Therapeutic Ultrasound Chapter 8

Description Acoustical energy (sound waves) above the range of human hearing Therapeutic range: 0.75 to 3.3 MHz Effects: Thermal Nonthermal (mechanical)

Uses Calcific bursitis Inflammatory conditions Joint contractures Pain Muscle spasm Acute orthopedic injuries (low pulses, low intensity)

Production of Ultrasound An alternating current is passed through a crystal The current causes the crystal to vibrate Electropiezo effect Vibrating crystal produce high-frequency sound waves

Effective Radiating Area (ERA) Area of the crystal that actually produces sound waves Produces more than 5% of the energy at 5 mm from the transducer face ERA is always smaller than the transducer face Energy is concentrated near the center ERA

Beam Profile Multiple waves emerge from the head Energy diverges as it moves away from the source Energy is uniform close to the head Near zone (Fresnel zone) Becomes less consistent farther away from the head Spatial peak intensity Spatial Peak Intensity

Beam Nonuniformity Ratio (BNR) Spatial Peak Intensity Describes the amount of variation in the beam Ratio between: Spatial peak intensity (SPI) Average intensity (SAI - metered output) BNR = SPI/SAI Perfect beam would have a BNR of 1:1 Minimally acceptable BNR is 8:1 The actual peak output is equal to the SAI * the BNR 10 W total output * 6:1 BNR 60 watt SPI Spatial Average Intensity (Displayed on the unit)

Modes of Application Continuous Ultrasonic energy is constantly produced Can produce thermal effects based on: Output intensity Treatment duration Pulsed Ultrasonic output is regularly interrupted Produces nonthermal effects

Continuous Output (100% Duty Cycle) Pulsed Output (67% Duty Cycle) Ultrasonic output is cycled “On” and “Off” On = Pulse length Off = Pulse interval Expressed as a Duty Cycle ON/(ON+OFF) * 100 20mSec/(20mSec+10mSec) * 100 20/30 * 100 67% Continuous Output (100% Duty Cycle) Pulsed Output (67% Duty Cycle)

Output Frequency Measured in megahertz (MHz) 1 MHz = 1,000,000 waves per second Determines the depth of effects 1 MHz Output Penetrates 5 to 7 cm Thermal effects last longer More divergent beam 3 MHz Output Penetrates 2 to 3 cm Heats 3 times faster than 1 MHz output More collimated beam

Power and Intensity Spatial Average Intensity Spatial Average Temporal Peak Intensity Spatial Average Temporal Average Intensity

Spatial Average Intensity (SAI) Describes the energy per unit of area Total output (watts)/area Watts/effective radiating area (cm2) W/cm2 15 watts being applied with a 10 cm2 ERA 15 Watts / 10 cm2 1.5 W/cm2

Power Measures – Pulsed Output Spatial Average Temporal Peak Intensity (SATP) The average energy delivered during the “On” time of the duty cycle. Spatial Average Temporal Average Intensity (SATA) Energy delivered over time Spatial Average Intensity * Duty Cycle Meaningful only during pulsed output

Biophysical Effects Thermal

Thermal Effects Increased sensory nerve conduction velocity Increased motor nerve conduction velocity Increased extensibility of collagen-rich Increased vascular permeability structures Increased collagen deposition Increased blood flow Reduction of muscle spasm Increased macrophage activity Enhanced adhesion of leukocytes to damaged endothelial cells

Heating Classifications Increase Used For Mild 1°C Mild inflammation Accelerate metabolism Moderate 2° – 3°C Decreasing muscle spasm Decreasing pain Increasing blood flow Chronic inflammation Vigorous 3° – 4°C Tissue elongation Scar tissue reduction

Heating Rate Heating rate and magnitude is based on: Duty cycle Output frequency Intensity Target tissues Size of the treatment area

