CORR Insights®: Does the Type of Extracorporeal Shock Therapy Influence Treatment Effectiveness in Lateral Epicondylitis? A Systematic Review and Meta-analysis

Where Are We Now?

Extracorporeal shockwave therapy (ESWT), initially introduced for treating urinary stones, has become a viable option for the treatment of musculoskeletal disorders, especially calcific tendinitis of the shoulder, epicondylitis of the elbow, and plantar fasciitis. Although the mechanism by which this treatment leads to symptomatic pain relief in tendinopathy is not completely understood, and reasonable questions have been raised about whether it works at all in some of those diagnoses [1, 11], potential explanations for observed effects include nociceptor blockage, stimulation of the reparative response by regulating inflammatory cytokines, and enhancing angiogenesis [5, 6].

In the past decade, ESWT has been used as definite or adjuvant treatment for lateral epicondylitis of the elbow. In 1996, the first published randomized controlled trial of 100 patients with lateral epicondylitis showed pain relief and improvement of function at 3, 6, and 24 weeks after ESWT [8]. Although the initial clinical trial showed satisfactory results in patients with lateral epicondylitis, subsequent studies have reported conflicting outcomes regarding the efficacy of ESWT [7, 10]. In the largest series with randomized multicenter trials with 272 patients, no difference was found between the placebo and ESWT groups [4]. In addition, the first meta-analysis of nine randomized controlled trials with a total of 1006 patients reported minimal or no benefit in terms of pain and function in LE of the elbow [1]. By contrast, several randomized controlled trials using radial type ESWT have been published and showed beneficial effects on pain relief in lateral epicondylitis [9, 13], whereas earlier studies used focused-type ESWT and reported conflicting pain and functional outcomes [3, 4].

The authors of the current study [14] conducted an updated meta-analysis including an additional six randomized controlled trials (for a total of 12 with 1104 patients) and found that ESWT did not show clinically important improvements in pain relief and grip strength. However, in the subgroup analysis, radial-type ESWT showed beneficial effects on pain relief, while the focused type did not show a notable difference between the two groups. In addition, ESWT was effective in patients with a duration from onset of < 6 months, and the effects were maintained for up to 23 weeks. The results of this updated systemic review imply that ESWT for lateral epicondylitis requires more research in terms of standardization protocols and efficacy in specific conditions. These results also suggest that some kinds of ESWT should not be used until more robust randomized trials and meta-analysis find them to be effective.

Where Do We Need To Go?

Future analysis regarding potential effect modifiers in patients, such as symptom duration, pain intensity, and a history of other treatments, may be necessary to better characterize the role of ESWT in treating patients with lateral epicondylitis, if any. In addition, long-term effects and cost effectiveness need to be considered for making treatment decisions.

Although there have been many studies using ESWT to treat lateral epicondylitis, there is no established or standardized protocol. Controversies persist about therapeutic intensity (low, middle, or high energy), dose partition, type (radial or focused), number of sessions, and the time between sessions or cycles. Future studies should seek to standardize protocols; presumably, this will require comparative trials.

It would also be important to try to identify early whether a patient is likely to respond; this would save both pain and cost. Future studies should seek to determine whether the lack of a response after the first session implies a low probability of positive response after further sessions; if so, we might be able to recommend early termination of ESWT treatment and initiation of other treatments.

In clinical practice, combination therapy such as ESWT with nonsteroidal anti-inflammatory drugs medication is commonly used; however, the benefits of such combinations are unclear. Muscle stretching exercises or braces also can be added to the regimen. Determining the synergy, if any, of these combinations would be important. Another consideration is the minimization of adverse events associated with ESWT. Some patients report worsening pain, skin changes, and other side effects after ESWT. Even though these adverse effects do not appear to last very long, minimizing them would be important.

How Do We Get There?

It seems to me that the most important next step in terms of the clinical application of ESWT pertains to identifying the patients most likely to benefit from its use, and the specific ESWT protocols most likely to deliver that benefit. To do this, studies should investigate the factors affecting response to ESWT in different patient groups and comparative trials focusing on ESWT parameters such as focused or radial type, energy density, frequency, and number of sessions are necessary.

Effectiveness of combination therapy can be studied by comparison of pain among the patients who received either combination therapy or monotherapy. Several combinations are possible including ESWT plus tendon stretching, brace, and injections. If there is significant synergistic effect is proved after combinations therapy, we may develop a definite protocol using ESWT rather than adjuvant therapy. To evaluate frequency of adverse events and causative factors, one study focusing on wave dependent parameter would be possible. Skin lesions and tingling sense could be assessed after different types and energy amount of ESWT.

We also need more basic research on ESWT; it should concern us that there seems to be little in the way of tendon healing or regeneration after these treatments. This should be investigated using imaging techniques such as high-resolution ultrasound or MRI [2]. Acquisition of periodic images to compare the control and treatment groups may reveal differences in tendon structures or vascular changes. Another method for confirming tendon healing after ESWT is histological analysis, which can be performed in animal models or in primary cultured human tenocytes derived from healthy and pathological tendon tissues [12].