Abstract
Background
Extracorporeal shock wave therapy (ESWT) has been used in various musculoskeletal disorders, including lateral epicondylitis. However, in 2005, a meta-analysis of randomized controlled trials showed that ESWT provides minimal or no benefit in terms of pain and function in patients with lateral epicondylitis. Since the review, several randomized controlled trials including different types of ESWT such as radial type for lateral epicondylitis have been published. Investigations of the effect modifiers such as symptom and follow-up duration on the effects of ESWT on lateral epicondylitis have not been performed.
Questions/purposes
(1) Does ESWT reduce pain and improve grip strength in patients with lateral epicondylitis? (2) Which type of ESWT, radial or focused, is more effective? (3) Is the duration of symptoms associated with the efficacy of ESWT for lateral epicondylitis? (4) Do improvements in pain scores remain in patients with longer follow-up?
Methods
The PubMed, Embase, and Cochrane Central Register of Controlled Trials databases were searched up to July 2019 for articles published in English or Korean. Studies were included if patient allocation was randomized, the sample was composed of patients with lateral epicondylitis, interventions were ESWT (focused or radial), comparison group only received sham stimulation or no additional treatment, and the study outcome was pain intensity or grip strength. The quality of the evidence was assessed using the Cochrane risk of bias tool. Twelve studies including 1104 participants fulfilled the inclusion criteria and were included in the meta-analysis. The mean difference for pain reduction and improvement in grip strength was calculated.
Results
The meta-analysis showed no clinically important difference in the VAS score (2.48 ± 7.55 versus 3.17 ± 9.78, mean difference -0.68 [95% confidence interval -1.17 to -0.19]; p = 0.006) and grip strength (38.02 ± 70.56 versus 34.85 ± 108.26, mean difference 3.33 [95% CI 0.93 to 5.73]; p = 0.007) after ESWT relative to the comparison group’s score. Even though radial ESWT showed more improvement than focused, the mean difference for VAS did not exceed the minimal clinically important differences threshold. There were no clinically important effects on the VAS scores of patients with lateral epicondylitis (2.78 ± 5.57 versus 3.92 ± 6.29, mean difference -1.13 [95% CI -1.84 to -0.42]; p = 0.002) and focused ESWT did not improve pain in patients with lateral epicondylitis. In the subgroup analysis, ESWT was effective in patients with a symptom duration of more than 6 months (2.28 ± 8.48 versus 3.31 ± 11.81, mean difference -0.95 [95% CI -1.75 to -0.15]; p = 0.02) but not for those with shorter symptom duration. The effects did not last beyond 24 weeks (2.52 ± 9.19 versus 3.34 ± 5.93, mean difference -0.82 [95% CI -2.57 to 0.93]; p = 0.36).
Conclusions
ESWT did not show clinically important improvement in pain reduction and grip strength. Radial ESWT, symptom duration of longer than 6 months, and short follow-up duration (less than 24 weeks) were related to better effects. Further studies are needed to determine the appropriate protocol and elucidate the effects according to the intervention type and specific disease condition.
Level of Evidence
Level I, therapeutic study.
Introduction
Lateral epicondylitis is characterized by degeneration of the tendon at the origin of the wrist extensor muscles on the lateral epicondyle of the humerus [23, 36]. Nonoperative treatments including rest, application of ice, administration of analgesic medications, orthopaedic devices, ultrasound, transcutaneous electrical nerve stimulation, eccentric training, and extracorporeal shock wave therapy (ESWT), might have value in treating lateral epicondylitis. Although controversial, corticosteroid injections are still used [11]. A small proportion of patients eventually undergo surgery, although surgery for lateral epicondylitis is no more effective than nonsurgical treatment, based on evidence [1].
ESWT stimulates soft-tissue healing by inhibiting the function of afferent pain receptors immediately after treatment [28], and it downregulates the expression of inflammatory cytokines [32], enhances angiogenesis [27], and improves cellular proliferation and synthesis of the extracellular matrix at approximately 1 month [4]. In the management of this tendinopathy, the effectiveness of ESWT has been assessed in previous randomized controlled trials (RCTs), yielding a success rate ranging from 43% to 75% [16, 42]. The FDA has approved two ESWT devices to treat lateral elbow pain [35].
