The 50 Most Cited Articles in Shoulder Arthroplasty

AIM: Citation analyses are often used as a measurement of an article’s impact in a specific field of study. Clinically, shoulder arthroplasty has been a rapidly growing field, and there has been ample research done on it in the past few decades. The purpose of this study is to determine the 50 most cited articles in shoulder arthroplasty and their characteristics. METHODS: The Science Citation Index Expanded was searched for citations of articles related to shoulder arthroplasty (including total shoulder, reverse shoulder arthroplasty, and hemiarthroplasty) published in the 72 journals in the category “Orthopedics”. The 50 most cited articles were determined and the following characteristics were analyzed in each article: authors, journal, year of publication, country of origin, number of citations, citation density (total number of citations/years since publication), article type (clinical or basic science), article subtype via study design and level of evidence. RESULTS: The number of citations ranged from 594 to 104, with citation density ranging from 28.8 to 4.1. The 50 most cited articles in shoulder arthroplasty were published in 6 of the 72 journals, most from 1970s to 2010s and represented by 10 countries. The articles were composed of 7 study designs with the most common being case series and 7 topics within shoulder arthroplasty. The most common level of evidence was IV (35 out of 50 studies). CONCLUSION: Articles with the highest citation density were those discussing reverse shoulder arthroplasty. The top 50 list provides residents, fellows and researchers with a comprehensive list of the major academic contributions to shoulder arthroplasty.


INTRODUCTION
Citation analyses have been widely used as a means to measure the academic impact an article instills on a medical specialty [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] . Lefaivre et al [7] has provided the 100 most substantial articles in the field of orthopaedics in terms of times cited. The publication focused on orthopedics as a whole and did not hone in on any topic specifically. Namdari et al [11] narrowed their approach to only evaluating the top 50 most cited articles regarding orthopedic shoulder surgery including articles discussing topics such as labral instability, rotator cuff repair, impingement, arthroplasty, and fractures.
Although Namardi et al [11] covered shoulder arthroplasty articles in their review, they arecomprised ofonly four articles out of their top 50. Within the past couple of decades shoulder arthroplasty has grown in popularity [16] , mainly driven by the increased interest in

The 50 Most Cited Articles in Shoulder Arthroplasty
Karim Sabeh, MD, Joseph Barbera, BS, Sarah Altajar, BS, MS, Samuel Rosas, MD, Jonathan C. Levy, MD Int. J. of Orth. 2016 August 23;3(4): 603-608 ISSN 2311-5106 (Print), ISSN 2313-1462 Online Submissions: http://www.ghrnet.org/index.php/ijo doi: 10.17554/j.issn.2311-5106.2016.03.180 International Journal of Orthopaedics total and reverse shoulder arthroplasty. However, a detailed literature search was unable to identify a publication specifically evaluating the top cited articles regarding this procedure. The purpose of this study is identify the top 50 most influential papers in shoulder arthroplasty as defined by the number of times cited in the literature.

MATERIALS AND METHODS
We utilized the ISI Web of Knowledge's database to conduct this cross-sectional study. The ISI Web of Knowledge contains 72 journals which are listed under the subject category "Orthopedics" [17] . In March 2016, we utilized the Web of Science's "basic search tool" to search its database for articles evaluating shoulder arthroplasty from 1900 to the present. We were then able to display our results by times cited with the database ranking how often each article was cited starting in the order of most cited to least. The top 500 most cited articles were reviewed and any articles that did not include shoulder arthroplasty in its content were excluded. If an article mentioned shoulder arthroplasty but this subject was not the major focus of the publication, the article was excluded. From the top 500 articles whose primary content was based upon the discussion of shoulder arthroplasty, we determined the top 50 mostcited. Resultantly, our analysis included publications discussing total shoulder arthroplasty, reverse total shoulder arthroplasty, as well as hemiarthroplasty of the shoulder.
In a similar fashion to the methods of Lefaivre et al [7] and Namdari et al [11] , each of the top 50 articles was reviewed for the following criteria: authors, year of publications, source journal of the article, geographic origin of the authors, article type (basic science article, clinical research article), article subtype (basic science, biomechanics, basic science-animal research, basic science-in vitro study, clinicalrandomized controlled trial, prospective cohort study, case series, review article, case report, or expert opinion), and level of evidence for clinical articles based on guidelines published by The Journal of Bone and Joint Surgery American [18] .
The level of evidence for each article was determined by consensus by two authors (J.B. and S.A.). As in the Lefaivre et al [7] and Namdari et al [11] articles, we classified each article as methodologic or not based on if it introduced or tested a classification or scoring system. For each article, the citation density was calculated by dividing the number of total citations by the number of years since the article was published. Articles were then classified into one of the following subtopics of shoulder arthroplasty: total arthroplasty, reverse arthroplasty, hemiarthroplasty, revision (all), fracture, and other.

