Global Research Trends and Hotspots in Lateral Epicondylitis During the Past 30 Years: A Bibliometric and Visualization Study

Abstract

Background

Lateral epicondylitis is a common clinical disease characterized by lateral elbow pain, seriously affecting patients’ daily life and work. There is a lack of comprehensive and systematic visual analysis of the literature in this field. Therefore, we analyzed the literature on lateral epicondylitis in the past 30 years and summarized the hot spots and frontiers of research in this field to provide ideas and references for subsequent researchers.

Material/Methods

CiteSpace, VOSviewer, and R-Bibliometrix tools were primarily used to collect, visualize, and analyze data from the literature on lateral epicondylitis in the Web of Science database’s core dataset from 1990 to 2022.

Results

There were altogether 1556 items in the literature. Recent years have seen a noticeable development trend in the volume of pertinent literature that is published annually. The United States took first place with 447 papers. Univ Queensland ranked first with 42 papers. Vicenzino B, an academic at the University of Queensland, Australia, ranked first, with 48 papers.

Conclusions

Yearly volumes and forecasts suggest the USA will continue to lead the world in publications on lateral epicondylitis, with extensive collaboration among authors. More collaboration is still needed in various nations and organizations, according to an analysis of the research literature from the previous 30 years. The mechanism of action of different injectable preparations, such as corticosteroids for the treatment of LE is still unclear, as well as the cellular transduction pathways through which PRP affects LE.

Background

Lateral epicondylitis (LE), also known as tennis elbow, is a common orthopedic disease and is frequently seen in professional athletes, such as tennis players and badminton players. The prevalence of LE is as high as 1% to 3% [1], and is most prevalent in people aged 35 to 50 years [2]. The prevalence of LE in professional athletes is 7% [3]. There is no significant gender difference. Patients usually present with unilateral and, less commonly, bilateral epicondylitis, with the dominant arm being the most commonly affected [4]. It is usually self-limiting, but in a small number of individuals, symptoms can last for 18 months to 2 years [5]. It is a chronic injury of the extensor carpi radialis brevis, with the main clinical manifestation being pain over the elbow joint and, in some cases, impaired movement of the elbow joint, particularly during hand shaking or professional sports [6]. The pathology is based on the degeneration of the tendon tissue. In recent years, with the spread of information technology and electronic products, the age of onset of the disease is becoming younger, its prevalence is increasing year by year, and the disease is prone to recurrence [7]. It has a significant negative impact on patients’ physical and mental health as well as their quality of life [8]. We found no relevant bibliometric studies based on visual analytics software in this area at present. Therefore, this article aims to map the scientific knowledge of the study of LE using visualization tools, with the aim of analyzing the hotspots, frontiers, and evolutionary pathways and gaining insight into the state of research in this field to provide a reference for researchers.

Material and Methods

Methodological Data Sources and Retrieval Methods

Co-citation networks are produced utilizing reference citations in the VOSviewer program, developed by Professors Waltman and Van Eck, and the CiteSpace software, developed by Professor Chen C. These networks highlight the organization of certain study topics [9]. The relevant literature over the past 30 years was examined in terms of high-impact nations or regions, organizations, authors, journals, keywords, and co-cited literature using the visualization applications CiteSpace 6.1, R-Bibliometrix 4.6.1, and VOSviewer 1.6.18. The search term “TS=(Lateral Humeral Epicondylitis OR Lateral Epicondylitis OR Tennis Elbow)” was searched for the period 1990-01-01 to 2022-12-04. A total of 1638 relevant articles were retrieved by selecting “Article” and “Review” as the document type and “English” as the language. After excluding the abstracts of conferences, announcements, news, conference papers, and retraction notices, a total of 1556 relevant papers were finally included. The articles screened were all peer-reviewed journal articles, which have good authority and representativeness. Consider importing data into the CiteSpace visual analysis software as an example. The output “plain text” format for the obtained literature records includes “complete records and references”; with every 500 documents, a file is produced. The file is then renamed in “download” form, imported into the CiteSpace software input folder, and visual analysis is then started. In Figure 1, the workflow diagram is displayed.

Figure 1.

Workflow diagram.

Selection of Literature

Two reviewers read the literature independently. Title and abstract screening were done on articles before inclusion and exclusion criteria were used. In the event of a disagreement during screening, a third reviewer was tasked with reading the full manuscript and rendering a judgment.

Data Analysis

CiteSpace 6.1 analyzes important information from publications, such as information about the author, keywords, research institution, and other factors, to identify the information relationships in the literature. The settings for CiteSpace 6.1’s visualization software include 1990–2022, 1 year as the time interval, “Top N” as the threshold object with a value of 50, and “Pathfinder” as the cut connection to disassemble the network model and highlight key elements. Author, institution, keyword, cited literature, nation (region), cited author, and author were chosen for co-occurrence analysis and visual charting for node kinds [10]. Co-occurrence (characteristic words or keywords) mapping is more useful for analyzing the evolution of research hotspots and hotspots, especially with the use of burst term; the most popular method is co-citation mapping, which facilitates the analysis of a research topic’s development through the use of important nodes, clusters, and colors in the mapping, for example, co-citation analysis of literature refers to the phenomenon of 2 or more references being cited by the same publication [11].

