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. 2022 Mar 28;17:194. doi: 10.1186/s13018-022-03068-7

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© The Author(s) 2022

Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

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Fig. 8 — A Network visualization map of the co-occurrence network of keywords using VOSviewer. Each node represents a certain keyword. Nodes and font size represent the number of keyword occurrences. Keywords with close correlation will be assigned to one cluster with the same color. B Overlay visualization map of keywords analysis in the ONFH field. The color of each node shows the average appearing year (AAY) of the keyword, according to the color gradient shown at the bottom right. The blue-purple color reflected the keywords appeared relatively earlier, while the dark red nodes represented the recent occurrence