Publications
APS Bulletin • Volume 15, Number 1, Winter 2005
Innovations in Practice
Norman Harden, MD, Department Editor
A New Look at Heat Treatment for Pain Disorders, Part 2
Annie O‘Connor, PT OCS, and Bill McCarberg, MD FABPM
Editor’s Note
In this second article of a two-part series, we look at new developments and research for treating common pain problems with heat therapy, comparing the risks and benefits of heat treatment with other methods of treating pain.
A New Look at Heat Treatment for Pain Disorders, Part 1 (November/December APS Bulletin 14(6))
Bigos et al. (1994) reported a lack of evidence supporting the use of heat to treat pain. More recent research, however, arrives at a different conclusion. Not only do researchers find heat to be effective in reducing acute low back pain, but they also find that it reduces wrist and neck pain. The new data suggests the usefulness of continuous, low-level, and long-term heat, rather than the more common practice of intermittent, brief exposures to heat. In this article we will present the results of several trials with heat treatment.
Low Back Pain
Nadler et al. (2002) compared the efficacy of continuous, low-level heat worn directly on the skin in ambulatory patients and with the efficacy of using ibuprofen and acetaminophen in the treatment of acute, nonspecific low back pain. Subjects received randomized treatment with heat wraps for 8 hr/day (n = 113), oral acetaminophen (n = 113), or ibuprofen (n = 106). The ibuprofen dose was 1200 mg/day, and acetaminophen was 4000 mg/day. Efficacy was measured over two treatment days and two follow-up days. The investigators reported that the heat wrap, when compared to ibuprofen and acetaminophen respectively, provided significantly better pain relief on Day 1 (p = .0007, p = .0001) and extended pain relief on Days 3 and 4 (p = .0001, p =. 0009).
In another study, Nadler et al. (2003) compared the efficacy and safety of the overnight use of continuous heat versus ibuprofen and placebo for relief of low back pain. Treatments were administered for three consecutive nights (8 hr/night), with two days of follow-up. Seventy-six subjects were randomized to evaluation of efficacy: heat wrap (n = 33); oral placebo (n = 34); blinding (unheated wrap, n = 5); oral ibuprofen (n = 4). The study showed that heat-wrap therapy was significantly better than placebo for
- Morning pain relief on Days 2–4 (p = .00005)
- Daytime pain relief on Days 2–4 (p < .001)
- Extended pain relief on Days 4–5 (p < .001)
In addition, heat-wrap therapy:
- Reduced considerably morning muscle stiffness on Day 4 (p < .001)
- Increased lateral trunk flexibility on Day 4 (p < .002)
- Decreased low back disability on Day 4 (p = .005).
The positive effects of heat therapy persisted more than 48 hours after treatment was discontinued. This extended pain-relief phenomenon appears to be a unique therapeutic benefit of continuous heat.
Neck Pain
Neck pain can result from a variety of etiologies, and it is often difficult to find a definitive diagnosis. Heat applied for 8 hr/day was significantly more effective than placebo in reducing neck pain, muscle tension, and disability in persons with trapezius myalgia (Steiner, Erasala, Hengehold, Goodale, & Weingand, 2000). Heat significantly reduced muscle tension (p = .01) when compared to ibuprofen alone. Heat provided significantly greater pain relief as compared to an unheated wrap (p = .048) and ibuprofen alone (p = .024). Subjects using the heat and ibuprofen had significantly more pain relief when compared to subjects using the unheated wrap and ibuprofen (p = .02).
There was significantly more pain relief (p = .02) and less muscle tension (p = .01) for the heat and ibuprofen group as compared to the unheated ibuprofen group. In addition, heat resulted in significantly less disability as compared to the unheated wrap (p = .012) or no wrap (p = .0001). The relief from neck pain also lasted for several days after discontinuation of the treatment.