Thermal Effects Same as other heat modalities Smaller volume of tissue Shorter duration of effects Preheat the skin with a moist heat pack Decreases the time to reach vigorous heating Poorly vascularized, collagen-rich tissues are preferentially heated Fascia, tendon, scar tissue Tissues containing an increased proportion of fluid do not heat as well Adipose tissue, articular fluid

Biophysical Effects Nonthermal

Nonthermal Effects Granulation tissue production Synthesis of protein Increased cell membrane permeability Altered rates of diffusion across the cell membrane Increased vascular permeability Secretion of cytokines Increased blood flow Increased fibroblastic activity Stimulation of phagocytosis Granulation tissue production Synthesis of protein Synthesis of collagen Reduction of edema Diffusion of ions Tissue regeneration Formation of stronger deformable connective tissue

Nonthermal Application Pulsed output 20 to 25% duty cycle Nonthermal output intensity Continuous output 100% duty cycle Output intensity of less than 0.3 W/cm2

Acoustical Streaming Ultrasound causes interstitial fluids to flow Fluids strike cell membranes Produce eddy currents Eddy currents displace ions and molecules Alter: Cell membrane permeability Cellular function

Effect on Injury Response

Cellular Response Acoustical streaming: Thermal effects: Increases cell membrane permeability Alters cell membrane diffusion rate Increased histamine release Mast cell degranulation Increased rate of protein synthesis Thermal effects: Increased cell metabolism Increased rate of inflammation

Inflammation May lead to an earlier onset of proliferation Increased fibroblast proliferation Release of growth factors and platelets Increased macrophage activity Leukocytes bind to damaged endothelial cells Cell division is increased

Inflammation Frequency Specificity 1 MHz Output 3 MHz Output Release of preformed fibroblasts 3 MHz Output Increased synthesis and secretion of fibroblast precursors Increased in areas of high collagen concentration

Blood and Fluid Dynamics May increase blood flow for 45 minutes Thermal effects Decreased vascular tone Histamine release Causes vasodilation Moist heat application prior to treatment decreases net increase in blood flow

Pain Control Direct Pain Reduction Increased nerve cell sodium permeability Alters nerve function Increases pain threshold Indirect Pain Reduction Increased blood flow Increased capillary permeability Increased oxygen delivery Decreased muscle spasm

Muscle Spasm Reduced secondary to: Decreased pain Altered nerve conduction velocity Increased temperature (counterirritant effect) Muscle relaxation

Tissue Elasticity Ultrasound preferentially heats collagen-rich tissues (tendon, fascia, scar tissue) Temperature must be increased 7.2°F Stretching window lasts approximately 3 minutes following the treatment Place tissues on stretch during application Perform stretching/mobilization immediately following the treatment Multiple treatments are required to gain length

Wound Healing Tendon Healing Continuous US application may: Increase tensile strength Increase collagen deposition Skin Ulcers 3 MHz, low-intensity pulsed output may assist the healing process Cover the wound with an occlusive dressing

Electromagnetic Field In vitro bone deformation produces piezoelectric currents and streaming potentials Electromagnetic (EM) devices are based on Wolff’s Law that bone responds to mechanical stress: Exogenous EM fields may simulate mechanical loading and stimulate bone growth and repair Clinical efficacy very controversial Buckwalter, Einhorn, Simon (ed.) Orthopaedic Basic Science 2nd ed. AAOS, 1999.

Types of EM Devices Microamperes Direct electrical current Capacitively coupled electric fields Pulsed electromagnetic fields (PEMF) Buckwalter, Einhorn, Simon (ed.) Orthopaedic Basic Science 2nd ed. AAOS, 1999.

PEMF Approved by the FDA for the treatment of non-unions Efficacy of bone stimulation appears to be frequency dependent Extremely low frequency (ELF) sinusoidal electric fields in the physiologic range are most effective (15 to 30 Hz range) Specifically, PEMF signals in the 20 to 30 Hz range appear more effective than those below 10 Hz Buckwalter, Einhorn, Simon (ed.) Orthopaedic Basic Science 2nd ed. AAOS, 1999.

