Superficial anterior atlanto-occipital ligament: Anatomy of a forgotten structure with relevance to craniocervical stability

Abstract

Introduction: The superficial anterior atlanto-occipital ligament (SAAOL) is a narrowband located anterior to the anterior atlanto-occipital membrane. Nearly forgotten, it has not been well described in older anatomical textbooks and is missing in the current anatomical literature. As all of the binding structures of the craniocervical junction (CCJ) are important in maintaining stability, this study aims to clarify the anatomy and potential function of the SAAOL. Materials and Methods: The CCJ from ten fresh-frozen cadavers was studied. These specimens were derived from three males and seven females, and the age at death ranged from 57 to 91 years (mean, 79.8 years). The length, width, and thickness of the SAAOL were measured. In five specimens, the force to failure was recorded. Results: The SAAOL was found between the anterior tubercle of the atlas and the occiput and located as central thick fibers in front of the anterior atlanto-occipital membrane in 9 (90%) specimens. In one specimen, the vertical band to the occipital bone did not attach to the anterior tubercle of the atlas, but extended to the anterior aspect of the axis. The mean length, width, and thickness of the SAAOL were 19.8, 6.2, and 0.6 mm, respectively. The force to failure for the ligament was 38.8 N. Conclusion: The SAAOL was a constant structure of the anterior atlanto-occipital joint. This ligament seems to be a secondary stabilizer of the CCJ by limiting the extension of CCJ. Knowledge of this ligament may help in further understanding of craniocervical stability.

Anatomic, functional, and radiographic review of the ligaments of the craniocervical junction

“…The superficial anterior atlanto-occipital ligament (SAAOL) is the most anterior CCJ ligament and is infrequently described in the literature. [ 10 ] Older anatomic texts and one recent cadaveric study of ten patients describe the SAAOL as a thin, midline ligament running anterior to the anterior atlanto-occipital membrane (AAOM) running between the basion of the clivus and anterior tubercle of C1. The ligament becomes taut with hyperextension and lax with hyperflexion with a relatively low tensile strength compared with the alar and transverse ligaments.…”

Tectorial Membrane Injury, Frequently Identified in Adult Trauma Patients Who Undergo Occipital-Cervical Fusion for Craniocervical Instability

“…Multiple additional CCJ ligaments, including the anterior atlantooccipital membrane (AAOM), apical ligament, and the superior band of the cruciform ligament, play a nominal role in maintaining CCJ stability. Even more obscure CCJ ligaments, such as the superficial anterior atlantooccipital ligament, atlantodental ligament, and transverse occipital ligament, are not routinely visualized on cervical MRI [ 9 - 11 ]. Of note, the transverse band of the cruciform ligament, which tightly maintains the atlantoaxial joint, is not considered a craniocervical ligament since it does not maintain structural integrity between the cervical spine and skull base.…”