Chapter 76: Modalities

INTRODUCTION

Modalities are physical agents used to produce a therapeutic change in tissue.¹ These agents are typically used in conjunction with a comprehensive treatment plan. Their use starts with a modality prescription (Table 76–1). The prescription is then utilized to follow through with the application of the specific modalities. This chapter will discuss those modalities, physiology, applications, and evidence for their use.

HEAT THERAPY

Heat Transfer and Physiology

There are a number of modes of heat therapy that are currently used in practice. They include types of superficial and deep heating. The superficial types most commonly utilized are heating pads, heating packs, fluidotherapy, and paraffin baths. Deep heating modalities include ultrasound, shortwave diathermy, and microwave diathermy.

Heat transfer occurs through one of the following processes:

• Conduction: Between 2 bodies in contact

• Convection: Through a medium (air, water, blood)

• Evaporation: Transferred from a liquid to a gas

• Radiation: Emitted from a body with a surface temperature above zero

• Conversion: Transformation of electromagnetic or sound energy into thermal energy

Physiologically, heat produces therapeutic benefits on the body through various effects. Heat causes vasodilatation on the arterioles and venous systems allowing increased blood flow to and from an injury site. Nerve conduction velocity is seen to modestly increase, which may aid in proprioception retraining after an injury. Muscle and tendon extensibility has been shown to increase as well as an improvement in joint stiffness. Finally, analgesia is experienced through thermotherapy.¹ General indications are discussed in the text and contraindications are listed in Table 76–2.

Superficial Heat

Superficial heat involves the transfer of thermal energy to the patient from a device or object. Examples include heating pads, hot packs, paraffin baths, and fluidotherapy (whirlpools). Importantly, these mechanisms can heat structures no more than 2 cm deep, therefore, utilization for deeper structures will not be effective. Contraindications to superficial heat include edema and malignancy (see Table 76–3).