Therapeutic Interventions Week 10 - Ultrasound (mixed)

Physical Principles of Ultrasound

• Ultrasound is a high-frequency mechanical wave that uses acoustic/sound energy.
• Sound waves use mechanical action by pressing vibrating molecules into adjacent molecules, which then vibrate and transmit energy to their neighbors.
• Ultrasound transmits more efficiently in denser tissues due to a higher concentration of molecules.
• Aqueous gels serve as coupling agents to enhance transmission of wave energy.
• Sound waves are transmitted through alternating compressions and rarefactions of molecules.
• Compressions have increased molecular density, while rarefactions have decreased density.
• The degree of compression/rarefaction depends on the energy wave's magnitude.
• The duration depends on the wave's generated frequency.
• Longitudinal waves disperse in all directions, but collimation can focus the beam.
• Waves can be reflected, refracted, or absorbed when encountering changes in tissue density.
• Absorption turns kinetic energy into thermal energy.
• Waves passing through denser tissue refract or bend, altering their path.
• Reflected waves can interact with incident waves, either enhancing intensity (standing wave) or diminishing intensity.
• Body tissues behave like liquids of varying densities, except bone, which acts as a solid.
• Bone transmits both longitudinal and transverse waves.
• Dense tissues like ligaments and tendons attenuate ultrasound waves faster than muscle or adipose tissue.
• Connective tissues experience higher temperatures than less dense tissues during ultrasound.
• Reflection of sound waves in high-density tissues can create standing waves, increasing intensity at junctions.
• Applying ultrasound over bone can significantly raise the temperature of the periosteum, causing discomfort and a burning sensation.

Production of Ultrasound Waves

• Ultrasound devices contain an applicator and generator.
• The applicator has a piezoelectric crystal and a sound head.
• A thin sheet of lead zirconate or titanic ceramic makes up the piezoelectric crystal.
• The piezoelectric crystal expands/compresses when alternating current passes through it, which is called the reverse piezoelectric effect.
• Polarity changes cause compression or expansion of the crystal which produces an acoustic wave.
• The crystal's compression and expansion occur between 1 and 3 million times/second.
• The effective radiating area (ERA) is the area of the crystal that moves.
• Due to the crystal's non-uniformity, acoustic energy varies across the beam.
• The sound head (aluminum, stainless steel, or ceramic) covers the radiating surface and connects to the crystal.
• Acoustic energy transfers from the crystal to the sound head, then to the gel and skin.
• The ERA is smaller than the sound head itself.
• The generator produces a high-frequency alternating current matching the intensity and frequency parameters of the crystal.

Phonophoresis

• Ultrasound enhances the absorption of topical agents through the skin.
• Applying ultrasound directly to the agent or adding it to the gel helps absorption.
• The agent is pushed through the skin and permeability of the dermal layer is increased.
• Phonophoresis can be done with pulsed or continuous ultrasound.
• Current evidence does not fully support phonophoresis.

Treatment Parameters – Frequency

• Frequency is the number of waves/second delivered to the patient.
• Ultrasound units typically range from 0.75 to 3.3 MHz.
• Most units deliver frequencies of 1 MHz and 3 or 3.3 MHz.
• Lower frequencies penetrate deeper.
• 1 MHz can penetrate up to 6 cm, and 3 MHz up to 2.5 cm.
• Increasing intensity does not increase penetration depth.
• Instead, increasing power increases energy at the penetration depths produced by the frequency.
• Tissue absorbs 3 MHz ultrasound three times faster than 1 MHz.
• 3 MHz ultrasound heats tissues three times faster than 1 MHz.
• 3 MHz is used for superficial structures like tendons and ligaments, while 1 MHz is used for deeper structures like muscles and fascia.
• Penetration depth depends on frequency, not intensity, and is inversely proportional to the ultrasound frequency.

Treatment Parameters; Intensity and Dosage

• Ultrasound energy is the product of wave phase duration and amplitude/intensity.
• Amplitude/intensity is adjusted to change power because wave duration is fixed.
• Power is measured in watts, but is commonly expressed as spatial average intensity (SAI) in watts/cm².
• SAI is calculated by dividing power (watts) by the ERA.
• SAI is often incorrectly described as power divided by the sound head area.
• The ERA is determined by the crystal size and mobility and it varies among units and manufacturers.
• There are no definitive guidelines for optimal intensity.
• Practitioners should use the lowest intensity possible to achieve the desired effect.
• Variance in ERA can affect treatment, so dosage should be considered.
• Dosage is affected by the sound head area or ERA.

