The Alar Ligaments: A Cadaveric and Radiologic Comparison Study Juan P. Sardi 1 , Joe Iwanaga 2-4 , Vlad Voin 2 , Cameron Schmidt 2 , Marios Loukas 6 , Jens R. Chapman 5 , Rod J. Oskouian 2,5 , R. Shane Tubbs 2,6 - OBJECTIVE: A precise anatomical description of the alar ligaments is important to better understand their biome- chanical and pathologic implications. Although there are several studies regarding their anatomy, the literature is inconsistent. To our knowledge, there are no reports that compare cadaveric morphologic findings with computed tomography (CT) images of the alar ligaments. - METHODS: Eight sides from 4 fresh-frozen cadaveric specimens were used in this study. After routine dissection of the craniocervical junction, the alar ligaments were exposed. We carried out measurements of the alar liga- ments, their position within the craniovertebral junction, and their relation to the dens and adjacent structures. Fine- cut CT of the specimens was performed, and the mea- surements were later compared with the original cadav- eric dissections. - RESULTS: Alar ligaments were attached to the upper half of the lateral surface of the dens and ran laterally to its insertion just medial to the occipital condyle. The ligaments were found to have an ovoid cross-sectional area with a nearly horizontal caudocranial trajectory and comparable diameters in both anteroposterior and superoinferior directions between the CT and cadaveric measurements. - CONCLUSIONS: There were small but not statistically significant differences in the measurements between the cadaver specimens and the CT images. There was how- ever, a strong correlation between the proximal and distal insertions, as well as the orientation of the fibers, that suggests CT images can be an appropriate approach to the study of the anatomical and 3-dimensional features of the alar ligaments. INTRODUCTION D etailed knowledge of the complex array of ligaments in the craniovertebral junction (CVJ) is imperative from a clinical and biomechanical point of view. The paired alar ligaments originate on each side of the dens and run laterally to their distal insertion just medial to the occipital condyles serving as stabilizing structures. 1 They are the main restraints for axial rotation and lateral bending on the contralateral side while serving a secondary role in preventing anterior displacement in case of cruciate ligament lesions. 2-6 Various authors have described the structures at the CVJ, but the anatomy of the alar ligaments is still controversial. 2,7,8 Recent reports have focused on the radiologic morphology of the alar ligaments; however, there are no reports of a cadaveric correlation with the radiologic appearance of such structures. An accurate description is important for better under- standing the implications that can arise from trauma and other pathologies in the craniovertebral region. 9-12 Therefore, the purpose of this study is to clarify the detailed anatomy of the alar ligaments by the use of fresh cadaveric specimens and compare them with findings on computed tomography (CT). MATERIALS AND METHODS Eight alar ligaments from 4 fresh-frozen cadaveric heads of white specimens were used in this study. The specimens were derived Key words - Alar ligaments - Anatomy - Occipito-atlantoaxial complex - Spine - Tomography Abbreviations and Acronyms CT : Computed tomography CVJ: Craniovertebral junction W1: Proximal superoinferior diameter the alar ligaments W2: Middle superoinferior diameter the alar ligaments W3: Distal superoinferior diameter the alar ligaments From the 1 Departamento Neurociencias, Hospital Universitario San Ignacio, Unidad Neurocirugía, Bogotá, Colombia; 2 Seattle Science Foundation, Seattle, Washington, USA; 3 Department of Anatomy and 4 Dental and Oral Medical Center, Kurume University School of Medicine, Fukuoka, Japan; 5 Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington, USA; and 6 Department of Anatomical Sciences, St. George’s University, St. George’s, Grenada To whom correspondence should be addressed: Juan P. Sardi, M.D. [E-mail: jsardi2@hotmail.com] Citation: World Neurosurg. (2018) 110:517-520. http://dx.doi.org/10.1016/j.wneu.2017.07.080 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2017 Elsevier Inc. All rights reserved. WORLD NEUROSURGERY 110: 517-520, FEBRUARY 2018 www.WORLDNEUROSURGERY.org 517 Craniovertebral Junction e Pathology and Surgery