Introduction

Since the first face transplant in 2005, no more than 47 such procedures have been carried out worldwide [1, 2]. Despite the relative infancy of the field and in contrast to the small number of completed procedures, hundreds of studies have been published on the topic, covering themes from surgical technique and post-operative outcomes to the psychological and ethical implications of the procedure.

This disproportionate research productivity in the field of face transplantation is in line with the exponential growth of academic research in general. Owing to this, various metrics and measurement tools have been developed to assist in categorizing the publications, particularly with regard to the influence they have on their respective field. One such tool is bibliometric analysis. Coined by Pritchard in 1969, bibliometrics is a quantitative evaluation of publications, including the journal, author, and the number of citations, that is, the number of times these are cited in publications written by other scientists [3]. The impact of a scientific publication, particularly in recent years, is evaluated based on the number of citations it accrues. However, the ranking created by such bibliometric analysis is based on the scientific interest shown by other researchers rather than on the actual quality of the studies assessed. Regardless, the most frequently cited studies are also essential papers of high methodological quality and, therefore, of high scientific merit [4]. Broadly, the general assumption is that the number of citations directly reflects the impact of a paper. [5]

Bibliometric analyses have been previously conducted to identify the most cited publications in multiple surgical specialties, including in general surgery [6], transplantation [7], orthopedics [8, 9], robotics [10], pediatric surgery [11], plastic surgery [12], hand surgery [13], and oral and maxillofacial surgery. [14, 15]

A 2022 study by Hoffman et al. evaluated the entire body of face transplantation literature and identified trends in the publications over time [16]. A limitation of this study, as stated by the authors, was that, given their methodology, they did not consider the quality of publications, treating all publications as equivalent. To date, no bibliometric analysis has focused on the most influential—based on citation power—literature pertaining to face transplantation. In this bibliometric analysis, we analyze the most-cited papers in the field of face transplantation with the aim to obtain a better understanding of the traits and characteristics that render such research influential.

Methods

Following the methodology for bibliometric analysis from prior publications [9, 17, 18], the term “face transplantation” was used to search the “Topic” field of the Clarivate Analytics’ Web of Science database (available at https://www.webofscience.com/woscc). The “Topic” field searches the title, abstract, author keywords, and Keywords Plus of publications. The search was performed on April 1, 2022, and no limitations on publication date, language, article type, or article length were applied. The obtained dataset was downloaded and sorted by the number of citations in Microsoft Excel® 2020 (Microsoft, Redmond, WA, USA) and the 100 most cited publications were identified according to the selection process in Fig. 1.

Fig. 1
figure 1

Study selection process

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During evaluation of the publications, the title, first and corresponding author, year of publication, the number of citations, publishing institution, journal, journal impact factor, and the country of origin of each manuscript were recorded. The publishing institution and country of origin were determined from the information listed for the corresponding author. The citation density was calculated by dividing the total number of citations by the number of years since publication. The journal impact factor was the latest available impact factor, as listed on the website of each respective journal. Information on the publishing model of journals (open, subscription, or hybrid) was also obtained. The content was analyzed, and a methodological design and corresponding level of evidence (LoE) were assigned to each publication. Publications were categorized into one of three broad categories: clinical, basic science, and other, for publications that did not have a clear clinical or basic science focus. Categories of subject foci were also identified.

Graphical presentation was performed in GraphPad Prism (Version 8.00; MacOS, GraphPad Software, La Jolla, CA, USA).

Results

The initial database search returned 536 full-length publications (Fig. 1). The top 100 most cited publications are summarized in Table 1. The number of citations of the top 100 cited publications ranged from 305 (“Outcomes 18 months after the first human partial face transplantation” Dubernard et al. [19]) to 21 (“A retrospective analysis of secondary revisions after face transplantation: assessment of outcomes, safety, and feasibility” Aycart et al. [20]). Citation density ranged from 21 citations/year (“Facial transplantation: the first 9 years” Khalifian et al. [21]) to 1.2 citations/year (“Face transplantation: part II—an ethical perspective” Clark [22]). The oldest publication included on the list, “Face transplantation—fantasy or the future?,” by Hettiaratchy and Butler [23] was published in 2002, 3 years before the first successful face transplant. The most recent publication, “Five-year follow-up after face transplantation,” was published in 2019 by Tasigiorgos et al. [24]

