Disc herniation may be purely annular, purely nuclear, or consist of a combination of annular and nuclear tissues. Nuclear disc herniation track posteriorly between the anterior surface of the posterior longitudinal ligament and the posterior surfaces of the annulus and vertebral body and then into the spinal canal. Disc herniation may be described as protrusion or extrusion (or sequestration, if the displaced disc material has lost completely any continuity with the parent disc); contained or uncontained.