Research Trends of Acupuncture Therapy on Myofascial Pain Syndrome from 2000 to 2022: A Bibliometric Analysis

Introduction

Myofascial Pain Syndrome (MPS) is considered as one of the most common chronic musculoskeletal pain syndromes.¹ In pain clinics, the prevalence of MPS may reach highly up to 85%.² MPS is always characterized by the presence of myofascial trigger points (MTrPs). A MTrP is defined as a specific sensitive zone or point, tender region or a taut band contained in the skeletal muscle fibers, which produces the significant pain as well as motor dysfunction of the muscle.^3,4 Additionally, MPS is often associated with anxiety and depression.^5–7 The existence of MTrPs always seriously reduce the patients’ quality of life.

The goal of MPS treatment is pain relief. Nonsteroidal anti-inflammatory drugs (NSAIDs) and muscle relaxants are commonly used on patients with MPS.⁸ However, there is not enough evidence to determine if they are effective and they always tend to cause gastrointestinal discomfort and drowsiness.^9,10 Some studies reveal that extracorporeal shockwave, low power laser and therapeutic ultrasound can be used for MPS.^11,12 The evidences of these therapies’ beneficial effect remain inconclusive. Acupuncture and dry needling are more and more recognized as effective treatments with minimal side effects for MPS.^2,13–16 However dry needling is similar to acupuncture and frequently is regarded as a form of acupuncture.¹⁷ During the past decades, clinical and scientific interest in acupuncture for MPS has grown significantly. Some clinical trials and systematic reviews showed that acupuncture could significantly relieve pain and reduce irritability of MPS.^18–21 While the exact mechanism of acupuncture or dry needling for MPS is not unraveled nowadays. The mechanism researches mainly focus on the peripheral and central aspects. Researches revealed that acupuncture could inhibit pain transmission by decreasing SP and increasing endogenous opioids.^14,22 A recent research suggested that dry needling improved strength, functionality and locomotor activity in a rat model of muscle pain syndromes by inducing an antioxidant effect.²³ Another research showed that the needling on trigger point changed the gene expression of muscle tissue to accelerate the muscular regeneration.²⁴ As for the central aspect, some scholars supported that acupuncture could activate the supraspinal and higher centres involved in pain processing.²⁵ In contrast, some researchers argued that there was no significant difference between acupuncture and placebo acupuncture for treating MPS.²⁶

There are many studies on the curative effect and mechanism of acupuncture treatment for MPS. However, to the best of our knowledge, a bibliometric analysis of the use of acupuncture for MPS has not yet been performed. Therefore, the present study aims to evaluate the research trends and hot spots of acupuncture treatment on MPS within the past 23 years (from 2000 to 2022) through bibliometric analysis by using CiteSpace. CiteSpace is a widely used visualization tool invented by Professor Chaomei Chen, which can produce co-occurrence network maps of countries, institutions, authors, keywords and co-citation network of cited journals, cited authors, cited references through a series of mathematical tools.^27–29

Methods

Data Collection

Literatures were obtained from the Science Citation Index Expanded (SCI-expanded) of the Web of Science (WoS) Core Collection database. To prevent the omission of searching the literature, we obtained the synonyms for “myofascial pain syndrome” and “acupuncture” through the Medical Subject Heading (MeSH) Database in PubMed. The data search strategy included the topic “myofascial pain syndrome” and “acupuncture”. The publication period of the literature ranged from January 1, 2000 to June 30, 2022. Specific search strategies and results are shown in Table 1. There were no restrictions on language, categories or document types. A total of 405 references were acquired, while 403 references were used for bibliometrics analysis after CiteSpace removed duplication.

Table 1 The Topic Search Query

Analysis Tool

Bibliometric analysis was performed by CiteSpace (6.1.R3) software, which is an excellent scientific econometric analysis software based on the Java platform for analyzing and visualizing network.³⁰ It can be used to analyze the annual output counts, the prolific authors, journals, institutions and countries. It also can be used to explore the co-occurrence relationships of countries, institutions, authors and keywords, and the co-citation relationships of authors, journals and references.

