Focused Shock Wave and Radial Pressure Wave: A Comparison In recent years, the use of extracorporeal shock wave therapy (ESWT) in medicine of the musculoskeletal system has been described favourably many times. Success in many orthopaedic disorders such as epicondylitis, tendinosis calcarea, tendinitis of the Achilles tendon, fasciitis plantaris etc. has been documented in various studies. Some publications have, however, created the impression that the ballistic or radial pressure wave involves the same principle as the shock wave (ESWT). devices using a simple mechanical The focused shock hammer. The impact wave used in ESWT of the hammer diis a special acousrectly on the skin tic pressure wave deforms the tissue characterised by a and the pressure high positive preswave propagates disure amplitude and vergently (not focusan abrupt rise and ed) through the boshort pulse duratidy. In contrast to on. When the presfocused shock-wave sure wave amplitu- H. MĂźller-Ehrenberg, MĂźnster units, the highest des reach high vavalues of the pressulues (typically 20-100 MPa), the re and energy are achieved at the steepening pressure wave becocoupling point (proportionally mes a shock wave. Using shock 1/r2). The maximum effect on tissue is therefore at the surface of waves generated extracorporeally the skin. The energy coupled in allows non-invasive coupling of attenuates very quickly the further therapeutically effective energy it penetrates through the tissue. into the body over a large surface Even after a few millimetres, the area of the skin. This is then focupulse energy is so low that after sed accurately in the precisely reaching a penetration depth of 5delineated therapy zone (therapy 10 mm only a minimum, practifocus) in deeper lying tissue cally undetectable dosage is poswithout any detrimental effects to sible. the surface of the skin or surface tissue. The entire research into ESWT was undertaken using focused Pressure waves are generated ESWT devices. The previous stuballistically at the surface of the dies that demonstrated an effect skin by radial pressure wave Physical Principles
of ESWT in the tissue layers and at a cellular level were performed exclusively using focused ESWT devices. Apart from the effects of the mechanical pulse, the therapeutic effects that arise following the ESWT applications are the main benefits described in the discussions of focused shock waves. The most significant effects of ESWT are to be found at molecular-biological and cellular levels. These include neovascularisation, specific stimulation of bone growth, resorption of calcific deposits, alleviation of pain among other things due to the permanent suppression of the production of substance P etc. The precise mechanism by which effects are achieved with the radial pressure wave are not described. An unspecific stimulation similar to that of a good massage is conceivable by producing effects in the upper skin layers and spreading to the connective tissue.
Typical Values Focused shock-wave units: Peak pressure: 0-100 MPa Energy density: 0-2 mJ/mm2 Radial pressure wave devices: Peak pressure: 0-12 MPa Energy density: 0-0.3 mJ/mm2 Tab.: Typical Values for Focused and Radial Pressure Wave Devices
The application of this method is based on the principles of biological feedback and includes the most important diagnostic criteria. In 95% of patients, the diagnostic criteria referred pain and recognition can be ascertained with focused ESWT. This allows the existing MTrP to be diagnosed specifically. Following this highly accurate focused ESWT therapy, there was a highly significant improvement in pain within the course of treatment after six weeks. Summary
Focused shock waves of the ESWT devices on the other hand generate shock waves according to three different principles. The oldest method is the electrohydraulic spark gap principle with which the first extracorporeal stone fragmentation was performed. There are also the electromagnetic and piezoelectric methods. Piezoelectric systems have the advantage of high repetition accuracy and good dosability even at low energy ranges. Precise focusing is achieved that reduces or at least minimises side-effects in neighbouring tissue. Economic Aspects Piezoelectric devices also have significant economic advantages. There is no wear and tear on electrodes. This means that there are practically no costs for the user resulting from worn-out parts.
Shock Waves in Trigger Point Treatment An expansion of the indications for focused shock waves and radial shock waves is the treatment of the musculature and this has become a major focus of interest in treatment of the musculoskeletal system with respect to trigger point therapy. Following the principles of myofascial trigger points introduced by Travell / Simons more than 50 years ago and the definition of myofascial pain syndrome, it is clear that precise and specific procedures are necessary in both diagnostics and treatment. In particular, the diagnostic criteria referred pain and recognition are signposts both for the classification of myofascial trigger points in the mechanism of pain as well as for the precise treatment of the pain. Due to the physical properties of the focused shock wave, MTrP can be located precisely and treated with millimetre accuracy.
1. The shock wave (ESWT) and the radial pressure wave are two completely different physical principles in which the physical parameters such as pressure, energy density and energy are totally different (Tab). 2. The radial pressure wave works only on the superficial skin layers and cannot be applied with any accuracy. In contrast, the focused ESWT penetrates accurately into deep tissue layers bringing therapeutically beneficial energy. 3. With focused ESWT, trigger points can be diagnosed specifically and successfully treated. 4. Piezoelectric systems have the advantage of high repetition accuracy and good dosability even at low energy ranges. 5. From an economic perspective, there is nothing on the market comparable with the piezo shock wave source with its guaranteed working life of 5 million shock waves. Literature from author Author: Dr. med. H. MĂźller-Ehrenberg Specialist for orthopaedics Trigger point therapist IMTT Tibusplatz 6, 48143 MĂźnster or040500