Fifty Most Cited Articles for Femoroacetabular Impingement and Hip Arthroscopy

Growing awareness of femoroacetabular impingement (FAI) and recent innovations in management have resulted in hip arthroscopy becoming one of the fastest-growing orthopedic subspecialties. The purpose of this study was to identify the 50 most cited articles related to the topic of FAI and hip arthroscopy and to analyze their characteristics. The overall number of citations within these articles ranged from 99 to 820. Citation density ranged from 4.41 to 74.55. Seven countries produced these articles with the majority attributed to the United States (n = 26) and Switzerland (n = 18). Clinical studies made up more than half of the top articles (n = 27). The Journal of Bone and Joint Surgery level of evidence most commonly encountered was level IV (n = 24), while the remaining articles were level III (n = 3). No randomized controlled trials or non-randomized controlled trials were encountered in this search. The level of evidence was not significantly correlated with the overall number of citations, publication year, or citation density. The current top 50 list provides orthopedic surgeons interested in hip arthroscopy with an up-to-date core list of the most cited articles in the scientific literature and represents a foundation to use to develop their knowledge regarding hip arthroscopy and FAI.


Introduction
Analyses of "most cited articles" have been performed in the field of orthopedics as a specialty in general (1,2), as well as in various orthopedic subspecialties, including pediatrics, hand, shoulder, arthroscopy, and total joint arthroplasty (3)(4)(5)(6)(7). However, no such study has been published on "hip arthroscopy" or "femoroacetabular impingement (FAI). " In the current literature, a study identifying the top 25 cited articles in orthopedic arthroscopy in 2012 by Gheiti et al. (5) included only one article related to hip joint.
While Smith-Peterson first described FAI in 1935 as the "impingement of the femoral neck on the anterior acetabular margin" in a 55-year-old male patient, the concept of FAI has only relatively recently become widely accepted as a source of hip pain and dysfunction. This is due, in large part, to the extensive work by Ganz and colleagues (8)(9)(10). Similarly, the first clinical report of hip arthroscopy was published by Takagi in 1939 (11), but it was not until the 1980s that hip arthroscopy became more widely utilized in the diagnosis and treatment of hip pathology (12). The understanding of FAI as well as the surgical technique and clinical outcomes following hip arthroscopic procedures has grown exponentially.
The purpose of this study was to identify the 50 most cited articles related to the topic of FAI and hip arthroscopy and to analyze their characteristics. By this method, we sought to create an up-to-date list of the most important articles in this emerging field.

Methods
This study did not require approval from institutional review board as it involved publicly available data. Following previously described methods (2,4,6), we used the "cited reference search" through the ISI Web of Knowledge (Thompson Reuters, New York, NY, USA) to identify the top 50 cited articles in FAI and hip arthroscopy. The search was performed in October 2014. Articles published in any of the 67 journals categorized under the topic heading of "orthopedics" in the ISI Web of Science, which include general and subspecialty-specific, clinical, and basic science orthopedic journals, as well as physical therapy journals, were considered. The following search terms were used: "Hip Arthroscopy, " "Femoroacetabular Impingement, " and "Hip Labral Tears. " Although our primary aim was to include articles that arthroscopic hip surgeons would find relevant to their practice, we also chose to include articles describing open management of FAI as we felt that the history and evolution as well as alternative treatments of FAI would be of interest to an arthroscopic hip surgeon. Moreover, studies pertaining to diagnostic, perioperative, and postoperative management of FAI were included. Articles that were considered to be relevant to FAI and hip arthroscopy were reviewed by two authors and the decision to include or exclude was made through consensus. The articles were then ranked according to the number of highest citations to generate a list of 50 articles. When the articles had identical number of citations, the paper with higher citation density (defined as numbers of citations per year since publication) was ranked higher.
While reviewing the identified articles, the following information was recorded: article title, source journal of the article, first author, corresponding author, year of publication, country of origin (in accordance with the corresponding author's address), and article type (basic science, clinical research article, and diagnostic studies). Clinical studies were further subtyped as randomized controlled trial, cohort study, case series, review article, case report, or expert opinion and assigned a level of evidence based on the Journal of Bone and Joint Surgery (JBJS) criteria (13).
All statistical analyses were calculated using SPSS statistical software (SPSS Inc., Chicago, IL, USA).