Results

Trends in Quantity of Published Articles

The Web of Science database is one of the largest citation databases in the world. There were 1556 recovered LE-related papers, and Figure 2A displays the yearly publishing output in various nations. From 1990 to 2022, the quantity of research articles on LE usually increased with time, with the number of publications increased by nearly 44% in 2019 compared to the previous year and maintained at around 110 thereafter, reaching an all-time high in 2021. The most publications are published each year in the United States, and the share of publications from Turkey and China has been increasing in recent years. We discovered significant correlations using a polynomial fit analysis between the year of publication and the total number of publications (coefficients of determination (R2) for total papers, articles, reviews, and there were 0.9197, 0.9347, 0.7831, and 0.8807 randomized controlled trials (RCTs), respectively). As shown in Figure 2, we anticipated that 138 publications, consisting of approximately 101 articles, 37 reviews, and 40 RCTs, will be published in 2025 based on the polynomial fit research Figure 2B. Generally, the growth of orthopedics and sports medicine has resulted in more in-depth research. However, it is clear that there are still relatively few high-caliber RCT studies, despite the fact that the number of publications grows each year.

Figure 2.

(A) Bibliometric analysis of the WoS core database SCIE output. The number of publications on research on lateral epicondylitis in different countries has changed year by year from 1990 to 2022. (B) Publication trends in the field of lateral epicondylitis research and the corresponding polynomial fit curves. (C). Econometric analysis of national collaborative literature in the field of lateral epicondylitis research, with darker colors representing more publications and connecting lines representing collaborative relationships. (D) Institutional co-occurrence network diagram for lateral epicondylitis. The circles in the chart indicate the volume of articles issued, with larger circles indicating more articles issued by the institution, the thickness of the outer purple circle representing the centrality of the institution, and the connecting lines indicating the existence of a collaborative or co-occurring relationship.

Cooperation Networks Across Nations or Regions

The visualization covered a total of 65 nations or areas, of which 20 had fewer than 20 articles. The USA had the most articles, with 447, followed by the UK with 141 and Australia with 122. According to the analysis of the countries, the USA (0.53), Australia (0.30), and Italy (0.25) are the top 3 countries in terms of centrality and have strong ties to other nations, as shown in Figure 2C and Table 1.

Table 1.

Top 10 high-impact countries and institutions for research on lateral epicondylitis.

Country	Number of articles published	Centrality	Institutions	Number of articles issued	Centrality
USA	447	0.53	Univ Queensland	42	0.04
England	141	0.24	Griffith Univ	27	0.03
Australia	122	0.3	Univ Wisconsin	19	0.01
Turkey	108	0	Hosp Special Surg	19	0.02
Canada	76	0.04	McMaster Univ	17	0.1
South Korea	71	0.02	Mayo Clin	16	0.08
Germany	70	0.2	Sapporo Med Univ	16	0.01
PR China	66	0.08	Monash Univ	14	0.03
Netherlands	60	0.06	Univ Amsterdam	14	0.03
Italy	60	0.25	Univ Milan	13	0.08

Networks of Collaboration and Research Institutes

A topological density of 0.002 and a total of 1997 nodes and 3989 connections were produced. There were 1997 universities publishing research on LE, of which 21 produced ≥10 papers. The University of Queensland was the most active, publishing 42 articles, followed by Griffith University with 27 articles and University of Wisconsin with 19. According to the visualization of research institutions, the top 3 institutions in terms of centrality were McMaster Univ (0.1), the University of Milan (0.08), and the Mayo Clinic (0.08). Research partnerships between these 3 universities and other institutions are widely established, as shown in Table 1 and Figure 2D.

Networks of Collaborators and High-Impact Authors

A total of 4831 authors were included in the visualization chart, of which 22 had ≥10 publications, the most prominent being Vicenzino B (38) from the University of Queensland, Australia, the second most frequent being Bisset L (24) from the University of Queensland, Australia; the third most frequent being Lee SY (20) from Chung-Ang University, South Korea. The highest document centrality was with Bisset L from the University of Queensland, Australia and Maffulli N from Queen Mary University of London, UK, both with a centrality of 0.05. The most highly cited author was Nirschl of Georgetown University (511 times), followed by Smidt N of the University of Amsterdam (34 times). The top cited author was Nirschl RP (511) from Georgetown University (USA), followed by Smidt N (348) from the University of Amsterdam (Netherlands) and Rompe JD (262) from Johannes Gutenberg University (Germany). The research team from the University of Queensland, Australia, represented by professors Vicenzino B, Bisset L, and Coombes BK, collaborate closely and constitute a densely clustered research group, and they produce many articles. The results of this team regarding this study focus on the clinical efficacy study of physiotherapy using elbow tui na (Chinese therapeutic massage) and exercise interventions combined with corticosteroid injections for LE and the use of hypersensitivity responses to hot and cold pain thresholds to differentiate the severity of patients with LE; a research team led by Korean academics Lee SY and Lee JH, who study the cellular molecular biology of platelet-rich plasma (PRP) release for tendon healing and mesenchymal stem cell therapy for the safety and efficacy of MSCs in the treatment of epicondylitis; a team centered on the Dutch academics Smidt N, Assendelft WJ and Van der Windt DA, whose areas of research were the clinical efficacy and meta-analysis of corticosteroids in the treatment of LE; and a team centered on the German academics Rompe JD and Maffulli N from the UK, whose area of expertise was the extracorporeal shock wave therapy’s analgesic effects on chronic tennis elbow. The figure shows that there was some collaboration between the author teams and was more evident among the high-yielding authors, with a lack of highly centered authors in the literature. See Figure 3A–3C and Table 2.

Figure 3.