The parameters of CiteSpace were set as follows: time slicing (2000–2022), years per slice (1), pruning (pathfinder). Visualization knowledge maps consist of nodes and links. Different nodes in the map represent different elements such as author, keyword, institution, country, etc. Links between the nodes signified relationships of cooperation or cooccurrence or co-citation. A larger size of the node represents a high frequency of publications and a larger width of the link indicates stronger co-operation/co-occurrence/co-citation. The color of nodes and lines represents different years. The purple circle represents centrality. Nodes with high centrality usually mean turning points or pivotal points in a specific field.^31,32

Results and Discussion

Annual Publication

A total of 403 publications were included by searching the SCI-expanded database from 2000 to 2022 using the aforementioned search strategy. The annual number of publications is presented in Figure 1. There was a small number of articles published before 2004. The number of publications continued to increase to 16 from 2004 to 2008. There was a slight decrease in 2009. From 2009 to 2012, the number slowly increased to 22. But it was suddenly decreased to 15 in 2013. While from 2013 to 2015, the number increased rapidly and continually, reaching a peak of 36. It decreased in 2016 and then increased slowly from 2017 to 2020. The number slightly dropped to 28 in 2021. Additionally, given that we performed the search on June 30, 2022, the total number of retrieved publications in 2022 cannot reflect the publication of the whole year. In summary, the total number increased over the past 23 years but with some fluctuations. The results indicate that more acupuncture researches on MPS were performed and acupuncture, as a complementary and alternative treatment, is receiving more attention.

Figure 1 The annual number of publications on acupuncture for MPS from 2000 to 2022.

Analysis of Documents Type

Four document types were identified in the total of 403 records. Articles (259) were the most frequently used document type, accounting for 64.27% of the total records. They are followed by reviews (105, 26.05%), letter (8, 2%) and editorial material (4, 1%; Table 2).

Table 2 Document Types for Documents Referencing Acupuncture for MPS

Analysis of Cited Journals

The cited journal map was generated by CiteSpace, which resulted in 549 nodes and 2949 links (Figure 2). The Journal of Pain ranked first in the frequency of cited journals, followed by Arch Phys Med Rehab and Acupunct Med (Table 3). The Journal of AM J Chinese Med ranked first in the centrality, followed by Anesth Analg and Neuroscl Lett (Table 3). In the journal cited in 294 records of Pain, one article got largest citations, which performed a meta-analysis of acupuncture for four chronic pain conditions and supported that acupuncture was effective and was more than a placebo for the treatment of chronic pain, including MPS. The meta-analysis provided robust evidence that acupuncture was a reasonable referral option for patients with chronic pain.³³ While in the highest centrality of AM J Chinese Med, the article which got largest citations was a guideline for the management of chronic nonspecific low back pain, and it did not recommend acupuncture for the treatment of chronic low back pain, because of that there was conflicting and limited evidence that acupuncture was better than a sham procedure or standard treatment such as exercise, NSAIDs.³⁴ Some conditions of chronic nonspecific low back pain belong to MPS in clinical.³⁵ More high-quality clinical trials are needed in the future researches to further confirm the efficacy of acupuncture on MPS.

Table 3 Top 10 Cited Journals Related to Acupuncture on MPS

Figure 2 Cited journal maps of acupuncture on MPS from 2000 to 2022. The nodes in the map represent journals, and the lines between the nodes mean co-citation relationships. The different colors of the nodes represent the different years. The larger the node area, the greater the number of co-citations. The purple ring represents centrality, and nodes with high centrality are considered as pivotal points in the publications.

Analysis of Country and Institution

The merged network of countries/regions comprised 46 nodes and 109 links (Figure 3), indicating that the 403 references were published by researchers in 46 countries/regions. As shown in Table 4, the top 5 countries/regions of publications were USA (90), Peoples R China (71), Spain (45), Taiwan (34) and England (28). The top 5 countries/regions for centrality (purple ring) were USA (0.25), England (0.23), Germany (0.20), Spain (0.15) and Peoples R China (0.12). China was one of the important countries on researching acupuncture for MPS, maybe because of that acupuncture originated from China. USA, England, Spain, Germany are all developed countries, which means that acupuncture was popular in developed countries. Interestingly, USA was first both of publications and centrality, which indicated the much attention on acupuncture treatment for MPS in USA. Further analysis from the citations revealed that more meta-analysis of randomized controlled trials (RCTs) of acupuncture therapy on MPS were being performed. Most of the meta-analysis indicated that acupuncture was beneficial for MPS and the acupuncture was more than a placebo.^21,35,36 However, additional well-designed studies are needed to support the recommendation due to the small number of high-quality RCTs published to date according to a meta-analysis.²¹

