{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,23]],"date-time":"2026-04-23T11:53:15Z","timestamp":1776945195856,"version":"3.51.4"},"reference-count":47,"publisher":"Public Library of Science (PLoS)","issue":"8","license":[{"start":{"date-parts":[[2025,8,21]],"date-time":"2025-08-21T00:00:00Z","timestamp":1755734400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS One"],"abstract":"<jats:sec id=\"sec001\">\n<jats:title>Background<\/jats:title>\n<jats:p>The intrinsic foot muscles (IFM), or foot core, provides stability to the foot skeleton. IFM dysfunction has been linked to foot and ankle injuries; however,\u00a0the functional assessment of IFM in lower extremity conditions remains a clinical conundrum. We undertook a large study to understand the differences in muscle size and quality of IFM across a spectrum of conditions including Chronic Ankle Instability (CAI), Patellofemoral Pain (PFP), 1<jats:sup>st<\/jats:sup> Metatarsophalangeal Joint (1<jats:sup>st<\/jats:sup>\u00a0MTPJ)\u00a0 arthrodesis\u00a0and in patients with diabetes. This study compares IFM morphology and tissue quality in patients across these conditions and healthy control group individuals.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec002\">\n<jats:title>Methods<\/jats:title>\n<jats:p>This study included 119 participants: 35 PFP, 29 CAI, 8 with 1<jats:sup>st<\/jats:sup> MTPJ arthrodesis, 9 with Diabetes, and 38 healthy controls. Ultrasound imaging (USI) assessed cross-sectional area (CSA) for muscle size and echogenicity for muscle quality in the Abductor Hallucis (AbH) and Flexor Digitorum Brevis (FDB). All size measures were normalized to body mass. Analysis of Coavariance (ANCOVA) was performed between groups, controlling for age and sex, to identify differences.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec003\">\n<jats:title>Results<\/jats:title>\n<jats:p>Significant differences (P\u2009&lt;\u20090.05) in the CSA of the AbH were found between all pathology groups and healthy control group, except for the 1<jats:sup>st<\/jats:sup> MTPJ group. CSA of FDB showed significant differences (P\u2009&lt;\u20090.01) in all groups except the PFP and 1<jats:sup>st<\/jats:sup> MTPJ groups. For echogenicity, significant differences (P\u2009&lt;\u20090.05) were found between groups for both AbH and FDB, while CAI, 1st MTPJ, and PFP groups showed higher FDB echogenicity. Large effect sizes were found for CSA and echogenicity in all groups except PFP.<\/jats:p>\n<\/jats:sec>\n<jats:sec id=\"sec004\">\n<jats:title>Conclusion<\/jats:title>\n<jats:p>This is the first study to our knowledge to collectively analyze multiple clinical groups with suspected IFM weakness in functional position for both muscle size and quality. Significant changes in muscle size and quality were observed, suggesting that clinicians should assess and target IFM rehabilitation to improve foot and ankle function in these populations.<\/jats:p>\n<\/jats:sec>","DOI":"10.1371\/journal.pone.0325028","type":"journal-article","created":{"date-parts":[[2025,8,21]],"date-time":"2025-08-21T17:39:10Z","timestamp":1755797950000},"page":"e0325028","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":2,"title":["Comparison of intrinsic foot muscle function in patients with different lower extremity conditions"],"prefix":"10.1371","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-4134-8540","authenticated-orcid":true,"given":"Abbis","family":"Jaffri","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Joseph","family":"Park","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Joe","family":"Hart","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Jay","family":"Hertel","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Susan","family":"Saliba","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"340","published-online":{"date-parts":[[2025,8,21]]},"reference":[{"issue":"5","key":"pone.0325028.ref001","doi-asserted-by":"crossref","first-page":"290","DOI":"10.1136\/bjsports-2013-092690","article-title":"The foot core system: a new paradigm for understanding intrinsic foot muscle function","volume":"49","author":"PO McKeon","year":"2015","journal-title":"Br J Sports Med"},{"key":"pone.0325028.ref002","article-title":"The positional effects of weight-bearing foot and ankle musculature on muscle stiffness using shear wave elastography","author":"J Arellano","year":"2025","journal-title":"Gait & Posture"},{"issue":"4","key":"pone.0325028.ref003","doi-asserted-by":"crossref","first-page":"327","DOI":"10.1123\/jsr.21.4.327","article-title":"Differences in static- and dynamic-balance task performance after 4 weeks of intrinsic-foot-muscle training: the short-foot exercise versus the towel-curl exercise","volume":"21","author":"SK Lynn","year":"2012","journal-title":"J Sport Rehabil"},{"issue":"4","key":"pone.0325028.ref004","doi-asserted-by":"crossref","first-page":"691","DOI":"10.1007\/s00421-014-3056-x","article-title":"Coordination of intrinsic and extrinsic foot muscles during walking","volume":"115","author":"KE Zelik","year":"2015","journal-title":"Eur J Appl Physiol"},{"key":"pone.0325028.ref005","doi-asserted-by":"crossref","first-page":"79","DOI":"10.1016\/j.foot.2019.08.009","article-title":"Ultrasound examination of intrinsic foot muscles in patients with 1st metatarsophalangeal joint arthrodesis","volume":"41","author":"AH Jaffri","year":"2019","journal-title":"Foot (Edinb)"},{"issue":"102","key":"pone.0325028.ref006","doi-asserted-by":"crossref","first-page":"20141076","DOI":"10.1098\/rsif.2014.1076","article-title":"Active regulation of longitudinal arch compression and recoil during walking and running","volume":"12","author":"LA Kelly","year":"2015","journal-title":"J R Soc Interface"},{"key":"pone.0325028.ref007","doi-asserted-by":"crossref","DOI":"10.1242\/jeb.174425","article-title":"Rethinking the evolution of the human foot: insights from experimental research","volume":"221","author":"NB Holowka","year":"2018","journal-title":"J Exp Biol"},{"issue":"5","key":"pone.0325028.ref008","doi-asserted-by":"crossref","first-page":"112432","DOI":"10.1016\/j.isci.2025.112432","article-title":"Are there changes in the foot biomechanics during the before and after fifth metatarsal fracture running stance phase?","volume":"28","author":"H Zhou","year":"2025","journal-title":"iScience"},{"key":"pone.0325028.ref009","doi-asserted-by":"crossref","first-page":"5","DOI":"10.5114\/jhk\/174311","article-title":"Can the Entire Function of the Foot Be Concentrated in the Forefoot Area during the Running Stance Phase? 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