The ultrasounds are acoustic waves with frequencies above 20 kHz (20,000 Hertz), the maximum frequency audible to the human ear (hence the name). These waves are generated by soliciting quartz with an electric field whose polarity is periodically reversed due to the electromagnetic field that is created. The quartz compresses and expands, generating mechanical vibrations that cause the acoustic waves of ultrasound.
Penetrating a biological system, the waves lose energy, transferring it to the system they pass through with an attenuation mechanism. The higher the frequency of the wave, the greater the attenuation (therefore it penetrates less deeply); generally, the waves enter up to depths between 1.5 and 5 cm.
The biological system can be a tendon, a muscle, or a bone. The release of energy is converted into heat, whose therapeutic properties have been well known for hundreds of years.
Ultrasound therapy is the application for the therapeutic purposes of this type of sound energy. The production of ultrasound is obtained by exploiting the piezoelectric effect, which is the property of some mineral crystals, to produce vibrations by compressing and decompressing when subjected to an alternating current field.
Tourmaline, topaz, quartz, which until recently was the most used, have piezoelectric properties.
The ultrasound therapy devices consist of a high-frequency current generator, a shielded cable, and an emitting head. They supply us with a frequency of 1MHz and/or 3MHz and output power, which is measured in Watts/cm (from 3 to 5 Watts) with continuous or pulsed mode.
The use of ultrasound for therapeutic purposes in orthopedics has been exploited since the mid-twentieth century. The heat-induced in the tissues is linked to the viscosity of the tissue, its composition, and thermal properties (conductivity). But heat transfer isn't the only effect. In fact, there is mechanical stress which produces a movement of the tissue molecules, inducing pressure variations. These allow the liquid to move inside the biological tissues and therefore have an effect in the presence of spills or to realign the collagen fibers.
The further effect of the acoustic waves that pass through a biological system is chemical, the pH and permeability of cell membranes are modified, facilitating the exchange and migration of liquids.
There are two techniques by direct contact (with the head of the appliance, always in contact with the skin, which is moved with a slow rotating or back and forth movement. A conductive gel is spread on the head, which allows better transmission of vibrations sound) or immersion (indirect contact), the latter particularly suitable when the areas to be treated are too small or painful.
If the water temperature drops, the effectiveness of the therapy is lost. Application times vary from 5 to 10 minutes for the contact mode, and from 10 to 15 minutes for the immersion mode. In the direct contact mode, the most used, if the area that needs treatment is well defined, small and limited, ultrasound can be delivered intermittently.
All these microscopic effects are physically proven, but the real effectiveness of ultrasound on real cases of tendon, muscle, or bone pathologies, for inflammations, hematomas or fractures is linked to multiple factors that are not always quantifiable.
Given the variability and uncertainty of these factors, It seems reasonable not to expect qualitatively striking healing results; the efficiency index of orthopedic ultrasound care is also quite low, which indicates that ultrasound is a soft therapy that tends to use the time effect to simulate healing.
Ultrasound is used essentially to reduce pain; they can be useful in sciatica, neuritis, periarthritis, tendinitis, tendinosis, tenosynovitis, epicondylitis, sub-acromial conflict of the shoulder, etc. Some argue that they can have a healing effect to break down calcifications.
According to some authors, in addition to the pain-relieving (analgesic) effect, other effects of ultrasound therapy are anti-edema (reduction of swelling), fibrinolytic, and relaxing.
Research from a few years ago showed some effect in reducing recovery times following fractures to the tibia, although the sample appears to be quite limited.
The concepts presented in this research have recently been reported in the non-specialist, but the popular, press, citing an unspecified American article in which the sample was decidedly larger (10,000 cases), also here confirming a decrease in order recovery times 38-40%.
NOTE - This would seem to contradict what was said above on the low-efficiency index of ultrasound. In fact, if you read the research, it turns out that ultrasound has been applied for a time and frequency (number of sessions per week) that it is unlikely to think that a normal patient can have. For example, for a given pathology in the research, the controlled subject undergoes treatment for a couple of hours a day every day (at intervals of 15′-20 ′), while your physiotherapist offers you three sessions of a quarter of an hour a week!
Ultrasound should not be used on the heart area, on the cephalic region, and on specialized tissues (testicle, ovary, fertile metaphyses, i.e., those that ossify later), which can be damaged.
Particular cautions must be taken when applying on the spine (vertebral column) of patients with laminectomy outcomes, for possible damage to the spinal cord.
In General, ultrasound should never be applied in the case of:
- high turnover osteoporosis
- presence of metal fragments
- joint prostheses
- varicose veins
- phlebitis and thrombophlebitis
- presence of pacemakers
- obliterating arteriopathies
- bleeding, menstruation
- neoplastic tissues
The biological effects of ultrasound are mainly -
- Mechanical: the vibration induces the oscillation of the tissue particles with the creation of micro-flows, splitting of complex molecules (proteins), and micro-massage.
- Thermal: the increase in temperature is a consequence of the mechanical friction effect of cellular structures and is proportional to the energy absorbed.
- Chemical: the destruction of bacteria, flocculation of colloids.
- Cavitation: formation of gas bubbles with the possible explosion of the same and destruction at a histological level. This phenomenon does not occur with the therapeutic dosages used.
- The resolution of muscle contractures due to the thermal effect and micro-massage.
- the fibrinolytic action due to the disruption of collagen in fibrous tissues and
- Trophic action induced by vasodilation with the elimination of catabolites and activation of cellular metabolism.
May 07, 2020