LIPUS (Low intensity pulsed ultrasound)
Ultrasounds are elastic waves with frequencies higher than the audible ones covering a wide range of frequencies. The frequencies used in physiotherapy are typically between 0.8 and 3.5 MHz. Ultrasounds intensity in physiotherapy (time peak value) ranges from 0.1 to 2 W/cm2 (in the US), and up to 3 W/cm2 (in Europe).
Biological action – low intensity ultrasound
In physiotherapy, a longitudinal ultrasound wave is used. The wave carries energy which, when absorbed by the tissue, is converted into heat. It also causes non-thermal effects in the form of cavitation, tension mechanisms, microfluidic flows. The greatest amount of ultrasound energy is absorbed in human tissues with a high content of proteins, such as tendons and articular cartilage.
The biological effect of ultrasound is the resultant of thermal, mechanical and physicochemical effects.
Ultrasounds in physiotherapy (LIPUS)
There is growing interest in the use of low-intensity pulsed ultrasound (LIPUS) in therapy. Low-intensity ultrasound is emitted in pulsed form with an average power [SATA] of up to 0.1 W/cm2 (100 mW/cm2), low frequency – usually 1.5 MHz, short duty cycles of 20%, pulse repetition rate of approximately 1 kHz. The ultrasound head remains in place during the treatment, the so-called stationary method. These parameters (low-intensity ultrasound) are very different from those used for thermal interventions. These are based on acoustic intensities that are 1-4 times higher than LIPUS.
Low-intensity ultrasounds have no thermal or destructive effects and accelerates the healing of open wounds, as well as tendons, nerves and bones. They support the healing of acute and subacute inflammatory conditions.
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Low-intensity ultrasound in fractures
Recent studies have shown that low-intensity ultrasound has a positive effect on the recovery of connective tissue in general and on bone tissue in particular.
Overview image of a bone fracture:
Laboratory experiments and animal studies have shown that they have a significant stimulating effect on bone growth. LIPUS has been shown to accelerate the healing of cortical and sponge bone fractures, as well as delayed bone fusion.
Bone fusion phase – overview image:
The study results suggest a stimulating effect of LIPUS on: osteoblasts, adult mezynchymal cells and chondrocytes. The location of the fracture and the spread of the ultrasound wave mean that the effects of low intensity pulsed ultrasound stimulation vary and depend on the depth of the fracture. The superficial effects of LIPUS stimulation of bone contribute to the formation of new ostein. The deep ones, on the other hand, improve the mineralisation of the newly formed bone tissue.
Complete bone fusion phase – overview image:
Literature data support the positive effect of LIPUS stimulation on the osteogenesis of non-diseased tissue.
LIPUS – low-intensity ultrasounds are also being used more and more in physiotherapy. Most commonly to treat soft tissue injuries, stimulating increased perfusion to the site of injury.