Stiffness of the Middle and Lower Cervical Spine Is Associated with Idiopathic Atlantoaxial Joint Disorder: A Retrospective Case-Control Study

Stiffness of the Middle and Lower Cervical Spine Is Associated with Idiopathic Atlantoaxial Joint Disorder: A Retrospective Case-Control Study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Stiffness of the Middle and Lower Cervical Spine Is Associated with Idiopathic Atlantoaxial Joint Disorder: A Retrospective Case-Control Study Yusuke Murakami, Tadao Morino, Mayu Ogura, Masaki Takao This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9279035/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Background Atlantoaxial joint disorders (AAD), including instability and retro-odontoid pseudotumors, can cause serious neurological deficits; however, some patients lack an identifiable primary disease. We hypothesized that stiffness of the middle and lower cervical spines contributes to idiopathic AAD. This study aimed to compare the range of motion (ROM) of the middle and lower cervical spines and extent of ossification of the anterior longitudinal ligament (ALL) in patients with cervical spondylotic myelopathy (CSM) due to idiopathic AAD and age- and sex-matched patients with CSM without AAD. Methods We enrolled 56 patients who underwent surgery for myelopathy due to AAD between 2007 and 2020. Among them, 27 (48.2%) patients without a primary disease were classified into the idiopathic AAD group. The CSM group included patients who underwent surgery at the same time and included two age- (± 1 year) and sex-matched patients for each patient in the idiopathic AAD group. The ROM (C2–7) and extent of ALL ossification were compared between the groups, and the correlation between the extent of ossification and ROM was assessed. Results Patients with idiopathic AAD demonstrated a significantly reduced ROM and more severe ligament ossification than the matched patients without AAD. A significant negative correlation was found between ROM and ALL ossification. Conclusion The ROM of the middle and lower cervical spines were significantly lower in patients with idiopathic AAD. The extent of ossification of the ALL, which negatively correlated with the ROM of the cervical spine, was also greater in patients with CSM with idiopathic AAD. anterior longitudinal ligament ossification atlantoaxial joint disorder stiffness of middle and lower cervical spine Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Background The atlantoaxial joint, composed of the atlas and axis vertebrae, supports the cranium and enables cervical rotational movements.1 Disorders of this joint — such as instability and formation of retro-odontoid pseudotumors — can lead to severe neurological deficits, including tetraplegia and sudden death.［1,2］ These complications commonly arise from conditions like rheumatoid arthritis (RA), Down syndrome, cerebral palsy, trauma, and congenital malformations; however, cases without primary diseases are frequently encountered.［2-7］ The pathophysiology of myelopathy due to atlantoaxial joint disorders (AAD) is categorized into two types: 1) cases caused by ligament laxity or synovitis, and 2) cases caused by mechanical stress.［2,4,5,］ RA and Down syndrome are associated with ligament laxity, which leads to instability and spinal canal stenosis.［6］ By contrast, patients with middle and lower cervical fusion surgery, congenital fusion disease, and athetotic cerebral palsy have increased chronic mechanical stress on the atlantoaxial joints owing to decreased mobility in the middle and lower cervical spine, causing retro-odontoid pseudotumors and spinal canal stenosis.［2,7］Therefore, we hypothesized that stiffness of the middle and lower cervical spines is a contributing factor to idiopathic AAD. Diffuse idiopathic skeletal hyperostosis (DISH) is a progressive disease characterized by the ossification of ligaments and entheses.8 Several case reports have linked DISH to the development of retro-odontoid pseudotumors, ［11-13］ suggesting that ossification of the anterior longitudinal ligament (ALL) — which results in increased mechanical stress at the atlantoaxial joint — may be a significant risk factor for ligament formation. Thus, we focused on ALL ossification in patients with idiopathic AAD, as well as the range of motion (ROM) of the middle and lower cervical spines. The purpose of this study was to compare the ROM of the middle and lower cervical spines, and extent of ossification of the ALL in patients with cervical spondylotic myelopathy (CSM) due to idiopathic AAD versus in age- and sex-matched patients with CSM without AAD. Methods This study included 56 patients (27 men and 29 women) who underwent surgery for myelopathy due to AAD between 2007 and 2020. Twenty nine patients had primary diseases, including RA in 13 patients (23.2%); cerebral palsy, trauma, and congenital malformation in four patients (7.1%); os odontoideum in three patients (5.4%); and Down syndrome in one patient (1.8%). Twenty-seven (48.2 %) patients had no primary disease (Table 1). The ROM of the cervical spine was compared between two groups: patients with CSM associated with idiopathic AAD (idiopathic AAD group [27 cases]; male: 19, female: 8; mean age, 74.2 ± 6.4 years), and age- and sex-matched patients with CSM without AAD (CSM group [54 cases]; male: 38, female: 16; mean age 74.1 ± 6.2 years). The CSM group included patients who underwent surgery at the same time and included two age- (±1 year) and sex-matched patients for each patient in the idiopathic AAD group. The ROM was defined as the angle formed by the C2 and C7 vertebral body endplates and was calculated by subtracting the angle in the flexed position from that in the extended position. This angle was defined as the positive lordosis angle (Figure 1). Next, the extent of ossification of the ALL of the cervical spine was assessed. We used the scoring system developed by Murakami et al.