THERAPEUTIC ULTRASOUND IN VETERINARY PRACTICE
DR MD MOIN ANSARI
Division of Veterinary Surgery and Radiology
Faculty of Veterinary Science and Animal Husbandry
SKUAST K, Shalimar-190025
Fig: 1: Application of Therapeutic Ultrasound in a dog
Fig: 2: Application of Therapeutic Ultrasound in a horse
Ultrasound or ultrasono or ultrasonic (US) is characterized by sound waves with a frequency higher than the upper range of human hearing, approximately 20,000 cycles per second (20 kHz). Waves are generated by vibrating piezo electric disc and subjected to an alternating current (AC) of 1 million cycles per second. 1 million cycles per second is 1 megahertz (MHz). The piezo electric disc fitted on the transducer head of the ultrasound machine and former is placed on the area to be treated. Each type of tissue offers a varying resistance to the passage of ultrasonic waves described as acoustic impedance. Different resistance present at the tissue interfaces causes a rise in thermal energy.
Ultrasound can be used for treating certain disease known as therapeutic ultrasound and for scanning of internal structures known as diagnostic ultrasound. Therapeutic ultrasound is non-invasive, non-toxic and non- destructive therapy and one of the most common electrophysical modalities used in today’s technologically advanced nations.
Properties of Ultrasound:
The various properties of ultrasound are mentioned below:
physical, chemical and thermal.
Physical Property
• Propagation of vibratory motion is the basic element of sound wave production (longitudinal waveform associated with sound). A molecule set in motion will cause its neighbour to move, and in turn its neighbour, until the vibration has propagated throughout the material.
• The vibratory frequency of sound wave affects its absorption into body tissue.
• The higher the frequency, the less the sound waves diverge. Sound waves at greater than the audible sound range (20-20000 Hz) appear to spread out in all directions. Beam of sound at a frequency of one million cycles per second (1 MHz) that is sufficiently collimated to penetrate to selected target tissues.
• For therapeutic purpose, the ultrasound is produced from electromagnetic energy with a frequency of 1 to 3 MHz, which is converted by a transducer to mechanical energy.
• Frequency determines depth of penetration. The frequency of the ultrasound waves is actually opposite to how deep they will penetrate the body. As the frequency of the ultrasound waves increases, penetration decreases. One MHz heats at depths around 2 to 6 cm below the skin and 3 MHz heat at depths around 0.5 to 2 cm. While a low frequency means deeper penetration, using too low a frequency will mean that the waves are too wide to properly move the molecules. For therapeutic purpose, 1MHz is the optimal frequency for both effect and penetration. Tissues with a high fluid content, such as blood and muscle, will absorb sound waves better than less hydrated tissues.
• Nerve tissue has a high coefficient of ultrasound absorption. This expands treating possibilities to nerve roots that are associated with peripheral conditions.
Chemical Property:
• Therapeutic ultrasound is unique among the heating modalities because of it supplementary non-thermal effects, these chemical changes that must be attributed to mechanism other than tissues temperature increases.
• Ultrasound waves are made up of alternating areas of compression and rarefaction increased density and pressure (compression) areas of decreased density and pressure (rarefaction) in the area through it passes.
• Rarefaction causes air bubbles in the blood or tissues fluids to expand because of the decrease in pressure. During expansion gas enters the bubble.
• The compression phase for the wave caused the gas to flow out of the bubbles.
• Rarefaction and compression phase results in the gaseous exchange, with exerts mechanical stress on the surrounding called cavitations.
• Pulsed or continuous ultrasound increases cell permeability by setting up cavitation. Stable cavitation has multifactorial benefits: it has electrolytic effect, increases cell permeability, useful in the breaking up to calcified deposits, increasing in the extensibility of fibrous capsule and reduces the nerve conduction velocity of C fibers, thus decreasing pain.
• Other non-thermal effect of ultrasound is acoustic streaming also called micro streaming or micro massage. It refers to liquid flow along cell membranes pushed by the pressures of the sound wave. It is therapeutically valuable in facilitating diffusion of ions and metabolites across the membrane change in membrane permeability to sodium ions could be involved in the altered electrical activity in nerves, resulting in pain relief and increased membrane permeability to sodium and calcium exchange may explain the effect on contractile tissue in reduction of muscle spasm.
• The ultrasound wave travels through the medium, mechanical energy is converted to heat. The heat diffuses into surrounding tissues by waves reflecting off acoustic in homogenetics such as tissues interfaces or dissolved gas bubbles.
• Within the body tissue, wave reflection is greatest at interfaces of bone and soft tissue because of the greatest difference in their acoustical absorption.
