Trends in global publications
Number and trends of Global publications
A total of 3467 articles from 1999 to 2019 match the research inclusion criteria. We found that the number of publications per year about joint preserving procedures of ONFH demonstrated a steadily increasing trend in the past two decades, from 65 in 1999 to 339 in 2019 (Fig.1A). On the basis of the model fitting curves of publication growth, the cumulative publication number of global is shown in Fig. 1B. The number of publications in this field was estimated to grow by nearly 2 times from 339 in 2019 to approximately 600 by 2030.
Contribution of countries
There were total of 84 countries and regions published articles in this domain. China published the most papers (868, 25.04%), followed by United States (816, 23.36 %), Japan (336, 9.69%), Germany (186, 5.37%), and England (180, 5.19%). (Fig. 1C and D).
Quality of publications of different countries
As is shown in Fig. 2A, USA had the highest total citation frequencies (19,393). Then is China, ranked second (7,384), followed by Japan (5,507), England (3,850), and Germany (3,385). The involved articles from the USA had the highest H-index (65), followed by Japan (38), China (36), England (32), and Germany (31) (Fig. 2B). The average citation frequencies of top 20 countries are shown in Fig. 2c. Switzerland had the highest average citation frequencies (36.1). While Israel ranked second (29.40), followed by Canada (27.37), Belgium (26.25), and Australia (24.84) (Fig. 2C).
Analysis of global publications
The CLINICAL ORTHOPAEDICS AND RELATED RESEARCH (impact factor [IF] = 4.154, 2018) published the most studies with 160 articles. There were 100 articles in JOURNAL OF PEDIATRIC ORTHOPAEDICS (IF = 2.046, 2018), 95 articles in INTERNATIONAL ORTHOPAEDICS (IF = 2.384, 2018), 85 articles in JOURNAL OF BONE AND JOINT SURGERY AMERICAN VOLUME (IF = 4.716, 2018), and 67 articles in ARCHIVES OF ORTHOPAEDIC AND TRAUMA SURGERY (IF = 1.973, 2018) on joint preserving procedures of ONFH. The top 20 journals that published the most articles are listed in Fig. 3A.
As is shown in the Fig. 3B, orthopedics is the most popular research fields (1522, 43.90%), and the surgery ranked second (687, 19.82%), followed by general internal medicine (281, 8.11%), research experimental medicine (262, 7.56%) and radiology nuclear medicine medical imaging (253, 7.30%).
The fig. 3C shows the top 20 authors relate to the joint preserving procedures of ONFH. YAMAMOTO T published the most research on this field with 68 papers, followed by IWAMOTO Y with 57 papers, ZHANG CQ with 46 papers, KIM HKW with 43 papers, and MOTOMURA G with 39 papers.
The Shanghai Jiao Tong University had the highest number of papers among institutions worldwide (90 papers). Fig. 3D shows the top 20 contributive institution distribution of publications in this field. There were 9 China institutions followed by 5 United States institutions, 2 Japan institutions, 2 Switzerland institutions, 1 France as well as 1 South Korea institution.
The top 20 funding bodies are shown in Fig. 3E. National Nature Science Foundation of China provides financial support for 391 papers ranked the first, followed by National Institutes of Health NIH USA (112 papers) and United States Department of Health Human Services (112 papers).
Bibliographic coupling analysis
Bibliographic coupling is a well-established measure that uses citation analysis to establish a similarity relationship between documents. it was constructed on the shared references among publications, providing deeper insights into the journal, institution, and country. We use the VOS viewer to analyze the journal names in total publications. There were 134 journals appeared in total link strength (TLS) (Fig. 4A). The top five journals with greatest total link strengths are as follows: CLINICAL ORTHOPAEDICS AND RELATED RESEARCH (TSL=78,284), JOURNAL OF BONE AND JOINT SURGERY AMERICAN VOLUME (TSL=47,929), INTERNATIONAL ORTHOPAEDICS (TSL=38,065), JOURNAL OF BONE AND JOINT SURGERY BRITISH VOLUME (TSL=28,449), JOURNAL OF PEDIATRIC ORTHOPAEDICS (TSL=26,102).
