Extracorporeal shockwave therapy improves pain and function in subjects with chronic low back pain: a systematic review and meta-analysis of randomized clinical trials

DOI: https://doi.org/10.21203/rs.3.rs-2410607/v1

Abstract

Background: Extracorporeal shock wave therapy (ESWT) has been widely used for pain control in musculoskeletal disorders. Whether ESWT can relieve chronic low back pain and improve lumbar function is still controversial. Therefore, we designed a meta-analysis based on relevant studies to comprehensively analyze and determine the efficacy and safety of ESWT for chronic low back pain.

Methods:PubMed, Embase, Cochrane Library, and Web of Science were systematically searched for randomized controlled trials (RCT) studies on extracorporeal shock wave therapy for chronic low back pain from inception to September 2022. The quality of the included literatures was evaluated according to Cochrane systematic review criteria, relevant data were extracted, and meta-analysis was performed using RevMan 5.4 software.

Results:12 RCTs involving 632 patients were included to this investigation. In terms of pain relief, ESWT was associated with lower VAS scores in patients receiving ESWT in comparison with controls at 4 weeks (WMD =−1.04; 95% CI =−1.44 to −0.65; P <0.001) and 12 weeks (WMD =−0.85; 95% CI =−1.30 to −0.41; P <0.001). In terms of improvement of dysfunction index, ESWT significantly increased ODI score in comparison with control group at 4 weeks (WMD =−4.22; 95% CI =−7.55 to −0.89; P <0.001) and 12 weeks (WMD =−4.51; 95% CI =−8.58 to −0.44; P = 0.03). For mental health, there was no significant difference in the ESWT group compared with the control group after 4 weeks of intervention (SMD =1.17; 95% CI =−0.10 to 2.45; P = 0.07).

Conclusion: ESWT can relieve pain and improve lumbar dysfunction in patients with chronic low back pain, but has no significant effect on patients' mental health.

Background

Chronic low back pain (CLBP) refers to the pain syndrome that lasts for at least 12 weeks and occurs in the area below the margin of low ribs, above the transverse hip line and between the bilateral midaxillary line, usually accompanied by pain symptoms of one or both lower limbs [1]. The global prevalence rate of CLBP is 13.1%-20.3%, which has been on the rise in the past decade, with the number of patients rising from 370 million in 1990 to 570 million in 2017 [2]. CLBP has become a global public health problem due to its high incidence, long course and easy recurrence, which seriously affects the quality of life of patients and even causes adverse psychological effects [3].

At present, CLBP is mainly treated conservatively (e.g., physical exercise, physiotherapy and drugs and other non-surgical therapy) with the purposes of relieving pain and restoring physical function [4, 5]. However, as a self-exercise therapy, physical exercise has shortcomings such as lack of standard posture and poor adherence; physiotherapy is difficult to achieve a long-term analgesic effect, while drug treatment may be accompanied by nausea, constipation, fatigue and other side effects [6]. In addition, despite the availability of various interventions, more than two-thirds of patients with low back pain relapse within 12 months of recovery [7]. Therefore, it is particularly important to seek other safe and effective treatment strategies.

As an emerging therapeutic method, ESWT is a series of single sound pulses characterized by high pressure peak and short-term rapid pressure rises, and has achieved significant results in the treatment of musculoskeletal system diseases such as osteonecrosis of the femoral head and myofascitis [8, 9]. However, the use of ESWT in the treatment of CLBP is still controversial, and some clinical guidelines do not recommend it as a routine choice [10]. In recent years, there have been some randomized controlled trials (RCTs) focusing on the use of ESWT in the treatment of CLBP. Therefore, an updated meta-analysis is needed to synthesize the literature. The main purpose of this meta-analysis was to evaluate the efficacy and safety of ESWT in reducing pain, improving function, and promoting mental health in patients with CLBP compared with other treatment methods such as physical exercise, physiotherapy, and drugs.

Methods

Design

This systematic review and meta-analysis follow the guidelines of the Systematic Review and Meta-Analysis (PRISMA) Preferred Reporting Project Statement and the recommendations of the Cochrane Collaboration [11, 12]. 

Search strategy

PubMed, Embase, Web Sciences, and the Cochrane Library database were systematically searched from the initial release of the relevant database until November 20, 2022 to identify studies related to the use of ESWT for CLBP. The following search terms were used in the initial literature search: (Extracorporeal Shock Wave Therapy or ESWT) and (Chronic Low Back Pain or low back pain). Two researchers independently reviewed the selected studies, and any disagreements were resolved through discussion with the corresponding author. In addition, the reference lists of these articles were manually checked to identify other publications that might be relevant.

