Tears are almost always postero-lateral in nature owing to the presence of the posterior longitudinal ligament in the spinal canal.

Posterior longitudinal ligament (ligamentum longitudinale posterius)

In the intervertebral spaces, the canal is protected by the ligamentum flavum posteriorly and the posterior longitudinal ligament anteriorly.

The deep dorsal sacrocyccygeal ligament (ligamentum sacrococcygeum posterius profundum) is a continuation of the posterior longitudinal ligament.

It is a broad, strong band which covers the dens and its ligaments, and appears to be a prolongation upward of the posterior longitudinal ligament of the vertebral column.

Many important ligaments attach to the coccyx: The anterior and posterior sacrococcygeal ligaments are the continuations of the anterior and posterior longitudinal ligaments that stretches along the entire spine.

The ligament is thick and slightly more narrow over the vertebral bodies and thinner but slightly wider over the intervertebral discs which is much less pronounced than that seen in the posterior longitudinal ligament.

The deep dorsal ligament is a flat band which corresponds to the posterior longitudinal ligament (PLL) that run down inside the vertebral canal on the posterior surfaces of the bodies of the vertebrae.

The posterior sacrococcygeal ligament has a deep and a superficial part, the former is a flat band corresponding to the posterior longitudinal ligament (PLL) and the latter corresponds to the ligamenta flava.

The posterior longitudinal ligament is situated within the vertebral canal, and extends along the posterior surfaces of the bodies of the vertebræ, from the body of the axis, where it is continuous with the membrana tectoria, to the sacrum.

The anterior internal plexuses consist of large veins which lie on the posterior surfaces of the vertebral bodies and intervertebral fibrocartilages on either side of the posterior longitudinal ligament; under cover of this ligament they are connected by transverse branches into which the basivertebral veins open.