(A) Author co-occurrence network diagram for lateral epicondylitis. The circles in the chart indicate the volume of posts, with larger circles indicating more posts by the author, the thickness of the outer purple circle indicating author centrality, and the connecting lines indicating the existence of a collaborative or co-occurring relationship. (B) Plot of high-yielding authors of lateral epicondylitis over time. The top 20 most prolific researchers in the field and their publications. The larger the node, the more literature published. The darker the color, the more citations. Dark blue represents the number of publications and light blue represents the number of citations per year. (C) The three-field plot showing the knowledge flow of lateral epicondylitis. (D) Distribution of hotspots of research in the literature on lateral epicondylitis by discipline.

Table 2.

Top 10 high-impact authors for research on lateral epicondylitis.

Author	Country	Institutions	Number of articles issued	Author	Frequency of citations	Country
Vicenzino B	Australia	Univ Queensland	38	Nirschl RP	511	United States
Bisset L	Australia	Univ Queensland	24	Smidt N	348	Netherlands
Lee SY	Korea	Chung-Ang University	20	Rompe JD	262	Germany
Assendelft WJ	Netherlands	Dutch College of General Practioners	15	Shiri R	255	Finland
Smidt N	Netherlands	Univ Amsterdam	14	Bisset L	249	Australia
Rompe JD	Germany	Johannes Gutenberg University	14	Kraushaar BS	219	United States
Van der Windt DA	Netherlands	Univ Amsterdam	13	Coombes BK	218	Australia
Coombes BK	Australia	Univ Queensland	13	Verhaar JAN	187	Netherlands
MacDermid JC	Canada	McMaster Univ	13	Buchbinder R	163	Australia
Lee JH	Korea	Kyungdong University	13	Coonrad RW	158	United States

Literature Research Hot Topics

Of the 1556 articles retrieved, the literature was divided into 25 categories based on analysis of the distribution of the literature’s research hotspots. Of these, 617 were in the category of orthopedics, 436 in sports science, 346 in surgery, and 252 in rehabilitation disciplines. The information shows that LE has been the subject of substantial study and development in the areas of orthopedics, sports science, surgery, and rehabilitation (Figure 3D).

Relationships Between Citations and High-Impact Journals

The top 3 journals in terms of quantity of articles were the Journal of Shoulder and Elbow Surgery (64 articles with 1380 citations and an average of 21.56 citations), the American Journal of Sports Medicine (47 articles with 4012 citations and an average of 85.36 citations), and the Journal of Hand Surgery-American Volume (36 articles with 1095 citations and an average of 30.42 citations). The top 3 journals with a high H index for the study of LE were the American Journal of Sports Medicine (32), the British Journal of Sports Medicine (22), and the Journal of Shoulder and Elbow Surgery (22). The top 3 journals in this field in terms of co-citation frequency were the Journal of Bone and Joint Surgery-American Volume (899 times), the American Journal of Sports Medicine (873 times), and the Journal of Hand Surgery-American Volume (601 times), according to the co-citation analysis of journals done by VOSviewer (Figures 4, 5 and Table 3).

Figure 4.

H index of high-impact journals for lateral epicondylitis research, 1990–2022.

Figure 5.

Cluster visualization of journal co-citation analysis generated based on VOSviewer software. Each node represents a journal, and the size of each circle is determined by the journal’s co-citation, the link is https://tinyurl.com/2no7dorc.

Table 3.

Status of high-impact journals for lateral epicondylitis research, 1990–2020.

Journal Name	Total number of articles	Total number of applications	Average number of citations	IF (2022)	JCR (2022)	H-index
Journal Of Shoulder and Elbow Surgery	64	1380	21.56	3.507	Q2	22
American Journal Of Sports Medicine	47	4012	85.36	7.01	Q1	32
Journal of Hand Surgery – American Volume	36	1095	30.42	2.342	Q3	18
Brithish Journal of Sports Medicine	29	1486	51.24	18.473	Q1	22
Archives of Physical Medicine and Rehabilitation	26	1061	40.81	4.06	Q1	19
Arthroscopy – The Journal of Arthroscopic and Related Surgery	26	1044	40.15	5.973	Q1	16
BMC Musculoskeletal Disorders	26	315	12.12	2.562	Q2	11
Journal of Hand Therapy	24	540	22.50	1.908	Q3	13
Journal of Orthopaedic & Sports Physical Therapy	22	452	20.55	6.276	Q1	14
Archives of Orthopaedic and Trauma Surgery	21	574	27.33	2.928	Q2	15

Visual Analysis of Keywords

Keyword Co-Occurrence Clustering Analysis of Research Hotspots

To summarize research hotspots and identify research trends, keyword analysis is crucial [12]. As shown in Figure 6A, 6B, and Table 4, a total of 1168 nodes and 6799 connections were created and a there was strong co-occurrence of keywords. Keywords with a greater centrality and frequency signify the research hotspots at that period. Analysis of the top keywords revealed that research in this area focused on tennis elbow, lateral epicondyle, corticosteroid injections, randomized controlled trials, pain, double-blind, PRP, management, prevalence, tendinopathy, elbow, surgical treatment, treatment, epicondylitis, injections, medial epicondylar tendon, musculoskeletal disorders, follow-up, shoulder, shockwave therapy and physiotherapy. The keyword co-occurrence clustering map for this domain is shown in Figure 6C. The typical LLR approach produced a total of 16 clusters, and the keyword clustering analysis revealed that the degree of aggregation enhanced the homogeneity of the research [13]. Greater homogeneity of research is associated with a higher degree of aggregation. The cluster size is inversely correlated with the cluster number, with #0 being the largest cluster. The keyword clusters from #0 to #15 are prevalence, PRP, lateral epicondylitis, tennis elbow, grip strength, extracorporeal shock wave therapy (ESWT), surgical treatment, extensor carpi radialis brevis, substance p, low-power laser, visual analog score (VAS), local corticosteroid injection, randomized trial, plasma-mediated, work-related musculoskeletal disorder, and Chinese acupuncture. The 16 clusters formed were all very closely linked to each other. Tennis elbow, prevalence, corticosteroid injections, randomized controlled trials, PRP, surgical treatment, work-related musculoskeletal diseases, shockwave therapy, and physiotherapy were current study hotspots in this domain based on keyword co-occurrence and cluster analysis.

