DIATHERMY
Comprehensive Study Notes — Physiotherapy
Deep Heating Modality in Electrophysical Therapy
1. Introduction
Diathermy is a therapeutic procedure that uses high-frequency electrical energy to produce deep
heating within body tissues. It is one of the most widely used physical modalities in physiotherapy
practice, valued for its ability to deliver therapeutic heat deep beneath the skin surface without
causing surface burns.
The term diathermy is derived from Greek roots:
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Dia = through
Therme = heat
Combined meaning: "Heating through (the body tissues)"
Unlike superficial heating agents (e.g., hot packs, infrared lamps), diathermy produces heat deep
inside muscles, joints, and connective tissues. This deep heating capability makes it especially
effective for treating conditions located far below the skin surface.
Key Concept
Diathermy converts electromagnetic or sound energy into thermal energy within the tissues
themselves, making it distinctly different from conductive or radiant heat modalities.
2. Types of Diathermy
There are three main types of diathermy used in clinical practice, each differing in the energy
source and depth of tissue penetration.
2.1 Short Wave Diathermy (SWD)
Short Wave Diathermy is the most commonly used form of diathermy. It employs high-frequency
electromagnetic waves, typically operating at a frequency of 27.12 MHz with a wavelength of
approximately 11 meters.
Modes of Application
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Continuous Mode
◦ Produces sustained thermal (heating) effects in tissues
◦ Used when the goal is pain relief and increased tissue extensibility
◦ Contraindicated in acute conditions
Pulsed Mode (PSWD)
◦ Delivers energy in intermittent pulses, allowing tissues to dissipate heat between pulses
◦ Primarily non-thermal or sub-thermal effects
◦ Promotes cellular healing and reduces oedema without significant heating
◦ Safer to use in acute inflammatory conditions
Methods of Application
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Capacitive Method (Condenser Field Method)
◦ The body part is placed between two electrodes (condenser plates)
◦ High-frequency electric field passes through the tissues
◦ Best for tissues with high water content (muscles)
◦ Superficial fat layer may overheat — use with caution
Inductive Method (Cable/Drum Electrode Method)
◦ Uses a coil or drum electrode to create an electromagnetic (magnetic) field
◦ Eddy currents are induced in tissues with good electrical conductivity
◦ More selective heating of deeper tissues
◦ Less risk of overheating superficial fat
Clinical Uses of SWD
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Osteoarthritis and Rheumatoid Arthritis
Chronic muscle spasm
Chronic inflammatory conditions
Low back pain and pelvic pain
Post-fracture rehabilitation
Soft tissue injuries in the subacute/chronic stage
2.2 Microwave Diathermy (MWD)
Microwave Diathermy uses microwave radiation, typically at a frequency of 2450 MHz (wavelength
~12.25 cm). Microwaves are part of the electromagnetic spectrum between infrared and radio
waves.
Characteristics
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More superficial penetration than SWD — heats tissues 3–5 cm deep
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Better suited for localized, well-defined treatment areas
Simple to apply — uses a single director (applicator) aimed at the body part
Selective absorption in tissues with high water content
Not suitable for areas with bone close to the surface due to uneven absorption
Clinical Uses of MWD
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Shoulder periarthritis and supraspinatus tendinitis
Knee joint conditions (gonarthrosis, bursitis)
Muscle belly injuries and strains
Sinusitis (using special facial directors)
2.3 Ultrasound Diathermy (Therapeutic Ultrasound)
Ultrasound Diathermy — also called therapeutic ultrasound — uses high-frequency sound waves
(mechanical vibrations) in the range of 1–3 MHz to produce both thermal and non-thermal effects in
tissues.
Unique Features
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Not electromagnetic — uses mechanical (acoustic) energy
1 MHz frequency: deeper penetration (~5 cm), used for larger muscle groups
3 MHz frequency: more superficial (~2 cm), used for smaller, superficial structures
Can be applied in continuous mode (thermal) or pulsed mode (non-thermal)
Specific Effects
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Micromassage Effect: Cyclic pressure changes produce a micro-mechanical massage at the
cellular level, promoting fluid exchange and reducing oedema
Increases Tissue Extensibility: Thermal effect loosens collagen fibres in scar tissue and
tendons
Promotes Tissue Healing: Non-thermal effects stimulate protein synthesis and cell
membrane activity
Clinical Uses of Therapeutic Ultrasound
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Tendinitis (e.g., Achilles tendinitis, patellar tendinitis)
Bursitis
Ligament sprains (subacute/chronic stage)
Scar tissue and adhesion management
Plantar fasciitis
Muscle tears in the subacute phase
Summary Comparison of Diathermy Types
Feature
SWD
MWD
Ultrasound
Energy Type
Electromagnetic
Electromagnetic
Mechanical (Sound)
Frequency
27.12 MHz
2450 MHz
1–3 MHz
Penetration Depth
Deep (5–7 cm)
Moderate (3–5 cm)
1–5 cm
Best For
Large joints, muscles
Localised areas
Tendons, scars
Application
Electrodes/coil
Director/applicator
Transducer + gel
Modes
Continuous / Pulsed
Continuous
Continuous / Pulsed
3. Principles of Diathermy
Diathermy works by converting electrical or sound energy into heat energy within the body tissues.
