The Effect of Extracorporeal Shock Wave Therapy on Pain Intensity and Neck Disability for Patients With Myofascial Pain Syndrome in the Neck and Shoulder: A Meta-Analysis of Randomized Controlled Trials : American Journal of Physical Medicine & Rehabilitation

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Original Research Articles

The Effect of Extracorporeal Shock Wave Therapy on Pain Intensity and Neck Disability for Patients With Myofascial Pain Syndrome in the Neck and Shoulder

A Meta-Analysis of Randomized Controlled Trials

Jun, Ji Hyun MS; Park, Geun-Young MD, PhD; Chae, Choong Sik MD; Suh, Dong-Churl MBA, PhD

Author Information
American Journal of Physical Medicine & Rehabilitation 100(2):p 120-129, February 2021. | DOI: 10.1097/PHM.0000000000001493

Abstract

What Is Known

  • A previous review of six studies on the efficacy and extracorporeal shock wave therapy (ESWT) for myofascial pain syndrome (MPS) was published in 2015, but it failed to draw a conclusion because of the insufficient number of trials included and methodological limitations. It was recently reported that only the focused type of ESWT significantly improves pain intensity in MPS in the short term, but it is limited by a small number of selected literature. Therefore, to date, the effectiveness of ESWT, according to both types (focused and radical), on the pain intensity and neck disability for patients with MPS in the neck and shoulder remains unclear.

What Is New

  • This meta-analysis found that ESWT could improves the pain intensity and pressure pain threshold (PPT) of patients with MPS in the neck and shoulder for the short term. However, ESWT was not effective in relieving pain intensity and improving neck disability for the long term. Moreover, focused ESWT was statistically more effective on pain intensity and PPT in the short term compared with other treatments. However, radial ESWT still remained unclear.

Myofascial pain syndrome (MPS) is a noninflammatory disorder of musculoskeletal origin, characterized by the presence of myofascial trigger points (MTrPs), which are hyperirritable palpable nodules in the skeletal muscle fibers.1 The MTrPs are associated with muscle dysfunction at the end of the motor neuron and sarcoplasmic reticulum, which leads to local contraction with ischemic hypoxia.2

Myofascial pain syndrome is one of the most common causes of chronic musculoskeletal disorders, involving muscle stiffness, tenderness, and pain that radiates to other areas, also known as referred pain.3 Prevalence varies from 30% to 93% among individuals with musculoskeletal pain.1 It has a major impact on health services, accounting for approximately 15% of consultations in primary care and up to 90% of patients treated in pain clinics.4 Various parts of the body can be affected by MPS; among them, MPS in the neck and shoulder is typically associated with prolonged computer work and jobs with static neck and shoulder positions.5

At present, pain and disability in MPS are managed by various therapeutic methods. Some systematic reviews of therapeutic approaches for controlling MPS were performed for Kinesio taping,6 local anesthetic injections,7 low-level laser therapy (LLLT),8 dry needling (DN),9 and ultrasound therapy (US).10 Extracorporeal shock wave therapy is widely used clinically for muscle pain.11 It has also been tried as one of the treatments for MPS.

The effect of extracorporeal shock wave therapy (ESWT) on MPS was examined in several studies. Extracorporeal shock wave therapy may increase perfusion, promote angiogenesis to increase blood flow, and alter the pain signaling pathways of ischemic muscle tissue caused by calcium influx. Extracorporeal shock wave therapy results in the degeneration of free nerve endings and produces a transient dysfunction of nerve excitability at the neuromuscular junction, by causing the degeneration of the acetylcholine receptors.12 According to a purely mechanistic approach, shockwaves may break actin and myosin filament shortening them because they propagate perpendicular to the sarcomere contraction.13,14 Müller-Ehrenberg and Licht2 showed that 95% of 30 patients with MPS had recognition of pain and referred pain when ESWT was applied at those points. The referred pain and pain recognition according to Simon diagnostic criteria are both signposts for the classification of MTrPs.13 The criteria are as follows: electromyography and ultrasound imaging of local contractile responses, spontaneous electrical activity at multiple active loci of MTrP, and biopsy of MTrP showing contraction knots and giant circular myofibers.