［14］ — which is a modification of the scoring system developed by Mata et al.［15］— to evaluate the extent of ligament ossification (0, no ligament ossification; 1, ligament ossification of less than half of the intervertebral height; 2, ossification of more than half of the intervertebral height; and 3, complete ossification). Five vertebrae from C2/3 to C6/7 (Figure 2) were evaluated, and the total scores were compared between the two groups. Additionally, we combined all cases to investigate whether the ROM of the cervical spine correlated with the extent of ossification of the ALL. Statistical analyses were performed using JMP ver. 17.0 (SAS Institute, Cary, NC) for Macintosh. The Tukey–Kramer HSD test was used for group comparisons of age, ROM, and total scores. The χ2 test was used to analyze categorical data, and Spearman’s correlation coefficient was calculated to determine the association between the ROM and ligament ossification score. Results The ROM was significantly smaller in the idiopathic AAD group (25.4 ± 19.2°) than in the CSM group (40.1 ± 12.0°; p<0.001; Figure 3). The total ossification score of the ALL from C2/3 to C6/7 was significantly higher in the idiopathic AAD group (9.3 ± 3.9) than in the CSM group (5.4 ± 3.3; p<0.001) (Figure 4). A significant negative correlation was observed between the total ossification score and cervical spine ROM (ρ = -0.62; p<0.001; Figure 5). Discussion In this study, we demonstrated that patients with CSM associated with idiopathic AAD have a significantly reduced ROM in the middle and lower cervical spines compared with age- and sex-matched patients with CSM without AAD. This reduction was associated with extensive ossification of the ALL and was significantly negatively correlated with the ROM of the cervical spine. Chikuda et al.［2］ reported that retro-odontoid pseudotumors can develop even in the absence of atlantoaxial instability, which is often associated with extensive degenerative changes and anterior ligament ossification. In a multicenter cross-sectional study of patients with atlantoaxial subluxation without RA, Kuroshima et al.［16］ identified advanced intervertebral disc and facet degeneration, and an increased C2–C7 sagittal vertical axis as significant risk factors for retro-odontoid pseudotumor formation. Similarly, using a matched case–control design, Takahata et al.［17］demonstrated that a reduced C2–C7 ROM combined with an increase in C1–2 motion was associated with nonrheumatic retro-odontoid pseudotumors. Chen et al.［18］ performed finite element analysis and demonstrated that degeneration and reduced mobility of the cervical spine led to increased stress at the atlantoaxial joint. Several case reports have provided clinical evidence for this mechanism. ［11-13］ Jun et al.［11］ first described retro-odontoid pseudotumor formation in patients with DISH and proposed that the marked rigidity of the lower cervical spine results in relative hypermobility at the atlantoaxial junction. Overall, these studies consistently indicate that stiffness of the middle and lower cervical spines increases mechanical loading at the atlantoaxial joint. Our findings provide additional clinical evidence supporting this concept. Cervical spine stiffness is a multifactorial condition influenced by various degenerative changes, including intervertebral disc degeneration and facet joint arthropathy. However, it is difficult to objectively and consistently quantify these changes in clinical studies. By contrast, ossification of the ALL can be readily evaluated using established radiographic scoring systems,［14,15］ providing a simple and reproducible measure of the structural stiffness of the cervical spine. Therefore, the evaluation of ligament ossification may offer a practical approach for assessing the limitations of cervical spine mobility. Clinically, these findings highlight the importance of assessing middle and lower cervical spine stiffness in patients with CSM associated with idiopathic AAD. Given that such patients already exhibit reduced preoperative cervical mobility, careful attention should be paid to postoperative changes in ROM and their impact on activities of daily living. In surgical decision-making, the extent of fixation may need to consider preexisting fused segments, as well as the remaining mobile segments. However, this study was not designed to evaluate the optimal fixation range. Additionally, postoperative rehabilitation aimed at preserving cervical motion may be important for improving functional outcomes. Evaluation of the cervical ROM and ALL ossification provides useful information for understanding the underlying pathomechanics of this condition and may also facilitate more informed preoperative education regarding functional expectations. This