This conversion occurs through different mechanisms depending on the type of diathermy used.
3.1 Tissue Heating Mechanisms
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Ionic Oscillation (Capacitive): High-frequency electric fields cause charged ions in tissue
fluids to oscillate rapidly, producing frictional heat
Eddy Currents (Inductive): Alternating magnetic fields induce circular electric currents in
conducting tissues, which dissipate as heat
Dielectric Heating: Non-conducting tissues (e.g., fat) experience dipole rotation in an electric
field, generating heat
Acoustic Absorption (Ultrasound): Sound waves are absorbed by tissue proteins and
converted to heat
3.2 Factors Affecting Heat Production
Factor
Clinical Significance
Tissue Resistance
High-resistance tissues (fat) may overheat;
low resistance (muscle) heats efficiently
Frequency Used
Higher frequency = shallower penetration;
lower = deeper penetration
Intensity (Power)
Higher intensity = greater heat production;
must stay within patient tolerance
Factor
Clinical Significance
Duration of Treatment
Longer treatment = cumulative heating effect;
typically 15–30 minutes
Water Content of Tissue
Muscle (high water) heats faster than bone or
fat (low water)
Electrode Spacing
In SWD, incorrect spacing leads to uneven or
superficial heating
4. Physiological Effects of Diathermy
The therapeutic effects of diathermy are primarily a result of elevated tissue temperature, which
triggers a cascade of physiological responses. These effects are well-documented across multiple
organ systems.
4.1 Effects on the Circulatory System
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Vasodilation of local blood vessels (arterioles and capillaries)
Significant increase in local blood flow (up to 3–5x baseline)
Enhanced oxygen and nutrient delivery to healing tissues
Increased removal of metabolic waste products (lactic acid, histamine)
Accelerates resolution of chronic oedema in subacute conditions
Note: In acute inflammation, increased blood flow can worsen swelling — hence diathermy is
generally contraindicated in acute stages.
4.2 Effects on the Musculoskeletal System
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Decreased viscosity of muscle tissue — increases muscle elasticity
Relieves muscle spasm by reducing pain and increasing tissue compliance
Increases extensibility of collagen fibres in tendons, ligaments, and joint capsules
Reduces joint stiffness — particularly effective for chronic arthritic joints
Increases range of motion when combined with exercise or stretching
4.3 Effects on the Nervous System
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Reduces pain via gate control mechanism and direct effect on pain nerve fibres
Sedative effect on sensory nerve endings — reduces nerve irritability
Decreases nerve conduction velocity at high temperatures
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Reduces muscle guarding secondary to pain relief
4.4 Metabolic Effects
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Increases local metabolic rate (for every 1°C rise in temperature, metabolic rate increases
~13%)
Accelerates enzymatic activity involved in tissue repair
Promotes phagocytosis — faster removal of cellular debris
Facilitates collagen synthesis and fibroblast activity
5. Indications (When to Use Diathermy)
Diathermy is indicated for a wide range of musculoskeletal and neuromuscular conditions,
particularly those with a chronic or subacute presentation.
System / Category
Specific Conditions
Joint Conditions
Osteoarthritis, Rheumatoid arthritis (chronic),
Ankylosing spondylitis
Muscle Conditions
Chronic muscle spasm, Fibromyalgia,
Myofascial pain syndrome
Soft Tissue Injuries
Tendinitis, Bursitis, Ligament sprains
(subacute/chronic)
Spinal Conditions
Chronic low back pain, Cervical spondylosis,
Disc degeneration
Neurological
Neuralgia, Peripheral nerve injuries
(subacute)
Sports Injuries
Subacute muscle tears, Chronic overuse
injuries
Post-Surgical
Scar tissue management, Post-fracture
rehabilitation
6. Contraindications (When NOT to Use Diathermy)
Important Safety Warning
Contraindications must be assessed before every treatment session. Failure to do so can
result in serious patient harm, including burns, electrical interference with implants, or
acceleration of malignant processes.
