{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T12:42:27Z","timestamp":1753879347638,"version":"3.41.2"},"reference-count":39,"publisher":"Wiley","issue":"7","license":[{"start":{"date-parts":[[2025,5,31]],"date-time":"2025-05-31T00:00:00Z","timestamp":1748649600000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc-nd\/4.0\/"}],"funder":[{"DOI":"10.13039\/100012542","name":"Sichuan Provincial Science and Technology Support Program","doi-asserted-by":"publisher","award":["2024NSFSC0682"],"award-info":[{"award-number":["2024NSFSC0682"]}],"id":[{"id":"10.13039\/100012542","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Orthopaedic Surgery"],"published-print":{"date-parts":[[2025,7]]},"abstract":"<jats:title>ABSTRACT<\/jats:title><jats:sec><jats:title>Objective<\/jats:title><jats:p>Studies have described the nonuniform settlement of C2 lateral mass (C2LM\u2010NUS) as an asymmetrical change of the bilateral C2 lateral masses. This study aimed to: (1) identify the objective evidence for the C2LM\u2010NUS and clarify its anatomical basis; (2) explore the association between C2LM\u2010NUS and atlantoaxial osteoarthritis (AAOA), and verify the related biomechanics.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>Seventy\u2010nine dry axis specimens were measured macroscopically. The vertical distance between the superior articular surface and the lower edge of the vertebra was defined as the settlement value of C2 lateral mass (C2LMS). Twelve formalin\u2010embalmed axis specimens were scanned using micro\u2010computed tomography (Micro\u2010CT), and the trabecular microstructure of lateral masses was analyzed. 522 patients who underwent a head and neck or cervical spine CT scan were reviewed. The C2LMS was measured, and the bilateral difference (d\u2010C2LMS) was calculated. The AAOA was recorded. Normal and C2LM\u2010NUS upper cervical spine (C0\u2010C3) finite element models were established. The stress distributions on the alar ligament, transverse ligament, and lateral mass cartilage were analyzed using Abaqus software under varying torque conditions.<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Macroscopic analysis revealed that the C2LMS measured at the center point was comparable to the overall C2LMS (18.19\u2009\u00b1\u20091.83\u2009mm vs. 18.18\u2009\u00b1\u20091.82\u2009mm, <jats:italic>p<\/jats:italic>\u2009=\u20090.942). Twenty\u2010seven dry axis specimens (34.2%) were identified as C2LM\u2010NUS because they showed significant differences in bilateral C2LMS (d\u2010C2LMS: 1.21\u2009\u00b1\u20090.32\u2009mm). Micro\u2010CT analysis revealed that four formalin\u2010embalmed axis specimens with C2LM\u2010NUS exhibited a substantial difference in trabecular microstructural parameters between the settlement and the normal lateral masses. Clinical observations indicated that C2LM\u2010NUS was an independent risk factor for AAOA (adjusted odds ratio\u2009=\u20092.041, <jats:italic>p<\/jats:italic>\u2009&lt;\u20090.001). Finite element analysis revealed that in the C2LM\u2010NUS model, the maximum stress on the settlement side of the alar ligament increased by 47.4%\u201353.3% compared to the opposite side, and the cartilage stress increased by 15.0%\u201368.5%. Meanwhile, the maximum stress of the transverse ligament in the C2LM\u2010NUS model was 1.3\u20131.6 times greater than that of the normal model.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusions<\/jats:title><jats:p>The macroscopic measurement of the axis specimens provided objective anatomic evidence for C2LM\u2010NUS. Micro\u2010CT showed that C2LM\u2010NUS was associated with asymmetrical alterations of the trabecular microstructure of the lateral masses, suggesting that it is a pathological change rather than a normal phenomenon. The clinical study indicated that C2LM\u2010NUS is an independent risk factor for AAOA. Stress concentration in unilateral alar ligaments and articular cartilage is a biomechanical contributor to AAOA.<\/jats:p><\/jats:sec>","DOI":"10.1111\/os.70080","type":"journal-article","created":{"date-parts":[[2025,5,31]],"date-time":"2025-05-31T09:44:58Z","timestamp":1748684698000},"page":"2068-2081","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["The Anatomical Basis of Nonuniform Settlement of the <scp>C2<\/scp> Lateral Mass and Its Association With Atlantoaxial Osteoarthritis"],"prefix":"10.1111","volume":"17","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9352-6567","authenticated-orcid":false,"given":"Chao","family":"Tang","sequence":"first","affiliation":[{"name":"Department of Orthopedics The Second Affiliated Hospital (Xinqiao Hospital) of Army Medical University  Chongqing China"},{"name":"Department of Orthopedics The Affiliated Hospital of Southwest Medical University  Luzhou China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Chen Hui","family":"Cai","sequence":"additional","affiliation":[{"name":"Department of Orthopedics The Second Affiliated Hospital (Xinqiao Hospital) of Army Medical University  Chongqing China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Ying","family":"Zhang","sequence":"additional","affiliation":[{"name":"Department of Orthopedics The Second Affiliated Hospital (Xinqiao Hospital) of Army Medical University  Chongqing China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8010-3939","authenticated-orcid":false,"given":"Ye Hui","family":"Liao","sequence":"additional","affiliation":[{"name":"Department of Orthopedics The Affiliated Hospital of Southwest Medical University  Luzhou China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xian Ming","family":"Huang","sequence":"additional","affiliation":[{"name":"Department of Orthopedics The Second Affiliated Hospital (Xinqiao Hospital) of Army Medical University  Chongqing China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Xu","family":"Zhao","sequence":"additional","affiliation":[{"name":"Department of Orthopedics The Second Affiliated Hospital (Xinqiao Hospital) of Army Medical University  Chongqing China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"De Jun","family":"Zhong","sequence":"additional","affiliation":[{"name":"Department of Orthopedics The Affiliated Hospital of Southwest Medical University  Luzhou China"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Tong Wei","family":"Chu","sequence":"additional","affiliation":[{"name":"Department of Orthopedics The Second Affiliated Hospital (Xinqiao Hospital) of Army Medical University  Chongqing China"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2025,5,31]]},"reference":[{"volume-title":"Atlantoaxial Instability","year":"2023","author":"Lacy J.","key":"e_1_2_11_2_1"},{"key":"e_1_2_11_3_1","doi-asserted-by":"publisher","DOI":"10.4103\/jcvjs.JCVJS_209_20"},{"key":"e_1_2_11_4_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.yacr.2023.04.013"},{"key":"e_1_2_11_5_1","doi-asserted-by":"publisher","DOI":"10.1097\/BRS.0b013e3181b13320"},{"key":"e_1_2_11_6_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.neuchi.2023.101511"},{"key":"e_1_2_11_7_1","doi-asserted-by":"publisher","DOI":"10.1097\/00007632\u2010199906150\u201000006"},{"issue":"2","key":"e_1_2_11_8_1","first-page":"361","article-title":"Epigenetic Variation in the Human Cranium","volume":"101","author":"Carolineberry A.","year":"1967","journal-title":"Journal of Anatomy"},{"key":"e_1_2_11_9_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.spinee.2023.02.017"},{"key":"e_1_2_11_10_1","doi-asserted-by":"publisher","DOI":"10.1007\/s00586-024-08285-8"},{"key":"e_1_2_11_11_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.math.2015.03.006"},{"issue":"5","key":"e_1_2_11_12_1","first-page":"314","article-title":"Absence of Symmetry in Superior Articular Facets on the First Cervical Vertebra in Humans: Implications for Diagnosis and Treatment","volume":"17","author":"Gottlieb M. 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