Therapeutic Ultrasound

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Ultrasound in the medical community is used according to different purpose. It can be a diagnostic tool by imaging internal structures; the tumoricidal effects will help cancer patients in the destruction of tissue or as a valuable therapeutic agent in physical therapy. Ultrasound is one of the common deep heating therapeutic modality used by physical therapists today. Ultrasound consists of inaudible high‐frequency mechanical vibrations that produce thermal and nonthermal effects. The vibrations are created when an electrical energy is converted to acoustic energy through mechanical deformation of the piezoelectric crystal within the transducer/probe. The sound waves that pass through the skin causes a local deep heating and usually no sensation of heat will be felt by the patient. 




Therapeutic Effects

• Scar tissue breakdown by gentle massage of muscles, tendons and/ or ligaments in the treated area 
• Decrease joint stiffness
• Pain relief from the reduction of swelling and edema
• Increase local blood flow reduces local swelling and chronic inflammation
• Decrease muscle spasm

Nonthermal Effects

• Stimulation of tissue regeneration
• Increase macrophage responsiveness
• Pain relief from tissue relaxation
• Speed up soft tissue repair from increased blood flow
• Increase blood flow according to some studies promotes fracture healing
• Increase skin and cell membrane permeability enhance the cell repair effects of the inflammatory response, especially in soft tissue injuries

Indications                                                                                                                                         

• Ligament Sprains
• Muscle Strains
• Tendonitis
• Joint Inflammation
• Plantar fasciitis
• Metatarsalgia
• Facet Irritation
• Impingement syndrome
• Bursitis
• Rheumatoid arthritis
• Osteoarthritis
• Scar tissue adhesion
• Bone fracture
• Contracture
• Trigger point
• Dermal ulcer
• Plantar wart
• Pain

          

Contraindications

• Vascular abnormalities - thrombophlebitis
• Impaired pain or temperature sensory deficits
• Directly on the abdomen of pregnant women
• Directly over active epiphyseal regions (growth plates) in children
• Metal implants below the area being treated
• Local acute infection 
• Over the eyes, skull, testes, or cervical ganglia
• Over local malignancy
• Over the spine after laminectomy
• Over cemented prosthetic joint

Treatment Parameters

The treatment will be based on the diagnosis and the desired effects. Define the duration, frequency, duty cycle and intensity of treatment. 

Therapeutic ultrasound is in the frequency range of about 75 and 3 MHz. A frequency setting of 1 MHz is used for heating deeper tissues (up to 5 cm). A setting of 3MHz produces a higher temperature with a depth of penetration of less than 2 cm. 

The ultrasound can be administered using a pulsed or a continuous transmission mode. The pulsed mode is used in situations where a heating effect is not desirable, such as a fresh injury with acute inflammation because it minimizes the thermal effects (nonthermal effect). A continuous mode is effective in elevating the tissue temperature to produce the thermal effects on the tissues (due to the absorption of the sound waves). Nonthermal effects are from cavitations, micro-streaming, and acoustic streaming.

Ultrasound is applied using a transducer in three different techniques. One is in direct contact with the skin, the other way is to slightly hold one half-inch above a body part for water immersion technique, and lastly the indirect contact using a fluid-filled bag (bladder technique). The direct contact technique can be either the stationary or moving techniques. In the moving technique, the transducer should continuously move in a small circular manner or in a longitudinal stroke over the treated area. Each motion should cover half of the previous circle or stroke. The water immersion technique is recommended if the area to be treated is smaller than the diameter of the available transducers or if the body area is irregular with bony prominences. The body part is immersed in a plastic or rubber basin (no metal) filled with tap or degassed water. Move the transducer in a longitudinal stroke while keeping a 1/2' to 1' distance from the skin. The bladder technique is also ideal for bony prominent areas. This technique uses a thin plastic bag (surgical gloves or balloon) filled with water and is placed on the area to be treated. A coupling media are applied and slowly move the transducer on top of the bag.

The application requires a coupling medium (gels) applied on the area to be treated to reduce surface friction and assist transmission of the ultrasonic waves by preventing reflection of the waves away at the soft tissue air interface. Besides gels as a coupling media, mineral oil is can also be used. Different media have also different acoustic impedance that affects the transmission and absorption of the ultrasound. A two media having the same impedance will produce maximal transmission of energy or else a greater the difference in impedance, the greater the reflection that will occur, and therefore, the smaller the amount of energy that will be transferred.

The ultrasound intensity of continuous US is normally set between 0.5 to 2 W/cm2 of thermal effects while pulsing US normally set between 0.5 to 0.75 W/cm2 with a 20% duty cycle. Maximum energy absorption in the soft tissue occurs from 2 to 5 cm. Intensity decreases as the US waves penetrate deeper. They are absorbed primarily by connective tissue: ligaments, tendons, and fascia.

A typical ultrasound treatment will take from 3-5 minutes, depending on the size of the area being treated. Larger areas require duration of 5 minutes.

Duty cycles are the portion of treatment time that ultrasound is generated during the entire treatment or a Pulse ratio, which determines the proportion of time that the machine is ON compared with the OFF time. Some machines use ratios, and some percentage.

• In continuous US, the machine continuously generates ultrasound, giving 100% duty cycle and produces thermal effects.
• In pulsed US, a 50% duty cycle if the machine US generation (ON) have equal duration with machine in not generating US (OFF). This is a pulse ratio of 1:1.This is the nonthermal effects. 
• If the duty cycle is 20%, the US generated (ON) is 20% of the treatment, while the other percentage the machine is not generating US (OFF). This is the machine pulsed at a ratio of 1:4

Mode              Pulse Ratio                            Duty Cycle

Continuous                                                          100%

Pulsed                  1:1                                           50%

                             1:2                                           33%

                             1:3                                           25%

                             1:4                                           20%

                             1:9                                           10%

Phonophoresis

This is a non-invasive way of administering medications to tissues below the skin. This transdermal delivery of medication is recommended for patients who are uncomfortable with injections. Medications regularly used include anti-inflammatory agents or analgesics (cortisone). It is effective with both continuous and pulsed techniques.

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