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Years ago I worked as a physical therapy aid in a hospital where they gave treatments for knee arthritis using diathermy. Now I'm a patient with knee osteoarthritis and I don't see anyone using this modality. Why not? We always got good results with it way back when.

Diathermy was indeed a very popular modality used by physical therapists 30 years ago. But with the invention of new technology and new techniques, it eventually fell out of favor. But there has been renewed interest in this form of deep heat just in the last five years or so. Diathermy uses high-frequency energy to move ions, distort molecules, and create eddy currents. The result is heat that reaches deep into the soft tissues and connective tissue. The patient experiences pain relief, decreased joint stiffness, and decreased muscle spasm. Diathermy can also reduce swelling and promote healing in the joint. Studies show that short-wave diathermy (preferred over microwave diathermy) heats tissue up to five centimeters below the skin surface. This compares to one centimeter depth for heat packs placed on the skin. The diathermy heating elements can be placed directly over clothes so there is easy application without undressing or the use of messy gels as with ultrasound., A recent study comparing different modalities in the treatment of chronic pain from knee osteoarthritis showed that all forms of heat or electrical treatments gave the same benefit. Diathermy equipment is expensive so therapists may opt for a less expensive but equally effective approach. It is a useful treatment tool when large areas of muscle need treatment. It should not be used over a metal implant such as a knee replacement.

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