Table 1 The 100 most cited publications with a focus on face transplantation
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On content analysis eight subject foci were identified: anatomy, ethics and psychology, immunosuppression and rejection, post-operative outcomes, pre-operative preparation and surgical procedure, prognosis and risks, public health and costs, and update of previous literature (Fig. 2). The most common subject foci were post-operative outcomes and updates, with a total of 23 papers each, followed by ethics and psychology, with a total of 16 papers (Table 1, Fig. 2). The least common focus was anatomy with two papers [56, 58]. Furthermore, six out of 10 of the most cited publications focused on post-operative outcomes [19, 25,26,27, 29, 31]. Most publications had a clinical focus (n = 67), followed by other (n = 22), and basic science (n = 11). Of the 11 basic science studies, four were cadaver studies [44, 60, 79, 86] and seven were animal studies. [33, 43, 48, 59, 80, 96, 107]

Fig. 2
figure 2

Study-type analysis. a, b Top 100 cited papers by subject focus. c Total number of citations versus type of study. No significant differences in number of citations were identified between the three types of study (p = 0.12)

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The majority of studies had a LoE of V (n = 41), followed by VI (n = 36), and VII (n = 19). Only four studies had a LoE of IV (Table 2) [29, 55, 99, 116]. Most studies were reviews and meta-analyses (n = 29), followed by case reports (n = 24), and ideas, editorials, and opinions (n = 19). Only one prospective cohort was found. [29]

Table 2 Number of papers for each level of evidence (LoE) and type of study. No significant correlation was identified between LoE and number of citations (p = 0.77)
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The top five countries with the highest number of influential papers were the USA (n = 68), France (n = 10), the UK (n = 6), Belgium (n = 5) and Spain (n = 4). The order was different when the total citations per country were pooled, with the USA having a total of 3509 citations, followed by France with 979 citations, the UK with 291, China with 269, and Belgium with 150 (Fig. 3).

Fig. 3
figure 3

Country analysis. a Top 100 cited papers by country. b Total number of publications in the top 100 per region. c Total number of citations per region. Country selected based on institution of corresponding author

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The year with the highest number of influential papers was 2011 (n = 11), followed by 2012 and 2013 (n = 10 each). Six of the top 10 most cited publications were published in the 5-year period between 2006 and 2010, [19, 25,26,27, 30, 32] indicating that the oldest papers were not the most cited (Fig. 4).

Fig. 4
figure 4

Year analysis. a Top 100 cited papers by year of publication. b Correlation between the publications’ number of citations and year of publication. No significant correlation was identified between year of publication and number of citations (p = 0.05)

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The top 100 manuscripts were published in 26 journals (Table 3). Plastic and Reconstructive Surgery published the majority of papers (n = 27), followed by American Journal of Transplantation (n = 11), Journal of Plastic Reconstructive and Aesthetic Surgery (n = 8), and Lancet (n = 6). The journals’ impact factor (IF) ranged from 1.05 to 91.25. A positive correlation between journal IF and total citations was identified (R2 = 0.4525, p =  < 0.0001; Fig. 5). Four of the journals are open access (Psychosomatics, Journal of Materials Science-Materials in Medicine, Medicina Oral, Patologia Oral, Cirugia, and Bucal Medical Science Monitor). The remaining journals are hybrid journals, and of the 100 publications, 30 were published open access and 70 by subscription.

Table 3 Number of papers per journal
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Fig. 5
figure 5

Correlation between journal impact factor and total citations. Impact factor positively correlated with total citations (R2 = 0.4525, p =  < 0.0001)

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The department with the highest number of publications in the top 100 was the Department of Plastic Surgery of Cleveland Clinic (n = 22), followed by the Division of Plastic Surgery, Department of Surgery, of Brigham and Women’s Hospital (n = 20). Of the top 11 institutions with the most publications in the top 100, six are based in the USA, two in France, one in the UK, one in Belgium, and one in China (Table 4).

Table 4 Institutions with more than one paper in the top 100. Institution as listed for corresponding author
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Dr. Maria Siemionow had the highest number of corresponding author publications in the top 100 (n = 18), followed by Dr. Bohdan Pomahac (n = 16; Table 5). The top 10 most influential publications were published by six corresponding authors, with Dr. Maria Siemionow, Dr. Bohdan Pomahac, and Dr. Laurent Lantieri each contributing two publications.