A previous review of six studies on the efficacy of ESWT for MPS was published in 2015, but it failed to draw a conclusion because of the insufficient number of trials and methodological limitations.11 It was recently reported that focused ESWT significantly improve pain intensity on MPS of the trapezius muscle.15 However, it included a small number of studies with only short-term follow-up and limited measurements.

The aim of this study was to determine the efficacy of ESWT in alleviating pain intensity and disability in the neck and shoulder of patients with MPS at short- and long-term follow-up in comparison with the efficacy of other treatments including LLLT, DN, US, and general exercise. We investigated the efficacy of ESWT depend on the type of ESWT and comparator through subgroup analyses.

Our meta-analysis provides the evidence-based information on ESWT for clinicians who make treatment decisions based on the symptoms of patients with MPS.

METHODS

Search Strategy

The literature search was conducted using a combination of search keywords described in online databases (PubMed, EMBASE, and Web of Science). The search dates were from June 1, 2000, to May 30, 2019. The method of reporting the results of meta-analysis was based on the Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines (see Supplementary Appendix 1, Supplemental Digital Content 1, https://links.lww.com/PHM/B25).16 Several different combinations of key words were used, such as “myofascial pain syndrome,” “trigger point,” “extracorporeal shockwave therapy,” “radial shockwave,” “pain,” and so on. The detailed search strategy is presented in Supplementary Appendix 2 (Supplemental Digital Content 2, https://links.lww.com/PHM/B26).

The search for and extraction of documents were performed by two independent authors. After the removal of duplicate publications, the titles and abstracts were reviewed to identify studies that met all of the following criteria: (1) patients diagnosed with MPS according to clinical impression or Simon criteria,13 (2) randomized controlled trials (RCTs), (3) application of ESWT in an experimental group compared with other treatments or sham ESWT in control group, and (4) outcomes related to pain intensity, pressure pain threshold (PPT), and neck disability.

Studies were excluded if (1) a low-quality randomized controlled design was implemented; (2) patients were presented with fibromyalgia, calcific tendinopathy, impingement syndrome, bursitis, and calcific lesions; and (3) outcome data were insufficiently reported. After carefully reviewing the titles and abstracts to ensure that all inclusion and exclusion criteria were met, the studies were included in the meta-analysis. A decision was reached through discussion if the authors did not agree with the final selection of the studies.

Quality Assessment

The methodological quality of the included trials was assessed according to the risk of bias for each RCT using the Cochrane Handbook.17 Each RCT was classified as having unclear risk, low risk, or high risk based on (1) random sequence generation, (2) allocation concealment, (3) blinding of participants and personnel, (4) blinding of outcome assessment, (5) incomplete outcome data, (6) selective reporting, and (7) other biases. Two authors assessed each article independently. A third reviewer participated when necessary.

Data Extraction

Three researchers extracted the data from the selected studies, which included the following variables: sample size; sex; mean age of the patients; device type; intensity; frequency and duration of intervention; and control treatment groups. The means and standard deviations (SDs) with 95% confidence intervals (CI) were calculated for all measured outcomes. Pooling for meta-analyses was performed when a particular outcome was used in at least three RCTs.

The included studies investigated the different outcomes related with pain intensity, PPT, and neck disability. When multiple time points were available within the same follow-up period, the time point closest to the end of the intervention was used for postintervention. The time point with more than 1 mo after baseline was defined as the follow-up regardless of the variation of time (at postintervention and follow-up with >1 mo after baseline).

Statistical Analysis

All statistical analyses were performed using RevMan V5.3 (Cochrane, London, United Kingdom). Pooled effect estimates were analyzed by comparing the change, calculated as the difference between baseline and postintervention outcome: Outcomepostsintervention Pooled effect estimates Outcomebaseline. The weighted mean difference (MD) was used with 95% CI because consistent outcomes were obtained across the included trials. The I2 statistic was used to examine the statistical heterogeneity (25%–49%, 50%–74%, and >75% indicate low, moderate, and high heterogeneity, respectively).18 A fixed effects model was used to combine studies when I2 values of less than 50%. Otherwise, random effect models were used.19 The effect size was assessed using Cohen d coefficient according to the following parameters20: 0.2 for a small effect, 0.5 for a medium effect, and 0.8 for a large effect. A funnel plot was visually inspected for indications of publication bias when at least 10 studies were pooled.21 When a comparison of three groups was performed, data on comparisons between the ESWT group and control groups with sham ESWT or an exercise regimen were included. If some studies lacked acquirable data, they were treated based on the guideline in the Cochrane Handbook.17

