Diathermy is a therapeutic technique that uses high-frequency electromagnetic energy to generate heat deep within the body’s tissues. Derived from the Greek words dia and therme, the term means “heating through.” This modality is primarily employed in physical therapy and rehabilitation settings to address a variety of musculoskeletal and soft tissue conditions. Unlike a heating pad that warms the skin’s surface, diathermy provides a controlled method of delivering therapeutic warmth to deeper structures like muscles, tendons, and joint capsules. The goal of this process is to stimulate natural physiological responses that promote healing and reduce discomfort.
How Deep Tissue Heat is Generated
Diathermy machines do not directly apply heat; instead, they generate electromagnetic fields that penetrate the tissue, causing the body itself to produce therapeutic warmth. This process converts electromagnetic energy into thermal energy through tissue resistance or molecular movement. When high-frequency waves (such as radio waves or microwaves) pass through the body, they cause polar molecules within the cells to rapidly vibrate and oscillate.
This molecular friction generates heat deep beneath the skin, potentially reaching tissues up to two inches deep. In some applications, the electromagnetic field induces tiny electrical currents, known as eddy currents, within the tissue. The resistance these currents encounter creates frictional heat, delivering a deep thermal effect that differentiates diathermy from traditional surface heat treatments.
The Three Main Delivery Methods
The deep heating effect of diathermy is delivered using specific types of equipment, primarily categorized into shortwave diathermy (SWD) and microwave diathermy (MWD). SWD operates in the radiofrequency range and utilizes two distinct methods for application: capacitive and inductive.
Capacitive Method
In the capacitive method, the body part is placed between two condenser plates or electrodes, acting as a dielectric in a capacitor circuit. The rapidly alternating electric field between these plates causes the charged particles in the tissue to oscillate, generating heat through dielectric losses.
Inductive Method
The inductive method uses a coil applicator, typically wrapped around the treatment area. The current flowing through this coil produces a magnetic field that induces eddy currents inside the underlying tissues. This technique preferentially heats tissues with high electrical conductivity, such as muscle and synovial fluid. SWD is often administered at a frequency of 27.12 MHz, allowing it to treat both superficial and deeper tissues.
Microwave Diathermy (MWD)
MWD utilizes higher frequencies (typically 915 MHz or 2450 MHz) and is applied using a directional applicator. These applicators transmit the electromagnetic waves directly toward the treatment area, similar to a focused beam. MWD is best suited for heating tissues closer to the skin, such as the shoulder or knee, because it is less effective at penetrating deep muscles. MWD can more selectively target a specific area compared to the broader field of SWD.
Conditions Treated with Diathermy
The deep heating generated by diathermy produces beneficial physiological changes within the targeted tissues. A significant effect is the increase in localized blood flow, known as vasodilation. This improved circulation delivers more oxygen and nutrients to the area, promoting tissue repair and accelerating the healing process. Diathermy is commonly used to manage chronic inflammation in conditions like arthritis and bursitis.
The thermal energy also helps relax muscles that are in spasm, providing relief from tension and pain. By warming the collagen fibers in connective tissues, the treatment temporarily increases the extensibility of structures like joint capsules and tendons. This effect is useful when applied immediately before therapeutic exercise or stretching to improve a patient’s range of motion. Diathermy is indicated for a range of musculoskeletal issues, including chronic back pain, fibromyalgia, sprains, strains, and tendonitis.
Essential Patient Safety Guidelines
Patient safety is a serious consideration when administering diathermy treatment due to the intense electromagnetic energy involved. The most important contraindication involves the presence of any metal within or near the treatment field. Metal implants, such as pacemakers, joint replacements, dental fillings, or surgical clips, can absorb the electromagnetic energy and heat up rapidly. This excessive heating can lead to severe burns in the adjacent tissues or cause a malfunction of electronic implanted devices.
Diathermy is also contraindicated over areas of malignancy, where increasing circulation and temperature could affect tumor growth. Treatment should be avoided during pregnancy, over open growth plates in children, and in regions with reduced sensation, as the patient may not be able to accurately report excessive heat. Patients must remove all metal jewelry and accessories before the procedure to prevent burns. Careful patient screening and adherence to established protocols are necessary to mitigate the risks associated with this powerful therapy.