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To deeply heat the body’s soft tissues, therapeutic ultrasonography is a technique that is frequently applied in physical therapy. These tissues consist of ligaments, joints, muscles, and tendons. Therapeutic Ultrasonography is distinct from ultrasound used in physical therapy.

Read more: click here to understand the guidelines about How does therapeutic ultrasonography work?

What is Ultrasound? – Therapeutic Ultrasonography

Ultrasound is made up of inaudible, high-frequency mechanical vibrations produced when a generator’s electrical energy is changed into acoustic energy by mechanically deforming a piezoelectric crystal inside the transducer. Sound waves are able to travel long distances with rarefaction and compression zones. For many years, using ultrasound for therapeutic purposes has been a recognized and advantageous application of the biological effects of ultrasound. Since the 1950s, low power ultrasonography with a frequency of roughly 1 MHz has been frequently used for physical treatment in disorders like tendinitis or bursitis.

Characteristics of Therapeutic Ultrasonography

Frequency

Frequency is defined as how many times a cycle repeat in one second. With most machines set at a frequency of 1 or 3 MHz, Therapeutic Ultrasonography has a frequency range of 0.75 to 3 MHz While being less focused, low-frequency ultrasound waves have a deeper penetration. It is advised to use ultrasound at a frequency of 1 MHz because most of the energy is absorbed by tissues at a depth of 3-5 cm.

Acoustic Impedance

The acoustic impedance of tissues, determined by the ratio of their density to the speed at which ultrasound can pass through them, can be used to identify them. Ultrasound waves penetrate deeply into tissues with high water content (such as fat) but are only weakly absorbed by those with a high protein content (e.g. skeletal muscle). The less transmission from one tissue to another, the greater the differential in acoustic impedance between them. A standing wave (hot spot) may be produced when reflected ultrasound collides with other waves that are being transmitted, which could harm tissue. These effects are reduced by ensuring that the device delivers a consistent wave, using pulsed waves (see below), and repositioning the transducer during therapy.

Wavelength

The wavelength of a waveform in a given medium is the separation between two equivalent places on the waveform. The wavelength in a “average tissue” at 1 MHz and 3 MHz would be 1.5 mm and 0.5 mm, respectively.

Coupling Media

Coupling media, such as

• Water,
• Creams,
• Oils, or, most frequently,
• Gels,

stop waves from reflecting away at the soft tissue/air interface by keeping air out of the space between the transducer and the patient. Impedances vary depending on the type of media. Any coupling medium should be equivalent in acoustic impedance to the transducer, absorb less ultrasound, be devoid of air bubbles, and facilitate the transducer’s mobility over the skin’s surface.

In order to treat problems like bursitis of the shoulder or tendinitis, qualified physical therapy personnel apply coupling gel to the hand-held transducer and move it in a circular manner over the injured or uncomfortable area of the anatomy. To enhance blood flow and hasten healing, it is intended to warm tendons, muscles, and other tissue. To improve the treatment, the coupling medium may also contain a variety of substances. Application of Therapeutic Ultrasonography, commonly known as sonophoresis or phonophoresis, can also help by increasing the transport of the substance into the skin.

Intensity

The rate at which ultrasound is delivered per unit area of the transducer surface (watts/cm2) is altered to modify ultrasound dosage. Regarding the definition selected for their intensity setting, machines vary. Diagnostic ultrasonography differs from Therapeutic Ultrasonography in several ways. It is used by PTs to treat some chronic pain and injuries. On the alleged advantages of therapeutic ultrasonography, the evidence is contradictory. Though it is generally low-risk, it might be worth a shot, particularly if you deal with chronic pain.

Velocity

Velocity is defined as the rate at which a wave moves through any material.

Density of medium is directly proportional to the velocity of ultrasound

The velocity of US in a saline solution is about 1500 m/s, but it is only about 350 m/s in air. More dense the medium, more will be velocity of sound waves.

Modes of Ultrasound

Additionally, Therapeutic Ultrasonography has

• Pulsed or
• Continuous ultrasound therapy

is an option.

Effect of Ultrasound – Therapeutic Ultrasonography

Non Thermal Effects

While both forms of Therapeutic Ultrasonography have non-thermal effects at low intensities, continuous ultrasound has a more powerful heating effect. Tissues may experience both thermal and non-thermal physical impacts from ultrasound. It is possible to generate non-thermal effects both with and without thermal effects.

The non-thermal effects of ultrasound, such as

• Cavitation and
• Sonic microstreaming.

have been argued to be more significant than the thermal effects in the therapy of soft tissue lesions.

