Table 2.

Definition of criteria employed for scoring for histologic analysis (Barbera et al. [17])

Grade 0 (none)	Absence of fibrosis
Grade 1 (minimal)	Fibrosis not adherent to the dural sac or nerve roots, less than 25% involvement
Grade 2 (moderate)	Fibrosis adherent to the dural sac or nerve roots, less than 50% involvement
Grade 3 (extensive)	Fibrosis adherent to the dural sac and nerve roots, less than 75% involvement
Grade 4 (severe)	Fibrosis throughout the vertebral canal encompassing the dural sac and nerve root, up to 100% involvement