Therapeutic Modalities
Comparison of Shortwave Diathermy
and Microwave Diathermy
David O. Draper, EdD, ATC, FNATA • Brigham Young University
A
ny therapeutic modalities textbook includes
information about a myriad of therapeutic
modalities used for the treatment and
rehabilitation of injuries. Two frequently
used modalities are ice and ultrasound; probably the
modality used least often is diathermy. The purpose of
this report is to contrast shortwave diathermy (SWD)
and microwave diathermy (MWD), and to present two
cases that involved administration of pulsed shortwave
diathermy (PSWD) over surgically implanted metal.
The word diathermy means “through heat” (dia
and therm). Therapeutic diathermy is defined as highfrequency electromagnetic waves that heat tissues up
to 5 cm deep.1 Heat is produced by the resistance of
tissue to the passage of energy.1,2
There are two classifications of diathermy: medical
and surgical. Medical diathermy is used for a therapeutic purpose, such as heating of deep tissues. Surgical
diathermy is used for cauterizing or burning tissue.
Two main types of medical or therapeutic diathermy
are microwave and shortwave.
Microwave diathermy, seldom used in the United
States, uses high-frequency electromagnetic waves
(2450 MHz; wavelength of 11 m) to heat tissues. Shortwave diathermy uses high-frequency electromagnetic
waves that are similar to radio waves (10–100 MHz) to
heat deep tissues. Table 1 presents key characteristics
that differentiate microwave diathermy and shortwave
diathermy.
Physiological Effects
Both thermal and nonthermal physiological effects are
created by SWD, which are similar to those of ultrasound. Nonthermal effects include acceleration of cell
growth,3 repolarization of damaged cells (enabling them
to perform normal functions),4,5 and wound healing.6
The main reason diathermy is used relates to its
thermal effects. Thermal SWD has been shown to
increase tissue temperature, 7-11 increase blood flow,10
decrease joint stiffness,11,12 increase metabolism,5
relax muscles,11,13 relieve pain,5,14 facilitates resolution
Table 1. Microwave Diathermy Versus Shortwave Diathermy
Microwave
Shortwave
2456 and 915 MHz frequency
Heating mainly due to electrical fields
Penetration of fat is only one third of SWD
Can create hot spots
Spacing required between skin and applicator
No metal can be within 4 ft of applicator
Becoming obsolete
10–100 MHz frequency
Heating mainly due to magnetic fields
Penetrates fat layer easily
Unlikely to create hot spots
Can apply directly to skin
Does not heat metal as much as MWD
Most commonly used in orthopedics
© 2013 Human Kinetics - IJATT 18(6), pp. 13-17
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of hematomas,5 and increase extensibility of collagen
fibers. 11,13 Table 2 presents recommended PSWD
parameters for attainment of specific treatment goals.
Many athletic trainers and therapists believe that
ultrasound can heat deep tissues as well as diathermy.
Although the magnitudes of tissue temperature elevation are similar, diathermy heats a much larger area
than ultrasound.20 Ultrasound will heat up an area
about as large as a catsup packet, whereas diathermy
can heat up an area as large as a salad plate.
Much of the widely-accepted misinformation
about diathermy has failed to differentiate SWD from
MWD. The contraindications of MWD have often been
attributed to both types of treatment. This misinformation led to the widespread beliefs that no type of
diathermy should be administered in the same room
with a pregnant therapist,26 and that it should not be
used over surgically implanted metal.2 These are both
contraindications for MWD, but they are only precautions for SWD.5 In the text Therapeutic Modalities: The
Art and Science,5 the Megapulse II PSWD device is
described as safe for use over metal implants, based
on years of using this device on patients with surgically
implanted metal rods, plates, and screws.5 However, no
form of diathermy treatment should be administered
over looped wires, which can act as an antenna and
overheat surrounding tissues. Also, SWD should be
pulsed (PSWD), not continuous.5
Why Diathermy Is Seldom Used
Diathermy has fallen out of favor among athletic trainers and therapists in many parts of the world, with the
exceptions of the United Kingdom and Japan. Surveys
of physical therapists in Canada15 and Australia16 have
documented that diathermy was used on a daily basis
by 0.6% and 8% respectively, whereas ultrasound was
used daily by 93.5%.15,16 Diathermy is seldom used in
the United States, which is probably due to its expense,
outdated research, and misinformation.
The price of a diathermy device can range from
USD $6,000 to $25,000. Because many insurance companies do not provide reimbursement for diathermy
treatments, insufficient revenue is likely to be generated to cover the cost of acquiring the equipment.
Prior to the last 15 years,7-11,17-25 little research evidence of therapeutic benefit from diathermy existed.
Many improvements in the function of the devices
started taking place in the 1990s. One improvement
was proper shielding from electromagnetic waves,
which improved safety for both the patient and the
clinician.
