This word has slightly different meanings according the author involved. Basically, it directs attention to the outer anatomic boundary confining the disc herniation. However, different posterior boundaries may be decided upon, according to the author (either the outer annular layers or the posterior longitudinal ligament or both). Some use contained to show a herniated disc has ruptured through the outer annular layer but is confined by the posterior longitudinal ligament (subligamentous). Others suggest, and it seems more acceptable, for it to be confined by the outer border of the annulus (subannular).