Table 1. IVD degeneration grading scale.

The scale is modified from previously developed and validated IVD degeneration grading schemes proposed by Masuda et al. [35] and Rutges et al. [36].

Annulus fibrosus
Grade	0	Normal, pattern of fibrocartilage lamellae (U-shaped in posterior aspect and slightly convex in the anterior aspect) without ruptured fibers and without a serpentine appearance anywhere within the annulus
	1	Ruptured or serpentined pattern fibers in less than 30% of the annulus
	2	Ruptured or serpentined pattern fibers in greater than 30% of the annulus
Border between annulus fibrosus and nucleus pulposus
Grade	0	Normal
	1	Minimally interrupted
	2	Moderate/severe interruption
Cellularity of nucleus pulposus
Grade	0	Normal cellularity with large vacuoles in the gelatinous structure of the matrix
	1	Slight decrease in the number of cells and fewer vacuoles
	2	Moderate/severe decrease (>50%) in the number of cells and no vacuoles
Matrix of nucleus pulposus
Grade	0	Normal gelatinous appearance
	1	Slight condensation of the extracellular matrix
	2	Moderate/severe condensation of the extracellular matrix
Endplate
Grade	0	Homogenous structure; regular thickness
	1	Slight irregularity with limited number of microfractures; locally decreased thickness
	2	Severe irregularity with multiple microfractures of EP; generalized decrease of thickness