However, there is mixed evidence on the efficacy of ESWT for lateral epicondylitis [49]. This is partly attributed not only to the study design and study populations but also to the increasing array of shock wave systems and treatment protocols, as well as basic differences in the forms of shock waves used [45]. The effectiveness of ESWT to treat lateral epicondylitis has been systematically reviewed before [5, 7, 48]. One of these studies performed a methodologic assessment of included trials but did not perform a meta-analysis of the available data [48]. In 2005, a Cochrane systematic review including 10 RCTs showed that there is platinum-level evidence that ESWT provides minimal or no benefit in terms of pain and function in patients with lateral epicondylitis and that there is a silver level of evidence that steroid injections may be more effective than ESWT, based on one trial involving 93 participants [6]. However, owing to heterogeneity, the Cochrane review only included six studies in the quantitative analysis: five studies assessing pain and three assessing grip strength. Since this review, several RCTs on the effects of ESWT for lateral epicondylitis have been published [8, 12, 47]. In studies conducted during the early 2000s, focused ESWT was usually investigated for the treatment of lateral epicondylitis; conversely, recent studies have evaluated the efficacy of radial ESWT [8, 15, 51]. Studies on the comparison of the effects between radial and focused ESWT for lateral epicondylitis have not been performed yet. And the investigations of effect modifiers such as duration of symptom and follow-up duration for the effects of ESWT on lateral epicondylitis have not been conducted.
Therefore, we asked: (1) Does ESWT reduce pain and improve grip strength in patients with lateral epicondylitis? (2) Which type of ESWT, radial or focused, is more effective? (3) Is the duration of symptoms associated with the efficacy of ESWT for lateral epicondylitis? (4) Do improvements in pain scores remain in patients with longer follow-up?
Materials and Methods
This systematic review was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Study selection, application of eligibility criteria, data extraction, and statistical analyses were performed in accordance with the Cochrane Collaboration guidelines [18, 31].
Search Strategy and Study Selection
We searched for references in the MEDLINE (PubMed), Embase, and Cochrane Central Register of Controlled Trials databases up to July 2019, without any date restriction. The database searches were limited to articles published in English or Korean. Key terms used to conduct the search were selected and combined with the following English terms and their equivalents: “extracorporeal shock wave therapy” AND “lateral epicondylitis” (see Appendix, Supplemental Digital Content 1, http://links.lww.com/CORR/A333). Studies were included if patient allocation was randomized, the sample was composed of patients with lateral epicondylitis, the intervention was ESWT (focused or radial), the comparison group only received sham stimulation or no additional treatment, and the study outcome was pain intensity or grip strength. Studies were excluded if the trial was not conducted with a comparison group, the trial conducted direct comparisons between ESWT and another treatment such as an injection, the study design was a cross-over type, or data of pain intensity or grip strength were not provided sufficiently. Abstracts and conference proceedings were excluded if they lacked sufficient reporting details. Review articles, editorials, and other nonclinical trials were also excluded.
Two reviewers (SYY, YWK) independently reviewed the titles and abstracts of the articles to determine their eligibility for inclusion. Studies that clearly failed to meet the inclusion criteria were not reviewed further. Those that were not excluded were retrieved, and the full text was reviewed by the two reviewers. In all instances, differences in opinion were resolved by discussion with a third reviewer (SCL). Studies that met the criteria were retrieved and reviewed in detail.
Data Extraction and Quality Assessment
The following information was extracted from the included studies: first author, year of publication, trial design, patients’ demographics and clinical presentations, types of interventions (radial or focused ESWT), intervention protocols, total sample size and sample size per arm (ESWT and control groups), scales and measures used to evaluate the efficacy of the interventions, baseline and endpoint measurements, and adverse events. The outcomes of interest were measures of pain such as the VAS score and grip strength. Symptom duration was categorized into two groups: more than 3 months or more than 6 months. Where appropriate, results were grouped according to the timing of follow-up from the completion of treatment as one of the following: 4 weeks after the end of treatment, 5 to 23 weeks after the end of treatment, or at least 24 weeks after the end of treatment. A plot digitizer was used to obtain data values from studies in which only graphs were published.
Study quality was assessed by rating the risk of selection bias, performance bias, detection bias, attrition bias, reporting bias, and other sources of bias using the Cochrane risk of bias tool [18]. Two reviewers (SYY, YWK) independently assessed whether each of the following domains was adequate (that is, low, unclear, or high risk of bias): sequence generation, allocation concealment, blinding, incomplete outcome data addressed, selective outcome reporting, or other bias. Disagreements in the initial ratings of the methodologic quality assessment were resolved by discussion with a third reviewer (SCL).
Description of the Selected Studies
A total of 1683 studies were identified in the initial search. After duplicates were removed, 1062 studies remained. After screening the titles and abstracts, we discarded 1046 studies. The full texts of the 16 remaining articles were assessed in more detail for eligibility [8, 9, 12, 13, 15, 17, 29, 30, 35, 38, 39, 40, 44, 46, 47, 51]. Three studies were excluded owing to insufficient information on clinical outcomes [29, 30, 40]; finally, 13 studies were included in the review [8, 9, 12, 13, 15, 17, 35, 38, 39, 44, 46, 47, 51]. In one study [44], the confidence interval did not overlap with the CI of the other studies, and the effect size was too extreme (mean difference -5.50 [95% CI -6.06 to -4.94]); thus, it was considered an outlier and removed from the final quantitative analysis. Instead, a sensitivity analysis was performed to evaluate the effects of the excluded study [44] on the pooled results. Finally, 12 studies including 1104 participants fulfilled the inclusion criteria and were included in the final meta-analysis [8, 9, 12, 13, 15, 17, 35, 38, 39, 46, 47, 51] (Fig. 1).
