THE application of high-energy sound waves known as extracorporeal shock wave therapy (ESWT) has developed into a noninvasive technique that is used to stimulate and potentiate the inflammatory response while boosting circulation in the target area.
Two types of shock wave emitting devices are available and the two should be differentiated. Mclure in 2011 describes “true” shockwaves in the form of pressure waves that meet specific physical parameters including a rapid rise time (within nanoseconds), high peak pressure, and a more gradual decrease in pressure of a few milliseconds, often with a negative pressure component. Radial systems are less focused emitting radial pressure waves (RPWs), which provide significantly less energy, and dissipates as it travels through the tissue.
This article refers to the evidence relating to focused “true” ESWT devices. ESWT’s primary use in rehabilitation medicine is recognised both in human and veterinary fields where it has been successfully used to help heal soft tissue, tendon, muscle and bone injuries.
At present, due to the initial outlay, practical use and lack of client education in this area, clinicians may only be introduced to its benefits once injuries and wounds have failed to heal by more traditional means, but this may be about to change?
Development of ESWT
The science behind ESWT initiates from lithotripsy, a technology that uses targeted acoustic shockwaves to break up kidney stones.
In the process of treating many thousands of human patients, it was found that treatment did not just reduce the size of kidney stones, but also seemed to result in a marked decrease in non-related pain and discomfort.
Recent studies confirm that ESWT reduces inflammation (by potentiating its effect) and promotes tissue proliferation. It was at this point that scientists began to consider that shockwaves may have a beneficial effect on a wider range of tissue and applications.
Specialised machines were developed with the idea of using the effect of shockwaves on other parts of the body leading to the development of modern ESWT systems.
Use produced very satisfactory outcomes in the treatment of painful chronic conditions in humans such as tennis elbow and plantar fasciitis leading to use in veterinary practice for the treatment of tendon and ligament injuries, bone spavin, and navicular syndrome in horses.
How it works
It is a non-invasive therapy which uses high-energy sound waves that increase in pressure as they travel through living tissue. ESWT devices control and focus the shockwaves to such an extent that technicians are able to pass them through healthy tissue to deliver mechanical pressure and tension force directly to the target area.
An increase in cell membrane permeability causes an increase in microscopic circulation to the tissues and the metabolism within the treated tissue.
A secondary effect is the production of “cavitation bubbles”: small empty cavities which expand to a maximum size, then collapse, like a bubble popping. As these bubbles burst, they create additional forces which stimulate the production of fibroblasts.
Improved blood supply and provision of tissue nutrients are important features of the healing process. It is believed that ESWT works by firing shockwaves repeatedly at tissue; creating microtrauma, it causes increased blood flow and encourages new blood vessel formation in the target area.
Studies have also shown that production of fibroblasts, crucial in the formation of extracellular matrix which enables collagen to form a healthy connective tissue framework and scar elasticity, are also stimulated by ESWT use.
ESWT has also been shown to have significant antibacterial effects, which has exciting clinical implications for managing chronic, non-healing wounds. The shock waves appear to weaken protective barriers of bacterial cells, thus diminishing microbial contamination and reducing the risk of infection.
ESWT’s use in wound care is proving remarkably effective in the treatment of deep partial/full thickness burns, due to its ability to increase perfusion, stimulate growth factors and reduce inflammation. Alongside its antimicrobial effect, ESWT can mediate the body’s acute response to a severe or chronic burn, allowing the wound to heal appropriately.
Additional studies have demonstrated that ESWT increases tissue flap survival by altering free radicals, preventing leukocyte infiltration and tissue apoptosis (cell death) major factors in acceleration of healing.
The exact mechanism of action of ESWT for wound healing is likely to be complex and is still under investigation, but there are to date compelling clinical signs that the treatment causes a substantial localised increase in specific proteins associated with wound healing which include proliferating cell nuclear antigen (PCNA), endothelial nitric oxide synthase (eNOS), and vascular endothelial growth factor (VEGF), all of which are key elements in process of neovascularisation – the formulation of new capillaries.
An additional benefit to ESWT is a localised analgesic effect at the treatment site, which lasts for several days following treatment. The analgesic effect is created by stimulating the nerves to deactivate pain impulses sent to the brain. It is recommended that horses treated with ESWT should be rested for several days after treatment to avoid inadvertent re-injury due to the anaesthetic effect.
The provision of a bio-chemical effect that initiates proliferation of new blood vessels, release of growth factors, and facilitating the healing process in damaged tissue is clearly valuable.
ESWT has been shown to have a positive effect on healing rates in chronic wounds, and may further have a useful potentiation effect for wounds.
Whilst the exact mechanism of action of ESWT for wound healing continues to be investigated, it has been demonstrated clinically that ESWT results in improved quality and speed of healing and may as a result have an important role as an adjuvant therapy in wound healing.
In any injury, the physiological response involves the inflammatory process as a precursor to proliferation of new tissue. The early inflammatory response begins within hours and brings with it an influx of proteins, chemical messengers and leukocytes that will begin to remove any potential barriers to healing. This inflammatory event will be superceded by a later, more prolonged inflammatory phase which can become chronic.
Rehabilitation medicine’s focus has a significant emphasis on the treatment and rapid resolution of inflammation in order for tissue to heal more rapidly, to preserve function and reduce scarring, while minimising pain.
The development of clinical tools that stimulate a rapid and efficient progression through inflammation has been an area of considerable development in the past two decades. The application of shockwave energy is a popular choice for human, and veterinary, medicine as a result.
- List of references available on request.