Results
There were 50 total publications included in this top FAI and hip arthroscopy articles list ( Table 1). The overall number of citations within these articles ranged from 99 to 820, with an average of 182.70 ± 133.50 citations per article. Citation density for these articles ranged from 4.41 to 74.55, with an average density of 18.55 ± 13.33. The total amount of citations attributed to these articles was calculated to be 9135. These articles were published between 1987 and 2009, with 2004 producing the greatest number of top articles (n = 8) (Figure 1). The average number of years since publication of these articles was 11.34 ± 4.88. The selected articles were published in 10 of the 67 examined orthopedic journals, with Clinical Orthopaedics and Related Research containing the greatest amount of publications (n = 18) followed by Arthroscopy: The Journal of Arthroscopic and Related Surgery (n = 11) ( Table 2). When analyzed by total citation, Clinical Orthopaedics and Related Research represented the highest citation count (n = 3611) followed by the JBJS-British Volume (n = 1600). Every article was published in the English language.
Seven countries produced these top articles with the vast majority being attributes to the United States (n = 26) and Switzerland (n = 18). Canada (n = 2), Brazil (n = 1), Italy (n = 1), Japan (n = 1), and the United Kingdom (n = 1) did not produce more than two articles each. Clinical studies made up more than half of the top articles (n = 27), while the remaining articles comprised review type articles (n = 12), radiographic and/or diagnostic based articles (n = 7), and basic science articles (n = 4). Among the clinically based articles, the JBJS level of evidence most commonly encountered was level IV (n = 24), while the remaining articles were level III (n = 3). No randomized controlled trials or non-randomized controlled trials were encountered in this search. The level of evidence was not significantly correlated with the overall number of citations (R = 0.043, P = 0.767), publication year (R = 0.211, P = 0.142), or citation density (R = −0.014, P = 0.924).
The most recently published article on the top 50 list was published in 2009 by Leunig et al., and while it ranks 33rd in total citations (124 total citations), this article ranked 11th in terms of citation density. The earliest article was published in 1987 by Glick, ranking 41st in terms of total citations (119 total citations); however, it was the least densely cited article among the top 50 papers (4.41). Interestingly, while the year of publication does not significantly correlate with total citations, it does so with citation density (R = 0.023, P = 0.002). There were no significant differences when comparing clinical basic science type studies in relation to total citations or citation density (P > 0.05).