Table 4 Top 10 Publications and Centrality of Countries/Regions Related to Acupuncture on MPS

Figure 3 Map of countries/regions researching acupuncture on MPS from 2000 to 2022. The nodes in the map represent countries or territories. The lines between the nodes means cooperation relationships. The different colors of the nodes represent the different years. The larger the node area, the larger the number of publications. The purple ring represents centrality, and nodes with high centrality are considered as pivotal points in the literature.

The map of institutions consisted of 412 nodes and 471 links (Figure 4). The 403 publications were distributed among 412 research institutions. The top five institutions of publications were China Medicine University (22), Universidad of Rey Juan Carlos (11), Hungkuang University (10), Harvard University (8) and Chengdu University of Traditional Chinese Medicine (7) (Table 5). There were three institutions among the top five institutions of publications in China, which indicated that China was an important country on researching acupuncture for MPS. Further analysis indicated that the main research direction of China Medicine University was the remote effect of acupuncture on the irritability of MTrPs and the spinal cord mechanism.^37–39 The centralities of all institutions were low. The institutions of China Medicine University and Hungkuang University had the strongest cooperation, while cooperation among other institutions should be further strengthened.

Table 5 Top 5 Publications and Centrality of Institutions Related to Acupuncture on MPS

Figure 4 Map of institutions researching acupuncture for MPS from 2000 to 2022. The nodes in the map represent institutions, and the lines between the nodes represent collaborative relationships. The different colors in the nodes represent the different years, and the larger the node area, the larger the number of publications.

Analysis of Author and Cited Author

Distribution of authors map consisted of 497 nodes and 684 links (Figure 5). Table 6 shows the top ten authors who have published articles related to acupuncture for MPS. Liwei Chou was the most productive author who have published 14 articles, followed by Changzern Hong (13), Cesar Fernandezdelaspenas (11) and Yuehling Hsieh (9). Among the ten authors, Liwei Chou, Changzern Hong, Yuehling Hsieh and Chenchia Yang all came from Taiwan and had close cooperation with each other on the remote effects and mechanism of dry needling at myofascial trigger points.^22,38,40,41 Their researches revealed that acupuncture had remote effectiveness on suppressing the myofascial trigger point irritability and this effect may be related to the normal spinal cord function, interactions within the endogenous opioid system and biochemicals associated with pain, inflammation, and hypoxia. The links showed that the cooperation between authors in this field was not close. Moreover, the centrality for each collaboration was 0, suggesting that collaboration between research authors should been further strengthened.

Table 6 Top 10 Active Authors Related to Acupuncture on MPS

Figure 5 Map of authors related to acupuncture on MPS from 2000 to 2022. The nodes represent authors, and the lines between the nodes represent the collaborative relationships. The different colors of the nodes represent the different years. The larger the node area, the greater the number of publications.

The map of cited authors consisted of 683 nodes and 2786 links (Figure 6). The top five frequency and centrality of cited authors are shown in Table 7. In terms of co-citation counts, Simons DG (151) ranked first, followed by Hong CZ (119), Melzack R (97), Tough EA (94) and Dommerholt J (79). The top five centrality of cited authors were Furlan AD (0.25), Ceccherelli F (0.17), Berman BM (0.14), Itoh K (0.11) and Deyo RA (0.11). A comprehensive analysis of co-citation counts and centrality revealed that Simons DG and Furlan AD had an important influence in the field of researching acupuncture on MPS. Simons DG was a clinical professor coming from University of California (USA). One of his biggest achievements was the book of “Myofascial Pain and Dysfunction: The Trigger Point Manual”, in which he explained the clinical characteristics, causes and mechanisms of the myofascial trigger points.^42,43 Although his hypothesis of energy crisis about the mechanism of MPS was widely accepted by researches, the precise mechanism of MPS is still not clear nowadays. More basic researches are necessary to explore the mechanism of MPS. Furlan AD focused on the treatment of low back pain who was from the institution of work and health in Toronto (Canada). Some of his system reviews and meta-analysis articles indicated that acupuncture and dry-needling might be safe and useful for chronic low back pain, while more high-quality trials with low risk of bias, large sample size are urgently needed to provide sufficient evidences to demonstrate the therapeutic effects of acupuncture therapy on low back pain.^44–46