Fig. 1.
This flow chart shows the study search and selection methods.
Risk of Bias
Four studies provided insufficient detail about the methods of randomization and were considered to have an unclear risk of bias [12, 15, 39, 46]. Six studies did not describe the methods of allocation concealment and were also considered to have an unclear risk [8, 12, 13, 38, 39, 46]. Because these studies were experimental trials applying real or sham ESWT, complete participant blinding seemed to be difficult. Thus, if there were descriptions regarding participant blinding, we regarded these studies as having a low risk. Most of the studies properly blinded the participants and outcome assessment. Almost all studies applied sham ESWT to their comparison groups; however, one study compared the effects of combined physiotherapy and ESWT with those of physiotherapy only [13] and was judged to have a high risk of participant blinding. Eight studies performed intention-to-treat analyses and were considered to have a low risk [9, 13, 17, 35, 38, 46, 47, 51]. A high risk of bias for other reasons was ascribed to five studies that did not control other treatments such as medication administration, splinting, or physiotherapy during the study period [9, 12, 13, 17, 47] and one study that received funding from the manufacturer of the ESWT device [35] (See Figure, Supplemental Digital Content 2, http://links.lww.com/CORR/A334).
Study Characteristics
The number of participants in the included studies ranged from 28 [51] to 272 [17]. The mean age of the participants ranged from 44 years [12] to 51.1 years [51]. All studies except for one [13] (no report of participant sex) included participants of both sexes; however, there was a predominance of women in one study [8]. The mean duration after diagnosis ranged from 4.1 months [15] to 25.1 months [38]. Twelve studies compared the effects of real and sham ESWT, whereas one study [13] compared the effects of combined physiotherapy and ESWT with the effects of physiotherapy only. Seven studies [9, 12, 35, 38, 39, 46, 47] used focused ESWT, four studies [8, 15, 44, 51] used radial ESWT, and the two other studies [13, 17] did not report the exact type of ESWT used. Nine studies [8, 9, 13, 17, 35, 38, 39, 47, 51] performed ESWT three times at weekly intervals, whereas two studies [12, 15] performed ESWT for only one session. One study performed ESWT three times at monthly intervals [46], and another study conducted ESWT four times at weekly intervals [44]. Low- to medium-energy stimulation was performed, with the energy values varying from 0.03 mJ/mm2 to 0.17 mJ/mm2 or from 1 bar to 2.4 bars [9, 15, 44]. Two studies did not perform ESWT with routine intensity settings; instead, ESWT was performed with an intensity at the maximum level tolerated by each patient [47, 51]. The follow-up period ranged from 1 week [13] to 12 months [38] after completion of ESWT. All 12 studies included in the meta-analysis reported pain intensity as an outcome variable. The VAS score according to various situations such as the overall status, rest, night, activity, palpation, pressure, Thompson test, finger extension, or chair test was reported according to the outcome of interest of each study. Grip strength was reported in eight studies [8, 9, 15, 17, 35, 38, 47, 51]. The other outcome variables included the Roles and Maudsley score, patient-related tennis elbow evaluation results, DASH outcome scores, SF-36 results, and EuroQol 5D results. Local anesthesia was used in two studies [12, 17] (Table 1).
Table 1.