Figure 6.

(A) Keyword co-occurrence diagram for lateral epicondylitis. The circles in the diagram represent keywords, the larger the circle the more frequently the keyword appears. Dark to light colors represent years from far to near, connecting lines represent links between keywords, and the thickness of the outer purple circle represents the centrality of the keyword. (B) VOSviewer-based time view of keywords for lateral epicondylitis. (C) Keyword co-occurrence clustering for lateral epicondylitis. The dark to light colors represent the years from far to near and the connecting lines represent the links between keywords.

Table 4.

High-frequency keywords and centrality of lateral epicondylitis TOP10.

Keywords	Frequency	Keywords	Centrality
Tennis elbow	828	Pain	0.12
Lateral epicondyliti	751	Musculoskeletal disorder	0.08
Corticosteroid injection	223	Injury	0.08
Randomized controlled trial	205	Elbow	0.07
Pain	205	Epicondyliti	0.07
Double blind	187	Injection	0.06
Platelet rich plasma	176	Lateral epicondylalgia	0.06
Management	158	Disorder	0.06
Prevalence	142	Muscle	0.05
Tendinopathy	134	Corticosteroid injection	0.05

Research Horizons Trend Analysis Based on Keyword Timeline Views

The literature filtering of the Web of Science database displays the temporal dynamics of the grouped keywords in a timeline [14] (Figure 7). A strong cluster is indicated by the mean profile value (Silhouette: S value) of 0.8221 >0.5. From 1990 to 1995, prevalence, musculoskeletal disorder, population, laser, placebo, conservative treatment, exercise, lateral epicondylitis, tennis elbow, surgical treatment, low-level laser, and acupuncture were widely followed. From 1995 to 2000, upper-limb disorder, risk factor, physical therapy, clinical trial, randomized controlled trial, management, ultrasound, efficacy, grip strength, corticosteroid injection, reliability, and medial epicondylitis were the keywords that began to receive attention. From 2000 to 2005, double-blind, follow-up, shock wave therapy, disability, carpi radialis brevi, chronic tennis elbow, and expression were the keywords that received attention. From 2005 to 2010, arthroscopic treatment, validation, and 830 nm laser received the most attention. From 2010 to 2015, PRP, autologous blood, growth factor, and autologous conditioned plasma received the most attention. From 2015 to 2022, musculoskeletal manipulation, quality of life, mesenchymal stem cell, prognosis, hyaluronic acid, network meta-analysis, therapeutic ultrasound, cyriax physiotherapy, radiation therapy, VAS score, and clinical application began to be followed as keywords. It is predicted that the in-depth study of LE will continue to focus on musculoskeletal-based physiotherapy (cyriax physiotherapy), physical factor therapy (laser, ultrasound, shockwave), clinical application of combined PRP therapy, prognosis and quality of life, and network meta-analysis.

Figure 7.

Timeline view of keywords for lateral epicondylitis. The circles in the diagram represent keywords, the larger the circle the more frequently the keyword appears. Dark to light colors represent years from far to near, connecting lines represent links between keywords and the thickness of the outer purple circle represents the centrality of the keyword.

Study of Modern Research Trends via Emergent Word Emergence

The 20 most commonly referenced terms in the Web of Science database are made up of keywords that have been used often throughout time, highlighting hotspots and trends. The strongest mutation was “platelet-rich plasma” (22.49), followed by “management” (18.21), and in the third ranking was “efficacy” (14.48). The keywords with higher mutation intensity in the last 5 years include: “management” (2018–2022), “injection” (2018–2020), “efficacy” (2019–2022), and “reliability” (2018 to 2020) (Figure 8A). The phrases “platelet-rich plasma,” “management,” “efficacy,” and “epicondylitis” have remained to date and are anticipated to continue to be widely investigated, which allows one to create a broad picture of the evolution of research and future research trends in the field of LE.

Figure 8.

(A) Keyword emergence diagram for external lateral epicondylitis. In the graph, “ ” is a 1-year keyword marker and “ ” is the year of occurrence of the highlighted word. (B) Co-cited literature network for lateral epicondylitis. The circles in the graph represent cited literature (showing the first author’s name), with larger circles indicating more citations. The connecting lines represent co-citations among the literature, and the thickness of the purple outer circle represents the centrality of the literature. (C) Clustering of co-cited literature for lateral epicondylitis. The circles in the diagram represent keywords. The larger the circle, the more frequently the keyword appears. The grey to colored represents the years from far to near, the connecting lines represent the links between keywords, the thickness of the outer purple circle represents the centrality of the keyword. This diagram is arranged in chronological order by clustering colors from light to dark. (D) Key literature on the emergence of lateral epicondylitis. The figure “ ” shows the year of the appearance of the emergent citation, and the figure “ ” shows the nodes where the number of citations for the emergent citation suddenly increased, in chronological order from top to bottom.

