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The Most-Cited Ankle Arthroplasty Implant Articles

Background: Citation analysis is a useful way of evaluating the impact, importance, and merit of articles within a medical specialty. Our study identified and analyzed the most-cited articles on ankle arthroplasty implants to evaluate their importance in the field of ankle arthroplasty research. Methods: Using the keywords “ankle arthroplasty” and “ankle replacement” and the search period 1970-2021, we found 3728 articles on ankle arthroplasty implants in the Scopus, Web of Science, and MEDLINE/PubMed databases. We included original articles, reviews, clinical trials, and case reports in the study. We retrieved the 50 most-cited articles published during the time frame and then screened them for studies of specific ankle arthroplasty implants and their postoperative outcomes. We also recorded and analyzed the articles’ subjects, authorship, journals, countries of origin, and years of publication. Results: The 50 most-cited articles were published between 1983 and 2014, with the majority (33) published between 2000 and 2010. They generated 9012 citations in the literature. The most-cited study accounted for 497 citations; the mean number of citations per article was 180.24 ± 76.24. Twenty-three (46%) of the articles addressed postoperative outcomes following a specific type of arthroplasty implant. Arthroplasty implant studies accounted for 4726 citations, or 52.4% of the citations of the 50 articles. The most frequently studied arthroplasty implant was STAR (15), followed by Agility (7), Buechel Pappas (5), and Salto (4). STAR accounted for 3311 citations, or 37% of the total citations of the 50 articles. Conclusion: Ankle arthroplasty research has made great progress in the past 2 decades, particularly in the area of postoperative outcomes of specific ankle implants, but continued research and publication on additional arthroplasty implants should become a priority. Level of Evidence: Level V, Review Article.


Introduction
Since the introduction of ankle arthroplasty in the 1970s, 41 several generations of new arthroplasty implants have been developed, each introducing improvements such as hydroxyapatite coating, minimal bone resection techniques, 3-component design, and cementless fixation. 22 These innovations, combined with a growing population in need of ankle replacement, have led to an increase in both procedure volume and research. 39 In any field, a large and rapidly expanding body of research can obscure the studies that historically have made the greatest impact. Citation analysis is a useful way to highlight the impact and significance of specific publications and to identify research trends. 17,44 Although several bibliometric analyses of the ankle have been conducted previously, none have examined specific types and generations of ankle arthroplasty implants.
This study identified and analyzed the most-cited research on ankle arthroplasty implants and their outcomes in an effort to understand its impact on the field of ankle arthroplasty.

Methods
Using the keywords "ankle arthroplasty" and "ankle replacement," we found 5501 articles on ankle arthroplasty implants in our initial search of the Scopus, Web of Science, and MEDLINE/PubMed databases-2203 in Scopus, 1525 in Web of Science, and 1773 in MEDLINE/PubMed. The studies were published between 1970 and July 2021 and included original articles, reviews, clinical trials, and case reports. From the initial pool of 5501, we retrieved the 50 articles with the most citations. We reviewed the articles from most to least cited, analyzing them for title, authorship, subject, journal, country, and year of publication.
We then conducted full-text reviews of each article to select those that studied specific ankle arthroplasty implants. All ankle arthroplasty implants were included in our assessment. We also conducted a subanalysis of outcomes, survivorship, revisions, arthrodesis, and other reoperation of arthroplasty implants. Revision was defined as replacement of any implant component without removal. Arthrodesis was defined as subsequent fusion of the ankle. Other reoperation was defined as any surgery not including revision or arthrodesis. Table 1 shows the 50 most-cited articles. The number of citations of each article ranged from 112 to 497, with a mean of 180.24 ± 76. 24. In all, the 50 articles were associated with 9012 citations. The average number of citations per article per year from the date of publication through July 2021 ranged from 3 to 36, with a mean of 12 ± 6.20. The 50 articles were published between 1983 and 2014, with a majority (33) published between 2000 and 2010. Eighteen of the articles originated in the United States; 10 in the United Kingdom; 4 in Canada; 3 each in Denmark, France, Sweden, and Switzerland; 2 in Japan; and 1 each in the Netherlands and New Zealand.

Studies of Implant Survivorship and Complications
Of the 23 articles on ankle arthroplasty implants, 17 were primary studies assessing implant survivorship and complications, leading to 3508 citations (Table 3). Complications included revision, delayed wound healing, fracture, loosening, periarticular bone formation, osteolytic lesions, talar subsidence, and cysts. Follow-up ranged from 2 to 15 years. Ten of the 17 studies focused on STAR implants, leading to 1947 citations. Eight of the 10 STAR implant primary studies included survival analysis of at least 5 years. There were 41 revisions and 9 removals for 538 Agility ankles; 2 revisions and 0 arthrodesis for 50 Buechel-Pappas ankles, with follow-up ranging from 2 to 16 years; 8 revisions and 0 removals for 122 HINTEGRA ankles, with follow-up of 1.6 years; 18 revisions and 6 arthrodeses for 98 Salto ankles; and 174 revisions and 30 arthrodeses for 1060 STAR ankles. There were 6 revisions or arthrodeses for 32 TPR ankles. There were 230 revisions or arthrodeses for 1471 STAR ankles.

Most-Cited Journal and Authors
The most-cited article, with 497 citations, was an article on arthroplasty vs arthrodesis published by Haddad et al 23

Levels of Evidence
Most of the articles (42 of 50) had a level of evidence of IV. Among the remaining 8 articles, 4 had a level of evidence of V, 2 had a level of evidence of III, 1 had a level of evidence of II, and 1 had a level of evidence of VII. There were 42 original articles, 5 review articles, and 3 systematic reviews. The original articles included 1 randomized controlled trial.