• Sound wave reflection occurs at interface such as nerve and nerve sheath, muscles sheath and muscle, point capsule tissue and the tissue surroundings it. The interaction of incoming and reflected waves at these interfaces causes selective heating of these tissues.
• Ultrasound can impart both thermal and non-thermal effects to the body tissues to depths of 4 cm or more, although the effectiveness of penetration depends on the frequency used and the type of the tissue.
• Tissue heating depends on frequency, intensity, duration, treatment area and the characteristics of the tissue. Intensities employed in therapeutic ultrasound normally range from about 100 mW/cm2 to 3 W/cm2. The sound waves penetrate homogenous tissue readily and are primarily absorbed by tissue with high protein content.
• Skin and subcutaneous fat cannot absorb ultrasound well, absorption takes place on the molecular level and protein molecules are the major absorbers. So the skin surfaces may again cool while underlying structures are heated. These characteristics of ultrasound made an ideal therapeutic protocol for treating sports injuries that occur at the nerve, ligaments, tendons, joint capsules, muscles and all tissues with a high protein component.
• In soft tissue, this absorption may be directly related to the protein content of the tissue.
• Tissues with a high fluid content, such as blood and muscle, will absorb sound waves better than less hydrated tissues.
• Local temperature elevation produces many responses like increase in blood flow, increased extensibility of collagen tissues, increased capillary permeability, and enzymatic activity.
Mechanism of Action
The mechanism of action of ultrasound for reduction of skeletal muscle spasm may rely on thermal (heating) effects that alter the skeletal muscle contractile process, reduce muscle spindle activity, or break the pain-spasm- pain cycle in order to relieve pain and muscle spasm to increase tissue extensibility.
The heating effect of the sound waves also cause vessel vasodilatation and increase circulation to the area that assists in healing. The results in wound healing appear to depend on the intensity and duration of treatment and the time after injury. Low intensities appear to enhance healing whereas high intensities may have pro-inflammatory effects. Heating of the deep tissues alters the elastic properties of collagen tissue and its molecular bonding. Deep tissues surrounding a joint are rich in collagen. Scar tissue is also rich in collagen and denser than the surrounding tissue. Because of ultrasound has more affinity towards collagen tissues it can be selectively targeted.
Acoustic micro streaming, the unidirectional movement of fluids along cell membranes occurs as a result of the mechanical pressure changes within the ultrasound field. Micro streaming may alter cell membrane structure, function and permeability. Insonation of peripheral nerves with pulsed ultrasound reduces neural conductivity, both afferent and efferent, so that muscular spasm and pain in the area is reduced.
Effects of Therapeutic Ultrasound:
• It stimulates tissue repair without irritation by acoustic streaming and promotes the healing of pressure sores by increasing the rate of protein synthesis by fibroblasts and increased lysosomal permeability.
• It increases cell membrane permeability
• It increases vascularity with associated hyperemia/inflammatory response
• It excitated calcium bound to proteins may promote the fragmentation and resorption of calcified masses within soft tissue
• It improves range of motion of the joint and improves circulation to the scar tissue. Joint capsule and scar tissue are rich in collagen. Because of ultrasound has more affinity towards collagen tissues. Ultrasound also as it is rich in collagen
• It decreases pain and muscle spasm
• It is used to enhance the delivery of topically applied anti- inflammatory drugs across the skin by means of phonophoresis. It is a special use of therapeutic ultrasound in which the sound waves aid in the transport of medications through tissue membranes
• The sound wave drives whole molecule subcutaneously up to a depths of 6 cms. The medications used in phonophoresis are anti-inflamatory agents and anaesthetics. Hydrocorotisone, dexamethasone, salicylates, indomethacin or lidocaine are the drugs used most often in the treatment of localized musculoskeletal inflammatory conditions (tendoints, epicondylitis, burnitis and other myofacial pathologies). For this technique mix the drug in proportions of 5 to 10% into the transmission gel. Use the continuous wave mode and an intensity range of 0.3 to 0.5 W/cm2. The duration of application is up to ten minutes for a 5 cm2 area
• It affects the oxidant/ antioxidant status in patients suffering from neurological and orthopaedic disorders.
Technique of Therapeutic Ultrasound:
• The area to be treated should be shaved/clipped and cleaned. The presence of the hair coat may be a major drawback to therapeutic ultrasound. Because ultrasound energy is absorbed by tissues with high protein content, and deflection of the ultrasound beam occurs at tissue interfaces, it would be expected that ultrasound penetration through the hair coat into underlying tissues would be poor.