Visual Examination of Key Literature

Key Literature Analysis of Research Hotspots

The overall number of articles found in this region was 1556, with a total citation frequency of 7260. The research literature’s co-citation graph produced 2271 nodes and 7779 connections. Figure 8B and Tables 5 and 6 display the top 10 publications with a high citation frequency and high centrality. Citation status and centrality are important indicators reflecting the hotspots of research. Review and analysis of the highly cited and central literature is needed to comprehend some of the study findings with a high level of interest and to identify research topics of interest.

Table 5.

Top 10 cited literature centrality rankings for lateral epicondylitis.

Author	Centrality	Year	Title	Periodicals
Krischek O [16]	0.23	1998	Extracorporeal shockwave therapy in epicondylitis humeri ulnaris or radialis – a prospective, controlled, comparative study	Z Orthop Grenzgeb
Buchbinder R [17]	0.14	2005	Shock wave therapy for lateral elbow pain	Cochrane Databae Syst Rev
Connell DA [18]	0.12	2006	Ultrasound-guided autologous blood injection for tennis elbow	Skeletal Radiol
Hammer DS [19]	0.12	2000	Extracorporal shock wave therapy in patients with tennis elbow and painful heel	Arch Orthop Traum Surgery
Coombes BK [20]	0.11	2010	Efficacy and safety of corticosteroid injections and other injections for management of tendinopathy: A systematic review of randomised controlled trials	Lancet
Uzunca K [21]	0.11	2007	Effectiveness of pulsed electromagnetic field therapy in lateral epicondylitis	Clin Rheumatol
Fink M [22]	0.1	2002	Acupuncture in chronic epicondylitis: A randomized controlled trial	Rheumatology
Miller TT [23]	0.09	2002	Comparison of sonography and MRI for diagnosing epicondylitis	J Clin Ultrasound
Owens BD [24]	0.09	2001	Arthroscopic release for lateral epicondylitis	Arthroscopy
Aoki M [25]	0.08	2005	Magnetic resonance imaging findings of refractory tennis elbows and their relationship to surgical treatment	J Shoulder Elbow Surg

The main nodes are often those that propose important theories or ground-breaking ideas in the discipline and are more likely to spark new areas of research. We can identify the research hotspots and the development of the field of LE by examining the co-citation status of the literature at key nodes and the literature most often referenced. These 20 papers can serve as a good representation of the most significant classic literature in the discipline and the main research topics in the area. Clinical studies, reviews, and epidemiological studies are the 3 categories into which research can be classified. Center degree 1^st, 3^rd, 4^th, 6^th, 7^th, 8^th, 9^th, and 10^th and citation frequency ^1st, 2^nd, 4^th, 5^th, 6^th, 7^th, and 8^th are clinical studies. Center degrees 2^nd and 5^th and citation frequencies 3^rd and 9^th are review studies and citation frequency 10^th is epidemiological studies. The highly cited literature in clinical studies relates to injectable treatments (center degree 3^rd and citation frequency 1^st, 2^nd, 4^th, 5^th, 6^th, 7^th, and 8^th studies), physical factor treatments (center degree 1^st, 4^th, 6^th studies), surgical treatments (center degree 9^th and 10^th studies), and acupuncture treatments (center degree 7^th studies). The double-blind randomized controlled method (cited frequency 1^st, 2^nd, 4^th, and 6^th studies) and experimental method are the techniques employed in the literature (center degree 3^rd, 6^th, and 7^th studies and cited frequency 5^th, 7^th, and 8^th studies). For the assessment of treatment outcome, most of the visual analog rating scales (VAS, DASH, PRTEE) are used as the test indicators. The visual analog rating scales are compared through a certain time of follow-up changes in the values of these scales and are compared over a certain period of time to illustrate the effectiveness of the treatment of LE. In the treatment of LE with different injections, the 6^th centrality and 1^st and 5^th cited frequency studies showed a short-term pain reduction with glucocorticoid injections at 1 month, with a significant difference in the VAS values before and after treatment. However, in the 7^th most cited study in the literature, the authors found worse clinical outcomes at 1 year with corticosteroid injections compared to placebo injections. The 3^rd centrality and 2^nd, 4^th, 6^th, and 8^th cited frequency studies showed that injections of PRP or autologous blood were also better at reducing pain and increasing function at 2-year follow-up, but in the 1^st cited study in the literature, the authors found that none of the PRP injections was superior to saline in reducing pain at the 3-month endpoint. The study suggests that PRP injections may have a slower onset of action in the treatment of LE. The effectiveness of extracorporeal shockwave treatment for LE was demonstrated in studies 1^st and 4^th of the Central Degree by using different physical factors to treat epicondylitis. The 6^th study at the center showed that pulsed electromagnetic fields appear to be effective in the treatment of LE, but lacked a significant difference. In the surgical treatment of LE, centrality studies 9^th and 10^th showed that excision of granulation foci with high T2 signal at the origin of the wrist extensor tendon was effective in improving pain and that arthroscopic release was effective and minimally invasive for recovery. Centrality studies 7^th, which used acupuncture to treat LE, revealed a considerable increase in arm function and a decrease in discomfort, especially early on.

