Therapeutic Ultrasound Notes PDF

THERAPEUTIC ULTRASOUND S. Blose  INTRODUCTION Therapeutic ultrasound (US) -one of the most commonly used, and misused, biophysical agents. Used for: decreasing soft tissue inflammation and pain; increasing tissue extensibility; scar tissue remodelling; &...

THERAPEUTIC ULTRASOUND S. Blose  INTRODUCTION Therapeutic ultrasound (US) -one of the most commonly used, and misused, biophysical agents. Used for: decreasing soft tissue inflammation and pain; increasing tissue extensibility; scar tissue remodelling; & healing acute soft tissue injuries. Commonly used in Rx of: back, shoulder, knee, and neck pain and difficulty in walking and other gait abnormalities. Study reported 82.4% of physical therapists use US—and 36.4% use it daily. Therapists use it on an average of 40% of their patients. Despite its use -evidence of effectiveness not well documented. Report: only 13% of therapists using US make their clinical decisions using research evidence while 40% use their own clinical experiences.  PHYSICAL PRINCIPLES OF ULTRASOUND US - high-frequency mechanical waves delivered using acoustic energy. Sound waves - action by pressing the initially vibrating molecules into adjacent molecules, which in turn causes them to vibrate. No molecules present (vacuum) - no transmission of sound energy. Substances (or tissues) with higher molecular densities, transmission of US would be more efficient because there are more molecules per given volume. Ultrasonic energy can be dissipated (attenuated) more quickly in denser substances because denser substances offer more resistance to molecular motion (i.e., acoustic impedance). Because of the poor transmission of US waves through air, a coupling agent is needed. Sound waves - transmitted in a medium longitudinally (along the direction of the sound wave) by alternative compressions and rarefactions of the molecules in the medium. Compressions are areas of increased density of the molecules. Rarefactions are areas of decreased density. The degree of compression and rarefaction is dependent upon the magnitude of the wave energy. The duration of these compressions and rarefactions is determined by the frequency at which the wave was generated. PHYSICAL PRINCIPLES OF ULTRASOUND … These longitudinal waves move away from the emitter in all different directions - called dispersion. Waves can be reflected, refracted, or absorbed. When the wave is absorbed, the kinetic energy of movement is transformed into thermal energy. Reflected waves can interact with the incident waves by enhancing the wave intensity if the waves interact in synchrony (forming what is called a standing wave) or by diminishing wave intensity if the waves interact asynchronously. You can apply these principles to the application of ultrasonic energy to human tissues. Most body tissues behave as liquids of varying densities. Bone is an exception, as it acts as a solid. Thus, although longitudinal waves predominate in most tissues, both longitudinal and transverse transmission of ultrasonic waves occur in bone. PHYSICAL PRINCIPLES OF ULTRASOUND … In the body, ultrasonic energy is more rapidly attenuated and converted from acoustic energy to thermal energy in dense tissues, such as ligaments, tendons, and other connective tissues, than in the less dense muscle or even less dense adipose tissue. Higher tissue temperatures will result when US is applied to connective tissues than when applied to muscle and other less dense tissues. Additionally, when sonicating an area with high-density tissues, acoustic wave reflection can potentially produce standing waves, which may increase the intensity of the acoustic wave at the junction between the high-density and lower-density tissues. In this way, applying US over bone may dramatically increase the temperature of the periosteum and result in discomfort. PRODUCTION OF ULTRASOUND WAVES The piezoelectric crystal is transversely compressed and expanded by sending an alternating electrical current through it, referred to as the reverse piezoelectric effect. When no current is sent through the crystal, it maintains its normal shape. When current of one polarity is sent through the crystal, a compression (concavity) of the crystal occurs. When the polarity is reversed in the alternating current, an expansion (convexity) of the crystal occurs. This rapid transverse compression and expansion produces the acoustic wave, which is then transmitted through the sound head connected to the piezoelectric crystal Schematic of the conformational shape change of the piezoelectric crystal under the influence of an applied alternating current A: With no current flow, the crystal shape remains unchanged B: A concave or convex C: Change in shape occurs as the direction of current flow across the crystal alternates.  CHARACTERISTICS OF THE ULTRASOUND WAVE AND TREATMENT PARAMETERS Frequency Frequency - number of waves per second delivered to the patient. In most US units, frequency ranges from 0.75 to 3.3 MHz (millions of cycles per second). Most therapeutic US units designed and manufactured have dual- frequency applicators designed to deliver frequencies of both 1 MHz and 3 or 3.3 MHz. Lesser frequencies penetrate deeper. 1 MHz of up to 6 cm deep and 3 MHz being effective up to 2.5 cm deep. A common misconception is that increasing the intensity of the ultrasonic energy will produce a deeper penetration. Increasing the power of the US only increases the energy at the depths of penetration produced by changing the frequency.  