{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,12]],"date-time":"2026-06-12T14:00:16Z","timestamp":1781272816791,"version":"3.54.1"},"reference-count":40,"publisher":"MDPI AG","issue":"16","license":[{"start":{"date-parts":[[2025,8,19]],"date-time":"2025-08-19T00:00:00Z","timestamp":1755561600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Key Research and Development Program of Shaanxi Province","award":["2022ZDLSF04-10"],"award-info":[{"award-number":["2022ZDLSF04-10"]}]},{"name":"Key Research and Development Program of Shaanxi Province","award":["QCYRCXM-2022-34"],"award-info":[{"award-number":["QCYRCXM-2022-34"]}]},{"name":"Qin Chuang Yuan Talent Project","award":["2022ZDLSF04-10"],"award-info":[{"award-number":["2022ZDLSF04-10"]}]},{"name":"Qin Chuang Yuan Talent Project","award":["QCYRCXM-2022-34"],"award-info":[{"award-number":["QCYRCXM-2022-34"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Knee joint stiffness occurs and severely limits its range of motion (ROM) after facture around the knee. During mobility training, knee joints need to be flexed to the maximum angle position (maxAP) that can induce pain at an appropriate level in order to pull apart intra-articular adhesive structures while avoiding secondary injuries. However, the maxAP varies with training and is mostly determined by the pain level of patients. In this study, the feasibility of utilizing electromyogram (EMG) activities to detect maxAP was investigated. Specifically, the maxAP detection was converted into a binary classification between pain level three of the numerical rating scales (pain) and below (painless) according to clinical requirements. Firstly, 12 post-fracture patients with knee joint stiffness participated in Experiment I, with a therapist performing routine mobility training and EMG signals being recorded from knee flexors and extensors. The results showed that the extracted EMG features were significantly different between the pain and painless states. Then, the maxAP estimation performance was tested on a knee rehabilitation robot in Experiment II, with another seven patients being involved. The support vector machine and random forest models were used to classify between pain and painless states and obtained a mean accuracy of 87.90% \u00b1 4.55% and 89.10% \u00b1 4.39%, respectively, leading to an average estimation bias of 6.5\u00b0 \u00b1 5.1\u00b0 and 4.5\u00b0 \u00b1 3.5\u00b0. These results indicated that the pain-induced EMG can be used to accurately classify pain states for the maxAP estimation in post-fracture mobility training, which can potentially facilitate the application of robotic techniques in fracture rehabilitation.<\/jats:p>","DOI":"10.3390\/s25165142","type":"journal-article","created":{"date-parts":[[2025,8,19]],"date-time":"2025-08-19T11:41:41Z","timestamp":1755603701000},"page":"5142","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Pain State Classification of Stiff Knee Joint Using Electromyogram for Robot-Based Post-Fracture Rehabilitation Training"],"prefix":"10.3390","volume":"25","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9118-8333","authenticated-orcid":false,"given":"Yang","family":"Zheng","sequence":"first","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"},{"name":"State Industry-Education Integration Center for Medical Innovations, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dimao","family":"He","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"},{"name":"State Industry-Education Integration Center for Medical Innovations, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuan","family":"He","sequence":"additional","affiliation":[{"name":"TCM Rehabilitation Department, Honghui Hospital, Xi\u2019an Jiaotong University, Xi\u2019an 710001, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xiangrui","family":"Kong","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"},{"name":"State Industry-Education Integration Center for Medical Innovations, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xiaochen","family":"Fan","sequence":"additional","affiliation":[{"name":"TCM Rehabilitation Department, Honghui Hospital, Xi\u2019an Jiaotong University, Xi\u2019an 710001, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2959-9147","authenticated-orcid":false,"given":"Min","family":"Li","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"},{"name":"State Industry-Education Integration Center for Medical Innovations, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Guanghua","family":"Xu","sequence":"additional","affiliation":[{"name":"School of Mechanical Engineering, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"},{"name":"State Industry-Education Integration Center for Medical Innovations, Xi\u2019an Jiaotong University, Xi\u2019an 710049, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jichao","family":"Yin","sequence":"additional","affiliation":[{"name":"Xi\u2019an Health School, Xi\u2019an 710054, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,8,19]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"16","DOI":"10.1186\/s13037-019-0196-2","article-title":"Outcomes after surgical treatment of acetabular fractures: A review","volume":"13","author":"Ziran","year":"2019","journal-title":"Patient Saf. 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