Treatment Parameters – Mode

• Most machines deliver continuous and pulsed ultrasound.
• Continuous ultrasound delivers constant energy throughout the treatment.
• Pulsed ultrasound has periods with no energy delivery.
• Total energy is reduced, and temporal average intensity describes this lesser energy level.
• Continuous ultrasound used for heating, and pulsed ultrasound is used to reduce energy level for non-thermal effects.

Other Principles of Therapeutic US

• BNR (Beam Non-uniformity Ratio) is the ratio of spatial peak intensity within the radiating area.
• Peak intensity areas can form hot spots.
• Hot spots are distributed by continuously moving the ultrasound head.
• Higher BNR units are more likely to cause discomfort due to hot spots.
• The treatment area should be two to four times the ERA when using 1 MHz, heating less intensively.
• Treating an area larger than four times the ERA lessens the treatment dose.
• Ultrasound is used to heat exposed tendons, ligaments, and small muscles.

Variation in Treatments and Ultrasound Units

• Treatment duration, number and frequency of treatments, and ultrasound units vary.
• Vigorous heating increases the distensibility of connective tissues (increase of about 7 degrees Fahrenheit).
• At 1 MHz US at 1.5 watts/cm² over an area two times the ERA, it takes 11 minutes to heat skeletal muscle to 6 degrees Fahrenheit.
• At 3 MHz with 1 watt/cm² and two times the ERA, superficial muscles can be heated to about 9.5 degrees Fahrenheit in 8 minutes.
• Treatment duration depends on the size of the area, ultrasound settings, intensity, frequency, mode, and specific condition.
• Treatments are often administered two to three times a week for 10-15 treatments.
• Units differ in ERA and efficiency.
• Clinicians must adjust treatment protocols by considering unit, applicator, patient, and the condition.

Variability in Application Medium

• Radiating waves should be perpendicular to the skin.
• The applicator should remain in contact with the skin.
• Use a coupling medium between the applicator and the skin.
• The applicator face plate must be continuously moved.
• Waves should enter the skin at a 90-degree angle to avoid reflection.
• Reflection happens when transitioning between mediums; if the incident angle is greater than 15 degrees off perpendicular, complete reflection occurs.
• Ultrasound waves are not transmitted through air, so a coupling medium is required.
• Aqueous gel, water immersion, and gel pads can be used.
• Ultrasound gel lubricates for easy movement and has 100% wave transmission.
• Creams and ointments have low transmission alone or when mixed with gel.
• Water immersion is used when there is irregular surface.

Moving the Sound Head

• Move slowly over the skin at about 3 to 4 cm/second.
• There are no significant differences in tissue heating between varying speeds.
• Problems with heat can occur when too large of an area is being treated.
• Apply ultrasound using slow stroking pattern in overlapping circles.

Proper Application of US

• Treat the correct size area.
• Select the appropriate duration.
• Adjust intensity for desired effect.
• Use the correct frequency.
• Do not treat all tissues with same parameters.
• Denser tissues absorb and move heat differently than less dense tissues.
• Move the sound head at appropriate speed.
• Stretch during the last few minutes of the treatment or immediately after heating.

Documentation Tips for US

• Document ultrasound parameters: intensity, frequency, duty cycle.
• Document the treatment duration and sound head size.
• Note the treatment area, coupling agent, and patient position.
• Document the patient response.

Tissue Response

• Ultrasound applied to tendons produces greater temperature rises than in muscle.
• Tendons heat two and a half to three times faster than skeletal muscles under similar conditions.
• There is a rapid cooling phase immediately following ultrasound, lasting about 5 minutes.
• This is followed by a slower cooling rate until the tissue temperature returns to normal.
• There are only about four to five minutes to give co-treatments while the tissue is heated before temperatures start to drop.
• Cooling depends on how warm tissues are, but does not differ between tissue types.

Variability in Responders

• There is a wide variability of heating, even when identical treatments are given to different patients.
• Variability arises from percentage of body fat, tissue hydration, blood flow to the tissues, variable change in tissue metabolism, and protein content of the tissues.

