Chapter 3: Therapeutic Heat

INTRODUCTION

The use of therapeutic heat (thermotherapy) in the treatment of various conditions has been around for thousands of years. Understanding the physiological and biomechanical principles of therapeutic heat is one of the elements of successful patient treatment. The clinician must be well versed with the various conditions for which these biophysical agents are used and must be aware of the contraindications to the use of therapeutic heat. This text provides the clinician with the tools necessary to have a safe and effective patient outcome.

Warmth is associated with tranquility and relaxation. Heating of injured tissue has been used for centuries for pain relief and reduction of muscle spasm. In physical therapy, locally applied heating modalities are used to promote relaxation, provide pain relief, increase blood flow, facilitate tissue healing, decrease muscle spasm, decrease tissue tightness and joint stiffness, and prepare stiff joints and tight muscles for exercise.^1-30 Several studies^31-36 have examined the frequency of thermal agent use as an intervention in physical therapy treatments. These studies from Australia,^31,32 Canada,^33,34 England,^35,36 and the United States³⁷ indicated that the percentage of daily use of therapeutic heating agents, such as hot packs and paraffin wax, ranged from 36.5% to 95% in various practice settings.

The physiological effects that occur from tissue temperature elevation are included in the rationale for selecting these modalities as part of a therapy paradigm. Elevation of collagen tissue temperature, for example, can alter viscoelastic properties, thus enhancing the effects of passive stretch for increasing range of motion (ROM).^{9-11,14-16,23,26-28}

Many thermal modalities are available for tissue heating (Box 3-1). Some heating modalities primarily cause an increase in skin and superficial subcutaneous tissue temperature. Thermotherapy modalities, such as moist heat packs, paraffin wax, and fluidized therapy (fluidotherapy), are used to:

1. Heat superficial joints, such as the hand, which has little soft tissue covering

2. Cause a heating effect in deeper structures, such as muscle, through reflex mechanisms

3. Heat soft tissue (muscle, tendon, superficial joint capsule) to increase its extensibility

If the goal of intervention is to increase the temperature of deeper tissues, such as the knee joint capsule or the muscle belly of the quadriceps muscle, then another heating modality is logically selected.

Heating modalities, including continuous shortwave diathermy and continuous-wave ultrasound, can increase tissue temperature at depths ranging from 3 to 5 cm without overheating the skin and subcutaneous tissues. Therapeutic ultrasound is discussed in Chapter 4 and shortwave diathermy is covered in Chapter 6...