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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Bioeng. Biotechnol.</journal-id>
<journal-title>Frontiers in Bioengineering and Biotechnology</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Bioeng. Biotechnol.</abbrev-journal-title>
<issn pub-type="epub">2296-4185</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="publisher-id">893800</article-id>
<article-id pub-id-type="doi">10.3389/fbioe.2022.893800</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Bioengineering and Biotechnology</subject>
<subj-group>
<subject>Editorial</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Editorial: Post-Traumatic Osteoarthritis After Meniscus Injury</article-title>
<alt-title alt-title-type="left-running-head">Patel et al.</alt-title>
<alt-title alt-title-type="right-running-head">Editorial: PTOA After Meniscus Injury</alt-title>
</title-group>
<contrib-group>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Patel</surname>
<given-names>Jay M.</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1217797/overview"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Haut Donahue</surname>
<given-names>Tammy L.</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1186979/overview"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Galbusera</surname>
<given-names>Fabio</given-names>
</name>
<xref ref-type="aff" rid="aff4">
<sup>4</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/60387/overview"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Drews</surname>
<given-names>Bj&#xf6;rn H.</given-names>
</name>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1240055/overview"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Seitz</surname>
<given-names>Andreas M.</given-names>
</name>
<xref ref-type="aff" rid="aff6">
<sup>6</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/812982/overview"/>
</contrib>
</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>Department of Orthopaedics</institution>, <institution>Emory University</institution>, <addr-line>Atlanta</addr-line>, <addr-line>GA</addr-line>, <country>United States</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>Atlanta VA Medical Center</institution>, <addr-line>Decatur</addr-line>, <addr-line>GA</addr-line>, <country>United States</country>
</aff>
<aff id="aff3">
<sup>3</sup>
<institution>Department of Biomedical Engineering</institution>, <institution>University of Memphis</institution>, <addr-line>Memphis</addr-line>, <addr-line>TN</addr-line>, <country>United States</country>
</aff>
<aff id="aff4">
<sup>4</sup>
<institution>Schulthess Klinik</institution>, <addr-line>Z&#xfc;rich</addr-line>, <country>Switzerland</country>
</aff>
<aff id="aff5">
<sup>5</sup>
<institution>St. Vinzenz Hospital</institution>, <addr-line>Pfronten</addr-line>, <country>Germany</country>
</aff>
<aff id="aff6">
<sup>6</sup>
<institution>Institute of Orthopaedic Research and Biomechanics</institution>, <institution>Ulm University Medical Center</institution>, <addr-line>Ulm</addr-line>, <country>Germany</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>
<bold>Edited and reviewed by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/463089/overview">Markus O. Heller</ext-link>, University of Southampton, United Kingdom</p>
</fn>
<corresp id="c001">&#x2a;Correspondence: Jay M. Patel, <email>jay.milan.patel@emory.edu</email>
</corresp>
<fn fn-type="other">
<p>This article was submitted to Biomechanics, a section of the journal Frontiers in Bioengineering and Biotechnology</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>05</day>
<month>04</month>
<year>2022</year>
</pub-date>
<pub-date pub-type="collection">
<year>2022</year>
</pub-date>
<volume>10</volume>
<elocation-id>893800</elocation-id>
<history>
<date date-type="received">
<day>10</day>
<month>03</month>
<year>2022</year>
</date>
<date date-type="accepted">
<day>16</day>
<month>03</month>
<year>2022</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2022 Patel, Haut Donahue, Galbusera, Drews and Seitz.</copyright-statement>
<copyright-year>2022</copyright-year>
<copyright-holder>Patel, Haut Donahue, Galbusera, Drews and Seitz</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<related-article id="RA1" related-article-type="commentary-article" journal-id="Front. Bioeng. Biotechnol." xlink:href="https://www.frontiersin.org/researchtopic/19271" ext-link-type="uri">Editorial on the Research Topic <article-title>Post-Traumatic Osteoarthritis After Meniscus Injury</article-title>
</related-article>
<kwd-group>
<kwd>meniscus</kwd>
<kwd>osteoarthiritis</kwd>
<kwd>biomechanics</kwd>
<kwd>PTOA</kwd>
<kwd>meniscus repair</kwd>
</kwd-group>
</article-meta>
</front>
<body>
