Modalities are commonly used to produce a response in tissues and include heat, water, cold, sound, and electricity. These modalities should not be used as the primary mode of treatment but rather used in adjunct with the main intervention such as physical or occupational therapy. This chapter will discuss the more common modalities used as well as briefly discussing electrical stimulation. Box 97-1 describes factors to consider prior to selection of a specific therapeutic modality.

HEAT

Therapeutic uses for heat are based on analgesia, increase in collagen elasticity, and hyperemia to decrease pain, reduce contractures and joint stiffness, and decrease muscle spasms.¹ Therapeutic range for heat is 40° to 45°C and is commonly maintained for about 5 to 30 minutes. It is important to note that the temperature for pain threshold in humans is 45°C.² Heat can be divided by superficial and deep heat and is dependent on depth of heat and form of transfer of heat which include convection, conversion, conduction, and radiation. Convection is the contact between two surfaces at different temperatures with resultant flow through this medium to transport thermal energy. Examples include contrast baths and hydrotherapy. Conduction is the transfer of thermal energy between two bodies by contact at different temperatures with examples such as hot water and hot packs. Conversion is the transformation of energy to heat such as ultrasound and microwave diathermy. Lastly, radiation involves thermal radiation from any surface or body with temperature above absolute zero. General precautions for the use of heat are listed in Box 97-2 but can include acute inflammation, ischemic locations, bleeding disorders, impaired sensation, malignancy, scar tissue, and those with inability to communicate or respond to pain.³

Superficial heat is considered to be 1 to 2 cm and deep heat generally involves increasing tissue temperature to a depth of 3 to 5 cm or more. Examples of superficial heat include heating pads, hydrocollator packs, whirlpool baths, and paraffin baths which achieve maximal tissue temperature in the skin and subcutaneous fat. Hot packs such as hydrocollator packs are commonly stored in heated water tanks and need to be wrapped in layers of insulation prior to being applied to the skin. Caution should be used as this type of modality is one of the most common reasons for burns in therapy sessions. Radiant heat in the form of heat lamps can also be used therapeutically and is usually placed 30- to 60 cm from the patient’s body and is useful when the patient cannot tolerate the weight of the heating pads. Paraffin baths is another type of modality that is used with wax and mineral oil. Immersion technique has been shown to provide the greatest duration of temperature increase and is commonly applied in scleroderma patients.⁴ Superficial heat is commonly used to treat low back pain, arthritic conditions, neck pain, and various chronic musculoskeletal injuries.⁵ Examples of deep heat include ultrasound, shortwave, and microwave diathermy. These modalities transfer heat through conversion and the differences are outlined in Table 97-1. Ultrasound diathermy should not be confused with diagnostic ultrasound. Ultrasound heats the greatest at the bone-tissue interface while short wave diathermy heats fat more so than muscle. Ultrasound that is therapeutic in nature uses high frequency energy to produce a deeper tissue response and the most commonly used frequency is a range from 0.8 to 1.1 MHz. Thermal response in tissues involves energy absorption causing heat production in tissues whereas nonthermal responses cause distortion and movement of tissues.⁶ Techniques for ultrasound application can vary with the most common technique involving stroking the probe over the affected site as opposed to static application. Contraindications for therapeutic ultrasound include areas over fluid-filled cavities, laminectomy sites due to concern for heating the spinal cord, open epiphysis in the growing adolescent, pacemakers, and prosthetic cements.⁷

Shortwave diathermy is used to treat deep muscles and joints and commonly uses a frequency of 27.12 MHz. This type of modality can involve two condenser plates placed on either side of the body part or induction coils that can be molded to the body part. Through conversion, electromagnetic energy converted to thermal energy travels between the coils or condensers to cause deeper heating of tissues. Contraindications for this type of treatment include pacemakers, metal objects, and heating over the eyes. General contraindications for the three modalities for deep heat are listed in Table 97-2

CRYOTHERAPY

Therapeutic uses for cold are based on immediate local vasoconstriction to reduce swelling and acute inflammatory response, decreased pain and muscle spasm, decreased spasticity, slowing of the nerve conduction velocity, and decrease in local metabolism. Cryotherapy is often used in acute musculoskeletal conditions as well as for spasticity management.⁸ Mechanisms for cold transfer include conduction, convection, and evaporation. Examples of conduction include cold packs and ice massage; convection includes cold baths; and evaporation includes vapocoolant sprays. Cold packs can generally be applied for 20 to 30 minutes with external compression providing increased effectiveness of cooling.⁹ Vapocoolant sprays are commonly combined with stretching of a contracted muscle to treat various musculoskeletal related conditions.¹⁰

General precautions and contraindications for cryotherapy are listed in Box 97-3 and include cold intolerance or hypersensitivity, impaired sensation, communication or cognitive deficits, arterial insufficiency, and cryopathies such as paroxysmal cold hemoglobinuria or cryoglobulinemia. In general, cold application should be avoided over superficial nerves due to increased risk of affecting nerve conduction.