Discussion
Since the introduction of ankle arthroplasty, a variety of new ankle arthroplasty implants have been created and researched. 39 The goal of this study was to analyze landmark research on the outcomes of specific types of ankle arthroplasty implants. Many of the 50 ankle arthroplasty articles we identified were studies of specific ankle arthroplasty implant devices, possibly reflecting the rapid rate of innovation over the past few decades. Ankle arthroplasty was first introduced in the 1970s by Lord and Marotte, who used a ball and socket implant that they based on hip replacement designs. 41 Complication rates were high, and many studies at the time recommended arthrodesis instead of arthroplasty. 42 For decades afterward, arthrodesis was considered the gold standard for treatment of ankle osteoarthritis. 31,57 In the meantime, however, second-, third-, and fourth-generation ankle replacement devices were developed, with new designs and techniques that required additional research on safety and efficacy. 21,22 This may explain the finding that the majority of the 50 articles were studies of outcomes of arthroplasty implants and were published between 2000 and 2010.
The most-cited article in our analysis was a systematic review published by Haddad et al 23 in 2007, nearly 3 decades after the introduction of ankle arthroplasty. The article assessed literature on the relative efficacy of ankle arthroplasty vs arthrodesis published during the time when the topic was still heavily debated. The authors reviewed second-generation implants and found that arthroplasty and arthrodesis had similar scores on the American Orthopaedic Foot & Ankle Society (AOFAS) ankle-hindfoot scale, 2 similar meta-analytic mean results, and similar revision rates. Although ankle arthroplasty historically was associated with poorer postoperative outcomes, the review by Haddad et al 23 seemed to support the conclusion that foot and ankle surgeons should favor ankle arthroplasty over arthrodesis because arthroplasty gave patients higher ankle mobility. 51 The authors acknowledged at the time that the data were sparse and that comparative studies were needed to strengthen this conclusion.
A prospective multicenter study by Daniels et al, published in 2014, received the third most citations per year in our review. The study built on the research by Haddad et al 23 and performed a comparative analysis of ankle arthroplasty and arthrodesis based on the Canadian Orthopaedic Foot and Ankle Society (COFAS) Prospective Ankle Reconstruction Database. This study had a level of evidence of II. Before it was undertaken, most of our knowledge of the results of ankle arthroplasty came from level IV evidence. 22 Daniels et al 12 found that the intermediate-term clinical outcomes of arthroplasty and arthrodesis were similar. However, rates of revision and major complications were higher after ankle replacement. The authors suggested that as prosthetic designs improved, revision and complication rates might also improve.
The market landscape of arthroplasty implant devices is continuously evolving. Most of the second-generation ankle implant devices identified in our bibliometric analysis, including the Buechel-Papas, Agility, and Mobility implants, are no longer used, and only the STAR implant continues to be widely used. Among our 50 studies, the ones that mentioned STAR implants were cited 3311 times, receiving 37% of the citations in our analysis. Furthermore, 10 of the 17 primary arthroplasty implant studies assessed STAR implants. Several newer implants, such as the INFINITY and the INBONE, do not appear in our analysis. 40,50,52 Future research should assess the influence of studies of these modern implants on the ankle arthroplasty literature.
Our study has several limitations. First, although Scopus, Web of Science, and MEDLINE/PubMed are comprehensive databases, there are other databases such as Embase that might contain works that do not appear in Scopus, Web of Science, and MEDLINE/PubMed. Furthermore, the databases we used contain primarily works written in English, and we may have omitted relevant articles in other languages. Third, this analysis does not account for self-citation. Authors may tend to cite their own articles to increase citation counts, which could skew the analysis. Future study is needed to understand the prevalence of self-citation and its impact on citation counts. Further, citation count is not always the best measure of an article's impact; level of evidence must also be taken into consideration. Finally, certain well-known journals and authors may have a wider reach than others, leading to higher citation counts for those journals and authors. Higher-quality articles by lesser-known journals and authors may have a deflated citation count.
Despite the limitations of bibliometric analysis, citation counts are used to calculate journal impact factors as well as  Top 50 Generation   STAR  15  3311  35  II  Agility  7  1942  20  II  Buechel Pappas  5  1157  12  II  Salto  4  1106  12  III  TNK  3  911  10  II  HINTEGRA  3  746  8  III  Mobility  2  478  5  III  TPR  1  141 1.5 II The Agility total ankle arthroplasty: seven to sixteen-year follow-up Agility Revision (7); removal for arthrodesis (7); reoperation any reason (46) Peri-implant lucency (89); death (36); subtalar arthritis (22); talonavicular arthritis (17); syndesmosis nonunion (9) H-index, both widely used measurements for research impact. 11 None of these measures are perfect, but they exist to provide an additional objective and quantifiable source of information that can aid in the discussion of what articles, individuals, or topics were most impactful over time. This is the first bibliometric analysis of ankle arthroplasty implants, which have grown in both research and procedure volume over the last few decades. By broadly assessing the literature, our research has identified high-quality articles as well as topics that may be more likely to make an impact within the field.

Conclusion
This study analyzed the most-cited literature on ankle arthroplasty implants according to topic, authors, journals, countries, and citations per year. Ankle arthroplasty research has greatly increased in the past 2 decades, particularly in the area of postoperative outcomes of specific ankle implants, and continued research and publication in additional areas should be a priority in the ankle arthroplasty medical community.

Acknowledgments
For their editorial assistance and assistance with submission of this manuscript, we thank Rachel Box, MS, Denise Di Salvio, MS, and Sandy Crump, MPH, in the Editorial Services group of The Johns Hopkins Department of Orthopaedic Surgery.

Ethical approval
Ethical approval was not sought for the present study because the study did not involve patient data.

Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. ICMJE forms for all authors are available online.

Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.