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Structure and Function
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Atlanto-Occipital and Atlantoaxial Joints
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The atlanto-occipital joint is composed of the right and left deep concave superior facets of the atlas (C1) that articulate with the right and left convex occipital condyles of the skull (Fig. 11.1).
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The atlantoaxial joint is composed of three separate articulations: the median atlantoaxial and two lateral joints. The median atlantoaxial joint consists of an anterior facet on the dens (the odontoid process of C2) that articulates with a facet on the internal surface of the atlas (C1). The two lateral joints are composed of the right and left superior facets of the axis (C2) that articulate with the right and left slightly convex inferior facets on the atlas (C1) (Fig. 11.2).
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The atlanto-occipital and atlantoaxial joints are reinforced anteriorly by the anterior–occipital and atlantoaxial membranes (Fig. 11.3A) and posteriorly by the posterior atlanto-occipital, atlantoaxial, and tectorial membranes (Fig. 11.3B).
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The atlanto-occipital joint, which is composed of the atlas (C1) and occipital condyles (Oc), is a condylar synovial joint that permits active flexion–extension as a nodding motion.1 A limited amount of axial rotation and lateral flexion may also be produced. Flexion–extension takes place in the sagittal plane around a medial–lateral axis. Extremes of flexion are limited by osseous contact of the anterior ring of the foramen magnum with the dens. Normally, flexion is limited by tension in the posterior neck muscles and tectorial membrane and by impaction of the submandibular tissues against the throat. Extension is limited by the occiput compressing the suboccipital muscles. Combined flexion–extension is ...