From a strictly anatomical point of view the posterior joints of the spine are the true joints of the spine. The extent and the variety of movements depends on the shape and direction of the facet joints. They determine the extent of movement and direction of a particular segment. These facet joints are covered by a dense articular capsule which is quite elastic. thin and loose. They are attached just beyond the margins of the articular facets, and are larger and looser in the cervical than in the thoracic and lumbar spine.
The facet joints are supplied by a nerve which runs to the two adjacent joints. Each joint therefore derives its nerve supply from two segments. Each vertebra has a pair of superior and a pair of inferior facet joints. These play an extremely important role in the minor traumatic pathology of the spine, as they have a central area of rich blood and nerve supply. They are the most richly innervated structures of the entire spinal column. This innervation helps the spine to adapt to the variation of tensions to which the capsule of facet joints is exposed. Derangement of these joints can be extremely painful.
In the cervical region the superior facet joints are inclined upwards at forty-five degrees. This helps in free flexion and extension of the neck. At this level usually, extension can be done more easily than flexion. Lateral bending and rotation are always combined. In the thoracic region, the facet joints are more oblique, say, at an approximately sixty degree inclination.
In the upper part of the thoracic spine, movements are greatly restricted due to the direction of the facet joints and attachment of the ribs to the body of vertebrae. Rotation at this level is of a greater range than flexion and extension. Lateral bending is restricted due to the ribs and the sternum. Extension (backward bending) is freer in the lumbar spine. A considerable amount of side bending and a small amount of rotation can occur at this level.