evaluation method has a practical advantage in that it does not require specialized equipment or complex analyses. This study had several limitations; first, the sample size is relatively small. Second, the alignment of the entire spine and corresponding extent of ligament ossification were not assessed. Third, other contributors to cervical stiffness, such as disc degeneration and facet joint arthropathy, were not quantitatively examined. Additionally, upper cervical kinematics — including motion at the atlantoaxial joint — were not directly evaluated. In this study, the C2–7 ROM was selected because it represents a parameter that can be readily assessed in routine clinical practice. Patients with CSM were selected as the control group because they presented with clinical features similar to those of myelopathy, allowing us to evaluate differences in the underlying pathomechanisms associated with idiopathic AAD. Age and sex matching was performed to minimize the potential confounding effects of demographic factors on cervical ROM and ligament ossification. Despite these limitations, the present study provides clinically relevant insights by demonstrating a clear association between cervical spine stiffness and idiopathic AAD using simple and reproducible parameters. Conclusions In patients with CSM and idiopathic AAD, the ROM of the middle and lower cervical spine was significantly lower than that in patients without AAD. Ossification of the ALL negatively correlated with the ROM of the cervical spine, suggesting that ossification of the cervical ALL may cause idiopathic AAD. Declarations Ethical Approval This study was approved by the Institutional Review Board of Ehime University School of Medicine. (IRB approval no., 2207011). All procedures were performed in accordance with the ethical standards of the institutional research committee and with the Declaration of Helsinki and its later amendments. Informed Consent: Informed consent was obtained from all individual participants included in the study by posting the opt-out information in our hospital. Data availability The datasets generated during and/or analyzed in the current study are available from the corresponding author upon reasonable request. Conflict of interest The authors declare no relevant conflicts of interest. Funding The authors received no financial support for this article’s research, authorship, and/or publication. Consent for publication: Not applicable. Author contributions YM was responsible for the organization and coordination of this study. TM, MO and MT were responsible for data analysis. YM, TM, MO and MT developed the study design. All authors contributed to the writing of the final manuscript. References Lindenmann S, Tsagkaris C, Farshad M, Widmer J. Kinematics of the Cervical Spine Under Healthy and Degenerative Conditions: A Systematic Review. Ann Biomed Eng Dec. 2022;50(12):1705–33. https://doi.org/10.1007/s10439-022-03088-8 . Chikuda H, Seichi A, Takeshita K, et al. Radiographic analysis of the cervical spine in patients with retro-odontoid pseudotumors. Spine (Phila Pa 1976). Feb. 2009;1(3):E110–4. https://doi:10.1097/BRS.0b013e31818acd27 . Wasserman BR, Moskovich R, Razi AE. Rheumatoid arthritis of the cervical spine–clinical considerations. Bull NYU Hosp Jt Dis. 2011;69(2):136–48. Magarelli N, Simone F, Amelia R, et al. MR imaging of atlantoaxial joint in early rheumatoid arthritis. Radiol Med Oct. 2010;115(7):1111–20. https://doi:10.1007/s11547-010-0574-4 . Sharif K, Sharif A, Jumah F, Oskouian R, Tubbs RS. Rheumatoid arthritis in review: Clinical, anatomical, cellular and molecular points of view. Clin Anat Mar. 2018;31(2):216–23. https://doi:10.1002/ca.22980 . Hayes A, Batshaw ML. Down syndrome. Pediatr Clin North Am Jun. 1993;40(3):523–. 10.1016/s0031-3955(16)38548-0 . https:// . 35. Yin YH, Yu XG, Qiao GY, Guo SL, Zhang JN. C1 lateral mass screw placement in occipitalization with atlantoaxial dislocation and basilar invagination: a report of 146 cases. Spine (Phila Pa 1976). Nov. 2014;15(24):2013–8. https://doi:10.1097/BRS.0000000000000611 . Resnick D, Shaul SR, Robins JM. Diffuse idiopathic skeletal hyperostosis (DISH): Forestier's disease with extraspinal manifestations. Radiol Jun. 1975;115(3):513–24. https://doi:10.1148/15.3.513 . Kagotani R, Yoshida M, Muraki S, et al. Prevalence of diffuse idiopathic skeletal hyperostosis (DISH) of the whole spine and its association with lumbar spondylosis and knee osteoarthritis: the ROAD study. J Bone Min Metab Mar. 2015;33(2):221–9. https://doi:10.1007/s00774-014-0583-9 . Kuperus JS, Mohamed Hoesein FAA, de Jong PA, Verlaan JJ. Diffuse idiopathic skeletal hyperostosis: Etiology and clinical relevance. Best Pract Res Clin Rheumatol Jun. 2020;34(3):101527. https://doi:10.1016/j.berh.2020.101527 . Jun BY, Yoon KJ, Crockard A. Retro-odontoid pseudotumor in diffuse idiopathic skeletal hyperostosis. Spine (Phila Pa 1976). May. 2002;15(10):E266–70. https://doi:10.1097/00007632-200205150-00024 . Bamps S, Roosen G, Put E, et al. Retro-odontoid pseudotumor (pannus) with Forestier's disease presenting with severe tetraparesis: A case report and literature review. Surg Neurol Int. 2020;11:111. https://doi:10.25259/SNI_163_2020 . Prata AR, Saraiva L, Salvador MJ, Malcata A. Retro-odontoid pseudotumor: a rare complication of Diffuse Idiopathic Skeletal