Fig. 1. Images of categories of adolescent herniated lumbar discs in accordance with the guideline issued by the Korean military medical directorate. Mild disc bulging without compression of thecal sac was considered as grade 2 (A, B). Disc protrusion or extrusion without compression of thecal sac was classified to grade 3 (C, D). Disc protrusion or extrusion with compression of thecal sac was considered to grade 4 (E, F). Disc protrusion or extrusion with canal compromise more than 50% at the mid-sagittal diameter in the same plane was defined as grade 5 (G). Disc protrusion or extrusion with positive cut-off sign, the loss of neuromuscular signal at the level of interest identified by imaging, was also classified as grade 5 (H).