Surgical Procedures for Hip Joint Preservation for Osteonecrosis of the Femoral Head: A Bibliometric Analysis

Background and Objective. Studies have concentrated on the surgical procedures for hip joint preservation for osteonecrosis of the femoral head (ONFH). This study is aimed at presenting a bibliometric analysis of the relevant articles published from 1999 to 2019. Method. Articles which concentrated on surgical procedures for hip joint preservation for ONFH were searched using Web of Science database. The data were analyzed by using bibliometric analysis. Additionally, VOS viewer software was used for bibliographic coupling, coauthorship, cocitation, and cooccurrence analyses and to investigate the publication trends of the mentioned field. Results. A total of 3467 articles were included. China had the highest number of relevant published articles. However, the USA made the highest contributions to the global research with the highest citations and h-index. The journal of Clinical Orthopaedics and Related Research published the highest number of relevant articles. Studies could be classified into four clusters: “process and clinical treatment,” “risk factors and diagnosis,” “pathophysiology,” and “basic research.” “Pathophysiology” and “basic research” clusters were predicted as the next hot topics of surgical procedures for hip joint preservation for ONFH. Conclusion. Based on the current global trends, the number of published articles related to surgical procedures for hip joint preservation for ONFH has increased. The USA was noted as the leading country in global research in the target field. “Pathophysiology” and “basic research” clusters may be the next hot spots, and scholars need to further concentrate on the target topic.


Background
Osteonecrosis of the femoral head (ONFH) is a devastating condition, mainly influencing patients in their third to fifth decades of life that typically progresses to cell death, fracture, and collapse of femoral head [1,2]. The processes could be the result of trauma, corticosteroids, alcohol, blood dyscrasias, idiopathic, and miscellaneous factors [3]. However, the underlying pathogenesis has still remained elusive. The incidence of ONFH in the UK (1.4 per 100,000) is comparable with Japan (1.9 per 100,000) [4,5], and 20,000-30,000 new cases are annually diagnosed in the USA [6]. Although ONFH has a low incidence compared with primary hip osteoarthritis, it negatively influences individuals' quality of life. Besides, spontaneous regression of ONFH is extremely rare. In case of late treatment, it may lead to complete collapse of the femoral head within 2-3 years, and the vast majority of untreated patients undergo total hip arthroplasty (THA) [7]. Hence, early intervention is highly essential to stop or reverse the progression of the disease, ultimately preserving joint and preventing the need for THA. The surgical treatment of ONFH can be divided into two major branches: FH sparing procedures (FHSP) and FH replacement procedures (FHRP). In general, FHSP are indicated at precollapse stages with minimal symptoms, whereas FHRP are preferred at postcollapse symptomatic stages [8]. However, the global research trends related to surgical procedures for hip joint preservation for ONFH have not been reported yet. Therefore, it is urgent to investigate the global status of surgical procedures for hip joint preservation for ONFH.
Bibliometrics is quantitative analysis of scientific publications and their citations [9]. It is developed for a wide range and can serve as an important tool for monitoring research trends, determining the impact of research funding, as well   BioMed Research International as comparing research progress among different countries, institutions, etc. [10]. Furthermore, bibliometric analysis is valuable in formulating policy and clinical guideline of various diseases [11]. However, the analysis of bibliometric variables regarding surgical procedures for hip joint preservation for ONFH remains elusive. Thus, the present study is aimed at providing a full-scale insight into the status and global trends of surgical procedures for hip joint preservation for ONFH. Meanwhile, in order to carry out a deeper analysis on the bibliometric information, we used graphical mapping of the bibliographic data with the purpose of determining how the leading actors of the publication were connected with each other.

Materials and Methods
2.1. Search Strategy. It has been extensively accepted that Web of Science (WoS) is the most appropriate database for performing bibliometric analysis [12]. In the current research, a comprehensive search was undertaken from 1999 to 2019 using WoS database with document types restricted to articles and reviews. Besides, only Englishlanguage articles were included.