Characteristics of the included studies
| Study | Participants (experimental/comparison groups) | ESWT group | Comparison group | Outcome measures |
| Capan et al. [8] | n = 28/28 | Type: radial intensity (bar): 1.8 | Without contact of the applicator | Pain: VAS score |
| Age (years): 48.4 ± 9.0/46.2 ± 7.4 | Impulse: 2000 × 3 | Roles and Maudsley score | ||
| Sex (M/F): 2/44 | Frequency: 10 Hz | PRTEE results | ||
| Duration (months): 7.9 ± 5.2/7.7 ± 5.2 | Three sessions at weekly intervals | Grip strength | ||
| Site: epicondylar area of maximum pain, tenderness | Follow-up: 1 and 3 months | |||
| Local anesthesia: NR | ||||
| Chung and Wiley [9] | n = 31/29 | Type: focused (electromagnetic) intensity (mJ/mm2): 0.03-0.17, determined by the participant’s pain tolerance | An air buffer pad was placed between the head of the machine and the skin of the participant’s elbow | Pain: VAS score (overall, night, sleep, activity, worst, and least) |
| Age (years): 46.8 ± 9.2/45.5 ± 6.6 | Impulse: 2000 × 3 | Intensity (mJ/mm2): 0.03 | EuroQol 5D results | |
| Sex (M/F): 37/23 | Frequency: NR | Grip strength | ||
| Duration (weeks): 19.3 ± 13.2/22.1 ± 15.7 | Three sessions at weekly intervals | Follow-up: 2 and 6 weeks | ||
| Site: at the point of maximum pain | ||||
| Local anesthesia: no | ||||
| Collins et al. [12] | n = 93/90 | Type: focused (electrohydraulic) intensity (kV): 18 | Styrofoam block to absorb shock waves | Pain: VAS score (activity) |
| Age (years): 44 ± 7.61/46 ± 7.52 | Impulse: 1500 | Fluid-filled intravenous bag between the Styrofoam block and the patient’s elbow to mimic the feel of the coupling membrane | SF-36 results | |
| Sex (M/F): 96/87 | Frequency: NR | Follow-up: 4 and 8 weeks | ||
| Duration (years): 1.9 (range 5 months to 13.5 years/2.1 (range 4 months to 22 years) | One session | |||
| Site: NR | ||||
| Local anesthesia: yes or Bier block | ||||
| Eraslan et al. [13] | n = 15/15 | Type: NR | No treatment | Pain: VAS score (worst, rest, night, repeated elbow movement, and carrying heavy object) |
| Age (years): 48 ± 5.7/47.2 ± 8.5 | Intensity (mJ/mm2): 0.06-0.12 | Physiotherapy only | Cyriax’s resisted muscle test results | |
| Sex (M/F): NR | Impulse: 2000 × 3 | Grip strength | ||
| Duration (years): NR | Frequency: NR | PRTEE results | ||
| Three sessions at weekly intervals | Follow-up: 1 week | |||
| Site: point of maximal tenderness | ||||
| Local anesthesia: NR | ||||
| Combined with physiotherapy | ||||
| Guler et al. [15] | n = 20/20 | Type: radial intensity (bar): 2.4/1.8 | No electric current applied | VAS score (rest, compression, and activity) |
| Age (years): 46.3 ± 8.1/45.8 ± 10.8 | Impulse: 1500 + 1500 | PRTEE results | ||
| Sex (M/F): 12/28 | Frequency: 15/21 Hz | Roles and Maudsley score | ||
| Duration (months): 4.1 ± 2.4/4.4 ± 2.2 | One session | Grasp force | ||
| Site: marked area/peripheral muscles | Pinch force | |||
| Local anesthesia: no | Follow-up: 0 and 1 months | |||
| Haake et al. [17] | n = 135/137 | Type: NR | Polyethylene foil filled with air and fixed with ultrasound gel in front of a coupling cushion totally reflected the shock waves | Pain: 11-point scale score |
| Age (years): 46.9 ± 8.5/46.3 ± 9.6 | Intensity (mJ/mm2): 0.07-0.09 | Grip strength | ||
| Sex (M/F): 128/143 | Impulse: 2000 × 3 | Roles and Maudsley score | ||
| Duration (months): 27.6 ± 35.5/22.8 ± 21.4 | Frequency: 3 Hz | Follow-up: 6 and 12 weeks | ||
| Three sessions at weekly intervals | ||||
| Site: continuous ultrasound imaging, insertion of the muscles at the lateral epicondyle of the humerus | ||||
| Local anesthesia: yes (3 mL of 1% mepivacain) | ||||
| Pettrone and McCall [35] | n = 56/58 | Type: focused (electromagnetic) intensity (mJ/mm2): 0.06 | Sound-reflecting pad between the patient and the application head of the machine | Pain: VAS score (Thompson test) |
| Age (years): 47.0 (range 35-71)/47.3 (range 35-60) | Impulse: 2000 × 3 | Upper-extremity function scale score | ||
| Sex (M/F): 54/60 | Frequency: NR | Subjective evaluation results of the disease status | ||