Cavitation

Cavitation happens when gas-filled bubbles in tissue fluids expand and compress due to ultrasonically induced pressure changes, increasing the flow of the surrounding fluid. Injured tissue is thought to benefit from stable (regular) cavitation, whereas unstable (transient) cavitation is thought to harm the tissue. The former can be suppressed by extremely brief pulses and sustained at an intensity lower than those needed for unstable cavitation.

At therapeutic doses of US, STABLE CAVITATION does appear to develop. This is the development of gas bubbles through the buildup of dissolved gas in the medium. About 1000 cycles are needed for them to attain their maximum size. The ‘cavity’ appears to be advantageous since it enhances the auditory streaming phenomenon (see below). At the low pressure portion of the US cycle, bubbles occur and are known as UNSTABLE (TRANSIENT) CAVITATION. These bubbles then swiftly burst, releasing a significant quantity of energy that is harmful to tissue viability.

Sonic Microstreaming

The unidirectional flow of fluids over cell membranes, known as acoustic microstreaming, is brought on by the mechanical pressure changes within the Therapeutic Ultrasonography field. It has been proposed that microstreaming may drive tissue repair by changing the structure, functionality, and permeability of cell membranes. In vitro experiments have shown the effects of cavitation and microstreaming are to enhance collagen synthesis and repair of fibroblasts, bone healing, and regeneration of the tissues.

• The earlier resolution of inflammation,
• Accelerated fibrinolysis,
• Stimulation of macrophage-derived fibroblast mitogenic factors,
• Increased fibroblast recruitment,
• Accelerated angiogenesis,
• Increased matrix synthesis,
• More dense collagen fibrils, and
• Increased tissue tensile strength are all examples of how ultrasound is helpful in these conditions.

These results are the foundation for using Therapeutic Ultrasonography to encourage and hasten tissue healing and repair.

Thermal Effects

As an alternative, Therapeutic Ultrasonography may be utilized for its thermal effects to reduce pain and muscle spasms and promote tissue extensibility. This method is used with stretching exercises to attain the ideal tissue length. Thermal dosages of ultrasound have been shown to lengthen scar tissue and the ligament in normal knees (Speed, 2001). 

• Fastens blood flow to the affected area
• Lessens the spasm in muscles
• Increases the extension in collagen fibers
• Promote tissue repair

are just a few of the thermal effects of ultrasound on tissue. Thermal effects are thought to manifest when tissue temperature is raised to 40–45 °C for at least five minutes. The tissue may be harmed by excessive heat effects, especially at higher ultrasonic intensity.

The treatment of muscle, joint, and ligament edema with Therapeutic Ultrasonography is successful. 
Numerous medical conditions can be treated with ultrasound technology. But the most typical application is for treating issues with muscle tissue. The ultrasound’s heating impact helps to treat muscle discomfort and lessens persistent inflammation.
In thermal Therapeutic Ultrasonography, the wand vibrates and heats the muscles and skin.

Ultrasound Effects in Inflammation

The use of Therapeutic Ultrasonography during the inflammatory, proliferative, and repair phases is beneficial not because it alters the order of events that normally take place, but rather because it has the power to accelerate or amplify these regular occurrences, improving the effectiveness of the repair phases. It would seem that applying therapeutic ultrasound at the right dose will promote tissue repair in cases when it is hindered or impeded. It would seem that if the tissue is healing “naturally,” the application will quicken the process and allow the tissue to reach its destination sooner than would otherwise be possible. It depends on the dose if Therapeutic Ultrasonography can be used to accomplish these goals.

Literature Review

Although Therapeutic Ultrasonography has been shown to raise temperature,52 degrees of tissue heating depends on various factors. Heating depends on intensity. Compared to continuous ultrasound, pulsed ultrasound experiences less heating, with lessening being related to the on: off pulse ratio. 15 According to a study on human muscle by Draper et al. 53, the temperature in the gastrocnemius muscle increased by five °C at a depth of 3 cm after 10 minutes of continuous 1-MHz ultrasound at an intensity of 1.5 W/cm2 with a 20-cm2 transducer applied to a skin surface of 80 cm2.

These researchers stressed limiting the treatment area and thought it was essential to administer ultrasound for at least 7 or 8 minutes to achieve a temperature rise. Clinical research offers data for modality review, including randomized, randomized controlled trials and other types.

