Extracorporeal Shock Wave Therapy (ESWT) is a conservative treatment modality with still growing interest in musculoskeletal disorders. This narrative review aims to present an overview covering 20-year development in the field of musculoskeletal ESWT. Eight historical paradigms have been identified and put under question from a current perspective: energy intensity, focus size, anesthesia, imaging, growth plates, acuteness, calcifications, and number of sessions. All paradigms as set in a historical consensus meeting in 1995 are to be revised. First, modern musculoskeletal ESWT is divided into focused and radial technology and the physical differences are about 100-fold with respect to the applied energy. Most lesions to be treated are easy to reach and clinical focusing plays a major role today. Lesion size is no longer a matter of concern. With the exception of nonunion fractures full, regional, or even local anesthesia is not helpful in musculoskeletal indications. Juvenile patients can also effectively be treated without risk of epiphyseal damage. Further research is needed to answer the question about if and which acute injuries can be managed effectively. Treatment parameters like the number of sessions are still relying on empirical data and have to be further elucidated.
Explosive events in nature (e.g., lightning stroke) and technics (e.g., airplanes breaking through the sound barrier) create shock waves. In principle, these acoustic waves transmit energy “from the point of generation to remote regions.” The principle of this natural phenomenon has been transferred to medical application. “Shock and pressure waves are pulses, while ultrasound is a continuous oscillation” [
Starting in 1980, extracorporeal shockwaves were applied transcutaneously for the first time in medicine to destroy a kidney stone in a human [
In the early 2000s, devices featuring ballistic pressure waves were introduced into the Extracorporeal Shock Wave Therapy (ESWT) market. These waves are produced mechanically by a compressed air driven projectile which hits the applicator. This technology is since named radial ESWT (rESWT). The respective devices are much cheaper, smaller, and easier to handle. However, the maximum rESWT energy is delivered at the applicator to skin interface and focused shock waves peak pressure is about 100 times higher while the pulse duration is 1000 times shorter [
This review paper updates the current knowledge with respect to the historical paradigms as set in 1995 [
This narrative review presents eight different ESWT paradigms which were extracted from a historical German consensus meeting held in 1995. We evaluated if these paradigms are still true after 20 years of further development of the method.
Historically, most research related to musculoskeletal ESWT literature was published in German language and in books or journals which are not referenced in Medline. Therefore, a systematic search was judged not to be a reasonable approach.
The bases for the current investigation are the authors’ databases, containing both historical Medline listed papers on ESWT and also historical ESWT articles which were published in German language. The content of these articles is further reported.
For each of the eight individual paradigms, the historical background is addressed. Developments over time and recent perspectives to these topics were analysed also from the authors’ literature databases.
Historically, the companies provided the users with different specifications of the used energy levels, some of them used the applied energy flux density (ED), and others used the voltage (kV) led into the device to produce the shock waves. In particular, the description of the voltage is device depending and therefore a comparison between different technologies (devices from different producers) is meaningless. So the convention was made to use ED (mJ/mm2) as the comparable parameter. It turned out that it is not enough to look at only one parameter. So it is no wonder that there are many conflicting publications due to the different energy descriptions [
Beside the well-known shock wave effect of disintegration of concrements, a stimulation of fibrous tissue could be demonstrated to occur and this different biologic mechanism was dose-dependent [
Consequently and already in the early 1990s musculoskeletal ESWT was divided into “low” (0.08–0.23 mJ/mm2) and “medium” (14–18 kV) energy applications [
Historically, ESWT was performed with lithotripters and also the first generation of musculoskeletal ESWT devices was based on the focused technology. Respectively, maximum energy was applied to a small area 5–10 cm below the applicator and this energy was concentrated in an area with a diameter of 5–10 mm [
At that time, the fact that relevant energy is also measurable peripherally to the focal zone was neglected. Accepted indications were nonunion fractures, plantar fasciitis, tennis elbow, and calcific shoulder tendinopathy [
In a next step, rESWT was applied to treat more complex musculoskeletal symptoms associated with trigger points. The underlying mechanism of action is explained by the concept of myofascial pain [
Anesthesia allows applying shockwaves with higher intensities. Derived from kidney stone and nonunion fracture experience, high energy was proposed for orthopedic ESWT indications [
Nowadays, (local) anesthesia is still regarded as helpful for bone indications [
Meanwhile, there is evidence from experimental research that the pain producing effect of ESWT is responsible for the release of neuropeptides (like substance P) initiating both central and local trophic effects to increase metabolism in bradytrophic tissues [
At the beginning of the orthopedic shock wave era, it was generally agreed that focal degenerative lesions within the injured tissues are responsible for the painful syndromes and should be exactly targeted by ESWT. Therefore, visualizing aiming devices were demanded [
Initiation of the ESWT technology to treat Olympic athletes during the 1996 Olympic Games in Atlanta.