• Apply the specially formulated ultrasound gel (coupling agent) liberally to ensure good contact between the ultrasound head (transducer) and the treatment area. Ultrasound without gel is ineffective and can damage the ultrasound machine. Without the gel, the ultrasound waves won’t penetrate the skin and the pain relieving ingredient (infused in the gel) won’t get to the affected area. Because air is a very poor sound conductor, ultrasound gels must be used to conduct the wave energy to the skin.
• Press the ON button and start the therapy.
• Treatment duration is determined by the practitioner. The machine will automatically shut off after about 10 minutes. It may range from 2-10 minutes depending on the conditions treated and anatomic target site.
• After required frequency and time, keep the sound head (transducer) moving slowly and steadily in small circles over the treatment area. The purpose of the motion is to distribute energy as evenly as possible though our the tissue. Several techniques like direct coupling, under water immersion and coupling cushions have been used for therapeutic ultrasound.
• Direct coupling is preferred when the skin surface is flat and is larger than the applicator surface. Apply the specially formulated ultrasound gel (coupling agent) liberally to ensure good contact between the ultrasound head (transducer) and the treatment area.
• The underwater immersion method was popular before smaller transducer heads became available. This can be recommended when the skin surface is so uneven that direct contact is difficult, such as occurs in the distal limbs. The part to be treated can be immersed in a container of tap water at room temperature, but both the water and skin must be clean. Water in a whirlpool is not recommended if it has been agitated. Because metal containers reflect some of the ultrasound beam, which could increase the intensity in areas near the metal, rubber or plastic containers are preferred as they cause less reflection. The transducer should be held underwater 0.5-3.0 cm from the skin of the area to be treated. As air bubbles accumulates on the skin surface or on the face of the sound head they must be wiped away. The intensity may be increased by 0.5 W/cm2 to compensate for absorption of the ultrasound by water.
• A coupling cushion method is a method in which, placing a water- filled balloon between the transducer head and the skin, with coupling gel at the interfaces.
Indications:
It has been successfully indicated for a variety of lesions involving skin, muscle, tendons, ligament, bone and joints like:
• Musculoskeletal pain
• Acute and chronic arthritis
• Acute synovitis
• Exostosis and myositis
• Acute tendonitis, desmitis and calcific tendonitis
• Improvement of range of motion in rheumatoid disease
• Back pain and herniated intervertebral disc syndrome
• Spondylosis
Contraindications
• It should not be used 48 to 72 hours of injury (cause haematoma or seroma).
• It can spread infection.
• It can spread cancer cells.
• It is not used when local anesthesia is given
• It should not be used an incision site before 14 days as it can result into wound dehiscence.
• It should never use over metal implant.
• Better to avoid using in the spinal cord following laminectomy and in cardiac area if the patient suffering from advanced heart disease.
• It should not use over areas containing fluid such as the eyes, over amniotic fluid in pregnant patient and over joints with active effusion.
Precautions:
• Always use the lowest intensity which produces a therapeutic response.
• If pain, discomfort or unexpected sensations are experienced by the patient, the therapeutic intensity should be reduced. If the symptoms persist, the treatment should be terminated.
• Ensure that the applicator is moved throughout the therapy.
• Anaesthetic areas should be treated with caution if a thermal dose is being applied.
• Avoid subcutaneous major nerves and bony prominences.
References:
Ansari, M.M. 2016. Principles of Veterinary Physiotherapy (A book for both veterinary students and practitioner). First edition, Published by Educationist Press, A Division of Write and Print Publications, New Delhi-110015 (India). ISBN 978-93-84649-49-4.
Ansari, M.M., Zama, M.S., Amarpal, Saxena, A. and Gugjoo, M.. 2012. Clinical studies on therapeutic ultrasound and diathermy in dogs with hind quarter weakness. Indian J Vet Surg, 33 (2): 136-139.
Ansari, M.M., Zama, M.S., Hoque, M., Pawde, A.M., John, R. and Shakya, G. 2011. Application of ultrasound therapy in equine – a clinical evaluation. International symposium and XXXIVth Annual Congress of the Indian Society for Veterinary Surgery on “Nanobiomaterials in biomedical research: their application in veterinary surgery. w.e.f. 11th- 13th, November 2011; organized by Department of Veterinary Surgery and Radiology, West Bengal University of Animal & Fishery Sciences, Kolkatta-37.
Ansari, M.M. 2014. Physical therapy for small animal practice in orthopaedic post-operative rehabilitation- a review. Livestock Line, 7(10): 29-37.
Ansari, M.M. and Zama, M.S. 2012. Physiotherapeutic modalities for rehabilitation of canine neurologic patients. Intas Polivet. 13 (2): 314-320.
APTA. 2008. Discovering Physical Therapy. American Phys Ther Assoc, 34: 2.
