CellSonic VIPP, Owner'S Manual

Page: 35 / 51

35
Principal of Shockwave Generation
There are three main techniques through which shockwaves are generated. These are elec-
trohydraulic, electromagnetic, and piezoelectric principles, and each of which represents a
different technique of generating shockwaves. Electrohydraulic principle represents the
first generation of orthopedic shockwave machine. Electrohydraulic shockwaves are high
-
energy acoustic waves generated by the underwater explosion with high - voltage electrode
spark discharge, and the acoustic waves are then focused with an elliptical reflector and
targeted at the diseased area to produce therapeutic effect [
26 ]. It is characterized by large
axial diameters of the focal volume and high total energy within that volume [ 27 ]. Shock-
wave generation through the electromagnetic technique involves the electric current pass-
ing through a coil to produce a strong magnetic field. A lens is used to focus the waves,
with the focal therapeutic point being defined by the length of the focus lens. The ampli-
tude of the focused waves increases by non
- linearity when the acoustic wave propagates
toward the focal point [ 26 , 27 ] Shockwave of piezoelectric technique involves a large
number (usually > 1,000) of piezocrystals mounted in a sphere and receives a rapid elec-
trical discharge that induces a pressure pulse in the surrounding water steepening to a
shockwave. The arrangements of the crystals cause self
- focusing of the waves toward the
target center, and lead to an extremely precise focusing and high - energy within a defined
focal volume. When comparing different shockwave devices, the important parameters
include pressure distribution, energy density and the total energy at the second focal point
in addition to the principle of shockwave generation of each device.
Shockwave pattern differs from ultrasound wave that is typically biphasic and has a peak
pressure of 0.5 bar. Shockwave pattern is uni
- phasic with the peak pressure as high as 500
bars [ 26 ]. In essence, the peak pressure of shockwave is approximately 1,000 times that of
ultrasound wave. There are two basic effects of shockwave. The primary effect is the di-
rect mechanical forces that result in the maximal beneficial pulse energy concentrated at
the target point where treatment is provided; and the secondary effect is the indirect me-
chanical forces by cavitation which may cause negative effect or damage to the tissues
[
26 , 27 , 28 , 29 , 30 ].
Mechanism of Shockwave Therapy
The mechanism of shockwave therapy is not fully understood. The most important
physical parameters of shockwave therapy for the treatment of orthopedic disorders
include the pressure distribution, energy flux density and the total acoustic energy. In
contrast to lithotripsy in which shockwaves disintegrate renal stones, orthopedic
shockwaves are not being used to disintegrate tissue, but rather to microscopically
cause interstitial and extracellular responses leading to tissue regeneration [
26 , 27 ].
Animal Experiments
Shockwave therapy for bone healing
Several studies had investigated the effects of shockwave therapy on fracture healing and
articular cartilage in animal experiments. Haupt et al in an experimental model in rats,
confirmed a positive effect of shockwave treatment on fracture healing [
31 ]. Johannes et
al showed the promotion of bony union with shockwave therapy in hypertrophic non -