Table 1.

Definition of a histological grading scale [45].^*

	Grade	Grade Description
I. Annulus fibrosus	1	Normal pattern of fibrocartilage lamellae (U-shaped in the posterior aspect and slightly convex in the anterior aspect) without ruptured fibers and without a serpentine appearance anywhere within the annulus.
	2	Ruptured or serpentine-patterned fibers in less than 30% of the annulus.
	3	Ruptured or serpentine-patterned fibers in more than 30% of the annulus.
II. Border between the annulus fibrosus and nucleus pulposus	1	Normal.
	2	Minimally interrupted.
	3	Moderate/severe interruption.
III. Cellularity of the nucleus pulposus	1	Normal cellularity with large vacuoles in the gelatinous structure of the matrix.
	2	Slight decrease in the number of cells and fewer vacuoles.
	3	Moderate/severe decrease (>50%) in the number of cells and no vacuoles.
IV. Matrix of the nucleus pulposus	1	Normal gelatinous appearance.
	2	Slight condensation of the extracellular matrix.
	3	Moderate/severe condensation of the extracellular matrix.

^*Histological grading scale based on 4 categories of degenerative changes, with scores ranging from a normal disc with 4 points (1 point in each category) to a severely degenerated disc with 12 points (3 points in each category).