Hyperostosis. Acta Reumatol Port. Jul-Sep. 2021;46(3):279–280. Retro-odontoid pseudotumor: a rare complication of Diffuse Idiopathic Skeletal Hyperostosis. Murakami Y, Morino T, Hino M, Misaki H, Imai H, Miura H. A Scoring System for Anterior Longitudinal Ligament Ossification of the Lumbar Spine in Diffuse Idiopathic Skeletal Hyperostosis: Relationship Between the Extent of Ligament Ossification and the Range of Motion. Global Spine J Mar. 2023;13(2):378–83. https://doi:10.1177/2192568221996681 . Mata S, Chhem RK, Fortin PR, Joseph L, Esdaile JM. Comprehensive radiographic evaluation of diffuse idiopathic skeletal hyperostosis: development and interrater reliability of a scoring system. Semin Arthritis Rheum Oct. 1998;28(2):88–96. https://doi:10.1016/s0049-0172(98)80041-3 . Kuroshima K, Yurube T, Kawabata S, et al. Risk factors for the development of retro-odontoid pseudotumor in non-rheumatoid arthritis patients with atlantoaxial subluxation: a multicenter cross-sectional study. Eur Spine J Jul. 2025;29. https://doi:10.1007/s00586-025-09129-9 . Takahata M, Hyakkan R, Oshima S, et al. Cervical Myelopathy Caused by Non-Rheumatic Retro-Odontoid Pseudotumor: An Investigation of Underlying Mechanisms and Optimal Surgical Strategy. Global Spine J Sep. 2023;13(7):2053–62. https://doi:10.1177/21925682211069542 . Chen Q, Chen J, Chen F, Lu X, Ni B, Guo Q. Biomechanics of the effect of subaxial cervical spine degeneration on atlantoaxial complex in idiopathic retro-odontoid pseudotumor development. Clin Neurol Neurosurg Oct. 2020;16:106314. https://doi:10.1016/j.clineuro.2020.106314 . Tables Table 1 Distribution of primary diseases associated with atlantoaxial joint disorder. Rheumatoid Arthritis N % 13 23.2 Celebral Palsy 4 7.1 Post trauma 4 7.1 Congenital malformation 4 7.1 Os odontoideum 3 5.4 Down syndrome 1 1.8 No primary disease 27 48.2 total 56 100 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 18 Apr, 2026 Editor assigned by journal 16 Apr, 2026 Editor invited by journal 02 Apr, 2026 Submission checks completed at journal 02 Apr, 2026 First submitted to journal 02 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9279035","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":626599608,"identity":"e447538c-59ef-453d-9d42-13d328b00737","order_by":0,"name":"Yusuke Murakami","email":"data:image/png;base64,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","orcid":"","institution":"Ehime University School of Medicine","correspondingAuthor":true,"prefix":"","firstName":"Yusuke","middleName":"","lastName":"Murakami","suffix":""},{"id":626599611,"identity":"8b24021b-6f36-42bb-bc3c-14a8792af954","order_by":1,"name":"Tadao Morino","email":"","orcid":"","institution":"HITO Hospital","correspondingAuthor":false,"prefix":"","firstName":"Tadao","middleName":"","lastName":"Morino","suffix":""},{"id":626599613,"identity":"d17a242c-93d8-4c28-a971-0e1ae0a2c183","order_by":2,"name":"Mayu Ogura","email":"","orcid":"","institution":"Japan Community Health care Organization Uwajima Hospital","correspondingAuthor":false,"prefix":"","firstName":"Mayu","middleName":"","lastName":"Ogura","suffix":""},{"id":626599615,"identity":"ce1b9a05-c443-49d4-bc8c-ccd7602bb82e","order_by":3,"name":"Masaki Takao","email":"","orcid":"","institution":"Ehime University School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Masaki","middleName":"","lastName":"Takao","suffix":""}],"badges":[],"createdAt":"2026-03-31 11:24:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9279035/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9279035/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107948398,"identity":"54ee29a7-a0b0-4738-8c70-1a646cb42711","added_by":"auto","created_at":"2026-04-28 00:20:43","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":36444,"visible":true,"origin":"","legend":"\u003cp\u003eMethod for measuring the cervical spine range of motion.\u003c/p\u003e\n\u003cp\u003eThe range of motion was evaluated as the difference between the angles formed by the endplates of the C2 and C7 vertebrae in extension (right) and flexion (left), determined using the lateral view of a functional radiograph of the cervical spine.\u003c/p\u003e","description":"","filename":"figure1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9279035/v1/01ce3773deb1d9627a196bab.jpeg"},{"id":108007626,"identity":"5d196d7d-ca6b-46fa-91aa-9f723f15247d","added_by":"auto","created_at":"2026-04-28 13:00:58","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":45381,"visible":true,"origin":"","legend":"\u003cp\u003eScoring of the extent of ossification of the anterior longitudinal ligament (modified Mata's score)\u003c/p\u003e\n\u003cp\u003e(Left) Scoring: No ossification (grade 0, 0 points); ossification of less than half of the intervertebral height (grade 1, 1 point); ossification of more than half of the intervertebral height (grade 2, 2 points); and complete bridging (grade 3, 3 points).\u003c/p\u003e","description":"","filename":"figure2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9279035/v1/2ef29f3e0815aa25e384d1f4.jpeg"},{"id":108007579,"identity":"1a4ff845-ee98-416d-bd22-07f9a99f71cf","added_by":"auto","created_at":"2026-04-28 13:00:37","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":19645,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the range of motion between the two groups\u003c/p\u003e\n\u003cp\u003eThe idiopathic AAD group had a significantly smaller range of motion than the CSM group.