RESULTS
There were 50 articles included in our list. The number of citations per article varied from 595 to 104 (Table 1). The articles were published from as early as 1974 up until 2011 with the 2000s contributing the most total articles (33) (Figure 1). The majority of the listed top 50 articles were published between 2000 and 2011 (34) and only 16 were published from 1970 to 1999. Only one article was published in the last decade. Evaluating each decade based on its mean number of citations displayed that the 1980s had the greatest mean number (267) followed closely by the 70s (256) ( Figure 2).
The top 50 articles were also analyzed based on total number of citations per year since publication (citation density) (Table 1) Table 2). Of these clinical articles, 35 had a level of evidence of IV, and there were no case reports or nonrandomized control trials ( Figure 3).
All 50 articles were published in English and in 7 different journals ( Table 3). Of those, 6 were journals in the orthopaedicspeciality and 1 was published in Instructional Course Lectures. The Journal of Bone and Joint Surgery -American Volume published 20 of the top 50 cited articles, the most of all the journals, and the Journal of Shoulder and Elbow Surgery trailed closely with 18. The authors originated from 10 different countries (Figure 4). The US (30) and France (11) contributed the majority of these publications while the other 8 countries combined for only 15 publications. Some articles had authors from multiple countries and were recorded as such. Dividing the articles by topic exhibited that total shoulder arthroplasty and hemiarthroplasty were the most common topics discussed ( Figure  5). Some articles discussed multiple topics and were recorded in multiple topic categories. The "Other" category covered an article about infection and 2 articles that generally discussed arthroplasty, not focusing on any topic in particular.Articles were further evaluated in terms of subtype of arthroplasty ( Figure 6). It is worth noting that publications assessing reverse shoulder arthroplasty had the greatest mean citation density (19.0) and maximum citation density (28.8). Many articles discussed hemiarthroplasty and total arthroplasty together resulting in similar mean citation densities and maximum citation densities in each category.

DISCUSSION
The number of times an article is cited has been shown to correlate with its relevance and consequently how impactful an article is on its field of publication [7,11] . The aim of this paper was to determine the most influential publications regarding the orthopaedic topic of shoulder arthroplasty including hemiarthroplasty, total shoulder arthroplasty, and reverse shoulder arthroplasty. Lefaivre et al [7] and Namdari et al [11] provided similar reviews of the top 100 articles in the orthopaedic field and the top 50 articles in shoulder surgery, respectively. Both articles covered only a few articles regarding shoulder arthroplasty. The intent of this study was to focus on shoulder arthroplasty given the explosive interest and recent technology that have developed in the past 30 years Table 1.
Determining which publications on shoulder arthroplasty are highly cited allowed us to analyze what factors make an article important. The Namdari et al [11] and Lefaivre et al [7] papers only referenced a few articles that includedclinical long-term outcome studies in their top 50 article. Namdari et al [11] and Lefaivre et al [7] reviewed broader topics which allowed for inclusion of older studies since the majority of their citations were published in the 1980s and earlier. Contrarily, the majority of papers in this study were more recent which provides the reader with more relevant, up-to-date information.
Similar to many other reviews and as demonstrated by Figure  4, the United States was responsible for predominant portion of publications [3,12,14,16,17,10] likely due to the level of interest in shoulder arthroplasty and a larger volume of this procedure performed annually in the United States compared to other countries. Time also plays an important role in an article's accumulation of citations, and despite categorizing the articles by citation density, only one article from this decade was included. Therefore, the authors hypothesize that, in general, there might be less interest in shoulder arthroplasty in this decade so far. The majority of articles were published in the 2000s; however, the 1970s and 1980s were responsible for the highest mean citations per decade. Recent changes in the indications of reverse shoulder arthroplasty, leading to the increase in the amount of reverse shoulder arthroplasty procedures performed, has spiked a great interest in this relatively new technology. This interest has lead to the publication of many articles discussing reverse shoulder arthroplasty in the 2000s compared to earlier decades. As a result, articles with the highest citation density were those discussing reverse shoulder arthroplasty. Additionally, the majority of articles were clinical and the most common level of evidence was level IV,

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Sabeh K et al. Top Articles in Shoulder Arthroplasty   which is also similar to other reviews [2,[6][7][8][11][12] . These findings raise the concern that most of our clinical practice guidelines in this field are derived from weak to moderate studies, and therefore highlight the need for strong level I (randomized control trials) or level II (prospective cohort) studies.   As Namdari et al [11] similarly noted, this data may indicate that the more recent influential papers were not accounted for in our review due to lack of time to accumulate citations. However, the methodologies used likely captured the impactful articles in the history of shoulder arthroplasty. Citation density was thus used to help account for the influence of time on the rank list.
Analyzing an article's influence with this method comes with some weaknesses. The first being that only choosing the top 50 articles could have not accounted for other influential papers. Second, selfcitation and citations in lectures and textbooks were unaccounted for, all factors that could influence an article's total citations. Additionally, there may be some bias generated by authors who preferentially cite articles from the journals which they are trying to publish in, as this helps drive the impact factor of a journal [7] . Namdari et al [11] and Lefaivre et al [7] limited their search to only journals categorized as "orthopaedics" on the Web of Science. To avoid this limitation, we searched all journals on the Web of Science. Thirdly, as mentioned in Namdari et al [11] and Lefaivre et al [7] , instead of citing articles based off of their content there is a tendency for authors to cite articles as a result of previous citations. This is known as the snowball effect [19] . Finally, the cross-sectional design of the study limits us from observing the constantly changing number of times each article is cited.

CONCLUSION
Our review of the top 50 cited articles (Table 1) sums up the major academic contribution to shoulder arthroplasty and may be beneficial for a variety of reasons. Not only is it a comprehensive list of the most influential articles discussing shoulder arthroplasty, but also these articles offer a background of important aspects that can be utilized to guide research and clinical practice in this field. Furthermore, this list can be used to supplement the American Shoulder and Elbow Surgeons (ASES) Curriculum Guide for Treatment of Shoulder Injury [20] . Lastly, the top 50 most cited list can provideorthopaedic surgery residents, fellows, orthopaedic surgeons, and healthcare professionals with valuable information regarding arthroplasty as an option for treatment of shoulder pathology.