Notably, in the second-most frequently cited study, the researchers assessed the effectiveness of PRP versus corticosteroids in the treatment of chronic LE and for the first time compared autologous PRP with corticosteroid injections as a treatment option for patients whose non-surgical treatment for LE failed. Before the study’s publication, corticosteroid injections for tendinopathy demonstrated good short-term effectiveness as the criterion standard for treating LE, but unsatisfactory results were frequently observed beyond 12 weeks of follow-up [15]. Compared to corticosteroid injections, a single PRP injection produced longer-lasting benefits in pain and functioning. Additionally, in the 6^th most frequently cited study, researchers assessed the effectiveness of leukocyte-rich PRP injections in treating chronic LE in patients who had previously failed physiotherapy, which for the most part did not distinguish between different leukocyte levels. In the study, there was a 71.5% increase in pain scores at 24 weeks after therapy, which treated 230 patients with chronic LE who had failed conservative treatment with leukocyte-rich PRP. For lateral epicondylitis, leukocyte-rich PRP provided longer-lasting symptomatic relief than corticosteroid injections and had a longer-lasting therapeutic benefit.

In studies addressing methods of assessing and diagnosing LE, the common tendon’s outward curvature, the presence of hypoechoic fluid close to the tendon, thickness, decreased echogenicity, and ill-defined tendon borders were identified to be sonographic characteristics of epicondylitis by the 8^th Center Degree Study. The range of sensitivity for epicondylitis was 64–82% for ultrasound and 90–100% for MRI. The specificity range for ultrasound was 67–100%, and for MRI it was 83–100%. Thus, ultrasound has the same specificity as MRI but is less sensitive than MRI in the assessment of epicondylitis. As an initial imaging tool, many patients may only need an ultrasound to diagnose this issue, thus allowing MRI to be reserved for patients who have normal ultrasound findings but are still symptomatic.

Co-Occurrence Clustering of Important Literature is Used to Analyze Research Hotspots

Cluster analysis can reveal subfields that serve as significant research hotspots based on literature that has been cited together [33]. The average cluster profile value (Silhouette: S)=0.8627 >0.5, indicating a convincing cluster, and the clustering module value (Modularity, Q)=0.8938 >0.5, demonstrating a strong cluster structure [14]. A total of 15 clusters were created using the traditional LLR technique. The homogeneity of research is better the greater the level of aggregation, Figure 8C. The cluster size and number are inversely associated, with #0 designating the largest clusters and so on. The clustering of the literature exposes the sub-thematic directions of the most-cited study on the subject. Keyword clusters from #0 to #14 in order of PRP were chiropractic, ultrasound, magnetic resonance imaging, ESWT, eccentric training, regional sympathetic block, low-intensity laser therapy, lateral epicondylalgia, common extensor tendon, review, manual therapy, occupational disease, pain syndrome, and pressure pain thresholds. In terms of the clustering order, the hotspots of research in this area are PRP, American chiropractic, ultrasound, magnetic resonance imaging (MRI), ESWT and eccentric training. In terms of the lighter-colored clusters, the trends in this area are PRP, ultrasound, lateral epicondylar pain, and American chiropractic.

Research Frontier Trends Based on the Appearance of Important Publications

Figure 8D shows the 25 citations found in the Web of Science database that received the most citations. The strongest mutation was in Smidt N’s 2002 study, which found that corticosteroid injections for the treatment of LE were effective in the short term at 6 weeks and that 52 weeks of long-term physiotherapy (including ultrasound, deep friction massage, and exercise programs) was better than the waitlisted observation group, but the difference was not significant (24.57) [15]. The second was Peerbooms JC in 2010, who found that PRP had a more sustained reduction in pain and improved function than corticosteroid injections at 1-year follow-up (24.22) [26]. Third-placed Krogh TP in 2013 discovered that glucocorticoid injections for LE decreased color Doppler activity and tendon thickness as well as short-term discomfort after 1 month (23.09) [2]. Four general categories can be used to categorize the literature. The first focuses on MRI imaging, immunological, surgical and histopathological manifestations of LE, and their correlation (1990–2001) [34,35]. The second part is a comparative study of the clinical efficacy of corticosteroid injections, physical factors (laser, ultrasound, shockwave, magnetic therapy) and exercise interventions in the treatment of LE (2001–2010) [15,36–38]. The third part focuses on the effectiveness and safety of different injections in the treatment of LE, especially the clinical efficacy of PRP and autologous blood, as well as longer-term follow-up studies (≥1 year) after treatment with different injections (2010–2015) [1,26,27,30,39]. A meta-analysis and retrospective review of the clinical efficacy of PRP in the treatment of LE from 2015 to the present are the main topics of Part IV [32,40–42]. These studies focus on epidemiological survey and analysis studies of LE based on data from various populations. Based on a detailed evaluation of the good level of citations, the future research frontiers can be predicted, including longer follow-up studies, network meta-analyses based on a substantial amount of research, studies on the efficiency of successive multiple PRP injections for tendon repair, studies on leukocyte-rich plasma and PRP, and studies on the efficacy of PRP over other injectable preparations in LE, as well as consistent dose and composition of PRP and preparations, PRP combination therapy (stem cells, eccentric exercise), and the mechanism of action of PRP and corticosteroids in the treatment of LE.

