Over the past 20 years, therapeutic modality researchers and educators have predicted a resurgence in the use of short-wave diathermy (SWD) in the United States. This prediction has proven to be correct. Clinicians working in skilled nursing facilities and athletic rehabilitation injury settings have reported a substantial increase in use of SWD. The term diathermy is from the Greek derivative meaning to heat through (dia = through; thermy = heat). The electromagnetic energy produced by a short-wave diathermy device can elicit both thermal and nonthermal physiologic effects in human tissue.
Contemporary short-wave diathermy devices are both safe and easy to use, provided the proper training has been completed. Clinicians who have limited exposure to this modality can receive proper training in the application, precautions and contraindications for SWD through continuing education workshops and contemporary textbooks/research.
Short-wave diathermy produces electromagnetic energy at 27.12 million cycles per second (MHz). Short-wave diathermy can be delivered using either a capacitive applicator or an inductive applicator. Both forms result in energy conversion of the electromagnetic field to a mechanical energy that creates physiologic effects within tissue. This occurs in the patient's tissue through the stimulation of ion acceleration (molecular vibration), which is converted to heat.
Capacitive generators produce a high-frequency electromagnetic field between two plates that also utilize the body's electrical conductivity in the energy field. The two plates can be comprised of a rigid metal or a flexible rubber material, depending on the manufacturer. The capacitive applicators are used to bracket the target tissue. The energy and related physiologic effects are transmitted to the tissues underneath and between the applicators. Capacitive field SWD applications result in energy being absorbed mostly in tissues with high electrical impedance such as skin and fat. Therefore, it is recommended for treatment of superficial tissue.
Inductive field SWD generators release energy from coils housed with in a drum or sleeve. The energy preferentially heats low impedance tissues (i.e., skeletal muscle, blood, and synovial fluid). The inductive technique is recommended for heating deeper tissue. The inductive short-wave diathermy drum is currently the most common applicator. The drum is attached to a pivoting arm that extends off of the SWD device. The drum is positioned over the area to be treated.
Decreased muscle flexibility and joint hypomobility are two common impairments that rehabilitation specialists treat. When selecting a deep heating agent prior to stretching or joint mobilization techniques, many clinicians turn to therapeutic ultrasound. However, ultrasound is limited to treating relatively small areas that do not exceed two times the size of the sound head, and it doesn't efficiently heat deep muscle. Short-wave diathermy effectively heats large areas, while safely heating deep muscle. It matches the depth of penetration and heating rate of 1 MHz ultrasound, with the added benefit of heating a larger area.1 Since properly applied SWD can preferentially heat low-impedance tissues (skeletal muscle, blood, synovial fluid) it can heat deep muscle more efficiently than therapeutic ultrasound.
In addition, soft tissue treated with SWD maintains the tissue temperature increase two to three times longer than an ultrasound treatment.1 Muscle only maintains its peak temperature for 3.3 minutes post-ultrasound treatment.1 Tendons and ligaments maintain therapeutic heating levels for up to 5 minutes post-ultrasound treatment.1 Shortwave diathermy extends these stretching windows, which gives the clinician more time to use passive stretching, joint mobilization and soft tissue mobilization before the tissue temperature retards to a baseline level. Low-load prolonged stretching techniques during and immediately after the SWD treatment can be especially beneficial in improving soft tissue extensibility. Recent research and clinical experience have shown that joint mobilization techniques and soft tissue mobilization techniques yield better results after reaching therapeutic temperature through preheating with shortwave diathermy.
Draper et al1 have led the way in SWD research in the United States. Their work focuses on using pulsed shortwave diathermy (PSWD) as a heating agent. It often seems counterintuitive to clinicians that PSWD can heat, but it's clear from the research that it can heat efficiently and, when used in combination with a heating and stretching regime, it can improve flexibility in subjects with tight hamstrings and plantar flexors. 2,3
The literature provides some guidelines as to the dosimetry associated with SWD, but the clinician should take additional considerations in dosing SWD. The ability of patient populations to dissipate heat may differ from those of healthy subjects, often used in research studies. It is also plausible that the heating rates may vary between SWD devices. It's important to note that dosing the intensity of SWD is based on patient feedback and tolerance. The qualitative method of dosing intensity is widely accepted. The four dose levels are:
Dose I: Just below any sensation of heat;
Dose II: Mild perception of heat;
Dose III: Moderate (comfortable) perception of heat;
Dose IV: Vigorous heating (no pain or burning). If pain threshold is reached, immediately decrease output.
Dosing is based on the level of perceived heating reported by the patient. When the goal of treatment is to preheat tissue prior to stretching or joint mobilization, the objective is to deliver an intensity that produces a patient's report of vigorous (or strong) heating, but with no pain or burning.
From a research perspective, vigorous heating has commonly been defined as heating tissue to 4° Celsius or greater above baseline temperature. For example, baseline temperature at 2 cm depth in the gastrocnemius has been shown to be on average 35.5° Celsius. A 4° Celsius increase yields an absolute temperature of 39.5° Celsius, which is well tolerated in human subjects.
Draper et al have been able to obtain this 4° Celsius increase using pulsed short-wave diathermy (induction drum) for 15 to 20 minutes (pulse width of 400 microseconds, pulse rate of 800 pps, average output of 48 W).4 Thermal SWD can serve as an efficient, safe deep heating agent that can enhance the effectiveness of passive stretching, joint mobilization or soft tissue manipulation.