The meta-analyses included comparisons between ESWT and other treatments for (1) pain intensity at postintervention and follow-up, (2) PPT at postintervention and follow-up, and (3) neck disability at postintervention. Subgroup analyses were performed with at least two RCTs. Subgroup analyses were used to investigate the effectiveness of ESWT, according to the types of ESWT (focused and radical ESWT) and control groups (US, DN, LLLT, and sham ESWT.

RESULTS

A total of 11,858 potential studies were identified by using the previously described search strategy. After removing duplicates, 11,641 titles and abstracts were screened, and 54 potential full texts were assessed. Among them, 11 published articles satisfied the inclusion criteria and were included in this meta-analysis. In the literature selection process, a study was restricted to a certain occupation and excluded by agreement after discussion.22 A flowchart illustrating the review process is shown in Figure 1.

F1
FIGURE 1:
Flow chart for the identification of included studies.

Characteristics of Studies

The characteristics of the included studies are presented in Table 1. Among the 11 included RCTs, 8 trials used ESWT as monotherapy. In three RCTs, ischemic pressure to MTrPs,27 exercise program,28 and exercise medication31 were used as adjunctive therapy31 in the ESWT groups. Regarding the comparative alternatives administered to their control group, two RCTs used sham-ESWT application,28,30 whereas other RCTs with a comparison control design used either noninvasive (exercise regimen,32,33 US,25,27,28 US plus that ischemic pressure to MTrPs,27 and LLLT29,31) or invasive (DN24,26,32 and DN with transcutaneous electrical nerve stimulation23) treatment as ESWT alternatives. Three RCTs compared outcomes among the three groups.28,32,33