\u003c/p\u003e\n\u003cp\u003eAAD, atlantoaxial joint disorder; CSM, cervical spondylotic myelopathy\u003c/p\u003e","description":"","filename":"figure3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9279035/v1/d92c406193018805791461d9.jpeg"},{"id":108006942,"identity":"340853e7-8af7-48e6-876b-f35f5b769998","added_by":"auto","created_at":"2026-04-28 12:57:59","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":17465,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the total ligament ossification score between groups\u003c/p\u003e\n\u003cp\u003eThe total ligament ossification score was significantly higher in the idiopathic AAD group than in the CSM group.\u003c/p\u003e\n\u003cp\u003eAAD, atlantoaxial joint disorder; CSM, cervical spondylotic myelopathy\u003c/p\u003e","description":"","filename":"figure4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9279035/v1/d2a5496d829ce19faabf321b.jpeg"},{"id":107948400,"identity":"3cc1c6b6-1c21-416b-bfc7-749f7b433287","added_by":"auto","created_at":"2026-04-28 00:20:43","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":19071,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between the range of motion and total ligament ossification score in all patients\u003c/p\u003e\n\u003cp\u003eThe range of motion and ligament ossification score were negatively correlated.\u003c/p\u003e","description":"","filename":"figure5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9279035/v1/07d2cad56102d4112e8c8c16.jpeg"},{"id":108008946,"identity":"5d386add-c571-45b7-91d4-c97570d43f2f","added_by":"auto","created_at":"2026-04-28 13:08:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":299231,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9279035/v1/9971666e-dd10-4901-8004-20c8e1310127.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Stiffness of the Middle and Lower Cervical Spine Is Associated with Idiopathic Atlantoaxial Joint Disorder: A Retrospective Case-Control Study","fulltext":[{"header":"Background","content":"\u003cp\u003eThe atlantoaxial joint, composed of the atlas and axis vertebrae, supports the cranium and enables cervical rotational movements.1 Disorders of this joint — such as instability and formation of retro-odontoid pseudotumors — can lead to severe neurological deficits, including tetraplegia and sudden death.［1,2］\u0026nbsp;These complications commonly arise from conditions like rheumatoid arthritis (RA), Down syndrome, cerebral palsy, trauma, and congenital malformations; however, cases without primary diseases are frequently encountered.［2-7］\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe pathophysiology of myelopathy due to atlantoaxial joint disorders (AAD) is categorized into two types: 1) cases caused by ligament laxity or synovitis, and 2) cases caused by mechanical stress.［2,4,5,］\u0026nbsp;RA and Down syndrome are associated with ligament laxity, which leads to instability and spinal canal stenosis.［6］\u0026nbsp;By contrast, patients with middle and lower cervical fusion surgery, congenital fusion disease, and athetotic cerebral palsy have increased chronic mechanical stress on the atlantoaxial joints owing to decreased mobility in the middle and lower cervical spine, causing retro-odontoid pseudotumors and spinal canal stenosis.［2,7］Therefore, we hypothesized that stiffness of the middle and lower cervical spines is a contributing factor to idiopathic AAD.\u003c/p\u003e\n\u003cp\u003eDiffuse idiopathic skeletal hyperostosis (DISH) is a progressive disease characterized by the ossification of ligaments and entheses.8 Several case reports have linked DISH to the development of retro-odontoid pseudotumors,\u0026nbsp;［11-13］\u0026nbsp;suggesting that ossification of the anterior longitudinal ligament (ALL) — which results in increased mechanical stress at the atlantoaxial joint — may be a significant risk factor for ligament formation. Thus, we focused on ALL ossification in patients with idiopathic AAD, as well as the range of motion (ROM) of the middle and lower cervical spines.\u003c/p\u003e\n\u003cp\u003eThe purpose of this study was to compare the ROM of the middle and lower cervical spines, and extent of ossification of the ALL in patients with cervical spondylotic myelopathy (CSM) due to idiopathic AAD versus in age- and sex-matched patients with CSM without AAD.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eThis study included 56 patients (27 men and 29 women) who underwent surgery for myelopathy due to AAD between 2007 and 2020. Twenty nine patients had primary diseases, including RA in 13 patients (23.2%); cerebral palsy, trauma, and congenital malformation in four patients (7.1%); os odontoideum in three patients (5.4%); and Down syndrome in one patient (1.8%). Twenty-seven (48.2 %) patients had no primary disease (Table 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe ROM of the cervical spine was compared between two groups: patients with CSM associated with idiopathic AAD (idiopathic AAD group [27 cases]; male: 19, female: 8; mean age, 74.2 ± 6.4 years), and age- and sex-matched patients with CSM without AAD (CSM group [54 cases]; male: 38, female: 16; mean age 74.1 ± 6.2 years). The CSM group included patients who underwent surgery at the same time and included two age- (±1 year) and sex-matched patients for each patient in the idiopathic AAD group. The ROM was defined as the angle formed by the C2 and C7 vertebral body endplates and was calculated by subtracting the angle in the flexed position from that in the extended position. This angle was defined as the positive lordosis angle (Figure 1).