3.1 Publication outputs and growth trends
We collected a total of 5,569 papers at first and excluded 1,885 non-article or non-review papers and 114 non-English papers. Eventually, a total of 3,570 papers met the inclusion criteria (Figure 1A). Figure 1B shows the trend of annual publication steadily growing over time with minimal fluctuations. Compared with 22 publications in 1980, the number of published papers in 2018 showed an approximately 10-fold increase. Trends in annual output were analyzed via the linear regression model, indicating significant growth in the past 40 years (t=10.612, P<0.001). The 3,570 papers were altogether cited 118,362 times, with 33.15 average citations and 140 H-index. As shown in Figure1C, the trends in cited frequency per year exhibited a smooth upward curve. Similarly, the result displayed increased significance over time through linear regression analysis (t=10.638, P<0.001). We divided the period studied into eight time partitions, 1980–1984, 1985–1989, 1990–1994, 1995–1999, 2000–2004, 2005–2009, 2010–2014, and 2015–2019 (Figure 1D). The period of 1990–1994 had the most number of published papers (1,920), the period of 2005–2009 had the most cited frequencies (27,829), the period of 1995–1999 received the maximum number of citations per paper (67.84), the period of 2015–2019 had the most open access articles (347), the period of 2000–2004 had the maximum value of H-index (91), and the period of 2010–2014 had the most cited frequencies in 2019 (479). Overall, the six aspects showed an increasing trend.
3.2 Distribution by journals
The 844 journals published 3,570 articles on comorbid pain and disability research (Additional file 1). Pain accounted for the maximum output (178), followed by Spine (163), Clinical Journal of Pain (96), Headache (92), and Cephalalgia (76). Only Pain and Spine had more than 100 publications, with over 4.50% of the total. As shown in Table 1, Pain had the most cited frequencies in WoS (15,418), the highest impact factor index in 2017 (5.559), and the highest H-index (68). The Journal of Rheumatology had the maximum number of citations per paper (94.85), whereas BMC Musculoskeletal Disorders had the most open access articles (60). Among the 20 journals with the most publications, 11 were in the first quartile of WoS, 7 were in the second quartile of WoS, and 1 was in the third and fourth quartiles.
The dual-map overlay of journals presented the distribution of journals across subject and paths of citation (Figure 2). The citing pattern was on the left, and the cited pattern was on the right with labels regarded as the disciplines involved in corresponding periodicals. The citation line was connected from the citing periodicals to the cited periodicals. Notably, these articles were mainly published by journals in the field of neurology, sports and ophthalmology, and a majority of them cited psychology, education and social journals.
3.3 Distribution by countries and institutions
The 3,570 papers on pain and disability comorbidity were contributed by 82 countries (Additional file 2, Figure 3A). In terms of publications, USA was the most prolific country (1,267), followed by England (315), Canada (278), Australia (275), and the Netherlands (202). The proportion of USA (35.490%) was approximately four times higher than England (8.824%). Figure 3B shows the basic situation of the top 10 countries via the maximum number of publications. The USA had the most cited frequencies (53,247), open access articles (339), and maximum value of H-index (113). England received the maximum number of citations per papers (5,479). In the country collaboration map, England and Australia both had the highest value of centrality (0.59), followed by Taiwan (0.58), Germany (0.57), and Switzerland (0.57) (Figure 3C).
A total of 3,252 institutions contributed to the 3,570 papers on pain and disability comorbidity (Additional file 3). Harvard University was the leading institution (100), with the largest proportion (2.802%), followed by the University of Washington (87, 2.437%), the University of Washington Seattle (87, 2.437%), the University of Texas System (67, 1.877%), and the University of Sydney (60, 1.681%). Three institutions showed proportions of more than 2%. As shown in Figure 3D, the most cited frequencies and maximum number of citations per paper corresponded to Maastricht University (4,034, 69.55), and the most open access articles were from Harvard University (37). The top three institutions, including Harvard University, the University of Washington, and the University of Washington Seattle, had the same highest value of H-index (33). Moreover, the University of South Australia had the maximum centrality (0.28), followed by the University of Alabama Birmingham (0.22), Vrije Universiteit Amsterdam (0.19), the University of Copenhagen (0.19), and Aalborg University (0.19) (Figure 3E).