TABLE 1 - Characteristics of the literatures included in this meta-analysis
Studies Population ESWT Group Control Group(s) Outcome
Region Involving Muscles Follow-ups ESWT Control Group(s)
Jeon et al.23 (2012) Korea Trapezius 4 wks, no further follow-up n = 15 (M:F = 12:3)
Mean (SD) age: 40.86 (13.07) yrs
n = 15 (M:F = 9:6)
Mean (SD) age: 45.00 (15.46) yrs
ESWT device: EvoTron RFL0300 (SwiTech Medical AG)
1500 shock waves/session
EFD: 0.10 mJ/mm2
1/wk × 3 wks = total 3 sessions
TPI = 1/wk × 3 wks = total 3 sessions
Plus
TENS = 20 mins/session × 5/wk × 3 wks = 3 sessions
VAS
PPT
Cho et al.22 (2012) Korea Upper trapezius 4 wks, no further follow-up n = 12 (sex not reported)
Mean (SD) age: 47.06 (13.53) yrs
Int1: n = 12 (sex not reported)
Mean (SD) age: 48.08 (12.24) yrs
Int2: n = 12 (sex not reported)
Mean (SD) age: 47.67 (10.49) yrs
ESWT device: JEST-2000 (Joeunmedical, Korea)
1000 shock waves/session
EFD: 0.12 mJ/mm2
3/wk × 4 wks = total 12 sessions
Int1: ESWT plus shoulder stabilization exercises
Int2: shoulder stabilization exercises
3/wk × 4 wks = total 12 sessions
VAS
PPT
NDI
Luan et al.24 (2019) China Upper trapezius 4 wks, 12 wks n = 30 (M:F = 8:22)
Mean (SD) age: 32.47 (10.58) yrs
n = 32 (M:F = 11:21)
Mean (SD) age: 33.09 (12.78) yrs
ESWT device: Swiss Dolor Clast (Electro Medical Systems, Nyon, Switzerland)
2000 shock waves/session
EFD: 0.10 mJ/mm2
1/wk × 3 wks = total 3 sessions
Dry needling
1/wk × 3 wks = total 3 sessions
VAS
PPT
NDI
Gur et al.25 (2013) Turkey Trapezius 3 wks, 12 wks n = 30 (M:F = 5:25)
Mean (SD) age: 37.00 (11.51) yrs
n = 29 (M:F = 9:20)
Mean (SD) age: 35.07 (12.53) yrs
ESWT device: Minilith SL1 (Storz Medical, Switzerland)
1000 shock waves/session
EFD: 0.25 mJ/mm2
3 sessions with 3-d intervals
US: 1.5 Wt/cm2 dosage and 1 MHz in pulse mode for 5 mins
5/wk × 2 wks = total 10 sessions
PGA
NPADS
Manafnezhad et al.26 (2019) Iran Upper trapezius 4 wks, no further follow-up n = 35 (sex not reported)
Mean (SD) age: 37.0 (9.1) yrs
n = 35 (sex not reported)
Mean (SD) age: 39.2 (7.2) yrs
Radial ESWT device: enPuls Pro1.4 (Zimmer MedizinSysteme, Germany)
1000 shock waves/session frequency of 16 Hz with 60 mJ power
EFD: 0.25 mJ/mm2
1/wk × 3 wks = total 3 sessions
Dry needling
1/wk × 3 wks = total 3 sessions
NPRS
PPT
NDI
Ali et al.27 (2016) Egypt Rotator cuff muscles 4 wks, no further follow-up n = 15 (M:F = 3:12)
Mean (SD) age: 34.67 (5.95) yrs
n = 15 (M:F = 9:6)
Mean (SD) age: 34.07 (4.51) yrs
Radial ESWT device: shock master 500
2000 shock waves/session
EFD = 0.38 mJ/mm2
3/wk × 4 wks = total 12 sessions + ischemic pressure to MTrPs
US: 1 MHZ in continuous pulse for 5 mins
3/wk × 4 wks = total 12 sessions + ischemic pressure to MTrPs
VAS
PPT
Akturk et al.28 (2018) Turkey Trapezius, scalene, semispinal muscle of head, and sternocleidomastoid muscles 2 wks, 6 wks n = 20 (M:F = 5:15)
Mean (SD) age: 33.45 (8.02) yrs
n = 20 (M:F = 7:13)
Mean (SD) age: 35.45 (8.07) yrs
Radial ESWT device: Masterpulse MP200 (Storz Medical, Switzerland)
1.6–3.0 bar × 2000–3000 shock/session, 4 sessions with 3-day intervals + exercise program
Int1: US
1.5 w/cm2 for 5 mins
5/wk × 2 wks = total 10 sessions + exercise program
Int2: sham ESWT with the same intervention protocol except 1.0–1.3 bar + exercise program
VAS
PPT
Király et al.29 (2018) Hungary Trapezius 3 wks, 15 wks n = 30 (M:F = 3:27)
Mean (SD) age: 57.26 (14.31) yrs
n = 31 (M:F = 4:27)
Mean (SD) age: 62.62 (9.62) yrs
Radial ESWT device: BTL-6000 SWT Topline Power
2000 shock waves/session (1000 impulses 1.5 bar, 10 Hz + 1000 impulses 2.0 bar, 10 Hz)
EFD = 0.25 mJ/mm2
1/wk × 3 wks = total 3 sessions
Laser: PR999
4 W scanning laser)
palpable trigger point was treated with 5000 Hz (2000 mW), 9 J/cm2 + regions around the trigger point 2000 Hz (800 mW), 3 J/cm2 for 2 mins
5/wk × 3 wks = total 15 sessions
VAS
NDI
Ji et al.30 (2012) Korea Upper trapezius 2 wks, no further follow-up n = 9 (M:F = 1:8)
Mean (SD) age: 32.82 (12.71) yrs
n = 11 (M:F = 2:9)
Mean (SD) age: 34.00 (15.56) yrs
ESWT devices: Dornier AR2 (MedTech, Munchen, Germany)
1000 shock waves/session (700 impulses to the taut band + 300 impulses surrounding the taut band)
EFD: 0.056 mJ/mm2
2/wk × 2 wks = total 4 sessions
Sham ESWT
1000 shock waves/session
EFD: 0.001 mJ/mm2
2/wk × 2 wks = total 4 sessions
VAS
PPT
Taheri et al.31 (2016) Iran Upper trapezius 2 wks, 6 wks n = 26 (M:F = 2:24)
Mean (SD) age: 42.3 (10.4) yrs
n = 20 (M:F = 1:19)
Mean (SD) age: 45.3 (7.7) yrs
Radial ESWT device: DUOLITH SD1-shock
1000 impulse/session
EFD = 0.003 J/mm2
Total 3 sessions in 2 wks + exercise medication
LLLT: Indolaser device, type Ga-AL-As with 6 J/cm2, 100 mW for 3 mins on each spot
Total 10 sessions in 2 wks + exercise-medication
VAS
NDI
Lee et al.32 (2012) Korea Trapezius 2 wks, no further follow-up n = 10 (M:F = 1:9)
Mean (SD) age: 48.2 (12.0) yrs
Int1: n = 13 (M:F = 1:12)
Mean (SD) age: 47.9 (7.8) yrs
Int2: n = 8 (M:F = 2:6)
Mean (SD) age: 46.5 (13.1) yrs
ESWT device: JEST-2000 (Joen Medical, Republic of Korea)
Low power shock with air-cylinder method
5 Hz * 800 times
1/wk × 2 wks = total 2 sessions
Plus stabilization exercise
Int1: dry needling
1/wk × 2 wks = total 2 sessions
Plus stabilization exercise
Int2: stabilization exercise
1/wk × 2 wks = total 2 sessions
VAS
PPT
F, female; M, male; NPADS, Neck Pain and Disability Scale; NPRS, Numerical Pain Rate Scale; PGA, Patient Global Assessment; TENS, transcutaneous electric nerve stimulation; TPI, trigger point injection.