There also can be a significant difference in heating
effect between various SWD devices. A recent study24
compared the heating effect of the ReBound SWD
device (ReGear Life Sciences, Inc., Pittsburg, PA) and
the Megapulse II SWD device (Accelerated Care Plus,
Reno, NV). Temperature probes were inserted 3 cm
into the triceps surae of 12 human subjects. Treatments
were administered for 30 minutes. The Megapulse II
SWD device increased the muscle temperature 4.32°C,
whereas the ReBound SWD device increased the temperature only 2.3°C.24
Case Report 1
A 38-year-old construction worker fell two stories
onto a concrete floor. The impact collapsed a lung and
caused a humerus fracture. The fractured humerus was
surgically repaired with a metal rod. At approximately
6 months postinjury, two thermocouples were inserted
into his upper arm to measure the tissue heating effect
of PSWD. One thermocouple was inserted until it came
into contact with the metal at a depth of 2.6 cm. The
other thermocouple was inserted into muscle tissue
at the same depth (Figure 1). The Megapulse II drum
Table 2. Shortwave Diathermy Parameters
for Specific Treatment Goals
Dose
Indications
Pulse width
Pulse rate
Average watts
n/a
Acute trauma, edema reduction,
cell repolarization, and repair
Subacute inflammation
Pain reduction, muscle spasm,
chronic inflammation
Stretch collagen-rich tissues
65 μs
100–200 pps
n/a
100–200 μs
200–400 μs
400–800 pps
400–800 pps
12
24
400 μs
800 pps
48
1°C
2°C
4°C
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international journal of Athletic Therapy & training
(Accelerated Care Plus, Reno, NV) was applied to the
skin over the thermocouples. A 20-minute diathermy
treatment was administered at 27.12 MHz, 800 μsec,
400 Hz, and 100 Watts average power (Figure 2). Previous research has documented that this technique will
raise the temperature in the deep tissues over 4°C.1
The temperature was recorded every 10 minutes. At
the end of the 20-minute treatment, the temperature
had increased 4.5°C on the metal rod and the surrounding muscle.
Case Report 2
pronation and supination. Four months earlier, she had
dislocated the elbow and fractured her distal humerus
when she fell during a gymnastics event (Figure 3). The
humerus fracture was surgically repaired with titanium
pins and screws. After several weeks of immobilization,
she received extensive physical therapy treatments
(ultrasound and passive stretching). Her full range of
elbow flexion was restored, but elbow extension, forearm pronation, and forearm supination were restricted.
The treatment regimen consisted of 20 minutes
of PSWD at an average of 48 Watts (Figure 4), which
was followed by 8–10 minutes of joint mobilization
A female collegiate gymnast presented an elbow that
she could not extend beyond the last 30° of the normal
arc of motion. She also lacked full range of motion in
Figure 1 Patient 1 with a metal rod in his humerus. Note the two
temperature probes in his tissue.
Figure 3 Radiograph of patient 2.
Figure 2 Patient 1 receiving PSWD treatment.
Figure 4 Beginning ROM for patient 2.
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november 2013  15
(traction, anterior glides of the distal humerus on the
ulna, and radial head glides). After seven treatments,
she had attained full range of motion in extension,
pronation, and supination (Figure 5).
implant should be viewed as a treatment precaution.
However, any type of diathermy treatment is always
contraindicated over metal implants that have circular
wire components or elements that form loops, which
may result in excessive heating of the metal.2,5,26 
References
Figure 5 Full ROM was reached with a regimen of PSWD and joint
mobilizations.
Discussion
One of the most promising applications of PWSD is
facilitation of stretching and joint mobilization for restoration of joint range of motion.11,13,17-19,21,23 A heat and
stretch regimen using PSWD can increase the flexibility
of subjects with tight muscles,17 and improve the joint
mobility of patients with limited ankle dorsiflexion.22
These effects likely result from reduction of muscle
guarding and pain, decreased tissue stiffness,22 and
increased extensibility of collagen fibers.5-7,11-13
Many clinicians believe that the administration of
PSWD over surgically implanted metal screws, rods,
or pins is contraindicated.2,5,18,19,22 The close proximity
of a radio frequency field to a metal implant is widely
believed to cause a greater temperature increase in
the adjacent tissue than in tissue that does not contain a metal implant.2,5,18,19,22 This concern should be
viewed as more of a precaution than a contraindication,
because therapeutic benefits have been documented
when the power level was 100 Watts or less.5
Conclusion
Pulsed shortwave diathermy (< 100 Watts) is a safe
therapeutic procedure, and the presence of a metal
16  november 2013
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international journal of Athletic Therapy & training
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international journal of Athletic Therapy & training
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David O. Draper is a professor in the Exercise Sciences division at
Brigham Young University in Provo, UT.
Lindsey Eberman, PhD, ATC, LAT, Indiana State University, is the
report editor for this article.
november 2013  17