Wrist Pain
Despite interventions, patients with work-related musculoskeletal disorders continue to have symptoms interfering with work and recreational activities more than one year after presentation (Keough, Nuwayhid , Gordon, & Gucer, 2000; Pransky, Benjamin, Hill-Fotouhi, et al., 2000). Continuous heat is significantly better than oral placebo in relieving wrist pain (Michlovitz et al., 2002). Patients with a variety of problems resulting in wrist pain were randomized into the following treatments: heat (n = 42), oral placebo (n = 42), oral acetaminophen (n = 6), and unheated wrap (n = 6). Subjects were treated for three consecutive days with two additional follow-up days.
Heat therapy was significantly more effective (p < .05) than placebo for subjective pain relief and grip strength improvement among patients with strains, sprains, tendonosis, or osteoarthritis. Heat was also significantly more beneficial than oral placebo in patients with carpal tunnel syndrome, as shown by increased pain relief, decreased joint stiffness, increased grip strength, improvements on patient-rated wrist evaluation, and carpal tunnel syndrome symptom severity and functional status scales (p < .05).
New Developments and Research with Heat Therapy in Common Pain Problems
In ambulatory patients, continuous, low-level heat delivered for at least 8 hours directly on the skin provides more pain relief for low back pain, neck pain, and wrist pain than short duration heat treatments and commonly used nonprescription analgesics.
Because risk of side effects is so low, heat therapy may be considered for treatment of other conditions encountered frequently in the primary-care setting (e.g., abdominal pain, including menstrual pain and cervical muscle spasm that may result in headaches). Recent studies on continuous, low-level heat suggest a different approach to common treatments for pain. Practitioners need to reinforce this updated knowledge so that their patients can use heat therapy effectively.
Practices that deal with musculoskeletal pain (e.g., physical therapy, chiropractic therapy, osteopathy, sports-team training, massage therapy) use the following traditional methods of heat therapy: whirlpools, silicate gel moist-heat packs, electric heating pads, contrast bath therapy, continuous wave ultrasound, and pulsed shortwave diathermies. All of these heat therapy methods are applied with brief exposure to heat at intermittent periods of time. There is lack of evidence, however, supporting the effectiveness of these methods in decreasing low back pain (Bigos et al., 1994). In fact, new data suggests that continuous, low-level, long-term heat therapy is more useful in treating low back pain (Nadler, Steiner, Petty, et al., 2003). Heat transfer is directly related to temperature gradient, the surface area covered, and the duration of application. In order for practitioners to make better recommendations to their patients whose pain results from ischemia, spasm, or the evolution of chemical mediators of inflammation (e.g., prostaglandins), they need to understand the effectiveness of different heating methods in producing a heat transfer.
Heat Transfer Parameters
The intramuscular temperature should reach at least 40 °C in order to achieve the effects of muscle lengthening and increase in tissue metabolism, deep tissue temperature, and blood flow. This requires at least a 3 °C–4 °C increase in surface temperature (Kankaanpaa, Taimela, Airaksinen, & Hanninen, 1999). A 1 °C increase in tissue temperature is associated with a 10%–15% increase in tissue metabolism (Smith, 2002). Recent research has shown that heat applied directly to the skin at 40 °C increases muscle tissue temperature by at least 1 °C at depths ranging from 2.0–3.8 cm below the surface of the skin (Mulkern et al., 1999).
Comparison of Heat Therapy Options
The following information is a review of the ability of common heat therapy methods to meet the parameters discussed above.
- Warm whirlpool therapy (40.6 °C) can raise the temperature of muscle tissue 1 cm below the skin’s surface by 2.8 °C (Myrer, Draper, & Durrant, 1994).
- Application of silicate gel moist-heat packs has been shown to increase the muscle temperature in the lower leg by 3.8 °C at 1 cm below the skin’s surface(Draper et al., 1998).
- Ultrasound and shortwave diathermy pulsed at 48 watts can raise the temperature as much as 4 °C–6 °C (Draper, Castel, & Castel, 1995).
