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

J Craniovertebr Junction Spine. 2019 Jan-Mar;10(1):42-45. doi: 10.4103/jcvjs.JCVJS_110_18.

Kikuta S, Iwanaga J, Watanabe K, Tubbs RS.

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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.

KEYWORDS:

Anatomy; cadaver; cervical vertebra; craniocervical joint; ligaments

Figure 1

Photograph of failure for the SAAOL (white arrows). The anterior tubercle of the atlas (A) and the basilar base of the occipital bone (O) held with bone clamps with vertical traction applied. The tensile force (N) was recorded as the force at failure of the ligament

Figure 2

(a) Anterior view of the anterior craniocervical junction in a cadaver after removing the longus capitis, rectus capitis anterior, and longus colli muscles. (b) lateral view shows the separated layers of each ligament. The superficial anterior atlanto-occipital ligament was located superficial to the anterior atlanto-occipital membrane. (1) SAAOL; (2) anterior atlanto-occipital membrane; (3) anterior atlanto-axial membrane; (4) anterior longitudinal ligament. TP – Transverse process of C1

Figure 3

Lateral view (left) of the superficial anterior atlanto-occipital ligament with neck motion (hyperextension, neutral, and hyperflexion)