Inclusion criteria

  1. Patients: clinically diagnosed with chronic low back pain;
  2. Experimental group: ESWT or ESWT combined with other intervention methods;
  3. Control group: physical exercise, physiotherapy, medicine or other similar interventions;
  4. Results: Visual analogue scale (VAS), Oswestry Disability Index (ODI), mental health and other functional parameters.
  5. Study design: Randomized controlled trial (RCT).

Exclusion criteria

(1) Non-human research or animal experiments;

(2) The subject had acute lumbago;

(3) Articles are abstracts, letters, editorials, expert opinions, comments, and case reports;

(4) Non-English studies;

(5) Studies without sufficient data for analysis.

Data extraction

The demographic characteristics extracted by the systematic review were: first author, year of publication, study design, sample size of each study, mean age of patients, sex ratio, and follow-up. The main outcome measures of treatment effect in this study included VAS pain score, ODI dysfunction index and patients' mental health score. If scores were recorded at different follow-up times, we chose the time points closest to 4 weeks and 12weeks to predict efficacy. In addition, adverse events were recorded.

Bias assessment and quality classification

The quality of included studies was assessed by the Cochrane Collaboration’s tool for assessing the risk of bias which was recommended for systematic reviews of interventions in Cochrane Handbook version 5.4.0 [13]. 7 domains of bias including selection bias, performance bias, detection bias, attribution bias, reporting bias, and other sources of bias were evaluated. Judgments were presented as "high risk," "low risk," or "risk ambiguous," and the quality assessment numbers were generated by Revman version 5.4. Two independent reviewers assessed the risk of bias and a third senior investigator resolved cases of disagreement between the former. 

Statistical analyses

Meta-analysis was performed using RevMan5.4 software provided by the Cochrane Collaboration network, and forest maps were used to display the results. Since the measured data were continuous variables, the standardized mean difference (SMD) or weighted mean difference (WMD) and 95% confidence interval were selected as the main effect parameters according to the differences in the measurement methods of the indicators. Heterogeneity was tested by I2 test. If I2 was less than 50%, there was no significant heterogeneity in the experimental results and fixed effects model was used to analyze the results. When I2 ≥ 50%, the heterogeneity was significant, the random effects model should be adopted. Furthermore, the source of heterogeneity can be explored by sensitivity analysis and subgroup analysis. Publication bias was analyzed by funnel plot when more than 10 RCTs were included.

Results

Selection of studies

In the initial literature search, there were 186 papers retrieved. 80 articles were deleted by double-checking, and 84 studies were excluded after a review of the title and abstract. Then, after a full text review, we excluded 10 articles that did not meet the inclusion criteria. Finally, 12 RCTs involving a total of 632 patients (318 in the ESWT group and 314 in the control group) were included in this study. The selection process is represented in the PRISMA flowchart (Fig. 1).

Study Characteristics and Risk of Bias

These studies are characterized by Table 1. All articles were published in English between 2014 and 2022. Sample sizes range from 28 to 200. All the experimental groups received ESWT treatment, while the control group received different conservative treatments including exercise therapy [14-17], physiotherapy [18-20], drug injection [21, 22], oral medication [23, 24], and manual therapy [25]. The items for risk of bias included in each study were shown in Fig. 2

Pain score at 4 weeks

12 articles included in our study compared pain scores at 4 weeks between the ESWT group and the control group. There was significant heterogeneity (I2 = 86%, P <0.001), so we conducted subgroup analysis according to the intervention methods of the control group using the random-effects model. The results showed that the trigger drug injection group had high heterogeneity (I2 = 94%, P <0.001), but there was no significant difference between this group and ESWT, so the overall results were still consistent. The present meta-analysis demonstrated that ESWT was associated a significant reduction of pain score at 4 weeks (WMD =−1.04; 95% CI =−1.44 to −0.65; P <0.001, Fig. 3).

Pain score at 12 weeks

A total of 5 studies reported pain scores at 12 weeks. There was significant heterogeneity, and random-effects model was used (I2 = 87%, P <0.001). This meta-analysis showed that pain score of the ESWT group was significantly lower than that of the control group at 12 weeks (WMD =−0.85; 95% CI =−1.30 to −0.41; P <001, Fig. 4).