Table 7 Top 5 Frequency and Centrality of Cited Authors Related to Acupuncture on MPS

Figure 6 Map of cited author related to acupuncture on MPS from 2000 to 2022. The nodes represent authors, and the lines between the nodes represent the co-citation relationships. The different colors of the nodes represent the different years. The larger the node area, the greater the number of co-citations. The purple ring represents centrality, and nodes with high centrality are considered as pivotal points in the publications.

Analysis of Cited Reference

A total of 13,136 references were generated from 403 publications to analysis cited references, and the map with 788 nodes and 2846 links was generated (Figure 7). The top five frequency and centrality of cited references were shown in Table 8 and Table 9 respectively. According to the frequency of cited references, three articles among the top five articles were all the meta-analysis of acupuncture treatment on MPS, indicating that acupuncture, compared to sham or placebo, had overall treatment effects on relieving myofascial trigger point pain, while the evidence was limited. The general problems of most RCTs were the limited sample size and poor quality.^21,47,48 A double-blinded and randomized controlled trial of acupuncture on MPS conducted by Tekin L, which was ranked third, showed the effectiveness of dry needling compared to sham needling on relieving the pain and improving the quality of life of patients with MPS.⁴⁹ In terms of the centrality, the first was a review published by Simons DG which introduced the clinical features, etiology and treatments of MTrPs and explored how MTrPs may relate to musculoskeletal dysfunction.⁵⁰ The second paper in the ranking list published by Shah JP revealed that the biochemical milieu of the upper trapezius muscle in subjects with active myofascial trigger points differed from subjects without active MTrPs. There were higher concentrations of inflammatory mediators, neuropeptides, cytokines, and catecholamines in the subjects with active MTrPs than in latent or normal subjects.⁵¹ Irnich D and Tekin L conducted a randomized controlled trial, respectively, to identify the effectiveness of acupuncture on MPS, and the results both supported that true acupuncture was superior to sham acupuncture in relieving pain.^49,52 Over the past 23 years, the researches in this topic mainly focused on meta-analyses, RCTs, analgesic mechanisms based on biochemical. Generally, the well-designed RCTs with higher quality are urgently needed in the future researches.

Table 8 Top 5 Frequency of Cited Reference Related to Acupuncture on MPS

Table 9 Top 5 Centrality of Cited Reference Related to Acupuncture on MPS

Figure 7 Map of cited references related to acupuncture on MPS from 2000 to 2022. The nodes represent cited references, and the lines between the nodes represent the co-citation relationships. The different colors of the nodes represent the different years. The larger the node area, the greater the number of co-citations. The purple ring represents centrality, and nodes with high centrality are considered as pivotal points in the publications.

Analysis of Keywords

The map of keywords occurrence consisted of 489 nodes and 1996 links (Figure 8) which could indicate hot topics. According to the frequency and centrality, the hot keywords were “acupuncture”, “management”, “low back pain”, “dry needling”, “pain”, “double blind”, “myofascial pain” (Table 10). There were three hot topics: (1) The clinical feature of MPS: muscle pain was the most common and distressing symptom in patients with MPS. It may be accompanied by a sensory of paresthesia and dysesthesia.⁵³ Researches have showed that there were peripheral and central sensitization in MPS.⁵⁴ Therefore, the peripheral and central modulation of acupuncture on MPS was one of the main mechanism research directions. (2) Measure of intervention: acupuncture or dry needling has been widely used for treating MPS.⁵⁵ A randomized controlled trial comparing dry needling to sham dry needling demonstrated that dry needling was effective in relieving the pain and in improving the quality of life of patients with MPS.⁴⁹ Another randomized controlled trial revealed that trigger point acupuncture may be more effective on patients with chronic neck pain than the standard acupuncture therapy.¹⁷ A meta-analysis of 12 RCT studies comparing dry needling to sham or placebo showed that dry needling decreased pain immediately after treatment and at 4 weeks in patients with upper-quarter MPS.²¹ However, more high-quality RCTs were proposed. Additionally, the acupuncture treatments for patient with MPS were diverse in different studies, and this has emphasized the importance of developing treatments with uniform and optimal parameters such as frequency, duration, and intensity of acupuncture in future researches. (3) Research method: randomized controlled trial was the most effective method to evaluate the clinical efficiency of acupuncture on MPS. Implementation of blinding was an important principle of randomized controlled trial. However, double blinding method to both the acupuncturist and subject was difficult to be conducted in many acupuncture studies, instead single blinding to evaluator and subject was often been performed.^17,37,52 The implementation of sham acupuncture or placebo was another problem in acupuncture researches. There was no criteria of placebo acupuncture method. Actually, placebo acupuncture may be an effective control with a certain specific effect.⁵⁶ Therefore, the setting of sham acupuncture or placebo should be more strict.

