Chapter 10: Therapeutic Ultrasound

OBJECTIVES

Following completion of this chapter, the student will be able to:

• Analyze the transmission of acoustic energy in biologic tissues relative to waveforms, frequency, velocity, and attenuation.

• Break down the basic physics involved in the production of a beam of therapeutic ultrasound.

• Compare both the thermal and nonthermal physiologic effects of therapeutic ultrasound.

• Evaluate specific techniques of application of therapeutic ultrasound and how they may be modified to achieve treatment goals.

• Choose the most appropriate and clinically effective uses for therapeutic ultrasound. Explain the technique and clinical application of phonophoresis.

• Identify the contraindications and precautions that should be observed with therapeutic ultrasound.

• Discuss the advantages of sustained acoustic medicine (SAM).

In the medical community, ultrasound is a modality that is used for a number of different purposes including diagnosis, destruction of tissue, and as a therapeutic agent. Diagnostic ultrasound has been used for more than 50 years for the purpose of imaging internal structures. Historically, diagnostic ultrasound has been used to image the fetus during pregnancy. More recently, with a reduction of equipment costs, significant improvements in image resolution, real-time ultrasonographic imaging and detailed anatomic imaging, diagnostic ultrasound has expanded to various clinical practices that evaluate, diagnose, and treat musculoskeletal disorders. Diagnostic musculoskeletal ultrasound (MSK) can identify pathology in muscle, tendons, ligaments, bones, and joints.¹ Ultrasound has also been used to produce extreme tissue hyperthermia that has been demonstrated to have tumoricidal effects in cancer patients.

In clinical practice, ultrasound is one of the most widely used therapeutic modalities in addition to superficial heat and cold and electrical stimulating currents.² Ulrasound requires the biologic medium so the vibrations created by the mechanical energy wave travels into soft-tissue. It has been used for therapeutic purposes as a valuable tool in the rehabilitation of many different injuries primarily for the purpose of stimulating the repair of soft-tissue injuries and for pain relief³, and as a heating modality,¹⁸⁸ although some studies have questioned its efficiency as a treatment modality.^{4,177,178,179,197}

As discussed in Chapter 1, ultrasound is a form of acoustic rather than electromagnetic energy. Ultrasound is defined as inaudible acoustic vibrations of high frequency that may produce either thermal or nonthermal physiologic effects.⁵ Ultrasound requires a biologic medium through which vibrations created by a mechanical energy wave travels into soft-tissue. The use of ultrasound as a therapeutic agent may be extremely effective if the clinician has an adequate understanding of its effects on biologic tissues and of the physical mechanisms by which these effects are produced.³

ULTRASOUND AS A HEATING MODALITY

Chapter 9 discusses heat as a treatment modality. Warm whirlpools, paraffin baths, and hot packs, to name a few, all produce therapeutic heat. However, the depth of penetration of these modalities is superficial and at best ...