MICROWAVE DIATHERMY
Microwave diathermy, which employs a form of electromagnetic radiation, is another deep heat modality that selectively heats tissues with high water concentration.
Hyperemia, sedation, and analgesia are the physiologic effects, similar to the results of shortwave diathermy. Secondary, local vascular dilatation results in increased local metabolism.
The 2 frequencies designated for microwave diathermy are 915 MHz and 2456 MHz, with the former being the most commonly used. Because the frequencies are higher than those used in shortwave diathermy and the wavelengths are the same size as the applicator, microwave diathermy can be focused more easily than can shortwave diathermy.
The lower frequency is preferred because it provides selective heat deep into muscle, and less energy is converted to heat in the subcutaneous fat. Direct contact applicators with full aperture skin contact are optimal for improved coupling and for reducing stray radiation.
Because microwave diathermy selectively heats muscles and deep heat improves the flexibility of collagen tissues, muscle contractures can be treated with this modality (in combination with a physical therapy stretching program).
Microwave diathermy can also be used to reduce secondary muscle spasm under a trigger point. In addition, this modality can effectively treat the superficial joints of the hands, feet, and wrist because of the thin soft-tissue layer overlying these joints.
A microwave director is used to aim the microwaves at the area of treatment, allowing observation of the treatment site. Heat can be reduced by increasing the distance of the microwave director from the treatment site.
As with shortwave diathermy, microwave diathermy can result in hot spots and burns; these can occur secondary to localized perspiration associated with selective heating of the treatment zone.
The microwave diathermy equipment should be adjusted to provide comfortable heating, with treatment time ranging from 20-30 minutes.
The previously mentioned contraindications to shortwave diathermy also apply to microwave diathermy. Additional precautions include synovitis with joint effusion, systemic/local infection, and use over bony prominences. The aforementioned therapeutic indications for shortwave diathermy are similar to those for microwave diathermy.