CHARACTERISTICS OF THE ULTRASOUND WAVE AND TREATMENT PARAMETERS Frequency Tissues absorb 3-MHz US at a rate three times faster than 1-MHz US. Because the rate of tissue heating is also related to the rate of absorption, US at 3 MHz will heat tissues three times faster than 1 MHz. US delivered at 3 MHz is used for more superficial structures, such as exposed tendons and ligaments, while 1 MHz is used to treat deeper structures such as most muscles and fascia. The rehabilitation professional can use frequency differences to change the rate of heating of the tissue being sonicated.  Intensity Power of the ultrasonic energy is the product of wave phase duration and wave amplitude (intensity). Wave duration is not changed at a fixed frequency, amplitude or intensity is adjusted to change the power or magnitude of the acoustic energy. Power is measured in watts, but in therapeutic US application, power is most commonly expressed as the spatial average intensity (SAI) measured in watts/cm2. SAI is calculated by dividing the power in watts by the ERA. No definitive guidelines are available that state an optimal intensity for therapeutic US despite the widely held perception that US should be delivered at an intensity of 1.5 watts/cm2. It is generally recommended that practitioners use the lowest intensity possible to achieve the desired therapeutic effect.  Mode Most US devices can deliver both continuous and pulsed US. In continuous - delivered at a constant energy level throughout the treatment. In pulsed - periodic cessation of the energy flow, so no US is delivered for a period of time. As a result, the total energy level delivered is reduced. The term temporal (or time) average intensity (TAI) is used to describe this lesser level of energy. The time that the energy is flowing is termed the pulse duration, and the combined time of energy flow and lack of flow is termed the pulse period. The degree to which the total energy level is reduced is dependent upon the duty cycle, which is defined as pulse duration (on-time) divided by the pulse period (on-time + off-time) times 100 to result in a percentage of on-time to total-time of the pulse period. Continuous US is used when heating is needed, and pulsed US is used when the energy level needs to be reduced to produce the so-called non-thermal US. EXAMPLE OF MODE Illustration of continuous US and pulsed US. For pulsedUS, the pulse duration and pulse period are illustrated. Note that temporal peak intensity (TPI) is the same for both continuous and pulsed US, but the time (or temporal) average intensity (TAI) forpulsed US is less due to the periodic cessation of energy flow. For the pulsed US, the pulse duration is 2 msec on-time, 8 msecoff-time, and pulse period (total time) is 10 msec, which yields aduty cycle of 20%. Notice that the TAI is 20% of the TPI.  TREATMENT AREA The appropriate size of a treatment area is likely the most problematic issue surrounding the use of therapeutic US. To get significant heating effect, US must be applied in an area preferably two times the ERA (and no greater than four times), particularly when using 1 MHz, which heats less intensively. When treating an area larger than four times the ERA, the “dose” of the treatment is consequently and significantly lessened. US can be used to heat most exposed tendons and ligaments and small muscles, such as para-spinal muscles of a given spinal level (i.e., single segment). However, a common use seen in many clinics is sonicating long areas of muscles (e.g., para-spinal muscles over multiple levels), which will not significantly heat any area of the tissue. Heating large muscles—such as the quadratus lumborum, quadriceps femoris, hamstrings, and other similarly large muscles— can be deep- heated only using diathermy.  Duration of Treatment and Number and Frequency of Treatments Vigorous heating is defined as an increase of approximately 4°C in the tissue because this has been shown to increase the distensibility of connective tissues in vitro. However, 1-MHz US (1.5 watts/cm2, 2 × ERA), it takes 11 minutes to heat skeletal muscle to 3.5°C and even longer to heat to vigorous heating of 4°C. More superficial muscles can be heated to 5.3°C in 6 minutes using 3 MHz (1 W/cm2, 2 × ERA). Each application of US is unique. The treatment’s duration is dependent upon the size of the area being treated, the settings of the US unit (intensity, frequency, and mode), and the specific condition being treated. Treatments are often administered two to three times per week for 10 to 15 treatments. When pairing thermal US with stretching techniques, the US would be applied immediately before (and perhaps during) the application of the stretching.  Variation in Ultrasound Units US units can vary in the ERA of their applicators, which can have an impact on treatment effectiveness. However, treatment effectiveness can vary beyond what can be predicted by differences in ERA: Variation in Tissue Response to Therapeutic Ultrasound Cooling of Tissues after Ultrasound Application Variability of Patient Response: Responders and Non-responders Variability in Application Medium: Three important principles should guide the application of US; viz: The radiating waves of US must be kept perpendicular to the skin surface; thus, the applicator must remain in contact with the skin surface. A coupling medium must be used between the US applicator and the skin. The applicator faceplate must be continually moved during the treatment.  