The idea of using shockwaves in a medical context was first introduced in the 1970s with the goal of treating kidney stones (International Society for Medical Shockwave Treatment [ISMST], n.d.). Extracorporeal generated shockwaves were administered through a non- invasive device called a lithotripter to break up kidney stones and later gallstones (ISMST, n.d.). In 1985, the application of shockwaves expanded beyond urology into the field of orthopedics, specifically in the treatment of non-union fractures (ISMST, n.d.). In the early 1990s, this evolved to include tendinopathies and eventually other musculoskeletal conditions (ISMST, n.d.).
Currently, it is being used to treat plantar fasciitis (with or without heel spur), lateral epicondylitis of the elbow, calcific tendinitis of the shoulder, patellar tendinopathy, Achilles tendinopathy, delayed and non-union fractures and more (Wang, 2012). For several of these tendinopathies and osteopathic or musculoskeletal conditions, it is considered first choice treatment (Wang, 2012).
But what actually is a shockwave? A shockwave can be described as a sudden change in pressure, that travels very quickly through a medium (Chung & Wiley, 2002). It is defined by having a single pulse, a high pressure amplitude, a low tensile wave, a brief life-cycle (below 10 msec), a broad frequency spectrum and a negative pressure at the tail end (Chung & Wiley, 2002; Extracorporeal Shockwave Therapy [ESWT], 2021). The positive phase of the wave generates direct mechanical forces, while the negative phase creates cavitation and gas bubbles, producing another release of shockwaves (ESWT, 2021). An image demonstrating a single shock wave profile is included below.
There are three main technology types that produce focused shockwaves: electrohydraulic, electromagnetic and piezoelectric (Wang, 2012). The electrohydraulic principle was the first machine developed for orthopedic use (Wang, 2012). It is characterized as high-energy acoustic waves created by an underwater explosion with high-voltage electrode spark discharge (Wang, 2012). An elliptical reflector then focuses the acoustic waves to be directed at the injured area (Wang, 2012). The electromagnetic principle, on the other hand, uses a coil to transmit electric current, resulting in a strong electromagnetic field (Wang, 2012). The waves are then focused through a lens, with length of lens distinguishing the focal point (Wang, 2012). The piezoelectric technique uses a large quantity of crystals (typically over 1000), placed in a spherical formation (Wang, 2012). A high voltage pulse is applied to the crystals, making them expand, creating a pressure pulse in the encompassing water that builds to a steepening shockwave (Wang, 2012). The formation of the crystals naturally induces self-focusing of the waves to the target center, making it incredibly precise and high-energy (Wang, 2012). All of the three techniques use water as the medium along with a coupling gel, as the attenuation of the shockwaves weakens drastically in air (Chung & Wiley, 2002).
There are several parameters when it comes to the application of extracorporeal shockwaves. This includes energy level (low, medium, high), shockwave generation (focused or radial), application of anaesthetics, method of localisation, and principle of shockwave generation (van Leeuwen et al., 2009). This is dependent on the type and area of injury, as well as resources and time (van Leeuwen et al., 2009). The exact mechanism or effects of extracorporeal shockwave therapy is not fully known (ESWT, 2021). It is proposed that ESWT does the following: increases blood flow to the targeted site, stimulates proliferation of tenocytes (tendon cells), raises leukocyte infiltration and enhances growth factor and protein synthesis, generating new collagen and tissue remodelling (Chung & Wiley, 2002; ESWT, 2021). One theory states that ESWT could have an initial analgesic effect through modification of the permeability of neuron cell membranes (Chung & Wiley, 2002).
There is considerable evidence that supports the use of ESWT for tendinopathies and bone healing (Wang, 2012; Kudo et al., 2006). However, some studies have also reported little to no effect (Wang, 2012). In a review by Wang (2012), it is stated that the highest success rate of shockwave therapy was seen with calcific tendinitis of the shoulder, producing a rate of 78% - 91%. Several studies have shown a significant decrease in pain, complete or partial elimination of the calcium deposits and improved range of motion in the majority of participants receiving treatment compared to the control group (Wang, 2012). Rompe et al. (2001) stated that ESWT offers similar or better outcomes than surgical intervention for the treatment of calcific tendonitis of the shoulder. With reference to plantar fasciitis, many studies have demonstrated positive results in alleviating pain and improving overall function (Wang, 2012). In a randomized, placebo-controlled, double-blind study, representing the highest level evidence, significant change was recorded between the intervention and placebo group in the primary outcome measure of pain (Kudo et al., 2006). There was also a statistically significant difference between the number of intervention and placebo participants that achieved the clinical success criteria (> 60 % improvement in pain scores 3 months since baseline) (Kudo et al., 2006). The treatment of plantar fasciitis using ESWT has been recorded as a safe and effective intervention with minimal complications (Kudo et al., 2006; Wang, 2012).
Despite this, there have been some studies that have reported opposing or varying results, with little to no difference seen between intervention and placebo groups (Wang, 2012). Many factors can influence this discrepancy including energy levels, patient selection, treatment frequency and product type, highlighting the importance of standardization. A similar response was seen in the literature surrounding the treatment of lateral epicondylitis with ESWT (Wang, 2012). Overall, a positive effect was shown, however there was still some contradictory results, which may be attributed to the factors previously described (Wang, 2012). Research regarding the use of ESWT in bone disorders (non-union and delayed fractures) shows effects akin to surgical intervention (Wang, 2012). This holds great benefit as ESWT does not pose the same risks as surgery, as well as resources.
Overall, ESWT presents a safe and effective treatment intervention for musculoskeletal conditions and bone disorders. It shows significant effects in terms of pain management, function and range of motion. It also presents as a strong alternative to surgery or other invasive treatments, saving time and resources. Moving forward, more research is needed regarding effective protocols for different injury types and manufactured devices, as well as further standardization to help eliminate inconsistencies in the literature.
References
Chung, B., & Wiley, J. P. (2002). Extracorporeal shockwave therapy. Sports Medicine, 32(13), 851-865. https://doi.org/10.2165/00007256-200232130-00004
Extracorporeal Shockwave Therapy (ESWT). (2021, October 28). Physiopedia. Retrieved January 27, 2022 from https://www.physio-pedia.com/index.php?title=Extracorporeal_Shockwave_Therapy_(ESWT)&oldid=284313.
Kudo, P., Dainty, K., Clarfield, M., Coughlin, L., Lavoie, P., & Lebrun, C. (2006). Randomized, placebo‐controlled, double‐blind clinical trial evaluating the treatment of plantar fasciitis with an extracorporeal shockwave therapy (ESWT) device: A North American confirmatory study. Journal of Orthopaedic Research, 24(2), 115-123. https://doi.org/10.1002/jor.20008
Rompe, J. D., Zoellner, J., & Nafe, B. (2001). Shockwave therapy versus conventional surgery in the treatment of calcifying tendinitis of the shoulder. Clinical Orthopaedics and Related Research, 387, 72-82. https://doi.org/10.1097/00003086-200106000-00010
The International Society for Medical Shockwave Treatment. (n.d.). Shockwave History. https://www.shockwavetherapy.org/about-eswt/shockwave-history/
van Leeuwen, M.T., Zwerver, J., & van den Akker-Scheek, I. (2009). Extracorporeal shockwave therapy for patellar tendinopathy: a review of the literature. British Journal of Sports Medicine, 43(3), 163-168. http://dx.doi.org/10.1136/bjsm.2008.050740