Selection criteria and data collection

The inclusion criteria were articles related to the nonsurgical treatment of knee OA (such as the mechanism, outcome, side effect and patients’ adherence etc.), covering all types of studies. The exclusion criteria were the articles that were not relevant to nonsurgical treatment or knee OA (i.e false-positive data). We also excluded trials published only as abstracts (with no additional data available from other sources).

The information of all eligible publications including title, author, year of publication, nationalities, affiliations, journal, keywords and abstract, was downloaded from the WoS database. Two authors (Wang K and Xing D) independently verified the data collection and entry. The disagreement was resolved by the third author (Lin JH) to reach a consensus.

Bibliometric analysis

The basic characteristics of publications were described by using the intrinsic function of WoS. The H-index, a useful measure of the impact of scientific study, shows that a scientist or scholar has published H papers, each of which has been cited at least H times by other publications. Thus, the H-index reflects both the number and citation impact of publications [21, 22]. Relative research interest (RRI) is defined as the number of publications in a certain field divided by all-field publications per year. The time trend of the publications was analyzed by using R software (version 3.1.3). The logistic regression model: f(x)=c/[1+a×exp(−b×(x-1994))] was used to model the cumulative volume of documentation. In this formula, the symbol x refers to the year, and f(x) represents the cumulative amount of papers. The time when the growth rate of publications changed from positive to negative was defined as the inflection point, which was generated using the formula T=lna/b+1994.

Quality of the publications

Papers from the United States had the highest citation frequencies (84,952). England ranked second in total citation frequency (27,536), followed by Canada (19,871), Germany (19,516) and France (16,248) (Fig. 2a). The average citation frequencies of top 20 countries were shown in Fig. ​Fig.2b.2b. Norway had the highest average citation frequencies (56.15), followed by Belgium (52.97) and Sweden (50.77).

Open in a separate window

Fig. 2

a The top 20 countries of total citations. b The top 20 countries of the average citations for each article. c The top 20 countries of the H-index of publications

As far as the H-index was concerned, United States outranked other countries with H-index of 125, followed by England (80), Canada (72), Germany (69) and Australia (63) (Fig. ​(Fig.22c).

Analysis of global publication

Journal analysis

OSTEOARTHRITIS AND CARTILAGE published the most articles, with 683 publications. There were 275 articles in ANNALS OF THE RHEUMATIC DISEASES, 194 articles in ARTHRITIS AND RHEUMATISM and 184 articles in THE JOURNAL OF RHEUMATOLOGY on the nonsurgical treatment of knee OA. The top 20 journals with most papers were shown in Fig. 3a.

Open in a separate window

Fig. 3

a The top 20 journals with most publications related to the nonsurgical treatment of knee OA. b The 20 main research orientations and the number of publications in each orientation. c The top 20 institutions of high-impact and the number of their publications. d The top 20 authors with most publications in this field

Bibliographic coupling analysis

Journals

Bibliographic coupling analysis is a well-established method which helps create a relationship of document similarity based on the number of references they share. The VOSviewer was used to analyze the names of journals in total publications. As illustrated in Fig. 4a, 315 journals appeared in the bibliometric map. The top five journals with greatest total link strengths were as follows: OSTEOARTHRITIS AND CARTILAGE (525,463 times), BMC MUSCULOSKELETAL DISORDERS (228,254 times), ANNALS OF THE RHEUMATIC DISEASES (212,472 times), THE JOURNAL OF RHEUMATOLOGY (198,529 times) and CLINICAL RHEUMATOLOGY (140,629 times).

Open in a separate window

Fig. 4

Bibliographic coupling analysis of worldwide research on nonsurgical treatment of knee OA. a Mapping on the 315 identified journals on nonsurgical treatment of knee OA. b Mapping on 815 institutions on nonsurgical treatment of knee OA. c Mapping on the 69 countries in this field. The line between two icons in the figure indicates that two journals/institutions/countries had created a similarity relationship

Coauthorship analysis

Authors

Coauthorship analysis means that the relationship of items is built according to the number of coauthored documents; 1447 authors were identified (the minimum number of publications from an author was over five) and their publications were analyzed by VOSviewer (Fig. 5a). The top five authors with greatest total link strengths were as follows: Martel-Pelletier J (361 times), Dekker J (344 times), Pelletier JP (334 times), Li X (289 times), and Wang Y (246 times).

