What are the effects of shock wave therapy?

Posted on | by Cliff Eaton

Shock wave therapy – a term that continues to be used to encompass both focused shock wave and radial pressure wave therapies – can be used to stimulate the body’s natural healing process, with positive effects demonstrated on bone and tendon repair and tissue regeneration1. But how does this work?

Both focused shock waves and radial pressure waves influence cellular activity by mechanotransduction, where the mechanical energy of an acoustic wave is converted into biochemical energy in the cell and extracellular matrix1.

With focused shock wave (F-SW) therapy, this is primarily achieved through the effects of cavitation, whereas radial pressure wave (RPW) therapy uses pressure waves to cause cellular change.

What is cavitation?

Cavitation occurs during the tensile phase of a shock wave. The negative pressure created by the wave generates gas-filled bubbles in water at room temperature, which are normally only seen in boiling water.

When these bubbles are concentrated in a small area, such as in F-SW therapy, they generate secondary pressure waves in a process known as “stable cavitation.” When the bubbles burst, they release energy at the focal point of the application. This “microtrauma” stimulates the body’s self-healing ability and leads to tissue regeneration2,3.

If the bubbles are encouraged to expand, they will continue to store energy until they become so large that they implode, releasing a large amount of energy in a microjet. This is known as “unstable cavitation,” and can be used to break down kidney stones4,5.

While some cavitation also occurs during RPW therapy, the level is only superficial, and not thought to be significant.

How shock wave therapy helps the body to heal

F-SW and RPW therapies are pro-inflammatory modalities which can be used to “reboot” the healing process in stalled, chronic conditions1.

The normal healing process of the body occurs in four stages. First the body responds to injury by bleeding, which is then followed by inflammation. Within a few hours to days, the third stage begins, known as proliferation, where new tissue is created to rebuild the wound. Finally, after a few weeks, the remodelling stage starts, during which the wound fully closes.

Of all these stages of the healing cascade, the most important is inflammation. Without it, proliferation and remodelling will not take place. In chronic conditions, something has gone wrong during the later proliferation and remodelling stages of the normal healing process, preventing it from progressing. Like a computer with a serious error, this process needs to be rebooted for progress to be made by using the pro-inflammatory action of F-SW or RPW therapy.

Other physiological effects of shock wave therapy

Along with its influence on inflammation, shock wave therapy has been shown to have a number of other physical effects on the body:

New blood vessel formation

Due to microtraumas caused by shock wave therapy, there is a significant increase in the expression of growth factors such as eNOS, VEGF, PCNS and BMP. These growth factors are involved in the process of neovascularization, where arterioles are stimulated to form and grow, which has a positive effect on improved blood supply, bone and tendon repair, and tissue regeneration6.

Collagen production

Shock wave therapy stimulates procollagen synthesis, necessary for the repair of damaged musculoskeletal and ligament structures. It forces the newly created collagen fibers into a longitudinal structure, making the newly formed tendon fibers denser and stiffer, with a firmer structure7.  

Tenocyte proliferation

Shock wave therapy leads to an increase in transforming growth factor beta 1 (TGF-β 1), which is known to regulate tendon repair8.

Fibrotic tissue and scar remodelling

Shock wave therapy alters the expression of fibrosis-related molecules in fibroblasts, which affects scar remodelling and resorption1.

Osteoblast and osteoclast activity

Alongside TGF-β 1, fibroblast growth factor 2 (FGF2) is also increased by shock wave therapy, and together they are influential in bone healing1,9.

Analgesia

RPW therapy has a confirmed effect in improving the symptoms of pain10.

Reducing hypertonia in spastic muscles

Both F-SW and RPW have been proven effective here11, with RPW particularly effective in aiding increased range of movement12.

To learn more about the effects and applications of shock wave therapy:

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References

  1. d’Agostino MC, Craig K, Tibalt E, Respizzi S. Shock wave as biological therapeutic tool: From mechanical stimulation to recovery and healing, through mechanotransduction. Int J Surg. 2015 Dec;24(Pt B):147-53. 
  2. Ogden JA, Tóth-Kischkat A, Schultheiss R. Principles of shock wave therapy. Clin Orthop Relat Res. 2001 Jun;(387):8-17.
  3. Császár NB, Angstman NB, Milz S, Sprecher CM, Kobel P, Farhat M, Furia JP, Schmitz C. Radial Shock Wave Devices Generate Cavitation. PLoS One. 2015 Oct 28;10(10):e0140541.
  4. Chaussy C, Brendel W, Schmidt E. Extracorporeally induced destruction of kidney stones by shock waves. Lancet 2:1265–1268, 1980.
  5. Streem SB. Contemporary clinical practice of shock wave lithotripsy: a reevaluation of contraindications. J Urol. 1997 Apr;157(4):1197-203.
  6. Wang CJ, Wang FS, Yang KD. Biological mechanism of musculoskeletal shockwaves. ISMST Newsletter 2006, 1 (I), 5-11.
  7. Vetrano M, d’Alessandro F, Torrisi MR, Ferretti A, Vulpiani MC, Visco V. Extracorporeal shock wave therapy promotes cell proliferation and collagen synthesis of primary cultured human tenocytes. Knee Surg Sports Traumatol Arthrosc. 2011 Dec;19(12):2159-68.
  8. Berta L, Fazzari A, Ficco AM, Enrica PM, Catalano MG, Frairia R. Extracorporeal shock waves enhance normal fibroblast proliferation in vitro and activate mRNA expression for TGF-beta1 and for collagen types I and III. Acta Orthop. 2009 Oct;80(5):612-7.
  9. Frairia R, Berta L. Biological effects of extracorporeal shock waves on fibroblasts. A review. Muscles Ligaments Tendons J. 2012 Apr 1;1(4):138-47.
  10. Rompe JD, Hope C, Küllmer K, Heine J, Bürger R. Analgesic effect of extracorporeal shock-wave therapy on chronic tennis elbow. J Bone Joint Surg Br. 1996 Mar;78(2):233-7.
  11. Dymarek R, Ptaszkowski K, Ptaszkowska L, Kowal M, Sopel M, Taradaj J, Rosińczuk J. Shock Waves as a Treatment Modality for Spasticity Reduction and Recovery Improvement in Post-Stroke Adults – Current Evidence and Qualitative Systematic Review. Clin Interv Aging. 2020 Jan 6;15:9-28.
  12. Marinelli L, Mori L, Solaro C, Uccelli A, Pelosin E, Currà A, Molfetta L, Abbruzzese G, Trompetto C. Effect of radial shock wave therapy on pain and muscle hypertonia: a double-blind study in patients with multiple sclerosis. Mult Scler. 2015 Apr;21(5):622-9.