6.1 Absolute Contraindications
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Cardiac Pacemaker: Electromagnetic fields interfere with pacemaker function — can be fatal
Metal Implants in Treatment Area: Screws, plates, prostheses concentrate heat and cause
deep burns
Pregnancy (abdomen and pelvis): Possible teratogenic effects on developing fetus
Active Malignancy: Heat can stimulate tumour growth and metastasis
Haemorrhage / Bleeding Disorders: Vasodilation worsens bleeding
Active Tuberculosis: Heat may spread the infection
Over the Eyes: Risk of cataract formation from heat
Over the Testes: Sperm are heat-sensitive; risk of infertility
Loss of Skin Sensation: Patient cannot report overheating, risk of burns
6.2 Relative Contraindications (Use with Caution)
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Acute inflammation or oedema
Ischaemic areas (poor blood supply cannot dissipate heat)
Children (over growth plates)
Elderly patients with thin skin
Wet dressings or clothing on treatment area
Areas near surgical metallic clips or sutures
7. Dosage and Treatment Parameters
7.1 Treatment Duration
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Standard treatment time: 15–30 minutes per session
For pulsed SWD: may extend up to 30–45 minutes as thermal effects are minimal
Ultrasound: 5–10 minutes over a localised area (3 cm² per minute guideline)
7.2 Intensity Levels
Intensity Level
Description
Clinical Use
Sub-thermal (Mild)
Patient feels no warmth
Acute or sensitive conditions,
pulsed mode
Thermal (Mild Warmth)
Gentle, comfortable warmth
Subacute conditions, elderly
patients
Thermal (Moderate Warmth)
Definite, comfortable warmth
Chronic conditions, muscle
spasm
Thermal (Strong Warmth)
Intense but tolerable warmth
Chronic deep conditions in
robust patients
8. Safety Precautions
Diathermy is generally safe when applied correctly, but strict precautions must be followed at every
treatment session.
8.1 Pre-Treatment Precautions
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Screen patient thoroughly for all contraindications
Remove all metal objects (jewellery, clips, hearing aids, watches, coins)
Assess skin sensation in the treatment area — patient must be able to feel heat
Inspect skin for open wounds, rashes, or recent scars
Ensure no wet clothing or moisture on the skin
8.2 During Treatment
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Maintain correct and consistent electrode spacing throughout treatment
Monitor patient continuously — check for complaints of excessive heat or discomfort
Keep patient still to avoid uneven heating
Never leave patient unattended during treatment
Instruct patient to call out immediately if they feel burning or pain
8.3 Post-Treatment
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Inspect treated area for signs of erythema, burns, or unusual redness
Record treatment parameters (intensity, duration, mode) and patient response
Document any adverse reactions
Ensure proper machine calibration and maintenance
9. Advantages and Disadvantages
Advantages
Disadvantages
Deep tissue penetration (5–7 cm with SWD)
Risk of burns if not applied carefully
Can treat large surface areas simultaneously
Expensive equipment with high maintenance
costs
Non-invasive and comfortable for patient
Requires trained and skilled operator
Accelerates natural healing processes
Not suitable for all patients (many
contraindications)
Reduces pain and muscle spasm effectively
Cannot be used over metal implants
Available in pulsed mode for acute cases
Machine malfunction risk if not regularly
serviced
Improves joint mobility and flexibility
May have limited effect if applied incorrectly
10. Summary and Key Clinical Points
Core Definition
Diathermy is a deep-heating physiotherapy modality that uses high-frequency electrical or
acoustic energy to convert into therapeutic heat deep within body tissues, improving
circulation, reducing muscle spasm, and promoting healing.
Key Clinical Points to Remember:
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Always assess for contraindications before every session — especially pacemakers and
metal implants
Diathermy is most effective for chronic and subacute conditions, not acute inflammation
Pulsed SWD can be used in acute stages for its non-thermal, cellular healing effects
Ultrasound is particularly powerful for tendon, ligament, and scar tissue management
Patient must have intact skin sensation for safe treatment
Standard treatment: 15–30 minutes at comfortable warmth intensity
Combine diathermy with therapeutic exercise for maximum outcomes
End of Diathermy Notes
Prepared for Physiotherapy Academic Study