Thermal Effects

• Increase extensibility of collagen fibers.
• Decrease joint stiffness.
• Reduce muscle spasm.
• Modulate pain.
• Increase blood flow.
• Mild inflammatory response.
• Tissues must be raised to 40-45 degrees Celsius for a minimum of five minutes to receive the majority of these effects.
• Tissue temperature increase of 1-degree Celsius increases metabolism and healing.
• Tissue temperature increase of 2-3 degrees Celsius decreases pain and muscle spasm.
• Tissue temperature increase of 4 degrees Celsius or greater increases collagen extensibility and decrease joint stiffness.
• Temperatures above 45 degrees Celsius may damage tissues, but patients usually experience pain prior to these extreme temperatures.
• Tissues high in collagen (tendons, muscles, ligaments, capsules, and meniscus) can be selectively heated to the therapeutic range.
• There is little temperature increase in skin or fat.
• Ultrasound penetrates skin and fat with little attenuation.
• There is an inverse relationship between depth of penetration and frequency.
• Most of the energy at 3 MHz is absorbed into superficial tissues up to 3 cm depth.
• Less attenuation at 1 MHz allows energy to penetrate to deeper tissues.
• 3 MHz ultrasound should be used in the heating of tissues up to a depth of 3 cm.
• Heating occurs with both continuous and pulsed ultrasound depending on the intensity.
• Using spatial average temporal average intensity is in the 0.1-0.2 watts per centimeter squared range, the intensity is too low to produce a tissue temperature increase and only non-thermal effects will occur.
• Non-thermal changes occur simultaneously when using ultrasound.
• Body area and tissue type affect heating and non-thermal effects.
• If the patient does not feel warmth, the dose is inadequate.
• This can be caused by covering too large of an area or moving the sound head too fast.

Non-Thermal Effects

• Cavitation is when gas-filled bubbles expand and compress due to pressure changes in tissue fluids.
• It can be stable or unstable.
• Therapeutic benefits derive from stable cavitation, where bubbles expand and contract.
• The collapse of bubbles in unstable cavitation can cause increased pressure and high temperature, which can cause local tissue damage.
• Unstable cavitation should be avoided.
• High-intensity, low-frequency ultrasound can produce unstable cavitation, especially if standing waves develop at tissue interfaces.
• However, research has not proven this to occur in human tissue.
• Acoustic streaming (microstreaming) involves unidirectional movement of fluids along cell membranes due to mechanical pressure waves.
• It produces high viscous stresses that alter cell membrane structure and function through changes in permeability to sodium and calcium ions, which are important in healing.
• Microstreaming can accelerate healing.
• Non-thermal effects of therapeutic ultrasound can be as important as thermal effects in treating injured tissues.
• Non-thermal effects include stimulation of fibroblast activity, increased protein synthesis, tissue regulation, blood flow in ischemic tissues, bone healing, and repair of non-union fractures.
• Treatment with therapeutic levels may alter the course of immune response.

Evidence for Treatment of Pain

• Myofascial pain, trigger points: strong evidence; substantiated therapeutic effectiveness.
• Myofascial pain, trigger points – pressure-pain threshold: strong evidence; conflicting therapeutic effectiveness.
• Myofascial pain, trigger points – cervical ROM: strong evidence; unsubstantiated therapeutic effectiveness.
• Back pain: strong evidence; substantiated therapeutic effectiveness.
• Back dysfunction: strong evidence; substantiated therapeutic effectiveness.
• Nonspecific shoulder conditions – pain: lacking evidence; lacking therapeutic effectiveness.
• Nonspecific shoulder conditions – dysfunction: moderate evidence; substantiated therapeutic effectiveness.
• Myofascial pain: 10 min treatments, 4-5 times/week, 1-2 MHz applied continuously, 1-1.5 watts/cm² for two to three weeks.
• Back pain: Continuous US, 3 times/week for 10 min, 1 MHz at 2 watts/cm² for 4 weeks.
• Hip pain: Not enough evidence to guide clinical use for hip pain.
• Shoulder pain: Continuous US, 3-5 times/week, 1 MHz applied continuously for 3-4 weeks; could be beneficial when accompanied by stretching and other exercise.

Evidence for Treatment of Inflammation

• Lateral epicondylitis: lacking evidence; lacking therapeutic effectiveness.
• Carpal tunnel syndrome – pain: strong evidence; substantiated therapeutic effectiveness.
• Carpal tunnel syndrome – dysfunction: strong evidence; substantiated therapeutic effectiveness.
• Carpal tunnel syndrome – electrophysiological results: lacking evidence; lacking therapeutic effectiveness.
• Calcific tendinitis – pain or function: moderate evidence; substantiated therapeutic effectiveness.
• Bursitis – pain or function: moderate evidence; substantiated therapeutic effectiveness.
• Arthritis – pain: strong evidence; substantiated therapeutic effectiveness.
• Arthritis – function: moderate evidence; conflicting therapeutic effectiveness.
• Arthritis – range of motion (ROM): strong evidence; conflicting therapeutic effectiveness.
• Carpal tunnel syndrome: At least 5 times/week for 5-10 min, 1-3 MHz from 0.5-1.5 watts/cm², continued for 4 weeks.