| Duration (months): 21.3 (range 6-178)/20.8 (range 6-176) | Three sessions at weekly intervals | Patient-specific activity score | ||
| Site: maximal tenderness on the lateral epicondyle | Grip strength | |||
| Local anesthesia: no | Follow-up: 1, 4, 8, and 12 weeks | |||
| Rompe et al. [39] | n = 50/50 | Type: focused (electromagnetic) intensity (mJ/mm2): 0.08 | Same protocol with impulse of 10 × 3 | Pain: VAS score (night, rest, pressure, Thompson test, finger extension, and chair test) |
| Age (years): 43.9 (range 26-61)/41.9 (range 26-58) | Impulse: 1000 × 3 | Grip strength | ||
| Sex (M/F): 42/58 | Frequency: 3 Hz | Roles and Maudsley score | ||
| Duration (months): 24.8 (range 10-20)/21.9 (range 10-46) | Three sessions at weekly intervals | Follow-up: 0, 3, 6, and 24 weeks | ||
| Site: anterior aspect of the lateral epicondyle and at three points around this site at a radius of 1.5 cm to 2 cm | ||||
| Local anesthesia: no | ||||
| Rompe et al. [38] | n = 38/40 | Type: focused (electromagnetic) intensity (mJ/mm2): 0.09 | Polyethylene foil filled with air and fixed with ultrasound gel in front of a coupling cushion totally reflected the shock waves | Pain: VAS score (Thompson test) |
| Age (years): 45.9 ± 12.3/46.2 ± 11.2 | Impulse: 2000 × 3 | Roles and Maudsley score | ||
| Sex (M/F): 40/38 | Frequency: 4 Hz | Upper-extremity function score | ||
| Duration (months): 23.3 (range 12-120)/25.1 (range 12-131) | Three sessions at weekly intervals | Grip strength | ||
| Site: maximal reproduction of discomfort | Overall satisfaction | |||
| Local anesthesia: No | Follow-up: 3 and 12 months | |||
| Spacca et al. [44] | n = 31/31 | Type: radial intensity (bar): 1.2/1 | Intensity (bar): 1.2/1 | Pain score (rest, palpation, and Thompson test) |
| Age (years): 46.8 ± 9.5/47.0 ± 9.2 | Impulse: (500 + 1500) × 4 | Impulse: (5 + 15) × 4 | Grip strength | |
| Sex (M/F): 32/30 | Frequency: 4/10 Hz | Frequency: 4/10 Hz | DASH score | |
| Duration (months): 12 ± 5.0/13 ± 5.0 | Four sessions at weekly intervals | Follow-up: 0 and 6 months | ||
| Site: insertion of the wrist’s extensors muscles, on the lateral epicondyle | ||||
| Local anesthesia: no | ||||
| Speed et al. [46] | n = 40/35 | Type: focused (electromagnetic) intensity (mJ/mm2): 0.12 | The treatment head was deflated | Pain: VAS score (day and night) |
| Age (years): 46.5 (range 26-70)/48.2 (range 31-65) | Impulse: 500 × 3 | No coupling gel was applied | Follow-up: 1 month | |
| Sex (M/F): 33/42 | Frequency: NR | Standard contact with the skin was avoided | ||
| Duration (months): 15.9 (range 3-42)/12 (range 3-40) | Three sessions at monthly intervals | Intensity (mJ/mm2): 0.04 | ||
| Site: ultrasonographic localization, site of maximum reproduction of local pain | ||||
| Local anesthesia: no | ||||
| Staples et al. [47] | n = 36/32 | Type: focused (electromagnetic) intensity (mJ/mm2): maximum level tolerated by the patient | Intensity (mJ/mm2): not exceeding 0.03 | Pain: VAS score (overall) |
| Age (years): 49.8 ± 7.4/49.1 ± 8.8 | Impulse: 2000 × 3 | Impulse: subtherapeutic dose of 100 shocks × 3 | Upper-limb function | |
| Sex (M/F): 40/28 | Frequency: 4 Hz | Frequency: 1.5 | Pain-free function index | |
| Duration (weeks): 52.6 ± 64.3/68.0 ± 98.8 | Three sessions at weekly intervals | DASH score | ||
| Site: area of maximal tenderness, origin of the common extensor tendon | SF-36 results | |||
| Local anesthesia: NR | Grip strength | |||
| PET results | ||||
| Follow-up: 6 weeks and 3 and 6 months | ||||
| Yang et al. [51] | n = 15/13 | Type: radial intensity (bar): maximum level tolerated by each patient | Intensity (bar): 0.1 | Pain: VAS score |
| Age (years): 50.9 ± 8.4/51.1 ± 9.5 | Impulse: 2000 × 3 | Grip strength | ||
| Sex (M/F): 12/16 | Frequency: 10 Hz | DASH score | ||
| Duration (months): 6.5 ± 6.5/7.3 ± 7.6 | Three sessions at weekly intervals | Ultrasonographic results | ||
| Site: NR | Real-time sonoelastographic results | |||
| Local anesthesia: NR | Follow-up: 4, 10, and 22 weeks |
M = male; F = female; NR = not reported; PRTEE = patient-related tennis elbow evaluation; PET = problem elicitation technique.