Using Thematic Maps to Analyze Research Hotspots and Cutting-Edge Trends

The R-Bibliometrix software’s thematic maps are shown in a two-dimensional matrix. The x-axis and y-axis are matrix centrality and density, respectively. Therefore, the motor themes refer to first quadrant, which are both significant and well established; the niche themes to second quadrant, which are significant but not significant to the present field; the emerging or declining themes to third quadrant, which are not significant but have just emerged or may soon disappear; and the basic themes to 4^th quadrant, which are important to the sector yet lack sufficient development (Figure 9). There is a keyword bubble for elbow, epicondylitis, and ultrasound within the first quadrant. In the second quadrant there are 2 bubbles for reliability, validity, injection, corticosteroid, and medial epicondylitis. There is 1 bubble for pain, rehabilitation, and corticosteroids in the third quadrant. In the 4^th quadrant, there are 2 bubbles for tendinopathy, PRP, ultrasonography, tennis elbow, LE, and lateral epicondylalgia. It may be inferred that LE, ultrasound, reliability, validity, injections, and corticosteroids are the hotspots of study in this field based on the quadrant in which the important bubbles are placed. While the themes of corticosteroids and rehabilitation could be generated or abandoned in the future, the thematic directions of tendinopathy, PRP, and ultrasound will require more in-depth research in the future.

Figure 9.

Thematic map of the lateral epicondylitis.

Discussion

At present, there is no unified criterion standard for the clinical treatment of LE, as the pathogenesis of the disease is still unclear. Because conservative treatment is non-invasive or less invasive, is effective, has a low recurrence rate, and is easily accepted by patients, it is often used in the early stages of LE. Because of the high recurrence rate of LE, surgical treatment is often used for intractable LE. The main conservative treatment modalities are closed therapy (corticosteroids), non-steroidal anti-inflammatory drugs, PRP, extracorporeal shock waves, ultrasound, exercise interventions, and acupuncture. The most common surgical procedures are percutaneous surgery, open surgery, and arthroscopic surgery. Arthroscopic surgery is mostly used in the treatment of intractable LE. Arthroscopic treatment can be divided into arthroscopic intra-articular surgery and extra-articular surgery. As there is no natural space in the joint cavity, arthroscopic extra-articular surgery is very limited and technically demanding. Most of the available literature describes intra-articular surgery as the treatment of choice, with few records of extra-articular surgery [43,44].

Top research keywords were tennis elbow, PRP, corticosteroid injections, shockwave therapy, ultrasound, exercise interventions, manipulative therapy, and randomized controlled trials. Research trend keywords were PRP, musculoskeletal physiotherapy, management, efficacy, ultrasound, lateral epicondyle, physiotherapy, prognosis, and network meta-analysis. Local injection of drugs is the most common treatment used by clinicians, and the use of different drugs and choice of injection site can lead to different treatment outcomes. Coombes BK [20], in a meta-analysis of 41 studies in 2010, found that corticosteroid injections for LE reduced pain in the short term (4 weeks), but this effect was reversed in the medium term (26 weeks) and in the long term (52 weeks). In contrast, sodium hyaluronate injections reported a reduction in pain in the short, medium, and long term [45], and botulinum toxin injections reduce pain in the short term [46]; although it is frequently used in neurological disorders, the underlying mechanism is unclear. Augmentation injection therapy reduces pain in the medium term [47]. Lauromacrogol (polidocanol) [48] and aprotinin injections are ineffective [49]. In clinical practice, corticosteroid injections are often used in combination with NSAIDs or physiotherapy, but lack efficacy [29]. Smidt N [15] 2002 studied corticosteroid injections, physiotherapy, and wait-and-see treatment for epicondylitis and found that corticosteroid injections were effective in the short term (6 weeks) and that physiotherapy (pulsed ultrasound therapy, deep friction massage and exercise programs) was more effective than wait-and-see treatment, but the difference was not significant. However, some academics have used physical factors alone to treat LE and found that shockwave [19], magnetic therapy [21], ultrasound [50], and low-intensity laser [51] can all reduce LE pain. However, the optimal dose and interval between injections of injectable agents for the treatment of LE are unclear, as are as the principles and mechanisms by which injectable agents work, and the dose and frequency of physiotherapy are equally controversial.

