Heat therapy & Ultrasound

Heat therapy is popularly believed to reduce pain and muscle spasm following some types of injury, and heat is sometimes recommended prior to exercise for athletes with ‘stiff’ muscles or in the treatment of chronic conditions in which restricted muscle or joint motion may interfere with recovery (1). Another popular notion is that any positive effects associated with stretching activities may be enhanced by applying heat to the muscles before the stretching is carried out. However, the application of heat to injured parts of the body has also been linked with increases in tissue swelling (oedema), and heat can spur metabolic activity and increase capillary blood flow, effects which may be counterproductive in the early treatment of some injuries. In addition, heat may increase connective-tissue extensibility, augmenting the instability of some injured areas. Thus, the overall importance and applicability of heat as a valid therapeutic treatment is equivocal.

A study in New Mexico

Recently, researchers at the VA Medical Center and the Lovelace Medical Center in Albuquerque, New Mexico, examined the question of whether superficial heat or deep heat actually improves muscle flexibility (2). In this interesting study, 97 individuals (59 women and 38 men; average age 27) who had limited dorsiflexion range of motion at the ankle were randomly assigned to one of five groups. The first group was a control group whose members did not perform any stretching or receive any heat applications to their calf muscles. Meanwhile, the four experimental groups (groups two through five) carried out a static-stretching routine three days a week for a period of six weeks. Group two carried out the static-stretching regimen only, group three performed active heel raises prior to stretching, group four received 15 minutes of superficial, moist heat to the calf muscles before stretching, and group five received continuous ultrasound for seven minutes before engaging in stretching. Dorsiflexion range-of-motion measurements were taken at the beginning of the study and after two, four, and six weeks. Why was ultrasound therapy utilised (in group five) in this study, which had as its focus the effects of heat on muscle stretchiness? Bear in mind that although heat therapy is commonly administered with hot packs and hydrotherapy, ultrasound is also considered a form of heat therapy. Basically, hot packs heat up affected body parts by the process of conduction, hydrotherapy heats by convection, and ultrasound heats tissues as the result of the transduction of sound waves to heat. Radiant heat, short-wave diathermy, and paraffin baths are also used on occasion to heat up troublesome body regions.

What happened

As it turned out, all four experimental groups improved both active and passive range of motion (during dorsiflexion), compared with the control group. However, group members receiving the ultrasound before performing their stretching protocols achieved the greatest increase in both active (6.2 degrees) and passive (7.35 degrees) range of motion; this contrasted with enhancements of about four degrees in the other groups. Thus, it appeared that one form of heat therapy – ultrasound – was uniquely able to facilitate positive changes in ankle flexibility. A couple of caveats are in order, however: first, bear in mind that the heating associated with ultrasound may not have provided the actual mechanism for the upswing in calf-muscle extensibility; some other aspect of ultrasound might have produced the effect. Secondly, it should not be assumed that improving range of motion is automatically a good thing. There is no guarantee, for example, that the enhanced calf-muscle flexibility observed in this study would upgrade efficiency of movement or overall performance, nor is there any certainty that the risk of injury would be lowered as a result of more facile dorsiflexion.

Injuries to the skin

Ultrasound does seem to be able to increase flexibility, but is there any evidence that heat treatments (including ultrasound therapy) could speed up the recovery process following injury? In addition to their interest in heat-related flexibility improvement, scientists have been very interested in the idea that heat therapy might be particularly useful for the treatment of injuries to the skin, especially the kinds of abrasions commonly seen in wrestlers, American footballers, rugby players, cricketers, and even footballers. There is indeed some evidence in the scientific literature to suggest that the use of heat helps to upgrade oxygen flow to parts of the body like the skin which do not necessarily receive ample inputs of blood – and that this oxygen flow can boost the healing of acute wounds. Because the situation with chronic wounds has been less clear, researchers at the School of Care Sciences at the University of Glamorgan in Wales recently employed a radiant-heat-therapy system for the treatment of Stage 3 and Stage 4 pressure ulcers. The radiant heat did produce an accelerated rate of healing, compared with standard treatments (3).

Not all studies concerning heat’s effectiveness as a wound healer have such a happy ending, however. In a separate investigation, for example, various intensities of heat and ultrasound treatments were applied to deep skin wounds for five and 10 minutes per day, and healing was assessed with wound-breaking-strength measurements taken 14 days after the original injury (4). In this investigation, neither standard heat application nor ultrasound treatment produced greater wound-breaking strength, and in fact higher intensities of ultrasound (0.1 and 0.15 W/cm2) and heat (0.15 W/cm2) actually resulted in poorer healing (decreased wound-breaking strength).

The Dutch look at ankle sprains

Of course, ultrasound is often used to treat common athletic injuries like sprained ankles; somewhat surprisingly, the evidence that such therapy is useful is actually fairly flimsy. In an excellent review article (5), scientists from the Institute for Research in Extramural Medicine at Vrije University in Amsterdam evaluated the effects of ultrasound therapy in the treatment of acute ankle sprains by searching the Cochrane Musculoskeletal Injuries Group specialised register, the Cochrane Controlled Trials Register, MEDLINE, EMBASE, CINAHL, the Physiotherapy Evidence Database, and the Cochrane Rehabilitation and Related Therapies Field database for relevant articles. Five trials involving 572 patients were selected for analysis. Four of these five trials were placebo-controlled (using sham ultrasound as the placebo), but none of the four trials could demonstrate statistically significant differences between true and sham ultrasound therapy (after seven to 14 days of follow-up) for pain relief, reduction in swelling, improvement in range of motion, improvement in functional ability, or general improvement. Just one of the trials reported significant differences in pain-free status and swelling in favour of the ultrasound treatment. The Dutch reviewers concluded that ‘the extent and quality of the available evidence for the effects of ultrasound therapy for acute ankle sprains is limited’.