Evidence for Treatment of Soft Tissue and Scars

• Soft tissue healing, dermal wounds: strong evidence; conflicting therapeutic effectiveness.
• Tissue extensibility: combined adhesive capsulitis, knee extensibility, limited ankle dorsiflexion, hip contracture and Dupuytren’s contracture – ROM: strong evidence; conflicting therapeutic effectiveness.
• Scar tissue remodeling: combined burn scars, keloid scars, lacerations, Dupuytren’s contracture – ROM: lacking evidence; lacking therapeutic effectiveness.
• Tissue swelling: Ankle edema following acute sprain: lacking evidence; lacking therapeutic effectiveness.

Recommended Protocols for Conditions with Substantiated Effect

• Myofascial pain, MTrPs: 3x per week, 10 min each treatment, using 1 MHz at 1-2 watts per cm^2.
• Back pain: 3x per week, 10 min each treatment, using 1 MHz at 1-2 watts per cm^2.
• Back dysfunction: 3x per week, 10 min each treatment, using 1 MHz at 1-2 watts per cm^2.
• Nonspecific shoulder conditions – dysfunction: 3-5 per week, 10 min each treatment, using 1 MHz at 0.5-2 watts per cm^2 for 3-4 weeks may be beneficial, particularly when accompanied by stretching and exercise.
• Carpal tunnel syndrome – pain: 5x per week, 5-10 min with either 1 or 3 MHz at 0.5-1.5 watts per cm^2 with treatments continuing for 2-4 weeks.
• Carpal tunnel syndrome – dysfunction: 5x per week, 5-10 min with either 1 or 3 MHz at 0.5-1.5 watts per cm^2 with treatments continuing for 2-4 weeks.
• Calcific tendinitis – pain or function: 3x per week, 10 min with either 1 or 3 MHz at 1-2 watts per cm^2 with treatments continuing for 4-8 weeks but may have to last longer if sufficient improvement is not seen.
• Bursitis – pain or function: 3x per week, 5-10 min using 1 MHz at 1 watt per cm^2 over a period of 3-4 weeks.
• Arthritis – pain: 3x per week, 5-10 min using 1 MHz at 1-2 watts per cm^2 for 2-3 weeks.

Evidence for Treatment – Clinical Practice Guidelines

• Therapeutic ultrasound should not be used as part of routine care for non-surgical management of chronic primary low back pain in adults in primary and community care settings.
• Clinicians should not use US to enhance the benefits of stretching treatment in those with plantar fasciitis.
• Clinicians may use phonophoresis with ketoprofen gel to reduce pain in individuals with heel pain/plantar fasciitis.
• Clinicians should not use phonophoresis with 10% hydrocortisone gel, topical prednisolone, or diclofenac sodium gel for the treatment of lateral elbow pain and muscle function impairments (LET).
• A recommendation cannot be made for the use of US as a stand-alone treatment.

Ultrasound: Contraindications, Precautions

• Pregnancy – over the abdomen, low back.
• Active bone growth at the epiphysis.
• Cancer – over an area of malignancy.
• Tuberculosis infection – infected tissue.
• Hemorrhagic conditions – over an area of active bleeding.
• Impaired circulation.
• Myositis ossificans.
• Deep vein thrombosis or thrombophlebitis.
• Acute injury – signs or suspicion of inflammation.
• Recently irradiated tissue.
• Impaired sensation.
• Impaired cognition, communication.
• Skin disease – including damaged and at-risk skin.
• Implanted cardiac pacemaker or other implanted electronics.
• Reproductive organs – particularly tests.
• Eyes.
• Anterior neck – particularly over the carotid arteries, carotid sinus, and vagus/phrenic nerves.
• Plastic or cemented implants – moderate evidence for damage to these.
• Spinal cord and superficial or regenerating nerves.
• Over metal implants or over the chest, heart, or head.

Contraindications for Use of Pulsed US; Evidence

• Pregnancy – over the abdomen or low back.
• Cancer – over an area of malignancy.
• Hemorrhagic conditions – over an area of active bleeding.

Contraindications for Use of Pulsed US; Consensus Opinion

• Myositis ossificans
• Deep vein thrombosis or thrombophlebitis
• Recently irradiated tissue
• Implanted cardiac pacemaker or other implanted electronics
• Reproductive organs – particularly testes
• Eyes
• Anterior neck - particularly over the carotid arteries, carotid sinus, and vagus/phrenic nerves

Precautions for Use of Pulsed US

• Active bone growth at the epiphysis
• Areas of infection
• Acute injury – signs or assumption of inflammation
• Impaired sensation
• Impaired cognition or communication
• Impaired circulation
• Skin disease, including damaged and at-risk skin
• Plastic or cemented implants
• Spinal cord and superficial or regenerating nerves
• Over metal implants or the chest, heart, and head