Physics and technology of shock wave and pressure wave therapy

Extracorporeally generated shock waves were first used for kidney stone fragmentation in 1980 and have since become the method of choice for most kidney and ureteral stones. More than 10 years later, shock waves were successfully utilized for the treatment of several musculoskeletal diseases. Shock waves are mechanical waves passing through the surface of a body without causing injury and may act therapeutically in predetermined areas within the body. Shock wave generation makes use of different principles, one of them is the electromagnetic system. They are focused using acoustic lenses or reflectors. Important parameters are pressure, energy, energy flux density and different definitions for focal and treatment areas. Besides mechanical effects on acoustic interfaces, cavitation bubbles are generated which, in turn, cause needle-like punctures at interfaces. Due to both effects, fragmentation of brittle material such as kidney stones and stimulating effects such as the generation of action potentials of nerve cells take place. Biological reactions of liberation of different agents are reported. Shock waves are successfully applied to increase local blood circulation and metabolism, although the biological working mechanism is still incompletely known. Final healing is considered to be the result of these effects.