- Bath therapy, which involves alternately immersing an extremity in warm (38 °C–44 °C) and cold (10 °C–18 °C) water, has been proven ineffective for muscle tissue warming because the cold negates the heat produced by the warm water treatment (ThermaCare® Heat wraps).
While the above choices provide the deepest and warmest heating, they are not practical with ambulatory therapies. Not only are they expensive, they require an office visit.
Prolonged use of an electric heating pad on one area of the body, in addition to being inconvenient, may cause a severe burn, even if the pad is set at a low to medium temperature (Bill, Edlich, & Himel, 1994). Both the Food and Drug Administration and the Consumer Product Safety Commission have received many reports of injury and death from burns, electric shocks, and fires associated with the use of electric heating pads. Infants and persons who may be unable to feel heat because of advanced age, diabetes, spinal cord injury, or medication that alters cognition or sensibility are at particular risk. Practitioners should give safety guidelines when patients choose to use heating pads at home (e.g., restrict application time to 20–30 min for devices that heat to an unknown temperature or that heat to more than 40 °C).
Silicate gel hot packs and whirlpools provide moderate heat to muscles, but the heat is short-lived and not portable. More recent development of wearable, continuous heat sources that are convenient, safe, and effective make heat therapy an option that leads not only to increased comfort but also accelerates pain resolution. New heat wrap technology applied directly to the skin provides a continuous, low-level heat therapy for several hours and is the first to be deemed safe enough for use while sleeping (Trowbridge et al., 2002).
Until the recent introduction of air-activated, self-regulating devices, portable sources of constant-temperature heat therapy did not exist. Heat wraps worn in direct contact with the skin for at least 8 hr/day enable patients to remain mobile and active while receiving treatment. As a result, patients retain control over their own care and pain management. This can increase both treatment time at home and allow them to participate in other activities.
Recent published research has compared the effectiveness of an air-activated heat wrap to two other wearable products that produce a warming sensation on the skin (Trowbridge et al., 2002). In the first study, the two comparison products were adhesive plasters containing capsaicin, a derivative of the hot pepper plant. The proposed mechanism of action of capsaicin involves the sustained release followed by depletion of substance P, a neurotransmitter involved in pain. A counterirritant effect may also lead to reduced pain through gate-controlled mechanisms. Researchers evaluated the muscle warming effects of capsaicin plasters compared to the heat wrap method by inserting a thermocouple probe 2 cm deep into the belly of the lumbar paraspinal musculature. After 120 min, the capsaicin plasters increased muscle temperature by less than 0.2 °C and skin temperature by less than 3.2 °C, This result did not meet theparameters to produce a heat transfer, thereby not producing the physiological benefits of heat therapy. The air-activated heat wraps, on the other hand, increased muscle temperature by 1.1 °C and skin temperature by 5.8 °C. The depth of muscle warming produced by the heat wrap is similar to that reported for whirlpools and moist-heat packs and falls well within the parameters to produce a heat transfer and the occurrence of the physiological benefits of heat therapy noted earlier.
Summary
Portable heat therapy helps keep patients’ joints and muscles warm while at the same time restoring functions and movements that the patients lost temporarily because of pain. In addition to being efficient, portable heat therapy speeds up the healing process. Moreover, patients can choose a convenient time to have the treatment; they do not have to make an appointment, and as a result they can have treatments more frequently than patients who rely on office visits for the passive heat therapy treatments. All this reinforces the control patients have to get better and lessens the dependency patients tend to form on palliative care.
References
Bigos, S., Bowyer, O., Braen, G., et al. (1994, December). Acute low back problems in adults (Clinical Practice Guideline No. 14. Health Care Policy and Research, Public Health Service, AHCPR Publication No. 95-0643). Washington, DC: U.S. Department of Health and Human Services.
Bill, T.J., Edlich, R.F., & Himel, N.H. (1994). Electric heating pad burns. Journal of Emergency Medicine, 12, 819–824.