The total number of enrolled participants was 505 participants (231 in the ESWT group and 274 in the control group). The sample size ranged from 20 to 70 per study with the mean age of the participants ranging from 32.5 to 62.6 yrs. Myofascial pain syndrome was diagnosed in seven trials based on Simon criteria24–26,28–30,32 and patients in the other trials were classified as having clinically diagnosed MPS with the presence of painful palpable taut bands and referred pain. The pain duration was described in patients in 6 trials among 11 RCTs, ranging from 1 mo to approximately 3 yrs. Among them, four RCTs had enrolled participants with chronic episodes of MPS (at least 3 mos).24–26,28 In addition, 9 of RCTs 11 used a visual analog scale to assess patients’ pain intensity. Two other studies included the Patient Global Assessment25 and Numerical Pain Rate Scale26 as pain intensity–related outcomes were reported in one study as visual analog scale–like scale with self-estimated 10-cm points. Various devices were used to measure PPT with different metrics. Neck disability was measured by the Neck Disability Index in five trials24,26,29,31,33 and Neck Pain and Disability Scale in one trial.25 The total time of interventions and follow-ups ranged from 2 to 4 wks and from none to 15 wks, respectively. Energy flux density of ESWT ranged from 0.03 to 0.38 mJ/mm2. Only one RCT did not describe the energy flux density for ESWT.28

Methodological Quality

All included RCTs described a randomization method; only two studies with sham-ESWT control groups used reasonable methods such as blinding of participants and personnel.28,30 Except for the blinding of participants and personnel, other methodological qualities were acceptable and reasonable. The results of methodological quality assessment are presented in Supplementary Figure S1 (Supplemental Digital Content 4, https://links.lww.com/PHM/B28).

Outcome

Extracorporeal Shock Wave Therapy Versus Other Treatments at Postintervention

The efficacy of ESWT compared with other treatments for MPS at postintervention was assessed in terms of pain intensity in 11 trials with 460 patients, PPT in 8 trials with 294 patients, and neck disability in 6 trials with 322 patients.

Pooled estimates in random effect models showed the significant effect of ESWT on MPS in 11 trials for pain intensity (standardized mean difference [SMD] = 0.67, 95% CI = 0.11 to 1.23, P = 0.02, I2 = 87%; Fig. 2A)23–33 and in 8 trials for PPT (SMD = 1.19, 95% CI = 0.27 to 2.12, P = 0.01, I2 = 92%; Fig. 2B)23,24,26–28,30,32,33 at postintervention.

F2
FIGURE 2:
Forest plots showing the efficacy of ESWT compared with other treatments at postintervention. A, Pain intensity. B, Pressure pain threshold. C, Neck disability.