Understanding how therapies affect the body can be helpful for physicians even when it does not justify their usage. We believe that alleged physiological reactions to the biophysical effects of therapeutic ultrasound have played a vital role in the broad acceptance of this therapy method, despite the lack of clinical research. According to this review, ultrasound’s biophysical effects are not expected to be advantageous. This judgement is based on the lack of proof supporting a biological basis for the application of therapeutic ultrasonography. (Baker et al., 2001)

Sports-related musculoskeletal diseases, such as tendon injuries or tendinopathy, are frequently treated with Therapeutic Ultrasonography as a therapeutic tool. Despite therapeutic ultrasound’s widespread acceptance, few clinical investigations have demonstrated its effectiveness. Its effectiveness of it has been investigated in several animal experiments. Additionally, several in vitro research examining the processes underlying this physical modality’s capacity to promote tendon repair or treat tendinopathy are now being conducted. Animal studies have provided compelling evidence for tendon repair with the therapeutic ultrasonography.

Additionally, in vitro research has shown that ultrasound can promote tendon cell migration, proliferation, and collagen synthesis, which are beneficial for tendon repair. These beneficial benefits of therapeutic ultrasound on tendon repair that have been demonstrated by in vivo and in vitro research assist in explaining the physiologic responses to this physical modality and could provide the basis for clinical treatment. (Tsai et al., 2011)

Lacerations, contusions, and strains to the muscles are by far the most frequent injuries in sports. Therapy is individualized based on the degree of the injury and the knowledge gathered from experimental investigations on the regeneration of injured muscle after first aid using the RICE principle (Rest, Ice, Compression, and Elevation).

Most muscle injuries are managed conservatively with good results, but severe ruptures with total loss of function need to be surgically addressed. A brief period of immobilization-immobilization is required soon after the injury to hasten the development of the scar between the stumps of the ruptured myofibers to which the stumps cling. According to severity, the ideal period of immobilization should not be any longer than is necessary for the scar to withstand the pulling forces without rupturing.

Early mobilization is necessary to stimulate adhesion, the orientation of the regenerated muscle fibers, revascularization, and resorption of the connective tissue scar. Another crucial goal of early mobilization, particularly in clinical sports medicine, is to reduce the harmful effects of extended immobility, such as atrophy caused by inactivity and loss of strength and extensibility. (Järvinen et al., 2000)

Restoration of joint motion, pain relief, and a return to the patient’s prior level of daily activity are the main goals of treatments for joint pain and dysfunction. An extensively used noninvasive treatment method for musculoskeletal diseases is therapeutic ultrasonography. When treating knee, shoulder, and hip pain, therapeutic ultrasonography is routinely utilized in conjunction with other physiotherapeutic methods.

The body of research on knee arthritis is solid, and there is some evidence that therapeutic ultrasound is practical—although there is debate about whether ultrasound is delivered continuously or in pulses. Although ultrasound therapy alone may not affect functional improvement, it can be a fair adjunct when combined with other widely used modalities.

Impact of low-intensity ultrasound on the knee, shoulder, and hip pain in all three pain types, especially hip pain. For ideal conditions or session length, no definitive advice is given. Numerous musculoskeletal conditions, such as osteoarthritis of the knees, myofascial pain syndrome, low back pain, pelvic pain, and low back pain, have been successfully treated using therapeutic ultrasound. As tissues absorb mechanical ultrasonic energy, it has thermal and non-thermal actions that promote tissue healing and repair.

Although it has received a lot of research, few well-designed RCTs evaluate the efficacy of nanotherapeutic ultrasound. (Aiyer et al., 2020)       

Resources

• Aiyer, R., Noori, S. A., Chang, K.-V., Jung, B., Rasheed, A., Bansal, N., Ottestad, E., & Gulati, A. (2020). Therapeutic ultrasound for chronic pain management in joints: a systematic review. Pain Medicine, 21(7), 1437-1448. 
• Baker, K. G., Robertson, V. J., & Duck, F. A. (2001). A review of therapeutic ultrasound: biophysical effects. Physical therapy, 81(7), 1351-1358. 
• Järvinen, T. A., Kääriäinen, M., Järvinen, M., & Kalimo, H. (2000). Muscle strain injuries. Current opinion in rheumatology, 12(2), 155-161. 
• Speed, C. (2001). Therapeutic ultrasound in soft tissue lesions. Rheumatology, 40(12), 1331-1336. 
• Tsai, W.-C., Tang, S.-T., & Liang, F.-C. (2011). Effect of therapeutic ultrasound on tendons. American journal of physical medicine & rehabilitation, 90(12), 1068-1073. 

Summary

In the light of above all discussion, ultrasonography has wide application in the physiotherapy treatment regime. Its thermal and non-thermal effects are extraordinary in healing and repair. It is compulsory part of treatment and used as an adjunct also. In case of adhesions, contractures and connective tissue scar, its importance cannot be denied. Numerous musculoskeletal conditions, such as osteoarthritis of the knees, myofascial pain syndrome, low back pain, pelvic pain, and low back pain, have been successfully treated using therapeutic ultrasound.

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