Ultrasound Low-intensity ultrasound is approved by the FDA for stimulating healing of fresh fractures Modulates signal transduction, increases gene expression, increases blood flow, enhances bone remodeling and increases callus torsional strength in animal models

Ultrasound Human clinical trials show a decreased time of healing in fresh fractures Has also been shown to decrease the healing time in smokers potentially reversing the ill effects of smoking

Fracture Healing Low-intensity pulsed output Accelerates rate of fracture healing for: Acute fractures Nonunion fractures Stress fractures Requires specialized unit Biophysical Effects: Mechanical (sound) energy strikes bone Microvibration of bone triggers growth (osteogenesis) PARAMETERS Frequency 1.5 MHz ERA 3.88 cm2 Intensity 30 mW/cm2 Treatment Duration 20 minutes Daily

Contraindications Acute conditions (thermal mode) Ischemic areas Areas of impaired circulation Over areas of deep vein thrombosis Anesthetic areas Over cancerous tumors Sites of active infection or sepsis Over the spinal cord or large nerve plexus in high doses Exposed penetrating metal (eg, external fixation devices) Around the eyes, heart, skull, or genitals Over the thorax in the presence of an implanted pacemaker Pregnancy when used over the pelvic or lumbar areas Over a fracture site before healing is complete Stress fracture sites or sites of osteoporosis Over the pelvic or lumbar area in menstruating female patients

Where are we going?

Ultrsound Ultrasound uses: Therapeutic US widely used for deep heat Diagnostic (low intensity) Fracture Surgical (high intensity) Therapeutic Therapeutic US widely used for deep heat

Ultrasound Primary clinical use: Soft tissue repair Pain relief (analgesia)

Effective Radiating Area (ERA) Total area on surface of transducer producing soundwave Ideally ERA should match size of transducer Treatment area should not exceed 2-3 times ERA

Frequency of Ultrasound Determined by number of times crystal deformed/sec. 2 most common utilized in U.S. 1.0 MHz 3.0 MHz Determines depth of penetration, unlike ES

Frequency of Ultrasound Inverse relationship between frequency and depth of penetration Penetrating depths: 1.0 MHz: 2-5 cm 3.0 MHz: 1-2 cm Absorption rate increases with higher frequency

Pulsed vs Continuous Most new generators produce both Both produce thermal & nonthermal effects

Pulsed vs Continuous Continuous: Sound intensity remains the same Commonly used for thermal effects

Pulsed vs Continuous Pulsed: Intensity periodically interrupted Average intensity reduced over time

Physiological Effects of Ultrasound Thermal effects Non-thermal effects Cavitation Acoustic microstreaming

Thermal Effects Clinical effects: Increased extensibility of collagen fibers tendons joint capsule Decreased joint stiffness

Thermal Effects Clinical effects: Reduction in muscle spasm Pain modulation Increased blood flow Increased nerve conduction

Thermal Effects Primary advantage of US Selective heating of tissues high in collagen Non-thermal effects are occurring

Non-thermal (Mechanical) Effects Primary physiological effects are cavitation and acoustic microstreaming Cavitation: Formation of gas-filled bubbles in tissue fluids Expansion/compression of bubbles either stable or unstable

Non-thermal (Mechanical) Effects Acoustic microstreaming: Unidirectional movement of fluids along cell membrane boundaries Produces high viscous stresses Alters membrane structure & function Increased permeability to ionic influx

Non-thermal (Mechanical) Effects Potential therapeutic effects from cavitation & microstreaming Stim. of fibroblast activity increases protein synthesis & tissue repair Increased blood flow bone healing & repair of non-union fractures

Ultrasound Indications Contraindications Increase deep tissue heat Decrease inflammation Decrease muscle spasms Decrease pain Increase extensibility of collagen tissue Decrease pain of neuromas Decrease joint adhesions Treat myositis ossificans Contraindications Hemorrhage Infection Thrombophlebitis Suspected malignancy Impaired circulation or sensation Stress fracture sites Epiphyseal growth plates Over the Eyes, Heart, Spine, or genitals