The ESWT had no significant effect on neck disability in six trials at postintervention (SMD = 0.03, 95% CI = −0.76 to 0.83, P = 0.93, I2 = 91%; Fig. 2C).24–26,29,31,33 The funnel plot is shown in Supplementary Appendix 3 (Supplemental Digital Content 3, https://links.lww.com/PHM/B27).

Subgroup Analysis Based on the Types of ESWT at Postintervention

Subgroup analysis according to the type of ESWT was done on pain intensity and PPT at postintervention. The focused ESWT had a significant effect on improving pain intensity with five RCTs (SMD = 0.75, 95% CI = 0.13 to 1.36, P = 0.02; Fig. 2A) and PPT with three RCTs (SMD = 1.70, 95% CI = 0.21 to 3.18, P = 0.03; Fig. 2B) at postintervention. However, a significant improvement of radial ESWT was not shown on pain intensity with six RCTs (SMD = 0.64, 95% CI = −0.26 to 1.55, P = 0.16; Fig. 2A) and PPT with five RCTs (SMD = 0.91, 95% CI = −0.25 to 2.06, P = 0.12; Fig. 2B) at postintervention.

Subgroup Analysis Based on the Treatments of Control Groups at Postintervention

Subgroup analyses of the outcomes between ESWT and US, DN, and LLLT were performed. Pooled estimates showed that ESWT was more effective than US in alleviating pain intensity in three trials at postintervention (SMD = 1.81, 95% CI = 0.26 to 3.36, P = 0.002, I2 = 92%).25,27,28 Furthermore, ESWT had no significant effect compared with DN in four trials (SMD = 0.11, 95% CI = −0.19 to 0.40, P = 0.48, I2 = 22%)23,24,26,32 and LLLT in two trials (SMD = −0.38, 95% CI = −1.31 to 0.55, P = 0.42, I2 = 82%)29,31 (Supplementary Fig. S2A, Supplemental Digital Content 5, https://links.lww.com/PHM/B29).

An improvement in PPT at postintervention was not observed for ESWT compared with US in two trials (SMD = 2.06, 95% CI = −0.49 to 4.60, P = 0.11, I2 = 93%)27,28 and with DN in four trials (SMD = 0.30, 95% CI = −0.60 to 1.2, P = 0.51, I2 = 87%)23,24,26,32 (Supplementary Fig. S2B, Supplemental Digital Content 5, https://links.lww.com/PHM/B29). A comparison between ESWT and LLLT was not performed because of the lack of trials with PPT measurement.

The effect of ESWT on neck disability was not significant at postintervention compared with the effect of DN in two trials (SMD = −0.36, 95% CI = −0.87 to 0.15, P = 0.16, I2 = 53%)24,26 and LLLT in two trials (SMD = −0.52, 95% CI = −1.87 to 0.83, P = 0.45, I2 = 91%),29,31 respectively (Supplementary Fig. S2C, Supplemental Digital Content 5, https://links.lww.com/PHM/B29).

Subgroup Analysis for Comparison Between ESWT and Sham ESWT

Subgroup analyses using a fixed model of two RCTs with sham ESWT showed significant effect of ESWT compared with sham ESWT on pain intensity (SMD = 1.29, 95% CI = 0.73 to 1.86, P < 0.00001, I2 = 0%)28,30 and PPT (SMD = 2.11, 95% CI = 1.45 to 2.76, P < 0.00001, I2 = 42%)28,30 at postintervention (Fig. 3).

F3
FIGURE 3:
Subgroup analysis for comparison between ESWT and sham ESWT.

Extracorporeal Shock Wave Therapy Versus Other Treatments at Follow-up

At follow-ups, ESWT was found to be unfavorable for relieving pain intensity in 5 trials with 268 patients (SMD = 0.28, 95% CI = −0.21 to 0.77, P = 0.27, I2 = 75%; Fig. 4A)24,25,28,29,31 and neck disability in 4 trials with 228 patients (SMD = 0.34, 95% CI = −0.05 to 0.72, P = 0.08, I2 = 52%; Fig. 4B).24,25,29,31 A forest plot for PPT at follow-up was not constructed because of the small number of included RCTs.

F4
FIGURE 4:
Forest plots about the efficacy of ESWT at follow-up compared with other treatments. A, Pain intensity. B, Neck disability.