<p>The menisci are fibrocartilaginous discs that are vital to load distribution and function of our knee joints. Due to their propensity for injury and relative lack of self-healing, these functions are often disrupted following traumatic injury. The result is the progression of post-traumatic osteoarthritis (PTOA), a huge burden on the population. In this Frontiers Research Topic, we bring together relevant contributions on various aspects of meniscal injury and PTOA progression, including meniscal function, metrics for studying PTOA, and repair considerations to prevent PTOA progression.</p>
<p>The meniscus has long been considered vital to distributing tibiofemoral loads in the joint (<xref ref-type="bibr" rid="B6">Lee et al., 2006</xref>). <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.765596/full">Sukopp et al.</ext-link> reviewed this literature, confirming that impaired knee joints (tears, meniscectomy, etc) consistently led to increased stresses. However, this review importantly noted that loading protocols were quite variable, and that future evaluation of load distribution may need better control to allow comparison across the field. Beyond load distribution, another meniscal function that has been up for debate is shock absorption. Classically, shock absorption had been cited as a key function of the menisci, until about 10&#xa0;years ago (<xref ref-type="bibr" rid="B1">Andrews et al., 2011</xref>), when a nearly decade-long drop in Pubmed results for a search on &#x201c;meniscus, shock absorption&#x201d; is noted. <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.837554/full">Seitz et al.</ext-link> performed a robust evaluation of loss factors for intact, torn, and removed conditions, clearly demonstrating that there is indeed a shock absorbing function of the meniscus. Another important function of menisci is lubrication; <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.779946/full">de Roy et al.</ext-link> performed a study showing that both root injuries and meniscectomy do not affect whole joint friction. In the absence of changes to joint friction, patients may not &#x201c;feel&#x201d; a change that otherwise may result from catching or locking, and the initiation of PTOA under such conditions is likely associated with other functional deficits.</p>
<p>The effects of meniscal injury and removal on time-zero mechanics, as described previously, have been clearly linked to PTOA progression, especially in animal models involving destabilization of the medial meniscus (DMM) (<xref ref-type="bibr" rid="B5">Glasson et al., 2007</xref>; <xref ref-type="bibr" rid="B3">Bansal et al., 2020</xref>). Conversely, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.835730/full">Haut Donahue et al.</ext-link> performed a morphological study on meniscus, cartilage, and bone health following a closed-joint traumatic injury model (resulting in ACL rupture), showing that even if the ACL was reconstructed after this injury, that the meniscus and cartilage still saw effects of damage. These new closed-joint models may better recreate the <italic>in vivo</italic> clinical situation, instead of the standard surgical DMM models. These models would also benefit from more standardized outcome metrics and guidance documents (<xref ref-type="bibr" rid="B8">Pfeifer et al., 2015</xref>), to truly evaluate the state of PTOA following meniscus injury, repair, and/or replacement. <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.787330/full">Trivedi et al.</ext-link> performed a systematic review of the outcome metrics of PTOA that were included in meniscus repair and replacement <italic>in vivo</italic> studies, showing that joint health is not always evaluated even if it is vital to determining the success of these approaches. Furthermore, new techniques are also being developed to analyze the state of articular cartilage, and could serve to identify early markers of PTOA that are not visible with current clinical imaging or arthroscopy. <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.744197/full">Gao et al.</ext-link> developed a novel confocal Raman microspectroscopy approach to spatially map glycosaminoglycan (GAG) loss, a technique that does not require tissue dissection or sampling, and that could be readily adapted toward non-destructive and potentially <italic>in vivo</italic> application (<xref ref-type="bibr" rid="B4">Gaifulina et al., 2021</xref>). Finally, in addition to establishing novel and consistent metrics for PTOA assessment, the identification of meniscal tears before PTOA initiation may be key to treating patients. <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.747217/full">Tack et al.</ext-link> utilized an MRI database from the Osteoarthritis Initiative, using a new neural network to identify meniscal tears. Combining these analytical advancements with technological innovations will give the field routes to identify both meniscal injuries and early markers of PTOA.</p>
