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The use of physical agents and devices to reduce pain and improve function has a long history in the practice in medicine. In recent decades, technology has increased the variety of modalities available to the practitioner. This chapter surveys the most commonly used options, with the goal of aiding the practitioner in choosing among alternatives. Despite widespread use and decades of experience, however, consensus is lacking regarding indications, implementation, and efficacy for many of these approaches.


Heat may be transferred to a patient from an object, a device, or water using hot packs, heat lamps, paraffin baths, and whirlpools. All of these options are considered superficial heating modalities because they are unable to produce temperature changes of more than a few degrees at depths of 1–2 cm. It is generally accepted that heat increases the extensibility of collagen tissue, decreases joint stiffness, relieves muscle spasms, provides pain relief, and increases both blood flow and metabolism. Superficial heat is an adjunctive treatment and generally not the primary curative intervention. Table 8–1 lists general precautions and contraindications for its use. Permanent brown skin discoloration (erythema ab igne) can result from repeated chronic overuse of superficial heat.

Table 8–1Precautions and contraindications for use of superficial heat.
Basford  JR, Baxter  DG: Therapeutic agents. In: Delisa’s Physical Medicine and Rehabilitation: Principles and Practice, 5th ed. Lippincott Williams & Wilkins, 2010:1691–1712.

Hot Packs

Many different varieties of hot packs are available. Outer layers may be made of rubber, cloth, or soft plastic; the interior may be filled with a gel, water, or another substance with a high heat capacity. A common type used in clinics is a hydro-collator pack, which contains a silicate gel that absorbs water and creates a high heat content. This pack is usually submerged in a self-contained heated water solution. It is removed and wrapped in towels to protect the patient from the pack temperature of 70–80° C. Some hot packs can be heated in a microwave. Other heating devices circulate a fluid through tubes to a pad or cuff. Electrical current can also be used to produce heat in a pad.

A. Physiologic Mechanism

Hot packs warm tissue by conduction. Heat conduction, also called diffusion, is the direct microscopic exchange of the kinetic energy of particles through the boundary between two systems. Skin tolerance, tissue thermal conductivity, and the body’s ...

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