Subgroup Analysis Based on the Treatments of Control Groups at Follow-up

The effectiveness of ESWT compared with US in reducing pain intensity was analyzed at follow-up (SMD = 0.24, 95% CI = −0.16 to 0.63, P = 0.24, I2 = 0%).25,28 In comparison with LLLT, there was no significant effect (SMD = −0.08, 95% CI = −0.46 to 0.30, P = 0.69, I2 = 0%)29,31 (Supplementary Fig. S3A, Supplemental Digital Content 6, https://links.lww.com/PHM/B30). In addition, compared with LLLT, ESWT was found to have no effect on neck disability at follow-up in two trials (SMD = 0.08, 95% CI = −0.30 to 0.46, P = 0.67, I2 = 6%)29,31 (Supplementary Fig. S3B, Supplemental Digital Content 6, https://links.lww.com/PHM/B30).

Adverse Events and Dropouts

No dropouts due to the adverse effects of therapies were recorded. There was some transient sensitivity as adverse events in only two patients in the ESWT group in one trial, but they did not drop out.25 In the ESWT group, two patients dropped out because of geographical accessibility problems in the RCT,30 and in another study, one patient in the control group dropped out because of lack of compliance.29 The number of dropouts due to follow-up loss was similar between the ESWT and control groups in two RCTs.25,26 In addition, three patients were dropped out as they received other treatments during the follow-up period in one trial.24

DISCUSSION

This is the meta-analysis to investigate effectiveness of ESWT compared with other treatments for patients with MPS in the neck and shoulder at postintervention and follow-up. Our results showed that ESWT reduced pain intensity and improved PPT at postintervention in patients with MPS. The effect size of ESWT in reducing pain intensity at postintervention was similar with 0.8 points, which is the minimum clinically important difference for neck pain reported by Lauche et al.34 In comparison with sham ESWT, ESWT showed an improvement of −2.02 cm in pain intensity at postintervention, which is much larger than the minimum clinically important difference.34 Moreover, the effect size for the change in PPT at postintervention was larger when compared between ESWT and sham ESWT than other control treatments.28,30 Therefore, the effect size of our meta-analysis may be underestimated when compared with sham ESWT because the treatments used in the control groups in most of the included studies were DN, US, and LLLT, which is consistent with the reports of several previous meta-analyses.8–10

At follow-up, however, ESWT did not have a superior effect on pain intensity and neck disability. Long-term effects in MPS treatment have not been reported because of the limited number of studies and heterogeneity.6,8,35–37 A meta-analysis was found that botulinum toxin type A injection to treat chronic MPS in the head and neck significantly reduced pain severity compared with the severity of the placebo group at 2–6 mos.38 Many factors could affect the long-term effects of MPS treatments. The model was proposed to integrate the physiological effects of trigger point DN at the periphery, the spinal cord, and the brainstem including those cognitive factors.37 In this model, MPS treatment was integrated in a comprehensive pain management programs with the patient’s expectations, experiences, beliefs, and patient-clinician interaction to contribute to prolonged/long-term effects with medium to large effect sizes.37 Because other factors were not considered in the included RCTs, there were some limitations regarding the follow-up effectiveness.

Although previous meta-analysis about the effectiveness of focused ESWT on MPS of the trapezius was published,15 our meta-analysis had some strengths in aspects of subgroup analysis based on the types of ESWT, comparison between ESWT and sham ESWT, and the result of the long-term effect (more than 4 wks) on relieving pain intensity. Moreover, besides visual analog scale (VAS), other measurements such as PPT and Neck Disability Index (NDI) were included as outcomes and analyzed in our meta-analysis.

Comprehensive subgroup analyses were performed to identify differences in the effect size between different study designs (comparison types including sham ESWT) and types of ESWT. In particular, compared with US, the effect of ESWT on pain intensity at postintervention and follow-up and PPT at postintervention was statistically more favorable. Furthermore, ESWT did not show significant effectiveness in reducing pain intensity when compared with DN and LLLT at follow-up. In particular, focused ESWT for patients with MPS was statistically more effective on pain intensity and PPT at postintervention than are other treatments. However, the effectiveness of radial ESWT remained unclear.