3.4 Distribution by authors
Included papers on pain and disability comorbidity were distributed over 12,200 authors. Figure 4A shows that the node representing Lipton RB was the largest in terms of maximum publications (37), followed by Bussone G (28), Jensen MP (26), D’Amico D (23), and Grazzi L (20). Only the proportion of Lipton RB was more than 1% (1.036%). It also outlined the cooperation between different authors. From the data generated by CiteSpace V, the value of every author centrality was 0, indicating that collaboration among these authors was not sufficient and frequent. The author’s co-citation map demonstrated that Waddell G had the largest node with 386 citation counts, followed by Turk DC with 302 citation counts, Jensen MP with 300 citation counts, Deyo RA with 299 citation counts, and Ware JE with 277 citation counts (Figure 4B, Table 3). Figure 4C shows the trends in percentage of multiple- and single-authored articles for each 5-year period. The percentage of multiple-authored articles grew from 73.74% in 1980–1984 to 98.80% in 2015–2019 with the percentage of single-authored articles gradually reducing from 26.26% in 1980–1984 to 1.20% in 2015–2019. Furthermore, linear regression analysis also revealed the tendency of papers with multiple authors increased significantly under the studied period (t=8.065, P<0.001).
3.5 Subject categories of WoS
All journals contributing to the 3,570 papers on pain and disability comorbidity were involved in 109 subject areas of WoS. Some related data of the top 20 subject categories in accordance with publication are shown in Figure 5A. Clinical Neurology was the most productive academic area (1,095), followed by Rehabilitation (628), Neurosciences (564), Orthopedics (523), and Anesthesiology (443). Clinical Neurology received the largest number of cited frequencies (51,214), open access articles (203), and maximum value of H-index (107). The subject area with the highest number of citations per paper was Anesthesiology.
3.6 Types of pain
As depicted in Figure 5B, LBP (1,114) was the most widely concerned type of pain, with almost twice the number of publications than the second pain type (headache: 506). The next popular topics were postsurgical cancer (403), neck pain (316), and neuropathic pain (315). In addition, LBP also had the most cited frequencies (42,732), open access articles (311), and maximum value of H-index (100). Arthritis was the topic that received the highest number of citations per paper. All top 10 types of pain increased significantly in publication over time through linear regression analysis.
3.7 Analysis of references
The co-citation reference map presented clear scientific relevance of pertinent literature (Figure 5C). These references were divided into separate categories and arranged by timeline, which were labeled with title terms extracted from themselves. The modularity Q score was 0.9157 (close to 1), indicating that the map had a good and reasonable clustering effect and distinctive knowledge feature. The “pain lead” was the largest cluster #0 with most papers on the topic, “affecting pain” was the second largest cluster #1, and “predicting disability” was the third largest cluster #2. Apparently, the node marked as “Fear-avoidance and its consequences in chronic musculoskeletal pain: a state of the art,” belonging to cluster #21 (pain-related fear), was the largest. The next most cited were “Pain-related fear is more disabling than pain itself: evidence on the role of pain-related fear in chronic back pain disability” and “The fear-avoidance model of musculoskeletal pain: Current state of scientific evidence” (Table 2). References published in the past several years were commonly concentrated in cluster #0 (pain lead), cluster #4 (subtle objective), and cluster #17 (patient-reported outcome instrument).
3.8 Analysis of keywords
A total of 68 keywords with the strongest citation bursts were obtained (Figure 6). Some keywords, including behavior, arthriti, health status, rheumatoid arthriti, fibrositi, illness, compensation, and sickness impact profile, were the first cited frequently in 1991. Basically, the citation burst continued until around the year 2000. Rheumatoid arthriti had the longest citation burst time and maximum strength. Disease, association, women, people, and children were all cited until 2019 and will likely to last over the coming years. Table 3 shows the top 20 keywords with the maximum number of citation counts and centrality. The most frequently cited term was LBP (694), followed by disability (647), pain (533), prevalence (427), and reliability (387). Validity garnered the highest value of centrality (0.32), followed by rheumatoid arthriti (0.29), depression (0.25), belief (0.25), and health (0.24).
3.9 Characteristics of the top 10 most frequently cited papers
Table 4 lists the top 10 papers by citation frequency on pain and disability comorbidity. The citation counts of the top 10 papers represented 7.83% of the total (9,271). The article by Roland, M et al. entitled “A study of the natural-history of back pain .1. development of a reliable and sensitive measure of disability in low-back pain”, was published in Spine, 1983 and received the maximum number of citation (2,066). A paper in Cephalalgia entitled “The global burden of headache: a documentation of headache prevalence and disability worldwide” was cited the most per year (90.00). Among the 10 papers, three were published in Pain, and two were published in Spine. “Burden of migraine in the United States - Disability and economic costs” was the only article published in Archives of Internal Medicine with impact factor of over 10 (17.333). Three types of journals with 5≤IF<10, 3≤IF<5, and 1≤IF<3 published three papers each.