All the papers were reported in 274 institutions and were analyzed via VOS viewer (the minimum number of publications of an institution was over five). The top five institutions with large total link strength are the following: Kyushu University (TSL=54,422), Shanghai Jiao Tong University (TSL=43,162), Chinese University Hongkong (TSL=30,624), Xi An Jiao Tong University (TSL=30,036), and Seoul National University (TSL=29,609) (Fig. 4B).
There are 48 countries identified by the papers and were analyzed using VOS viewer (the minimum number of publications from a country was over five). The top five countries with large total link strength are the following: USA (TSL=383,754), China (TSL=292,399), Japan (TSL=168,467), Germany (TSL=102,548) and South Korea (TSL=90,846) (Fig. 4C).
Coauthor analysis refers to the establishment of the relationship between items according to the number of coauthors. For instance, if an author coauthors an article with ten other authors, each of the 10 co-authorship links has a weight of 1/10. A total of 140 authors were identified were analyzed through VOS viewer (the minimum number of documents from an author was over five). The top five authors with large total link strengths are as follows: YAMAMOTO T (TSL=172), MOYOMURA G (TSL=165), IWAMOTO Y (TSL=155), IKEMURA S (TSL=104), and SUGANO N (TSL=81) (Fig. 5A).
Studies identified in the 249 institutions were analyzed using VOS viewer (the minimum number of publications from an institution was over five). The top five institutions with large TLS are as follows: Kyungpook National University (TSL=65), Chinese University Hongkong (TSL=61), Seoul National University (TSL=60), Chinese Academy of Sciences (TSL=51), and Stanford University (TSL=51) (Fig. 5B).
Publications (the minimum number of studies from a country was over five) identified in the 47 countries were analyzed using VOS viewer (Fig. 5C). The top five countries with large TSL are the following: USA (TSL=247), Englan (TSL=113), Germany (TSL=108), China (TSL=92), and France (TSL=76).
Co-citation analysis implied that the relatedness of items based on the number of times they were cited together. There were 612 references (the minimum number of citations of a reference was over 20 times) were analyzed by using VOS viewer (Fig. 6A). The top five papers with large TLS are as follows: Mont et al.  (TSL=4,082), Ficat et al.  (TSL=3,254), Mankin et al.  (TSL=2,573), Assouline et al.  (TSL=2,557), and Steinberget al.  (TSL=2,539).
A total of 630 journals of co-citation analysis were analyzed using VOS viewer (the minimum number of citations from a source was over 20 times). The top five journals with large total link strengths are as follows: CLINICAL ORTHOPAEDICS AND RELATED RESEARCH (TSL=314,286), JOURNAL OF BONE AND JOINT SURGERY AMERICAN VOLUME (TSL=295,588), JOURNAL OF BONE AND JOINT SURGERY BRITISH VOLUME (TSL=224,238), JOURNAL OF PEDIATRIC ORTHOPAEDICS (TSL=94,528), and Radiology (TSL=61,601) (Fig. 6B).
Co-occurrence analysis is a method to build the relationship of items base on the number of publications in which they occur together. The trends and current topics of the research area were established by the keyword network map, which was created by VOS viewer (the minimum number of occurrences of a keyword was over five). As is shown in Fig. 7A, total 1,002 included 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 are core decompression, necrosis, expression, natural-history, and risk. Within cluster of “Risk factors and diagnosis”, the relevant keywords are avascular necrosis, osteonecrosis, femoral-head, hip, and bone. In “Pathophysiology” cluster, the main keywords are necrosis, expression, risk, pathogenesis, and osteoporosis. As with the cluster of “Basic research”, primary keywords are also listed, including nontraumatic osteonecrosis, osteonecrosis of the femoral head, apoptosis, steroid-induced osteonecrosis, and differentiation. These results demonstrate the most core theme of joint preserving procedures of ONFH up till now.
VOS viewer can quantify and color-coded the relative novelty of a keyword through defining the average appearing year. The blue color means the keyword appeared early and yellow-colored keywords appeared later. The fig. 7B shows that during the early stage of joint preserving procedures of ONFH, “Process and clinical treatment”, and “Risk factors and diagnosis” are the major topics in this field (before 2014). However, the recent development trends show that the clusters of “Pathophysiology”, and “Basic research” will be extensively concerned in the future.