However, Brady et al.39 reported that the incidence of adverse effects after 7629 DN interventions for myofascial pain accounted for 19.18% of cases, including bruising (7.55%), bleeding (4.65%), pain during treatment (3.01%), and pain after treatment (2.19%). Considering that significant adverse events were not observed in the included RCTs of this meta-analysis, ESWT would be an acceptable tool with less painful and adverse events compared with DN. Comparisons between ESWT and LLLT need to also consider the differences in terms of the protocols used in two RCTs.29,31 The total sessions of ESWT and LLLT were different. Although ESWT was applied only 3 times in 2 or 3 wks, LLLT was applied at 5 times per week for 2 and 3 wks, ranging from 1029 to 15 sessions.31 Considering the clinical compliances in outpatient clinics, ESWT is thought to provide additional advantages, such as being less time-consuming and requiring fewer sessions. Therefore, ESWT could be recommended as a more convenient and affordable tool that is as effective as LLLT for MPS treatment. However, our subgroup analyses provide limited evidence because of the small number of RCTs. Although ESWT is associated with a higher device price and treatment cost compared with other treatments, ESWT is considered to be more effective than US, less painful and invasive than DN, and more comfortable than LLLT in actual clinical practice.

The efficacy of ESWT on neck disability was not significant at postintervention and at follow-up. Extracorporeal shock wave therapy was mainly performed for the trapezius muscles in the included studies. However, neck disability is correlated with masticatory myofascial pain and sensitivity of the paraneck muscles, such as the anterior temporalis, sternocleidomastoid, and upper trapezius muscles.40 Moreover, Lee et al.41 proposed that chronic pain in the low back and neck leads to disability with the mediating effects of self-efficacy, psychological distress, and fear, which underpins the direct targeting of these constructs in treatment. The regular monitoring of these mediators during treatment and targeting therapies to improve self-efficacy and minimize distress and fear may lead to lower levels of disability.41 The included RCTs mainly compared the effects in terms of the treatment and did not include these mediators and comprehensive pain management programs. Therefore, the result should be interpreted considering that neck disability is a more complex symptom, which could be significantly affected by self-efficacy, psychological distress, and fear.41

Study Limitations

Although some significant effects were observed, our meta-analysis included some potential limitations. First, most reviewed studies had methodological limitations because of the unblinding of participants and personnel, except for two trials with sham ESWT as the control group. This limitation was inevitable because it is difficult to blind the participants and personnel during the delivery of an intervention, such as ESWT. Second, the clinical heterogeneity cannot be ignored in these analyses although a random effect model was used. It may be explained by the variance in population and the protocol of ESWT such as the type and the energy flux density (EFD). The different protocols could potentially influence the statistical results, although a subgroup analysis according to the types of ESWT was done. For the EFD, further studies such as RCT and meta-analysis are needed based on more specific guidance in MPS. Third, comparator including various existing therapies used in the clinical treatment of MPS would make the results less consistent, although subgroup analysis for comparator groups (US, DN, and LLLT) was conducted. Fourth, studies typically had small sample sizes, with an average of 46 participants per study. It is, therefore, possible that the estimated effect may be larger than the true effect.42 Finally, data with long-term follow-up were insufficient and the time point at follow-up was different between the studies, ranging from 6 to 15 wks. This cannot be considered as a consistent point of evaluation despite the definition of follow-up.

CONCLUSIONS

This meta-analysis provided a moderate quality of evidence on ESWT compared with other treatments for reducing the pain intensity of patients with MPS in the neck and shoulder at postintervention. The follow-up efficacy of ESWT over other treatments still remains unclear. In particular, focused ESWT for patients with MPS was statistically more effective on pain intensity and PPT at postintervention than are other treatments. However, radial ESWT did not show significant improvement in pain intensity and PPT at postintervention. A large RCT will be needed to assess the ESWT protocol such as EFD, follow-up period, and other aspects. Network meta-analysis may be a suitable method in further studies on MPS symptom management to compare the effects of various treatments if more RCT accumulates. More precision is required regarding the parameters of pulses, especially the flux density, to obtain appropriate results. Nevertheless, this current study provides comprehensive guidance in the clinical application of ESWT for patients with MPS.

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Keywords:

Extracorporeal Shock Wave Therapy; Myofascial Pain Syndrome; Pain; Disability; Meta-analysis

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