\u003c/p\u003e\n\u003cp\u003eNext, the extent of ossification of the ALL of the cervical spine was assessed. We used the scoring system developed by Murakami et al.［14］\u0026nbsp;— which is a modification of the scoring system developed by Mata et al.［15］— to evaluate the extent of ligament ossification (0, no ligament ossification; 1, ligament ossification of less than half of the intervertebral height; 2, ossification of more than half of the intervertebral height; and 3, complete ossification). Five vertebrae from C2/3 to C6/7 (Figure 2) were evaluated, and the total scores were compared between the two groups. Additionally, we combined all cases to investigate whether the ROM of the cervical spine correlated with the extent of ossification of the ALL.\u003c/p\u003e\n\u003cp\u003eStatistical analyses were performed using JMP ver. 17.0 (SAS Institute, Cary, NC) for Macintosh. The Tukey–Kramer HSD test was used for group comparisons of age, ROM, and total scores. The χ2 test was used to analyze categorical data, and Spearman’s correlation coefficient was calculated to determine the association between the ROM and ligament ossification score.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe ROM was significantly smaller in the idiopathic AAD group (25.4 ± 19.2°) than in the CSM group (40.1 ± 12.0°; p\u0026lt;0.001; Figure 3). The total ossification score of the ALL from C2/3 to C6/7 was significantly higher in the idiopathic AAD group (9.3 ± 3.9) than in the CSM group (5.4 ± 3.3; p\u0026lt;0.001) (Figure 4). A significant negative correlation was observed between the total ossification score and cervical spine ROM (ρ = -0.62; p\u0026lt;0.001; Figure 5).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we demonstrated that patients with CSM associated with idiopathic AAD have a significantly reduced ROM in the middle and lower cervical spines compared with age- and sex-matched patients with CSM without AAD. This reduction was associated with extensive ossification of the ALL and was significantly negatively correlated with the ROM of the cervical spine.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eChikuda et al.［2］\u0026nbsp;reported that retro-odontoid pseudotumors can develop even in the absence of atlantoaxial instability, which is often associated with extensive degenerative changes and anterior ligament ossification. In a multicenter cross-sectional study of patients with atlantoaxial subluxation without RA, Kuroshima et al.［16］\u0026nbsp;identified advanced intervertebral disc and facet degeneration, and an increased C2–C7 sagittal vertical axis as significant risk factors for retro-odontoid pseudotumor formation. Similarly, using a matched case–control design, Takahata et al.［17］demonstrated that a reduced C2–C7 ROM combined with an increase in C1–2 motion was associated with nonrheumatic retro-odontoid pseudotumors. Chen et al.［18］\u0026nbsp;performed finite element analysis and demonstrated that degeneration and reduced mobility of the cervical spine led to increased stress at the atlantoaxial joint. Several case reports have provided clinical evidence for this mechanism.\u0026nbsp;［11-13］\u0026nbsp;Jun et al.［11］\u0026nbsp;first described retro-odontoid pseudotumor formation in patients with DISH and proposed that the marked rigidity of the lower cervical spine results in relative hypermobility at the atlantoaxial junction. Overall, these studies consistently indicate that stiffness of the middle and lower cervical spines increases mechanical loading at the atlantoaxial joint. Our findings provide additional clinical evidence supporting this concept.\u003c/p\u003e\n\u003cp\u003eCervical spine stiffness is a multifactorial condition influenced by various degenerative changes, including intervertebral disc degeneration and facet joint arthropathy. However, it is difficult to objectively and consistently quantify these changes in clinical studies. By contrast, ossification of the ALL can be readily evaluated using established radiographic scoring systems,［14,15］\u0026nbsp;providing a simple and reproducible measure of the structural stiffness of the cervical spine. Therefore, the evaluation of ligament ossification may offer a practical approach for assessing the limitations of cervical spine mobility.\u003c/p\u003e\n\u003cp\u003e Clinically, these findings highlight the importance of assessing middle and lower cervical spine stiffness in patients with CSM associated with idiopathic AAD. Given that such patients already exhibit reduced preoperative cervical mobility, careful attention should be paid to postoperative changes in ROM and their impact on activities of daily living. In surgical decision-making, the extent of fixation may need to consider preexisting fused segments, as well as the remaining mobile segments. However, this study was not designed to evaluate the optimal fixation range. Additionally, postoperative rehabilitation aimed at preserving cervical motion may be important for improving functional outcomes. Evaluation of the cervical ROM and ALL ossification provides useful information for understanding the underlying pathomechanics of this condition and may also facilitate more informed preoperative education regarding functional expectations. This evaluation method has a practical advantage in that it does not require specialized equipment or complex analyses.