Data Synthesis and Statistical Analysis
A meta-analysis represents the quantitative findings of each study in the form of effect sizes, producing statistical standardization [25]. The calculation of the effect sizes of ESWT for lateral epicondylitis was based on the mean difference. The mean VAS pain score, mean grip strength, SDs before and after treatments, and number of patients in the treatment and control groups were used to calculate the mean difference. The mean difference and 95% confidence interval of the treatment and comparison groups were calculated for each study, and the results were pooled. Studies in which the CI did not overlap with the CI of other studies or the effect-size estimate was too extreme (more or less than 3) were considered outliers. Where it was inappropriate to pool data, data were presented in tables and synthesized qualitatively. Analyses were conducted using the RevMan 5.3 software (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark). The I2 measure of inconsistency was used to examine between-study variability, with values greater than 50% indicating high heterogeneity [19]. This statistic, expressed as a percentage between 0% and 100%, can be interpreted as the percentage of heterogeneity in the system or the amount of total variation accounted for by between-study variance [19]. We used a fixed-effect model where there was no evidence of significant heterogeneity between studies and a random-effect model when such heterogeneity was likely. A sensitivity analysis was performed to evaluate the stability and reliability of the pooled results by excluding each study individually and re-analyzing the remaining studies. Subgroup analyses according to the type of ESWT, symptom duration, and follow-up period were also performed. We used two-tailed p values, and p values of < 0.05 were considered statistically significant. Also, changes of 2 cm on a 10-cm VAS scale for pain and 6 kg for grip strength between the two groups were defined minimal clinically important differences (MCID) [33]. Publication bias was explored using funnel plots.
Results
The meta-analysis showed no clinically important difference in the VAS score after ESWT (2.48 ± 7.55 versus 3.17 ± 9.78, mean difference -0.68 [95% CI -1.17 to -0.19]; p = 0.006) relative to the comparison group’s score. This was based on 12 studies [8, 9, 12, 13, 15, 17, 35, 38, 39, 46, 47, 51] that reported the VAS score for pain intensity. The duration of follow-up was different across the studies, varying from 1 week to 12 months, and we included the VAS score at the longest follow-up period in each study. A sensitivity analysis was performed after including an outlying study [44], and the effect size increased to -1.03; however, the heterogeneity value also increased to I2 = 96%. A further sensitivity analysis was performed by excluding the studies individually, which also revealed similar results for the effects of ESWT on lateral epicondylitis; there was no clinically important difference between the two groups. The meta-analysis for the grip strength after ESWT also revealed no clinically important difference (38.02 ± 70.56 versus 34.85 ± 108.26, mean difference 3.33 [95% CI 0.93 to 5.73]; p = 0.007) relative to the comparison group’s grip strength. Of the eight studies [8, 9, 15, 17, 35, 38, 47, 51] with the results of grip strength, six studies [8, 9, 15, 35, 38, 51] that measured grip strength using hand dynamometer were included in the meta-analysis (Fig. 2A-B).
Fig. 2.
A-B This figure shows our meta-analysis of extracorporeal extracorporeal shock wave therapy (ESWT) for (A) pain intensity and (B) grip strength in patients with lateral epicondylitis.
In the subgroup analysis for the type of ESWT, even though radial ESWT showed more improvement than focused, the mean difference for VAS did not exceed the MCID threshold. There was no clinically important beneficial effect on the VAS scores of patients with lateral epicondylitis (2.78 ± 5.57 versus 3.92 ± 6.29, mean difference -1.13 [95% CI -1.84 to -0.42]; p = 0.002). Focused ESWT did not improve pain of patients with lateral epicondylitis (2.66 ± 8.40 versus 3.27 ± 10.93, mean difference -0.67 [95% CI -1.41 to 0.07]; p = 0.08) (Fig. 3A-B). Three studies [8, 15, 51] performed radial ESWT, whereas seven studies [9, 12, 35, 38, 38, 46, 47] used focused ESWT. One study [17] had a multicenter-based design and was conducted by using different shock wave devices; thus, it was excluded from this analysis. Eraslan et al. [13] did not report the exact type of ESWT; thus, this study was also removed from the subgroup analysis.
Fig. 3.
This figure shows our subgroup analysis of extracorporeal shock wave therapy (ESWT) for lateral epicondylitis according to the stimulation type: (A) radial and (B) focused.
Five studies [12, 17, 35, 38, 39] enrolled patients with a symptom duration of longer than 6 months, and the meta-analysis showed no clinically important improvement in the VAS score after EWST (2.28 ± 8.48 versus 3.31 ± 11.81, mean difference -0.95 [95% CI -1.75 to -0.15]; p = 0.02) relative to the comparison group’s score (Fig. 4). In the five studies [8, 13, 46, 47, 51], enrolled patients with lateral epicondylitis had a symptom duration of longer than 3 months, and there were no differences in the VAS score between the two groups (2.57 ± 8.09 versus 2.95 ± 7.98, mean difference -0.49 [95% CI -1.35 to 0.37]; p = 0.26).
Fig. 4.
This figure shows our subgroup analysis of extracorporeal shock wave therapy (ESWT) for lateral epicondylitis according to the symptom duration.
