Introduction

Overview of tennis elbow (lateral epicondylitis)

Tennis elbow (also known as lateral epicondylitis) is a painful condition affecting the outermost aspect of the elbow. The term epicondylitis is misleading, as rather than being inflammatory in nature, the condition results from repeated mechanical damage to the tendons of the forearm muscles at their point of insertion into the bone. Overuse of the forearm muscles leads to microscopic tears forming within the tendon.¹ The condition was first described in tennis players in the late 19th century and affects up to half of all regular players. It is generally found in late to middle age, and despite its name, tennis players do not make up the majority of cases. Most commonly, it is found in those performing forceful, repetitive movements, often in an industrial setting.¹

Extracorporeal shockwave therapy (ESWT)

Extracorporeal shockwave therapy (ESWT) involves the use of pulsed acoustic waves to deliver energy directly to the tissues. Commonly used in the treatment of kidney stones, where shock waves are used to break kidney stones into smaller pieces that can be passed in the urine (lithotripsy), ESWT has been adapted for use in the treatment of bone and tendon injuries. Although not fully understood, shock waves generate changes at an intracellular level within the tissues, leading to the release of chemicals which can promote healing processes, the formation of new blood vessels and the modification of pain perception. The use of ESWT in the treatment of tennis elbow presents a non-invasive treatment option with minimal side effects. This article will focus on the use of ESWT for treating tennis elbow.

Symptoms and diagnosis

The usual symptoms of tennis elbow are pain and tenderness overlying the lateral epicondyle (the outermost bony prominence of the elbow) made worse by straightening the arm or rotating it. The severity and persistence of pain are variable, ranging from mild and intermittent to severe and constant. The diagnosis can usually be made on a clinical basis, confirming pain on palpation (feeling) of the affected area and pain on resisted wrist extension and resisted extension of the middle finger. Grip strength is frequently diminished. Other clinical tests such as the chair pick test (the ability to lift a lightweight chair with the arm fully extended and the wrist flexed), Mill’s test (pain induced by rotating an extended arm with the wrist flexed) and Cozen’s test (pain induced by resisted wrist extension) are sometimes used to confirm the diagnosis.²

Current treatments for tennis elbow

One of the main problems faced in evaluating a treatment for tennis elbow is the vast number of proposed treatments currently in existence. Around 40 different treatments have been described with varying rates of success. A meta-analysis, which is a type of scientific study that attempts to compare the results of multiple studies in order to determine overall conclusions about effectiveness, was attempted in 1992 to determine the best treatment for tennis elbow, but was unable to be completed and had to be published in a different format.³ The reason for this was the variation in the way successful treatment outcomes in tennis elbow have been measured. Whilst simple cases may resolve with analgesia (painkillers) and rest alone, the following treatments have all been advocated:¹

• Local application of ice and rest
• Non Steroidal Anti-Inflammatory Drugs (NSAIDs), eg, Ibuprofen
• Local ultrasound therapy
• Laser therapy
• High frequency Galvanic stimulation
• Massage
• Local injection of corticosteroids
• Exercise/Physiotherapy
• Autologous blood injection
• Platelet rich plasma injection
• Orthotics
• Wrist extension splints
• Botox
• Acupuncture
• ESWT
• Surgical treatment - either open surgery, percutaneous release, arthroscopic surgery.

In order to simplify this list somewhat, treatments can be divided into conservative (rest, ice, analgesia), non-operative treatments (e.g., local steroid injection, autologous blood injection) and surgical (operative) treatments. Surgical treatment is reserved for cases which are resistant to less invasive treatment options.

The effectiveness of ESWT needs to be taken in context with currently available treatments, specifically those that represent an alternative to surgery, such as autologous blood injection, botox, platelet-rich plasma and steroid injections.

Mechanism of action of ESWT in tennis elbow

The effect of shock waves on human tissue helps to promote tissue repair and regeneration. This happens on an intracellular level in a process termed “mechano-transduction”. Studies of animal cells exposed to shock waves show the production of a cascade of chemicals that promote cell growth and repair.⁴ VEGF - vascular epithelial growth factor is one such chemical. This increases the formation of tiny blood vessels in the damaged tissue, a process called “neo-vascularisation,” which aids healing. Expression of other growth factors, such as IGF-1 (Insulin-like growth factor-1) leads to the production of a chemical called lubricin, which stimulates tendon cell growth.⁵ Furthermore, EWST appears to have an effect on pain perception by desensitising nerve fibres and decreasing the effect of a chemical called substance P, which makes pain receptors more sensitive.⁶ The overall effect of these changes is to promote the repair of the microscopic tears present in the tendons of the forearm muscles and to reduce pain.