Treatment Frequency Ultrasound has cumulative effects · Daily for 10 days – low irritability and scar · 3-4 times/week – moderate irritability for 3- 4 weeks · 2 times /week – high irritability 4-5 weeks · If no change after 3-4 sessions, change settings or discontinue. · Stop after 10-15 treatments

Sound Head Movement Never stay stationary Keep it moving, slow and gentle with constant pressure. This will minimize the risk of creating unstable cavitation and Standing waves that is detrimental damaging to soft tissue 1 inch = 1 second

Movement of the Transducer 4 cm2/sec Remaining stationary can cause problems Moving too rapidly decreases the total amount of energy absorbed per unit area May cause clinician to treat larger area and the desired temps. May not be attained Slower strokes can be easier maintained If patient complains of pain or excessive heat, then decrease intensity but increase time Apply constant pressure – not too much & not too little

Coupling Agents Optimal agent – distilled H20 (.2% reflection) Modern units have a shut down mechanism if sound head becomes too hot (Dynatron beeps; red lights on Chattanoogas) Improperly coupled head causes  temp. Types of agents: Direct H20 immersion Bladder Reduce amount of air bubbles

Direct Coupling Effectiveness is  if body part is hair, irregular shaped, or unclean Must maintain firm, constant pressure Various gels utilized

Water Immersion Used for odd shaped parts Place head approx. 1” away from part Operator’s hand should not be immersed No metal on part or operator’s hand Ceramic tub is recommended If nondistilled H20 is used, intensity can be  .5 w/cm2 because of air & minerals Don’t touch skin except to briefly sweep skin when bubbles form

Bladder H20 filled balloon or plastic bag coated with coupling gel Use on irregular shape part Place gel on skin, then place the bladder on the part, and then place gel on bladder Make sure all air pockets are removed from bladder

US Specifics Burning Tissue Density Gel application Burning the US head with no tissue contact

Phonophoresis

Description Use of therapeutic ultrasound to assist in diffusion of medication through the skin Increases the diameter of skin portals to allow the medication to pass Pores Hair follicles

Biophysical Effects Medication is introduced over a large area Relative to an injection Noninvasive Medication may not be filtered by the liver Reducing metabolic elimination of the medicine

Transdermal Application Medication must diffuse through: Enzymatic barrier of the epidermis Stratum corneum Rate-limiting barrier to absorption Medications must be able to diffuse across this barrier Medication is stored in subcutaneous tissues for some time before being diffused deeper

Skin Influences Medication uptake is improved when the skin is: Well hydrated Has a high density of skin portals Highly vascularized Relatively thin “Younger” skin tends to have better diffusion characteristics than “older” skin.

Ultrasound Influences on Diffusion Thermal Effects Increase kinetic energy Increase portal cross-section Increase circulation Increase capillary permeability Nonthermal Effects Altered cell resting potential Increased cell membrane permeability Increased molecular permeability

Phonophoresis Medications Either prescription or nonprescription Low molecular size and weight Most medications used can be applied transdermally without ultrasound Controlled medications require a prescription for the patient being treated Medication is often mixed in an inert base Base must be able to transmit ultrasonic energy

Common Medications Type Indications Example Corticosteroid Inflammation Hydrocortisone Dexamethasone Salicylates Inflammation Pain Anesthetic Pain Lidocaine Trigger points

Application Tips Moist heat pack prior to application: Increase blood flow Increase kinetic energy Increase skin portals Following treatment Leave medication on skin Cover with an occlusive dressing Moist heat pack re-application may assist in further absorption

Low-frequency US Phonophoresis Parameters: 20 kHz output frequency 125 mW/cm2 Pulsed output Benefits: Allows medications with a larger size and weight to diffuse More efficient medication delivery