Shortwave and microwave diathermy. Physical characteristics, application techniques, dosage, therapeutic effects, indications, contraindications, and safety considerations

At a glance

1. Shortwave diathermy (UHF in the course) uses 27.12 MHz (the course also gives 40.68 MHz) and heats 5 to 6 cm deep. Capacitive plates heat fat and low-water tissue most; inductive coils heat water-rich muscle.
2. Microwave diathermy uses radiated waves: decimetric (433 or 460 MHz) for the deepest, broadest heat, centimetric (2450 MHz) for focused, shallower heat in water-rich tissue.
3. The dose is set by the patient's warmth: athermic, oligothermic, thermic or hyperthermic. Low doses for acute and subacute stages, warmer ones for chronic. Usually 10 to 15 minutes, 10 to 15 sessions, daily or on alternate days.
4. Indications are chronic and subacute musculoskeletal pain, stiffness and inflammation, deep muscle spasm, and, in the course, chronic pelvic, sinus and respiratory inflammation.
5. Ruled out: pacemakers, defibrillators and implanted stimulators, even switched off; metal in the field; pregnancy; tumours; bleeding; acute inflammation; poor circulation; lost sensation.
6. Safety: dry skin, no metal on or under the patient, plates and cables placed correctly, eyes and gonads out of the beam, and the therapist keeps away from the running device (about 2 metres from continuous shortwave).

01Physical characteristics

Diathermy means heating through: the tissue is warmed from inside by a high-frequency field. The physics common to all high-frequency methods (why the skin is no barrier, how fields carry the energy, why fat or muscle heats) is in high-frequency electromagnetic modalities. Here are the two methods used for deep heat.

Shortwave can run continuously or in pulses. Continuous shortwave heats. Pulsed shortwave sends short bursts (often 400 microseconds) a few dozen to several hundred times a second, with long pauses in which the tissue loses its heat. The peak power is high, but the mean power, which decides the warming, can be set from a few watts (no warmth) to tens of watts (clear warmth).

02Application techniques

Shortwave: capacitive plates

The part lies between two plates, rigid (in glass or plastic housings, set at a distance) or soft (rubber, laid on felt spacers). The field always takes the easiest, shortest path, and where it crowds, it burns. Every rule of placement follows from this.

1. 1

   Contraplanar (transverse)

   Plates on opposite sides of the part, such as either side of the knee. The field crosses the whole thickness: the deepest heating.

2. 2

   Coplanar

   Plates side by side on one surface, such as along the back. The field runs between them through the surface layers. The gap between the plates must be at least as wide as one plate, or the field jumps between the near edges and burns there.

3. 3

   Longitudinal

   Plates at two ends of a limb. The field runs along the limb and mostly follows the muscles and vessels.

• Distance from the skin. The course gives a working range of 3 to 10 cm between the plate and the body. A larger gap makes the field more even and relatively deeper, but weaker. A plate too close concentrates the field in the skin and fat.
• Equal gaps. With different gaps on the two sides the near side heats more.
• Plate size. Plates a little larger than the part give even heat; a larger plate acts deeper but less intensely. Devices come with small, medium and large plates.
• Bony points and two segments. The field crowds at bony prominences and between two touching parts. Two knees or two hands treated together are separated by a felt pad or a folded dry towel.

Shortwave: inductive coils

A coil carries the current and its magnetic field induces eddy currents in the tissue, which heat water-rich muscle best and spare fat.

• Cable: wound in loops round a limb (the strongest field is inside the loops) or laid flat as a spiral. Turns are kept apart with spacers, and a towel of 1 to 2 cm lies between cable and skin.
• Drum (monode): a flat coil inside a housing, placed over the back, thigh or shoulder.
• Solenoid: a large coil the limb or trunk goes through.

Microwaves: radiating applicators

The applicator is an aerial that sends a beam, aimed straight at the skin, usually 3 to 10 cm away.

Microwaves reflect from metal and from tissue interfaces and are absorbed strongly by water, so wet skin and metal near the beam are especially dangerous, and the eyes are kept out of it.

Before and during every session

1. 1

   Check

   Ask about implants, pacemakers, stimulators, pregnancy, bleeding and sensation; test hot and cold on the skin of the area.

2. 2

   Prepare

   Bare and dry the area; remove all metal (jewellery, watch, hearing aid, phone, clothes with zips); seat or lay the patient on wood or plastic, never a metal couch.

