Original ArticleAnatomy of Alar Ligament Part I: Morphometrics and Variants
Introduction
The alar ligaments are thick cords that unite the dens to the medial side of the occipital condyles.1 These ligaments have been reported to serve as a primary restraint to atlantoaxial rotation, the left becoming taut on rotation to the right and vice versa.1, 2 Although a proven important biomechanical structure, anatomic descriptions of the alar ligaments have been varied and inconsistent.3, 4, 5, 6, 7 Therefore as most studies of the alar ligaments have used embalmed cadavers, the present study seeks to better elucidate the detailed anatomy of the alar ligaments using fresh cadaveric specimens.
Section snippets
Materials and Methods
The Anatomical Quality Assurance checklist, known as “AQUA,” was used for this study.8, 9 Twenty-two sides from 11 fresh, frozen cadaveric Caucasian heads were used. The specimens were derived from 8 males and 3 females, and the age of the cadavers at death ranged from 67–99 years old (mean age; 78.9 ± −10.4 years old). The occiput, C1, and C2 were removed en bloc from the specimen. The posterior elements, dura mater, tectorial membrane, and cruciate ligaments were removed, and the alar
Results
Eleven cadavers were dissected for a total of 22 alar ligaments. In all specimens, the alar ligaments attached to the lateral surface of the upper half of the dens, attached or covered the tip of the dens bilaterally, and ran laterally (Figure 2). Ten specimens had both alar ligaments inserted distally to the medial aspect of the occipital condyles. Of these, insertion of the alar ligaments into the condyle could be observed in detail in 9 specimens. In 8 specimens, the alar ligaments inserted
Discussion
The craniocervical junction (CCJ) is responsible for the majority of the cervical spine's range of motion. It encompasses 2 major joints: the atlanto-occipital and the atlantoaxial joints, which are held together by a complex array of ligaments.5 Of these, the transverse and alar ligaments are perhaps the most important. They allow for adequate mobility while protecting the neurovascular structures that enter and exit the skull at the CCJ. The transverse ligament has been thoroughly studied in
Conclusions
The function of the alar ligaments is determined by its origin, direction, and insertions; hence an accurate anatomic description is important. The ligaments connect the superior half of the lateral surface of the dens and project in a nearly horizontal plane to end just medial to the occipital condyles. This disposition explains their main role in limiting axial rotation and lateral flexion, as well as their secondary function in limiting flexion in the sagittal plane. The current cadaveric
Acknowledgments
The authors wish to thank individuals who donated their bodies for the advancement of education and research.
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Conflict of interest statement: The authors have no conflict of interest to declare.