The VAS scores show no difference between the ESWT and comparison groups when analyzed in reports with at least 24 weeks of follow-up (2.52 ± 9.19 versus 3.34 ± 5.93, mean difference -0.82 [95% CI -2.57 to 0.93]; p = 0.36) [38, 39, 47] (Fig. 5). Nine studies [8, 9, 12, 13, 15, 35, 39, 46, 51] included the VAS scores within 4 weeks after completion of the study, and the meta-analysis showed no clinically important improvement in the VAS score after EWST (3.21 ± 10.89 versus 3.87 ± 10.41, mean difference -0.80 [95% CI -1.11 to -0.48]; p < 0.001). The effects of ESWT at the 5 to 23-week follow-up interval were reported in nine studies [8, 9, 12, 17, 35, 38, 39, 47, 51], and there were also no clinically important beneficial effects of ESWT (2.38 ± 6.85 versus 3.18 ± 10.26, mean difference -0.76 [95% CI -1.13 to -0.19]; p = 0.009) in the meta-analysis.
Fig. 5.
This figure shows our subgroup analysis of extracorporeal shock wave therapy (ESWT) for lateral epicondylitis according to the follow-up duration: (A) 4 weeks or less and (B) 5 to 23 weeks and at least 24 weeks
Adverse Events
Of the 13 studies included in this review, four [8, 40, 44, 51] reported there were no adverse events. Two studies did not report about adverse events during their study periods [13, 15]. One study reported worsening of symptoms only in the ESWT group [46]. The adverse events reported in the six other studies [9, 12, 17, 35, 38, 47] included reddening, swelling of the skin, bruising or petechiae, burning or tingling sensation, pain during or after ESWT, nausea, dizziness, sweating, headache, and tremor. Although no statistical comparisons were made between the groups, there seemed to be more adverse events in the real ESWT group than in the sham ESWT group. All adverse events were resolved at the final follow-up evaluation, and there were no severe adverse events or reports of safety issues during the intervention in all studies. In only one study [35], two participants in the real ESWT group withdrew from the study owing to nausea (n = 1) and pain and tremor (n = 1).
Discussion
Although ESWT has been used to treat lateral epicondylitis in previous studies [9, 17, 40], a meta-analysis [6] in 2005 presented minimal or no benefit of ESWT for pain and function in lateral epicondylitis. Since the review, a few RCTs [8, 15, 51] including different types of ESWT such as radial type for lateral epicondylitis have been published, and a comparison of effects between focused and radial ESWT for lateral epicondylitis has not been performed. Also, the investigation of effect modifier such as duration of symptom and follow-up duration for the effects of ESWT on lateral epicondylitis has not been conducted. Therefore, our objective was to investigate the effect of ESWT on lateral epicondylitis for reducing pain and improving grip strength and to determine the effects according to the specific type of ESWT, symptom duration, and follow-up duration. We found that ESWT did not show clinically important improvement in pain reduction and grip strength, radical ESWT was more effective than the focused type, patients with a longer duration of symptoms had better improvement, and effects did not last beyond 24 weeks.
Our study has several limitations. The first limitation is the heterogeneity of the included studies. Regarding the methodologic aspects of this meta-analysis, we thought diversity among the studies was not only inevitable but also desirable. According to Borenstein et al. [3], a meta-analysis may (and usually must) address a broader question than those addressed by the primary studies it includes. Further, a good meta-analysis will anticipate this diversity and interpret the findings with attention to dispersion of the results across studies. Thus, we additionally performed sensitivity and subgroup analyses to overcome the heterogeneity among studies and clarify our findings. Second, although we included a relatively large number of RCTs, we could not draw conclusions about the optimal protocols of ESWT for lateral epicondylitis. The optimal protocols of ESWT for lateral epicondylitis have not been established. In a previous animal study, high-energy shock waves were reported to damage the tendon [41]. ESWT with low and medium energies was used in the studies included in the current meta-analysis. In the subgroup analysis, we determined that radial ESWT, symptom duration of longer than 6 months, and follow-up duration of fewer than 24 weeks were positively related to beneficial effects. Studies comparing radial and focused ESWT and evaluating patients according to symptom duration are warranted. Third, we only included studies published in English or Korean.
In our analysis, ESWT did not show clinically important improvement in pain reduction and grip strength in patients with lateral epicondylitis. We excluded an outlying study [44] reporting that ESWT had too-positive effects, but the analysis still revealed similar results with statistical significance. The sensitivity analyses, which was performed by excluding the studies individually and re-analyzing the remaining studies, revealed consistent results. In this meta-analysis, the effects of ESWT on lateral epicondylitis did not reach the MCID, but, the statistical significance still remained consistently in the sensitivity analyses; these are somewhat different than a previous meta-analysis reporting minimal or no benefit in terms of pain and function in patients with lateral epicondylitis [6, 7]. There have been a limited number of RCTs on the effects of ESWT in patients with lateral epicondylitis; thus, only five studies on pain reduction were included in the meta-analysis [17, 35, 38, 39, 46]. Of these five included studies, three [35, 38, 39] reported ESWT had positive effects, whereas two studies [17, 46] revealed negative results. A multicenter RCT by Haake et al. [17] included a large number of participants (272); the negative effects of ESWT in that study might have influenced the results of this meta-analysis. Although Haake et al.’s [17] study was a well-designed RCT, the results were controversial because there were three major issues: use of local anesthesia, diverse shock wave devices with various application parameters, and anti-inflammatory drugs administered during and 3 days after ESWT. We subsequently evaluated more RCTs revealing better effects of ESWT on pain reduction and grip strength in patients with lateral epicondylitis compared to previous meta-analyses.