Draper, D. O., Castel, J.C., & Castel, D.(1995). Rate of temperature increase in human muscle during 1MHz and 3 MHz continuous ultrasound. Journal of Orthopaedic & Sports Physical Therapy, 22, 142–150.
Draper, D.O., Harris, S.T., Schulthies, S.S., Ricard, M.D., Knight, K.K., & Durant, E. (1998). Hotpack and 1 MHz ultrasound treatments have an additive effect on muscle temperature increase. Journal of Athletic Training, 33, 21–24.
Kankaanpaa, M., Taimela, S., Airaksinen, O., & Hanninen, O. (1999). The efficacy of active rehabilitation in chronic low back pain. Effect on pain intensity, self-experienced disability, and lumbar fatigability. Spine, 249(10), 1034–1042.
Keough, J.P., Nuwayhid, I., Gordon, J.L., & Gucer, P.W. (2000). The impact of occupational injury on injured worker and family outcomes of upper extremity cumulative trauma disorders in Maryland workers. American Journal of Industrial Medicine, 38(5), 498–506.
Michlovitz, S.L., Erasala, G.N., Hengehold, D.A., et al. (2002). Continuous low-level heat therapy for wrist pain. Orthopedics, 25(S), 1467.
Mulkern, R.V., McDannold, N., Hynynen, K., Fielding, J., Panych, L., Jolesz, F.A. et al. (1999, May 22–28). Temperature distribution changes in low back muscles during applied topical heat: A magnetic resonance thermometry study. Proceedings of the Seventh Annual Meeting of the International Society of Magnetic Resonance in Medicine (p. 1054). Philadelphia, PA.
Myrer, J.W., Draper, D.O., & Durrant, E. (1994). Contrast therapy and intramuscular temperature in the human leg. Journal of Athletic Training, 29, 318–322.
Nadler, S.F., Steiner, D.J., Erasala, G.N., Hengehold, D.A., Hinkle, R.T., Goodale, M.B., et al. (2002). Continuous low-level heat wrap therapy provides more efficacy than ibuprofen and acetaminophen for low back pain. Spine, 27(10), 1012–1017.
Nadler, S.F., Steiner, D.J., Petty, S.R., Erasala, G.N., Hengehold, D. A., & Weingard, K. W. (2003). Overnight use of continuous low-level heatwrap therapy for relief of low back pain. Archives of Physical Medicine and Rehabilitation, 84, 335–42.
Pransky, G., Benjamin, K., Hill-Fotouhi, C., et al. Upper extremity and low back injuries: Results of a retrospective study. American Journal of Industrial Medicine, 37(4), 400–409.
Smith, R.P. (2002). Heat therapy: The next hot topic. The Female Patient; 27, 25–31.
Steiner, D., Erasala, G., Hengehold, D., Goodale, M.B., & Weingand, K. (2000). Continuous low-level topical heat therapy for trapezius myalgia [Abstract]. Proceedings of the 19th Annual Scientific Meeting of the American Pain Society, 171. ThermaCare® Heat wraps, Procter & Gamble Co., Cincinnati, OH.
Trowbridge, C.A., Draper, D.O., Jutte, L.S., Feland, J.B., Eggett, D.L., & Ricard, M.D. (2002). A comparison of the Capsicum Back Plaster, the ABC Back Plaster, and the ThermaCare® Heat Wrap on paraspinal muscle and skin temperature. Journal of Athletic Training, 37(2), S–102.
Annie O’Connor, PT OCS, is corporate director of musculoskeletal practice at the Rehabilitation Institute of Chicago. She is also a postgraduate faculty member of the College of Chiropractic, Southern California University Health Sciences.
Bill McCarberg, MD FABPM, is the founder of the chronic pain management program of Kaiser Permanente San Diego. He is also a clinical assistant professor (voluntary) at the University of California San Diego.
Please direct your comments or suggestions about this article or department to Norman Harden, MD, Department Editor, at nharden@ric.org.