CLASSIFICATION OF FSW VERSUS RPW
Generally speaking, there are two primary families of devices under the ESWT umbrella, the focused shockwave (FSW) and radial pressure wave (RPW) devices. While the two waves possess different physical characteristics, they generate similar results when treating various conditions in the musculoskeletal system with equivalent dosing. 2, 3
Definition of shockwave components and characteristics.
A FSW is a high intensity, low-frequency (1 to 8 Hz) wave that impacts tissue differently than therapeutic ultrasound (US). Therapeutic shockwaves are non-thermal waves that create mechanotransduction and in some cases cavitation in tissues as deep as 12 cm. 4, 8 FSW energy delivery is measured in mJ/mm 2 which is referred to as Energy Flux Density (EFD). EFD ranges between 0.01 and 0.55 mJ/mm 2 on Chattanooga FSW equipment. 5 Preferable dosing ranges exist when treating different conditions. For example, treating with extremely low energy levels (below 0.08 mJ/mm 2 ) has been shown to be ineffective and/or less effective than treating in higher energy ranges. 3, 9 On the other end of the spectrum, treating at energy levels >0.60 mJ/mm 2 has been shown to be deleterious to tendons. 9 Understanding correct dosing parameters and treatment approaches is imperative to achieving consistent results with this equipment.
Interpreting bar pressure vs energy flux density (EFD)
RPW devices are commonly measured in bar pressure. This is likely due to the pneumatic mechanism that generates pressure waves. Bar pressure should ideally be measured at the point where the applicator meets the skin to ensure accurate clinical relevance. 1 bar is equivalent to 14.5 psi. With the correct conversion factors, bar pressure can be converted to EFD. This allows for equivalent dosing parameters to be calculated when comparing RPW and FSW treatments of a given condition. An example of a radial pressure wave is pictured here next to a traditional focused shockwave for ease of comparison. Notice the differences in peak pressure, rate of the wave cycle, as well as the general shape of the 2 waves.
The physical impact of shockwaves can help improve the environment surrounding recalcitrant problems in muscle, calcific tendons, plantar fasciitis, as well as different connective tissues.
Image obtained from Reference 10 in the bibliography.
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