Since the 1990s, extracorporeal shock wave therapy, or ESWT, has been considered by physicians as an effective form of treatment for certain musculoskeletal injuries and problems where other more conventional options have not been successful. 

But how safe is ESWT? Whilst generally deemed a safe form of therapy, there can be some side effects associated. In this article we will explore what ESWT is, how it works, and what the potential side effects and risks can be. 

What is extracorporeal shock wave therapy? 

Extracorporeal shock wave therapy, or EWST, was originally developed from the concept of extracorporeal shock wave lithotripsy, a non-invasive method used to break down kidney stones using shock waves.¹

Since the beginning of the nineties, it has been recommended as a safe treatment option for tendinopathies (tendon disorders) and other disorders in the musculoskeletal system.²

Some of the disorders often treated with ESWT are plantar fasciitis (pain in the heel), tennis elbow (lateral epicondylitis), calcific tendonitis (calcium build-up in the tendons that becomes inflamed) and certain types of osteonecrosis (also called avascular necrosis – when bone tissue dies due to a disrupted blood supply).³

It has also been deemed an effective way of healing bones and therefore can be used to treat a condition called ‘nonunion’ – referring to when bones fail to heal following a break – or to treat ‘delayed union’ – when the healing of a fracture takes longer than is normal or expected.³

In general, expert research and literature show that extracorporeal shock wave therapy can be a very useful treatment when other non-invasive/non-surgical treatment options have not been effective.²

Aside from suiting patients who have not had success with other non-surgical options, it can also be a good treatment choice for those who do not wish to undergo surgical treatment for various reasons.⁴

Forms of extracorporeal shock wave therapy 

There are two forms of ESWT that can be delivered: 

• Focused shock wave therapy, or F-SWT, provides a wide field of waves which come together and focus on one particular area within the body. This can be delivered through an electrohydraulic, electromagnetic, or piezoelectric device⁵
• Radial shock wave therapy, or R-SWT, does the opposite by generating high-pressure waves which weaken as they travel to the targeted area. This means that R-SWT produces slower waves⁶

Both forms have been proven to be effective. 

How does extracorporeal shock wave therapy work? 

The exact way in which ESWT works as a treatment is not fully understood. However, it is known that ESWT produces acoustic waves – shock waves – which carry energy through the body’s tissues to the target area. The energy can then cause certain responses within the body, leading to regeneration of tissues and pain relief.

The most notable ways it does this are by acting on nerve fibres to alleviate pain, encouraging the growth of blood vessels (vascularisation) to regenerate tissue and reducing calcium build-ups.⁴ All of which ultimately speeds up the time the body takes to heal. 

Usually, the ESWT process will take about five minutes. The practitioner will locate the source of pain by feeling around the area (palpating), mark the targeted area with a pen, apply contact gel and then begin to use the ESWT device. If you undergo ESWT, you will be required to go to three sessions spread over three weeks consecutively (National Health Service (NHS)). 

Who cannot have extracorporeal shock wave therapy?

While extracorporeal shock wave therapy is generally deemed a safe therapy, there are certain contraindications – situations or conditions – that mean somebody should not undergo this treatment. 

Among others, some listed by the NHS are:

• A latex allergy 
• Infection around the targeted area
• Pregnancy 
• A cardiac pacemaker 
• A recent cortico-steroid injection around the targeted area (three months)
• Open wounds or rashes around the targeted area
• Treatment with anticoagulants or a coagulation disorder 
• ESWT over lung tissue or ischemic tissue (tissue deprived of blood supply) if the patient has a vascular disease

How to access extracorporeal shock wave therapy

To access extracorporeal shock wave therapy through the NHS in the UK, you will need a referral from your general practitioner (GP). However, as ESWT is considered an effective treatment if other treatment options have failed, you will need to have tried other forms of therapy beforehand, like physiotherapy.

If you are referred by your GP, you will need to undergo a specialist assessment and likely some kind of imaging. 

Side effects of extracorporeal shock wave therapy 

In general, extracorporeal shock wave therapy has proven to be a very safe treatment option. There are not many side effects reported from patients – in fact, a review of studies on this showed that only 403 out of 1946 individuals with pain undergoing ESWT experienced side effects. With only 20.7% of individuals involved in the study reporting side effects, therefore, it appears that side effects are relatively uncommon.⁸ 

However, the side effects reported did include: 

• Pain during the treatment session around the targeted area (the most common reported side effect)
• Redness of the skin around the targeted area afterwards
• Dysesthesia: an abnormality in their touch sensations 
• Swelling around the targeted area following treatment 
• Bruising around the targeted area 
• Petechiae: little blood spots under the skin 
• Severe headaches after the treatment 
• A throbbing feeling around the targeted area

Very few patients experienced pain for longer than one week following the treatment.⁸

There have also been some reports of nerve irritation following ESWT, presenting as a feeling of numbness or a tingling sensation.⁵

Several factors can influence the likelihood of an individual experiencing pain as a side effect during the treatment session. For example, in studies which used high-dose ESWT, half of the patients reported feeling pain during the treatment. 

However, in studies using low-dose ESWT, just under a quarter of patients reported feeling pain during the treatment. This evidence suggests that you are less likely to experience pain during an ESWT treatment if the dose is lower. 

It has also been shown that administering a local anaesthetic can make pain during treatment less likely.⁵

Complications of extracorporeal shock wave therapy 

The current available research and literature surrounding extracorporeal shock wave therapy indicates that there is an almost negligible risk associated with this treatment, aside from the listed side effects, which generally resolve within one week.

On one hand, the NHS does state that there is a slight risk of damaging the recipient’s soft tissue or of rupturing a tendon or ligament. However, many studies conclude that long-term complications like this are virtually unreported and extremely rare. 

Extracorporeal shock wave therapy: risk vs benefit

As with any medical treatment, it is important to weigh up the associated risk and whether it is worth the proposed benefit. Your medical specialists will be able to discuss this with you regarding extracorporeal shock wave therapy. If you do not meet the contraindication criteria listed above, it is likely that ESWT will come with very minimal risks. 

The mild side effects which have been reported in various studies have not been proven to last longer than a week, and virtually no long-term complications have been reported in the relevant literature.⁸ 

If a patient has tried other treatment options for a musculoskeletal disorder and has not had any success, the potential for ESWT to be effective and therefore have a positive impact on their quality of life (if they are a safe candidate for it) far outweighs the negligible associated risks.

Summary 

• Extracorporeal shock wave therapy (ESWT) is a safe treatment option for musculoskeletal disorders when other non-invasive treatment options have not been successful
• Developed from the idea of extracorporeal shock wave lithotripsy (ESWL) – a non-invasive method to bread down kidney stones using shock waves
• Effective for certain disorders such as plantar fasciitis, lateral epicondylitis, calcific tendonitis and certain types of osteonecrosis
• Also useful for healing breaks and fractures where they are not healing as they should naturally
• ESWT can be delivered in 2 forms: Focused shock wave therapy (F-SWT) and Radial shock wave therapy (R-SWT)
• It works by sending shock waves through tissues to stimulate healing processes in the body
• Patients who are pregnant, have certain conditions, or are taking certain medications cannot undergo EWST
• Your GP can refer you for EWST if you are a candidate
• There are a few, uncommon side effects
• Side effects include pain during treatment, swelling/redness, bruising, headaches, nerve irritation, and throbbing sensations. 
• High-dose EWST may cause more pain than low-dose EWST but both are safe 
• Long-term complications are scarcely reported
• The potential benefits of EWST for the right patient can outweigh the mild side effects