…and musculoskeletal disorders

The same research group conducted an even broader review to see if ultrasound therapy could be found to be helpful in treating musculoskeletal disorders in general; again, the researchers used databases to track down relevant, published scientific articles (6). 38 separate studies were included in this review, with the investigations evaluating the effects of ultrasound therapy on lateral epicondylitis, shoulder pain, degenerative rheumatic disorders, ankle distortions, temporomandibular pain, myofacial pain, and a variety of other problems. Just 13 of the studies were actually placebo-controlled, and in 11 of these there was no evidence that ultrasound therapy led to clinically important or statistically significant improvements, compared with a placebo. As the researchers concluded, ‘As yet, there seems to be little evidence to support the use of ultrasound therapy in the treatment of musculoskeletal disorders.’ Out of the array of conditions examined, there was only one disorder for which ultrasound therapy looked slightly promising – lateral epicondylitis (inflammation of the outer bottom of the upper arm bone).

The Canadians follow suit

Of course, knee (patellofemoral) pain is ubiquitous in sports, and ultrasound therapy is commonly utilised to treat such pain. Taking a page out of the Vrije-University book, rehabilitation specialists at the School of Rehabilitation Sciences, University of Ottawa in Canada, recently checked on the effectiveness and side effects of ultrasound therapy for treating patellofemoral pain syndrome by poring through MEDLINE, Embase, Healthstar, Sports Discus, CINAHL, the Cochrane Trials Register, the PEDro database, the specialised registry of the Cochrane musculoskeletal group, and the Cochrane field of physical and related therapies; key experts were also contacted for additional articles (7). 85 articles were retrieved, but the overall methodology of the underlying research was rather poor, and in fact just one randomised, controlled trial was identified.

In this investigation, ultrasound combined with ice-massage contrast was not statistically different from ice massage alone in terms of patient-rated knee-pain relief or improvement in quadriceps and hamstring strength. In other words, even though ultrasound is widely used for knee pain, such treatments have not been scientifically validated.

Ultrasound helps bone fractures

If you are a big fan of ultrasound and/or heat therapy, we do have some slightly better news for you at this point: there is positive evidence about ultrasound’s ability to promote the repair of fractured bones. For example, in very recent research carried out at the Institute of Biomedical Engineering at Chung-Yuan Christian University in Taiwan, scientists divided 45 adult New Zealand White rabbits with uniformly fractured fibulas into control, microwave-treated, and ultrasound-stimulation groups (8). After ultrasound stimulation, new bone formation at the fracture site was 23 to 36% faster, compared with the sham-treated bone; in addition, torsional stiffness of the ultrasound limb was up to 80% greater than the stiffness of the ultrasound-free bone. Meanwhile, the microwave-hyperthermia treatment was unable to produce statistically significant improvements in bone healing or strength. It would be nice to close on that positive note, but we feel compelled to offer you a few more hot items. As you are well aware, heat is a popular treatment for individuals suffering from arthritis, and rheumatoid-arthritis patients often report that heat palliates their symptoms and improves range of motion at troubled joints. Searching for a scientific basis for these beliefs, the University of Ottawa team completed yet another database exploration(9). Again, they were hampered by the poor quality of published research in this area, but they did find seven studies with 328 subjects which met their inclusion criteria. Their extensive review determined that there was no significant effect of hot- and ice-pack applications, cryotherapy, or faradic baths on objective measures of rheumatoid-arthritis disease activity, including joint swelling, pain, medication intake, range of motion, grip strength, or hand function. In addition, therapeutic ultrasound was found to be no better than the application of wax to battered joints, and there was no difference in patient preference for various types of thermotherapy. 94% of patients, however, preferred heat therapy to no therapy at all, and the researchers concluded that superficial moist heat and cryotherapy could be utilised by rheumatoid-arthritis victims to help them gloss over their symptoms. There was also some evidence that paraffin-wax baths, combined with exercises, might produce beneficial short-term effects in arthritic hands.

The bottom line? Don’t get overheated by our comments, but if you are a heat-therapy zealot, we cannot provide much scientific support for your practices.

Owen Anderson

References

1. Sullivan, J. & Anderson, S. (Eds.). (2000). Care of the Young Athlete. American Academy of Orthopaedic Surgeons
2. ‘Effect of Superficial Heat, Deep Heat, and Active Exercise Warm-Up on the Extensibility of the Plantar Flexors’, Physical Therapy, Vol 81 (6), pp1206-1214, 2001
3. ‘The Effect of a Radiant Heat Dressing on Pressure Ulcers’, Journal of Wound Care, Vol 9 (4), pp201-205, 2000
4. ‘The Effect of Ultrasonics and Thermal Treatment on Wounds’, Plastic Reconstructive Surgery, Vol 68 (6), pp860-870, 1981
5. ‘Ultrasound Therapy for Acute Ankle Sprains’, Cochrane Database Syst Rev, 2002; (1): CD001250
6. ‘Ultrasound Therapy for Musculoskeletal Disorders: A Systematic Review’, Pain, Vol 81(3), pp257-271, 1999
7. ‘Therapeutic Ultrasound for Treating Patellofemoral Pain Syndrome’, Cochrane Database Syst Rev, 2001; (4): CD003375
8. ‘Study of Thermal Effects of Ultrasound Stimulation on Fracture Healing’, Bioelectromagnetics, Vol 23(4), pp256-263, 2002
9. ‘Thermotherapy for Treating Rheumatoid Arthritis’, Cochrane Database Syst Rev, 2002; (1): CD002826