Intervertebral joints

Each motion segment forms a three-joint complex: the intervertebral symphysis (body–disc–body) bears most axial load and permits small rocking movements; the two zygapophysial (facet) joints are plane synovial joints whose orientation determines the type of movement allowed in each region (coronal in the thoracic spine favouring rotation, sagittal in the lumbar spine resisting rotation). In the cervical spine, uncovertebral joints (of Luschka) at the lateral margins of the bodies limit lateral flexion.

Ligaments: the anterior longitudinal ligament (broad, strong band on the front of the bodies and discs from the occiput to the sacrum; resists hyperextension); the posterior longitudinal ligament (narrower, weaker, inside the vertebral canal on the back of the bodies; resists hyperflexion — its narrowness in the lumbar region explains posterolateral disc herniations); the ligamenta flava (yellow elastic ligaments between laminae; maintain posture and help return from flexion); the interspinous, supraspinous (expanded as the ligamentum nuchae in the neck) and intertransverse ligaments.

Range of movement differs by region: the cervical spine has the greatest overall mobility, the thoracic spine is mainly rotational, and the lumbar spine permits flexion–extension (greatest at L4–L5 and L5–S1).