Indications for ESWT in Tennis Elbow

The vast majority of cases of tennis elbow (70-90%) will resolve within a year of onset with basic measures (rest, simple painkillers or non-steroidal anti-inflammatory drugs, eg., ibuprofen, and local corticosteroid injections). However, in the remainder of persistent cases, surgery is frequently recommended. In addition, conservative treatment is not possible  without certain risks, particularly those associated with the long-term use of non-steroidal anti-inflammatory drugs (renal complications, gastrointestinal side effects) or corticosteroid injections. Some studies have shown EWST to have a similar effectiveness to percutaneous tenotomy surgery (the least invasive surgical option), however, this hasn’t been reproduced by other researchers.⁷ Nevertheless, ESWT offers an alternative with an excellent safety profile as an alternative treatment for chronic tennis elbow resistant to conservative treatment.

Procedure

Another difficulty in the study of ESWT for tennis elbow is that treatments are not standardised. ESWT can vary both in the intensity of the shock waves used and in the number of treatments and the duration, and the spacing of the treatments. In terms of intensity, both low-intensity (0.10mJ/mm2) and high-intensity (0.20mJ/mm2) shockwaves have been used, with one study comparing the two favouring low-intensity treatment.⁸ A typical treatment regime is 2400 pulses delivered in one session, with a session per week for three to five weeks, but these vary according to local protocols.⁸ 

Focussed shock waves are produced by a generator which may be electro-hydraulic, piezo-electric or electro-magnetic connected to a hand-held probe which is in direct contact with the treated area. Focussed shock waves allow the delivery of the shock wave to a specific site in the body. All these devices produce similar shock waves. Another type of shockwave therapy, radial shock wave therapy, differs from focussed waves in that, rather than being focussed at a particular depth, the wave dissipates the further it gets from the skin. Loud clicking sounds may be heard as the wave is transmitted to the treatment area, and it is normal to experience some pain, usually tolerable in nature. Each session lasts between 10-30 minutes. In some studies, local anaesthesia was given to minimise pain.⁹

Evidence for the efficacy of ESWT in tennis elbow

The evidence for the effectiveness of ESWT for tennis elbow is conflicting and difficult to interpret. One of the problems is that the treatment protocols vary greatly in different studies. Whilst there are several studies that appear to demonstrate the benefits of ESWT, there are also many studies showing no benefit. In 2005, a Cochrane review (a type of review of multiple studies performed according to rigorous academic standards) concluded that there was high- quality evidence that ESWT provided little or no benefit in the treatment of tennis elbow, based on the analysis of 10 separate studies.¹⁰ Since then, there have been multiple conflicting results; even systematic reviews or meta-analysis (studies that take into account the results of multiple different studies to provide a consensus) have failed to reach an agreement.

A systematic review comparing ESWT with other non-surgical treatments conducted in 2020 by Yao et al. appears to show overall improvement in pain scores and overall function as measured by grip strength, with a favourable safety profile compared with other methods, although the authors conceded that better quality clinical trials were necessary.¹¹

However, another systematic review performed in 2020 by Yoon et al. concluded that there was no clinically significant improvement in pain score or grip strength in patients treated with ESWT, in line with the 2005 Cochrane review. This study also related better outcomes in the use of radial vs focussed ESWT and better outcomes with ESWT in cases where symptoms had been present for greater than 6 months. Again, the authors concluded that better research was needed, especially with regard to standardising the treatment protocols and type of ESWT used (focussed vs radial).¹²

Nevertheless, the use of ESWT for tennis elbow has secured approval from the FDA (US Food and Drug Administration) as a recognised treatment. In the UK, NICE (National Institute for Health and Care Excellence), recognises ESWT as a treatment option for tennis elbow, quoting several randomised controlled trials (the highest quality of clinical evidence) in its guidelines comparing ESWT to a sham treatment, although it commented on the data from clinical trials being different to interpret for the reasons already discussed.¹²

Side Effects and Risks

One of the distinct advantages of ESWT as a treatment for tennis elbow is its excellent safety profile and lack of significant side effects. Side effects are mainly confined to local skin reactions to the treatment, including localised reddening, short-lived swelling and bruising. ESWT may not be suitable for patients who suffer from bleeding disorders.⁹ 

Summary

Tennis elbow (lateral epicondylitis) is a relatively common condition causing pain and restriction of movement in the forearm. Although many cases will settle with simple rest and anti-inflammatory painkillers, persistent cases may require further treatment, including surgery. A plethora of treatments have been advocated for persistent tennis elbow, but there is  a lack of consensus amongst experts as to the most effective. Extracorporeal shock wave therapy (ESWT) has been used to treat tennis elbow, however, the scientific evidence for its effectiveness has been difficult to interpret. Despite this, ESWT has minimal side effects and is recognised for use in selected cases of tennis elbow by regulatory bodies governing medical treatment, including the FDA and NICE. Most experts agree that better quality research is still required to determine its effectiveness.