ODI score at 4 weeks

A total of 10 articles compared ODI scores at 4 weeks between the ESWT and control groups. The difference was significant (I2 = 96%, P <0.001). Subgroup analysis was conducted according to the intervention methods of the control group, and random effects model was selected. The physical therapy group was the main source of heterogeneity (I2 = 83%, P <0.001), but there was no significant difference between the control group and the ESWT group, so the overall results were consistent and reliable. In the present meta-analysis, ESWT was associated with a significant increase in ODI scores at 4 weeks (WMD =−4.22; 95% CI =−7.55 to −0.89; P <0.001, Fig. 5).

ODI score at 12 weeks

ODI scores at 12 weeks were obtained from 4 studies with significant heterogeneity (I2 = 56%, P = 0.08) and random effects model was used. The combined results showed a significant difference between the groups (WMD =−4.51; 95% CI =−8.58 to −0.44; P = 0.03, Fig. 6).

Mental health score at 4 weeks

A total of 5 studies reported mental health scores at 4 weeks, with significant heterogeneity (I2 = 96%, P <0.001). The questionnaires used for mental health scores were inconsistent, so SMD was selected for meta-analysis. The results showed no specific significant difference in mental health score between the control group and ESWT 4 week (SMD =1.17; 95% CI =−0.10 to 2.45; P = 0.07, Fig. 7).

Sensitivity analysis 

When comparing the effects of ESWT on pain at 12 weeks and mental health at 4 weeks, we performed a sensitivity analysis due to considerable heterogeneity. A single study was excluded each time to assess the impact of individual data on the overall outcome. The results showed that the merger effect was robust and no significant deviation from the overall results was found in our study (Fig. 8).

Publication bias

Stata 15.0 software was used to conduct funnel plot analysis of the included literature on ESWT for 4-week pain and ODI outcome indexes. The funnel plot showed a basically symmetrical scatter point, indicating that there was no significant publication bias in the included literature, and the results of meta-analysis were credible (Fig. 9).

Discussion

The effectiveness of ESWT on pain, function and mental health of patients with CLBP was systematically reviewed. The results of this meta-analysis showed that ESWT, either as stand-alone or adjuvant treatment for CLBP, significantly reduced VAS scores at week 4 and week 12 compared to the control group, with a “moderate” recommended level based on GRADE [26]. Further, “low-to-moderate” quality evidence showed significant improvement in ODI scores at week 4 and week 12 for ESWT compared to other conservative treatments. However, with regard to mental health scores at week 4, we did not find significant differences between the two groups. Due to the limited number of articles included, further randomized controlled trials are needed to investigate the effectiveness of ESWT. In addition, no ESWT-related adverse events were found (not recorded or did not occur) in any of the 12 RCTs included in the study.

According to our information, there was only one previous meta-analysis about the application of ESWT in CLBP, but we found that this study had high heterogeneity in both pain and dysfunction index analyses, and no subgroup analysis or sensitivity analysis was conducted [27]. In addition, we found that this previous meta-analysis included an unpublished master's thesis and a study of participants with postpartum low back pain that may have affected the reliability of the results and were excluded from our study. Finally, we included 12 RCTs with a total of 632 patients, and explored the sources of the associated heterogeneity. Moreover, studies have shown that the occurrence of chronic low back pain is rarely caused by a single factor, but by a variety of physical and psychological mechanisms [28]. Holmes [29] believed that the limitations or disabilities in patients' daily life would lead to some psychosocial problems, which would further damage their quality of life. Therefore, we conducted the first meta-analysis about mental health scores in CLBP patients.

Low back pain is one of the most common conditions in clinical practice, with pain and movement limitation being the most basic symptoms. Pain alters the contraction pattern of the trunk muscles, resulting in spasm, increased tone and even atrophy of the low back muscles, significantly reducing the ability of the muscles to engage and destabilising the spine and vertebral balance [30, 31]. In addition, prolonged poor posture in the low back can lead to fatigue of the low back muscles and oedema of the surrounding soft tissues, exudation of inflammatory cells, accumulation of metabolic products and degeneration of muscle fibres, resulting in local adhesions, chronic hypoxia of the muscles and pain, all of which can contribute to recurrent episodes of CLBP [32, 33].

