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The spinal column has a total of 23 paired intervertebral joints (articulationes intervertebrales), whereby each vertebra has 2 superior and 2 inferior articular processes (processus articulares inferiores and superiores), which are surrounded by an articular capsule. The inferior articular process of the upper of any two jointed vertebrae forms an intervertebral joint (facet joint) with the superior articular process of the lower of the two vertebrae. Distinct variations are seen in the orientation of the articular processes in the different spinal segments, reflecting the varying mobility requirements for each segment.
The articular processes of the cervical spine are slanted at about a 45° angle to the horizontal plane, whereas the articular processes of the thoracic vertebrae are nearly parallel to the frontal plane. Despite the fairly limited mobility of each vertebral body in relation to the adjacent ones, the interaction of all vertebral joints gives the spinal column a considerable degree of mobility. The vertebral joints in the atlanto-occipital joint between the occipital bone and the 1st cervical vertebra (atlas) and in the atlanto-axial joint between the atlas and the 2nd cervical vertebra (axis) have special qualities that are detailed below in the ”ligamentous apparatus of the spinal column” chapter.
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