3. 3

   Place

   Position plates, coil or applicator; keep cables away from the skin, from each other and from metal; tune the patient circuit to the device.

4. 4

   Dose and watch

   Raise the output slowly to the chosen warmth; tell the patient to report any burning or unexpected heat at once and not to move or touch the device; check the skin afterwards.

03Dosage

The patient's sense of warmth is the gauge, on the four-step scale:

per session, the course's usual time

10–15minper session, the course's usual time

daily or on alternate days

10–15sessionsdaily or on alternate days

plate or applicator to skin

3–10cmplate or applicator to skin

Western practice often gives continuous shortwave for up to 20 minutes at a thermal dose. Whatever the scheme, the rule is the same: the felt warmth is a crude gauge, and a patient who cannot feel or report heat is not dosed this way at all.

04Therapeutic effects

The effects are those of deep heat, explained in high-frequency electromagnetic modalities:

• Analgesic: pain eases while the tissue is warm and for a while after.
• Spasmolytic: deep muscle spasm relaxes.
• Vascular: deep vessels open; the course adds a resorptive effect, helping subacute infiltrates and old haematomas to clear.
• Mechanical: warm capsules, ligaments and scars stretch more, so heat before stretching or mobilisation gains range.
• Metabolic: faster tissue metabolism, which the course links to faster repair.

Honest evidence: in knee osteoarthritis, a meta-analysis found small benefits on pain and muscle strength only when the dose was warm enough to be felt, and none on function. Diathermy is an adjunct to exercise, never the treatment itself.

05Indications

Heat suits what is chronic, stiff and cold, and the method suits the depth and tissue.

Microwaves in the course: decimetric waves for broad, deep heat (back, pelvis, large joints); centimetric waves for focused heat in a small area (a tendon, a small joint).

06Contraindications

Each one follows from what deep electromagnetic heat does.

07Safety considerations

For the patient

• Water and metal gather the field. Skin is dried, sweat is soaked by a dry towel checked during the session, wet dressings come off, and nothing metal is on, under or near the patient.
• Cables never touch the skin or each other, and do not cross; where they come near, the field crowds and burns.
• Plates keep equal gaps, coplanar plates are spaced at least a plate's width apart, and two parts treated together are separated by felt.
• The patient stays still, does not touch the cables or the device, and reports any burning at once. A burn from diathermy lies deep and may show only later.
• Microwaves: the beam is never aimed at the eyes or gonads, and protective goggles are worn for treatment near the head.

For the therapist and others

• The therapist sets the device, then keeps away from the plates, cables and beam while it runs: about 2 metres from continuous and at least 1.5 metres from pulsed shortwave. The old rule of 1 metre is not enough: stray fields near the cables can still exceed exposure limits there.
• Pregnant staff do not operate diathermy or stay near it.
• People with pacemakers or stimulators are kept out of the treatment area, and other electrical devices, especially those connected to patients, are kept a few metres away.

For the equipment

Cables are checked for damage, plates and applicators are intact, and the device is serviced. A device that will not tune, or a patient circuit that heats unevenly, is not used.

Check yourselfAnswer, then say how sure you were: a lucky guess still counts as a weak point.

1A woman with chronic low back pain has a spinal cord stimulator that she switched off a year ago. She asks for shortwave diathermy to her back. What do you tell her?

It is fine because the stimulator is switched offIt is fine at an athermic doseIt is ruled out, and so are microwave diathermy and any diathermy anywhere on her bodyIt is fine if the plates are placed away from the stimulator

2A man has a plate and screws in his ankle after a fracture and now has stiffness there. Which treatment is ruled out over the ankle?

Shortwave diathermyActive exerciseIce after exerciseMassage of the calf

3During a thermic shortwave session to the knee, a burn appears under a fold of damp towel. Why?

The towel insulated the skin and trapped heatWater concentrated the field, so the energy built up thereThe dose was too low to be feltThe plates were too far from the skin

4Two capacitive plates are placed side by side on the lower back, 2 cm apart. What happens?

The field runs deep through the spineNothing changes; distance between plates does not matterThe plates short-circuit and the device switches offThe field takes the shortest path between the near edges and heats the skin there

5A patient has a subacute ankle sprain five days ago, with some swelling still present. If the course's shortwave therapy is used, which dose fits?

Hyperthermic, to resolve the swelling fastThermic, 30 minutes dailyAthermic or oligothermic, short sessionsNo dose; shortwave is never used in sprains