Table 10 Top 10 Frequency and Centrality of Keywords Related to Acupuncture on MPS

Figure 8 Map of keywords occurrence related to acupuncture on MPS from 2000 to 2022. The nodes represent key words, and the lines between the nodes represent the co-occurrence relationships. The different colors of the nodes represent the different years. The larger the node area, the higher the frequency.The purple ring represents centrality, and nodes with high centrality are considered as pivotal points in the publications.

The burst keywords mean keywords that were cited frequently over a period of time. The burst keywords are indicators of the research frontier trends. The top 20 keywords with the strongest citation bursts in the researches of acupuncture on MPS from 2000 to 2022 are shown in Figure 9. The keywords “meta-analysis”, “acupuncture point”, “double blind”, “mechanism”, “irritability” had the strongest citation bursts. As a method of evaluating the effectiveness of acupuncture therapy, meta-analysis was popular in recent four years. Results demonstrated that acupuncture therapy was beneficial in relieving pain, reducing muscle irritability and improving life quality.²¹ In recent years, the mechanism researches of acupuncture on MPS mainly focused on acupuncture to the spontaneous electrical activity of the MTrPs, releasing of local pain-causing substances at MTrPs, modulating of peripheral nociception and dorsal horn neuron activity.^37,55,57 While the basic researches or animal experiments were insufficient compared to clinical researches on acupuncture for MPS, and most of the results were preliminary. More deep basic researches are needed in future researches.

Figure 9 Top 20 keywords with the strongest citation bursts. The red bars mean that the keywords were cited frequently, the green bars showed that the keywords were cited infrequently.

Conclusion

The current study shows that MPS received more and more attention in the recent 23 years. According to the analysis of country, institution and author, it was obvious that acupuncture, as a traditional treatment of Chinese medicine, received full attention in China. What is more, acupuncture was also more and more acceptable and popular in the world, especially in developed countries. However, the cooperation between different countries, institutions and authors, especially transnational cooperation, should be further strengthened to promote acupuncture as a complementary therapy method to control pain for MPS.

The main research directions were the therapeutic effect and mechanism of acupuncture therapy for MPS. According to the cited reference and keywords, the randomized controlled trial and meta-analysis were the main methods to evaluate the effectiveness of acupuncture treatment on MPS. However, most meta-analysis affirmed the effects of acupuncture on relieving pain, reducing muscle irritability and improving life quality. There was controversy about the therapeutic effects of acupuncture for MPS. Limited sample size and high risk of bias were the common problems. In future researches, more randomized controlled trial studies with multi-center, large scale, double-blinding and high quality are needed. Clinical trials to unify the optimal parameters such as frequency, duration, and intensity of acupuncture should be carried out in the future. The mechanism of acupuncture on MPS mainly focused on pain regulation and electrophysiological mechanism. More deep basic researches are needed in future researches.

In summary, this study provides a perspective to the potential collaborators and institutions, hot topics and research frontiers of acupuncture therapy on MPS. The results may help researchers explore new direction for the future research. However, there are some limitations in the present study. Due to the limitation of CiteSpace software, we only included publications in English from the database of SCI-Expanded, which may result in that the data not be comprehensive enough.