Diathermy is a therapeutic modality that generates deep heat within body tissues using high-frequency electromagnetic or sound energy. The word itself, from Greek roots, means "heating through". This controlled, internal heating is used in physical therapy to increase blood flow, relax muscles, improve the extensibility of connective tissues, and accelerate the healing process. The choice of diathermy type depends on the targeted tissue depth and the specific condition being treated. The three main types are shortwave, microwave, and ultrasound diathermy, each with distinct mechanisms and applications.
Shortwave Diathermy (SWD)
Shortwave diathermy uses high-frequency electromagnetic energy, typically around 27.12 MHz, to produce heat within the body. The energy can be applied in either a continuous or pulsed mode, depending on the therapeutic goal. There are two main methods of application:
- Capacitive Field Method: Uses two condenser plates positioned on either side of the body part being treated. A rapidly alternating electric field is created between the plates, causing molecules within the tissue to oscillate and generate frictional heat. This method produces more heat in superficial tissues, such as skin and fat.
- Inductive Field Method: Utilizes a magnetic coil applicator. A rapidly reversing magnetic field is created, which induces circulating electrical currents within the body's tissues. This method is more effective at heating tissues with higher water and electrolyte content, such as muscles.
SWD is commonly used for deep musculoskeletal conditions that cause pain and muscle spasms, including sprains, strains, bursitis, and tenosynovitis.
Microwave Diathermy (MWD)
Microwave diathermy employs microwaves, a form of electromagnetic radiation with very high frequencies (e.g., 2450 MHz), to produce heat. The microwaves are transmitted through a specialized applicator that is positioned near the treatment area.
Key characteristics of MWD include:
- Limited Penetration: Microwaves have a shorter wavelength compared to shortwaves, which results in a smaller depth of penetration. This makes MWD best suited for heating superficial tissues and structures closer to the skin's surface, such as the shoulder joint.
- Effective Heating of Water-Rich Tissues: MWD is particularly effective at heating tissues with high water content, like muscle, by causing the water molecules to vibrate.
- Even Heating: When applied correctly, MWD can provide even heating to the target tissue without significantly heating the skin.
Ultrasound Diathermy (US)
Although technically a form of sonic therapy, ultrasound is often grouped with electromagnetic diathermy as a deep-heating modality. It operates differently from SWD and MWD, using high-frequency sound waves rather than electromagnetic energy. The sound waves are transmitted into the body via a wand, which is moved over the skin with the aid of a coupling gel.
How it works:
- Vibrational Heating: As the sound waves travel through the tissues, they cause the molecules to vibrate and collide, generating localized heat.
- Deep Penetration: The sound waves can effectively penetrate deep tissues, making ultrasound diathermy suitable for conditions affecting deeper muscles and joints.
Common applications of US diathermy include the treatment of:
- Musculoskeletal sprains and strains
- Muscle spasms
- Joint contractures or adhesions
- Neuromas
Comparison of the Three Diathermy Types
| Feature | Shortwave Diathermy (SWD) | Microwave Diathermy (MWD) | Ultrasound Diathermy (US) |
|---|---|---|---|
| Energy Source | High-frequency electromagnetic waves | Microwaves (high-frequency EM waves) | High-frequency sound waves |
| Heating Mechanism | Oscillation of molecules in an electric field (capacitive) or induced currents (inductive) | Vibration of water molecules in tissues | Frictional heat from tissue vibration |
| Penetration Depth | Deep | Superficial to moderate | Deep |
| Target Tissues | Subcutaneous tissues, deep muscles, joints | Superficial muscles and joints (e.g., shoulders) | Deep tissues, muscles, joint capsules |
| Application | Capacitive plates or inductive coil placed near the body, no gel | Radiator/applicator held near the skin, no gel | Wand and coupling gel moved continuously over the skin |
| Common Uses | Sprains, strains, bursitis, tenosynovitis, back pain, fibromyalgia | Shoulder pain, superficial injuries | Muscle spasms, sprains, joint contractures |
Risks and Contraindications
While diathermy is generally safe when performed by a qualified professional, there are important risks and contraindications to be aware of.
Risks include:
- Burns: Excessive heat or improper application can cause burns to the skin and underlying tissues. This is especially a risk with metal implants, which can become extremely hot.
- Electrical Shock: In shortwave and microwave diathermy, the patient is part of an electrical field, and touching bare metal objects can cause a shock or burn.
Contraindications (when to avoid diathermy):
- Implanted Metal Devices: This includes pacemakers, joint prostheses, or metal sutures, which can overheat.
- Pregnancy: Diathermy should be avoided during pregnancy.
- Malignancy: Not used over areas of known or suspected cancer.
- Reduced Sensation or Circulation: Impaired sensation or vascular disease increases the risk of burns and complications.
- Infections and Bleeding Disorders: These conditions can be exacerbated by heat therapy.
- Specific Areas: Treatment should not be applied over the eyes, brain, heart, reproductive organs, or open growth plates in children.
Conclusion
Diathermy represents a powerful set of tools in rehabilitative medicine, providing targeted, deep-heating therapy for a variety of musculoskeletal conditions. The three distinct types of diathermy—shortwave, microwave, and ultrasound—each offer unique advantages in terms of energy source, penetration depth, and application method. The selection of the correct modality is a critical decision made by a physical therapist to ensure maximum therapeutic benefit while minimizing risk. By increasing blood flow and promoting tissue healing, diathermy can help manage pain and improve function for countless individuals. As with any medical procedure, a thorough assessment and consideration of all contraindications are necessary to ensure a safe and effective treatment plan. For more detailed information on specific devices and applications, further research on resources like the FDA's guidance is recommended.
Food and Drug Administration (FDA)
Benefits of Diathermy
- Enhanced Blood Flow: The localized heat increases circulation to the treatment area, delivering more oxygen and nutrients to promote healing.
- Pain Relief: By relaxing muscles and reducing inflammation, diathermy helps alleviate pain associated with various musculoskeletal conditions.
- Reduced Inflammation and Edema: The increase in circulation helps clear inflammatory byproducts, minimizing swelling and fluid retention.
- Improved Tissue Mobility: The deep heat can increase the flexibility and elasticity of connective tissues, leading to a better range of motion.
- Muscle Relaxation: Heating the tissues helps to ease muscle spasms and tension, contributing to reduced pain and discomfort.