<p>The multi-functional attributes of the meniscus, their influence on the progression of degenerative changes, and methods to evaluate early PTOA are all certainly of interest to the field. These findings, both inside and outside of this Research Topic, can also help to inform various repair and replacement techniques. For example, medial meniscus root tears are common yet present a huge mechanical burden due to a loss in load distribution and shock absorption (as noted by <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.765596/full">Sukopp et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.837554/full">Seitz et al.</ext-link>). Repair of these root tears with transtibial techniques has shown promise (<xref ref-type="bibr" rid="B7">Pache et al., 2018</xref>); however, anatomic positioning of the repair site is also crucial. <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.744065/full">Floyd et al.</ext-link> show that non-anatomic repair of posterior medial meniscus root tears has consequences, including symptomatic extrusion, which may accelerate PTOA progression. Beyond root tears, research regarding the healing of the meniscal body post-injury is becoming increasingly common (<xref ref-type="bibr" rid="B2">Bansal et al., 2021</xref>), with the phrase &#x201c;Save the Meniscus&#x201d; commonly appearing in social medial and journal articles. Meniscus tear management often relies on the zone of tear; outer meniscus tears are repaired with suture and inner meniscus tears are typically treated with removal of the torn tissue (partial meniscectomy). This difference is often attributed to vascularity, however an opinion piece by <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.843166/full">Patel</ext-link> theorizes other factors that may be involved: circumferential disruption, obstruction by the dense matrix, and other joint factors (including inflammation). A couple of these factors were investigated by <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.837619/full">Andress et al.</ext-link>, where anti-inflammatory modulation via compressive or tensile loading was confirmed with RNA-sequencing, verifying the role that loading (or lack thereof with disruption) may have in meniscal repair. Moreover, this contribution represents an exciting trend in meniscus research, combining omics and engineering to simultaneously study mechano-transduction and identify novel therapeutic targets. Finally, while identification of these therapeutic targets is important, implementing them <italic>via</italic> new scaffold technologies is also paramount. <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.810705/full">Dorth&#xe9; et al.</ext-link> utilized a new technique called pneumatospinning, allowing the formation of thicker fiber mats that support fibrocartilage growth, and advancement over other nanofibrous scaffold fabrication techniques. This proof-of-concept study certainly warrants future exploration and may represent a method to better integrate with the native meniscal tissue.</p>
<p>As the meniscus research field continues to gain traction, this Frontiers Research Topic highlights new techniques in the field (<ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.835730/full">Haut Donahue et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.744197/full">Gao et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.747217/full">Tack et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.837619/full">Andress et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.810705/full">Dorth&#xe9; et al.</ext-link>), reviews the current state (<ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.765596/full">Sukopp et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.787330/full">Trivedi et al.</ext-link>), and establishes and/or challenges paradigms (<ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.837554/full">Seitz et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.779946/full">de Roy et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2021.744065/full">Floyd et al.</ext-link>, <ext-link ext-link-type="uri" xlink:href="https://www.frontiersin.org/articles/10.3389/fbioe.2022.843166/full">Patel</ext-link>), encompassing aspects of biomechanics, engineering, biology, and clinical management.</p>
</body>
<back>
<sec id="s1">
<title>Author Contributions</title>
<p>All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.</p>
</sec>
<sec sec-type="COI-statement" id="s2">
<title>Conflict of Interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec sec-type="disclaimer" id="s3">
<title>Publisher&#x2019;s Note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
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