In recent years, as PRP has been increasingly researched in the domains of orthopedics and sports medicine, more and more scholars have begun to explore the role of PRP in treatment of LE. Half of the top 10 most frequently cited studies involve PRP or autologous blood. Many studies have shown that PRP injection therapy can provide long-term improvement in LE compared to corticosteroid injection therapy [1,2,26,28]; this is assumed to be because PRP provides epicondylitis patients long-term relief. It is believed that PRP, which has the capacity to stimulate tendon repair, contains high concentrations of many growth factors, such as platelet-derived growth factor, insulin-like growth factor, and transforming growth factor beta [52,53]. In therapeutic applications, PRP is primarily created from the participant’s own blood and has very good effectiveness and safety, with few adverse effects, according to recorded RCTs [54]. Nonetheless, there has been debate concerning the method of preparation because PRP is frequently used to treat tendinopathies. The components of the equipment, the amount of whole blood that was centrifuged, the anticoagulation techniques used, and the rate, quantity, and duration of centrifugations, as well as the technique used to separate the groups after centrifugation, vary between different PRP preparation systems. As a result, the PRP preparations produced by various preparation processes have quite varied compositions [55,56]. For instance, there were noticeable differences in the leukocyte concentration, platelet capture efficiency, vascular endothelial growth factor concentrations, and platelet-derived growth factor AB and BB concentrations of the PRP produced by the Cascade, Biomet GPS III, and Magellan systems [57]. The concentrations of platelets, leukocytes, and related factors in PRP currently do not have uniform standards, and most studies merely reference the manufacturer of the PRP preparation kit without going into detail about the specifics of the extracted PRP [58]. In addition, PRP is activated in a variety of ways, with the more widely used being calcium chloride solutions, which maintain high growth factor concentrations for long periods of time, but with low platelet aggregation and a slow growth factor release [59]. The autologous thrombin preparation kit method is a special activation technique that combines the calcium chloride solution approach and the thrombin method; high safety and quick activation are advantages [60]. The approach using endogenous type I collagen is safer and more efficient than using bovine thrombin because its benefits include a high release of growth factors and the reduction of fibrin clot shrinkage. Finally, the timing of the PRP injection, the site of injection, the mode of administration, and the number of times it is administered can also have an impact on outcomes of experiments. Some studies have shown that PRP is more effective when received early in the course of tendinopathy than late in the course of treatment [61]. Achilles tendinopathy is a case where the disease site has been demonstrated to be more effective than the late stage. When treated with PRP, the disease location, such as the common lower and middle Achilles tendinopathy, also differs [62]. Several successive PRP injections are preferable to a single injection for treating tendinopathy [63]. The benefit of the multi-point injection method, known as peppering, is that it can treat a variety of inflammations [64]. Injectable hydrogel micro-spheres [65], injectable hydrogel dosage forms [66,67], and other PRP delivery techniques have been effectively developed in recent years to provide extended local effects. The study of PRP’s benefits on the management of disease has now given way to research into the biological processes of PRP in tendinopathies. There are several cytokines and growth factors in PRP. PRP releases various bioactive molecules, which stimulate cell migration, collagen expression, angiogenesis, differentiation, and proliferation, and also stimulate the synthesis of extracellular matrix, as shown by multiple in vivo animal models and in vitro experiments. A multitude of cell transduction pathways are activated by the cytokines found in PRP, some of which are downstream of a single receptor and can either inhibit or promote the activation of other pathways controlled by distinct receptors. However, signaling pathways and cellular responses that are activated during the treatment of LE are still under-researched.

Limitations of the Study

The setup of temporal segmentation, thresholding, and cropping techniques in producing visualization atlases is not standardized due to the many algorithms. Only English language literature was included in this study. Additionally, because all current visualization software can only analyze a single database, it is likely that excellent literature on the topic from other databases or from other languages went unrecognized.

Conclusions

This study offers a unique viewpoint for quick comprehension of the subject of LE by offering the first comprehensive bibliometric and visual examination for global research around LE over the past 30 years. The USA will maintain its lead in the number of articles issued, although Turkey’s and China’s volume will increase. High-impact writers are collaborating to some extent, but more collaboration is required in many institutions and nations. Hot keywords were tennis elbow, PRP, corticosteroid injections, shockwave therapy, ultrasound, exercise interventions, manipulative therapy, and randomized controlled trials. Research trend keywords were PRP, musculoskeletal physiotherapy, management, efficacy, ultrasound, lateral epicondyle, physiotherapy, prognosis, and network meta-analysis. Due to the lack of comprehensive basic molecular biology studies, especially with regard to animal models and in vitro experiments, the exact cellular transduction pathways through which PRP affects LE are still unknown, as are the mechanisms of action of various injectable preparations, such as corticosteroids for the treatment of LE. We hope our study will aid in the exploration of new research areas, including the standardization of PRP dosage and preparation composition, time, place, route, and frequency of administration, and PRP combination treatment (stem cells, eccentric exercise).

Table 6.

Top 10 cited literature rankings for lateral epicondylitis.

Author	Frequency of citations	Year	Title	Periodicals
Krogh TP [2]	51	2013	Treatment of lateral epicondylitis with platelet-rich plasma, glucocorticoid, or saline: A randomized, double-blind, placebo-controlled trial	Am J Sport Med
Peerbooms JC [26]	47	2010	Positive effect of an autologous platelet concentrate in lateral epicondylitis in a double-blind randomized controlled trial: Platelet-rich plasma versus corticosteroid injection with a 1-year follow-up	Am J Sport Med
Krogh TP [27]	46	2013	Comparative effectiveness of injection therapies in lateral epicondylitis: A systematic review and network meta-analysis of randomized controlled trials	Am J Sport Med
Gosens T [1]	46	2011	Ongoing positive effect of platelet-rich plasma versus corticosteroid injection in lateral epicondylitis: A double-blind randomized controlled trial with 2-year follow-up	Am J Sport Med
Smidt N [15]	45	2002	Corticosteroid injections, physiotherapy, or a wait-and-see policy for lateral epicondylitis: A randomised controlled trial	Lancet
Mishra AK [28]	44	2014	Efficacy of platelet-rich plasma for chronic tennis elbow: A double-blind, prospective, multicenter, randomized controlled trial of 230 patients	Am J Sport Med
Coombes BK [29]	43	2013	Effect of corticosteroid injection, physiotherapy, or both on clinical outcomes in patients with unilateral lateral epicondylalgia: A randomized controlled trial	JAMA – J Am Med Assoc
Thanasas C [30]	36	2011	Platelet-rich plasma versus autologous whole blood for the treatment of chronic lateral elbow epicondylitis: A randomized controlled clinical trial	Am J Sport Med
Vaquero-Picado A [31]	35	2016	Lateral epicondylitis of the elbow	Efort Open Rev
Sanders TL [32]	34	2015	The epidemiology and health care burden of tennis elbow: A population-based study	Am J Sport Med