Open in a separate window

Fig. 5

Coauthorship and cocitation analysis of global research about nonsurgical treatment of knee OA. a Mapping on the 1447 identified authors by coauthorship analysis on nonsurgical treatment of knee OA. b Mapping on the 816 identified institutions by coauthorship analysis on nonsurgical treatment of knee OA. c Mapping on the 69 identified countries by coauthorship analysis on nonsurgical treatment of knee OA. The size of the icons indicates the coauthorship frequency. The line between two icons in the figure indicates that two authors/institutions/countries had established collaboration. d Mapping on the 1470 identified journals by cocitation analysis. The size of the icons indicates the citation frequency. A line between two icons indicates that both were cited in one journal. e Mapping on the 1730 identified references by cocitation analysis. The size of the icons indicates the citation frequency. A line between two icons indicates that both were cited in one paper

Cocitation analysis

Status and quality of global publications

The H-index and total number of citations represent the academic impact and quality of publications of a country [30]. The United States was the leading country in both the total number of publications and total citation frequency. England also made a tremendous contribution to this field when considering the total number of papers and the total citation frequency. Some countries——such as Norway and Belgium——have also played an important role because of their high average citation frequencies.

The OSTEOARTHRITIS AND CARTILAGE, ANNALS OF THE RHEUMATIC DISEASES, ARTHRITIS AND RHEUMATISM and THE JOURNAL OF RHEUMATOLOGY published the most studies on the nonsurgical treatment of knee OA. Future findings in this field are more likely to be reported by the listed journals (Fig. ​(Fig.44a).

Almost all of the top 20 institutions were from the top five countries, implying that establishing first-class research institutions is essential to improving a country’s academic level. Pelletier JP, Martel-Pelletier J and Dekker J were the top three authors who published the most articles in this field. The top 20 authors could be regarded as the pioneers in the nonsurgical treatment of knee OA. Their future studies may have a substantial impact on the development in this field and should be closely monitored to grasp the latest advancement.

In this study, the relatedness between papers with regards to country, institution and journal was established by bibliographic coupling analysis. Bibliographic coupling was constructed on the shared references among publications, providing deeper insights on how authors use and build links among the existing literature. The analysis showed that OSTEOARTHRITIS AND CARTILAGE published the most relevant articles, and the United States was in the leading position in this field. Coauthorship analysis was used to assess collaboration among countries, institutions and authors. The one with greater total link strength suggested that the country/institution/author would be more likely to cooperate with others. Cocitation analysis was conducted to evaluate the academic influence of studies. The top studies with larger total cocitation frequency could be regarded as the landmark studies about the nonsurgical treatment of knee OA. OSTEOARTHRITIS AND CARTILAGE was the journal with the highest citation frequency in this domain.

Research focus on the nonsurgical treatment of knee OA

The research directions and hotspots in this field were identified by using the co-occurrence analysis. The map of the co-occurrence network was created based on the keywords of all included studies. As shown in Fig. ​Fig.6a,6a, five research directions were discovered, including articular cartilage study, biomechanics study, physiotherapy study, oral pharmacologic study and intra-articular injection study. This result could help clarify the trend of future research. In the co-occurrence map, the keywords, including arthritis, articular cartilage, exercise and management, were highlighted with bigger icons. Thus, further high-quality studies concerning articular cartilage study and physiotherapy study may still be required.

The overlay visualization map was color coded by VOSviewer based on the average time the keywords appeared in the publications [31]. This was an important method for monitoring the progress of research. In this overlay visualization (Fig. ​(Fig.6b),6b), the color bar indicated the year of publication. According to the results, articular cartilage and physiotherapy (yellow color) may be the next hot topic in this field. Studies on articular cartilage, especially the development of regenerative medicine and tissue engineering techniques to restore articular cartilage, have been widely emerged [15, 32–34]. Additional research is required to develop truly biomimetic cartilage regenerative therapies and translate these approaches to clinical practice [35, 36]. Physiotherapy, like exercise, is recommended by many guidelines for osteoarthritis [26, 28, 37], which plays a key role in preventing osteoarthritis and improving the daily function and quality of life of patients. Primary studies investigating the efficacy and individualization of physiotherapy for knee OA remain the focus of this research field.

Based on the results of our study, the increasing number of publications indicated that the nonsurgical treatment serves a crucial position in managing knee OA. This promising result will also in turn encourage investigators to conduct further research. The bibliometric and visualized analyses could provide the researchers with the knowledge of the leading countries, authors and institutions in this field. With these information, the researchers could have the ‘main channel’ to get the advanced knowledge and future discoveries. Additionally, the co-occurrence analysis and overlay visualization map specifically delineated the hotspots and future research directions, which may help the funding agencies to make a more rational investment plan and provide the evidence for health-care policy making.

We are grateful to Yu Zhao and Huibin Long for statistical input into the database and the regression model, and Rujun Li for discussions and support on the project.