Discussion
Femoroacetabular impingement is a relatively new concept when compared to other classically described pathologies in the field of orthopedic surgery. However, growing awareness of this condition and its management as well as recent technical advancements have resulted in arthroscopic hip surgery becoming one of the fastest-growing orthopedic subspecialties. The rapid development of this field has been closely correlated with increasing interest in the subspecialty as well as the amount of new hip arthroscopists entering practice. Therefore, we believe that it is important to identify and analyze the most important articles in the field of hip arthroscopy in order to provide the orthopedic community with a list of essential publications critical to this emerging field. This list represents a basis of fundamental knowledge for hip arthroscopy and can act as a starting point for residency and fellowship programs aiming to train future hip arthroscopists. Although the presented articles are relatively contemporary as compared to other classic orthopedic publications, these articles were written during the development of the essential knowledge of FAI and the field of hip arthroscopy. Therefore, they represent the field's scientific foundation and are valuable for clinicians who are developing their own management techniques. We analyzed the characteristics of these articles to determine what qualities make an orthopedic article important to authors writing about FAI and hip arthroscopy. We found that the majority of articles where either published from the United States or Switzerland. Other reviews of classic articles in general surgery, plastic surgery, anesthesia, emergency medicine, and orthopedic surgery have similarly found a predominance of American authors within classic literature (1,2,(61)(62)(63)(64). However, this current review found that the number of articles originating from the United States when compared to other countries is proportionally lower as compared to the previously referenced specialties. Switzerland in particular represents a high proportion of top articles within the classic FAI and hip arthroscopy literature. This is not surprising as several of the clinicians who initially and extensively studied FAI in hip arthroscopy originate from Switzerland.
We found that the majority of published articles were clinical studies; however, these papers were primarily limited to level IV and level III evidence. Given the relative infancy of the field, such level of evidence is not unexpected. However, we do not believe that this lower level of evidence detracts from the value or importance of these articles. We expect that as the quantity of practitioners and patients continues to grow with time, additional studies with increasing patient cohort sizes and possibly higher levels of evidence will be conducted and published. The recent emphasis placed on "evidence-based medicine" in clinical practice encourages high-quality research to provide a basis for clinical management paradigm, and current and future studies will draw from classic literature presented in this list to accomplish this goal.
In addition to the clinical studies, we also found that a significant number of the top 50 articles were categorized as basic science studies. Many of these articles were biomechanical studies utilizing cadaveric tissue to elucidate the potential pathophysiology of symptomatic hip pain related to FAI or to develop novel surgical techniques. The remaining articles were imagingbased in nature and sought to improve the ability of clinicians to appropriately diagnose and evaluate pathological FAI lesions, as well as allow increased precision in preoperative planning. As we develop new surgical techniques, improve preoperative planning, and optimize postoperative rehabilitation, these articles provide the basis of knowledge necessary to advance these areas. Additionally, a minority of the articles found in this list were review type publications. As the current scientific literature for FAI and hip arthroscopy is still developing, the process of understanding this disease process and surgical technique is ongoing. As the scientific literature continues to mature in volume as well as quality, more comprehensive reviews will be possible, providing valuable summaries for the aspiring clinician.
Although the total amount of citations attributed to articles listed in the current top 50 list is lower as compared to the top 100 articles in orthopedic surgery and even when compared to the top 50 articles in shoulder surgery, we found that the citation density of top FAI and hip arthroscopy articles was generally greater. For example, Lefaivre et al. identified "Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation" by Harris as the top-cited article in orthopedic surgery with 1748 total citations; however, the citation density of this article was only 41.62 (2). Similarly, Namdari et al. identified "A clinical method of functional assessment of the shoulder" by Constant et al. as the top-cited article in shoulder-specific orthopedic surgery with 1211 total citations, but this paper only had a citation density of 50 (4). The top-cited article in the current study by Ganz had a total of 820 citations, significantly lower than the top orthopedic surgery or shoulder specific articles, but its citation density was higher at 74.55. We found this to be a trend within the current top 50 articles list when compared to other top-cited article publications in the scientific literature. As citation density may be used as a proxy of current interest in any particular field or article, the current study demonstrates that FAI and hip arthroscopy are emerging and impactful topics in the current orthopedic scientific community. Therefore, while the articles identified within this analysis are significantly more contemporary as compared to other "classic" orthopedic concepts, the high level of activity within the subspecialty may benefit from this list.

Limitations
This study has limitations. All previously established methods of analyzing and ranking the top articles within the specific medical field contain limitations in their evaluation processes, including those directed toward orthopedic surgery. Similar to previously described methods, our analysis did not account for self-citations, oral or poster presentations, textbooks citations, as well as the intrinsic bias of citing articles from the Journal of which they intend to publish. Self-citation in particular may be particularly important as high-volume authors may have a tendency to cite their own previous articles in their newly submitted work. An additional limitation of our methodology is that the categorization of journals and citations in web of science may lead to the omission of influential articles about FAI and hip arthroscopy from known-orthopedic journals. However, our aim was to provide orthopedic surgeons list of the top 50 most impactful articles on a specific subspecialty as opposed to orthopedic surgery in general, so therefore we believe that the vast majority of articles on FAI and hip arthroscopy will be found within these 61 analyzed orthopedic journals and that these publications truly reflect the most important works in this subspecialty. An additional weakness attributed to this methodology is that work published prior to 1945 could not be included within the initial search as the citation database was non-existent at that time. The impact of this, however, was probably minimal within our research for articles about FAI and hip arthroscopy, since these concepts are relatively recent and have only been established in the scientific literature within the past three decades. In fact, while the initial article that we encountered within the top 50 list was published in 1987, the vast majority of the remaining articles were produced in the 2000s.
Finally, as this analysis is a cross-sectional study at one point in time, we can only develop conclusions based on the citation counts of these articles at that particular time. As new developments and scientific knowledge and techniques continue to evolve within the subspecialty, major paradigm shifts in management based on more relevant articles may significantly altered this list in the future. In this situation, it would be prudent to establish the validity of this list at a later time as the field continues to mature.

Conclusion
We rank the top 50 articles in the subspecialty of arthroscopic hip surgery and FAI. We found that these articles written in English, most commonly published in Clinical Orthopaedics and Related Research, were primarily level III and level IV observational clinical studies, but with a significant amount of basic science research as well. The current top 50 list provides orthopedic surgeons interested in hip arthroscopy with a list of the most important articles in the scientific literature currently and represents a foundation that young clinicians can use to develop their knowledge regarding hip arthroscopy and FAI.