In the subgroup analysis of the stimulation type, radial ESWT was more effective than the focused type; the effects of radial ESWT were different between the groups, but the results did not show a clinically important difference. Although the effect size of radial ESWT did not reach the MCID of VAS 2, it increased to more than 1 compared with the results of an analysis that included both types of ESWT. However, focused ESWT was not different between the groups. This might explain why pain was effectively reduced in patients with lateral epicondylitis in our review; studies investigating the effects of radial ESWT were newly included in this meta-analysis. In studies conducted in the early 2000s, focused ESWT was investigated to treat lateral epicondylitis [9, 17, 35, 46]; in recent studies [8, 15, 44, 51], the efficacy of radial ESWT was evaluated. Generators producing focused shock waves are based on the electrohydraulic, electromagnetic, or piezoelectric principle. In radial ESWT, shock waves are generated based on the pneumatic principle [14, 20]. They are propagated radially because the focal point of energy is achieved at the top of the applicator and decreases when it penetrates up to 3 cm, which is in contrast to focused ESWT, in which the focal point of energy is centered in the target zone [20, 34]. Based on the different mechanisms according to ESWT type, one possible explanation of why radial ESWT may have a better effect on lateral epicondylitis compared with focused ESWT may be that radial ESWT stimulates a much larger area of tissue including the lateral epicondyle and the adjacent muscles in the forearm.
Three studies investigating the effects of radial ESWT enrolled a relatively small number of participants (range 30 to 56) [8, 15, 51]. The follow-up duration of each study was relatively short: 1 month, 3 months, or 22 weeks; thus, we could not determine whether the positive effects of radial ESWT would continue in the long term. Studies directly comparing the effects of radial and focused ESWT for lateral epicondylitis have not been performed. One study evaluated the efficacy of radial and focused ESWT for lateral epicondylitis, and both types of ESWT yielded beneficial effects regarding pain and function; however, there were no sham comparison groups or a direct comparison between the two stimulation types [24]. Some comparative studies have evaluated the effects of radial and focused ESWT in other diseases; focused ESWT was more effective than radial ESWT in treating plantar fasciitis [26] and there was no difference between the two methods in treating patellar tendinitis [50]. Radial ESWT is easier to administer, less expensive, better tolerated by patients, and has fewer adverse effects than focused ESWT [20]. Studies on the effects of radial ESWT for lateral epicondylitis with well-controlled designs, large numbers of participants, and longer follow-up durations are warranted.
Patients with a symptom duration of longer than 6 months experienced better effects than those with a symptom duration of longer than 3 months. ESWT’s mechanism of action is not clearly understood. The operating logic of ESWT is to create an acute or new injury at the lesion site over a chronic condition, thereby triggering the self-repair mechanisms of the body [2, 21]. There have been several studies on the effects of ESWT in patients with chronic lateral epicondylitis [38, 39, 44]. One study reported that the number of patients with lateral epicondylitis who responded to ESWT was higher at a symptom duration of ≤ 16 weeks than at an symptom duration of more than 16 weeks [10]. Recently, one study evaluated the efficacy of ESWT in patients with acute (less than 3 months) and chronic (more than 6 months) lateral epicondylitis, and both groups experienced beneficial effects in terms of pain reduction [22]. However, the authors did not compare the effects of ESWT between patients with acute lateral epicondylitis and those with chronic lateral epicondylitis. The duration of symptoms might be an effect modifier of the success of ESWT, which needs further investigation.
In the subgroup analysis of the follow-up duration, positive effects were detected until 23 weeks; however, the effect did not persist after 24 weeks. A possible explanation for the non-significant difference between the two groups in the long-term follow-up period is the placebo effect related to participation in a trial or the self-limiting natural history of the condition, whereby most patients with lateral epicondylitis recover within 1 year [7, 37, 43].
Our meta-analysis revealed that ESWT did not show clinically important improvement in pain reduction and grip strength. Radial ESWT showed better effects than the focused type. In the subgroup analysis, patients with a longer duration of symptoms, that is, more than 6 months, had better improvement and the effects did not last beyond 24 weeks. ESWT for lateral epicondylitis deserves more attention, and future studies on specific conditions and parameters for optimal protocol settings are needed.
Supplementary Material
Footnotes
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.
Each author certifies that neither he or she, nor any member of his or her immediate family, has funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.
Each author certifies that his or her institution waived approval for the reporting of this investigation and that all investigations were conducted in conformity with ethical principles of research.
This work was performed at Yonsei University College of Medicine, Seoul, Republic of Korea.
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