Table 5 Corresponding authors with more than one paper in the top 100
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Discussion

This bibliometric analysis reflects the evolution of the field of face transplantation which transitioned from hypothesis to reality. The 12 earliest publications in the top 100, which were published before the first successful first transplant in 2005, focused on outlining the ethics of the procedure and contemplated whether such a procedure should solely be considered a “fantasy.” The success of the first face transplant was then followed by multiple case reports outlining the pre-operative preparation and peri-operative outcomes of the procedure. More recent publications have focused on the long-term outcomes of the procedure, as well as on immunosuppression and rejection.

The total citations of the 100 most cited papers in our analysis ranged from 21 to 305, a number considerably lower than citation numbers seen in other fields such as transplantation (576–3078) [7], liver cancer (612–5358) [117], orthopedic surgery (757–3860) [8], and hand surgery (88–455). [13]

The lower number may reflect the youth of the field, as well as the number of.

researchers focusing on face transplantation [117], as face transplantation is a niche field with a relatively small number of researchers focusing on the subject.

Although it is commonly believed that older publications accrue more citations, owing to the time factor, in this analysis, we identified an inverted U pattern, with most publications in the top 100 being published between 2010 and 2013, and the top 10 all published after 2007. This is in agreement with a bibliometric analysis of the most cited articles in surgery [6]. Vázquez et al. performed a bibliometric analysis of the top 100 most cited articles in the five surgery journals with the highest impact factor and identified that 20% of these papers were published after 2000.

They hypothesize this phenomenon to be due to “obliteration by incorporation,” that is, once scientific ideas and hypotheses become generally proven and accepted, the articles which originally proposed these ideas are no longer cited. [6, 7, 17, 118,119,120,121]

It has also been argued that the number of citations an article accrues is dependent on the IF of the journal in which it was published [120, 122]. This is a pattern we identified in our bibliometric analysis, as we identified a significant positive correlation between IF and total citations.

As described by O’Sullivan and Hurley in their bibliometric analysis of publications in the field of transplantation [7], the field is unique within the practice of medicine and surgery, as it required extensive and revolutionary in vitro and in vivo technical, procedural, immunological, and tissue-specific research to achieve the landmark steps seen in clinical practice. In just two decades, we have witnessed the field of face transplantation progress from a written hypothesis to a worldwide clinical occurrence.

Reflective of the youth of the field is also the fairer distribution of citations in terms of author gender, with Dr. Maria Siemionow being the corresponding author with the greatest number of citations. In addition, 33% of the most cited corresponding authors were female. In contrast, a recent cross-sectional study analyzing more than 5000 articles published in high-impact medical journals identified that work published by women first or corresponding authors had fewer citations than those written by men first or corresponding authors [123]. This is not seen in our bibliometric analysis and may be a hopeful reflection of the future of academia.

It is important to note that the list of the top 100 most cited manuscripts will undoubtedly change in the future, as multiple multicenter collaborations, studies known to have strong citation potential [10], are now underway or have been recently published [124, 125]. Ongoing advancements in the field, including re-transplantation procedures [126, 127], and modifications in monitoring and immunosuppression recommendations [128] will also impact the list of the 100 most cited. As such, bibliometric analyses of fast-paced medical fields, such as that of face transplantation, require regular 5- to 10-year updates to reflect the ongoing evolution. [10]

Limitations

This bibliometric analysis is associated with limitations inherent to bibliometric analyses. One such limitation is “incomplete citing,” whereby publications are cited to persuade the reader rather than to credit the most influential work [13]. Although we did not have set exclusions based on language, language bias toward the English language does exist in academia [129]. Other biases include journal bias, influential person, state or institution, bias, in-house bias, and self-citation bias [13]. Omission bias, whereby researchers purposely avoid citing competitors, has also been noted [130]. Furthermore, for this bibliometric analysis, we opted to exclude studies which did not focus primarily on face transplantation, choosing to exclude studies which also discussed limb transplantation resulting in selection bias. A further limitation in our methodology was that we chose to focus only on the first and corresponding authors, but authors in the top 100 did contribute to multiple other publications, and their overall contribution to the field is as such underestimated [13]. Despite these biases, the top 100 most-cited papers which we identified in this bibliometric analysis are a great representation of some of the most influential work over the past two decades.

Conclusions

This bibliometric analysis identifies the most influential papers, in terms of citation power, in the field of face transplantation. The evolution of the publications in this list broadly represents the landmark developments in the field of face transplantation. The bibliometric analysis helps researchers identify the authors and institutions who have led innovation in face transplantation and comprehend the rapid rate of progression of the field. Lastly, our data summarizes important information on what establishes a publication as influential.