Data
Collection. Two reviewers independently checked and extracted the following information from eligible articles: year of publication, authors' full name, title, name of journal, authors' affiliation, authors' nationality, keywords, sum of citations, h-index. Any disagreement was resolved by consensus-based discussion.
2.3. Bibliometric Analysis. The index of h means that an author or country has published h articles, and each of which has been cited in other publications at least h times [11]. Therefore, it is an author/country-level metric, implied both the productivity and citation impact of the publications of a scientist or a country [13]. We used the Microsoft Excel 2016 to generate a prediction model formulated as follows: f ðxÞ = ax 3 + bx 2 + cx + d where x refers to year of publication, and f ðxÞ represents the cumulative number of articles published in a certain year; besides, we analyzed the time trend of the publications, as well as tendency in the future based on the cumulative number of articles published [14].

Visualized Analysis.
Herein, VOS viewer (Leiden University, Leiden, The Netherlands) was used for mapping and visualizing bibliometric networks of the publications [15]. It offers text mining functionality that can be used to construct and visualize cooccurrence networks of important terms extracted from a body of scientific literature. The following settings were chosen during the import: "Create a map based on bibliographic data," "read data from bibliographic database files," "type of analysis: bibliographic coupling," "unit of analysis: sources, organizations, countries," and "counting method: full counting"; "create a map based on bibliographic data," "read data from bibliographic database files," "type of analysis: coauthorship," "unit of analysis: authors, organizations, countries," and "counting method: full counting"; "create a map based on bibliographic data," "read data from bibliographic database files," "type of analysis: cocitation," "unit of analysis: cited references, cited sources," and "counting method: full counting"; "create a map based on bibliographic data," "read data from bibliographic database files," "type of analysis: cooccurrence," "unit of analysis: all keywords," "counting method: full counting," "network visualization," and "overlay visualization"; through these options, the VOS viewer analyzes and visualizes them in the form of bubble maps.  Figure 2(a), the USA had the highest proportion of citations (19,393), followed by China (7,384), Japan (5,507), the UK (3,850), and Germany (3,385). The involved articles from the USA had the highest proportion of h-index (65), followed by Japan (38), China (36), the UK (32), and Germany (31) (Figure 2(b)). The average frequency of citation of articles is displayed in Figure 2 Figure 3(b), orthopedics is the most popular research field (1522, 43.90%), followed by surgery (687, 19.82%), general internal medicine (281, 8.11%), experimental medicine (262, 7.56%), and medical imaging (253, 7.30%).        3.6. Cocitation Analysis. Cocitation analysis provides a forward-looking assessment on document similarity in contrast to bibliographic coupling, which is retrospective. There were 612 references that were analyzed by using VOS viewer (Figure 6(a)). The top 5 articles with large TLS were as follows: Mont and Hungerford [16] (TLS = 4,082), Ficat [17] (TLS = 3,254), Mankin [18] (TLS = 2,573), Assouline et al. [19] (TLS = 2,557), and Steinberg et al. [20] (TLS = 2,539).  (Figure 6(b)).

Cooccurrence Analysis.
Cooccurrence analysis is a technique often applied in text mining, comparative genomics, and promoter analysis. The trends and current topics of the research area were assessed by the keyword network map, which was created by VOS viewer. As depicted in Figure 7(a), a total of 1,002 keywords were grouped into approximately 4 clusters: "process and clinical treatment," "risk factors and diagnosis," "pathophysiology," and "basic research." In the "process and clinical treatment" cluster, the main keywords were core decompression, necrosis, expression, natural-history, and risk. In the "risk factors