Nonthermal effects SWD can be achieved by using pulsed short-wave diathermy (PSWD) with a low enough duty cycle and intensity to minimize heat build-up in the tissue. For treatments that are intended to be nonthermal, it is recommended that the average power level not exceed 5 watts average intensity.5 The widely recommended nonthermal PSWD parameters associated with tissue healing, acute pain, and edema reduction include a short pulse width of 65 µsec, pulse rate of 400 PPS, with an average power of 4 watts. Nonthermal PSWD for 40 to 45 minutes has been shown to increase local microcirculation in both healthy subjects and around the wound margins in patients with diabetic ulcers.6,7 Benefits of increasing microcirculation, but still being in the subthermal range, include increasing local tissue oxygenation, nutrient transport and phagocytosis.
Nonthermal pulsed short-wave diathermy has been shown to accelerate fibroblastic activity, collagen deposition, and tissue healing in animal studies.11,12 The limited number of human studies that have been performed to date indicate it is likely that nonthermal PSWD enhances the rate of wound healing .6-10,13
However, some of the existing studies have small samples sizes, and others do not report on all of the essential dosing parameters, or are uncontrolled. Itoh et al13 performed treatment to patients classified as unhealed Stage II or III ulcers with nonthermal PSWD. All unhealed ulcers showed complete healing. In a randomized double-blinded nonthermal PSWD study, Salzberg et al12 treated individuals with spinal cord injury classified as having Stage II and III decubitus ulcers. The Stage II treatment group showed significant improvement in treatment times. The Stage III wounds showed improvements, however was not significant due to small sample size. Further research is necessary to gain more insight into PSWD's effectiveness in tissue healing, and to establish optimal dose response relationships.
Clinically, nonthermal pulsed short-wave diathermy has gained considerable positive reviews by front line clinicians as an adjunctive treatment in the management of wounds. This has been especially common in rehabilitation programs within skilled nursing facilities.
The modulation of pain can prevent muscle inhibition that can lead to atrophy, weakness, and contracture due to the patients' unwillingness or inability to move the painful joint. The mechanisms associated with the pain modulation effect of thermal short wave diathermy is similar to other heating modalities, decreasing muscle spasm, accelerating metabolic responses to acute injury, increasing the pain threshold to damaged tissue and influencing pain reception through sensory afferents. Mild heating with SWD in patients with knee osteoarthritis has been shown to reduce both pain and synovial sac thickness.14
Nonthermal PSWD has been advocated for the treatment of pain associated with acute and subacute injuries. The mechanism of action is not completely understood, but is thought to be related to alterations cell membrane function. Additional research is necessary to further investigate the capabilities of diathermy to reduce pain, and to determine the modalities effectiveness compared to other interventions.
1. Draper, D., & Knight, K. (2008). Therapeutic modalities: The art and science. Philadelphia: Lippincott Williams & Wilkins.
2. Draper, D., Castro, J., Feland, B., et al. (2004). Short-wave diathermy and prolonged stretching increase hamstring flexibility more than prolonged stretching alone. Journal of Orthopedic Sports Physical Therapy, 34, 13-20.
3. Peres, S., Draper, D., Knight, K., et al. (2002). Pulsed short-wave diathermy and prolonged long-duration stretching increases dorsiflexion range of motion more than identical stretching without diathermy. Journal of Athletic Training, 37, 43-50.
4. Draper, D., et al. (1999). Temperature change in human muscle during and after pulsed short-wave diathermy. Journal of Orthopedic Sports Physical Therapy, 29, 13-22.
5. Al-Mandeel, M., & Watson, T. (2010). The thermal and nonthermal effects of high and low doses of pulsed shortwave diathermy (PSWT). Physiotherapy Research International, 15, 199-211.
6. Mayrovitz, H., & Larsen, P. (1995). A preliminary study to evaluate the effect of pulsed radiofrequency field treatment on lower-extremity peri-ulcer skin microcirculation of diabetic patients. Wounds, 7, 90-93.
7. Mayrovitz, H., & Larsen, P. (1992). Effects of pulsed electromagnetic fields on skin microvascular blood perfusion. Wounds, 4, 197-202.
8. Salzberg, C., Cooper-Vastola, S., Perez, F., et al. (1995). The effect of non-thermal pulsed electromagnetic energy (diapulse) on wound healing of pressure ulcers in spinal cord injured patients: A randomized, double-blind study. Ostomy/Wound Management, 3, 42-51.
9. Sheffet, A., Cytryn, A., et al. (2000). Applying electric and electromagnetic energy as adjuvant treatment for pressure ulcers: A critical review. Ostomy/Wound Management, 46, 28-40.
10. Spielholz, N., Kloth, L., et al. (2000). Electrical stimulation and pulsed electromagnetic energy: Differences in opinion: Applying electric and electromagnetic energy as adjuvant treatment for pressure ulcers: A critical review. Ostomy/Wound Management, 46, 28-44.
11. Brown, M., & Baker, R. (1987). Effect of pulsed short-wave diathermy on skeletal muscle injury in rabbits. Physical Therapy, 67(2), 208-214.
12. Bansal, P., et al. (1990). Histomorphochemical effects of short-wave diathermy on healing of experimental muscular injury in dogs. India Journal of Experiential Biology, 28, 766-770.
13. Itoh, M., Montemayor, J., & Matsumoto, E., et al. (1991). Accelerated wound healing of pressure ulcers by pulsed high-peak power electromagnetic energy (diapulse). Decubitus, 2, 24-28.
Joseph A. Gallo is an associate professor in the Sport and Movement Science Department at Salem State University in Salem, MA. Christopher M. Proulx is an assistant professor in the Movement Science, Sport and Leisure Studies Department at Westfield State University in Westfield, MA.