ESAT 3640 Therapeutic Modalities Ultrasound ESAT 3640 Therapeutic Modalities

Ultrasound in Sports Medicine One of the most widely used therapeutic modalities Overused? Primary use is for stimulating the repair of soft tissue injuries and pain relief

Background Acoustic energy Produces thermal or non-thermal physiological effects Deep heat

Basic Physics of US Ultrasound unit construction Transducer Sound head Piezoelectric crystal Piezoelectric effect

Transmission of Acoustical Energy in Biological Tissue Acoustic energy requires molecular collision for transmission “Stone in a pool of water” US is a mechanical wave in which energy is transmitted by the vibrations of the molecules of the biological medium through which the wave is traveling

Transverse vs. Longitudinal Waves Transverse wave Compressions Rarefactions

Frequency of Wave Transmission US has frequency greater than 20 kHz 0.75 – 3 MHz Audible sound (16 – 20 kHz) The lower the frequency, the greater the depth of penetration

US Wave Attenuation Decrease in energy intensity as the US wave is transmitted through various tissues due to scattering and dispersion US penetrates tissues high in H2O content Absorbed in dense tissues high in protein Penetration and absorption are inversely related

Ultrasound Beam Larger diameter and higher frequency = more focused beam Smaller diameter and lower frequency = more divergent beam

Wave Reflection Some of the wave may be reflected or refracted as it encounters various tissue Acoustic impedance Standing waves Hot spots

Effective Radiating Area Portion of the transducer that actually produces the sound wave Dependant on the surface area of the crystal Transducer is not indicative of the actual radiating surface

Frequency of US 3 MHz = superficial heat 1 MHz = deep heat US and fracture detection?

Amplitude, Power, & Intensity Amplitude – Magnitude of the vibration in a wave Power – Total amount of US energy in the beam (Watts) Intensity – Measure of the rate at which energy is being delivered per unit area (Watts/cm2)

Intensity Spatial average intensity Spatial peak intensity Intensity of beam averaged over area of transducer Spatial peak intensity Highest value occurring w/in beam Temporal peak intensity Max intensity during on period w/ pulsed US

Intensity Continued Temporal averaged intensity Average power during pulsed US during on and off periods Spatial averaged temporal peak intensity Spatial mean during a single pulse

Beam Non-uniformity Ratio BNR % to which intensity of beam varies SPI/SAI

Pulsed vs. Continuous Wave US Continuous wave – sound intensity remains constant Thermal effect Pulsed wave – intensity is periodically interrupted with no US energy being produced during the off period Duty cycle Nonthermal effect

Physiological Effects US may cause clinically significant responses in cells, tissues, and organs through both thermal and nonthermal mechanisms

Thermal Effects Increase in the extensibility of collagen Decrease in joint stiffness Reduction of muscle spasm Modulation of pain Increased blood flow Mild inflammatory response May help in the resolution of chronic inflammation Increased blood flow for healing and pain reduction through heating Chronic inflammation

Thermal Effects Tissue must be raised to a level of 40 to 45° C for 5 minutes. Dyson, M. Physiotherapy, 73(3): 116-120, 1987 Temperature rise above base line is key factor increases of 1° C increases metabolism and healing Increases of 2 - 3° C decreases pain and muscle spasm Increases of 4° C and greater increase extensibility of collagen and decrease joint stiffness Lehmann et al

Nonthermal Effects Cavitation – Formation of gas-filled bubbles that expand and compress due to ultrasonically induced pressure changes in tissue fluids Acoustic streaming – Unidirectional movement of fluids along the boundaries of cell membranes resulting from the mechanical pressure in an ultrasonic field

Cavitation Stable vs. unstable Results in increased flow in the fluid around the vibrating bubbles

Acoustic Streaming Produces high viscous stresses that can alter cell membrane structure and function Changes in cell permeability to sodium and calcium ions

Nonthermal Effects Increased cell membrane permeability Altered rate of diffusion across cell membrane Increased vascular permeability Secretion of cytokines Increased blood flow Increased fibroblastic activity Stimulation of phagocytosis Production of healthy granulation tissue Synthesis of protein Synthesis of collagen Reduction of edema Diffusion of ions Tissue regeneration Formation of stronger, more deformable scar

Techniques of Application Frequency of treatment Acute vs. chronic How many treatments should be given? Duration of treatment Dependent on treatment goal Keep the transducer moving!!!

Coupling Methods Direct contact Immersion Bladder Technique Watch for bubbles Bladder Technique

Clinical Applications of US Soft tissue healing and repair Scar tissue and joint contracture Stretching of connective tissue Chronic inflammation Bone healing Pain reduction Plantar warts Placebo effects

Phonophoresis The use of ultrasound to drive a topical application of a selected medication into the tissues Safer than iontophoresis Potentially deep penetration What is effect on medication when mixed with coupling agent? Not as point specific as iontophoresis Wave attenuation

Contraindications Areas of decreased temperature sensation Areas of decreased circulation Vascular insufficiencies Eyes Reproductive organs Pelvis immediately following menses Pregnancy Pacemaker Epiphyseal areas in developing individuals Total joint replacements Infections Over spinal column