The posterior longitudinal ligament is situated within the vertebral canal, and extends along the posterior surfaces of the bodies of the vertebrae, from the body of the axis, where it is continuous with the membrana tectoria, to the sacrum.
It is broader above than below, and thicker in the thoracic than in the cervical and lumbar regions.
The ligament is more narrow at the vertebral bodies and wider at the intervertebral disc space. This is significant in understanding certain pathological conditions of the spine such as the typical location for a spinal disc herniation.
At intervertebral fibrocartilages and contiguous margins of the vertebrae, the ligament is more adherent and broad.
It is narrow and thick over the centers of the bodies, from which it is separated by the basivertebral veins.
It has an anterior counterpart called anterior longitudinal ligament.