CLBP is treated with a variety of clinical approaches, including conservative treatment and surgical treatment. In its initial clinical use, ESWT was used by German medical scientists to save patients from surgical pain treatment [34]. With the passage of time, ESWT technology is gradually mature, and its clinical application is also increasing. Many clinical trials have shown that ESWT treatment can significantly reduce pain and complications of patients with CLBP [14, 22]. ESWT mainly treats chronic low back pain through the direct mechanical action of shock wave, and indirectly causes mechanical action through cavitation [35]. Firstly, when shock wave enters the human body, different mechanical effects will be generated at the interface of different tissues due to different contact media such as fat, tendon, ligament and bone tissue, and finally different forces will be generated on cells [36]. In these forces, tensile stress can relax tissues. It promotes microcirculation, while compressive stress can change the elasticity of cells and increase their ability to absorb oxygen for therapeutic purposes [37, 38]. Secondly, ESWT causes a large number of tiny bubbles to be created in the tissue, which rapidly expand and burst under the action of the shock wave, producing a high speed fluid microjet and a shock effect [39]. This cavitation effect is particularly effective in reopening occluded microvasculature and releasing soft tissue adhesions at the joint. The exact mechanism of the pain-relieving and functional properties of ESWT is not fully understood, and several studies have attempted to elucidate the mechanisms of shock waves from basic science and clinical studies. Studies have shown that the energy released by ESWT is well able to stimulate pain receptors located in skin, muscle, connective tissue, bone and joints, and activate unmyelinated C and A delta fibers to initiate the "gated" pain control system and block nerve transmission, resulting in analgesic effects [40, 41]. In addition, ESWT has been shown to significantly downregulate the levels of IL-1, TNF-α and MMPs in degenerated joint tissues, thereby reducing the local inflammatory response [42, 43]; At the same time, it also promotes the secretion of pain-reducing chemicals (e.g. endorphins), inhibits the release of pain factors such as substance P and calcitonin gene-related peptides, reduces peripheral nerve sensitivity and increases pain threshold levels [44, 45].

It is well known that adverse reactions are a major concern when evaluating the efficacy of ESWT. Therefore, the higher the risk of adverse reactions, the lower the clinical value of ESWT. In our study, 12 RCT articles all reported the incidence of adverse reactions after ESWT treatment. Therefore, based on the current meta-analysis, ESWT did not increase the risk of local reactions. However, considering the small sample size included in the study, the safety of ESWT needs to be further discussed.

Some limitations of this study should be noted. First, there are differences in etiology, pain duration, and related parameters used by ESWT in each study, which may lead to heterogeneity in the combination of results and limited evidence. Second, there are inevitably heterogeneous factors among the included researchers, such as age, gender, and racial differences. Next, different biases, including selection bias, language bias, data provision bias and publication bias, may reduce the accuracy of the results. Last but not least, the pain, function and mental health scores included in this meta-analysis were all obtained through questionnaires, and the outcome indicators may be subjective. If there are enough articles with objective observation indicators in the future, relevant studies can be improved.

Conclusion

ESWT is effective in reducing pain and dysfunction in CLBP patients without increasing the risk of adverse reactions, but it should be performed with caution. However, no significant effect was found on the improvement of mental health. More RCT are needed to verify findings in the current study.

Abbreviations

ESWT: Extracorporeal shock wave therapy; RCT: Randomized controlled trials; CLBP: Chronic low back pain; VAS: Visual analogue scale; ODI: Oswestry Disability Index; WMD: weighted mean difference; SMD: standardized mean difference; SD: standard deviation.

Declarations

Funding statement

This work was partially supported by the Young Scholars Program of Shandong Provincial Hospital, the Young Taishan Scholars Program of Shandong Province (Grant number tsqn201909183), the Academic Promotion Program of Shandong First Medical University (Grant number 2020RC008), and the Natural Science Foundation of Shandong Province (Grant numbers ZR2020QH072 and ZR2020MH098).

Acknowledgements

Not applicable.

Authors’ contributions

JD, KL, and QYZ conceived and designed the study. KL, LLC, and HRZ searched and selected relevant studies. QYZ,XQX extractedand interpreted data. KL, JD, and ZNY analyzed the data. KL and QYZ wrote the paper. JD and XQX revised the manuscript. All authors read and approved the final manuscript.

Availability of data and materials

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate

Not applicable

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

Author details

1Shandong Provincial Hospital1Shandong Sport University, Jinan, Shandong, China.

2Department of Orthopedics, Shandong Provincial Hospital Affiliated to Shandong First Medical University,Jinan, Shandong, China.

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Table

Table 1 is available in the Supplementary Files section