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BioMed Research International and diagnosis" cluster, the relevant keywords were avascular necrosis, osteonecrosis, femoral head, hip, and bone. In the "pathophysiology" cluster, the main keywords were necrosis, expression, risk, pathogenesis, and osteoporosis. In the "basic research" cluster, primary keywords were nontraumatic osteonecrosis, osteonecrosis of the femoral head, apoptosis, steroid-induced osteonecrosis, and differentiation. These clusters covered the most fundamental themes related to surgical procedures for hip joint preservation for ONFH. In VOS viewer, blue color means that a keyword appeared early and yellow-colored keywords appeared later. Figure 7(b) shows that during the early stage of surgical pro-cedures for hip joint preservation for ONFH, "process and clinical treatment" and "risk factors and diagnosis" clusters are the major topics. However, the recently developed trends showed that "pathophysiology" and "basic research" clusters will be extensively concerned in the future. joint preservation for ONFH, according to statistics extracted from WoS. In the current study, the authors from 84 countries participated in publication of relevant articles. Additionally, China and the United States stood at the first and second places in the total number of published articles, respectively. However, the USA had the highest proportion of contributions to surgical procedures for hip joint preservation for ONFH in terms of the total number of citations and h-index. To our knowledge, the h-index and the total number of citations represent the academic impact and quality of a nation's publication. Therefore, the USA was found as the leading country in this field, because the USA has markedly concentrated on ONFH via diverse financial and nonfinancial resources. It is noteworthy that the National Natural Science Foundation of China stood in the first place in this domain. The contradiction between the quantity and quality of publications in China might attribute to several reasons. Firstly, Chinese academic evaluation system is based on quantity of publications rather than the quality, indicating an urgent need for Chinese investigators to improve the quality of research articles in the future. Secondly, in China, the number of publications in the relevant field remained relatively small before 2010. Hence, Chinese scholars need to dedicate more effort to dramatically increase average frequency of citation of articles. Clinical Orthopaedics and Related Research, Journal of Pediatric Orthopaedics, International Orthopaedics, Journal of Bone and Joint Surgery American Volume, and Archives of Orthopaedic and Trauma Surgery published the highest number of articles about studies on surgical procedures for hip joint preservation for ONFH. Figure 1(c) lists the top 20 authors who have published the highest number of articles about surgical procedures for hip joint preservation for ONFH, and they were pioneers in this area. Of the top 20 institutions, there were 9 institutions from China, and 5 from the USA. At the same time, China has invested millions of Chinese Yuan on surgical procedures for hip joint preservation for ONFH. Thus, the quality of researches should be greatly improved in China in the future.

Discussion
According to bibliographic coupling analysis, Clinical Orthopaedics and Related Research is the most appropriate journal, and the USA is the leading country in this field. Coauthorship analysis indicated that the country/institution/ author, with the highest TLS, would be more likely to cooperate with others. We employed cocitation analysis to assess the influence of the number of citations. Clinical Orthopaedics and Related Research had the highest average frequency of citation of articles related to surgical procedures for hip joint preservation for ONFH.

Researches on Surgical Procedures for Hip Joint
Preservation for ONFH. The cooccurrence analysis revealed the possible research orientation to be helpful in the future. Therefore, we used this method to identify future trends and hot spots about surgical procedures for hip joint preservation for ONFH. The cooccurrence network was created by the keywords of the included studies. As revealed in the current study, four research-based clusters were dis-covered, including "process and clinical treatment," "risk factors and diagnosis," "pathophysiology," and "basic research" (Figure 7(a)).
Overlay visualization map is a significant analysis to predict the research direction. As illustrated in Figure 7(b), the color bar indicates how the scores are drawn, in which "pathophysiology" and "basic research" clusters (yellow color) will be the next hot topics in this field. Further concentration on pathophysiology may assist scholars to better understand ONFH and develop more effective diagnostic and therapeutic approaches. Several scholars have concentrated on traumatic or nontraumatic causes of risk factors for ONFH [21]. Therefore, further attention needs to be paid to pathophysiology in the future. Research that utilized stem cells and growth factors has shown promising outcomes in terms of clarifying both the etiology and treatment of ONFH [22,23].

Strengths and
Limitations. This study, for the first time, assessed the status and trends of studies which concentrated on surgical procedures for hip joint preservation for ONFH through bibliometric and visualized analyses. However, this study contains a number of limitations. Firstly, only English-language articles were included, leading to language bias. Secondly, differences may exist between the real world and the present results. For instance, other databases (PubMed and Google Scholar) were not analyzed, which could increase the number of published articles.

Conclusions
In summary, the current status and global trends of surgical procedures for hip joint preservation for ONFH could be studied. Although China made the highest contribution to the total number of published articles, the USA was globally found as the leading country in this field. Clinical Orthopaedics and Related Research published the highest number of relevant articles. According to bibliometric and visualized analyses, we could predict that further studies related to surgical procedures for hip joint preservation for ONFH will be published in the coming years. Pathophysiology and basic research will significantly attract scholars' attention and will be the next hot spot in the future.

Data Availability
The first author can provide all data.