That new technology produced pressure waves and not real shock waves, but the term radial shock wave was generally agreed upon and is used since [
Users and investigators found out that aiming at the most painful area was sufficient or even superior to aiming just at an anatomically given landmark which was identified by imaging. This procedure has consequently been demonstrated to be superior and was termed “biofeedback” [
Actually, focusing by biofeedback is also the cornerstone for myofascial trigger point ESWT [
In an experimental study on proximal rat tibiae, dysplastic lesions could be identified following high energy fESWT (20 kV, 1500 shock waves) [
Only two years later, another animal study was published demonstrating no negative histological differences comparing fESWT effect with the untreated contralateral femoral head of immature rabbits [
Even if initially mentioned anecdotally already in 1995 [
When introducing musculoskeletal ESWT, it was declared to be indicated for chronic injuries. The reason for this was that in general a new treatment modality should provide evidence before being spread out to the public, and, as long as the evidence is missing, it should be recommended only for patients, who already have been treated by other options. This means that three months of conservative treatment should have been performed without success before ESWT is indicated as an alternative to operative treatment [
If ESWT can be relevant to effectively treat acute muscular or tendon strains is currently not known and respective research is needed.
Historically, only mechanical (and not biologic) ESWT effects were regarded as relevant in medicine. At the transmission through tissues with similar acoustic properties (soft tissue) a minor amount of energy is released. It was assumed that the resulting mechanical effect is negligible. In contrast, high acoustic impedance differences exist between cortical bone (6.12 × 106 kg/m2s) and soft tissue (e.g., muscle = 1.66 × 106 kg/m2s). ESWT consequently releases a large amount of mechanical energy at the interface. This concept was the rationale not only to treat kidney stones but also to treat soft tissue calcifications [
These treatment principles were held until the invention of the rESWT with a completely different technology. Historically, the main differences between fESWT and rESWT are as follows: (a) principle of generation = pneumatic rESWT versus electrohydraulic, piezoelectric, or electromagnetic fESWT, (b) wavelength = 0.15 to 1.5 m (rESWT) versus 1.5 mm (fESWT), and (c) maximum pressure = 1 (rESWT) versus 10–100 (fESWT) MPa and penetration depth = 2–5 cm (rESWT) versus 5–20 cm (fESWT) [
As a result, rESWT was applied to tendon lesions, featured by their immediately subcutaneous localization and by a large area of injured tissue. Midportion Achilles tendinopathy and patellar tendinopathy fulfil these criteria and have been demonstrated to be an indication for rESWT [
The number of required treatment sessions is a relevant parameter in principle. Recently, systematic research recommends “three treatment sessions at 1-week intervals, with 2000 impulses per session and the highest energy flux density the patient can tolerate” [
Recently, there have been a few reports which retrospectively addressed the number of rESWT sessions needed to treat soft tissue pathologies such as trigger digits, symptomatic calcified shoulder tendinopathy, and plantar fasciitis. These studies revealed that pretreatment symptom duration was significantly correlated with the number of rESWT sessions applied [
Discussion is still going on about which parameters or which combination of parameters should be used to maximize the effect of ESWT treatment for a specific indication. In this context, it has to be mentioned that comparability of studies should not be reduced on one single parameter (e.g., energy flux density).
In clinical practice, ESWT is rarely used as a monotherapy. Strategic loading and/or exercises are usually prescribed in addition to shock waves, a fact that in general RCTs have not adequately addressed. An individualized intervention should be considered depending initially on the type and characteristics of the pathology [
The most important finding of this review is that all historical paradigms as set for musculoskeletal ESWT in 1995 did not withstand the technical and clinical developments over the last 20 years. The initial phase of the musculoskeletal ESWT was driven by side effect research in context with lithotripsy investigation and the first orthopedic applications have been performed by urologists [
At the beginning of the musculoskeletal shock wave age it was thought that the higher the energy is, the better the outcome would be. For soft tissue pathologies it was early realized that lower ESWT intensities are able to induce tissue regeneration instead of necrotic reactions [
There are an increasing number of high quality ESWT studies for musculoskeletal conditions published in the literature. It can be summarized without exaggeration that ESWT is the best analyzed treatment modality in the orthopedic field. This statement includes also operative interventions. A recent systematic musculoskeletal ESWT review concludes that there is more need for high level studies [
Until now, clinical ESWT research is aiming exclusively at detecting the success of ESWT applied following a standardized protocol. The question, however, if ESWT is similarly effective in each stage of a given musculoskeletal indication is completely unanswered up to date. For instance, a “tendon pathology continuum model” has been described [
With the exception of bone related conditions, modern musculoskeletal ESWT is performed with energy below 0.28 mJ/mm2 and without anesthesia. The size of the tissue area to be treated can be small or large. “Biofeedback” is superior to imaging guided focusing. ESWT application in apophyseal osteochondral lesions in patients with open growth plates seems to be promising and safe. ESWT protocols should be adapted to the stage and chronicity of the treated pathology.
Heinz Lohrer received fees for lecturing from Storz Medical AG, Tägerwilen, CH. Employment of Tanja Nauck was partially paid by Storz Medical AG, Tägerwilen, CH.
The authors are grateful to Ms. Grainne Mc Ginley for her valuable help in language editing of the paper as a native English speaker. The authors are grateful to Storz Medical, Lohstampfestrasse 8, 8274 Tägerwilen, Switzerland, for funding the open access publication article processing charge.