Deep Heat

[Peter Kevin]

What is deep heat and its use in orthopedics?

[Samira]

@peter-kevin Deep heat is produced when energy is converted into heat as it passes through body tissues. Energy sources include the following:

High-frequency currents (shortwave diathermy)
Very-high-frequency electromagnetic radiation (microwave diathermy)
High-frequency sound (ultrasound diathermy)
The temperature distribution in the tissues heated by any of these modalities results from the pattern of relative heating, which is the amount of energy converted to heat at any given location. The practitioner should choose a heating modality that produces the highest temperature at the site of concern without exceeding the temperature tolerance at the affected site or in tissues above or below that site. The temperature rise depends on the properties of the tissue, including the specific heat, thermal conductivity, and the length of time for which the heating modality is applied.

The temperature rise and distribution of heat that are associated with these modalities are superimposed on the physiologic temperature distribution in the tissues prior to diathermy application. Usually, the superficial temperature is low at the skin surface and higher at the core.

The physiologic effects of temperature occur at the site of the application and in distant tissue. The local effects are caused by the elevated temperature response of cellular function by direct and reflex action. Locally, there is a rise in blood flow with associated capillary dilatation and increased capillary permeability. Initial tissue metabolism increases, and there may be changes in the pain threshold. Distant changes from the heated target location include reflex vasodilatation and a reduction in muscle spasm (as a result of skeletal muscle relaxation).

Vigorous heating produces the highest temperature at the site where the therapeutic result is desired. The tissue undergoes a rapid temperature rise, with the temperature coming close to the tolerance level. Vigorous heating is used for chronic conditions that require deep structures, such as large joints, to be heated. When acute inflammatory processes are occurring, deep heating requires extreme care, because it can obscure inflammation.

Local tissue temperature is maintained during mild heating, the primary effect being the production of a higher temperature at a site distant from the heating modality's application. Reflex vasodilatation occurs when the rise in temperature is slow for short periods, such as during a subacute process. With the proper application, superficial and deep heating methods can accomplish mild heating.

Shortwave diathermy
The best method for large-area deep heating is shortwave diathermy. This modality is useful for various indications.

The following problems can be treated with shortwave diathermy, depending on the individual condition of each patient and the desired treatment goals :

Localized musculoskeletal pain
Inflammation (joint or tissue)
Pain/spasm
Sprains/strains
Tendonitis
Tenosynovitis
Bursitis
Rheumatoid arthritis
Periostitis
Capsulitis
Microwave diathermy
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.

Ultrasound diathermy
Therapeutic use of ultrasound is ideal for providing deep heat to large joints. For example, it is effective in treating the shoulder or hip, because a standing wave is produced as a result of the curved reflection of the glenoid or the acetabulum; this effect concentrates heat energy at the articular surfaces of the joint.

In combination with a physical therapy program utilizing range of motion (ROM) and stretching activities, the localized, intra-articular heating produced by ultrasound diathermy greatly facilitates the mobilization of joint adhesions or capsular restrictions caused by tightness or scarring. This modality is also used to treat osteoarthritis, tendinitis, and bursitis. Ultrasound-based deep heating has not been found to be effective for the preventive management of posteccentric exercise, delayed-onset muscle soreness.

Most of the indications for ultrasound diathermy are similar to those for other deep heating modalities. Additional indications include the following:

Joint contracture
Joint adhesions
Calcific bursitis
Hematoma resolution
Neuromas
Other conditions that may be treated with ultrasound, though with limited therapeutic benefit, include the following:

Fibrosis
Phantom limb pain
Myofascial pain
Reflex vasodilatation
Ulcer debridement