THERMAL EFFECTS OF ULTRASOUND US is a series of high-frequency sound wave. It is thought that when these high-frequency sound waves are absorbed by a tissue, the sound waves’ mechanical energy is converted into thermal energy due to vibrating the molecules within the tissue. Greater levels of power (expressed usually as power density [W/cm2]) and duration (in minutes) and reduced treatment area (generally expressed in multiples of ERA) increase this local effect and increase the heating of the tissue. The use of a higher frequency of US (3 MHz) heats the tissue to a greater extent than using lower frequencies (1 MHz). It is thought that with the lack of penetration of the US with higher frequencies, all of the ultrasonic energy is confined to a smaller volume of tissue, thus increasing both the energy density and the temperature of the tissue. The amount of heating may also be related to tissue density with tissues such as tendons heating faster and to a greater degree than less dense tissues such as muscle. NON-THERMAL EFFECT TO READ AT HOME  USE OF Ultrasound for Painful Conditions Painfull Conditions Pain is a common symptom that is treated by US. Much of the pain is secondary to inflammatory conditions, tissue swelling, or lack of tissue extensibility. The use of US has been extensively studied for three common painful conditions: myofascial pain syndrome (specifically myofascial trigger points), back pain, and nonspecific shoulder dysfunction. Ultrasound for Inflammation There have been quite a few studies on a variety of inflammatory conditions, including: lateral epicondylitis, carpal tunnel syndrome, calcific tendinitis, bursitis, and arthritis. USE of US … conti Ultrasound for Soft Tissue Healing Healing of dermal wounds has been the major form of soft tissue healing for which US has been used. Ultrasound for Improving Tissue Extensibility There are an insufficient number of studies in each area where US has been used to increase tissue extensibility. However, there are seven studies on the effect of continuous US on tissue extensibility, and they focused on adhesive capsulitis, knee extensibility, limited dorsiflexion of the ankle, hip contracture, and Dupuytren’s contracture. These studies are suggesting strong but conflicting evidence for an effect. Ultrasound for Remodelling Scar Tissue There are only four studies on the effects of continuous US on scar tissue remodelling, which represents insufficient evidence to make conclusions related to the effectiveness of this use of therapeutic US. Ultrasound for Tissue Swelling There are only four studies on the effects of continuous US on tissue swelling, specifically ankle oedema following acute sprain, which represents insufficient evidence to make conclusions related to the effectiveness of this use of therapeutic US. However, there are suggesting a strong unsubstantiated effect of US on tissue swelling.  REVIEW OF THE EVIDENCE There is a review of the evidence for the major suggested uses of continuous US in clinical practice. There is considerable evidence for US's effectiveness in treating a number of conditions. For example, there is strong substantiated evidence for the use of continuous US to treat: Pain of myofascial pain syndrome and trigger point Pain and dysfunction associated with painful back conditions Pain and dysfunction of carpal tunnel syndrome Pain associated with arthritis There is moderate substantiated evidence for the use of continuous US to treat: Dysfunction associated with nonspecific shoulder conditions Calcific tendinitis Bursitis  Review of the evidence … Condition Strength of Evidence Recommended Intervention Protocol Pain Myofascial pain, MTrPs—pain Strong Three times per week for 10 minutes each treatment, using 1 MHz at 1–2 W/cm2 for a 4-week course of treatment Back pain Strong Three times per week for 10 minutes each treatment, using 1 MHz at 1–2 Back dysfunction Strong W/cm2 for a 4-week course of treatment Nonspecific shoulder conditions— Moderate Three to five times per week for 10 minutes each treatment, using 1 MHz dysfunction at 0.5–2 W/cm2 for 3–4 weeks may be beneficial, particularly when accompanied by stretching and exercise Inflammation Carpal tunnel syndrome—pain Strong Five times per week for 5–10 minutes with either 1 or 3 MHz at 0.5–1.5 W/cm2 with treatments Carpal tunnel syndrome— Strong continuing for 2–4 weeks dysfunction Calcific tendinitis—pain or function Moderate Three times per week for 10 minutes with either 1 or 3 MHz at 1–2 W/cm2 with treatments continuing for 4–8 weeks but may have to last longer if sufficient improvement is not seen Bursitis—pain or function Moderate Three times per week for 5–10 minutes using 1 MHz at 1 W/cm2 over a period of 3–4 weeks Arthritis—pain Strong Three times per week for 5–10 minutes using 1 MHz at 1–2 W/cm2 for 2–3 weeks  CONTRAINDICATIONS AND PRECAUTIONS A special issue of Physiotherapy Canada, reviewed the evidence basis of the contraindications and precautions commonly listed for US. Evidence is moderate to strong for the contraindication of the use of continuous US in the following areas and conditions: Contra-indications Pregnancy Recently irradiated tissue Active bone growth at the Impaired sensation epiphysis Impaired cognition or Cancer communication Tuberculosis infection Skin disease Haemorrhagic conditions Implanted cardiac pacemaker or Impaired circulation other implanted electronics Myositis ossificans Reproductive organs Deep vein thrombosis or Eyes thrombophlebitis Anterior neck Acute injury PRACTICAL