Fig. 1
From: Full-endoscopic foraminoplasty for highly down-migrated lumbar disc herniation
The extent of down-migrated disc: Zone 1, low-grade downward: herniations within the height of the posterior margin of the disc in downward direction; Zone 2, high-grade downward: herniations extending beyond the height of the posterior margin of the disc in downward direction; Zone 3, very high-grade downward: herniations extending beyond the inferior margin of lower pedicle