\u003c/p\u003e\n\u003cp\u003eThis study had several limitations; first, the sample size is relatively small. Second, the alignment of the entire spine and corresponding extent of ligament ossification were not assessed. Third, other contributors to cervical stiffness, such as disc degeneration and facet joint arthropathy, were not quantitatively examined. Additionally, upper cervical kinematics — including motion at the atlantoaxial joint — were not directly evaluated. In this study, the C2–7 ROM was selected because it represents a parameter that can be readily assessed in routine clinical practice. Patients with CSM were selected as the control group because they presented with clinical features similar to those of myelopathy, allowing us to evaluate differences in the underlying pathomechanisms associated with idiopathic AAD. Age and sex matching was performed to minimize the potential confounding effects of demographic factors on cervical ROM and ligament ossification. Despite these limitations, the present study provides clinically relevant insights by demonstrating a clear association between cervical spine stiffness and idiopathic AAD using simple and reproducible parameters.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn patients with CSM and idiopathic AAD, the ROM of the middle and lower cervical spine was significantly lower than that in patients without AAD. Ossification of the ALL negatively correlated with the ROM of the cervical spine, suggesting that ossification of the cervical ALL may cause idiopathic AAD.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the Institutional Review Board of Ehime University School of Medicine. (IRB approval no., 2207011). All procedures were performed in accordance with the ethical standards of the institutional research committee and with the Declaration of Helsinki and its later amendments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed Consent:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eInformed consent was obtained from all individual participants included in the study by posting the opt-out information in our hospital.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated during and/or analyzed in the current study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no relevant conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors received no financial support for this article’s research, authorship, and/or publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYM was responsible for the organization and coordination of this study. TM, MO and MT were responsible for data analysis. YM, TM, MO and MT developed the study design. All authors contributed to the writing of the final manuscript.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLindenmann S, Tsagkaris C, Farshad M, Widmer J. Kinematics of the Cervical Spine Under Healthy and Degenerative Conditions: A Systematic Review. Ann Biomed Eng Dec. 2022;50(12):1705\u0026ndash;33. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10439-022-03088-8\u003c/span\u003e\u003cspan address=\"10.1007/s10439-022-03088-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChikuda H, Seichi A, Takeshita K, et al. Radiographic analysis of the cervical spine in patients with retro-odontoid pseudotumors. Spine (Phila Pa 1976). 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Best Pract Res Clin Rheumatol Jun. 2020;34(3):101527. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi:10.1016/j.berh.2020.101527\u003c/span\u003e\u003cspan address=\"https://doi:10.1016/j.berh.2020.101527\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJun BY, Yoon KJ, Crockard A. Retro-odontoid pseudotumor in diffuse idiopathic skeletal hyperostosis. Spine (Phila Pa 1976). May. 2002;15(10):E266\u0026ndash;70. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi:10.1097/00007632-200205150-00024\u003c/span\u003e\u003cspan address=\"https://doi:10.1097/00007632-200205150-00024\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBamps S, Roosen G, Put E, et al. 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Eur Spine J Jul. 2025;29. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi:10.1007/s00586-025-09129-9\u003c/span\u003e\u003cspan address=\"https://doi:10.1007/s00586-025-09129-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTakahata M, Hyakkan R, Oshima S, et al. Cervical Myelopathy Caused by Non-Rheumatic Retro-Odontoid Pseudotumor: An Investigation of Underlying Mechanisms and Optimal Surgical Strategy. Global Spine J Sep. 2023;13(7):2053\u0026ndash;62. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi:10.1177/21925682211069542\u003c/span\u003e\u003cspan address=\"https://doi:10.1177/21925682211069542\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen Q, Chen J, Chen F, Lu X, Ni B, Guo Q. Biomechanics of the effect of subaxial cervical spine degeneration on atlantoaxial complex in idiopathic retro-odontoid pseudotumor development. Clin Neurol Neurosurg Oct. 2020;16:106314. