatment with the same applied load.
Source: Reed BV, et al. Effects of ultrasound and stretch on knee ligament extensibility. J Orthop Sports Phys Ther 2000;30:341-347.
The use of heat and stretch to increase ligament extensibility has long been part of the standard of care in rehabilitation. Quite often, the choice of heat has been continuous wattage ultrasound (CWUS). In fact, ultrasound has long been a primary method of heat delivery in rehabilitation circles. A basic assumption has been that one of the effects of heat on connective tissue is that it increases extensibility. The purpose of this study was to determine whether ultrasound and stretching increased extensibility of the medial collateral ligament (MCL). Instrumentation included the Genucom knee joint arthometer that can introduce either anterior/posterior forces or medial/lateral forces that are quantifiable relative to the angle of the knee or displacement.
The sample included 21 normal adult female volunteers with a mean age of 31.5 years ± 11 years and with no history of pathology. The procedure included a 10 lb valgus force applied to the knee joint with displacement measured over a 40-minute time period. This was done on two separate testing dates 28 days apart to control for possible hormonal fluctuations of the subjects. Two pre-tests were done at five-minute intervals followed by treatment, which included either a static valgus stretch and ultrasound or static valgus stretch and a sham ultrasound. After treatment, three post-tests were performed again at five-minute intervals. All Genucom measurements and manual stretching were performed by the same tester. The soundhead movement was applied in a typical circular pattern at approximately 4 cm per second. The ultrasound dosage was 3 MHz; 1.25 W/cm2 ´ 2.5 min. Statistical analysis included a two-way factor repeated measures analysis of variance.
Results indicated that there was a significant difference with regard to stretching from the pre-test measures whether the sham ultrasound was applied or whether true ultrasound was applied. In other words, stretching caused ligament extensibility, but ultrasound did not contribute to that extensibility.
Comment by Clayton F. Holmes, EdD, PT, ATC
While ultrasound has long been used as a method of heat delivery in rehabilitation, there is little evidence to support its use. There is evidence in animal models that ultrasound does heat tissues below the surface; however, the clinical relevance of this heating has long been in question. In addition, the direct effects on tissue extensibility of heat delivered by any method needs further study.
This was an excellent study that controlled for several possible confounding variables. In addition, reliability of the genucom was well documented, including its use by these particular researchers. One concern regarding study design is whether the duration of ultrasound treatment would sufficiently heat the tissues to generate any effect. Comparing various durations of treatment might have been helpful. While this study did not measure heat delivery, it is clinically applicable because it measured a possible effect of that heat, tissue extensibility. In fact, the major finding of this study was that ultrasound did not affect tissue extensibility. This is critical because one of the most common physical agents prescribed in rehabilitation of soft tissue injury is ultrasound and this study did not support its effectiveness in performing a commonly assumed physiological effect. It is possible that ultrasound would have effects on scar tissue or contracture different than on the intact MCL. While more study certainly needs to be done, evidence such as this could indicate that ultrasound may not be the choice of heat delivery to soft tissue. It would be interesting to perform the same study and compare ultrasound with other forms of heat delivery. Perhaps moist heat and other less invasive forms of heat delivery may be more appropriate.
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