Elsevier

World Neurosurgery

Volume 107, November 2017, Pages 1001-1006
World Neurosurgery

Original Article
Anatomy of Alar Ligament Part I: Morphometrics and Variants

https://doi.org/10.1016/j.wneu.2017.07.187Get rights and content

Objective

The alar ligaments are among the primary ligamentous structures contributing to craniovertebral stability. The purpose of this study is to clarify the morphology of the alar ligament using fresh cadaveric specimens.

Methods

Twenty-two fresh, frozen cadaveric alar ligaments were used in this study. The occiput, C1, and C2 were removed en bloc from each specimen, and various measurements and observations including variations were documented.

Results

The angle formed by both alar ligaments was measured in a neutral position (149 ± 24.19 degrees), as well as during forced flexion (134.18 ± 27.08 degrees) and extension (163.81 ± 24.54 degrees).

Conclusions

The current cadaveric evaluation offers an interesting window into better understanding the anatomy of the alar ligaments.

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.

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