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi:10.1016/j.clineuro.2020.106314\u003c/span\u003e\u003cspan address=\"https://doi:10.1016/j.clineuro.2020.106314\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab1\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cdiv class=\"SimplePara\"\u003eDistribution of primary diseases associated with atlantoaxial joint disorder.\u003c/div\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003eRheumatoid Arthritis\u003c/div\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003eN\u003c/div\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e%\u003c/div\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e13\u003c/div\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e23.2\u003c/div\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003eCelebral Palsy\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e4\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e7.1\u003c/div\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003ePost trauma\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e4\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e7.1\u003c/div\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003eCongenital malformation\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e4\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e7.1\u003c/div\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003eOs odontoideum\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e3\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e5.4\u003c/div\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003eDown syndrome\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e1\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e1.8\u003c/div\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003eNo primary disease\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e27\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e48.2\u003c/div\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003etotal\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e56\u003c/div\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cdiv class=\"SimplePara\"\u003e100\u003c/div\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"anterior longitudinal ligament ossification, atlantoaxial joint disorder, stiffness of middle and lower cervical spine","lastPublishedDoi":"10.21203/rs.3.rs-9279035/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9279035/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eAtlantoaxial joint disorders (AAD), including instability and retro-odontoid pseudotumors, can cause serious neurological deficits; however, some patients lack an identifiable primary disease. We hypothesized that stiffness of the middle and lower cervical spines contributes to idiopathic AAD. This study aimed to compare the range of motion (ROM) of the middle and lower cervical spines and extent of ossification of the anterior longitudinal ligament (ALL) in patients with cervical spondylotic myelopathy (CSM) due to idiopathic AAD and age- and sex-matched patients with CSM without AAD.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eWe enrolled 56 patients who underwent surgery for myelopathy due to AAD between 2007 and 2020. Among them, 27 (48.2%) patients without a primary disease were classified into the idiopathic AAD group. The CSM group included patients who underwent surgery at the same time and included two age- (\u0026plusmn;\u0026thinsp;1 year) and sex-matched patients for each patient in the idiopathic AAD group. The ROM (C2\u0026ndash;7) and extent of ALL ossification were compared between the groups, and the correlation between the extent of ossification and ROM was assessed.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003ePatients with idiopathic AAD demonstrated a significantly reduced ROM and more severe ligament ossification than the matched patients without AAD. A significant negative correlation was found between ROM and ALL ossification.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eThe ROM of the middle and lower cervical spines were significantly lower in patients with idiopathic AAD. The extent of ossification of the ALL, which negatively correlated with the ROM of the cervical spine, was also greater in patients with CSM with idiopathic AAD.\u003c/p\u003e","manuscriptTitle":"Stiffness of the Middle and Lower Cervical Spine Is Associated with Idiopathic Atlantoaxial Joint Disorder: A Retrospective Case-Control Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-28 00:20:39","doi":"10.21203/rs.3.rs-9279035/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-04-18T19:33:35+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-16T15:58:02+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-02T11:16:07+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-02T10:15:37+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Musculoskeletal Disorders","date":"2026-04-02T09:33:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"bd24d07a-ece4-40f9-bc6d-75d858482bec","owner":[],"postedDate":"April 28th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-28T00:20:39+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-28 00:20:39","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9279035","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9279035","identity":"rs-9279035","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}