Cervical spine bones and ligaments: joints (English)

The atlas articulates with the occipital bone at the atlantooccipital joint, which presents the primary connection of the head with the trunk. This is a synovial joint formed by the occipital condyles and superior articular facets of the atlas. The joint is secured by the anterior and posterior atlantooccipital membranes and allows for flexion and extension of the head, as well as a limited degree of lateral flexion.The atlas and axis articulate via a complex atlantoaxial joint. This joint consists of three synovial components: a single median atlantoaxial joint and paired lateral atlantoaxial joints. The main movement of this complex joint is the axial rotation of the head, but it also allows limited flexion, extension and lateral flexion.The median atlantoaxial joint (a.k.a. atlantodental joint) is formed by the dens of axis, anterior arch of the atlas and transverse ligament of the atlas. It is composed of two elements: an articulation between the anterior articular facet of the dens axis and facet for dens located on the internal surface of the anterior arch of the atlas, as well as a second articulation between the posterior articular facet of the dens axis and the anterior surface of the transverse ligament of atlas. The joint is primarily reinforced by the cruciform ligament complex, which consists of the transverse ligament of atlas, superior and inferior longitudinal bands of cruciform ligament. The additional support is provided by the tectorial membrane, alar ligaments, apical ligament of dens, anterior and posterior atlantoaxial membranes. The left and right lateral atlantoaxial joints are formed by the inferior articular surfaces of the lateral masses of the atlas with the superior articular surfaces of the axis. They are reinforced by several ligaments e.g. the accessory atlantoaxial ligament, anterior/posterior atlantoaxial membranes, tectorial membrane etc.