Physical Basics of Shockwave Therapy

The Encyclopedia Britannica online (www.britannica.com) definition of shock wave is “a strong pressure wave in any elastic medium such as air, water, or a solid substance, produced by supersonic aircraft, explosions, lightning, or other phenomena that create violent changes in pressure. Shock waves differ from sound waves in that the wave front, in which compression takes place, is a region of sudden and violent change in stress, density, and temperature. Because of this, shock waves propagate in a manner different from that of ordinary acoustic waves. Shock waves travel faster than sound and their speed increases as the amplitude is raised. Furthermore, the intensity of a shock wave also decreases faster than does that of a sound wave because some of the energy of the shock wave is expended to heat the medium in which it travels. The amplitude of a strong shock wave, as created in air by an explosion, decreases almost as the inverse square of the distance until the wave has become so weak that it obeys the laws of acoustic waves. Shock waves alter the mechanical, electrical, and thermal properties of solids and thus, can be used to study the equation of state (a relation between pressure, temperature, and volume) of any material”.

Generation of Shockwave

The illustration shows that there are apparently very different devices. These differences are due to the different ways in which shock waves are generated. The shock waves are generated for medical applications in a therapy head and coupled by means of a usually flexible coupling piece in the form of a membrane or a three-dimensional body. To achieve a suitable coupling, it is necessary to introduce a coupling medium such as ultrasonic gel between the interfaces. Otherwise even the smallest air bubbles will interfere with the propagation of the sound. Since any layer of air effectively prevents the propagation of the shock waves.

Differences Between Shockwave Therapy & Ultrasound Therapy

  1. Therapeutic ultrasound utilizes high frequency sound waves, while ESWT utilizes lower frequency waves.
  2. Ultrasound may produce either thermal or non-thermal effects in tissues, while ESWT does not result in heating effects.

Similarities Between Shockwave Therapy & Ultrasound Therapy

  1. Both modalities employ acoustic waves to produce therapeutic benefits.
  2. Both make use of a coupling medium to transmit sound waves to the tissues being treated.
  3. Both are non-invasive forms of treatment.

Evidence-Based

According to a study performed by Rompe and coworkers[17], stretching exercises in combination with radial shock wave therapy is more efficient for the treatment of chronic symptoms of proximal plantar fasciopathy than repetitive radial pressure wave therapy alone. Patients were subjected to three sessions of 2000 radial pressure pulses (EFD = 0.16 mJ/mm 2) in weekly intervals, generated with a ballistic device (air compressor pressure 4 bar; rate 8 Hz) manufactured by Electro Medical Systems.

A study to investigate the clinical outcomes of ESWT on calcaneal spurs of 108 patients and its correlation with radiologic changes were reported by Yalcin et al. All the patients underwent radial pressure wave therapy once a week for 5 weeks (2000 pressure waves starting at an EFD of 0.05 mJ/mm 2 and increasing up to 0.4 mJ/mm 2). After the therapy, approximately 67 % of the patients reported no pain; however, there was no correlation between clinical outcome and radiologic changes. The authors concluded that even without radiologic change.